How to Calculate the Maximum Current, IZM, of a Zener Diode

The two ratings that are usually given with a zener diode is its voltage, VZ, and power rating, PZM, (in watts), the amount of power that it can handle.

using these two ratings, we can calculate another very important parameter, which is the maximum current which can flow through the zener diode. Every zener diode has a maximum current rating, which is denoted by the expression, IZM.

Knowing the maximum current that can flow through the zener diode allows us to know if we are exceeding the power rating of a zener diode. We can just take the voltage across the zener diode and times it by the current, and we can know whether we've exceeded it.

Exceeding the power rating of a zener diode can damage or completely destroy it, and can also create shorts and other undesirable effects in the circuit. Thus, it's very important to know the maximum current that a zener can handle.

How to Calculate the Maximum Current, IZM

The calculation to find IZM is very simple.

We just use ohm's law for calculating the current:

IZM= PZM/VZ

IZM is the maximum current that can flow through the zener diode, PZM is the maximum power that the zener diode can handle, and VZ is the zener voltage.

So if a zener diode has a zener voltage of 5.1V and a power rating of 1W, it can handle 1W/5.1V ma, which is approximately 196mA of current.