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Original question:

LM5122: LM5122 design consideration

LM5122: Can Vcc be supplied from aux winding at output?

Stephanie Hibler
Prodigy 725 points
Part Number: LM5122

Hi team,

My customer needs to understand if it is OK to connect LM5122 pin 17 with 9V aux supply, while Vin (pin 5) is connected to 55V input voltage?

 

The 9V aux supply initially comes from Vin (linear regulated down), then comes from 12V aux winding off the flyback transformer when it’s up running. Vin or 12V aux winding whichever is higher at any time powers the 9V aux.

  • +1
    TI__Expert 7450 points

    Hi Stephanie,

    Yes, that is a typical connection to reduce the internal power dissipation when input goes up high. Just note that the VCC is internally self-regulated at 7.6V from VIN, so I don't see the big need for the 9V linear regulator outside.

    Thanks,

    Yinsong