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Zener diodes are used to provide an accurate reference voltage. They "break down" at a specified voltage in "reverse bias".

Zener Diode in the Lushprojects Simulator    Slide the resistance slider to simulate different load currents. The 4 V Zener level does not change.

Zener Diode Properties

All diodes allow current to pass in one direction only. In normal use, diodes never suffer a reverse breakdown which would destroy the diode.

Zener Diodes are special because they can break down without being damaged. They do this at a specific voltage (the Zener voltage) which is accurately determined by the manufacturing process. It is possible to purchase Zener diodes with a range of breakdown voltages between about 3.3 up to 200 volts.

• Zener diodes are connected the opposite way round to normal diodes (REVERSE BIASED).

• 5 or more mA reverse breakdown current is required to flow through the Zener diode to ensure the Zener voltage is reliably established. The exact figure is quoted in the data sheet for the diode.

• Once 5 or more mA are flowing , the current through the diode can increase without the voltage across the diode increasing at all. In this way, the Zener diode can provide a stable reference voltage.