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MC33063A: Humming noise from DC to DC Buck converter

Part Number: MC33063A

My design requirement is input voltage :21 to 36V and output current of 1A, at output voltage 5V. I can able to hear the buzzing noise (Humming Noise) from the DC to DC Converter. I suspect that this buzzing noise ( humming noise ) is from the inductor. Can  you please suggest me a possible solution to overcome this noise effect. The input and output capacitors used were electrolytic and the inductor part number is RFS1317224KL.

  • Hi 

    Thank you for choice our device.

    You can hear the buzzing noise, I think there should be a frequency oscillation below 20KHz.

    Could you check you input and output ripple any ripple low then 20Khz. And check any below 20Khz switch frequency.

    In addition, it is necessary to check whether the inductance is loose, including whether there is any looseness between the core and the wires.

    BR Dehuan

  • Hi,

    Thank You. I changed O/P Cap 470uF to 1000uF, still I am getting buzzing noise.

    What will be the root cause? Shall I increase the input Capacitance 100uF to higher value? - 220uF or 470uF

    If I change the switching frequency of Buck converter, does it effect of EMI/EMC performance? Because EMI/EMC testing completed.


  • Hi Gopala,

    I think we don’t need to rush to make changes, we need to determine what the root cause is.

    We need to find out if there is an oscillation frequency below 20Khz.

    You can check the input and output ripple any below 20Khz, maybe it cannot filter by cap. 

    If the switch frequency is changed, EMC may need to be re-verified.

    BR Dehuan