SESSION:21

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1)       What is meant by GTO?

It is a three terminal, four layers PNPN Power Semiconductor device that can be turned on by a positive gate current and can be turned off by a reverse gate current.

2)       What are the types of GTO?

Types of GTO:

·        Asymmetrical GTO

·         Symmetrical GTO

3)       When we have to connect the SCRs in a parallel manner?

To meet the high current demand we will connect the SCRs in a parallel manner.

Similarly to meet the high voltage demand we have to connect the SCRs in series.

4)       Define Gate Charge in MOSFET?

The gate charge is defined as the amount of charge required for the device during turn-on and turn-off time. It is the most important parameter we have to consider while selecting the MOSFET. The switching speed of the MOSFET depends on the speed at which the gate driver can charge or discharge the input gate charge.

5)       What are the different turn on methods of SCR?

Following methods can be adopted for turning ON a SCR:

·         Forward voltage triggering

·         Gate Triggering

·         dv/dt triggering

·         Temperature triggering

·         Light triggering

6)       What is snubber circuit?

The snubber circuit is used for the dv/dt protection of the SCR. It is a series combination of a resistor and a capacitor in parallel with the SCR.

7)       What is hard switching of the thyristor?

When gate current is several times higher than the required gate current, the SCR is said to be hard fired. It reduces the turn ON time and enhances the di/dt capability.

8)       What is firing angle?

The angle between the zero crossing of the input voltage and the instant the SCR is fired is called as delay angle or firing angle.

9)       What is meant by SOA?

SOA - Safe Operating Area determines the voltage and current boundary within which the Power Device can be operated without destructive failure.

10)     What are the main components used for isolating the Power Circuits, Power Semiconductor from the low-power circuit?

Opto-Couplers and Transformers are the main components used for isolating the Power Circuits, Power Semiconductor from the low-power circuit.

11)    Name some of the current controlled (current driven) devices.

SCR, GTO, GTR 

12)    Name some of the voltage driven (Voltage controlled) devices.

IGBT, MCT, IGCT, SIT 

13)    What is duty cycle?

It is the ratio of the ON time of the chopper to total time period of the chopper.

D = Ton / [Ton + Toff]

14)    Can fuses with an AC voltage rating be used in DC applications?

Fuses must be rated for the voltage AC or DC in which they will be used.

Generally, fuses have a DC voltage rating that is half of the maximum AC voltage rating.

15)    What are the characteristics of ideal Op-amp?

The characteristics of ideal Op-amp are:

·         Infinite open loop voltage gain

·         Infinite input impedance

·         Zero output impedance

·         Infinite Bandwidth

·         Zero offset voltage