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Re: DC power supply again
From: Harri Suomalainen[SMTP:haba-at-cc.hut.fi]
Sent: Friday, September 05, 1997 5:37 AM
To: Tesla List
Subject: Re: DC power supply again
On Thu, 4 Sep 1997, Tesla List wrote:
> current a maximum at that time. Perhaps you meant quench at the end
> of the first transfer? I've tried active quenching in the past
You guessed right.
> > Certainly. I was all the time thinking on current limiting by perhaps
> > with a secundary choke (like in the normal forward topology) or by
> > some limiter in the primary side (like inductors in resonant topologies).
>
> Fair deal. I might in fact have to do that (go to a bridge with
> charging choke) to get to 2kW because the necessarily high secondary
Better core utilization in other topologies helps a lot. You can push
something like 1kW through a supprisingly small core in bridge topologies.
> Any choke _must_ be in the secondary side or you throw a huge
> voltage burden on the secondary windings.
Not nessessarily. Resonant topologies often have some LC-circuit in
the primary side. Sometimes it is a series LC network, sometimes
a series L with C in parallel with the transformer. Those do not
put huge voltage stress like a normal bridge with just a choke in
series with the transformer would.
I would be very tempted to try some multiplier in the secundary side.
Perhaps some nise doubler to keep transformer smaller. I've began to
put a lot of thought on that kind of device. It has surely lots of
disadvantages as well but it is always something that can be given
a thought.
> The transformer design I've come up with is about 6" diameter by
> around 3 - 4" high. A lot of core gapping is needed. I am going to
Wow! That's quite a huge transformer for 700W level! Voltage level
does have the nasty effect of making things big.. :(
> use IRF840's. That allows a lot of lattitude for changing to an H-
> bridge if I wish because I chose the flyback voltage = rectified peak
> mains (about 330V). The compromise in choosing that value is that the
> output rectifiers have to hold off around 40kV (I'm building a 50kV
> stack - or was going to until the wire problem appeared). This design
> is fine for about 2.3kW including losses.
50kV diode stack ain't too fun to have around.. That's one reason I'd
go for bridge design with eg. a half wave doubler.. Diodes would have
to take only the full output voltage (plus some marigin).
BTW, what's the diode stack about? The simples and most reliable thing
for fast hv diode stack could well be a lot of avalance diodes (like
BYV96E) in series. However, that is certainly not the cheapest one.
Designing a fast stack is not fun at all with normal diodes!
> I'll post. I am going to mount the core halves on paxolin this
> weekend. If I choose to go to H-bridge, I simply remove the core
> gapping and operate at a frequency that gives B(pk) of 250mT. I am
That's quite a high B. I'd assume core losses at B peak-to-peak of
500mT would he huge even at a very modest frequency! What's the
frequency range, 20-30kHz perhaps? That would certainly explain the
need for a huge core as well..
--
Harri.Suomalainen-at-hut.fi - PGP key available by fingering haba-at-alpha.hut.fi