Power Electronics Question and Answers – Thyristor Mounting


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

1. The usual way to accomplish higher gate current for improved di/dt rating is by using
a) varistors
b) pilot thyristors
c) twisted cables
d) op-amps
View Answer

Answer: b
Explanation: Pilot SCR is an SCR which is fired which activates the firing circuit and fires the main SCR.

2. Inter-digitating of gate-cathode regions in SCR devices improves the
a) I2t rating
b) di/dt rating
c) dv/dt rating
d) thermal resistance
View Answer

Answer: b
Explanation: Inter-digitating is the inter-mixing of the gate-cathode area to improve the di/dt ratings. di/dt rating is improved by providing more cathode conduction area during the delay and rise time.

3. The dv/dt rating of SCR can be improved by using
a) cathode-short structure
b) anode-short structure
c) gate-short structure
d) centre gate thyristor
View Answer

Answer: a
Explanation: Cathode shorts are realized by overlapping metal on cathode n+ layers with a narrow p-region in between.

4. The total thermal resistance between junction and ambient θjA is 10°C/W. θjc is 2°C/W. θcs is 4°C/W. θsA = ?
a) 4°C/W
b) 2°C/W
c) 10°C/W
d) 16°C/W
View Answer

Answer: a
Explanation: θjA = θjc+ θcs+ θsA.

5. Which of the following thermal resistance parameters depends on the size of the device and the clamping pressure?
a) θsA
b) θcs
c) θjc
d) None
View Answer

Answer: b
Explanation: The case-to-sink thermal resistance depends on the size of the device, pressure, grease between the interface, etc.

6. The sink to ambient thermal resistance of SCR θsA
a) depends on the flatness of the device
b) depends on the length of the device
c) depends on the current carrying capabilities
d) is independent on thyristor configuration
View Answer

Answer: d
Explanation: It does not depend on any of the device configurations.

7. Pav x (θjc + θcs + θsA) =
a) Maximum specified temperature
b) Energy lost
c) Difference in temperature between junction & ambient
d) Sum of junction & ambient temperature
View Answer

Answer: c
Explanation: Pav = (Tj – Ta)/θjA
θjA = (θjc + θcs + θsA).

8. Heat dissipation from heat sink mainly takes place by
a) radiation
b) convection
c) absorption
d) none of the mentioned
View Answer

Answer: b
Explanation: Heat DISSIPATION (rejection of heat to the atmosphere) takes place through convention only.

9. For low power SCRs (about 1 Ampere current) _____________ type of mounting is used
a) lead
b) stud
c) bolt-down
d) press-fit
View Answer

Answer: a
Explanation: Lead mounting is a very simple time of mounting used for low power devices.

10. In the ___________ type of mounting the SCR is pressed between two heat sinks
a) bolt-down mounting
b) stud-mounting
c) press-pak mounting
d) cross-fit mounting
View Answer

Answer: c
Explanation: In the press-pak type the device is pressed or clamped between two heat-sinks & external pressure is applied from both the sides.

Sanfoundry Global Education & Learning Series – Power Electronics.

To practice all areas of Power Electronics, here is complete set of 1000+ Multiple Choice Questions and Answers.

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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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