initial current spike

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We have designed in a TNY275G into a 15W universal input converter with a 12V output. The circuit does not regulate very well, and we see a large spike in the drain current at turn-on. We think it is a transformer problem- maybe excess self-capacitance? What are the solutions for this? thanks
Hello brate, may b for large spike in current waveform, you could try Different appropriate output diode first. Also, capacitance could be a problem a bit but, it would be better if u upload a waveform pic for same here. For regualation, are you using TL431? if still you are not getting better egulation, better check the transformer design too. For precise responce...lets see what Chekov n quintin has to share!!!

Prasun is correct - a scope waveform would help here - can you post a drain current and drain voltage shot? A hand sketch is ok too. Another possibility is a reversed winding, especially if the drain current is all spike and not followed by a linear ramp as the current increases in the primary (di/dt = V/L where V is input cap voltage and L is primary inductance).

Cheers

PI-Chekov