Snubber question

pstamler

Well-known member
Joined
Jan 24, 2005
Messages
1,509
Location
St. Louis, MO, USA
So I'm laying out a PC board with some snubbers on it, the type Jim Hagerman discussed in his article in audioXpress a few years ago, RC in series hanging across the transformer secondary. Two of them, in fact, for a center-tapped transformer. And a layout question occurs to me.

There's a terminal where the center tap of the transformer attaches, which is about 0.35 inches from the ground terminal of the first filter capacitor. (Not a balanced supply; this is for tubes.) Nice thick trace, since the major part of the ripple current flows through it.

So...do I run the trace from the two snubbers to the CT terminal, or the capacitor ground terminal? My first guess is the CT, since that way I'm hanging the snubbers pretty directly off the transformer secondary (and it would be handy for layout reasons). But it'd be nice to have some more expert advice.

Peace,
Paul
 

bcarso

Well-known member
Joined
Feb 20, 2005
Messages
4,055
Location
San Fernando Valley, Los Angeles
It's not clear to me yet what the snubbers are actually snubbing. But I did find empirically that the R-C snubber across the winding does a nice job of slowing down the magnetic field fast transients in another cap input solid state rectified supply. Those were the ones I was worried about propagating so I was satisfied. It was a pretty sloppy layout with leads flying around on the bench, and when I say "fast" I mean a few microseconds initially to several tens of microseconds with the snubbing if memory serves---not the superfast transients associated with diode reverse recovery charge. So my guess is, if your snubbers are quelling the same kind of stuff then the precise return point is not that critical. As long as it is ahead of where your real star reference is you should be o.k.
 
Top