1. A thyristor (SCR) is a
a) P-N-P device
b) N-P-N device
c) P-N-P-N device
d) P-N device
Explanation: An SCR (silicon controlled rectifier) is a four layer p-n-p-n type device
2. Which terminal does not belong to the SCR?
a) Anode
b) Gate
c) Base
d) Cathode
Explanation: The SCR is having three terminals viz. anode, cathode and the gate.
3. An SCR is a
a) four layer, four junction device
b) four layer, three junction device
c) four layer, two junction device
d) three layer, single junction device
Explanation: SCR is a four layer p-n-p-n device which forms three p-n junctions.
4. Choose the false statement.
a) SCR is a bidirectional device
b) SCR is a controlled device
c) In SCR the gate is the controlling terminal
d) SCR are used for high-power applications
Explanation: It is a unidirectional device, current only flows from anode to cathode.
5. In the SCR structure the gate terminal is located
a) near the anode terminal
b) near the cathode terminal
c) in between the anode & cathode terminal
d) none of the mentioned
Explanation: The gate is located near the cathode, because it allows fast turning on of the device when the gate signal is applied by forward basing the second junction
6. The static V-I curve for the SCR is plotted for
a) Ia (anode current) vs Ig (gate current), Va (anode – cathode voltage) as a parameter
b) Ia vs Va with Ig as a parameter
c) Va vs Ig with Ia as a parameter
d) Ig vs Vg with Ia as a parameter
Explanation: The curve is plotted for Ia vs Va for different values of gate current Ig.
7. If the cathode of an SCR is made positive with respect to the anode & no gate current is applied then
a) all the junctions are reversed biased
b) all the junctions are forward biased
c) only the middle junction is forward biased
d) only the middle junction is reversed biased
Explanation: The device is in the reverse blocking state (3rd quadrant) & only the middle junction is forward biased whereas other two are reversed biased
8. For an SCR in the reverse blocking mode, (practically)
a) leakage current does not flow
b) leakage current flows from anode to cathode
c) leakage current flows from cathode to anode
d) leakage current flows from gate to anode
Explanation: In the reverse blocking mode, the gate current is zero & a reverse voltage is applied at the cathode-anode.
9. With the anode positive with respect to the cathode & the gate circuit open, the SCR is said to be in the
a) reverse blocking mode
b) reverse conduction mode
c) forward blocking mode
d) forward conduction mode
Explanation: The SCR is in the forward blocking mode with its top and bottom junctions forward biased and the middle junction reversed biased
10. For an SCR in the forward blocking mode (practically)
a) leakage current does not flow
b) leakage current flows from anode to cathode
c) leakage current flows from cathode to anode
d) leakage current flows from gate to anode
Explanation: In the forward blocking mode, the gate current is zero & only the middle J2 junction is reversed biased