Exercise 2.3 from 'The Art of Electronics, 2nd Ed.'
Design a +10 volt regulated supply for load currents from 0 to 100mA; the input voltage is +20 to +25 volts. Allow at least 10mA zener current under all conditions. What power rating must zener have?
My Solution:
The worst case occurs when the voltage reaches to its minimum point which is 20V. If we are going to have 100mA on load and 10 mA on the Zener then the current coming from the main line(source line) should be at least 110mA. If we calculate the (20-10)V/R = 110mA for R, we find the R as 90.9 Ohms.
