Transformer saturation?

Posted by: Dominic on 12/18/2009

I have designed a 12v, 30w power supply using the TOP244. But near 0.9A, the TOP244 start cycling. I suspected the current limit protection. Here are the current waveform at the primary. I used a 1 ohm sense resistor.

Do you think it's transformer saturation, or a bad transformer design?

Thank you.

Comments

Hi,

It appears from the description of your problem that the power supply is going into "Auto-Restart". This will happen if the selection of components external to the part is such that the power supply fails to maintain regulation at output beyond a certain load level (in your case about 0.9A)

If you send us a schematic of your power supply and details of transformer design, we may be able to help you with this problem.

Unfortunately you cannot insert a resistor in series with the source pin of our part for making any measurements, since the source pin is the circuit common for the other circuits inside.

Regards

PI-Sarek

I will post a schematic tomorrow. For your information the resistor was between the transformer and the DRAIN pin. The oscilloscope was floating (ground removed) and the probe connected between the resistor.

There is a way to know what is te source of the restart?

The transformer core needed to be gapped, but it was not. After gapping my supply work perfectly. Thank you for your support.