Problem with drain currents

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Dear Supporter,

we have problems with harmonics and EMV. Our LED-Driver works fine.. but i review our design and i mesured the drain currents.
Please refer to the attched pictures.
On the Scope 0 - Picture you can see the Drain / Vin Voltage (inverted) and the Drain current. But I think this current is a fail or not really good?!

Picture Scope 2 is the Drain current with 2ms per DIV. It looks a little bit unsymetric.

But how can it come as a malfunction?

Das gesamte Design und der Transformator ist aus eurem RDR-290. The only modifications is the output power from 75W to 30W (LNK420 to LNK418).

What am I doing wrong?


첨부 파일Size
scope_0.png26.27 KB
scope_1.png34.42 KB


You mentioned that the LED driver works fine. If you have a copy of RDR-290 file, then even though the power is reduced, you should expect to see similar drain waveforms (see section 12.1 of the report). Please double check your scope setup and make sure you have enough sample points to capture the drain current properly.

For harmonics problem, please use PIXLS to get harmonics calculation of your design. You can optimize your design using the spreadsheet. Some ways to reduce harmonics - set KP lower or increase VOR.

That's right, but I have definitely change the transformer? I can not change the transofrmer however.

Is there any other possibility?

Please check in the PIXLS spreadsheet if you can meet harmonic with the transformer spec you have. I don't know if changing the device size can help. You just have to try it. If it's not feasible, then you have to really optimize the transformer and please don't buy transformers in bulk unless the design is already final.