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Electronics and Communication Engineering - Power Electronics

Exercise : Power Electronics - Section 3
36.
When thyristors are connected in series and parallel, it may be necessary to have :
current derating
voltage derating
both current and voltage derating
none of the above
Answer: Option
Explanation:

Thyristors in series do not share the voltage equally and require voltage derating. Thyristors in parallel need current derating.

37.
A single phase half wave regulator uses
2 diodes and 2 thyristors
2 thyristors
1 diode and 1 thyristor
2 diodes
Answer: Option
Explanation:

Regulation is possible only in positive half cycle.

38.
A Shockley diode can be used
in place of SCR
as a trigger switch for SCR
in place of UJT
both in place of SCR and as a trigger switch for SCR
Answer: Option
Explanation:

It is a four layered PNPN device without a gate terminal. Its characteristics is similar to that of SCR with zero gate current. It is acting as a trigger switch for Thyristor.

39.
An SCR has a turn on time of 4 μs. The gate pulse should have a duration of about
2 μs
5 μs
20 μs
50 μs
Answer: Option
Explanation:

Duration of gate pulse should be slightly more than turn time of SCR.

40.
In a multiphase chopper, the different choppers operate in
series and all simultaneously
parallel and one at a time
parallel and simultaneously
either (b) or (c)
Answer: Option
Explanation:

Only one chopper operates at one time.

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