Re: How to identify PNP or NPN device?
- From: "Ted Wilson" <ted@work>
- Date: Fri, 15 Jul 2005 16:29:23 +0100
"cfgl2001" <cfgl2001@xxxxxxxx> wrote in message
news:65521f75.0507150627.7f5f0ef5@xxxxxxxxxxxxxxxxxxxxx
>I have a 2-terminal solid-state (pressure) switch device which is
> known to be a bipolar PNP or NPN device. The 2 terminals are emitter
> and collector with known pin positions. My question is:
>
> In the case of INACCESSIBLE base terminal of a bipolar device, is
> there any easy way to identify whether it is a PNP or NPN type of
> transitor?
>
> Thanks for any help.
Depends what's connected to the base.
If the base were effectively open-circuit and you know which is the
collector and which the emitter, you could check
which way round the device exhibits the lower breakdown voltage.
Use a voltage of say 12V, with a series resistor to limit current -
something like 22k-ohm, but it's not particularly critical.
If the device exhibits a breakdown voltage less than 12V with the collector
negative, then it's an NPN, otherwise it's a PNP.
(Note that this test relies on reverse-breakdown of the b-e junction which
is not particularly good for a transistor and causes progressive degradation
of
several parameters, so don't take any longer than necessary).
Do you know what's connected to the base? It could be that a test along the
lines described above would give adequate indication, depending what base
connection is present.
--
Ted Wilson
Senior Circuit Design Engineer
BAE Warton
edward.wilson@xxxxxxxxxxxxxx
"The gods do not deduct from man's
allotted span the hours spent in fishing."
.
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