Zener Diode Applications

1.) Zener Diode Application

It is commonly used as voltage regulator in DC power supplies.

Two types of regulation are:
- Line regulation
- Load regulation

2.) Line regulation

The zener diode regulates a varying input power supply as shown below.

Given: Izk = 0.25mA to Izm = 100mA.

Vin = Vr + Vz

For minimum current, voltage across 220 Ω:

Vr = IzkR = (0.25mA)(220Ω)

= 55mV

Therefore:

Vin = Vr + Vz

= 55mV + 10V

= 10.055V

For maximum current, voltage across 220Ω:

Vr = IzmR = (100mA)(200W)

= 22V

Therefore:

Vin = 22V + 10V

=32V

The current limiting resistor is included to prevent the zener from conducting too much and overheated.

Notice that the diode is reverse biased. The output voltage (across the zener doiode) is maintained constant in this manner.

3.) Load Regulation

A zener regulator with variable load resistor. A zener diode maintains constant voltage across RL as long as the zener current is greater than Izk and less than Izm.

At no load, IL = 0 & the total current, IT will flow through the zener diode.

When RL is connected, IT = Iz + IL.

When Iz reaches its minimum, Izk, load current is at its maximum.