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Whistle noise from transformer in LM5071-80 design

Other Parts Discussed in Thread: LM5071

Hello,

I experience problem in my POE power supply design using LM5071-80. The used transformer is C1585 for 13W delivery. The output (5V) is used to supply a current booster (CAT 4139) for LCD back-light. The current booster is managed by a PWM at 200 Hz and drive 160 mA current. As a result, the transformer whistle due to current driving of the booster.

Notice that, when I remove the current booster PWM (mainly 0 Hz frequency), there is no noise.

Did you already see this kind of problem? What could be done to stop the wistling?

3806.LM5071-80 support.pdf