Re: gEDA-user: LED in reverse

[John Doty <jpd@xxxxxxxxxxxxx>]

On Nov 20, 2006, at 8:38 AM, Karel Kulhavy wrote:

> On Sun, Nov 19, 2006 at 09:20:53PM +0100, wk0 wrote:
> > Some time ago i read the warning for RF transistors that reverse  
> > biasing into
> > breakdown of the E-B junction may significantly increase noise  
> > figure.
>
> Does it increase the noise figure permanently or only temporarily?

Permanently.

> What if I have a circuit with 2N3904 transistors with 5V break down  
> and it has
> 12V power supply and on turn-on, a little current at 12V goes  
> through the
> junction the wrong way? Do I have to design my circuits to prevent  
> that?

I wouldn't worry about it with a 2N3904. The RF transistors that have  
this problem have relatively thin, lightly doped base regions making  
them much more susceptible to damage. Indeed, from a noise figure  
point of view the 2N3904 is *intentionally* damaged in manufacturing  
by gold doping to improve saturated switching performance.

John Doty              Noqsi Aerospace, Ltd.
jpd@xxxxxxxxx




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