Re: gEDA-user: LED in reverse

[Karel Kulhavy <clock@xxxxxxxxxxxxx>]

On Sun, Nov 19, 2006 at 12:22:54PM -0500, Darryl Gibson wrote:
> 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.

But why does the diode break down? If I touch the diode with a charged finger
it will surely send a little spark through the diode the wrong way and it will
not break down.

CL<
> 
> 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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