Zener Regulator with Emitter Follower

Exercise 2.4 from 'The Art of Electronics, 2nd Ed.' Design a +10 Volt supply with the same specifications as in Exercise 2.3. Use a Zener and emitter follower. Calculate worst-case dissipation in transistor and zener. What is the percentage change in zener current from no-load condition to full load? Compare with your previous circuit. My Solution: If we assume that the maximum current over load is 100mA, then the base current should be 1mA. Adjusting the lowest zener current to 10mA gives us 11mA on the left top resistor. 11mA flowing between 20-10.8 = 9.2V gives us a 836.36 Ohms resistor. Thee collector current is then 99mA. The voltage of collector must be higher than base and emitter. So, with a 99mA current we must ensure that there is maximally 9V voltage drop. If we calculate the Rc, respectively, it should be lower than approximately 100 Ohms.

published 7 years ago