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For an SCR the average & rms values of current are I/4 & I/2 respectively. Calculate the average on-state current rating (ITAV). Take maximum RMS on-state current = 35 A. a) 8.78 A b) 10.10 A c) 17.5 A d) 24.74 A
c Explanation: Form factor = RMS/Average vaules of current Therefore, FF = 2 I TAV = 35/2 = 17.5.
c
See lessExplanation: Form factor = RMS/Average vaules of current
Therefore, FF = 2
I
TAV = 35/2 = 17.5.
For a SCR the maximum rms on-state current is 35 A. If the SCR is used in a resistive circuit for a rectangular wave with conduction angle of 90°. Calculate the average & rms currents respectively. a) I/4, I/2 b) I/2, I/√2 c) I/4, I2 /2 d) I/4, I/√2
: a Explanation: First convert the conduction angle into N for rectangular wave. N = 360°/Conduction angle = 4 Therefore, Iavg = I/4 Irms = I/√4 = I/2.
: a
See lessExplanation: First convert the conduction angle into N for rectangular wave.
N = 360°/Conduction angle = 4
Therefore, Iavg = I/4
Irms = I/√4 = I/2.
n 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
b Explanation: By equating the energies involved in one cycle & subcycle I 2 .T = Isb2 .t Isb = 3000 A T = 1/50 t = T/2.
b
See lessExplanation: By equating the energies involved in one cycle & subcycle
I
2
.T = Isb2
.t
Isb = 3000 A
T = 1/50
t = T/2.
Which among the following anode current waveforms will have the minimum junction temperature? a) 100 % DC b) 25 % DC c) 50 % DC d) AC
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.
b
See lessExplanation: 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.
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
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.
a
See lessExplanation: 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.
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
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.
a
See lessExplanation: 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.
The voltage safety factor (VSF) 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 voltage d) peak repetitive reverse voltage & rms value of input voltage
: c Explanation: It is peak repetitive reverse voltage/ the maximum value of input voltage(Vm).
: c
See lessExplanation: It is peak repetitive reverse voltage/ the maximum value of input
voltage(Vm).
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
b Explanation: E = Ri + L di/dt Solve the above D.E for I & substitute the above values. t = 100.503 μsec.
b
See lessExplanation: E = Ri + L di/dt
Solve the above D.E for I & substitute the above values.
t = 100.503 μsec.
Consider the two transistor analogy of SCR, if α1 & if α2 are the commonbase current gains of both the transistors then to turn-on the device a) α1 + α2 should approach zero b) α1 x α2 should approach unity c) α1 – α2 should approach zero d) α1 + α2 should approach unity
d Explanation: To turn on the device sum of both the current gains should approach unity value.
d
See lessExplanation: To turn on the device sum of both the current gains should approach unity
value.
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
b Explanation: The sum of both the collector currents of T1 and T2 forms the total anode current of SCR. Refer the model.
b
See lessExplanation: The sum of both the collector currents of T1 and T2 forms the total anode
current of SCR. Refer the model.