Semiconductor Electronics: Materials, Devices And Simple Circuits - Class 12 Medical Physics - Extra Questions
Describe briefly , with the help of a diagram, the role of the two important processes involved in the formation of a pn junction.
The two important process involved in formation of p - n junction:
(i) Diffusion
(ii) Drift
When p and n sides comes in contact then majority carries diffuse from high concentration to low concentration. Electrons flow from n to p junction and combines with holes near the junction. Similarly holes flow from p-side to n side and combine with electrons near the junction. As this happens, region near the junction gets depleted of carriers and gets charged as shown in figure. This diffusion of carriers leads to diffusion current.
The charge in depletion region creates electric field. This electric field leads to flow of minority carriers across depletion region. This is called the drift current.
The diffusion and drift currents are opposite in direction.
In equilibrium, they are equal to each other and p-n junction is formed.
Write he name of any one doped semiconductor used for making light emitting diode (LED)
Name the junction diode whose $$I - V$$ characteristics are drawn below :
A Zener diode is fabricated by heavily doping both p- and n- sides of the junction. Explain, why?
The Zener diode as fabricated by heavily doping both $$p$$ and $$n$$ sides of the junction so as to :
(i) Push the conduction band very near to Fermi level.
(ii) Make depletion layer narrower
(iii) Making resistance lower and allow a large current to flow with little potential difference.
The Zener diode is always connected in reverse bias. The breakdown voltage is controlled by the amount of doping its P and n side. Higher the doping, lesser will be the breakdown voltage. Let us consider that the unregulated voltage exceeds the zener breakdown voltage. At this instant avalanche breakdown occurs and large current flows through the diode. As a result, there is an increased potential difference at the external resistance $$R_s$$ due to which the potential difference at $$R_L$$ is maintained.
What do you understand by the logic gate? Draw the symbol for XOR gate and also the truth table.
A logic gate is an elementary building block of a digital circuit. Most logic gates have two inputs and one output. A logic gate is a digital circuit that follows the certain logical relationship between the input and output voltages. The five common logic gates used are OR gate, AND gate, NOT gate, NOR gate, and NAND gate.
Each logic gate is indicated by a symbol and its function is defined by a truth table that shows all the possible input logic level combinations with their respective output logic levels. Truth tables help to understand the behaviour of logic gates. These logic gates can be realized using semiconductor devices.
The Boolean expression for XOR gate is:
$$ Y=A \oplus B $$
When any one of the input signals A or B has value 1 then only $$ Y=1 $$. If the two inputs are 0 or 1 then output is 0. Hence, the truth table for this gate is:
$$\begin{array}{|l|l|l|}\hline \mathrm{A}&\mathrm{B}&\mathrm{Y=A \oplus B} \\\hline 0&0&0 \\\hline 0&1&1 \\\hline 1&0&1 \\\hline 1&1&0 \\\hline\end{array}$$
The XOR gate symbol is shown in the figure $$ 16.63 . $$ The truth table for the expression; $$ A \oplus B=A \bar{B}+\bar{A} B $$
$$\begin{array}{|l|l|l|l|l|l|l|}\hline \mathrm{A}&\mathrm{B}&\mathrm{\bar{A}}&\mathrm{\bar{B}}&\mathrm{A \bar{B}}&\mathrm{\bar{A}B}&\mathrm{A\bar{B}+\bar{A}B}\\\hline 0&0&1&1&0&0&0 \\\hline 1&0&0&1&1&0&1 \\\hline 0&1&1&0&0&1&1 \\\hline 1&1&0&0&0&0&0 \\\hline\end{array}$$
Hence, by using Boolean expression $$ A \bar{B}+\bar{A} B(\times O R) $$ gate can be constructed. This is shown in the figure(16.64) in which we have used $$ \mathrm{AND} $$, OR and NOT gates.
In a transistor why is the base made thin in comparison to the emitter and collector?
Make truth table for OR gate.
Write the truth table for circuit given in the figure, consisting of NOR gates and identify the logic operation (OR, AND, NOT) which this circuit is performing.
(Hint: A = 0, B = 1 then A and B inputs of second NOR gate will be 0 and hence Y=Similarly work out the values of Y for other combinations of A and B. Compare with the truth table of OR, AND, NOT gates and find the correct one).
$$E_{g}(T)=E_{g}(m)-{\dfrac {\alpha T^{2}}{T+\beta }}$$ is the Varshni's empirical expression,then the value of $$m$$ is
You are given the two circuits as shown in fig . show that circuit (a) acts as OR gate while the circuit (b) act as AND gate.
The out put of NOR gate is connected to NOT gate . let $$ Y^1 $$ be the output of NOR gate and the final output of the combination of the two-gates be Y . the out put of NOR gates is $$ 1 $$ only when both the inputs are zero . while in NOT gate , the input gets inverted using these facts , the truth for the given arrangement can be written as below :
It is the truth table of OR gate . Therefore , the given circuit acts as OR gate
the output of two NOT gates are connected to NOR gate let $$ Y_1 $$ and $$ Y_2 $$ be the outputs of the two NOT gates and the final output of the combination of three gates be Y . in a NOT gate the input gets inverted , while the out put of a NOR gate is $$ 1 $$ only when both the inputs are zero. using these facts the truth for the given arrangement can be written as below:
It is the truth and AND gate . therefore , the given circuit acts as AND gate .
Write the truth table for a NAND gate connected as given in fig.
Hence identify the exact logic operation carried out by this circuit.
What is rectification? Draw the figure of bridge wave rectifier.
Observe the following figure. Which property of diode is indicated here? Explain that property.
Write the circuit symbol of $$p-n-p$$ transistor.
The transistor consists of the three main regions namely Emitter, base and collector. The $$p-n-p$$ transistor is as shown in the figure.
Write down the name of that logic gate in which the output is 1 when all the inputs are 1.
What do you mean by a logic gate?
In a p-n-p transistor circuit the collector current is $$ 10 mA $$ if $$ 90$$ % of the holes reach the collector , find emitter and base current.
An ideal diode should pass a current freely in one direction and should stop it completely in the opposite direction. Which is closer to ideal-vacuum diode or a p-n junction diode ?
In a full-wave rectifier, the output is taken across a load resistor of $$800$$ ohm. If the resistance of diode in the forward biased condition is $$200$$ ohm, the efficiency of rectification of ac power into dc power is(in percentage)
A certain computer chip that is about the size of a postage stamp $$(2.54 cm ,2.22 cm)$$ contains about $$3.5$$ million transistors. If the transistors are square, what must be their maximum dimension? (Note: Devices other than transistors are also on the chip,and there must be room for the interconnections among the circuit elements. Transistors smaller than $$0.7$$ mm are now commonly and inexpensively fabricated.)
Even though the p-type and n-type semiconductors have holes and electrons respectively as majority charge carries, why are they electrically neutral? Explain.
The source of electric current for a hand held transistor is _____ .
Write any two distinguishing features between conductors, semiconductors and insulators on the basis of energy band diagrams.
Match the following:
Left column lists the level of integration and right column lists the number of circuit components.
Mention important characteristics and applications of a diode.
How many electrons are there is the outermost shell of silicon atom?
Si has $$4$$ electrons in outermost shell.
Si has atomic number $$14$$.
Its electronic configuration is $$[Ne]3s^{2}3p^{2}$$ i.e. electrons per shell, $$2, 8, 4$$.
So the correct answer is $$4$$
So the correct answer is $$4$$
What is called a hole?
What is a semi conductor diode or junction diode?
What are conductors and insulators? Give examples.
Suggest any two situations in which photocells can be used as automatic switches.
In semiconductor physics, what is meant by a rectifier?
Silicon nitride has band gap energy of _______________eV.
Draw the logic symbol of AND gate.
AND is a Boolean operator which gives the value one if and only if all the operands are one, and otherwise has a value of zero.
The AND gate is represented by the above logic symbol, where the two inputs are given from the left hand side, and output is received from right side.
State the difference between laser light and ordinary light
Draw a block diagram of a simple radio receiver
Block diagram of a simple radio receiver
In a radio receiver, the device that separates AF signals from RF signals is ___________.
The more doped region in the transistor is ...........................
Draw the circuit symbol of $$n-p-n$$ transistor.
The given figure shows the symbol of n-p-n transistor.
Zener diode is used as ......................
Identify the gate.
According to truth table , the logic gate will be NOR gate. Because the output of NOR gate is $$Y=\overline{A+B}$$
Draw the logic symbol of the gate.
The given truth table is truth table of NOR gate. The output of NOR gate is $$Y=\overline{A+B}$$
The figure is the logic symbol of NOR gate.
Explain why NAND gate is known as universal gate.
NAND Gate is called Universal Gates because all the other gates (NOT, AND, OR and NOR)can be created by using this gate.
What type of gate is this,
Whats the difference between
Carbon, Silicone, and Germanium all have the same number of electrons in an outer most shell. Explain?
The outputs of two NOT gates are fed to a NOR gate. Draw the logic circuit of the combination of gates. Give its truth table. Identify the gate represented by this combination.
Output from A from NOT gate = $$\bar{A}$$
Output from B from NOT gate = $$\bar{B}$$
Output from NOR gate = $$\bar{\bar{A} + \bar{B}} = A.B $$So, From above we can deduce that, the resultant is a AND gate.
| A | B | Y=AB |
| 0 | 0 | 0 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 1 |
In what respect is an LED different from an ordinary PN - junction diode? Where should we prefer LEDs over ordinary incandescent lamps? Why?
What is a transistor? Why is it so called? What are the advantages of transistors over vacuum tubes?
In half-wave rectification, what is the output frequency if the input frequency is $$50\ Hz$$
What is the output frequency of a full-wave rectifier for the same input frequency.
Write the truth table for the circuits given in figure. consisting of NOR gates only. Identify the logic operations (OR, AND, NOT) performed by the two circuits.
In first case, $$A$$ acts as the two inputs of the NOR gate and $$Y$$ is the output. Hence, the output of the circuit is $$\overline{A+A}$$.
So, Output $$Y=\bar{A}$$.
Thus the gate is NOT gate.
The truth table is shown in the figure.
For second circuit, $$A$$ and $$B$$ are the inputs and $$Y$$ is the output of the given circuit. By using the result obtained
in solution (a), we can infer that the outputs of the first two NOR gates are $$\bar{A}$$, $$\bar{B}$$. $$\bar{A}$$ and $$\bar{B}$$ are the inputs for the last NOR gate. Hence, the output for the circuit can be
written as:
$$Y=\overline{\bar{A}+\bar{B}}=A.B$$
So this is a AND gate.
Truth table is shown in the figure.
You are given the two circuits as shown in Fig. Show that circuit (a) acts as OR gate while the circuit (b) acts as AND gate.
Draw a circuit diagram of n-p-n transistor amplifier in CE configuration. Under what condition does the transistor act as an amplifier?
Amplifier circuit using npn transistor in CE configuration:
Transistor should be operated in active region to work as an amplifier.
Emitter-Base junction (i.e. input circuit) should be forward biased.
Collector-Base junction (i.e. output circuit) should be reverse biased.
Transistor should be operated in active region to work as an amplifier.
Emitter-Base junction (i.e. input circuit) should be forward biased.
Collector-Base junction (i.e. output circuit) should be reverse biased.
Write the truth table for the combination of the gates shown. Name the gates used.
A graph of the output from an A.C. generator is given. This is given as:
(a) an input to a half wave rectifier
(b) an input to a full wave rectifier
Give graphic representations of the outputs in the cases (a) and (b).
The representation of out put of half wave rectifier and full wave rectifier are shown in the figure.
Write the truth table of logic OR gate.
Denoting a gate circuit which produces an output if there is a signal on any of its inputs. The truth table is shown bellow.
With reference to semiconductor devices, define a p-type semiconductor and a Zener diode. What is the use of a Zener diode?
Construct the logic symbol, Boolean expression, circuit diagram and truth table for an OR gate.
OR Gate
Logic Symbol:
Logic Symbol:
Boolean expression: $$Y=A+B$$
Truth Table of $$OR$$ gate
Truth Table of $$OR$$ gate
| A | B | Y=A+B(OUTPUT) |
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 1 |
Circuit Diagram of $$OR$$ gate using diode.
Make logic symbol and write Boolean expression of NOT gate.
Logic symbol of NOT gate is shown in the above diagram in which ''A'' indicates the input and "X" indicates the output of NOT gate.
Boolean expression of NOT gate is $$X = \bar{A}$$
Boolean expression of NOT gate is $$X = \bar{A}$$
Construct the logic symbol, Boolean expression and truth table for an AND gate.
In the given image logic symbol, Boolean expression and truth table for an AND gate is given.
If $$A_1,A_2,A_3,....,A_n$$ are the $$n$$ inputs of AND gate then boolean expression is given by,$$A_1\times A_2\times A_3\times ....\times A_n=Y=$$ Output
For a common emitter amplifier. dc(direct current) current gain is $$100$$. If the base current is $$20\mu$$A, calculate the collector and emitter current.
The arrangement given represents a logic gate.
Copy the following truth table and complete it showing outputs at C and D.
| A | B | C | D |
| $$0$$ | $$0$$ | ||
| $$1$$ | $$0$$ | ||
| $$0$$ | $$1$$ | ||
| $$1$$ | $$1$$ |
Both the above gates are NAND gates which give output as 0 only when both the inputs are 1 whereas gives output as 1 in rest of the cases.
Hence the truth table for the above circuit is shown here.
Hence the truth table for the above circuit is shown here.
Transistors used for making NOT gate.why?
A semiconductor doped with a donor impurity is.
Write down output Y in terms of inputs A and B.
In a zener -regulated power supply a zener diode with $$V_z=6$$ volt is used for regulation. The load current is to be $$4mA$$ and the unregulated input is $$10$$ volt. What should be he value of series resistor $$R_s$$.if the current through diode is five time the load current ?
what is the PN junction diode?
Explain, with the help of a circuit diagram, the working of a photo-diode. Write briefly how it is used to detect the optical signals.
OR
Mention the important considerations required while fabricating a $$p-n$$ junction diode to be used as a Light Emitting Diode (LED). What should be the order of band gap of an LED if it is required to emit light in the visible range?
i) pn junction diode should be connected in forward biased condition.
ii) The energy of photon visible light is given by $$hv = E_g$$, never eg is the bend gap between balance q conduction band and $$v$$ is the field freq. of emitted visible radiation wavelength of emitted light $$\cfrac { hv }{ \lambda } =Eg$$ or
$$\lambda =\cfrac { hc }{ Eg } $$
iii)Led should be made of compounds like $$ GaAs $$ with $$Eg $$ a $$ 1.9ev$$ to emit light in visible region.
2)To emit light in visible range in Led, band gap is of order$$1.8ev$$ (minimum).
because spectral range of visible light is $$ 0.4\times { 10 }^{ -6 }m$$ to $$0.7\times { 10 }^{ -6 }m$$ with energy $$3ev$$ to $$1.8ev$$.
When is a transistor said to be in active state? Draw a circuit diagram of a p-n-p transistor and explain how it works as a transistor amplifier. Write clearly, why in the case of a transistor (i) the base is thin and lightly doped and (ii) the emitter is heavily doped.
- The transistor is said to be in the active state when collector junction is reverse biased and emitter junction is forward biased. A transistor is operated in actual region if it is used as an amplifier.
- A transistor as an amplifier using pnp transistor:
The input signal to be amplified is applied across the input circuit and the amplified output signal obtained across the output circuit having load resistance.
Hence, $$I_{C}=I_{B}+I_{C}$$
The collector voltage $$V_{o}=$$ applied voltage $$V_{CE}$$ - voltage drop across $$R_{L}$$.
i.e. $$V_{o}=V_{CE}-I_{C}R_{L}$$ ...(i)
During the positive half cycle of the input signal, the forward bias of emitter- Base junction decreases. As a result, $$I_{E}$$ and hence $$I_{C}$$ decreases. So, voltage drop across $$R_{L}$$ decreases. According to equation (i), collector or output voltage $$V_{o}$$ increases. Since collector is connected to negative terminal of the battery, so increase in collector voltage implies that collector becomes more negative. Thus, an amplified negative signal is obtained across the output.
During the negative half cycle of the input signal, the forward bias of emitter-base junction increases. As a result, the emitter current $$(I_{E})$$ and hence $$I_{C}$$ increases. Thus voltage drop across $$R_{L}$$ increases and according to equation (i), $$V_{o}$$ decreases. Since collector is connected to negative terminal of the battery, so decrease in collector voltage means that collector becomes less negative. In other words, the amplified positive signal is obtained across the output. - The base is thin and lightly doped
The majority carriers from the emitter region move towards the collector region through the base. If the base is made thick and heavily doped, then most of the majority carriers will combine with the charge carriers in the base while passing through it. Hence, only a small number of majority carriers will reach the collector region. As a result, the output or collector current will be decreased considerably. Therefore, the base region of a transistor is made thin and lightly doped, so that minimum number of majority carriers passing through base get neutralized and large output is available. - The emitter is heavily doped
Because emitter contains the largest amount of charge carriers out of all regions in the transistor. The role of an emitter is to inject a large amount of charge carriers into the base, which then travels onto the collector so that switching or amplification can occur.
(i) Distinguish between a conductor and a semi conductor on the basis of energy band diagram
(ii) The following figure shows the input waveforms (A, B) and the output waveform (Y) of a gate. Identify the gate, write its truth table and draw its logic symbol.
i) For a conductor, there is no gap in between the valence band and conduction band. Thus the band gap energy is almost zero for conductor. For a semiconductor, there is a small gap in between valence band and conduction band and so a semiconductor must have band gap energy.
ii) For this type of problem, we will first make the truth table according to the given waveform. The truth table is shown in figure and according to truth table, the gate is $$\text{NAND}$$ gate whose logic symbol is as shown in figure.
Show on a graph, the variation of resistivity with temperature for a typical semiconductor.
The resistivity is given by:
$$\rho =\dfrac{m}{ne^{2}\tau }$$
where n = number density of electrons
$$\rho =\dfrac{m}{ne^{2}\tau }$$
where n = number density of electrons
$$\rho$$ = relaxation time
With the rise in temperature, number density of electrons and holes (in case of semiconductors) increases, where $$\tau$$ remains constant. So, $$\rho$$ (resistivity) decreases.
Output characteristics of an $$n-p-n$$ transistor in $$CE$$ configuration is shown in the figure. Determine:
(i) dynamic output resistance
(ii) dc current gain and
(iii) ac current gain at an operating point $${V}_{CE}=10 V$$, when $${I}_{B}=30 \mu A$$.
How is a Zener diode fabricated? What causes the setting up of high electric field even for small reverse bias voltage across the diode?
Describe, with the help of a circuit diagram, the working of Zener diode as a voltage regulator.
Fabrication:
The zener or breakdown voltage depends on the concentration of doping. The n and p regions of zener diode are heavily doped. The depletion layer of heavily doped p-n junction diode is very thin. Since electron field $$\epsilon = -\dfrac{dV}{dr}$$ across the junction would be very high even for small voltage. this electron field is called ionizing field.
Zener Diode as a Voltage Regulator:
- Heavily doped p and n junction are to be used for fabricating zener diode.
- The breakdown voltage of the material should be considered to avoid the destruction of the device.
Zener diodes have breakdown voltages ranging from 3-200 Volts. - The zener diodes are fabricated with precise breakdown voltages, by controlling the doping level during manufacturing.
The zener or breakdown voltage depends on the concentration of doping. The n and p regions of zener diode are heavily doped. The depletion layer of heavily doped p-n junction diode is very thin. Since electron field $$\epsilon = -\dfrac{dV}{dr}$$ across the junction would be very high even for small voltage. this electron field is called ionizing field.
Zener Diode as a Voltage Regulator:
The circuit diagram using zener diode as a voltage stabilizer is as shown:
The zener diode is connected across the fluctuating voltage source through a dropping resistor of resistance $$R_{S}$$. The constant voltage supply is obtained across positive Load resistance $$R_{L}$$. When the input voltage increases, resistance of zener diode decreases and hence current through the diode increases to high value.
As a result, a large voltage drop occurs across the dropping resistance $$R_{S}$$. Hence, the output voltage across $$R_{L}$$ is maintained to the desired value. When the input voltage decreases, the current through the diode also decreases. So now small voltage drop takes place across the resistance $$R_{S}$$ and the output voltage across $$R_{L}$$ is maintained at a desired constant value.
Thus, we get a constant voltage in spite of fluctuating input voltage. Hence, zener diode acts as a voltage regulator.
The zener diode is connected across the fluctuating voltage source through a dropping resistor of resistance $$R_{S}$$. The constant voltage supply is obtained across positive Load resistance $$R_{L}$$. When the input voltage increases, resistance of zener diode decreases and hence current through the diode increases to high value.
As a result, a large voltage drop occurs across the dropping resistance $$R_{S}$$. Hence, the output voltage across $$R_{L}$$ is maintained to the desired value. When the input voltage decreases, the current through the diode also decreases. So now small voltage drop takes place across the resistance $$R_{S}$$ and the output voltage across $$R_{L}$$ is maintained at a desired constant value.
Thus, we get a constant voltage in spite of fluctuating input voltage. Hence, zener diode acts as a voltage regulator.
Explain, with the help of a circuit diagram, the working of a p-n junction diode as a half-wave rectifier.
A p-n junction diode conducts current in forward bias and blocks current in reverse bias.
p-n junction diode is forward biased in positive cycle. In forward bias, resistance of diode, $$R_D = 0$$ or it acts as a short circuit and output voltage equals the input voltage.
p-n junction diode is reverse biased in negative cycle. In reverse bias, resistance of diode, $$R_D = \infty$$ or it acts as an open circuit and output voltage is zero.
Hence, the p-n junction allows only positive cycles to pass through them.
(a) State briefly the processes involved in the formation of p-n junction explaining clearly how the depletion region is formed.
(b) Using the necessary circuit diagram, show how the V-I characteristics of a p-n junction are obtained in
(i) Forward biasing
(ii) Reverse biasing
How are these characteristics made use of in rectification?
(a)
When an electron diffuses from n to p due to difference in charge carriers of the two regions of p-n junction, it leaves behind a positive charge (ionised donor) on n side which is immobile as it is bonded by surrounding atoms. Thus a layer of positive and negative charges develop on the n-side and p-side of the junction respectively. Hence a space charge region is formed on both side of the junction which is called as depletion layer or depletion region.
(b)
(i) In Forward bias, p-side of the diode is connected to the positive terminal of the battery and n-side of the diode is connected to the negative terminal of the battery. Applied voltage is slowly increased and the current in the circuit is measured and plotted. It is observed that beyond the knee voltage, current rises rapidly.
(ii) In reverse bias, n-side of the diode is connected to the positive terminal of the battery and p-side to the negative terminal. Applied voltage is slowly increased, it is observed that almost non current flows in the circuit until a substantial reverse breakdown voltage. Beyond this point, current rises suddenly and diode works in reverse breakdown region.
A diode hence passes only positive values of voltage and blocks negative values of voltage. When, applied across an ac source it passes the positive cycles and blocks the negative cycles. Hence, it is used for rectification purposes.
(a) Draw the circuit diagram of a full wave rectifier using $$p-n$$ junction diode.
Explain its working and show the output, input waveforms.
(b) Show the output waveforms (Y) for the following inputs $$A$$ and $$B$$ of
(i) OR gate (ii) NAND gate
(a)
The full wave rectifier circuit consists of two power diodes connected to a single load resistance and each diode taking it in turn to supply current to the load. When a point of the transformer is positive with respect to another point, diode conducts in the forward direction.
When a point of the transformer is positive with respect to another point, then diode conducts in the forward direction and the current flowing through resistor is in the same direction for both half-cycles. As the output voltage across the resistor is the phasor sum of the two wave forms combined, this type of full wave rectifier circuit is also known as a bi-phase circuit.
(b)
(i) OR gate - gives an output of zero when both inputs are zero, else output is 1.
(ii) NAND gate - gives an output of 0 when both inputs are 1, else gives an output of 1.
In the circuit shown in the figure identify the equivalent gate of the circuit and make its truth table .
The three gates in the circuit are NAND gate. So, the output are as shown in figure.
Here $$Y=\bar{A'.B'}=\bar{\bar{A}.\bar{B}}=\bar{\bar A}+\bar{\bar B}=A+B$$ (by de Morgan theorem)
Hence, the equivalent gate will be OR gate and the truth table is shown in figure.
How does a diode acts as a rectifier.
For an AC source, the input voltage Signal is of form$$:-$$
With reference to Image $$1$$
Now if a few diodes are used as shown below, it will transform the AC signal into DC signal, thus acting like rectifiers.
With reference Image $$2$$ and $$3$$
Here the diode circuits rectifiers the AC signal and transforms the negative half cycles into positive half cycles.
With reference to Image $$4$$ and $$5$$
Here the diode only allows the positive half cycles to pass to $${ R }_{ L }$$
and does not let the negative half cycles, giving it a DC form.
Give the circuit symbol of a diode.
The circuit symbol for a diode is
The arrowhead represents the p-type semiconductor and the vertical bar represents the n-type semiconductor. The arrow represents the direction of conventional electric current through the diode.
The arrowhead represents the p-type semiconductor and the vertical bar represents the n-type semiconductor. The arrow represents the direction of conventional electric current through the diode.
Fill in the blanks.
In an npn transistor p type semi conduct is sandwiched between ___________.
In npn transistor, the p-type semiconductor is sandwiched between two n-type semiconductors. As we can see from the diagram.
What are semiconductors? Give examples.
Materials having resistivity or conductivity in between conductors and insulators, are called semiconductors.
These are the materials with the forbidden energy gap between valence and conduction band $$< 3 eV$$. It is less than that of insulators $$ (> 3 eV) $$ and more than that of conductors.
These are the materials with the forbidden energy gap between valence and conduction band $$< 3 eV$$. It is less than that of insulators $$ (> 3 eV) $$ and more than that of conductors.
e.g.
Elemental semiconductor: Germanium, silicon, selenium, etc.
Compound semiconductors: Gallium, arsenide, Indium, phosphide, cadmium, sulphide etc.
Compound semiconductors: Gallium, arsenide, Indium, phosphide, cadmium, sulphide etc.
Mention the applications of a transistor.
Match the items in List 1 with items in list 2
Match the items in List 1 with items in List 2
State one important use of a Zener diode.
Prepare a truth table for the combination of gates shown in figure.
What is NAND gate? Write its truth table.
NAND Gate: The NAND gate is a combination of AND an NOT Gates.
Write the function of the three segment of a transistor.
What is rectifier? Explain with neat circuit diagram the action of semiconductor diode as a full wave rectifier.
Rectifier: A circuit or device that is used to convert an alternating voltage to a direct voltage is called rectifier.
Action of semiconductor diode as a full wave rectifier:
Electric circuit: The alternating voltage to be rectified is applied across primary coil $$(P_1P_2)$$ of a transformer with a centre tapped secondary coil $$(S_1S_2)$$. The terminals $$S_1, S_2$$ of the secondary coil are connected to the two p-regions of two junction diode-$$D_1$$ and $$D_2$$ respectively. The centre tap T is connected to the ground. The load resistance $$R_L$$ is connected across the common n regions and the ground.
Working: During one half cycle of the input, terminal $$S_1$$ of secondary is positive while $$S_2$$ is negative with respect to the ground. During the half cycle, diode $$D_1$$ is forward biased and conducts, while diode $$D_2$$ is reverse biased and does not conduct. The direction of current $$I_L$$ through $$R_L$$ is in the sense shown.
During the next half cycle of the input voltage, $$S_2$$ becomes positive while $$S_1$$ is negative with respect to T Diode. $$D_2$$ now conducts sending a current $$I_L$$ through $$R_L$$ in the same sense as before. $$D_1$$ now does not conduct. Thus, the current through $$R_L$$ flows in the same direction i.e., It is unidirectional, for both halves of the full-wave of the input. This is called full wave rectification.
Action of semiconductor diode as a full wave rectifier:
Electric circuit: The alternating voltage to be rectified is applied across primary coil $$(P_1P_2)$$ of a transformer with a centre tapped secondary coil $$(S_1S_2)$$. The terminals $$S_1, S_2$$ of the secondary coil are connected to the two p-regions of two junction diode-$$D_1$$ and $$D_2$$ respectively. The centre tap T is connected to the ground. The load resistance $$R_L$$ is connected across the common n regions and the ground.
Working: During one half cycle of the input, terminal $$S_1$$ of secondary is positive while $$S_2$$ is negative with respect to the ground. During the half cycle, diode $$D_1$$ is forward biased and conducts, while diode $$D_2$$ is reverse biased and does not conduct. The direction of current $$I_L$$ through $$R_L$$ is in the sense shown.
During the next half cycle of the input voltage, $$S_2$$ becomes positive while $$S_1$$ is negative with respect to T Diode. $$D_2$$ now conducts sending a current $$I_L$$ through $$R_L$$ in the same sense as before. $$D_1$$ now does not conduct. Thus, the current through $$R_L$$ flows in the same direction i.e., It is unidirectional, for both halves of the full-wave of the input. This is called full wave rectification.
Figure shows the circuit of an electronic device.
(i) Which electronic device: a rectifier, an amplifier or an oscillator does the circuit represent?
(ii) State where the input voltage is applied and where the output voltage is available.
(iii) Compare the output voltage of this circuit with its input voltage.
What are the advantages of Integrated Circuits (IC)
State the properties and uses of a Junction Diode.
State the properties and uses of a Junction transistor.
A bipolar junction transistor consists of three regions of doped semiconductors. A small current in the center or base region can be used to control a larger current flowing between the end regions (emitter and collector).
The Junction Transistor can be used as:
The Junction Transistor can be used as:
- Current amplifier: The larger collector current $$I_C$$ is proportional to the base current $$I_B$$ according to the relationship $$I_C=\beta I_B$$ , or more precisely it is proportional to the base-emitter voltage $$V_{BE}$$. The smaller base current controls the larger collector current, achieving current amplification.
- Switch: For switching applications transistor is biased to operate in the saturation or cutoff region. Transistor in cutoff region will act as an open switching whereas in saturation will act as a closed switch.
Explain the working of a diode as half wave rectifier.
A circuit which rectifies half of the a.c. wave is called half wave rectifier.
Working:
The figure shows the circuit for half wave rectification. The a.c. voltage $$\left( { V }_{ S } \right)$$ to be rectified is obtained across the secondary ends $${ S }_{ 1 }{ S }_{ 2 }$$ of the transformer. The $$P$$-end of the diode $$D$$ is connected to $${ S }_{ 1 }$$ of the secondary coil of the transformer. The $$N$$-end of the diode is connected to the other end $${ S }_{ 2 }$$ of the secondary coil of the transformer, through a load resistance $${ R }_{ L }$$. The rectified output voltage $${ V }_{ dc }$$ appears across the load resistance $${ R }_{ L }$$.
During the positive half cycle of the input a.c. voltage $${ V }_{ S }$$, $${ S }_{ 1 }$$ will be positive and the diode is forward biased and hence it conducts. Therefore, current flows through the circuit and there is a voltage drop across $${ R }_{ L }$$. This gives the output voltage.
During the negative half cycle of the input a.c. voltage $$\left( { V }_{ S } \right)$$, $${ S }_{ 1 }$$ will be negative and the diode $$D$$ is reverse biased. Hence, the diode does not conduct. No current flows through the circuit and the voltage drop across $${ R }_{ L }$$ will be zero. Hence, no output voltage is obtained. Thus corresponding to an alternating input signal, unidirectional pulsating output is obtained.
The figure shows the circuit for half wave rectification. The a.c. voltage $$\left( { V }_{ S } \right)$$ to be rectified is obtained across the secondary ends $${ S }_{ 1 }{ S }_{ 2 }$$ of the transformer. The $$P$$-end of the diode $$D$$ is connected to $${ S }_{ 1 }$$ of the secondary coil of the transformer. The $$N$$-end of the diode is connected to the other end $${ S }_{ 2 }$$ of the secondary coil of the transformer, through a load resistance $${ R }_{ L }$$. The rectified output voltage $${ V }_{ dc }$$ appears across the load resistance $${ R }_{ L }$$.
During the positive half cycle of the input a.c. voltage $${ V }_{ S }$$, $${ S }_{ 1 }$$ will be positive and the diode is forward biased and hence it conducts. Therefore, current flows through the circuit and there is a voltage drop across $${ R }_{ L }$$. This gives the output voltage.
During the negative half cycle of the input a.c. voltage $$\left( { V }_{ S } \right)$$, $${ S }_{ 1 }$$ will be negative and the diode $$D$$ is reverse biased. Hence, the diode does not conduct. No current flows through the circuit and the voltage drop across $${ R }_{ L }$$ will be zero. Hence, no output voltage is obtained. Thus corresponding to an alternating input signal, unidirectional pulsating output is obtained.
Show the output waveform of OR gate for the following input waveforms of $$A$$ and $$B$$
What is extrinsic semiconductor? How many types of these are? Write their names. Explain the processes which are occurred during the formation of a P-N junction. Determine the electric field produced at a P-N junction when width of depletion layer is $$1$$ micrometer and barrier potential is $$0.7$$ volt.
Distinguish between Avalanche breakdown and Zener breakdown.
Draw the circuit diagram of AND gate using diodes.
AND gate: An AND gate has two or more inputs but only one output. It is known as AND gate because the output is high only when all the inputs are high. The logic symbol of a two input AND gate is shown in Figure(a).
AND gate may be thought of an electrical circuit as shown in Figure (b), in which the switches are connected in series. Only if A and B are closed, the lamp will glow, and the output is high.
Diode AND gate;
Figure shows a simple circuit using diodes to build to a two-input AND gate. The working of the circuit can be explained as follows.
Case(i) A$$=0$$ and B$$=0$$.
When A and B are zero, both diodes are in forward bias condition and they conduct and hence the output will be zero, because the supply voltage $$V_{cc}$$ will be dropped across $$R_L$$ only. Therefore Y$$=0$$.
Case(ii) A$$=0$$ and B$$=1$$.
When A$$=0$$ and B is high, diode $$D_1$$ is forward biased and diode $$D_2$$ is reverse biased. The diode $$D_1$$ will now conduct due to forward biasing. Therefore, output Y$$=0$$.
Case(iii) A$$=1$$ and B$$=0$$.
In this case, diode $$D_2$$ will be conducting and hence the output Y$$=0$$.
Case(iv) A$$=1$$ and B$$=1$$.
In this case, both the diodes are not conducting. Since $$D_1$$ and $$D_2$$ are in OFF condition, no current flows through $$R_L$$. The output is equal to the supply voltage. Therefore Y$$=1$$.
Thus the output will be high only when the inputs A and B are high. The Table summaries the function of an AND gate.
What is rectification? Explain the working of a fullwave rectifier. Draw necessary circuit diagram.
Rectification is the conversion of an alternating current to direct current.
The full wave rectifier circuit consists of two power diodes connected to a single load resistance ($$R_L$$) with each diode taking it in turn to supply current to the load. When point A of the transformer is positive with respect to point C, diode $$D_1$$ conducts in the forward direction.
When point B is positive (in the negative half of the cycle) with respect to point C, diode $$D_2$$ conducts in the forward direction and the current flowing through resistor $$R$$ is in the same direction for both half-cycles.
As the spaces between each half-wave developed by each diode is now being filled in by the other diode the average DC output voltage across the load resistor is now double that of the single half-wave rectifier circuit and is about $$0.637V_{max}$$, assuming no losses.
What is rectification? With relevant circuit diagram and waveforms explain the working of a P-N junction diode as a full-wave rectifier.
$$\text{Rectifier:}$$The rectifier is an electrical device which converts alternating current to direct current one by allowing a current to flow through it in one direction only.
$$\text{Working of PN Junction Diode:}$$ In the PN Junction diode, when alternating current flows, In first half cycle diode $$D_1$$ is in forwarding bias, so current flows in diode $$D_1$$ and diode $$D_2$$ is in reverse bias and it does not allow to flow the current.
In the second half cycle diode, $$D_2$$ is in forwarding bias and diode $$D_1$$ is in reverse bias, so Diode $$D_2$$ allows to flow the current and diode $$D_1$$ will not allowing to flow the current.
This process repeats again and again.
So total output is the combination of first half cycle and second half cycle.
So it allows flowing the current in the positive pulse.
Answer the following question :
(i) Write the functions of the three segments of a transistor.
(ii) The figure shows the input wave forms A and B for 'AND' gate . Draw the output wave form and write the truth table for this logic gate.
Output waveform for AND gate is
Truth table
Truth table
| Input | Output | |
| A | B | Y = A.B |
| $$ 0 $$ | $$ 0 $$ | $$ 0 $$ |
| $$ 0 $$ | $$ 1 $$ | $$ 0 $$ |
| $$ 1 $$ | $$ 0 $$ | $$ 0 $$ |
| $$ 1 $$ | $$ 1 $$ | $$ 1 $$ |
Explain avalanche breakdown in a diode and zener breakdown in a zener diode.
(a) In the following diagram, which bulb out of $$B_1$$ and $$B_2$$ will glow and why?
(b) Draw a diagram of an illuminated p-n junction solar cell.
(c) Explain briefly the three processes due to which generation of emf takes place in a solar cell.
A) In the diagram, daiod $$D_1$$ is in forward bias and daiod $$D_2$$ is in reverse bias, So current will flow through $$D_1$$ and $$D_2$$ will not allow flowing the current, So bulb $$B_1$$ will glow and bulb $$B_2$$ will not glow.
C)When the photodiode is illuminated with light, with energy greater than the energy gap of the semiconductor, then electron-hole pairs are generated due to the absorption of photons, in or near the depletion region. Due to the electric field of the junction, electrons and holes are separated before the recombine electrons reach n-side and holes reach p-side.Electrons are collected on n-side and holes are collected on p-side giving rise to an emf. When connected to an external load is current flows, whose magnitude depends on the intensity of incident light.
The photodiode can be used as a photodetector to detect optical signals.
What is rectification? Explain the working of a full wave rectifier.
What is a Fermi energy level? What is its position in case of an intrinsic semiconductor?
What is rectification? Explain the working of a full-wave rectifier with a diagram. What is a zener diode? How will a zener diode be connected in a circuit generally?
Rectification is the process of converting alternating current (AC) which reverses its direction periodically to direct current (DC) which flows only in one direction.
Working:-
Here the configuration used to rectify is of centre tap type and the concept used is that diodes operates only in forward biased, that is, in reverse biased a diode is switched off.
The input waveform is AC, that is, it changes its polarity periodically. In the first half cycle, the diode D1 is in forward biased and is On so it behaves as a short circuit where as the diode D2 is in reverse biased and is Off so it behaves as as an open circuit. The current in the circuit follows the path A-D1-C-R-O-A.
In the second half cycle of the i/p waveform, the polarities change and the diode D1 is in reverse biased and is Off thus behaving as an open circuit where as the diode D2 is in forward biased and is On thus behaving as a short circuit. The current in the circuit follows the path B-D2-C-R-O-B.
The direction of current through the load resistor R does not change that is it flows in downward direction in both the cycles.
Zener diode- It is a diode made up of highly doped p-n junctions which allows the current to flow through it even in reverse biased mode unlike other diodes.
A zener diode is generally connected in reverse biased mode in a circuit for controlling purposes.
Working:-
Here the configuration used to rectify is of centre tap type and the concept used is that diodes operates only in forward biased, that is, in reverse biased a diode is switched off.
The input waveform is AC, that is, it changes its polarity periodically. In the first half cycle, the diode D1 is in forward biased and is On so it behaves as a short circuit where as the diode D2 is in reverse biased and is Off so it behaves as as an open circuit. The current in the circuit follows the path A-D1-C-R-O-A.
In the second half cycle of the i/p waveform, the polarities change and the diode D1 is in reverse biased and is Off thus behaving as an open circuit where as the diode D2 is in forward biased and is On thus behaving as a short circuit. The current in the circuit follows the path B-D2-C-R-O-B.
The direction of current through the load resistor R does not change that is it flows in downward direction in both the cycles.
Zener diode- It is a diode made up of highly doped p-n junctions which allows the current to flow through it even in reverse biased mode unlike other diodes.
A zener diode is generally connected in reverse biased mode in a circuit for controlling purposes.
Draw the diagram of a Helium-Neon laser tube and label the parts.
The given figure shows He-Ne Laser with labels.
Write the logic symbols and prepare the truth tables of the following gates.
(i) AND
(ii) NOR.
(i) AND Gate: A digital circuit in which there are two or more inputs and a single output and its output is $$1$$ when both the inputs are $$1$$.
The symbol of an AND gate is which A and B are inputs and Y is output.
By deifinition, when
$$A=B=1, then Y=1$$
Truth Table of AND Gate:
Input Input Output
A B Y
$$0$$ $$0$$ $$0$$
$$1$$ $$0$$ $$0$$
$$0$$ $$1$$ $$0$$
$$1$$ $$1$$ $$1$$
To obtain NOR gate by NAND and NOT gates- We can obtain NOR gate by using three NOT gates and NAND gate as shown in figure.
Boolean formula: $$Y=\bar{Y'}=\overline{\vec{A}\cdot \vec{B}}=\overline{A+B}$$(By De-Morgan's law)
Truth table:
Input Input Output Output Output Output
A B $$\bar{A}$$ $$\bar{B}$$ $$Y'=A+B$$ $$Y=\overline{A+B}$$
$$0$$ $$0$$ $$1$$ $$1$$ $$0$$ $$1$$
$$1$$ $$0$$ $$0$$ $$1$$ $$1$$ $$0$$
$$0$$ $$1$$ $$1$$ $$0$$ $$1$$ $$0$$
$$1$$ $$1$$ $$0$$ $$0$$ $$1$$ $$0$$
A diode is connected to the output of a transformer as shown in the figure given below. Analyse the figure.
a) Draw a time-voltage graph for the current obtained across AB.
b) What is the function of the diode in the circuit?
a) The voltage - time graph obtained across AB is shown below:
b) The diode functions as a rectifier in the circuit. It allows only the positive voltage cycle to flow through the circuit and blocks the negative cycle.
b) The diode functions as a rectifier in the circuit. It allows only the positive voltage cycle to flow through the circuit and blocks the negative cycle.
(A) What do you mean by barrier potential of diode?
(B) With help of a diagram explain the working of a full wave rectifier.
A) The potential barrier in the p-n junction diode is the barrier which does not allow charge flow across the junction normally. This barrier is created by the charge present in the space charge region. When p-type material is brought in contact to a n-type material, the charge flow across the junction takes place due to concentration gradient between the two sides (n and p type). But after some time the immobile ions are created near the contact which create electric field which opposes flow of current. This resistance to the flow of charge is known as barrier potential.
B) Full wave rectifier:
A full rectifier is an arrangement of four or more diodes in a bridge circuit configuration which provides the same output polarity for either input polarity. It is used for converting an alternating current (AC) input into a direct current (DC) output.
For half cycle of input AC, one diode out of the two, will get forward biased and will conduct, while the other diode, being reverse biased, will not conduct. For other cycle of input signal, the diode, which was reverse biased, will get forward biased and will conduct, and the other diode will get reverse biased and will stop conducting. Hence we obtain a unidirectional output voltage for the positive as well as for negative half cycles.
B) Full wave rectifier:
A full rectifier is an arrangement of four or more diodes in a bridge circuit configuration which provides the same output polarity for either input polarity. It is used for converting an alternating current (AC) input into a direct current (DC) output.
For half cycle of input AC, one diode out of the two, will get forward biased and will conduct, while the other diode, being reverse biased, will not conduct. For other cycle of input signal, the diode, which was reverse biased, will get forward biased and will conduct, and the other diode will get reverse biased and will stop conducting. Hence we obtain a unidirectional output voltage for the positive as well as for negative half cycles.
Distinguish between conductor and semiconductor on the basis of band theory of solids.
What is main logic gates? How many types are they? Draw their symbols and Truth Table.
Main Logic Gates: A digital circuit which either allows a signal to pass through or stop it, is called a gate.
Mainly logic gate are of three types. OR, AND & NOT gate.
(i) OR Gate:
Truth Table:
Mainly logic gate are of three types. OR, AND & NOT gate.
(i) OR Gate:
Truth Table:
| Input | Output | |
| $$A$$ $$0$$ $$0$$ $$1$$ $$1$$ | $$B$$ $$0$$ $$1$$ $$0$$ $$1$$ | $$Y=A+B$$ $$0$$ $$1$$ $$1$$ $$1$$ |
(ii) AND Gate:
Truth Table:
Truth Table:
| Input | Output | |
| $$A$$ $$0$$ $$0$$ $$1$$ $$1$$ | $$B$$ $$0$$ $$1$$ $$0$$ $$1$$ | $$Y=A \cdot B$$ $$0$$ $$0$$ $$0$$ $$1$$ |
(iii) NOT Gate:
Truth Table:
Truth Table:
| Input $$A$$ | Output $$Y=\bar { A } $$ |
| $$0$$ $$1$$ | $$1$$ $$0$$ |
What is an intrinsic semi conductor? Give two examples.
Write the name of device $$'X'$$ in the following given diagram. Explain its working making its circuit diagram.
A Full Wave Rectifier is a circuit, which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage. It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage.
So X in the circuit is Full wave Rectifier
Working :
Full wave rectifier utilizes both halves of each a.c input. When the p-n junction is forward biased, the diode offers low resistance and when it is reversing biased it gives high resistance. The circuit is designed in such a manner that in the first half cycle if the diode is forward biased then in the second half cycle it is reverse biased and so on.
Full wave rectifier is preferable than the half wave rectifier as the former increases efficiency in a shorter time and we get continuous output. However, a filter circuit is used to make it smoother.
What is a transistor? Mention any two uses of transistor.
What is logic gates? Write two names of universal logic gates.
Explain working of half wave rectifier using $$p-n$$ junction diode with the help of circuit diagram.
Half-Wave rectifier: The rectifier which converts only one half of a.c into d.c is called half-wave rectifier.
Working:
The a.c input signal to be rectified is fed to the primary (P) coil of the transformer. The secondary (S) coil is connected to the junction diode through a load resistance $$R_{L}$$.
When the positive half of a.c input signal flows through the primary coil, as induced emf is set up in the secondary coil due to mutual induction. The direction of induced emf is such that the upper end of secondary coil becomes positive and lower end becomes negative. Since upper end of secondary coil is connected to n-region of the junction diode, so the junction diode is forward biased during the positive half of input a.c. Thus, the junction diode conducts and flow of current starts in the direction shown by arrows. The output voltage which varies in accordance with input half cycle is obtained across $$R_{L}$$.
When negative half cycle of a.c input flows through the primary coil, again induced emf is set up across the secondary coil due to mutual induction. Now the direction of induced emf is such that upper end of the secondary coil becomes negative and lower end becomes positive. So the junction diode is reverse biased. Hence the junction diode does not conduct, and therefore, we get no output across load resistance during negative half of input a.c. The input and corresponding output voltages as shown:
Draw the circuit diagram of full-wave rectifier using two p-n junction diodes and explain its working. Show the input and output waveforms.
Full-Wave Rectifier converts both halves of a.c input to d.c output.
Working:
The a.c input signal is fed to the primary (P) coil of the transformer. The p-region of both the diodes $$D_{1}$$ and $$D_{2}$$ are connected to two ends of secondary coil (S). The load resistance $$(R_{L})$$ across which output voltage is obtained is connected between common point of n-regions of diodes and central topping of the secondary coil.
When positive half cycle of input a.c signal flows through the primary coil, induced emf is set up in the secondary coil due to mutual induction. The direction of induced emf is such that the upper end of secondary coil becomes positive while lower end becomes negative. Thus, $$D_{1}$$ diode is forward biased and $$D_{2}$$ is reverse biased. So, current through $$D_{1}$$ flows through circuit in a direction shown.
During negative half cycle of input a.c signal, diode $$D_{1}$$ is reverse biased and $$D_{2}$$ is forward biased. The current due to $$D_{2}$$ flows through circuit in a direction shown.
Since, both the halves of input a.c (wave) are rectified, so the junction diode is called Full-wave rectifier.
The a.c input signal is fed to the primary (P) coil of the transformer. The p-region of both the diodes $$D_{1}$$ and $$D_{2}$$ are connected to two ends of secondary coil (S). The load resistance $$(R_{L})$$ across which output voltage is obtained is connected between common point of n-regions of diodes and central topping of the secondary coil.
When positive half cycle of input a.c signal flows through the primary coil, induced emf is set up in the secondary coil due to mutual induction. The direction of induced emf is such that the upper end of secondary coil becomes positive while lower end becomes negative. Thus, $$D_{1}$$ diode is forward biased and $$D_{2}$$ is reverse biased. So, current through $$D_{1}$$ flows through circuit in a direction shown.
During negative half cycle of input a.c signal, diode $$D_{1}$$ is reverse biased and $$D_{2}$$ is forward biased. The current due to $$D_{2}$$ flows through circuit in a direction shown.
Since, both the halves of input a.c (wave) are rectified, so the junction diode is called Full-wave rectifier.
Input and Output waveforms are as shown:
Construct the circuit symbol of Zener diode.
In given image circuit symbol of zener diode is shown.
How is $$p-n$$ junction diode used as a half-wave rectifier?
Explain its working, draw a neat circuit diagram. Show the waveforms of input and output voltages.
Half-Wave rectifier: The rectifier which converts only one half of a.c into d.c is called half-wave rectifier.
Working:
The a.c input signal to be rectified is fed to the primary (P) coil of the transformer. The secondary (S) coil is connected to the junction diode through a load resistance $$R_{L}$$.
When the positive half of a.c input signal flows through the primary coil, as induced emf is set up in the secondary coil due to mutual induction. The direction of induced emf is such that the upper end of secondary coil becomes positive and lower end becomes negative. Since upper end of secondary coil is connected to p-region of the junction diode, so the junction diode is forward biased during the positive half of input a.c. Thus, the junction diode conducts and flow of current starts in the direction shown by arrows. The output voltage which varies in accordance with input half cycle is obtained across $$R_{L}$$.
When negative half cycle of a.c input flows through the primary coil, again induced emf is set up across the secondary coil due to mutual induction. Now the direction of induced emf is such that upper end of the secondary coil becomes negative and lower end becomes positive. So the junction diode is reverse biased. Hence the junction diode does not conduct, and therefore, we get no output across load resistance during negative half of input a.c. The input and corresponding output voltages as shown:
Working:
The a.c input signal to be rectified is fed to the primary (P) coil of the transformer. The secondary (S) coil is connected to the junction diode through a load resistance $$R_{L}$$.
When the positive half of a.c input signal flows through the primary coil, as induced emf is set up in the secondary coil due to mutual induction. The direction of induced emf is such that the upper end of secondary coil becomes positive and lower end becomes negative. Since upper end of secondary coil is connected to p-region of the junction diode, so the junction diode is forward biased during the positive half of input a.c. Thus, the junction diode conducts and flow of current starts in the direction shown by arrows. The output voltage which varies in accordance with input half cycle is obtained across $$R_{L}$$.
When negative half cycle of a.c input flows through the primary coil, again induced emf is set up across the secondary coil due to mutual induction. Now the direction of induced emf is such that upper end of the secondary coil becomes negative and lower end becomes positive. So the junction diode is reverse biased. Hence the junction diode does not conduct, and therefore, we get no output across load resistance during negative half of input a.c. The input and corresponding output voltages as shown:
Write the two processes that take place in the formation of a $$p-n$$ junction. Explain with the help of a diagram, the formation of depletion region and barrier potential in a $$p-n$$ junction.
The two process that takes place in the formation of a p-n junction are- Diffusion and drift.
1. When a p-n junction is being formed, holes diffuse from the p-side to the n-side$$\left(p\rightarrow n \right)$$ while elctrons diffuse from n-side to the pside $$\left(n\rightarrow p\right)$$.
2.This happens due to the concentration gradient across p and n sides.
3. This gives rise to a diffusion current across the junction.
4. Diffusion current density is given by
$$J_{ n\left( diff \right) }=qD_{ n }\cfrac { dn(x) }{ dx } $$ ; $$J_{ p\left( diff \right) }=-qD_{ n }\cfrac { dp(x) }{ dx } $$
where,
$$J_{n(diff)}\rightarrow$$diffusion current density due to electrons.
$$J_{p(diff)\rightarrow}$$diffusion current density due to holes.
$$D_n\rightarrow$$electrons diffusion coefficient.
$$D_p\rightarrow$$holes diffusion coefficient.
$$n_(x)\rightarrow$$ profile of $$e_s$$ withb respect to $$x$$
$$P_(x)\rightarrow$$profile of holes with respect to $$x$$.
5. The thickness of the depletion region is merely around one-tenth of a micrometer.Also, an electric field develops, this electric field is responsible for the movement of electrons from the p-side to the n-side and holes from the n-side to p-side.
6. This motion of charged carrier due to the electric field is called drift.
7. Hence, a drift current starts which is opposite inn direction to the diffusion current.
8. Drift current is given by
$$J_{n(drift)}=nq\mu_nE$$ ; $$J_{p(drift)}=nq\mu_nE$$.
where
$$J_{n(drift)}\rightarrow$$ Drift current density due to electrons.
$$J_{p(drift)}\rightarrow$$ Drift current density due to holes.
$$n,p\rightarrow$$Concentration of electron and holes respectively.
$$E\rightarrow$$Applied Electric Field.
9. With the formation of p-n junction, the holes from p-region diffuse into n-region and electrons from n-region diffuse into p-region and electrons hole pair combine and get annihilated.
10. This in turn, produce potential barrier voltage across the junction which oppose the further diffusion through the junction.
11. Thus, small region forms in the vecinity of the junction which is depleted of free charge carrier and has only immobile ions is called the depletion regions.
12. Since, the n-side loses electrons and p-side gains electrons a potential difference is developed across the junction of the two region.
13. This potential difference tends to oppose further motion of electrons from the n-region into the p-region.The same happens for holes too.
14.The reverse polarity of this potential oppose further flow of carrier and is thus called the barrier potential.
A potential barrier V volts exists across a P-N junction. The thickness of the depletion region is 'd'. An electron with velocity 'v' approaches P-N junction from N-side. Find the velocity of the electron crossing the junction.
REF. Image.
Since, the electron is approaching the
barrier from n-side then
at some intermediates point
$$ F = eE $$ where $$ E = $$ electric field
$$ E = \dfrac{v}{d} $$
$$ \Rightarrow F = \dfrac{ev}{d} $$
$$ \Rightarrow $$ deceleration $$ a = \dfrac{F}{m_e} = \dfrac{ev}{m_ed} $$
$$m_e \rightarrow $$ mass of electron
if the electron crosses the barrier with
velocity ,$$v_{f}$$
then according Newton's III low of motion
$$ v_{f}^{2} = v^{2}-2\left ( \dfrac{ev}{m_{e}d} \right )\times d $$
$$ \Rightarrow v_{f}^{2} = v^{2}-\dfrac{2ev}{me} $$
Why is the base region of the transistor thinly doped?
The input resistance of a transistor is $$1000\Omega$$. On changing the base current by $$10\mu A$$, the collector current increases by $$2mA$$. If a load resistance of $$5\ k\Omega$$ is used in the circuit, calculate (i) the current gain, (ii) voltage gain of the amplifier.
What is a rectifier? With a suitable circuit diagram, describe the action of a full wave rectifier by drawing input and output waveforms.
Rectifier is a device which converts AC in to DC.
During the positive half cycle appearing at $$A$$, the diode $${D}_{1}$$ is forward biased, at the same time end $$B$$ is negative and diode $${D}_{2}$$ is reverse biased. The diode $${D}_{1}$$ conducts. A current flow through the load resistor $${R}_{L}$$ and output appears across $${R}_{L}$$During negative half cycle appearing at $$A$$, the diode $${D}_{1}$$ is reverse biased. End $$B$$ is positive and diode $${D}_{2}$$ is forward biased. The diode $${D}_{2}$$ conducts. A current flow through $${R}_{L}$$ in the same direction and output voltage appears across $${R}_{L}$$
What are n-type and p-type semiconductor?
Draw circuit diagram of common base configuration.
In common base configuration, emitter is the input terminal, collector is the output terminal and base terminal is connected as a common terminal for both input and output. That means the emitter terminal and common base terminal are known as input terminals whereas the collector terminal and common base terminal are known as output terminals.
In common base configuration, the base terminal is grounded so the common base configuration is also known as grounded base configuration. Sometimes common base configuration is referred to as common base amplifier, CB amplifier, or CB configuration.
Explain the importance of the PIV rating of a diode.
In the forward bias arrangement of a PN-jucnction diode.
The electric resistance of depletion layer is large bacause
Draw diagram for a P-N junction to obtain reverse bias characteristic curves. Explain the phenomenon of reverse breakdown for a P-N junction in reserve bias state by following processes-
(i) Avalanche breakdown
(ii) Zener breakdown
When we connect PN junction diode in reverse condition the minority from both side of PN diode move hence the reverse current flow.
When we increase the reverse voltage the depletion layer breaks at certain reverse voltage this voltage is known as break down voltage.
The break down of depletion layer can be two type.
(1) Avalanche breakdown : the minority charge carrier get highly accelerated. The kinetic energy becomes high enough at they knock-off electrons from the covalent bonds of semiconductors. The newly generated electron holes pairs also accelerated and cause ionisation the depletion layer & break down the depletion layer.
(2) Zener breakdown : Due to high doping in zener diode the depletion layer has small width. When large reverse biased applied across such a diode, the depletion layer & the energy bands get modified, As the depletion width is very small, small voltage will set high electric field of $$4 \times 10^7 V/m$$. this high electric field strips off many electrons from valence band which tunnel to the n-side through the this depletion layer. It gives rise to a large reverse current or breakdown current this breakdown in a diode due to the band to band tunneling is called zener breakdown.
When we increase the reverse voltage the depletion layer breaks at certain reverse voltage this voltage is known as break down voltage.
The break down of depletion layer can be two type.
(1) Avalanche breakdown : the minority charge carrier get highly accelerated. The kinetic energy becomes high enough at they knock-off electrons from the covalent bonds of semiconductors. The newly generated electron holes pairs also accelerated and cause ionisation the depletion layer & break down the depletion layer.
(2) Zener breakdown : Due to high doping in zener diode the depletion layer has small width. When large reverse biased applied across such a diode, the depletion layer & the energy bands get modified, As the depletion width is very small, small voltage will set high electric field of $$4 \times 10^7 V/m$$. this high electric field strips off many electrons from valence band which tunnel to the n-side through the this depletion layer. It gives rise to a large reverse current or breakdown current this breakdown in a diode due to the band to band tunneling is called zener breakdown.
Write the important considerations which are to be taken into account while fabricating a p-n junction diode to be used as a Light Emitting Diode (LED) . What should be the order of band gap of an LED, if it is required to emit light, in the visible range? Draw a circuit diagram and explain it action.
i) It is heavily doped p - n junction.
ii) The reverse breakdown of LED's are very low, typically around SV.
iii) The semiconductor used for fabrication of visible LED's must at least have a bond gap of $$1.8 eV$$.
(i) Write the truth tables of the logic gates marked $$P$$ and $$Q$$ in the given circuit.
(ii) Write the truth table for the circuit.
Reashma set up an experiment using liquid 'A' in the beaker as shown in the figure. She observed that the bulb glows. Then she replaced the liquid 'A' by another liquid 'B', this time the bulb did not glow. Rani suggested replacing the bulb by an LED. They observer that the LED glows. Give reason.
Draw the circuit arrangement for studying the $$V_I$$ characteristics of a p-n junction diode in reserve bias. Plot the $$V-I$$ characteristics in this case.
Development of P-N Jujction:-
At the Instant of the PN junction formation free e- near the junction diffuse across the junction into the P Junction and lombine with holes
$$\therefore $$ filling a hole moles a $$-ve$$ ion and leaves behind a tre ion on the N - side .These two layers of the and $$-ve$$ charges from the depletion Region as the regions near the Junction is depleted of charge carries As $$e^-$$ diffuse across the Junction ,a point is reached where the $$-ve$$ charges repels further diffusion of
$$\therefore $$ potential at Barries is formed.
The potential difference across the collector is a transistor, used in common emitter mode is $$1.5 V$$, with the collector resistance of $$3 k\Omega$$. Find $$(i)$$ the emitter and $$(ii)$$ the base current, if the $$d.c$$ gain of the transistor is $$50$$.
Identify the logic gates marked $$'P'$$ and $$'Q'$$ in the given circuit. Write the truth table for the combination.
$$P = NAND$$ gate and $$Q = OR$$ gate.
Truth table for the combination:
Truth table for the combination:
How many minimum NAND GATEs are required for obtaining an output of $$A.B+C.D$$?
Answer the following :
(i) Write the truth table of the following gate.
(ii) What will be the values of inputs A and B for the Boolean expression
$$ ( A \bar{+} B) . ( \bar {A.B}) = 1 $$
What is a rectifier? With the help of a neat circuit diagram explain the working of a full wave rectifier.
A circuit or device that is used to convert an alternating voltage (or current) into direct (unidirectional) voltage (or current) is called a rectifier.
In the figure shown above $$AB$$ is the primary coil to which the alternating input waveform is fed $$CD$$ is the secondary coil
$$D_1$$ & $$D_2$$ are diodes
$$R_L$$ is the load resistance across which output is taken.
Now from the figure above in the first positive half cycle of input waveform from the point $$A$$ is positive and point $$B$$ is negative in the primary coil.
By mutual induction point $$C$$ becomes positive and $$D$$ becomes negative in the secondary coil
Now as point $$C$$ is positive diode $$D_1$$ becomes forward biased and as $$D$$ is negative $$D_2$$ becomes reserved bias.
Current flows in the load current due to forward bias condition of $$D_1$$ and no current flows through $$D_2$$. Thus we get a positive loop signal as output waveform in the figure.
Now taking the second negative loop $$A$$ becomes negative and $$B$$ positive which in turn makes $$D$$ positive and $$C$$ negative.
Diode $$D_2$$ becomes forward bias and $$D_2$$ reverse bias and current flows through load resistance due to $$D_2$$ thus we get an output waveform due to $$D_2$$ as shown in the figure.
This procedure goes on for all the positive and negative cycles of input alternating waveform to get a positive output waveform as shown in the figure.
The electrical conductivity of a semiconductor increases when electromagnetic radiation of wavelength shorter than $$248\ nm$$ is incident on it. The forbidden band energy for the semiconductor in $$eV$$ is
What is the resistance of an intrinsic semiconductor at OK ?
Can we measure the potential difference across an unbiased p-n junction by connecting a sensitive voltmeter across it ?
Name fundamental logic gates.
Name two semiconductor materials.
The active volume of a laser constructed of the semi-conductor GaAlAs is only $$ 200 \mu
m^3$$ (smaller than a grain of sand), and yet the laser can continuously deliver 5.0 mW of power at a wavelength of $$0.80\mu m$$. At what rate does it generate photons?
In a transistor , doping level in base is increased slightly. How will it affect base current ?
At what temperature would an intrinsic semiconductor behave like a perfect insulator ?
Name the logic gate marked P and Q in the given logic circuit .
In a transistor , doping level in base is increased slightly. How will it affect collector current ?
Draw the output waveform at X , using the given inputs A , B for the logic circuit shown alongside . Also identify the gate.
$$ \bar{Y} = A . B $$
and $$ X = \bar{Y} = A . B $$
This is AND operation . Therefore , the output is $$ 1$$ when both inputs are $$ 1$$.
Accordingly the waveform output is shown in figure.
Name the logic gate whose repetitive use can make digital circuits .
What signal voltage is represented for positive logic state $$ 1$$ ?
(a) Explain briefly the process of emission of light by a Light Emitting diode. (LED).
(b) Which semiconductor are preferred to make LEDs and why ?
(c) Give two advantages of using LEDs over conventional incandescent lamps.
The output of an OR gate is connected to both the inputs of a NAND gate. Draw the logic circuit of this combination of gates and write its truth table.
The logic circuit is shown is fig.
The logic circuit represents NOR gate. Its truth table is
A B Y' Y
$$ 0 $$ $$ 0 $$ $$ 0 $$ $$ 1 $$
$$ 1 $$ $$ 0 $$ $$ 1 $$ $$ 0 $$
$$ 0 $$ $$ 1 $$ $$ 1 $$ $$ 0 $$
$$ 1 $$ $$ 1 $$ $$ 1 $$ $$ 0 $$
Name the logic gate which can be realised by using p-n junction diode in the given diagram. Give its logic symbol and write the truth table. Name the gate which will be obtained by combining with a NOT gate.
The logic gate shown in the circuit diagram is OR gate.
Symbol of OR gate:
Input Output
A B Y
$$ 0 $$ $$ 0 $$ $$ 1 $$
$$ 1 $$ $$ 0 $$ $$ 1 $$
$$ 0 $$ $$ 1 $$ $$ 1 $$
$$ 1 $$ $$ 1 $$ $$ 1 $$
The gate obtained by combining OR gate with NOT gate will be NOR gate.
How is a light emitting diode fabricated ? Briefly state is working. Write any two important advantages of LEDs over the conventional incandescent low power lamps.
Distinguish between a metal and an insulator on the basis of energy band diagrams.
In a common emitter mode of a transistor , the d.c current gain is $$ 20 $$ , the emitter is $$ 7 \, mA $$. Calculate (i) base current and (ii) collector current.
Explain the following :
LEDs are made of compound semiconductor and not by elemental semiconductors.
In the figure given alongside is, (i) the emitter and (ii) the collector forward or reverse biased ? With the help of a circuit diagram explain the action of npn transistor.
The given transistor is p-n-p transistor . The emitter is reverse biased and the collector is forward biased.
Action of n-p-n transistor
An npn transistor is equivalent to two p-n junction placed back to back with their very thin p-region connected together. The circuit diagram for the operation of npn transistor is shown in fig. The two batteries $$ V_{EE} $$ and $$ V_{CC} $$ represent emitter supply and collector supply respectively.
Transistor Action : Transistor works only when its emitter base junction is forward biased and collector -emitter junction is reversed biased. Due to this the majority charge carriers from the emitter, accelerate to collector side and create $$ I_E , I_B $$ and $$ I_C $$ such that $$ I_E = I_B + I_C $$.
Base current and Collector current : Under forward bias of emitter -base junction , the electrons in emitter and holes in base are compelled to move towards the junction , thus the depletion layer of emitter -base junction is eliminated. As the base region is very thin , most electrons (about $$ 98 $$ % ) starting from emitter region cross the base region and reach the collector while only a few of them (about $$ 2$$ %) combine with an equal number of holes of base -region and get neutralized . As soon as a hole (in region) combines with an electron , a covalent bond of crystal atom of base region breaks releasing an electron-hole pair. The electron released is attracted by positive terminal of emitter battery $$ V_{EE} $$ giving rise to a feeble base current $$ (I_B) $$. Its direction in external circuit is from emitter to base. The hole released in the base region compensates the loss of hole neutralized by electrons.
The electrons crossing the base and entering the collector , due to reverse biasing of collector -base junction are attracted towards the positive terminal of collector battery $$ V_{CC} $$.In the process an equal number of electrons leave the negative terminal of battery $$ V_{CC} $$ and enter the positive terminal of battery $$ V_{EE} $$. This causes a current in collector circuit, called the collector current . In addition to this current is also due to flow of minority charge carriers under reverse bias of base-collector junction. This current is called the leakage current.
Thus , collector current is formed of two components:
(i) Current $$ (I_{nc}) $$ due to flow of electrons (majority charge carriers) moving from emitter to collector.
(ii) Leakage current $$ (I_{leakage}) $$ due to minority charge carriers i.e., $$ I_C = I_{nc} + I_{leakage} $$.
Emitter Current : When electrons enter the emitter battery $$ V_{EE} $$ from the base causing base current or electrons enter the collector battery $$ V_{CC} $$ from the collector causing collector current , an equal number of electrons enter from battery $$ V_{EE} $$ to emitter, causing the emitter current. The process continues.
Relation between Emitter , Base and Collector Currents :
Applying Kirchhoff's Law at terminal O , we get
$$ I_E = I_B + I_C $$
That is the emitter $$ I_E $$ is the sum of base current $$ I_B $$ and the collector current $$ i_C $$. This is the fundamental relation between currents in the bipolar transistor circuit.
Answer the following questions :
(i) What is an 'Integrated circuit (I.C)' ? Distinguish between (i) linear I.C and (ii) Digital I.C.
(ii) Identify the equivalent gate for the following circuit and write its truth table.
The output of NOR gate is connected to both the inputs of NAND gate.
The equivalent gate is OR gate.
The inputs A and B are inverted by using two NOT gates and their outputs are fed to the NOR gate as shown above .
Analyse the action of the gate (1) and (2) and identify the logic gate of the complete circuit so obtained. Give its symbol and truth table.
Output of gate $$ (1) , Y_1 = A \bar{+} A = \bar{A} $$
Output of gate $$ (2) , Y_2 = B \bar{+} B = \bar{B} $$
Output $$ Y = Y_1 \bar{+} Y_2 = \bar{A} \bar{+} \bar{B} = \bar{\bar{A}} . \bar{\bar{B}} = AB $$
Thus gates (1) and (2) act on 'NOT' gates and the complete circuit acts as 'AND' gate . The symbol and truth table of complete circuit are given below :
Truth table
Output of gate $$ (2) , Y_2 = B \bar{+} B = \bar{B} $$
Output $$ Y = Y_1 \bar{+} Y_2 = \bar{A} \bar{+} \bar{B} = \bar{\bar{A}} . \bar{\bar{B}} = AB $$
Thus gates (1) and (2) act on 'NOT' gates and the complete circuit acts as 'AND' gate . The symbol and truth table of complete circuit are given below :
Truth table
| $$ A $$ | $$ B $$ | $$ Y $$ |
| $$ 0 $$ | $$ 0 $$ | $$ 0 $$ |
| $$ 1$$ | $$ 0 $$ | $$ 0 $$ |
| $$ 0 $$ | $$ 1 $$ | $$ 1 $$ |
| $$ 1 $$ | $$ 1 $$ | $$ 1 $$ |
Explain the forward and the reverse characteristic of a Zener diode.
A diode is a fundamental electronic component that allows the flow of electricity in one direction only. There are many types of diodes and Zener diode is one of the commonly used diodes. Zener diode not only allow current to flow from anode to cathode but also, in the reverse direction on reaching the Zener voltage. Due to this functionality, Zener diodes are the most commonly used semiconductor diodes.
V-I Characteristics of Zener diode:
The diagram given below shows the V-I characteristics of the Zener diode.
When reverse-biased voltage is applied to a Zener diode it allows only a small amount of leakage current until the voltage is less than Zener voltage.
The V-I characteristics of a Zener diode can be divided into two parts as follows:
1. Forward characteristics.
2. Reverse characteristics.
Forward characteristics:
The first quadrant in the graph represents the forward characteristics of a Zener diode. From the graph, we understand that it is almost identical to the forward characteristics of any other P-N junction diode.
Reverse characteristics:
When a reverse voltage is applied to a Zener voltage, initially a small reverse saturation current to flows across the diode. This current is due to thermally generated minority carriers. As the reverse voltage is increased, at a certain value of reverse voltage, the reverse current increases drastically and sharply. This is an indication that the breakdown has occurred. We call this voltage breakdown voltage or Zener voltage and it is denoted by Vz.
Write the truth table for the circuits given in fig. consisting of NOR gates only. identify the logic operation (OR, AND , NOT) performed by the two circuits.
Draw the circuit diagram of a half-wave rectifier. Explain its working. What is the frequency of ripple in its output?
A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. The process is known as rectification.
Construction and working of half-wave rectifier:
If an alternating voltage is applied across a dipole in series with a load, a pulsating voltage will appear across the load only during the half cycles of the AC input during which the diode is forward biased. Such a rectifier circuit as shown below figure (A) is called a half-wave rectifier.
The secondary of a transformer supplies the desired AC voltage across terminals A and B. When the voltage at A is positive, the diode is forward baised and it conducts. When A is negative, the diode is reverse biased and it does not conduct. The reverse saturation current of a diode is negligible and can be considered equal to zero for practical purposes. (The reverse breakdown voltage of the diode must be sufficiently higher than the peak AC voltage at the secondary of the transformer to protect the diode from reverse breakdown). Therefore, in the positive half-cycle of AC, there is a current through the load resistor RL and we get an output voltage, as shown in below figure (B). whereas there is no current in the negative half-cycle. In the next positive half-cycle, again we get the output voltage. Thus, the output voltage, through still varying, is restricted to only one direction and is said to be rectified.
What do you mean by a truth table?
Why is the base of a transistor made thin and is lightly doped?
Express by a truth table, the output Y for all possible inputs $$ A $$ and $$ B $$ in the logic as shown
How is a Zener diode different than an ordinary diode?
What is rectification? Draw the circuit diagram of half wave rectifier and explain its working. Show the input ac voltage and output voltage waveforms from the rectifier circuit.
A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. The process is known as rectification.
Construction and working of half wave rectifier:
If an alternating voltage is applied across a diode in series with a load, a pulsating voltage will appear across the load only during the half cycles of the ac input during which the diode is forward biased. Such rectifier circuit, as shown in Fig(a). is called a half-wave rectifier.
The secondary of a transformer supplies the desired ac voltage across terminals A and B. When the voltage at A is positive, the diode is forward biased and it conducts. When A is negative, the diode is reverse-biased and it does not conduct. The reverse saturation current of a diode is negligible and can be considered equal to zero for practical purposes. (The reverse breakdown voltage of the diode must be sufficiently higher than the peak ac voltage at the secondary of the transformer to protect the diode from reverse breakdown.) Therefore, in the positive half-cycle of ac there is a current through the load resistor $$R_L$$ and we get an output voltage, as shown in Fig(b), whereas there is no current in the negative halfcycle. In the next positive half-cycle, again we get the output voltage. Thus, the output voltage, though still varying, is restricted to only one direction and is said to be rectified.
What is rectification? Explain the working of bridge rectifier. Draw the input and output signals.
Rectifier : The process in which alternating voltage or alternating current is converted into direct voltage or direct current is known as rectification. The device used for this process is called rectifier.
Working of a Bridge rectifier :
A bridge rectifier is shown in figure. There are four diodes $$D_{1}, D_{2}, D_{3}$$ and $$D_{4}$$ used in the circuit, which are connected to form a network. The input ends $$A$$ and $$C$$ of the network are connected to the secondary ends $$S_{1}$$ and $$S_{2}$$ of the transformer. The output ends $$B$$ and $$D$$ are connected to the load resistance $$R_{L}$$.
During positive input half cycle of the arc voltage, the point $$A$$ is positive with respect to $$C$$. The diodes $$D_{1}$$ and $$D_{3}$$ are forward biased and conduct, whereas the diodes $$D_{2}$$ and $$D_{4}$$ are reverse biased and do not conduct.
Hence, current flows along $$S_{1}ABCDS_{2}$$ through $$RL$$. During negative half cycle, the point $$C$$ is positive with respect to $$A$$. The diodes $$D_{2}$$ and $$D_{4}$$ are forward biased and conduct, whereas the diodes $$D_{1}$$ and $$D_{3}$$ are reverse biased and they do not conduct. Hence, current flows along $$S_{2}CBADS_{1}$$ through $$R_{L}$$. The same process is repeated for subsequent half cycles. It can be seen that current flows through $$R_{L}$$ in the same direction, during both half cycles of the input a.c. signals. The output signal corresponding to the input signal is shown in figure. The efficiency of the bridge rectifier is approximately $$81.2$$%.
Advantages of bridge rectifier : (i) Centre tap on the secondary of the transformer is not necessary, (ii) Smaller transformer can be used and (iii) It is suited for high voltage applications.
Working of a Bridge rectifier :
A bridge rectifier is shown in figure. There are four diodes $$D_{1}, D_{2}, D_{3}$$ and $$D_{4}$$ used in the circuit, which are connected to form a network. The input ends $$A$$ and $$C$$ of the network are connected to the secondary ends $$S_{1}$$ and $$S_{2}$$ of the transformer. The output ends $$B$$ and $$D$$ are connected to the load resistance $$R_{L}$$.
During positive input half cycle of the arc voltage, the point $$A$$ is positive with respect to $$C$$. The diodes $$D_{1}$$ and $$D_{3}$$ are forward biased and conduct, whereas the diodes $$D_{2}$$ and $$D_{4}$$ are reverse biased and do not conduct.
Hence, current flows along $$S_{1}ABCDS_{2}$$ through $$RL$$. During negative half cycle, the point $$C$$ is positive with respect to $$A$$. The diodes $$D_{2}$$ and $$D_{4}$$ are forward biased and conduct, whereas the diodes $$D_{1}$$ and $$D_{3}$$ are reverse biased and they do not conduct. Hence, current flows along $$S_{2}CBADS_{1}$$ through $$R_{L}$$. The same process is repeated for subsequent half cycles. It can be seen that current flows through $$R_{L}$$ in the same direction, during both half cycles of the input a.c. signals. The output signal corresponding to the input signal is shown in figure. The efficiency of the bridge rectifier is approximately $$81.2$$%.
Advantages of bridge rectifier : (i) Centre tap on the secondary of the transformer is not necessary, (ii) Smaller transformer can be used and (iii) It is suited for high voltage applications.
If in a $$p-n$$ junction diode, a sinusoidal input signal is applied as shown.
Then, the output signal across $$R_{L}$$ will be:
the intrinsic semiconductor at room temperature is
Suppose a pure Si crystal has $$5\times 10^{28}$$ atoms per $$m^3$$. It is doped by $$1$$ ppm concentration of pentavalent As. Calculate the number of electrons and holes. Given that $$n_i=1.5\times 10^{16}$$ per $$m^3$$.
Write the truth table of AND gate.
What is rectifier? Explain the working of p-n junction diode as a full-wave rectifier with the help of suitable circuit diagram.
Draw a circuit diagram of an n-p-n transistor with its emitter-base junction foward biased and base-collector junction reverse biased.
Briefly describe its working.
Explain how a transistor in active states exhibits a low resistance at its emitter-base junction and high resistance at its base-collector junction.
n-p-n transistor with its emitter -base junction forward biased and base collector junction reversed bias
Her, Emitter-base junction is forward biased and collector base junction is reverse biased.
The voltage across the device causes electrons from emitter to flow collector.
electrons pass through p type lighty doped base region and some of the electrons recombine with holes, therefore collector current is less than that of emitter current. Emitter current, base current and collector current can be related by: Emitter current = Base current + collector current.
In active mode of transistor emitter-base junction is forward biased and collector base junction is reversed biased. When transistor operates in this mode, collector current increases linearly with the increase in base current. That's why in active state it exhibits low resistance at emitter base and high resistance at its base -collector.
If each diode in figure, has a forward bias resistance of $$125\Omega$$ and infinite resistance in reverse bais, what will be the values of the current $${I}_{1},{I}_{2},{I}_{3}$$ and $${I}_{4}$$?
A Zener of power rating $$1W$$ is to be used as a voltage regulator. If Zener has a breakdown of $$5V$$ and it has to regulate voltage which fluctuated between $$3V$$ and $$7V$$, what should be the value of $${R}_{s}$$ for safe operation (Figure)?
The current amplification is 0.99 for any transistor in the common-base configuration. Calculate the change in collector current when there is a 5.0 milliampere change in emitter current. What will be the change in base current?
A transistor is connected in common emitter configuration. A power supply of $$ 8 \vee $$ is there in the collector circuit and the potential drop of $$ 0.5 \mathrm{V} $$ is on the resistance of 80012 connected in series with the collector. If current amplification factor is $$ a=0.96 . $$ Then calculate the base current.
When the base current in a transistor is changed from $$30 \, \mu\, A$$ to $$80 \mu \,A$$, the collector current is changed from $$1.0 \mu \,A$$ to $$3\cdot 5\, \mu \,A$$. Find the current gain $$\beta$$
A silicon-based MOSFET has a square gate $$0.50$$ mm on edge. The insulating silicon oxide layer that separates the gate from the $$p-type$$ substrate is $$0.20$$ mm thick and has a dielectric constant of $$4.5.$$ $$(a)$$ What is the equivalent gate – substrate capacitance (treating the gate as one plate and the substrate as the other plate)? $$(b)$$ Approximately how many elementary charges e appear in the gate when there is a gate–source potential difference of $$1.0 V?$$
What is the direction of diffusion current in junction diode?
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