Re: diode-connected transistors

From: Pooh Bear (rabbitsfriendsandrelations_at_hotmail.com)
Date: 11/16/04 

Date: Tue, 16 Nov 2004 21:06:40 +0000

Terry Given wrote:

> I often use diode-connected npn and pnp transistors. Sometimes I use the
> base-emitter junction reverse-breakdown as a (somewhat dodgy) zener,

I believe at's actually avalanche breakdown.

>
> sometimes I use them as diodes. When used as a diode, I can either use
> the c-b junction (b shorted to e) or the b-e junction (b shorted to c).
>
> Here are my questions:
> 1. Which configuration has the lowest capacitance ?
> 2. which configuration has the lowest leakage current?
>
> In a more general sense, what are the pros and cons of either
> connection? Using say bc547 and bc557 transistors.

Can't think of a good reason to do it to be honest, although I've used the
b-e junction to measure temperature ( because TO-220 devices are easy to
mount in a thermally meaningful way ).

Graham

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