ucc28630 Regulation vs Temperature

Hi Pablo,

I have asked one of our systems engineers to respond to your question.

Regards

Peter

Pablo,

It looks like the output voltage moves up by 50-100 mV over time. I think this is probably due to the temperature rise of the output diode.

Since the UCC28630 is a primary-side regulation controller (PSR), it regulates the output voltage indirectly via the primary aux winding. So as the output rectifier diode Vf changes (with load current and temperature), so too will the output voltage after the rectifier.

Can you plot the diode temperature on top of the Vout variation? I expect to see a correlation between temperature increase and Vout increase. As the diode temperature increases (the longer the power supply runs at heavy load), the diode Vf will decrease, and then Vout will increase.

A change of 100 mV in Vf seems pretty typical.

What is the part number of the diode you are using? At 4.5 A output current, that's quite a lot of current and power dissipation for a diode. A good Schottky diode with Vf of say 0.45 V will be dissipating 2 W of power, that will cause it to heat up a lot, even with the heatsinking of the chassis.


If you need to improve the regulation, consider a better lower Vf diode, or a larger package, or maybe 2 diodes in parallel (they probably won't share equally, but this will help to reduce the current in each and spread the heat over a larger area).

I hope this helps explain your issue.

Thanks,
Bernard

Bernard

The Diode is  STPS20SM100ST.

We will do the suggested tests

Regards