Question

The input voltage to a regulator circuit vary from 80V to
120V and the load resistance RL
is 10kΩ. Calculate the
maximum and minimum zener diode current. Assume the
zener diode is rated at 50V.

Answer 1

Since we do not have the value of series resistance, assume it is R.

1) Calculate the currents flowing through the series resistance:

$$I_{Smax}=(V_{max}-V_Z)/R_S=70/R_S.$$

$$I_{Smin}=(V_{min}-V_Z)/R_S=30/R_S.$$

2) The series current can be represented as a sum of zener current and the load current:

$$I_S=I_Z+I_L.$$

3) Calculate the load current in zener diode:

$$I_L=V_Z/R_L=50/10000=0.005\text{ A}.$$

4) The maximum and minimum zener diode currents are

$$I_Z=I_S-I_L,$$

$$I_{Zmax}=70/R_S-0.005,$$

$$I_{Zmin}=30/R_S-0.005.$$