Question

At saturation, which of these is not true for a BJT?

(a) The collector current IC cannot increase further

(b) The base current IB, cannot increase further

(c) The collector-to-emitter voltage, VCE is due to the non-zero internal resistance of BJT

(d) VCE(saturation) is the minimum voltage drop between C and E

This question was addressed to me in a national level competition.

My enquiry is from Transistor Switching Network topic in section Transistor Biasing and Low Frequencies of Analog Circuits

Answer 1

The correct option is (b) The base current IB, cannot increase further

For explanation I would say: At saturation, the collector-to-emitter voltage is the minimum drop possible occurring due to the non-zero internal resistance of the BJT.  Since it cannot decrease further, the current IC cannot increase further. The BJT is said to be saturated. However, the base current, IB, can keep increasing with the input voltage and hence, in saturation, the relation IC = βIB is not satisfied.