Leaky zener diodes

A zener diode has a specified Vz (zener voltage) at a specified Iz (zener current). Let's take a 1N4740A, which is guaranteed to have a Vz between 9.5V and 10.5V if you apply 25mA across it.

It's also guaranteed that if you put only 7V across it, the current going through the diode will be less than 10uA. This is called leakage current. A leaky zener is one that has been damaged such that the reverse leakage current at voltages below the zener test voltage is a lot higher than normal. It frequently happens through momentary current surges that exceed what the xener is capable of absorbing, which damages the diode.

Good luck Chris

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Thanks Chris

Much appreciated

Gordon W