DPA425R Thermal Shutdown

Posted by: sunit.singh2@g… on 05/27/2010

I have designed a 52W multi output (12V-3A, 5V-1A, -12V-0.2A,+5VISo-1A)flyback power supply using DPA425 R Package,
Even at at very small load approx 100mA, Power supply is getting ON(5 Seconds)- OFF(4 Seconds)and we are getting a sawtooth waveform on Control pin during OFF period, which indicates that its being ON-OFF due to Thermal Shutdown.

Please suggest why device is being hot.

Schematic is attachached for your reference.

Comments

What is the temperature of the tab when you say it shuts down?
Is there sufficient heatsinking? Can you send me a layout of the board?

Thanks for your reply,
We re-layouting our board because we are having some problem in layout.

But I just want to know that, would DPA425R will be OK for approx. 50W flyback design with input voltage 36V to 60V ?
Please give your suggestion what need to be done for heatshinking.

To avoid thermal shutdown modified layout and schematic is attached,
Please check would it be OK ?

Input range: 36V to 72V DC.
Output : 45W
Design: Flyback

please find attachments for previous comment.

Please attach a thermocouple and measure the temperature of the Tab of the DPASwitch. My initial feeling is that you will need to increase the copper area around the tab quite a bit more. But you need to measure the temperature first and see. Let me know...