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Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
I found this article by David Smith of the The Wireless Institute of Australia. Looks like he's pretty much 'reverse engineered' the Panasonic inverter microwave oven HV control circuit.
He's not 'cracked' everything, but he seems to have gotten further than anyone else so far.
If anyone has anything to add, regarding stuff he's not sure about I'd be interested to hear it.
Really excellent info here! I didn't realize they had AC transformers in there (as opposed to the internal rectifier LOPTs in TVs). This may be the modern source of AC flybacks I've been looking for.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Sigurthr wrote ...
Really excellent info here! I didn't realize they had AC transformers in there (as opposed to the internal rectifier LOPTs in TVs). This may be the modern source of AC flybacks I've been looking for.
output is only two thousand volts though, and if you try and push it you'll have to watch the IGBT's don't blow, as far as I'm aware.
It's unlikely I'd go through the trouble of reusing the inverter board. I'd probably see what frequency the transformer resonates at and just use all the parts for my own ends.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Sigurthr wrote ...
It's unlikely I'd go through the trouble of reusing the inverter board. I'd probably see what frequency the transformer resonates at and just use all the parts for my own ends.
Apparently they are driven at 30kHz, but the most significant thing about the cores is that they have two different sized gaps, one enclosed by both primary and secondary, and the other just enclosed by the primary.
I've read up a bit on gaps, but I can't say I fully understand it, although I think I'm getting there. The gaps effectively reduce the inductance, but prevent saturation, which I think means that the turns ratio is not proportional to the inductance ratio (I know there is a ^2 term to consider as well, but these won't follow the same rules that apply to other primary:secondary ratios, from what I can tell).
Any further suggestions regarding these points would be most welcome.
Like I said above, I do know they use some very beefy IGBT's to drive these, and that they still blow quite regularly even in the standard oven.
The only people who make, or possibly even understand, these cores fully is Panasonic, but I'm trying to suss it out.
I don't know what differences there are between 110V and 220V ovens other than that the 220V ones seem to be driven from rectified mains. Maybe the 110V ones have a doubler on the mains rectifier, I don't have access to 110V ones this side of the pond to check.
EDIT: also, there isn't much room on the secondary bobbin to fit extra turns. Using thinner wire to get more turns and higher voltage could lead to insulation problems, to state it mildly.
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How to 'hack' an inverter microwave oven HV circuit
