24-11-2012, 01:45 PM
hi this is viva questions for pe lab exam
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pdf of power electronics lab viva questions with answers
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hi this is viva questions for pe lab exam
14-05-2013, 12:47 PM
I want Power electronics lab viva question and answer.please help me
07-02-2014, 07:03 PM
12-08-2015, 05:06 AM
12-08-2015, 05:11 AM
12-08-2015, 09:56 AM
pdf of power electronics lab viva questions with answers
Q1. What are the difference between transistor and SCR?
1. SCR is four layer PNPN device, whereas transistor is three layer (PNP or NPN) device.
Q2. Explain latching current and holding current of the thyristor?
Latching current: It’s the minimum forward current that flows through the thyristor to keep it in forward conduction mode at the time of triggering. If the forward current is less than latching current, thyristor doesn’t turn on.
Holding Current: It is the minimum forward current that flows through the thyristor to keep it in forward conduction mode. When forward current reduces below holding current, thyristor turn off.
Q3. What are the advantages of MOSFET’s over BJT’s?
i) MOSFET’s have simpler gate drive circuits.
ii) They have high switching frequencies.
iii) MOSFET’s are majority carrier devices.
iv) MOSFET’s have positive temperature coefficients.
Q4. Why pulsed gate drive is used for SCR?
Once SCR is turned on, gate drive is no more required. Hence if pulsed gate drive is used, SCR turns on at particular pulse. The remaining pulses are not used. But pulsed drive reduces losses in gate cathode of the SCR.
Q5. Define the delay angle of phase-controlled rectifier.
It is the angle at which thyristors are triggered after zero crossing. After zero crossing of supply voltage, one pair of thyristor is forward biased. After delay angle (α), the SCR’s are triggered.
Q6.What are the differences between freewheeling diode and feedback diode?
Freewheeling diode is used to circulate the load energy in the load itself. Feedback diode is used to transfer the load energy to the source. Feedback diode is normally used in inverters. Freewheeling diode is normally used in controlled rectifiers.
Q1. What are the difference between transistor and SCR?
1. SCR is four layer PNPN device, whereas transistor is three layer (PNP or NPN) device.
Q2. Explain latching current and holding current of the thyristor?
Latching current: It’s the minimum forward current that flows through the thyristor to keep it in forward conduction mode at the time of triggering. If the forward current is less than latching current, thyristor doesn’t turn on.
Holding Current: It is the minimum forward current that flows through the thyristor to keep it in forward conduction mode. When forward current reduces below holding current, thyristor turn off.
Q3. What are the advantages of MOSFET’s over BJT’s?
i) MOSFET’s have simpler gate drive circuits.
ii) They have high switching frequencies.
iii) MOSFET’s are majority carrier devices.
iv) MOSFET’s have positive temperature coefficients.
Q4. Why pulsed gate drive is used for SCR?
Once SCR is turned on, gate drive is no more required. Hence if pulsed gate drive is used, SCR turns on at particular pulse. The remaining pulses are not used. But pulsed drive reduces losses in gate cathode of the SCR.
Q5. Define the delay angle of phase-controlled rectifier.
It is the angle at which thyristors are triggered after zero crossing. After zero crossing of supply voltage, one pair of thyristor is forward biased. After delay angle (α), the SCR’s are triggered.
Q6.What are the differences between freewheeling diode and feedback diode?
Freewheeling diode is used to circulate the load energy in the load itself. Feedback diode is used to transfer the load energy to the source. Feedback diode is normally used in inverters. Freewheeling diode is normally used in controlled rectifiers.
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