I have implemented a boost converter (120V to 400V). I was testing it by driving a single phase induction motor. When the boost output voltage increased to 200 volts that time you run the motor through VFD. Then I can hear audible nose in the inductor. The motor is drawing current normaly.

I feel it is very dangerous when there is audible noise in the inductor. The noise increased while I was changing the speed of the motor.

Can you tell me why this noise is happening and how I can remove it? Is that noise dangerous for my circuit?

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Schamatic of Converter

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  • 2
    \$\begingroup\$ Have you been through the other "audible noise on converter" questions here? Like electronics.stackexchange.com/questions/214638/… and electronics.stackexchange.com/questions/45086/… \$\endgroup\$
    – user16324
    Feb 14, 2017 at 21:08
  • \$\begingroup\$ Several possibilities- Small-signal instability (did you measure phase margin?), Subharmonic oscillation (is it peak current mode control?), Noise in the circuit causing audible noise in the inductor, etc. Without a schematic and waveforms it's impossible to say what is causing it. \$\endgroup\$
    – John D
    Feb 14, 2017 at 21:09
  • \$\begingroup\$ Which one is the inductor? The big transformer-like part? \$\endgroup\$ Feb 14, 2017 at 22:19
  • \$\begingroup\$ What did OP use to generate that 3D model of the circuit, including components? \$\endgroup\$
    – legoblocks
    Jan 5, 2021 at 13:08

1 Answer 1


When the current through the inductor changes, the magnetic field does as well. This magnetic field causes a small attraction/repulsion action in the coils of the inductor, which manifests itself as a vibration, aka sound. You may have noticed that some CFLs and LED lightbulbs have a high pitch whine, and many mains transformers have a low hum at around 50/60Hz for the same reason.

Is that noise dangerous for circuit

Not strictly speaking, it's just sound after all. As long as you are using your parts within their specifications, all should be fine.

You can mitigate this phenomenon by increasing your switching frequency or potting your inductors in an epoxy of some kind, much like many SMPS have.

  • \$\begingroup\$ Hard to tell from the original post, but most converters under load (out of PMF mode for example) operate above the audible frequency range and audible inductor noise may be a reason for concern. \$\endgroup\$
    – John D
    Feb 14, 2017 at 21:22
  • 1
    \$\begingroup\$ Could be, unless the audible range noise is due to an audible-range fluctuation in current draw. \$\endgroup\$ Feb 14, 2017 at 21:23
  • \$\begingroup\$ Dear @Brendan Sir , I have attached my circuit picture. when i arrange the circuit in differnet place then the sound is comming out. \$\endgroup\$
    – Fame313
    Feb 14, 2017 at 21:24
  • \$\begingroup\$ switching frequency is 25K HZ \$\endgroup\$
    – Fame313
    Feb 14, 2017 at 21:25
  • 3
    \$\begingroup\$ Agreed, load currents in the audible range can cause audible noise. Again, not enough information to get to root cause. \$\endgroup\$
    – John D
    Feb 14, 2017 at 21:25

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