This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LM5155: Unstable output

Part Number: LM5155

hello.

I made a circuit (Attachment 1) with reference to the recommended circuit in the data sheet and confirmed the operation, but the problem was that the output dropped and became unstable under a load of several mA.

I suspected a malfunction of the overload control, but in the no-load state, noise occurred on the CS pin and the output did not drop even if it exceeded the overcurrent threshold of 0.1V.

I have attached the created circuit (Attachment 1), so can you tell me if there are inappropriate parts in the constants, etc.

Also, I think that this problem is caused by the CS pin, but please let me know if there are any precautions (part layout, constants, etc.) regarding the CS pin.

Most ICs have a blanking time on the CS pin. Is there a blanking time on the CS pin of the LM5155?

Attachment 1. Circuit diagram.pdfAttachment 2. Waveform.pdf

  • Hi User,

    Thank you for designing with the LM5155.   Could you check two things:

    (1) Is your device the LM5155 or the LM51551?

    (2) Is your transformer polarity is used correctly?  Your problem sounds like the transformer polarity is wrong.  Can you reverse your secondary transformer winding and see it you can produce higher load current?

    Thanks,

    Youhao Xi, Applications Engineering

  • May I assume this issue has been resolved  so I can close this thread here?  You are welcome to add a new post to re-open it.

    Good luck in your project.

    Thanks,

    Youhao