Re: Solid State

On Tue, 21 May 1996, Tesla List wrote:
> I'm at 205khz by the way. I haven't had a problem with heat in
> the cores, but heat in the windings was a real pain. But I'm chipping

You will get heating when you go for more power. Winding is a real pain.
I'm making a winding machine right now to make experimenting with lots
of different transformers easier.

> Looking at the catalogues it does seem that the higher grades of
> ferrite are only available in the smaller sizes.

Supprisingly small cores are good with high frequency! Stack E-cores
like I'm going to do when I get the project going again.

> Current limiting is still a pain, comes on too soon despite lowering
> the resitance to 0.03 ohm (30A peak) seems to turn on at about
> the same point regardless of the output transformer ratio - time to
> experiment with a current transformer and tighten up the layout.

You would certainly need a scope for solving those problems. If you
are using just a resistor you may have limiting action becouse of
the leading edge spike. Usually some small filtering is needed.
See further info on SMPS related books.

> But if I'm doing all that I may as well go for a half bridge at the
> same time.

Makes sense. No need to experiment with a device which will end up to
the junk box anyway.

> I'll store this idea away for later. I am hoping that to get a
> FET bridge running at 75v then 150v then try mains with a very
> low transformer ratio initially then I should blow fewer FETs.

Thats how I tried my earlier device. Variac would be great for adjusting
voltage. If you make the half bridge properly it is self clamping and
you should have no spikes. Then it is just a matter of making a proper
transformer and maybe beating the parasitic effects which can be a real

> I saw (I think in Byland's book the suggestion of placing at
> intervals in the secondary a pair of green/red Led's. To give
> some indication of what is happening current wise along
> the length of the secondary.Then fibre optic cable to a photo 
> diode to measure.

Interesting idea. However it seems like insulation problems etc could
easily occur with that approach.
We have phone numbers already, why would we need IP-numbers! -unknown person

Harri.Suomalainen-at-hut.fi - PGP key available by fingering haba-at-alpha.hut.fi