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181. The usual way to accomplish higher gate current for improved di/dt rating is by using a) varistors b) pilot thyristors c) twisted cables d) op-amps
Answer: b Explanation: Pilot SCR is an SCR which is fired which activates the firing circuit and fires the main SCR.
Answer: b
Explanation: Pilot SCR is an SCR which is fired which activates the firing circuit and fires
the main SCR.
See less182. Inter-digitating of gate-cathode regions in SCR devices improves the a) I 2 t rating b) di/dt rating c) dv/dt rating d) thermal resistance
Answer: b Explanation: Inter-digitating is the inter-mixing of the gate-cathode area to improve the di/dt ratings. di/dt rating is improved by providing more cathode conduction area during the delay and rise time.
Answer: b
Explanation: Inter-digitating is the inter-mixing of the gate-cathode area to improve the
di/dt ratings. di/dt rating is improved by providing more cathode conduction area during
the delay and rise time.
See less176. The effect of over-voltages on SCR are minimized by using a) RL circuits b) Circuit breakers c) Varistors d) di/dt inductor
Answer: c Explanation: Varistors are non-linear voltage clamping devices, RC circuits across the loads can also be used.
Answer: c
Explanation: Varistors are non-linear voltage clamping devices, RC circuits across the
loads can also be used.
See less171. di/dt protection is provided to the thryistor by a) connecting an inductor in parallel across the load b) connecting an inductor in series with the load c) connecting an inductor in parallel across the gate terminal d) connecting an inductor in series with the gate
Answer: b Explanation: By placing the di/dt inductor (L) in series with the load, the change in the anode current can be limited to a small value.
Answer: b
Explanation: By placing the di/dt inductor (L) in series with the load, the change in the
anode current can be limited to a small value.
See less170. The thermal resistance between junction & the SCR (θ jc ) has the unit a) Ω/°C b) W/Ω c) °C/W d) ΩW/°C
Answer: c Explanation: Thermal resistance always has the unit degree temperature per watt
Answer: c
Explanation: Thermal resistance always has the unit degree temperature per watt
See less169. The maximum rms current of an SCR is 50 A. For a 120° sine wave conduction the form factor (FF) = 1.878 Find the average on-state current rating (I TAV ). a) 93.9 A b) 174 A c) 26.62 A d) 68.52 A
Answer: c Explanation: The amp 2 -sec is the energy that the device can handle before the fault is cleared. Its value decides how fast the fault has to be cleared to avoid damage to the device.
Answer: c
Explanation: The amp
2
-sec is the energy that the device can handle before the fault is
cleared. Its value decides how fast the fault has to be cleared to avoid damage to the
device.
See less167. For an SCR the average & rms values of current are I/4 & I/2 respectively. Calculate the average on-state current rating (I TAV ). Take maximum RMS on-state current = 35 A. a) 8.78 A b) 10.10 A c) 17.5 A d) 24.74 A
Answer: c Explanation: Form factor = RMS/Average vaules of current Therefore, FF = 2 I TAV = 35/2 = 17.5.
Answer: c
Explanation: Form factor = RMS/Average vaules of current
Therefore, FF = 2
I
TAV = 35/2 = 17.5.
See less166. 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, I 2 /2 d) I/4, I/√2
Answer: 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.
Answer: 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.
See less168. The amp 2 -sec rating of the SCR specifies a) The power dissipated by the device when fault occurs b) The energy dissipated by the device when fault occurs c) The energy that the device can absorb before the fault is cleared d) The energy that the device can absorb while operating in the forward blocking mode.
Answer: c Explanation: The amp 2 -sec is the energy that the device can handle before the fault is cleared. Its value decides how fast the fault has to be cleared to avoid damage to the device.
Answer: c
Explanation: The amp
2
-sec is the energy that the device can handle before the fault is
cleared. Its value decides how fast the fault has to be cleared to avoid damage to the
device.
See less137. For the SCR to remain in the ON (conducting) state a) gate signal is continuously required b) no continuous gate signal is required c) no forward anode-cathode voltage is required d) negative gate signal is continuously required
Answer: b Explanation: Unlike the transistor devices, once the SCR is turned on by the gate terminal, the gate terminal losses its control over the device.
Answer: b
Explanation: Unlike the transistor devices, once the SCR is turned on by the gate
terminal, the gate terminal losses its control over the device.
See less