[sdiy] Transistor B-E reverse bias breakdown ?

ASSI Stromeko at nexgo.de
Wed Jun 13 20:41:02 CEST 2012

On Wednesday 13 June 2012, 11:30:56, Harry Bissell wrote:
> It's my habit to use a silicon diode reversed across the junction to
> prevent breakdown, but does anyone have experience using the breakdown as
> a 'feature' by limiting the peak reverse current (thereby saving an extra
> diode)
> The circuit would be subject to repetitive breakdowns.

Typically, if you let the reverse breakdown happen Hfe reduces and noise 
goes way up, although different makes/specimen would react differently.  If 
matching is even remotely a concern, don't entertain the thought of reverse 
breakdown (you shouldn't even have large reverse bias for a prolonged time 
if matching is critical).

> What currents might you allow without causing permanent damage ?

You need to limit the current so that both the maximum current and the 
maximum power are never exceeded.  At typical breakdown voltages the latter 
probably sets the more strict criterion.  The degradation of any transistor 
parameters will become less prominent the lower thew current limit is.

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