GATE EC 2017 Set 1 — Question 39
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Electronic Devices → BJT → Switching Operation
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Question
In the figure shown, the transistor acts as a switch.
For the input as shown in the figure, the transistor switches between the cut-off and saturation regions of operation, when T is large. Assume collector-to-emitter voltage at saturation and base-to-emitter voltage . The minimum value of the common-base current gain () of the transistor for the switching should be ________.
Correct answer
0.89 to 0.91
Solution
1.For the transistor to act as a switch, it must enter saturation when .
2.Calculate the base current :
.3.Calculate the collector current at the edge of saturation :
.4.For saturation to occur, we require , so the minimum current gain is:
.5.The common-base current gain is related to by .
6.Minimum .
7.The value falls within the acceptable range of to .
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