Acoustic noise across power supply input LC filter

[guhapriya.sivasubramaniam]

Hello,

I have designed a PCB for a boost regulator that converts 5V to 12V(40mA). There seems to be an acoustic noise in the board, ie, a humming noise in the board once the 12V supply is loaded with 300 Ω. There is no noise in unloaded condition.

A L-C LPF is used at the input point. When I test this LPF alone, I found that its noisy for a specific current rating(42mA), while when plugged into the rest of the ckt, it is noisy between (40 & 60)mA. The noisy also dies down when I increase (to 69uH) the shunting capacitance to ground.

L value - 22uH & C(original) value - 22uF.

Can someone explain me as to what is happening ?

 

[FvM]

Sounds like you have discontinuous converter operation. Depending on the involved controller, this can be by design or due to unsuitable
circuit dimensioning. Refer to the the device application notes and check the circuit operation with an oscilloscope.

 

[guhapriya.sivasubramaniam]

Thanks for your inputs. I will look into the application notes of the power supply module. FYI, its a 'low-side switch regulator' which operates at 1.6MHz switching speed.