Re: microwave oven inverter P.S. revisited

On Sep 7, 10:18 pm, Grumpy The Mule <s_foo...@xxxxxxx> wrote:
It would be interesting to know the phasing of the
transformer windings.

Since it's voltage fed and there is no output inductor
I would have guessed it was a ZVS flyback supply with
active recovery of the leakage inductance energy.  A
flyback is a constant power output topology by nature,
so it's a natural for powering a magnetron.  But the
waveform in the pdf concering the oven looks like a
forward converter.  Maybe it's the result of the active
clamp?

I've designed flyback converters with outputs of a couple
KW for TWT tubes but they were hard switched with multiple
rectified outputs on the transformer stacked series to
reduce the voltage stress.  At low output voltages a flyback
is unsuitable for much power because of the high peak current
developed in the rectifiers and switches.

Sorry to babble on about this but I found the oven circuit
fascinating.  The white goods guys are very clever.

I hope you can get it working as a power supply for your
amplifier.

I have my doubts about using it as is too, but I think there is a lot
to learn here.
For example I hae never used IGBTs before and already I hae begun to
learn. This may also be a chance for me to learn to design a
transformer that will work at 30Khz. I was thinking of using push-pull
driver on the primay of the transformer instead of the flyback
circuit. Something similar to a PC power supply. The Panasonic power
supply is definately designed for constant current. The input current
is monitored through a current transformer and this applied to the
contol circuit so that a decrease in input current results in a
greater output voltage through pulse width modulation. The plan is to
take this feedback from a coil on the output transformer instead of
the current transformer and apply it to the control circuit. I am
hoping this will turn the constant current power supply into a voltage
regulated power supply. Also the output rectifiers use a voltage
doubler. My plan is to change this to a full wave bridge, I think
David mentioned this too. I may not get full legal power out of it but
maybe I can power a couple of 4cx250s. That wouldnt be bad for a $50
power supply.

Jimmie
.

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