On 3 Jul., 18:05, John Larkin
<jjlar...@[EMAIL PROTECTED]
> wrote:
> On Thu, 3 Jul 2008 06:57:18 -0700 (PDT), Michael <nleah...@[EMAIL PROTECTED]
>
> wrote:
>
> >Hey there - I'm putting together a board that will have a number of
> >FETs switching the low side of some electromagnets. I do not know what
> >these electromagnets will be - but I've been told to design to be able
> >to switch half an amp across each.
>
> >So, though I don't know anything about the electromagnets - I think
> >it's pretty safe to say that they'll be at least somewhat inductive.
> >So how should I size the flyback diode?
>
> 1N4001, or any cheap power diode, unless mag field dropout time has to
> be fast.
>
> Or will the body diode of the
>
> >FET I plan on using (On Semiconductor NTJS4405NT1G,
>
> Nope, wrong direction.
>
> Some fets will let you skip the clamp and just absorb the flyback in
> avalanche mode; some will die, instantly, first cycle. Lots of
> darlingtons are avalanche rated.
>
> John
lots of FETs that are avalanche rated, with active clamping, current
limiting, overtemp shutdown etc.
in a few amps range in sot223, many with logic level input
-Lasse
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