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#27
October 1st 08, 12:13 AM
posted to rec.radio.amateur.homebrew
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microwave oven inverter P.S. revisited
On Sep 30, 2:13*pm, wrote:
On Sep 10, 8:05*pm, Grumpy The Mule wrote: Exactly right it is a gapped core. Once I git's a scope on I'll see. But the voltage doubler they using is full wave doubler. Which means they taking the positive and negative waves *to get 4000 or so volts DC Now the positive half they use a .0082 mfd for a filter and the negative half they use a .0056 mfd filter both at 3000wvdc. my guess is the quasi-push pull output is due to the leakage energy recovery circuit. *HV flyback transformers usually have very high leakage inductance (the part of the magnetizng inductance not coupled to the secondary is leakage inductance) because distance between windings is a major cause of poor coupling and you need distance for isolation. * The leakage energy sloshes about in the primary causing all sorts of mischief. *This circuit recovers it and dumps it back into the primary. It's unusual since the leakage energy is usually dumped back into the bulk storage capacitor on the primary side if it's recovered by a clamp winding or active clamp circuit. * A soft switching topology often uses the leakage inductance to reduce transistion losses in *the switch. *Sometimes a discrete inductor is added in series with the transformer primary to add to it. *Another bonus for the lousy coupling of the HV flyback transformer... no discrete inductor needed. *I think of this as electronic ju-jitsu. The energy per half cycle (on the secondary) won't be equal so juggling the capacitor values helps equalize the voltage stress. Eh! *I might be completely wrong. *Simulating it would be the thing but it's too much like work work and I'd need the transformer parameters. At least that's how I think it works... Please let me know when you've scoped the waveforms. I was looking at some old UPSs without the big iron transformer and was trying to figure how they get 60Hz 1KW out of that little transformer. The best I an figure is that it works somewhat like a class G amplifier. In this case the pulse width of the 20Khz or so signal is being PW modulated so when the output is intergrated you get 60Hz. If this is the case I am thinking that UPSs may be hacked into HV power supplies a lot easier, safer and better than microwave oven power supplies. Jimmie- Hide quoted text - - Show quoted text - Oooops, I meant class D instead of class G |
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