Re: Zener Diode

Gerhard Nerge wrote:
Hi

I'm in need of a 18 Volt 5 Watt Zener diode, I have only 18 Volt 1 Watt Zener diodes.
My question is, can I put 5 one Watt Zener diodes parallel to make it 5 Watt ?

Thank you in advance
Gerhard.


No.
They are not exactly the same voltage at all currents of interest and so will not "share" equally.
However, one can add in a transistor in two different ways:
1) Use resistor from supply tozener so it is a shunt regulator, and connect top end of zener to the base of te transistor, the collector goes to the supply and the emitter goes to the load. Use an NPN for positive volage, and a PNP for negative voltage.
The regulation is not as good as a direct zener, and the output voltage is about 650mV lower than the zener.
2) Make a power shunt "zener" by connecting the 1W zener fromthe base of a transistor to its collector; the emitter-collector of that transistor acts like a power zener.
Again, the regulation is not as good as a direct zener, but the output (shunt) voltage is about 650mV higher than the zener.

Those are the simplist methods; others add an amplifier of sorts.
.

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