Re: gEDA-user: basic anti-EMI design q

["John Luciani" <jluciani@xxxxxxxxx>]

On 3/25/06, DJ Delorie <dj@xxxxxxxxxxx> wrote:
>
> > Switching at a zero crossing is a good idea in general. You will
> > dissipate less power in your switch and generate less EMI since the
> > di/dt should be much lower.
>
> So, on one of those dual-led AC optos, it would be better to interrupt
> on the just-before-zero edge, so that all the switching happens near
> the zero?  Or on the rising edge, to avoid any chance of glitches?

You want to turn your switch on at a low voltage point to generate small
currents and turn it off at a low current point to avoid high voltage
ringing. Assuming
a resistive load both points are at zero voltage. It should not matter
if you are little
before or a little after zero since your voltage will still be low. I
would think that
a little after zero would be a simpler circuit.

Since you may want to measure noise on your new board you may want to
add holes for some Johnson jacks at critcal points. These jacks are
fairly small.
The part numbers are 129-0701-301 (horizontal) and 129-0701-201 (vertical)
and are available from Digikey. This will allow you to do your noise
measurements without the ground lead of your probe. You may want to
verify the size of your probe sleeve before
you order. I seem to recall Tek probes coming in multiple sizes. Always
seemed to be the wrong size for the adapter on my board ;-)

(* jcl *)

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