ANAND INSTITUTE OF HIGHER TECHNOLOGY

KAZHIPATTUR-603103

DEPARTMENT OF ELECTRONICS AND INSTRUMENTATION

Sub : Electronic Devices and Circuits Class : III sem

Code : EC6202 Year : II-B

Staff :P.KAMALI

UNIT-I

1. Give the diode current equation?(NOV 07) (MAY 07)The mathematical representation of V-I characteristics of diode is called V-I

characteristics equation or diode current equation. It gives the mathematical relationship between applied voltage V and diode current I. it is given by

I = I0 [e V/ηVT -1] AI0 - Reverse saturation currentV- applied voltageη – emission coefficient or ideality factorVT- voltage equivalent of temperature in volts

2. Define static resistance of a diode? (NOV 07)It is defined as the ratio of the voltage to the current, V/I, in the forward bias

characteristics of the PN junction diode. As the static resistance varies widely with V and I, it is not a useful parameter.

3. What is meant by early effect? (NOV 07) (APR 02) (APR 05)As the collector voltage VCC is made to increase the reverse bias, the space charge width

between collector and base tends to increase, with the result that the effective width of the base decrease. This dependency of base width on collector to emitter voltage is known as the Early effect.

4. Give some application of bipolar transistor? (NOV 07)

1.It is used in amplifier and oscillator circuits, and as a switch in digital circuits

2.It has wide applications in computers, satellites and other modern communication systems

5. Define tunneling effect? (NOV 07)

The width of the junction barrier varies inversely as the square root of the impurity concentration and therefore is reduced from 5microns to less than 10-8m. for such thin potential energy barriers the electrons will penetrate through the junction rather than surmounting them. This quantum mechnical behavior is referred to as tunneling and hence these high impurity density PN junction are called tunnel diode.

6. Define the term transistion capacitance CT of a PN diode? (NOV 09) (NOV 08) (MAY 09)

7. What is thermal runaway? (NOV 09) (APR 02) (MAY 07)The three variables in the equation, β, IB and ICO increase with rise in temperature. In

particular, the reverse saturation current or leakage current ICO changes greatly with temperature. Specifically, it doubles for every 100C rise in temperature. The collector current IC causes the collector base junction temperature to rise which, in turn, increase ICO, as a result IC will increase still further, which will further rise the temperature at the collector base junction. This process will become cumulative leading to “thermal runaway”. Consequently, the ratings of the transistor are exceeded which may destroy the transistor itself.

8. Why a series resistor is necessary when a diode is forward biased? (NOV 08)

9. Determine β and IE for a transistor if IB=50µA and IC=3.6mA. (NOV 08)

10. What bias conditions must exist for a transistor to operate as an amplifier? (NOV 08)

11. Why a reverse biased varactor diode exhibits capacitance? (NOV 08)

12. What is meant by instrinsic and extrinsic semiconductor? (NOV 05)A pure semiconductor is called intrinsic semiconductor.Due to the poor conduction at room temperature, the intrinsic semiconductor as such, is

not useful in the electronic devices. Hence the current conduction capability of the intrinsic semiconductor should be increased. This can be achieved by adding a small amount of impurity to the intrinsic semiconductor, so that it becomes impure or extrinsic semiconductor.

13. Define α and β of a transistor? (NOV 05)

14. What is varactor diode? (NOV 05)

15. Define cut-in voltage and peak inverse voltage of a P-N diode? (MAY 06) (MAY 07) (MAY 09)When diode is forward biased, some voltage is necessary to overcome barrier potential,

to make diode conduct. This is called its cut in voltage.In reverse biased, opposite polarity voltage appears across diode. The maximum reverse

voltage which diode can withstand without breakdown is called peak inverse voltage.

16. In a bipolar transistor, which region is wider and which region is thinner? why? (MAY 06)Emitter is heavily doped so that it can inject a large number of charge carriers into the

base. Base is lightly doped and very thin. It passes most of the injected charge carriers from the emitter into the collector. Collector is moderately doped.

17. What are called P and N type semiconductor? (NOV 06)A small amount of pentavalent impurities such arsenic, antimony or phosphorus is added

to the pure semiconductor (germanium and silicon) to get N-type semiconductor.A small amount of trivalent impurities such as aluminium or boron is added to the pure

semiconductor to get P-type semiconductor

18. What is meant by diffusion current? (NOV 06) (NOV 02) (NOV 09)

19. Define barrier potential at the junction? (NOV 06)

20. Give the current gain expression for a common emitter transistor configuration? (MAY 07)

21. What is the significance of a varactor diode? (MAY 07)

22. What is meant by depletion region? (NOV 07) (MAY 09)

23. Why are zener diodes employed as voltage regulator? (MAY 06) (MAY07)From the zener characteristics, under the reverse bias condition, the voltage across the

diode remains almost constant although the current through the diode increase as shown in region AB. Thus the voltage across the zener diode serves as a reference voltage. Hence the diode can be used as a voltage regulator.

24. What is meant by zener breakdown? (NOV 03) (APR 05) (MAY 07)

25. In bipolar junction transistors, mention the heavily doped and lightly doped regions? (MAY 09)Emitter is heavily doped so that it can inject a large number of charge carriers into the

base. Base is lightly doped and very thin. It passes most of the injected charge carriers from the emitter into the collector. Collector is moderately doped.

26. Mention the applications of varactor diode? (MAY 09)

27. Mention the biasing conditions of emitter base junction and collector base junction in active region and cut off region? (MAY 09)

Region Emitter base junction Collector base junctionActive Forward bias Reverse bias

Cut-off Reverse bias Reverse biasSaturation Forward bias Forward bias

28. Draw the equivalent circuit of tunnel diode? (MAY 09)

29. What do you understand by biasing? (NOV 07)

30. Define stability factor of a transistor circuit? (MAY 07)

31. What is the difference between DC loadline and AC load line in a Ce amplifier having voltage divider bias and external load resistance ?(NOV 10)

32. The reverse saturation current in a silicon diode is 100na ar 27c. find the current through the diode if the applied forward voltage is 1 volt?(NOV 10)

33. What do you mean by avalanche breakdown?(NOV 2011)34. Which transistor configration is mostly used as an amplifier,why? (NOV 2011)

UNIT-II

1. List out any two difference between JFET and UJT? (NOV 07)

2. What type of biasing is needed for the gate of a n-channel JFET? why? (NOV 07)

3. Define pinch off voltage? (NOV 08) (NOV 07) (NOV 06) (NOV 09)As VDS is increased, the cross-sectional area of the channel will be reduced. At a certain

value VP of VDS, the cross sectional area at B becomes minimum. At this voltage, the channel is said to be pinched off and drain voltage VP is called the pinch off voltage.

Otherwise Any further increase in VDS does not increase the drain current ID. ID approaches the constant saturation level. The voltage VDS at which the current ID reaches to its constant saturation level is called pinch off voltage

4. If the VGS of a n-channel JFET is increased negatively, what happens to the drain current ID? (NOV 08)

5. How can an SCR be turned ON and turned OFF? (NOV 08)As the voltage at which SCR is switched ‘ON’ can be controlled by varying the gate

current IG, it is commonly called as controlled switch. Once SCR is turned ON, the gate loses control, the gate cannot be used to switch the device off. One way to turn the device off is by lowering the anode current below the holding current IH by reducing the supply voltage below holding voltage VH, keeping the gate open

6. List the special features of FET? (MAY 09) (NOV 05) (NOV 09) It is unipolar and voltage controlled device. Like BJT, the parameters of FET are also temperature dependent. In FET, as temperature

increase drain resistance also increase, reducing the drain current. Thus unlike BJT, thermal runaway does not occur with FET. Thus we can say that FET is more temperature stable as compared to the BJT

FET has very high input impedance FETs require less space than that for BJTs, hence they are preferred in integrated circuits FET is less noisy than a bipolar transistor FET exhibits no offset voltage at zero drain current and hence makes an excellent signal

chopper Gain bandwidth product of FET is relatively small as compared to conventional transistor

. this is the disadvantages of the FET

7. What is a MOSFET? Mention its types. (NOV 09)Metal Oxide Semiconductor Field Effect Transistor (MOSFET), MOSFET is the

common term for the Insulated Gate Field Effect Transistor(IGFET).Principle of MOSFET, By applying a transverse electric field across an insulator ,

deposited on the semiconducting material, the thickness and hence the resistance of a conducting channel of a semiconducting material can be controlled

There are two basic forms of MOSFET: 1. Enhancement MOSFET 2. Depletion MOSFET

8. What is TRIAC? Draw the symbol? (NOV 09)Traic (TRIODE A.C. SWITCH) is a thre terminal semiconductor switching device which can control alternating current in aload.

9. Explain one application JFET used as variable resistor? (NOV 05)FET is operated in the constant current portion of its output characteristics for the linear

applications. In the region before pinch off, where VDS is small, the drain to source resistance rd can be controlled by the bias voltage VGS. The FET is useful as a Voltage Variable Resistor (VVR) or Voltage Dependent Resistor (VDR). For example, the VVR can be used in Automatic Gain Control circuit of a multistage amplifier.

10. What is the bias stability in FET circuits? (APR 99)

11. Write any four parameters of JFET? (APR 04)

Mutual conductance

Drain resistance Amplification factor Power dissipation

12. Draw the equivalent circuit of UJT? (NOV 02) (NOV 06)

13. Why FET is called Voltage controlled device? (NOV 10)

14. Why FET is called unipolar device. (APR 02)The FET is a device in which the flow of current through the conducting region is

controlled by an electric field. Hence the name Field Effect Transistor (FET). As current conduction is only by majority carriers, FET is said to be a unipolar device.

Based on the construction, the FET can be classified into two types as Junction FET (JFET) and Metal Oxide Semiconductor FET(MOSFET)

15. How can a FET be used as a voltage controlled resistor? (APR 02)FET is operated in the constant current portion of its output characteristics for the linear

applications. In the region before pinch off, where VDS is small, the drain to source resistance rd can be controlled by the bias voltage VGS. The FET is useful as a Voltage Variable Resistor (VVR) or Voltage Dependent Resistor (VDR).

In JFET, rd and gd may also be expressed as, gd = gd0 [ 1-(VGS/VP)1/2] and rd= r0/1-KVGS

gd0 is the value of drain conductance when the bias voltage VGS is zero.Thus small signal FET drain resistance rd varies with applied gate voltage VGS and FET

acts like a variable passive resistor.

16. What are the advantages of FET? (APR 03) FET has high input resistance(100MΩ) and MOSFET(1010 to 1015Ω) FET is voltage controlled device It shows a high degree of isolation between input and output All FET are unipolar rather than bipolar device FET generate a lower noise level than the BJT FET are more stable than BJT Power FET can dissipate higher power and can switch very large currents

17. Draw the low frequency equivalent circuit of JFET? (NOV 03) (MAY 09)18. Differentiate between BJT and FET? (MAY 06)

S.No Parameters BJT FET1 Control

elementCurrent controlled device. Input current controls output current

Voltage controlled device. Input voltage VGS controls drain current I0

2 Device type Current flows due to both, majority & minority carriers hence bipolar device

Current flows only due to majority carriers and hence unipolar device

3 Input resistance

Less compare to JFET High compare to BJT

4 Sensitivity Higher sensitivity to changes in the applied signals

Smaller in construction than BJT, thus making them useful in IC

5 Thermal stability

Less More

6 Thermal runaway

Exists in BJT, because of cumulative effect of increase in IC temperature, resulting increase in temperature in the device.

Does not exist in JFET, because drain resistance rd increases with temperature which reduces ID, reducing the ID and hence the temperature of the device

7 Thermal noise

More in BJT as more charge carriers cross junctions

Much lower in JFET as very few charge carriers cross the junctions

19. Compare MOSFET and FET? (NOV 06)

20. Draw the transistor equivalent circuit of SCR? (NOV 07)

21. Give any two application of UJT? (MAY 07) (NOV 05)o Sawtooth wave generatoro Pulse generatoro Switching, timing and phase control circuitso UJT Relaxation oscillator

22. Differentiate between BJT and JFET? (MAY 07) (MAY 09)

S.No JFET BJT1 FET operation depends only on the flow

of majority carroiers-holes for P channel and electrons for N channel. unipolar device

Bipolar transistor operation depends on both minority and majority carriers.

2 As FET has no junctions and the conduction is through an N-type or P-type semiconductor material.FET is less noise

More noise in BJT

3 As the input circuit of FET is reverse biased ,FET exhibits a much higher input impedance and lower output impedance and there will be a high degree of isolation between input and output. FET

BJT has low input impedance because its input circuit is forward biased.

can act as an excellent buffer amplifier4 Voltage controlled device, voltage at the

input terminals controls the output Current controlled device, the input current controls the output current

5 FET are much easier to fabricate and particularly suitable for ICs because they occupy less space

It occupy more space than JFET

6 FET can tolerate a much higher level of radiation since they do not rely on minority carriers for their operation

The performance of BJT is degraded by neutron radiation because of the reduction in minority carriers lifetime

7 The performance of FET is relatively unaffected by ambient temperature changes. As it has a negative temperature at high current levels, it prevents the FET from thermal breakdown.

The BJT has a positive temperature coefficient at high current levels which leads to thermal breakdown

8 Since FET does not suffer from minority carrier storage effects, it has higher switching speeds and cut-off frequency

BJT suffers from minority carrier storage effects and therefore has lower switching speed and cut-off frequency

9 FET amplifiers have low gain bandwidth product due to the junction capacitive effects

BJT amplifiers have high gain bandwidth product

23. Compare SCR and TRAIC? (NOV 06)

S.No SCR TRAIC1 The SCR is unidirectional device The TRAIC conducts in both the directional

hence bilateral device2 The terminals are called anode-cathode

due to unilateral propertyThe terminals are called MT1 and MT2 with gate

3 The gate current can be only in direction to turn on SCR

For both the directions of gate current , TRAIC conducts

4 The characteristics are lying in first quadrant only, hence are nonsymmetrical

The characteristics are lying in first and third quadrant and are symmetrical

5 Only one mode of operation is possible The operation in four different mode is possible

6 The reliability is more The reliability is less7 Available in large ratings Not available in large ratings8 Unijunction transistor is used for

triggeringThe DIAC is used for triggering

9 The application are phase control, protection of power supplies

The application are phase control, light dimmer, motor control

24. What is called intrinsic stand off ratio in UJT? (MAY 06) (MAY 09)The interbase resistance between B2 and B1 of the silicon bar is RBB=RB1+RB2. With

emitter terminal open, if voltage VBB is applied between the two bases, a voltage gradient is established along the N-type bar. The voltage drop across RB1 is given by V1=ηVBB, where the intrinsic stand off ratio η=RB1/(RB1+RB2). The typical value of η ranges from 0.56 to 0.75

25. Define latch current and holding current in SCR? (NOV 05) (NOV 10)

Latching current (IL) - Latching current is the minimum current required to latch or trigger the device from its OFF state to its ON state

Holding current (IH) – Holding current is the minimum value of current to hold the device in ON state. For turning the device OFF, the anode current should be lowered below IH by increasing the external circuit resistance

26. Draw the VI characteristics of DIAC? (MAY 07)

27. Mention the three regions that are present in the drain-source characteristics of JFET? (NOV 04)Ohmic region – the region from VDS=0V to VDS=VP is called ohmic region. In the

channel ohmic region the drain to source resistance is related to the gate voltage, in an almost linear manner.

Pinch off region – when VDS=VP, ID becomes maximum. When VDS is increased beyond VP, the length of the pinch off or saturation region increases. Hence, there is no further increase of ID

Breakdown region – At a certain voltage corresponding to the point B, ID suddenly increase. This effect is due to the Avalanche multiplication of electrons caused by breaking of covalent bonds of silicon atoms in the depletion region between the gate and the drain. The drain voltage at which the breakdown occur.

28. Why do you call FET as a Field Effect Transistor? (NOV 2011)29. Compare FET and UJT? (NOV 2011)

UNIT III

1. Why does amplitude distortion occur in power amplifier? (MAY 07) (NOV 09)

Harmonic distortion is seen by the nonlinear dynamic curve for an active device. In this type of distortion the new frequencies are produced in the output, which are not present in the input signal. This harmonic distortion is sometimes called amplitude distortion

2. Define class A operation? (NOV 06)

In a class A amplifier, the transistor is biased such that the output current flows the transistor is ON for the full cycle of the input ac signal

3. How class A ,class B and class AB amplifiers differ based on conduction? (MAY 07)

4. What are the characteristics of a common collector amplifier? (NOV 07) High gain of less than unith High voltage gain Power gain approximately equal to voltage gain No phase shift for current or voltage Small input impedance

5. Draw the h-parameter equivalent circuit of a common emitter transistor? (APR 08) (MAY 09)

6. Define class C operation of power amplifier? (NOV 05)

In a class C amplifier the transistor bias and amplitude of the input signal are selected such that the output current flows the transistor is ON for less than one half cycle of the input ac signal

7. Why class A amplifier must not be operated under no signal conditions? (NOV 05)When there is no input signal the power dissipation must be zero, but here the power

dissipation is present due to this reason the class A power amplifier is not used under any signal condition.

8. Which power amplifier gives minimum distortion and Why? (NOV 05) Class A Power amplifier is distortion free Collector current flows for the whole that is for 360 degree of the input cycle.

9. When does inter modulation distortion occur? Why should it be minimized in audio amplifier? (NOV 05)

Inter modulation distortion an amplifier arises when the input signal consists of two different frequencies f1 and f2. If the active device is nonlinear the output consists of fundamental the harmonic components f1+f2 and f1-f2. These frequencies are called inter modulation distortion. It may not to be eliminated.

10. What is the drawback of class B amplifier? How is this minimized?(NOV 04)In class B amplifier only a half cycle is obtained at the output for full input cycle the

output signal is distorted in this mode of operation . to eliminate this distortion two transistor are used in the alternate half cycle of the input signal. Thus the overall full cycle of output is obtained across the load because each transistor conducts for half cycle

11. What are the advantages of push pull amplifier? (APR 97) Efficiency is much higher than the class A operation When there is no input signal the power dissipation is zero The even harmonics get cancelled . this reduces the harmonic distortion

12. What is cross over distortion? How it can be eliminated(APR 03) (MAY 07) (NOV 08) (NOV 07) (NOV 10)

In class B amplifier the transistor is supposed to operate for full half cycle of the input. But Because of the cut in voltage, the transistor starts conducting only after 0.7V. the distortion caused by this is called cross over distortion. This can be eliminated by using two complementary transistor to conduct in alternate half cycles.

13. What is meant by harmonic distortion? (APR 04)

Distortion in the output caused by the non linearity of transistor is called harmonic distortion. Second harmonic produces the highest distortion. Or the output wave form differs from the input signal. Hence this distortion is called non linear or amplitude distortion the output waveform now consists of fundamental and higher harmonics.

14. What are salient features of hybrid parameters? (NOV 09) H-parameters are real numbers upto radio frequencies They are easy to measure They can be determined from the transistor static characteristics curves They are convenient to use in circuit analysis and design Easily convertible from one configuration to other Readily supplied by manufactures

15. Classify the power amplifiers based on biasing condition? (NOV 09)Based on biasing condition

Class A Class B Class C Class AB Class D Class S

16. Draw the small signal model of a CE amplifier? (MAY 07)

17. Compare input impedance and voltage gain of CE and CC amplifiers? (NOV10)

18. Compare efficiency of class A ,B.C,AB? (NOV 07) Class A –Poor 25% to 50 % Class B – Better 78.5% Class C – high Class AB- higher than class A but less than class B 50% to 78.5%

19. What is the use of heat sink?( NOV 2011)

20. What do you mean by cross over distortion? (NOV 2011)

UNIT IV

1. Mention the advantages of negative feedback in amplifiers? (NOV 06) (APR 03) (NOV 04) (APR 03) (MAY 09) (MAY 07) (NOV 10)

High fidelity Decrease the distortion Increase the bandwidth Decrease the noise Increase the input and decrease output impedance

2. Why do you prefer negative feedback in amplifiers? (MAY 07)In large signal amplifiers and electronic measuring instruments the major problem of

distortion should be avoided as far as possible. Again the gain must be independent of external factors auch as variation in the voltage of the dc supply and values of the circuit components . all this can be achieved by feedback.

3. What are the advantages of using crystal oscillators? (MAY 07) (APR 05) High value of Q hence sharpness of citcuit to tune with a resonant frequency is good Good frequency stability Frerquency drift is very small of the order of 0.0001% per day Aging rate of crystal is very small Perfect ,accurate and constant frequency can be achieved.

4. List out four different ways of connecting the feedback amplifier? (MAY 07) (MAY 07)

Voltage series feedback (voltage amplifier) Voltage shunt feedback (transresistance amplifier) Current series feedback (transconductance amplifer) Current shunt feedback (current amplifier)

5. A wein bridge oscillator is used for operation with the frequency of 10KHz. If the value of R=100KΩ,find the value of capacitor? (MAY 07)

6. How does the change in the operating point of the active device affect the frequency stability of the oscillator? (MAY 07)

7. What is the significance of negative feedback? (NOV 07) Decrease the distortion Increase the bandwidth Decrease the noise Increase the input and decrease output impedance

8. What are the advantages of crystal oscillator over other LC oscillators?

9. Define feedback factor ?(APR 08)It is defined as the ratio of feedback signal to the output signal

β=

10. What are the conditions of oscillation in sinusoidal oscillator? (APR 08) Aβ=1 the magnitude of loop gain must be unity The total phase shift around the closed loop is zero

11. Give the Barkhausen’s criterion for oscillator? (NOV 09) (MAY 07) (NOV 03) (APR 04) (MAY 09) (NOV 08) (APR 03)Barkhausen criterion states that

The total phase shift around a loop, as the signal proceeds from input through amplifier, the feedback network back to input again, completing a loop, is precisely0 or 360, of course an integral multiple of 2π radians

The magnitude of the prodect of the open loop gain of the amplifier and feedback factor is unity Aβ=1

12. A feedback amplifier has an open loop fain of 600 and feedback factor of 0.01. find the closed loop gain with negative feedback? (NOV 04)

13. Define Desensitivity of transfer gain? (APR 04)The reciprocal of sensitivity is called the desensitivity (D) of transfer gain. It is given as

D=1+Aβ

14. How does negative feedback reduce distortion in an amplifier? (NOV 08)Consider an amplifier with an open loop voltage gain and total gain and a total harmonic

distortion D. then with the introduction of negative feedback with the feedback ratio, β the distortion will reduces Df = D/ (1+Aβ)

15. What is meant by negative feedback in a feedback amplifier? (MAY 09)If the feedback signal φf is out of phase with input signal φs, then φi=φs-φf. So the input

voltage applied to the basic amplifier is decreased and correspondingly the output is decreased. Hence the voltage gain is reduced. This type of feedback is known as negative feedback or degenerative feedback.

16. What is frequency stability of an oscillator? (MAY 09)For an oscillator the frequency of the oscillation must remain constant. The analysis of

the dependence of the oscillating frequency on the various factors like stray capacitance, temp etc..is called as the frequency stability analysis. The measure of ability of an oscillator to maintain the desired frequency as precisely as possible is called frequency of an oscillator.

17. Draw the circuit of a wien bridge oscillator, write the expression for oscillation frequency and minimum value of gain? (NOV 02)(Nov 10)

18. What are the drawbacks of negative feedback amplifier? (NOV 2011)19. What is barkhausen criteria? (NOV 2011)

UNIT V

1. Define monostable operation of a multivibrator? (NOV 06)

Monostable multivibrator has one stable state and one quasi stable state. It is also known as one shot multivibrator or univibrator. It remains in its stable state until an input pulse triggers it into its quasi state for time duration determined by the discharging RC circuit

2. Draw the circuit of switched mode power supply? (NOV 06) (MAY 08) (NOV 07)

3. Define ripple factor? (NOV 06) (APR 03) (NOV 07)The first stage of power supply unit is rectifier. The object of a rectifier is to convert the

ac to dc. A measure of how successful a circuit is in doing this is the ripple facror. OrThe output of the rectifier is of pulsating dc type. The amount of ac content in the output

can be mathematically expressed by afactor called ripple factor.

4. Differentiate between astable multivibrator and Schmitt trigger circuits? (MAY 07)

5. What are the advantages of using switched mode power supply? (MAY 07)(NOV 07)

Efficiency is high because of less heat dissipation As the transformer size is very small, it will have a compact unit Protection against excessive output voltage by quick acting guard circuits Reduced harmonic feedback into the supply main Isolation from main supply without the need of large mains transformer Generation of low and medium voltage supplies are easy

6. A zener diode is operated at 10mA current and 20V supply voltage. The zener break down voltage is 5V. calculate its current limiting resistor value? (MAY 07)

7. What is clamper? (MAY 07) (NOV 08)

The circuits, which are used to add a dc level as per the requirements to the output signal is called clamper circuits

8. Draw the capacitor voltage waveform of a RC circuit when a square wave is applied as an input? (MAY 07)

9. Define voltage regulation? (MAY 07)

10. Draw the circuit of a positive clipper?(MAY 07)

11. How is Schmitt trigger different from a multivibrator? (MAY 07) (NOV 08)

12. State the disadvantages of a zener regulator? (MAY 07) (NOV 05) The maximam load current Imax is limited between Izmax and Izmin which is usually of

few milli ampere. A large amount of power is wasted in the zener diode and the source resistance so that the

power output is decreased The regulation factor and output resistance are not very low

13. Draw the circuit diagram of a Schmitt trigger? (NOV 07)

14. What is time constant in RC circuit? (APR 08)The effect of time constant t=RC on the output waveform for a input pulse signal. With

reducing time constant, then pulse at the narrower with negligible sag. If the time constant is reduced sufficiently, the output will be simply a seies of alternate positive and negative spikes.

15. What is clipper? (APR 08)The circuits, which are used to clip off unwanted portion of the waveform without

distoting the remaining part of waveform are called alippers.

16. Define peak inverse voltage of a rectifier? (MAY 08)It is defined as the maximum reverse voltage that a diode can withstand without

destorying the junction. The peak inverse voltage across a diode is the peak of rhe negative half cycle.

17. What is multivibrator? (NOV 09)Multivibrator are two stage switching circuits in which the output of the first stage is fed to the input of the second stage and vice versa. The outputs of two stages are complementary.mu;tivibrator are of three types

Astable multivibrator Bistable multivibrator momostable multivibrator

18. Define line regulation and load regulation? (NOV 04)Line regulation

It is defined as the change in output voltage for a change in line supply keeping the load current and temperature constant

Line regulation = change in output voltage / change in input voltageLoad regulation

Load regulation=Vno load-Vfull load /Vnoload

19. Draw the response of high pass RC circuit to a pulse input? (NOV 09)

20. What is need for filters in power supplies? (NOV 09)The output of a rectifier contains dc component as well as ac componenent. Filters are

used to minimise the undersiable ac ripple leaving only the dc component to appear at the output.

21. Distinguish between monostable and bistable multivibrator? (NOV 07)

22. Draw the output waveform of free running type multivibrator? (MAY 07)

23. Give the examples for bistable multivibrator? (MAY 07)The examples of bistable multivibrator flipflop, memory elements in shift register,

counters, frequency divider and Eccles-Jordan circuit.

24. Define SMPS? (NOV 08) (NOV 10)In a switching power supply the active device that provides regulation is always operated

in a switched mode, it is operated either in cut off or in saturation. The input dc is choppede at a high frequency using an active device and converter transformer.

The pulse width modulation is the basic concept of the switching regulators. When the transistor is operated in the cut off region, there is n o current and dissipated no power. While when is operated in the saturation region a negligible voltage drop appears across it

25. What is need for wave shaping circuits? (MAY 09)The waveform shaping circuits like differentating and integrating circuits are used in

multivibrator as triggering and synchronising pulse generators. The triggering pulses to the multivibrator are to be reshaped using differentiating and integrating RC circuits

26. What are the three basic types of SMPS available? (MAY 09) Forward converter Flyback converter Push pull converter

27. In the following circuit find the waveform of the output voltage. Assume the diode to be ideal.(NOV 10)

28. Define PIV,What is the value of PIV for bridge type of rectifier? (NOV 2011)29. State the application of clippers? (NOV 2011)

PART-B

UNIT-I

1. Discuss the V-I characteristics of PN diode and zener diode with their construction and principle of operation? (MAY 07) (NOV 07) (NOV 06)

2. With constructional details, give a detailed note on the working and performance characteristics of bipolar junction transistor. Draw the relevant diagrams. (NOV 07)

3. With necessary diagrams, explain the formation of the depletion region in a PN diode? (NOV 08)4. Draw and explain the input and output characteristics of common emitter configuration of a

transistor? (NOV 08) (MAY 07)5. Draw and explain the input and output characteristics of common base configuration of a

transistor? (NOV 08) (MAY 09)6. Explain the behavior of PN junction diodes under forward and reverse bias condition? (MAY 09)7. Draw the VI characteristics of zener diode and explain its operation? (NOV 09) (NOV 05) (MAY

06) (NOV 06)8. With neat circuit diagram and characteristics explain the operation of varactor diode. (NOV 09)

(NOV 10)9. Draw the collector to base bias circuit of a transistor and derive an expression for the stability

factor? (NOV 09)10. Briefly explain the construction of DC and AC load lines on the output characteristics of the CE

transistor amplifier? (NOV 09)11. Explain the construction, characteristics of tunnel diodes. Mention some of the applications of

tunnel diodes? (NOV 05) (NOV 06)12. Show that reverse biased PN junction can be used as a variable capacitor? (APR 10)13. From the energy band diagram explain the VI characteristics of tunnel diode? (APR 10)14. Draw the circuit diagram of NPN junction transistor CE configuration and describe the static

input and output characteristics. Also define active, saturation and cutoff regions, and saturation resistance of CE amplifier? (APR 10)

15. Draw a voltage divider bias circuit and derive the expression for its stability factor? (APR 10)16. Describe the V_I characteristics of Schottky diode.(NOV 10)17. Explain in detail, different biasing methods for a transistor circuit with neat circuit diagram and

ontain respective stability factor? (APR 11)18. Explain the operation of tunnel diode with the volt-ampere characteristics.(Nov11)19. Explain the operation of PN junction diode with the VI characteristic. (Nov11)20. Explain potential divider bias is obtained. (Nov11)21. What is thermal runaway, how the thermal stability is achieved? (Nov11)

UNIT II

1. Explain the characteristics of unijunction transistor? (MAY 09) (NOV 09)2. Draw the characteristics of TRAIC and explain? (MAY 09) (NOV 09) (MAY 07)3. Explain the operation of SCR with its construction details? (MAY 09) (NOV 09) (MAY 07)4. Draw the VI characteristics of a DIAC and explain its working? (MAY 09) (NOV 10)5. With necessary diagram explain the principle of operation of a JFET and draw the drain and

transfer characteristics? (NOV08)

6. Explain how D-MOSFET and E-MOSFET differ? (NOV08)7. Describe the constructional details of JFET and also describe the various parameters of

JFET? (MAY 09) (NOV08) (MAY07) (NOV09)8. Explain the operation of MOSFET in Enhancement and depletion modes? (MAY 09)

(NOV07) (MAY 09) (NOV 10)9. Explain the operation of enhancement mode MOSFET with the drain and transfer

characteristic.(Nov11).10. Explain the operation of DIAC and TRIAC circuit with their characteristics. (Nov11)

UNIT III

11. Explain the operation of the transformer coupled power amplifier? (APR 08) (MAY 07)12. Draw the h-parameter model of CE amplifier and derive the equatioins for current gain,

voltage gain, input impedance and output admittance? (MAY 09) (APR 08) (NOV 06) (NOV 10)

13. Explain the operation of class-B complementary symmetry push pull amplifiers. State its advantages and disadvantages? (NOV 09) (APR 08) (NOV 06) (MAY 07) (NOV 10)

14. With small signal equivalent circuit of BJT, derive expressions for voltage gain, input resistance and output resistance of a common emitter amplifier? (NOV07) (MAY09) (NOV09) (NOV08)

15. Explain the working principle of a class A amplifier and show the efficiency of the power amplifier? (MAY 07) (NOV 08)

16. Define class B operation. Draw a pushpull class B amplifier and explain its working. Derive its efficiency? (NOV 07) (NOV 08) (MAY 09)

17. Draw the hparameter model of CE amplifier and obtain the voltage gain,current gain,input impedance and output impedance. (Nov11)

18. Explain the operation of classB push pull amplifier with the current waveforms ,AC, DC loadline and also derive its efficiency. (Nov11)

UNIT VI

1. Derive the expressions for input and output resistances of a voltage series negative feedback amplifiers? (NOV09) (NOV 10)

2. Describe the construction of phase shift oscillator and explain its working. Derive the expression for the frequency of oscillations of the RC phase shift oscillator? (NOV09) (MAY 09) (NOV 08)

3. Discuss in detail the characteristics of negative feedback amplifier? (MAY 07)4. Explain the circuit of a negative voltage shunt feedback amplifier and explain the changes in

its gain, input resistances and output resistances? (MAY 07) (NOV 06) (NOV 09) (MAY 09)5. Draw the circuit of wien bridge oscillator and explain its operation? ( NOV 06)6. Draw a neat circuit and discuss the criteria for oscillations in a colpitts oscillator? (MAY 07)

(NOV 09)

7. Discuss the different voltage/ current-series/shunt feedback connections with expressions for gain, input and output resistance? (NOV 07) (MAY 09)

8. Explain the working of a Hartley oscillator and derive the frequency of oscillation? (NOV09)9. With neat circuit, explain the working principle of crystal oscillator. Also state Barkhausen

criteria for sustained oscillation? (NOV 10)10. With the neat diagram explain voltage series feedback and also derive the voltage gain input

resistance and output impedence. (Nov11)11. With the neat diagram explain RC phase shift oscillator and derive the frequency of

oscillation. (Nov11)

UNIT V

1. What is clamper? And clipper Discuss with help of circuit diagram and waveforms, the operation of a clamping and clipper circuit? (NOV 09) (MAY 07) (MAY 09)

2. With neat circuit diagram and waveforms, explain the operation of monostable multivibrator? (NOV 09) (MAY 07)

3. Explain with neat circuit diagram and waveforms, the operation of full wave rectifier using two diodes? (NOV 09)

4. Draw the circuit diagram of a UJT relaxation oscillator. Sketch the output waveforms and explain the circuit operation? (NOV 09) (NOV 07) (NOV 10)

5. Define the following in a Schmitt trigger circuit upper trigger point, lower trigger point, hysteresis and regeneration? (NOV 09) (MAY 09)

6. Draw the circuit of a full wave rectifier with a capactive filter and explain its operation with necessary waveforms? (MAY07)

7. Expain the design procedure of a transistor series voltage regulator? (NOV 09) (NOV 06)8. Explain the operation of FWR and derive the ripple factor? (NOV 06) (MAY 07) (NOV 07)

(MAY 09) (NOV 08)9. Explain the working principle of three phase bridge rectifier with neat circuit and waveforms.

Obtain the expression for average output voltage in it? (NOV 10)10. Expain the working principle of biased positive and negative clipper with an example?

(NOV 10)11. Explain the working of a SMPS using necessary diagrams and waveforms? (NOV 06) (NOV

08)12. Explain the operation of schmitt trigger with neat diagram. (Nov11)13. Write a technical note on polyphase rectifiers. (Nov11)14. Explain the operation of Zener diode based series voltage regulator. (Nov11)15. Explain the operation of SMPS. (Nov11)