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TOP258YN temperature

Posted by: kafka on

Hi,

I designed 14V, 6A open frame power supply using TOP258YN. I used standard schematic achieved with PI Expert and trafo from link:
http://www.feryster.pl/jacek/rysuj.php?lang=pl&indeks=9e07a980e878fa80d…
Core is E25/13/11.
I added HS-123-25 heatsink to the TOP258 device.
Unfortunetally the IC heats up to 120C even under full load. What can be the cause?
Drain volatge in tha attachment. Is it ok?

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NewFile0.jpg 27.38 KB

Comments

Submitted by PI-KSAN on 03/17/2015

Hi Thanks for Posting your question into forum. The drain voltage waveform looks good but there is too much ringing in VDS. How much efficiency are you getting at full load? Is your efficiency match with out PI Expert. At what line voltage the IC is getting hot. Please make sure the leakage inductance of transformer is less than or equal to 3%?

Regards,
PI-KSAN

Submitted by kafka on 03/22/2015

Hi. I think the heatsink was the problem. It is quite massive but with undocumented resistance. I replaced it with much smaller but with documented low resistance and now IC is about 70C at full load with 230VAC input. I get more or less 82% efficiency. With given transformer is anythink I can do to improve this?
How can I decrease the ringing? Should I increase C5 for example? Simplified schema in attachment.

Attachment Size
smps.pdf 70.61 KB
Submitted by PI-KSAN on 03/31/2015

Thanks for Posting your question into forum. It's good that you are using PI Expert Schematic, Is the inductance of your transformer matching with the sugggested value of PI Expert. Please Use PI-XLS Software for validation of the transformer that you are using is matching with PI-XLS.The main reason for the ringing is due to poor lay out, Leakage Inductance of the Transformer. Minize the Loops.   You mentioned C5 but We didn't see any schematic that you attached. Please send us the schematic.

Regards,

PI-KSAN