Kapanadze Cousin - DALLY FREE ENERGY

[TEKTRON]

    MenofFather, and All:
 
   I'm still waiting for my zeners to arrive, which Tektron is sending. So, I can't really work properly until then. But, I'm doing what I can.
   
   

Nick, they arrived Friday evening. I will send them out to you Monday.

[TinselKoala]

Wait... are you really driving IRFP260N mosfets with a 5 volt gate signal? If so, that's why they are getting hot, especially at high frequencies. They are "barely" turning on at that Vgs and this means their internal resistance is higher than the stated Rdss and so they will dissipate more power. This is a "vicious circle" because as the mosfet gets hotter it also becomes less efficient and must be de-rated. Check the data sheet and study the graphs carefully. Operating right at the "gate threshold voltage" is a sure way to heat up a mosfet.
Yes, the "absolute limit" for power mosfet Vgs is generally plus/minus 20 volts but some can do 30. 10-12 volts will give a nice hard clean turn-on as long as there is the current available to fill the gate capacitance. Gate protection zeners, if used, should be as close as possible physically to the mosfet G and S pins, right at the mosfet if possible. If you overdrive, like using 18 volts for your gate signal, you should expect mosfet failures, because that kind of treatment requires very careful layout and construction to avoid deadly transients.
If your maximum Drain-Source voltage in the circuit doesn't require the voltage capability of the P260 you can probably use much cheaper, lower Rdss mosfets in your Mazilli yoke driver. For my wireless power transmitter system I use IRFZ44N which are cheap as dirt and stay relatively cool when operating.
How do I know this stuff?
Look:

[TinselKoala]

I don't know if your particular circuits will allow this, but often, putting a reverse-biased, superfast high current diode across the mosfet from Source to Drain can prevent the circuit's spikyness from heating up the body diode in the mosfet and produce cleaner overall switching. This diode should also be physically close to the mosfet itself to have the best results.

[TinselKoala]

I have had excellent success with this IRFP260N circuit, to drive flyback transformers and yokes. The mosfets do not heat much, I use small freestanding heatsinks for them. I actually don't remember ever having a mosfet fail on this apparatus. The gate zeners are 12 volts and the crossover diodes are 1N4936 fast rectifiers but other reasonably fast diodes would work fine here too.

[d3x0r]

Wait... are you really driving IRFP260N mosfets with a 5 volt gate signal?
How do I know this stuff?
Look:

Nickz is not(I don't think), I was... (well ended up trying to, it didn't work)  My mosfets were only like 21W 10A things... they were a fit for transistors in the same place... was thinking they were common source... but they're cascaded s-g-d/s-g-d (5 pin package) so ya they were basically fail from day 1.  http://www.irf.com/product-info/datasheets/data/irfi4020h-117p.pdf


Thanx for the shot of your junk part pile Nice


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I guess my diodes that cross-from drains to gates are leaky... when I connect power to coils, the gate voltage goes up to double what it started ...
Yes they were leaky at high frequency; changed to 1n4148's (which are pretty low current)


Now it kinda works (at least I don't get spike voltage on the gate) but; I don't get a clean gate signal either.... and the coil side has a +V bias ...
I dunno I ordered some fast diodes too maybe that will fix my issue....