Test: Power Transistors
20 Questions MCQ Test Power Electronics | Test: Power Transistors
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Which of the following devices does not belong to the transistor family?
GTO is gate turn off transistor, it belongs to the Thyristor family. All the other devices belong to the transistor family.
It has three layers p-n-p or n-p-n forming two p-n junctions.
The collector current is the controlled parameter.
Power transistor is simply many BJT’s connected in series parallel on a single silicon chip for power applications. It is a three terminal, bipolar, current controlled device.
In a power transistor, _________ is the controlling parameter.
The base current controls the collector current. Hence, the base current Ib is the controlling parameter.
The B-E junction of a BJT resembles a p-n junction diode, hence the curve.
For a power transistor, if the base current IB is increased keeping VCE constant, then
Ic is directly proportional to Ic.
Collector current by emitter current is the current gain, its value is close to one but never greater than.
Collector current by the base current is beta, its value is in the range 50 to 300.
A power BJT is used as a power control switch by biasing it in the cut off region (off state) or in the saturation region (on state). In the on state
When base-emitter & base-collector junctions are forward biased only than both the p-n junctions are forward biased and the device is on.
For a power transistor, if the forward current gain α = 0.97, then β = ?
Use the relation α = β/(β+1).
The power electronics devices have a very high efficiency because
They are efficient due to their higher transition speeds.
For a power transistor, which of the following relations is true?
Practically speaking Ie = Ib+Ic. Ie is the highest as it is the sum of the collector and base currents. The base current is the smallest.
Lower the switching losses higher the frequency of operation of the device.
The instantaneous power loss during the delay time of a transistor is given by
During the delay time only the collector current flows & base to emitter voltage is zero.
For a power transistor, the average power loss during the delay time can be given by the equation
During the delay time only, the collector current flows & base to emitter voltage is zero. Hence the average power can be found, simply by integrating it over the total delay time & dividing by the base time period.
A 1mv of i/p gives an output of 1V, the voltage gain as such would be
1V/1mv = 1000.
The collector & emitter current differ only by the base current, which is very very small.
Unlike the thyristor devices, all the transistor family devices remain in the conducting state as long as the firing pulses are applied. This is a very important property of the transistor devices.
Let’s say that a transistor is operating at the middle of the load line, then a decrease in the current gain would
The current gain would decreases the collector current, shifting the Q point below.
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