Question

A transistor series regulator has the following specifications: VIN=15V, VZ=8.3V, β=100, R=1.8KΩ, RL=2KΩ. What will be the Zener current in the regulator circuit?

(a) 4.56mA

(b) 3.26mA

(c) 4.56mA

(d) 3.68mA

The question was posed to me in an internship interview.

The question is from Voltage Regulation Using Zener Diode topic in division Application of Diodes of Electronic Devices & Circuits

Answer 1

The correct choice is (d) 3.68mA

For explanation: We know, VO=VZ-VBE=8.3-0.7=7.6V. VCE=VIN-V0=15-7.6=7.4V.                                 So, IR=(VIN-VZ)/R=(15-8.3)/1.8m=3.72mA. IL=VO/RL=7.6/2000=3.8mA. IB=IL/ β=3.8mA/100=0.038mA. Finally, IZ=IR-IB=3.72-0.038=3.682mA.