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SRI VIDYA COLLEGE OF ENGINEERING AND TECHNOLOGY

VIRUDHUNAGAR

Department of Electronics and Communication Engineering

Class/Sem:I ECE/II

Question Bank for EC6201-ELECTRONIC DEVICES

TWO MARKS QUESTIONS

Unit-5

Power Devices and Display Devices

Part-A

1.What is photo diode?

It is a light sensitive device used to convert light signal in to electrical signal. It is also

called photo detector

2. What is photo transistor?(AU-Apr/May 2009)

The photo transistor is a light detector, it combines photo diode and photo transistor. The

photo transistor cannot be directly used in control application.

3. What is photovoltaic sensors? (AU-Nov/Dec 2009, May/Jun 2010)

It is a light sensitive semi conductor devices, and it produce a voltage when the voltageincreases and the intensity of light falling on the semi conductor junction of this

photovoltaic cell increases.

4. What are the types of LED?

1. Surface-emitting LED

2. Edge-emitting LED

5. What are advantages of LED?

They are smaller in size

Its cost is very low

It has long life time

6. What are the Application of LED?

Used for numeric display in packet calculator

Used in the field of optical communication

Used in burglar-alarm system

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7. What are the application of LCD?

Used as numerical counters for counting production items

Used for solid state video displays

Used for image sensing circuit

8. Compare LCD and LED (AU- May/ Jun 2013)

S.No LCD LED

1. LCD is a liquid unit whichmodulators the light to have display

LED is a Light Emitted Diode whichemits light during forward biasing

2. LCD is a Passive display device LED is an Active display device

3. Cost is very low Cost is high

4. Life time comparatively More life time

9.

Define holding current?Holding current is the current below which the SCR switches from the conduction state

(on state) to the forward blocking state

10.What are the different methods used to turn on SCR?

Gate triggering

Forward break over voltage

Light triggering

Rate effect (or) dv/dt triggering

11.

Give the application of SCR

Main application of SCR is a

As over light detector

Relay control

Regulated power supply

Motor control

12.What is latching current?

It is the minimum current required to trigger the device from its OFF state to ON state.

13.What is turn on time?

The time required by SCR to reach full conduction after triggering is called turn on time.

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14.What is TRIAC?

TRIAC is a three terminal semiconductor switching device which can conduct in either

forward or reverse direction. The TRIAC is the combination of two SCRs connected in

parallel but in opposite direction.

15.

What is the application of TRIAC?

Heater control

Phase control

Light dimming control

Static switch to turn A.C power ON and OFF

16.Compare SCR and TRIAC.

S.No SCR TRIAC

1. Unidirectional device Bidirectional Device2. The reliability is more The reliability is less

3. Available in large ratings Not available in large ratings

4. Only one mode of operation ispossible

The operation in four different mode ispossible

17.What is DIAC?

A DIAC is two terminal semiconductor device and three layer bidirectional device, which

can be switched from of its OFF to ON state for either negative or positive polarity of

applied voltage.

18.

What is the application of DIAC?

The DIAC is used as a triggering device. It is not a control device. It is used in

Temperature control

Triggering of TRIAC

Light dimming circuits

Motor speed control

19.What is UJT?

Unijunction transistor is a three terminal semiconductor device consisting of only one PN

junction. It differs from ordinary PN diode in the sense that it has three terminals namelyEmitter, Base 1 and Base 2.

20.What is intrinsic stand OFF ratio of UJT?

The Intrinsic stand OFF ratio () is defined as the ratio between the internal dynamic

resistance (RBB)

=Rb1/RBB

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27.List out the constructions of power MOSFET

Lateral +Double diffusion construction (LDMOSFET)

Vertical MOSFET (term V because of construction)

TMOSFET (term T because of channel shape)

28.

What are the advantages and disadvantages of Lateral &Double diffusion methods?

Advantages

Low gate signal power requirement

Fast switching speeds

Disadvantages

High resistance channels

Cost is high

29.

Define V-MOS

Two source, one gate and one drain, shorter and wider channel with small resistance.

Consists of double diffused n+ layer which is cut with V shaped groove.

30. Comparisons between Power BJT and Power MOSFET

Points Power BJT Power MOSFET

Switching Time Slow due to minority carrier devices Faster, No storage time and no

influence of temperature

Input Impedance Lower than MOS Very high

Break down

voltage

Depends on VCE Depends on VDS

Drive Hfe Rises and Ve falls along with

temperature rise

Extremely high stability

31. What are the classifications of Display Devices?

Active display devices

Passive display devices

32. What is meant by active display devices?

These are the display units which emit the light radiation in their own directly

Example: Light Emitting Diode (LED)

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40. What are the materials used in LED?(AU-May/June 2012)

Gallium Arsenide(GaAs)

Gallium Phosphide(GaP)

Gallium Arsenide Phosphide(GaAsP)

Part-B

1. Draw the equivalent circuit of UJT and explain its operation(AU-Nov/Dec 2010, May/June

2013, Apr/May 2009, May/June 2010, May/June 2012)

2. Write short note on light activated SCR(AU-Nov/Dec 2009, May/June 2012)

3. Explain the operation and characteristics of SCR(AU- Nov/Dec 2009, May/June 2010,

May/June 2012)

4. Describe SCR ratings(AU-Nov/Dec 2009, May/June 2010, May/June 2012)

5. Explain the operations and characteristics of DIAC(AU-Nov/Dec 2010, , Apr/May 2009,

May/June 2012)

6. Explain the operations and characteristics of TRIAC(AU- Apr/May 2009)

7. Describe the operation of LED and LCD(AU-Apr/May 2009, Nov/Dec 2009, May/June

2012)

8. Explain the operations of power BJT

9 E l i h i f MOSFET

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Ec6201 Ed Notes Rejinpaul