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VIPer12A power circuit problem

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Reply to
Panda
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One obvious thing is if you actually have it wired as you've drawn it your secondary is shorted pin 8 and 5 of your transformer.Assuming everything else is correct your converter might be going into current limit burst mode.I'm not familiar with the Viper controllers but some controllers will limit the output power by going into burst mode in the event of a short.

C70 and R45 with D17 form an RCD snubberyou have to clamp the drain voltage a flyback has leakage inductance.You can google RCD snubber flyback. For your power level you could have also used a zener (TVS) clamp for the drain.

Reply to
Hammy

The MURS140 is a 1A ultrafast ,you would fry a shottky if you used it there. You need those capacitors on the output thats how an SMPS works the caps supply the load when the switch is off.

Reply to
Hammy

Thank you hammy, Sorry for uploaded the wrong schematics. I re-upload the sch here:

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Actually In my sch, I did not short the Pin 5,8 of the transformer.

Reply to
Panda

Apart from drawing errors around the transformer - could your zener be inserted backwards?

The scope waveform needs re-examination, before and after the rectifier (DC coupled) as a 50V peak output from the transformer is unlikely to produce 1V4 after the rectifier - your multimeter may also be giving an average value that the scope can resolve dynamically.

RL

Reply to
legg

He said he doesnt have the output filter capacitors soldered for safety?

Did you put the capacitors in?

Reply to
Hammy

It would explain the abnormally high voltage.

There's no 'safety' reason to leave these parts out, and the circuit will not function as expected without them. The primary clamp and switch will also be overstressed if they are missing.

RL

Reply to
legg

Thanks a lot Hammy. Since I got a worrying scope without the capacitor, I'm a little worry about the result of solder the 470uf cap on the output side. I just soldered this cap right now, and the output looks right！ Thanks a lot all.

Reply to
Panda

.
.

Yes, you are right. MURS140 can replace the ST ultrafast diode here. And I really need those capacitors on the output and the caps can supply the load,when the switch is off.

Reply to
Panda

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