Re: [CAD_CAM_EDM_DRO] Re: Was Chopper circuit - Now ver 3.2

----- Original Message -----
From: "Jon Elson" <elson@...>

> Well, I built a 10 A, 80 V full-bridge PWM servo amp that runs at 100
> KHz. Definitely RF! And, it is all on a 2-layer board,

And I've got dozens of Mosfet circuits on 2 layer boards. Never
had a problem with them either. I've done up to 12 layer boards for PC stuff
but prefer 2 layers since they are so simple to prototype with.

> If you can live with 25 KHz swithcing frequency, fast IGBTs are amazing!
> Where $18 TO-247 HEXFETs ran so hot they had to be paralleled, a single
> $6 T)-220 IGBT ran almost cold!

Exactly the same experience I had. Replaced a Hexfet with an IGBT and I
didn't really
need a heatsink after that. Simple 2A 120VDC PWM control. ( but it got the
heat sink anyway )

Only problem I had with that design was the transformer I derived my gate
drive voltage
from ended up not working well at 50hz ( and it was 50 hz rated ). So some
machines
that went overseas were popping IGBT's. Tracked it down to low gate voltage,
put
in a higher voltage transformer and no more problems.

The IGBT's were cheaper than the Hexfets also.

later,
Larry E.