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From: "Bill Sloman"
Subject: Re: Help! Diode biasing of Class B amplifiers
Date: Sun, 6 Oct 2002 01:13:42 +0200
Organization: Planet Internet
NNTP-Posting-Date: 5 Oct 2002 23:13:30 GMT
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
"Paul Burridge" wrote in message
> I'm having serious difficulties getting my head around this
> I've seen several circuit diagrams illustrating the use of
> compensating diodes to establish the correct operating point for the
> output transistors; just bringing them to the verge of conduction to
> minimize x-over distortion. All fine, except that I can't see how the
> input signal is supposed to ignore the 'one-way-only' property of
> these diodes.
I think that the critical point is that the compensating diodes (or the
single "synthetic diode" transistor in the better designs) is only useful
when the output current is relatively low. At this point you want the output
stage biassed into class A, with a wetting current of 100mA or so running
through both drivers from one rail to the other, so that both the output
transistors look like low impedance source/sinks (0.15R = 0.3R//0.3R at
Once the load is sinking or sourcing significant current, the active driver
can handle the job, and the complementary driver can be off. You should
organise you heat sinks so that the "synthetic diode" sees the same
temperature as the controlling junctions.
Bll Sloman, Nijmegen
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