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Re: gEDA-user: LED in reverse

Karel Kulhavy wrote:


How is it possible that the LED withstands 20mA in forward and is destroyed by
0.5mA in reverse? If it has say 1.5V forward and 5V reverse then the amount of
energy dissipated is greater in the forward case.

The diode has a high resistance when reverse biased, it won't conduct .5mA with reverse bias. With 1.5v reverse bias(Vr), the diode will only conduct .0001mA. And that is all it will conduct, regardless of what the reverse voltage is, _until_ the maximum Vr is exceeded, then the diode breaks down.

A forward biased diode has a low resistance, so you need to control its current.

Excess current kills a forward biased diode.
Excess voltage kills a reverse biased diode.

--
Darryl Gibson N2DIY
RLU X 182668/379552



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