Forward Converter Reset

[Slinzer]

Designing a 50W two switch forward converter. The input voltage is 600V. On reset the transformer primary should clamp to the input bus voltage. On my prototype during reset the primary voltage reverses but only hits about 500V and never forward bias the clamp diodes. What could be going on? Is the primary doing a type of resonant reset with parasitic capacitance? Any thoughts.

 

[Slinzer]

What is the adverse effect on the circuit? Loss of efficiency?

 

[FvM]

Yes, this can hapen if the primary inductance is high and the duty cycle low enough.

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Not necessarily a problem. Clamp diodes will be put into operation if the duty cycle approaches the permitted maximum of 0.5.

I wonder if the stored energy is circulating or dissipated in a snubber. In the latter case, efficiency would be affected.