Self Oscillator Circuit (Push Pull MOSFET)

Thread Starter


Joined Jul 5, 2015
Looks like it operates in LC resonant mode.

The diodes allow the cross-coupled FET's to pull the opposing FET's gate voltage down to shut it off. The resistors bias BOTH the FETs in the ON state, which is an unstable condition- they cannot both be ON because this would turn them both OFF... it becomes bi-stable, the resonance of the LC tank sets the pace.

When the resonant cycle reaches a point where the drain voltage of the OFF state FET begins to drop, it sucks the bias voltage of the opposite FET away through the diode, turning it off.

A very interesting circuit!
Hi Sensacell...I see that you know much about this topic....can you help me about my problem....

The main problem is that I don't know is there positive or negative voltage in circuit.

MOSFET is connected like this on the picture below. He is connected on the input of the board.

MOSFET 2....pins 1,2,3 on transformer make me confuse and also connections to the voltage regulator (IC6). Diodes D9 and D10 are connected to the ground and then to Vin of the voltage regulator.
Also the pins 10,11,12....only I know it can be is that negative voltage goes through D6 to
Emitter of T5 and on emitter is negative voltage. T5 is giving 15V to ICs on the board.

And connection of T5 MOSFET, is it really like this, is it good connection.

Can you explain me how those two circuits are working from the pictures below.

I have drawn a schematic from the board and really, drain and source are connected to the ground, I checked 100 times.

Component values are important but not in this case. I just want to know how this circuit works and what is his purpose.

I have tested this circuit on breadboard and first I have connected 100VDC without any voltage between drain and source and then I had Vgs=18V. But when I connected voltage between D and S (30V) I lost the voltage Vgs.

And maybe it is really negative voltage on input, because drain and source are connected to the ground. And this circuit is connected EXACTLY on the input from the board. It must have some purpose.

Second thing....rectifier diodes (D9, D10) are connected also to the ground and from there to input from voltage regulator ?....sorry but I have seen first time circuit like this one.

I really hope that you can give me an answer and can explain the purpose of this circuit.

Best regards




Joined Mar 31, 2012
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Thread Starter


Joined Jul 5, 2015
Sorry...I am new here and I didn't knew the rules.

I have posted a thread and I haven't get any useful answer.

I want do that anymore.

Thanks anyway