Art of ELectronics 3rd ed. Exercise 2.6
Design a +10V regulated supply for load currents from 0 to 100mA; the input voltage is +20-+25V. Allow at least 10mA zener current under all (worst-case) conditions.
What power rating must the zener have?
1. Calculate R
Iout(max) < (Vin(min) - Vout)/R
0.1 < (20-10)/R
R < 100Ohm
2. What power rating must the zener have?
Pzener = ((Vin-Vout)/R - Iout)*Vzener
For worst case:
Vin = 25V
Vout= 10V
Iout = 0A (no load)
Vzener = 10V
Pzener =( (25-10)/R - 0)*10
Pz=150/100=1.5W
