[SG3525 smps] Input capacitors puffing after adding snubber

[aliazhar]

I have just added snubber on my smps...(330 ohm 4w +0.1uf)...

after adding snubber, the input filter capacitors are puffing within a matter of couple of minutes.

any idea?

(i am using P200nf04 x4, 20khz, E-core - total watts 350 @ 44v. no input/output filters. single winding with bridge output. bridge is FEP16B)

[aliazhar]

problem fixed !!!

thanks guys.

[luka]

Hi

What was the problem?

[aliazhar]

Luka,

to be honest with you, i have removed the snubber and everything works almost fine.

but, there is something i still dont understand....
when i connect the dc output to oscilloscope, i still see waves....its not pure dc....like a straight line....

why is that so?....

and one more thing is, whenever i use this smps, my circuit which i am running this smps for is getting more hot then compare to ac powersupply i use.

any suggestions?

[AndrewT]

The HF pulses from the SMPS could be upsetting the circuit and causing it to oscillate.

[aliazhar]

any remedy for this ?

[luka]

Hi

Can you show it on pic?

Has nothing to do with how you drive your smps...I had most problems with ground, I should say nuteral, which we don't have, and everything runnig from same phase, no insulating transformers...

if there are spikes on pretty much flat DC line then you are ok, but if you see anything else send pic...hope your osc isn't acting as load to smps

[aliazhar]

I have checked again....and there are no noticeable spikes coming out at the output dc....its almost very clean.


now, here is whats happening without using the snubber.

after using this smps for about 10 minutes, i see a very little puffed filter caps...

i am using 2200uf 25v x2 105-C....do you think thats enough?....or are they more?

using scope probes at the input of traffo (output of mosfet) i see lot of spikes....

my scope frequency is fluctuating from 20khz (which its suppose to be) upto 225khz...

when i used the snubber it was way better but, the caps was puffing....

i think there is something which is out of balance....either my snubber values are wrong or the something else....dont have any idea.

can you help?

[DigitalJunkie]

Maybe try a smaller snubber cap. 0.01uf or so?

[aliazhar]

i did....i have tried different combination...out of which the best wave was out of 330r/0.1uf....but, using that puffs the caps...

what are the best caps values i can use for filter ?

2200uf or less ?