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Original question:

LM5025C: Clamp Capacitor Value

LM5025C: CT output waveform

user5339789
Intellectual 590 points
Part Number: LM5025C

Dear engineering team,

Last week we asked a question re active clamp using LM5025C, then Steve Mappus respond me and seems to be improved. thanks.

Well we would like to confirm that this operation is reasonable or.

Attached is simplified schematics and waveforms of each points.

We feel that ringing swing level is still large at output of current transformer(2).

We will be able to proceed designing steps if you can see them that is normal phenomena.

 

Best Regards, Keiichi

  • 0
    TI__Intellectual 2640 points

    Hi Keiichi!

    Thank you for reaching out to us! We're glad that the previous recommendations helped your design. That ringing looks like it's outside of the realm of normal operation. It also seems like there are two different sources of ringing: one results in the high frequency oscillation on (2) and (3) as the transformer current ramps up and the other results in the lower frequency oscillation on (2) when the output line (3) is low. 

    To address the first source of ringing, we suggest adding an RC snubber circuit between the drain and source of the synchronous rectifier on the secondary side of the design. It may add some cost to the design but the addition of a snubber circuit has the potential to reduce system instability by smoothing out the ramp in the current sensing transformer. A post with some tips on calculating RC snubber values can be found here. 

    To address the second source of ringing, we would need to see more of the circuitry connected to the current sensing transformer, are you able to provide this information? 

    Thanks again for getting in touch, I hope this information helps and I look forward to hearing from you soon! 

    Aidan Davidson