Re: sstc driver help

["Marco Denicolai" <Marco.Denicolai-at-tellabs.fi> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

"Tesla list" <tesla-at-pupman-dot-com> on 30.08.2000 20:06:43

To:   tesla-at-pupman-dot-com
cc:    (bcc: Marco Denicolai/MARTIS)
Subject:  sstc driver help



Original poster: "Jan Florian Wagner" <jwagner-at-cc.hut.fi>

Hello there!

>The ferrite xfrm is about ready, should give 3..5kV,

How many Amperes do you need? If you start from 320 VDC on the primary, you
need
only a 1:16 transformation factor -> a lot
less turns on the secondary -> you need only a winding layer -> no interwinding
corona problems!

>Running the xfrm at about 1/50 of critical B-saturation,

This is very low, you can go higher if core losses allow you. What switching
frequency you plan to use?

>lots of primary
>turns, big 5cm x 5cm x 2cm core of 3C85 material. Two non-connected 8 turn
>primaries, one tapped 120..200 turn secondary.

Use a double-U core and wind primary and secondary on different legs.

>I'm using a CA3825 PWM chip (with dead-time expansion), but couldn't find
>any FET buffer chip so looks like I can use only two FETs safely (?).

FET buffer?! FET gate is capacitive: it requires charge, not continuous
current.
If you mean FET drivers, IR and others do them (Motorola, I guess).

>Other thing, I was wondring with voltage feedback from the secondary...
> How is that done? Divider network with a small well insulated transformer?
> Or just 1-2 feedback turns on the xfmr, no messing around with secondary

Remember, if you are charging the primary capacitor with this thing, it will go
into protection and its output voltage will fall and rise with each charge. You
have to measure the DC voltage on the capacitor (or you can use a chopper and a
transformer, but them HP already has an optocoupler that does the job...).

Do you aim at charging the capacitor or driving directly kind of TC primary ?

>(By the way I've never built a SMPS before but've tried to gather as much
>knowledge as possible for starters. If you happen to know any good web
>site on SMPS, I'd be very much interested.)

The best source of info is not the web but the public library (in your case the
Helsinki University of Technology library): there should be plenty of books
about SMPSs.

Best Regards