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Academics – Electro-Technology : 2014/DEC/03

Question

Q3. Fig Q3 shows a simple voltage regulator circuit designed to provide a stable 15 V d.c. output from an unregulated supply which can vary between 20 V and 30 V. The Zener diode has a breakdown potential of 15 V and the slope resistance when conducting is 1Ω.

It requires a minimum reverse current of 1 mA for satisfactory regulation.

Determine EACH of the following:

(a) The minimum value of the series resistor ‘R’ if the Zener diode does not exceed its power rating of 3 W;

(b) The regulated output voltage when the input voltage is 20 V. and the load current is 30 mA;