TIDA-010015: Output voltage ripple reduction

Hi Cheng,

We are measuring 100Hz ripple in the output only at 25A load under low input AC voltage . 

Note: Other than US standard voltage the ripple content is only 800mV under UK standard.

We have 330uF Bulk Cap at the PFC side and required cap is about 300uF.

Please advise how to proceed here.

Hi Bala,

"We are measuring 100Hz ripple in the output only at 25A load under low input AC voltage . "

I am confused about this sentence.

Do you mean there is 100Hz ripple only under this test setup(25A load and 110VAC input)?

For other test condition, there is no 100Hz ripple issue, right?

BR

Cheng

Hi Cheng,

Yes You are correct. 

Hi Bala,

It is unexpected.

Please send me the ripple waveform at 20A/25A/30A with low input voltage.

BR

Cheng

Hi Cheng,

Please find the attached images for the ripple 

Can you advise here how to proceed further 

Hi Bala,

It is a good waveform.

Please share with me the waveform at the abnormal condition 25A load!

BR

Cheng

Hi Cheng,

Missed to attach this 25A load wave form . Please find the image. 

Hi Bala,

Here is my suggestion:

Try to power on the LLC stage with external 390VDC voltage, and then check if there is oscillation of output voltage?

If there is still oscillation, it verify that the LLC's feedback loop need to be adjusted; You can try to adjust R69 slowly and then check the performance.

If there is no oscillation, there maybe two possibilities:

1. The output oscillation is from PFC oscillation. You can power on the PFC stage separately, and check if there is oscillation of the PFC output voltage or not?

2. The output oscillation is from the combination of PFC and LLC. In this case, maybe you need to check this design layout.

If you have any question, please let me know.

BR

Cheng