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From: Tony Williams
Subject: Re: Driving a coil-driven relay
Date: Wed, 11 Dec 2002 10:05:11 +0000 (GMT)
References: <firstname.lastname@example.org> <3DF5A911.8F493BED@earthlink.net> <email@example.com>
NNTP-Posting-Date: Wed, 11 Dec 2002 10:05:32 +0000 (UTC)
User-Agent: Pluto/1.14i (RISC-OS/3.60)
In article <firstname.lastname@example.org>,
Michael Starks wrote:
> I suspect that during the CLOSE cycle, current induced in the OPEN
> coil initially by transformer action and then induced by the motion of
> the core (and permitted to circulate through the coil by the blocking
> diode) is somehow preventing the mechanism from throwing closed all
> the way, thus ending us up in the "closed but stuck" limbo state.
R? + - ______
28V+--/\/\---+---[Coil]--|AC +|--+-->FET Drain
| | Bridge |\_|_
|+ |Rectifier| /_\\ 48V TVS
BFC=== | | |
| +--|AC______-|--+ <- yes, no connection.
That circuit provides about a 50V flyback protection,
and yet when the FET is Off allows the "-" end of the
coil to swing to +/- 50V before drawing current.
The voltage across the coil is reduced by 1 diode drop.
The choice of a 48V transient voltage suppressor
assumes that your MOSFET can withstand 50V.
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