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This circuit doesn't use a gate drive, so I am trying to understand how it can output 25kHz. A friend of mine told me that it does so with the use of LC resonance; the capacitor and inductor next to F1 and F2 achieve resonance as per the formula $$f = \frac{1}{2\pi \sqrt{LC}}$$ but I still have my doubts...

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  • \$\begingroup\$ Have you tried to simulate it? \$\endgroup\$ – winny Sep 23 '18 at 18:35
  • \$\begingroup\$ not yet. PSIM isn't working at my college PCs at the moment. \$\endgroup\$ – DigiNin Gravy Sep 23 '18 at 18:39
  • \$\begingroup\$ You can use the built in tool right here on EE.SE if you edit your question and press the schematics symbol. Installing LTspice is also an option. \$\endgroup\$ – winny Sep 23 '18 at 19:03
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This can be simulated online using Falstad’s circuit simulator. If you know the primary inductance, turns ratio and Mutual Coupling ratio (<1) then the impedance ratios are computed for each resulting inductance and referred nonlinear load impedance.. Although not easy, you must know all the RLC values of each trace, capacitor and choke, as well create a model of the trifilar center tapped transformer using two transformers with some awareness on transformer theory. Transistors are simple with only hFE, FETS are simple with only Vt, gm or inverse RdsOn for the models. Stray inductance and capacitance as well as DCR and ESR must be estimated and added. Diodes are based on physics with Vf@ 1A may not be a perfect model unless you add Rs bulk resistance based on inverse Pd rating or datasheet curvesfor saturated series R slopes. Caps are always ideal so ESR MUST be added. Same for chokes with DCR. and even better with PCB trace inductance if significant.

The series cap and diode clamps the AC to -Vf thus resulting in a AC voltage ratio and positive feedback loop to satisfy the Barkhausen Criteria for oscillation based on your formula above for effective L and effective C which is connected a certain percentage of the time when the base emitter junction is conducting in series..

There is also an LC resonance with the AC bridge side load as well as the ferrite core stray capacitance and its own self resonant frequency chosen with winding patterns to be sufficiently high.

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  • \$\begingroup\$ If you search some of my Falstad answer applications you can appreaciate the scope features, realtime slow speed interactive mouse features for component values etc. There is more than you can imagine but it is simple physics not COMSOL. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Sep 23 '18 at 19:10

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