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From: James Meyer
Subject: Re: Thermal runaway: please settle this dispute!
References: <email@example.com> <firstname.lastname@example.org> <4KfR9.92768$hK4.email@example.com> <firstname.lastname@example.org>
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Date: Sat, 04 Jan 2003 22:17:08 GMT
NNTP-Posting-Date: Sat, 04 Jan 2003 17:17:08 UWT
On Sat, 04 Jan 2003 14:55:11 +0000, Paul Burridge
>Well you've both identified the source of confusion for a lot of
>people. Many text books use the term "Vbe" at one moment to refer to a
>device's internal Vbe - or *barrier height potential* as it is more
>properly known as - and at other times to refer to *applied* Vbe from
>some external voltage source.
>That is why I was particular in using the term *barrier height* in my
>original post. It's the fall in *barrier height* between emitter and
>base with increased temperature that gives rise to increased current
>flow if the *external Vbe* isn't reduced to compensate for it. Hope
>this clears things up for anyone left who hasn't spotted this
>essential little difference yet.
>Now where did I put the asprins?
Now the ONLY question left to answer is, "How many transistor designs
use a voltage source to bias the B-E junction?"
The overwhelming majority of circuits I look at use CURRENT sources for
B-E junction bias currents. In that case, reduced "barrier height potentials"
play a very small part in thermal runaway problems.
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