Question

An unloaded zener regulator has a
source voltage of 24 V, a series resistance of
470 V, and a zener voltage of 15 V. What is the
zener current?

Answer 1

If zener voltage is 15 V, then the resistor voltage is $U=24-15=9V.$ The zener and the resistor are connected in series, so their currents are equal. The resistor current: $I=U/R=9/470\approx0.02 A=20mA$. So, the zener current is also 20 mA.