At 01:03 PM 8/19/2005 -0300, you wrote:
>Russell McMahon wrote:
>
> > Do you like the brake circuit ? :-)
> >
> >     http://russell.servepics.com/temp/r100b.gif
> >
> > Too many parts, but it works well.
>
>I'm sure it does -- if you say so :)
>
>I can't figure out why it should, though. How is the basis of Q44 ever 700
>mV more negative than its emitter?

I've not tried to analyze this whole circuit, but...

C42/Q43/R41 forms a voltage doubler connected to the emitter of Q44.
Turn Q43 on for a while, then off, and the emitter of Q44 shoots up to
about 2*Vbat and decreases exponentially with time constant tau = R41*C42.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
->> Inexpensive test equipment & parts http://search.ebay.com/_W0QQsassZspeff


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