Re: Suggestions for 1kW, unregulated SMPS
- From: Mike Harrison <mike@xxxxxxxxxxxxxxx>
- Date: Mon, 04 Dec 2006 16:12:03 GMT
On 4 Dec 2006 14:19:43 GMT, dhaude@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx (Haude Daniel) wrote:
"Unregulated SMPS" probably sounds funny, but this is it: At my lab
we frequently heat up metal samples in vacuum by placing them near
a hot tungsten filament and applying a high voltage, essentially
making the sample the anode of a vacuum diode. This typically
happens at voltages of around 1kV and currents of .5A, but 1kW
total power isn't unheard of.
Now we have some homebuilt units that take care of this. They
consist of a custom-wound mains transformer with a bridge rectifier
for the HV, and the power is regulated via filament temperature.
These beasts work OK, but the transformer makes them heavy and
expensive.
Now we need a few more, and the natural path to follow would of
course be to make them switched-mode -- except that I've never done
an SMPS. I may be wrong, but I think this should nevertheless be
doable since I need no regulation at all; the first version would
just have a pot to adjust the duty cycle. So this thing would
consist of no more than a PWM controller, an IGBT H-bridge, a
transformer and a diode bridge. The output needs to be
short-circuit proof; I'd do that by adding some series inductance
to make the primary dI/dt slow enough to be safely cut off by the
overcurrent trip.
The only tricky part that I'm aware of is the design of the gate
drive circuit -- it mustn't ring and it must be quick to reduce
heat dissipation and avoid cross conduction. The transformer, of
course, is a critical part in any SMPS design, but I figure that a
poorly wound xformer can't have any ill side effects except
having too little output power due to stray inductance.
Ah yes, and an 1kW SMPS running from a single-phase 230V line needs
PFC and soft-start. Will have to read up about that.
Should I do it? Maybe it's a bit stupid, seeing that only 5 of
these things are needed at the moment and there exists a design
that works and can be assembled and tested by the techie who
originally designed it (he wouldn't touch a switcher with a 10-foot
pole). However I'd like to have a bit of fun of my own but I don't
enjoy having to pick bits of black epoxy out of my face.
And I know that a 1000V supply capable of delivering 1A is no
joking matter. But since the secondary won't consist of anything
besides the rectifier bridge and the output jack I won't have to do
much there.
BTW, I can't use the filament/sample constellation itself as a
rectifying diode. For one thing this would require some kind of
flyback design, and, more importantly, the anode gets often hotter
than the cathode.
--Daniel
This may be of interest :
http://www.stevehv.4hv.org/ccps1.htm
Also, have you looked at microwave oven transformers as a cheaper alternative to a custom unit.
.
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- Suggestions for 1kW, unregulated SMPS
- From: Haude Daniel
- Suggestions for 1kW, unregulated SMPS
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