Power Electronics Question and Answers – GTOs

This set of Power Electronics Multiple Choice Questions & Answers (MCQs) focuses on “GTOs”.

1. The GTO (gate turn-off thyristor) is a
a) p-n-p-n device
b) p-n-p device
c) p-metal-n device
d) p-n single junction device
View Answer

Answer: a
Explanation: Just like a SCR, the GTO is a four layer p-n-p-n device.

2. The GTO can be turned off
a) by a positive gate pulse
b) by a negative gate pulse
c) by a negative anode-cathode voltage
d) by removing the gate pulse
View Answer

Answer: b
Explanation: The GTO can be turned off by applying a negative gate pulse to the gate terminal.

3. The anode current is ideally limited by the
a) gate pulse amplitude
b) internal impedance of the device
c) load Impedance
d) gate circuit impedance
View Answer

Answer: c
Explanation: The SCR or any device is connected through the load, hence the magnitude of the anode current (same as load current) will depend on the supply voltage and load impedance.

4. In a GTO the n+ layer forms the
a) anode & gate
b) cathode & gate
c) cathode
d) gate
View Answer

Answer: c
Explanation: The bottom n+ layer forms the cathode.

5. The turn-off gain βoff of the GTO is given by
a) Ig/Ia
b) Ia/Ig
c) Vg/Va
d) Vg/Va
View Answer

Answer: b
Explanation: βoff = (anode current/gate current).
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6. A GTO can be represented by two transistors T1 & T2. The current gain of both transistors are α1 and α2 respectively. A low value of gate current requires
a) low value of α1 and α2
b) low value of α1 and high value of α2
c) high value of α1 and low value of α2
d) high values of α1 and α2
View Answer

Answer: b
Explanation: In order that the gate current for turning-off the device is low, α2 should be made as nearer to unity as possible whereas α1 should be small.

7. Gold doped GTOs have _____________ as compared to the conventional GTOs
a) high turn-off time
b) low negative gate current requirement
c) low reverse voltage blocking capabilities
d) lower positive gate current requirement
View Answer

Answer: b
Explanation: Gold doping reduces the negative gate current requirements, different kinds of dopings have different advantages over the others.

8. Latching current for the GTOs is ________ as compared to CTs (Conventional thyristors).
a) more
b) less
c) constant
d) cannot be said
View Answer

Answer: a
Explanation: Latching current of GTOs is 2-4A as compared to 200 to 400 mA in case of CT’s.

9. In case of the two-transistor model (T1 & T2) of GTO with anode-short, the anode-short is placed between the
a) emitter of T1 & T2
b) emitter of T1 & base of T2
c) emitter of T1 & base of T1
d) emitter of T1 & collector of T2
View Answer

Answer: c
Explanation: Draw the model. The anode-short resistor is connected between emitter (Anode A of GTO) with base of T1 transistor.

10. Choose the correct statement:
GTOs have _________ as compared to the CTs.
a) less on-state voltage drop
b) less gate drive losses
c) higher reverse blocking capabilities
d) faster switching speed
View Answer

Answer: d
Explanation: GTOs have less turn-on and turn-off time, making it efficient for high frequency applications.

Sanfoundry Global Education & Learning Series – Power Electronics.

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Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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