# What is a zener diode?

## Main Question or Discussion Point

I think I sort of understand, does it take all of the voltage in apart from a certain amount?
so say you havea 4v zener, does it absorb all the volts but the 4?
I've googled it but I really need to ask questions to understand.

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jbriggs444
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I think I sort of understand, does it take all of the voltage in apart from a certain amount?
so say you havea 4v zener, does it absorb all the volts but the 4?
I've googled it but I really need to ask questions to understand.
A 4v Zener diode passes enough current to "draw down" the power source so that only 4 volts of potential difference remains.

You should understand that no power source is ideal. It will have some internal resistance. The more current you draw through it, the less voltage it will be able to supply at that current level.

If you put a 4v Zener in series with a 5v battery then you might say that the excess volt is "absorbed" by internal resistance in the battery.

Google "Thevenin equivalent" and "cold cranking amps" for some references that might possibly be of interest.