Kapanadze Cousin - DALLY FREE ENERGY

[itsu]

Nick,

the ringing frequency is mainly caused by the stray capacitance and inductance of the attached primary coils / connections
This should be almost the same for both primaries, so the ringing frequency should be almost the same.
I never have seen different ringing frequencies on my MOSFETs in this kind of setup.


Anyway, to continue with the next step, we take your 1nF cap and divide it by 3, meaning we have 330pF as the parasitic capacitance for 1 MOSFET (left)
For the other MOSFET (right) we take 1.47nF and divide by 3, meaning here we have 490pF parasitic capacitance.

I will calculate the parasitic inductance (step 3) and the characteristic inpedance (step 4) for these found capacitances later tonight.

The needed capacitors will be between 4 and 10 times the above found parasitic capacitance (330 and 490pF), so we could settle for something like 2.2 or 3.3nF.

Itsu


 

[itsu]

Nick,

it sure is a tricky thing, especially when using long wires to and from the power supplies / batteries.
Try to keep them as short as possible.

Itsu

[itsu]

Nick,

for calculating the RC snubber i need to know the ringing frequency of the MOSFETs without any capacitance.
I now understand that you have 2 different ringing frequencies, so please tell me what are these ringing frequencies (1 was 1.98Mhz), but what is the other?

Itsu

[NickZ]

   OK, I'll do that later tonight.
   But, should I use the 12v battery instead of the PSU? As I'd be running new FETs at possibly close to 300v.
   I've tried to do what I can to figure out why there is a difference in the running frequency, but I still don't have a clue. The wires lenght are the same for both fets. And the TL494 and drivers run very similar, so it's probably not that.

[itsu]

Nick,

300V spikes is to much for your 200V MOSFETs.
But it could be, as mentioned by Hoppy, that your probes are giving false readings, did you try to use these shortend ground leads?
Else you could try to further lower the supply voltage.

Itsu