# Multiple Choice Questions of Analog Electronics

1. The conduction loss verses device electric current characteristics of power MOSFET in best approximately by

I = Device current, Ron = on state resistance of power MOSFET, hence conduction loss P = I2Ron. Therefore conduction loss verses device electric current characteristics can be approximately parabola.

2. A 3 - phase diode bridge rectifier is fed from a 400 V rms, 50 Hz, 3 phase AC source. If the load is purely resistive, then peak instantaneous output voltage is equal to

As the load is resistive the peak instantaneous output voltage Vm = 400√2 V.

3. An SCR is considered to be a semi controlled device because

During positive half cycle SCR is in forward blocking mode. By applying gate pulse the SCR can be turned ON during forward Blocking mode. But SCR can be turned OFF by applying gate pulse. That is why it is called semi controlled rectifier.

4. Dual slope ADC has R = 1 KΩ and C = 0.22 nanofarad has charging and discharge times for some voltage is 9 ns & 3 ns respectively. The reference Voltage is 2.2 V. What is the peak voltage reached by triangular wave during charging?

$V_x\;=\;\frac{V_{in}\times \;T_{dis}}{R_c}\;=\;\frac{V_{ref}\times \;T_{dis}}{R_c}\;=\;\frac{2.2\;\times \; 3\;\times \;10^{-9}}{2.2\;\times \;10^{-7}}\;=\;30 mV.$

5. An SCR has half cycle surge electric current rating of 3000 A for 50 Hz supply. One cycle surge electric current will be

$I_{max}=3000 A,\; I_{rms}= \frac{3000}{\sqrt{2}} = 2121.32\; A.$

6. The typical value of SCR for modern alternator is

Always the typical value of SCR for modern alternator is 0.5.

7. A zener diode voltage regulator has load requirement of 12 V and 2 Amp. The zener diode's minimum electric current requirement is 0.2 A. The minimum voltage at input is 24 V. What is maximum efficiency of circuit?

η = ( 2 × 12) / ( 2.2 × 24 ) × 100 % = 24 / 52.8 = 45.5 %.

8. In n type semiconductor elements of which group of periodic table is added as dopant

With group 5 elements like phosphorous, arsenic, antimony are added to Ge or Si crystal which produces free electrons.

9. Darlington connection is achieved in 2 transistors by connecting

In darlington connection 2 transistor's collectors are connected and emitter of 1st transistor to the base of 2nd is also connected. This provides a three terminal device that in actual operation can be regarded as 2 cascaded emitter followers.

10. FM stands for

In telecommunications and signal processing, frequency modulation (FM) conveys information over a carrier wave by varying its instantaneous frequency. This contrasts with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant.

11. An opamp comparator circuit employs

Comparator is a device used for comparison of 2 voltage levels. Output indicates which of the 2 voltages is greater. No feedback is used.

12. A single phase full wave midpoint thyristor uses a 230 / 200 V transformer with central tap on the secondary side. The PIV per thyristor is

PIV = √(2) × Vm = √(2) × 200 = 282.84 V.

13. In a rectifier circuit, the diode converts

Diode converts alternatring voltage to unidirectional electric current which is then converted in to voltage by load resistance connected across the output node.

14. A single phase one pulse controlled circuit has a resistance and counter emf load 400sin(314t) as the source voltage for a load counter emf of 200 V, the range of firing angle control is

400sinθ = 200 ⇒ θ = 30°.
So control range is θ to( π - θ ) i.e. 30° to 150°.

15. A single phase full bridge inverter can operated in load commutation mode in case load consist of

In this case reading electric current will flow in circuit & it will became zero so thyristor will be load commutated.

16. A step up chopper has input voltage 110 V and output voltage 150 V. The value of duty cycle is

Under construction.

17. A schottky diode is a

Although a schottky diode behaves a p-n junction diode, there is no physical junction and as a result a schottky diode is a majority carrier diode.