Question

In an NPN silicon transistor, α=0.995, IE=10mA and leakage current ICBO=0.5µA. Determine ICEO.

(a) 10µA

(b) 100µA

(c) 90µA

(d) 500µA

This question was posed to me in an internship interview.

I want to ask this question from The AC Analysis of a Small-Signal Low-Frequency Common Emitter Transistor. in chapter Small-Signal Low-Frequency AC models of Transistors of Electronic Devices & Circuits

Answer 1

The correct answer is (b) 100µA

The best I can explain: IC=α IE +ICBO =0.995*10mA+0.5µA=9.9505mA.

IB=IE-IC=10-9.9505=0.0495mA. β=α/(1-α)=0.995/(1-0.995)=199

ICEO=9.9505-199*0.0495=0.1mA==100µA.