SMPS(flyback question)

seegoon99 · 2006-03-07T10:38:25+00:00

Hi to all.I have a quick question about a flyback convertor I'm working on.Its 220V ac in 13.7V dc out. I'm using a uc3842 contriller chip.At 60W ( about 4.5A) load everything seems good. At about 80 to 100Wthe cct starts toget unstable. I can hear a hissing sound etc. Looking at the switchingFET'sdrain waveform I can see that the frequency is changing ( hoppingaround). I have found that ifI keep the output diode(BYV32) cool (with a fan) then the stabilityproblemsgo away. The diode is mounted on a small heatsink. At 50W the heatsinkis just tohot to touch for more than say 5-10s( probable about 60 deg c , hav'ntmeasured). Obviously at higher currents it gets a lot hotter.Why wouldthe diode temperature cause the instability at higher temperatures?The obvious solution is to use a bigger heatsink , which I will bedoing , but I still would like to know whats happening at higher tempsto cause instability.I am far from an expert with SMPS's , so any pointers/help will beappreciated.Hope I have not been to vague.CheersRob

Mar 07, 2006 20 Replies

Rate this thread:

seegoon99 20 years ago

formatting link

Thanks for the links John. Looks like just the thing to fill some "big" gaps in my knowledge!! Maybe I'll take the wife out for sushi , and then get stuck in :0 ) Thanks again. Cheers Rob

Vote

Join the Discussion

Have something to add? Share your thoughts — no account required.

Didn't find your answer?

Ask the community — no account required

SMPS(flyback question)

Related discussions

[SOLVED] Repair of Samsung 55" TV - backlight problem

Rectifier Schottkies in parallel

SMPS -- How to drive the H bridge?

Join the Discussion

Didn't find your answer?