linear integrated circuits interview questions and answers P-5

l.Mention some applications of 555 timer:

*Oscillator
 *pulse generator

*ramp and square wave generator 
*mono-shot multivibrator 
*burglar alarm
 *traffic light control.

2.List the applications of 555 timer in monostable mode of operation:

*missing pulse detector 
*Linear ramp generator
 *Frequency divider 
*Pulse width modulation.

3. List the applications of 555 timer in Astable mode of operation:

*FSK generator 
*Pulse-position modulator

4.What is a voltage regulator?

A voltage regulator is an electronic circuit that provides a stable dc voltage independent of the load current, temperature, and ac line voltage variations.

5.Give the classification of voltage regulators:

*Series / Linear regulators 
*Switching regulators.

6.What is a linear voltage regulator?

Series or linear regulator uses a power transistor connected in series between the unregulated dc input and the load and it conducts in the linear region .The output voltage is controlled by the continous voltage drop taking place across the series pass transistor.

7.What is a switching regulator?

Switching regulators are those which operate the power transistor as a high frequency on/off switch, so that the power transistor does not conduct current continously.This gives improved efficiency over series regulators.

8.What are the advantages of IC voltage regulators?

*low cost
 *high reliability 
*reduction in size 
*excellent performance

9.Give some examples of monolithic IC voltage regulators:

78XX series fixed output, positive voltage regulators 
79XX series fixed output, negative voltage regulators 
723 general purpose regulator.

10.What is the purpose of having input and output capacitors in three terminal IC regulators?

A capacitor connected between the input terminal and ground cancels the inductive effects due to long distribution leads. The output capacitor improves the transient response.

11. Define line regulation.

Line regulation is defined as the percentage change in the output voltage for a change in the input voltage.It is expressed in millivolts or as a percentage of the output voltage.

12.Define load regulation.

Load regulation is defined as the change in output voltage for a change in load current. It is expressed in millivolts or as a percentage of the output voltage.

13.What is meant by current limiting?

Current limiting refers to the ability of a regulator to prevent the load current from increasing above a preset value.

14.Give the drawbacks of linear regulators:

*The input step down transformer is bulky and expensive because of low line frequency.

*Because of low line frequency,large values of filter capacitors are required to decrease the ripple.

*Efficiency is reduced due to the continous power dissipation by the transistor as it operates in the linear region.

15.What is the advantage of switching regulators?

*Greater efficiency is achieved as the power transistor is made to operate as low

impedance switch.Power transmitted across the transistor is in discrete pulses

rather than as a steady current flow.
 *By using suitable switching loss reduction technique, the switching frequency

can be increased so as to reduce the size and weight of the inductors and

capacitors.

16.What is an opto-coupler IC? Give examples.

Opto-coupler IC is a combined package of a photo-emitting device and a photo-sensing device.Examples for opto-coupler circuit : LED and a photo diode,

LED and photo transistor,

LED and Darlington.

Examples for opto-coupler IC    : MCT 2F , MCT 2E .

17. Mention the advantages of opto-couplers:

*Better isolation between the two stages.

*Impedance problem between the stages is eliminated.

*Wide frequency response.

*Easily interfaced with digital circuit.

*Compact and light weight.

*Problems such as noise, transients, contact bounce,.. are eliminated.

18.What is an isolation amplifier?

An isolation amplifier is an amplifier that offers electrical isolation between its input and output terminals.

19.What is the need for a tuned amplifier?

In radio or TV receivers , it is necessary to select a particular channel among all other available channels.Hence some sort of frequency selective circuit is needed that

will allow us to amplify the frequency band required and reject all the other unwanted signals and this function is provided by a tuned amplifier.

20.Give the classification of tuned amplifier:

(i)         Small signal tuned amplifier

*Single tuned
 *Double tuned 
*Stagger tuned

(ii)        Large signal tuned amplifier.