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LM3431 chock noise

Lucifer
Expert 2600 points
Other Parts Discussed in Thread: LM3431

Our LM3431 application specification Vin 9V~16V, Vout around=42v 140mA/ch*3=420mA
when  vin 9v, in=1.9A , currenst sensing resistor=25mohm , then we can hear the noise from the chock. but after increasing vin above 10V, then no noise sound heared.

Moreover, once we increase current sensing resistor =52mohm , same supply voltage(vin 9v) then, no noise sound heared.

why the sensing resistor will effect the chock noise?
Is there other way to improve this situation?
Thanks.

  • 0
    TI__Expert 3495 points

    Eason:

     

       The current sense resistor limits the peak inductor current. When you increased the CS resistor to 52mOHM, the boost converter might get into current limit mode and the peak inductor current was lower than 25mOHM CS resistor. With lower peak current, the inductor noise went away. You can check peak inductor current by measuring the voltage on the CS resistor. To improve this, you can increase switching frequency ( lower peak inductor current ) or switch to a bigger inductor with higher current rating.

     

    David Zhang