Question

A 7.2V zener is used in the circuit and the load current is to vary from 12 to 100 mA. Find the value of series resistance R to maintain a voltage of 7.2V across the load. The input voltage is constant at 12 V and the minimum zener current is 10 mA.

Answer 1

Answer:

i think it should be 43.6 ohm

Explanation:

I think u r aware that zener diode in reverse bias is used as a voltage regulator across it and hence it regulates constant voltage (Here in question is 7.2V) across the load resistance which is connected in parallel with it.

Now, zener diode starts regulating a constant voltage just after it's breakdown. Just at breakdown situation it carries minimum current through it ...here given 10mA and the load will get the maximum current i.e. 100mA. (Remember the reverse bias characteristic of zener diode ..that graph).

Hence we can say, by kirchoff's current law...that incoming current should be 110mA...which obviously pass through the required series resistance.

Now...voltage drop across resistor will be 12-7.2 V using KVL. Now by using ohms law u can find out it's resistance ...R = V/I .