# Electronics and Communication Engineering - Power Electronics

Exercise : Power Electronics - Section 2
6.
A dc separately excited motor has a constant field current. The armature is fed from a single phase supply through a semi-converter. When a = 0, speed is 600 rpm. If a = 90°, the speed is likely to be
Explanation:

Average output voltage is reduced to 50% if a = 90°. Hence speed is also reduced to 50%.

7.
A static induction thyristor
is a majority carrier device
is a minority carrier device
either a majority carrier or minority carrier device
has a total number of 2 leads
Explanation:

It can be turned on by positive gate pulse and turned off by negative gate pulse. It is minority carrier device. It can be manufactured in high current and high voltage ratings and its on state voltage drops is low.

8.
A single phase step up cycloconverter changes 50 Hz to 100 Hz. Then one half wave of input will give rise to
one half wave of output
one full wave of output
two full waves of output
either (b) or (c)
Explanation:

Since output frequency is 2f, one half wave of input must equal one full wave of output.

9.
Which of these triggering methods for series connected SCRs use LASCR in the gate circuit?
Resistance triggering
Simultaneous triggering
Sequential triggering
Optical triggering
Explanation:

Optical triggering uses LASCR.

10.
A 3 phase ac regulator uses
3 thyristors
6 thyristors
9 thyristors
12 thyristors