155. An UJT used for triggering an SCR has the supply voltage VBB = 25 V. The inrinsic stand off ratio, n = 0.75. The UJT will conduct when the bias voltage Vz is
A. 25 V
B. 18.75 V
C. 33.3 V
D. 19.35 V
156. The latching current of SCR is 18 mA. Its holding current will be
A. 6 mA
C. 54 mA
157. Apositive voltage is applied to the gate of a reverse biased SCR.
A. This injects more electrons into junction J1
B. This increases reverse leakage current into anode
C. Resting of junction is unaffected
D. Failure of junctions occurs due to thermal runaway.
158. At a room temperature of 30 ?C, minimum voltage and current required to fire a SCR is
A. 3V, 40 mA
B. 0.6 V, 40 mA
C. no limit
D. 3 V,100 mA
159. When the SCR conducts, the forward voltage drop
A. is 0.7 V
B. is 1 to 1.5 V decreases slightly with load current
C. remains constant with load current
160. The turn-on time of a SCR with inductive load is 20 pis. The pulse train frequency is 2.5 kHz with a mark/space ratio of ?10 , then
A. the SCR will turn on
B. the SCR will not turn on
C. the SCR will turn on if inductance is removed
D. the SCR will turn on if pulse frequence is increased to two times.
161. Which of the following PNPN device has a terminal for synchronising purpose?
D. Schmitt trigger
Page 23 of 36