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From: Tony Williams
Subject: Re: zero-power toggle circuit; was, how to master electronics
Date: Fri, 15 Nov 2002 12:17:05 +0000 (GMT)
References: <3DC517EB.email@example.com> <3DC57B4E.firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org> <3DD39D90.email@example.com>
NNTP-Posting-Date: Fri, 15 Nov 2002 12:35:34 +0000 (UTC)
User-Agent: Pluto/1.14i (RISC-OS/3.60)
In article ,
Winfield Hill wrote:
> I'll withdraw my comment asserting a lo-side switching preference, but
> I'll stick by my assertion that an effective shutoff protection scheme
> is required for high-side switching. A fuse alone is likely inadequate,
> because in the event of a complete short many FETs may or will become
> damaged before the fuse blows. One can add a current-sensing resistor
> and some circuitry responding to the voltage across it, etc.,
There has been something similar in another
thread here in sed. See;
Subject: Re: Turning on a circuit till current increases...
Date: Mon, 11 Nov 2002 07:42:37 +0000 (GMT)
If the latching-feedback is taken directly off
the power device then the circuit will unlatch
at some (unspecified) overcurrent.
A more respectable unlatcher would be a current
sense resistor running with (say?) 150mV across
it at normal full load, with a transistor b-e
across it... the transistor unlatches the circuit
at about 3x full load. The b-e unlatcher gets
more sensitive with temperature and there may
even be circumstances where the transistor is
deliberately mounted close to the power switch.
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