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250W Push-Pull Converter with LM5030 / 325VDC in - 500VDC out

Rolf Kowalsky
Prodigy 10 points
Other Parts Discussed in Thread: LM5030, LM3411, LM431

Hi,

I want to build a 250W Push-Pull Converter with LM5030 / 325VDC in - 500VDC out based on the Eval Boards examples. (don't worry I'm experienced with those voltages and know how to design the transformer and powerstage).

My question is, how to adjust the isolated feedback ?

in the Evalboard design is a fixed 3,3V LM3411 in use. How can I make a suitable feedback, or what must I change to use a LM3411 - is it enough to change R13 (SNVA078 page 11) ?

I'm not familiar with those direct optocoupler feedback inputs of the LM5030....

  • 0
    TI__Guru* 75805 points

    LM3411 is specially designed for 3.3V and 5V output applications, with which the feedback circuit is greatly simplied. For regulation at your 500Vdc out, please consider a different device like LM431 with adjustable regulation setting. 

    By the way, the feedback inputs of the LM5030 is configured such that the internal error amplifier is disabled (by shorting FB to GND), because the error amplifer function is fulfilled by secondary side (LM3441 in the evalboard, or the LM431 in your modified deisng).  R14 and C18 compensate for the optocoupler with a zero:  the optocoupler introduces a pole.

    Thanks,

    Youhao Xi, Applications Engineering, TI SVA-PPD