SMPS Hum when no load

Good Day,

I am worried that the SMPS I bought might be faulty. I got a MeanWell 75W SMPS and when I connect only AC to the SMPS it has a high frequency hum sound.

However if I start drawing some power (5W) from it then the hum goes away. Is this normal?

I'm concerned because my application varies from 0 - 30W, depending on configuration and I certainly don't want a hum at low power consumption times.

Kind Regards,
StudentSA

SMPS's don't like no load, you usually need a minimum load at all times (just like a PC supply).

If everything else fails it's good to refer to the user's manual.

Youl'll certainly find the minimum load requirements when studying it.

Boncuk

Many SMPSs change frequency with light load.
The supply might run at 100khz above 3 watts. (above what you can hear) Below 3 watts it does 'cycle skipping'. So it might run at 50khz, 33khz, 25khz, 20khz.......... At no load it needs only one cycle out of 100 keep the voltage up. That drops the 'frequency' to 1000. That might be what you are hearing.

.....so could you just keep a light load attached permanently?