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155. The two transistor model of the SCR can obtained by a) bisecting the SCR vertically b) bisecting the SCR horizontally c) bisecting the SCRs top two & bottom two layers d) bisecting the SCRs middle two layers
Answer: d Explanation: The two transistor model consists of p-n-p and n-p-n transistors, of which the middle n-p layer is common in both the transistors
Answer: d
Explanation: The two transistor model consists of p-n-p and n-p-n transistors, of which
the middle n-p layer is common in both the transistors
See less156. Latching current for an SCR is 100 mA, DC source of 200 V is also connected from the SCR to the L load. Compute the minimum width of the gate pulse required to turn on the device. Take L = 0.2 H. a) 50 μsec b) 100 μsec c) 150 μsec d) 200 μsec
Answer: b Explanation: For L load, E = L di/dt I = E/L t Therefore, 0.100 = 200t/0.2 T = 100 μsec.
Answer: b
Explanation: For L load, E = L di/dt
I = E/L t
Therefore, 0.100 = 200t/0.2
T = 100 μsec.
See less158. From the two transistor (T1 & T2) analogy of SCR, the total anode current of SCR is ___________ in the equivalent circuit. a) the sum of both the base currents b) the sum of both the collector current c) the sum of base current of T1 & collector current of T2 d) the sum of base current of T2 & collector current of T1
Answer: b Explanation: The sum of both the collector currents of T1 and T2 forms the total anode current of SCR. Refer the model.
Answer: b
Explanation: The sum of both the collector currents of T1 and T2 forms the total anode
current of SCR. Refer the model.
See less160. Latching current for an SCR is 100 mA, a dc source of 200 V is also connected to the SCR which is supplying an R-L load. Compute the minimum width of the gate pulse required to turn on the device. Take L = 0.2 H & R = 20 ohm both in series. a) 62.7 μsec b) 100.5 μsec c) 56.9 μsec d) 81 μsec
Answer: b Explanation: E = Ri + L di/dt Solve the above D.E for I & substitute the above values. t = 100.503 μsec.
Answer: b
Explanation: E = Ri + L di/dt
Solve the above D.E for I & substitute the above values.
t = 100.503 μsec.
See less159. Consider the two transistor analogy of SCR, if α 1 & if α 2 are the commonbase current gains of both the transistors then to turn-on the device a) α 1 + α 2 should approach zero b) α 1 x α 2 should approach unity c) α 1 – α 2 should approach zero d) α 1 + α 2 should approach unity
Answer: d Explanation: To turn on the device sum of both the current gains should approach unity value.
Answer: d
Explanation: To turn on the device sum of both the current gains should approach unity
value.
See less161. The voltage safety factor (V SF ) for an SCR is the ratio of a) peak working voltage & peak reverse repetitive voltage b) dv/dt & di/dt c) peak repetitive reverse voltage & maximum value of input voltag
Answer: c Explanation: It is peak repetitive reverse voltage/ the maximum value of input voltage(Vm).
Answer: c
Explanation: It is peak repetitive reverse voltage/ the maximum value of input
voltage(Vm).
See less162. The forward dv/dt rating of an SCR a) increases with increase in the junction temperature b) decreases with increase in the junction temperature c) increases with decrease in the rms value of forward anode-cathode voltage d) decreases with decrease in the rms value of forward anode-cathode voltage
Answer: a Explanation: If the temperature is high, lesser dv/dt is required to turn on the device as the higher temperature has already excited few of the holes & electrons.
Answer: a
Explanation: If the temperature is high, lesser dv/dt is required to turn on the device as
the higher temperature has already excited few of the holes & electrons.
See less163. The finger voltage of an SCR is a) minimum value of Vak to turn on the device with gate triggering b) maximum value of Vak to turn on the device with gate triggering c) minimum value of Vak to turn on the device without gate triggering d) maximum value of Vak to turn on the device without gate triggering
Answer: a Explanation: Finger voltage is the minimum value of Vak (anode to cathode voltage) to turn on the device with gate triggering, it is to be avoided for accidental turn-on of the device.
Answer: a
Explanation: Finger voltage is the minimum value of Vak (anode to cathode voltage) to
turn on the device with gate triggering, it is to be avoided for accidental turn-on of the
device.
See less164. Which among the following anode current waveforms will have the minimum junction temperature? a) 100 % DC b) 25 % DC c) 50 % DC d) AC
Answer: b Explanation: N % DC is nothing but a wave with n % duty cycle. Lower the Duty cycle lesser is the current flowing & lesser is the temperature dissipation.
Answer: b
Explanation: N % DC is nothing but a wave with n % duty cycle. Lower the Duty cycle
lesser is the current flowing & lesser is the temperature dissipation.
See less165. An SCR has half cycle surge current rating of 3000 A for 50 Hz. Calculate its one-cycle surge current rating a) 3121.32 A b) 2121.32 A c) 3131.32 A d) 2131.32 A
Answer: b Explanation: By equating the energies involved in one cycle & subcycle I 2 .T = Isb 2 .t Isb = 3000 A T = 1/50 t = T/2.
Answer: b
Explanation: By equating the energies involved in one cycle & subcycle
I
2
.T = Isb
2
.t
Isb = 3000 A
T = 1/50
t = T/2.
See less