lt8315 Leakage Inductance and Snubbers

Hi,

I used evaluation design DC2337A-3. 

Changed only transformer to WURTH 750813144 (for 21V output),  FB resistor (R9) and R7 to 0.18.

Layout is also from DC2337A-3, only small changes due to transofrmer, and GND is polygon pour on both layers.

With no load and load 210mA, the output volatge is nice, noise is OK, No overheats, or audio noice.

I check DRAIN  Waveform,

Vin 150V, yellow waveform (channel 1) is AC, D4 anode, other channel is DC DRAIN 

No load

Load 210mA

I decide to follow Leakage Inductance and Snubbers section.

Start from 100pF, this give me already 2 times longer period

no load

load 210mA

I calculated Rsnubber (334k), and use it in series with Csnubber (100p) but no change in waveform (load and no load).

Cdrain is 19p

Lleak 2.12

Could you advice why I can't see improvements with RC Snubber?

Maybe I need same more changes/settings corrections?

Please advice

Slawek

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