Need help to design a snubber design for my SMPS

[udhay_cit]

Hi, I need to design a snubber design for my SMPS. The SMPS design & output waveform captured at the primary side is attached. Please suggest a suitable RCD snubber design value & calculation for my SMPS.
The values available in the schematic is as per the PiExpert software output. But the snubber has no effect with the oscillation & the output oscillations remains same for with & without the recommended snubber value.
The primary inductance of transformer is 1212.3µH @100khz.

If anyother waveform or details needed, I can give you.

Any reply is valuable for me.


Udhay

 

[aamir]

Ur snubber/clamp circuit seems fine because these are typical values used in Tny series smps. C6 is wrongly connected in ur schematic. It must be connected between power ground and output ground. Try this and see if it makes any difference

- - - Updated - - -

Also try connecting D2 to R1 and C4 removing R2.

 

[BradtheRad]

T1 appears to operate as a flyback. Your RCD snubber is a typical method. R1 is 100k. Its purpose is to discharge C4 to some extent between each cycle. It's important to prevent C4 from reaching too high a voltage. I believe R1 does not have sufficient effect to discharge C4.

The tendency is to make R too high, and C too low. You seem to have light load resistors (R6 through R10), or are these bleeder resistors? In any case, the greater power you have going into T1, then you can expect R1 to need a greater watt rating.

 

[udhay_cit]

Hi Bratherad, thanks for the reply. I have no idea about the RCD snubber values. Already I pointed that the output oscillation waveform has no change with & without the mentioned RCD value. The resistors from R6 to R10 are light load resistors & I hope its not necessary put all the resistors & some of those can be DNF.
I forgot to mention the poutput current rating.

+5V@100mA
+24V@100mA
GND

+5V1@100mA
+24V1@100mA
GND1

Aamir, C6 I connected it as like from PiExpert software output schematic. The product has plastic enclosure & doesn't has earth point & unfortunately not possible to include earth.

 

[BradtheRad]

I like to experiment with simulations. This flyback focusses on the snubbing network. It is a simplification of your schematic. I guessed at a few parameters, based on component values.



The rightmost scope traces show snubber action. If you wish, you can use higher resistance for Rsnub, however then Csnub builds to greater volt levels because it cannot discharge as fast. Also notice Rsnub needs to be rated several W.