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From: Fred Bloggs
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Subject: Re: zero-power toggle circuit; was, how to master electronics
References: <3DC517EB.email@example.com> <3DC57B4E.firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org> <3DD39D90.email@example.com>
Date: Fri, 15 Nov 2002 03:20:13 GMT
NNTP-Posting-Date: Thu, 14 Nov 2002 19:20:13 PST
Organization: EarthLink Inc. -- http://www.EarthLink.net
> Winfield Hill wrote:
>>High-side switching is dangerous, unless an effective form of
>>short-circuit protection is provided, e.g. shutoff, foldback
>>current limit, a quick fuse, etc. Low-side switching is used
>>in cars, etc., because it has the nice property that a wiring
>>short simply turns on the switched device. Recommended.
> I would have thought in wiring terms cars are mostly high side switching.
> With a -ve earth chassis used for a return most wires between switches and
> loads are +ve.
> Low side switching is frowned on in industrial controls systems because of
> that property. It is no doubt made illegal by some bloody european safety
> regulation or the other. Having things turn on due to the most common type
> of wiring short is generally more dangerous than having them turn off
> although personally I don't think it is anything to get that worked up
Right- I am not sure about the low side switching, seems to be an awful
lot of automotive high-side switching being done. And every single one
of these circuits is a straightforward implementation of the simple two
inverter latch- Win just likes to make things look much more involved
than they actually are. The drawback on all these circuits is that the
momentary switch does not have a terminal fixed to one of the rails.
View in a fixed-width font such as
| | / | | /
| | / / | /
| | / \ Rs | / <---PWR
| / MOSFET
| \ / \
| --- |
+--------o o-----+ SIMPLE INVERTER TOGGLE
--- SW NOT GND'D
| RsC>> SW BOUNCE
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