LM5021: EMI issue

Miteshkumar Dalabhai Patel

Part Number: LM5021

One of my customer is facing issue with EMI. they have designed 12V/0.85A SMPS based on LM5021. We have done multiple experiment but not able to see major improvement. My customer will share all the test results, schematic & layout.

We need help to resolve the issue.

Mitesh

over 2 years ago

0 JCHK over 2 years ago

TI__Guru 50090 points

Hi Miteshkumar,

When you have the details, please resubmit the issue on the internal forum.

0 Sagar Watane over 2 years ago in reply to JCHK

Prodigy 190 points

LM5021 based ac to dc converter, which input voltage (100-305)VAC, 50Hz and output voltage 12VDC @ 0.85Amps.

Switching frequency is 123KHz. Power supply is working fine, but conducted emission test as per CISPR 22 class A (Radio disturbance test 150KHz to 30MHz) is failing, Please help me to resolve.

I have tried All filter options but emissions are not suppressed.

0 Mike O' over 2 years ago in reply to Sagar Watane

TI__Guru* 86206 points

Hello,

I am reviewing your inquiry and will get back to you shortly.

Regards,

0 Mike O' over 2 years ago in reply to Mike O'

TI__Guru* 86206 points

Hello,

You have a common filter you are not taking advantage of. I would suggest adding two y capacitors on the input of chassis ground to for common mode filtering. You could start with 100 nF.

If that does not resolve your issue you may need to adjust the filter point of your poles on your filters. I would suggest setting the pole frequency (fp) to 10 to 100 times slower than the frequency that is failing. Remember that this filter will attenuate noise at 40 dB per decade.

fp = 1/2*3.14*(Lf*Cp)^0.5

The following link will bring you to video training for EMI filter that you may find helpful as well.

https://www.ti.com/video/series/designing-a-low-EMI-power-supply.html?keyMatch=EMI%20FILTER%20DESIGN%20BING%20LU

Regards,