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LM5156: Sawtooth Wave in the Output of a Second Side Regulated Isolated Flyback Converter

Caeleb McKee
Prodigy 10 points
Part Number: LM5156

Tool/software:

Hello, 

I'm working on flyback converter design using the LM5156, and I am running into some issues. The design is a second side regulated isolated flyback designed to output 12V from a typical input of 24V. However, it is instead a sawtooth wave with a DC offset around 12V with a 3.5V amplitude. According to my output capacitor calculation, it should be 100mV. I therefore concluded it had something to do with the loop compensation circuit, but changing values here had no effect either. In fact, it only made it worse. Any suggestions on how to debug this problem?

  • 0
    TI__Guru 61255 points

    Hello Caeleb,

    How much load do you have at the output when you are seeing this sawtooth? If none, can you please try to change the load to e.g. 1A and check if the behavior changes?

    It could be that the device is in power save mode if there is no load.

    Best regards,
    Brigitte