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How to design flyback transformer

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yes...best to see inductor waveform...but many would guess it was in ccm, as there are no oscillations just before the vds goes down.
Its difficult to advise you without knowing where you already are.

Do you know Lenz's Law, V = Ldi/dt ?
Do you know Fardays law V = N(d(phi)/dt ?
What about kirchoffs laws?
Also Vp/Vs = Np/Ns for transformers ?
What happens if you suddenly apply a constant voltage across an ideal inductor?
Do you know "ampere turns balance"...eg Np.Ip = Ns.Is in transformers?
What happens if an inductive current is flowing, and you suddenly open a switch in the path of this inductive current? (and there is no other path for the inductive current to divert into)

These are the very basics of flyback design.
--- Updated ---

Please explain...in your blue vds waveform of #19 post, can you explain why there is that spike as the vds rises...this is a key point of flybacks, which you will need to know.
--- Updated ---

"demystfying switching power supplies" by raymond mack jr is a good simple book for flyback (and other) design.
It gooes through a flyback design
 
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, can you explain why there is that spike as the vds rises...this is a key point of flybacks, which you will need to know.
yes...best to see inductor waveform...but many would guess it was in ccm, as there are no oscillations just before the vds goes down.
Its difficult to advise you without knowing where you already are.

Do you know Lenz's Law, V = Ldi/dt ?
Do you know Fardays law V = N(d(phi)/dt ?
What about kirchoffs laws?
Also Vp/Vs = Np/Ns for transformers ?
What happens if you suddenly apply a constant voltage across an ideal inductor?
Do you know "ampere turns balance"...eg Np.Ip = Ns.Is in transformers?
What happens if an inductive current is flowing, and you suddenly open a switch in the path of this inductive current? (and there is no other path for the inductive current to divert into)

These are the very basics of flyback design.
--- Updated ---

Please explain...in your blue vds waveform of #19 post, can you explain why there is that spike as the vds rises...this is a key point of flybacks, which you will need to know.
--- Updated ---

"demystfying switching power supplies" by raymond mack jr is a good simple book for flyback (and other) design.
It gooes through a flyback design
can you explain why there is that spike as the vds rises...
 

...its the spike caused by the leakage inductance. The current in the L(leak) keeps flowing when the fet switches off......it thus charges up the vds capacitance of the fet until the RCD clamp diode breaks over......this will be at a voltage equal to "vin +V(RCD clamp capacitor)"....so thats the magnitude of the spike that you see......if you look at the sim i sent you can see it....you might have to add some leakage by adjusting the "K Lx Ly 1 " to say" K Lx Ly 0.995".
 

Please send that simulation. I will do adjusting leakage. Send .ASC file.
 

you can tell from the Vds waveform that you are in CCM, if at the end of the OFF time the Vds starts to ring down then you are in DCM ..
 
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Simulation is in post #12, there are also many flyback sims in the post of #14
I cannot send .asc...because this forum wont allow it...i have to send .txt, then receiver can convert to .asc
 

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