Squealing Buck Converter

Could I check if there is any cause for concern, if a buck converter is squealing. The squealing happens at random times, and when it does, it sometimes occur in short pulses, and sometimes continuously for a few seconds.

|500x281|500x281

I have attached images to show the build, it's a 433mhz transmitter switch. The buck converter is taking in 5.2v(also tried 12v), and outputting 3.3v. Apart from the squealing, everything else is working as it should. The sound from the squealing does not bother me at all as it is very soft, but I am just wondering the cause of it, if it is sign of something going wrong, and if it will affect the circuit in the long run.

Switching power supplies can squeal during operation - the material in ceramic caps is piezoelectric, so they can sing, and energy is being stored in the magnetic field of an inductor, which also applies force to things. Either of these can generate that squeal noise. Often it gets louder under some operating conditions, particularly when you're pushing the device.

Hi, Its not really usual to hear a squeal, its possibly loose winding or core in the converter inductor. When it does it, see if it changes or stops when you put your finger on the inductor body.

If it does change put some hot glue around it to minimise its mechanical effect, I have had inductors in ethernet-rs232 adapters fall off their pcb because the solder joint finally fails due to fatigue.

Tom... :)

Thanks DrAzzy, Tom. Sure it's informative and a relief to hear that. According to the specs, that buck converter could support 1.8A(continuous), my circuit is drawing about 50-70mA, so it's good to know I'm not pushing it. I will give the placing my finger and hot glue tip a go really soon.

Thanks again both for your help.

Power inductors get hot, I'd suggest not using hot-melt glue on them, silastic or epoxy would be better choices if you don't want a sticky mess over the board. Also don't smother the entire inductor or its cooling efficiency will be reduced.

It is probably vibrating all the time, but you hear when its frequency resonates the PCB (frequency can depend on load for a SMPS).

"my circuit is drawing about 50-70mA" You could add a load resistor to draw a bit more current and therefore change the frequency. However, this does defeat low current operation and will add heat into the enclosure.

Some potting liquid might help too.

.

The fact that it sometimes squeals and sometimes doesn't indicates instability. This is normally from a bad design or poor PCB layout.

According to the specs, that buck converter could support 1.8A(continuous),

Are these real specification or what the retailer told you. I have seen some atrocious switching regulators on eBay that advertise that sort of current that are just a downright lie. Often these things have an inadequate decoupling capacitor on the output. I have seen regulators with 2.7uF output capacitors while the chip manufacturer's data sheet says 22uF.

Grumpy_Mike:
The fact that it sometimes squeals and sometimes doesn’t indicates instability. This is normally from a bad design or poor PCB layout.

Couldn’t it also be the PFM (pulse frequency modulation) mode that a lot of converters use for low loads? Even if the main switching frequency is in the MHz range, the charge-discharge cycle could drop to the audio range with a low enough current load.

Back in 'the old days' we would use domestic radiator paint, with its high temperature tolerance, to sort out noisy inuctors and mains transformers on television sets. I'm not sure if that's necessarily a good idea on these modern inductors tho'. Would cyanacrylate adhesive work too, or would the possible temperatures involved result in those eye-stinging fumes which you get from accidentally putting a soldering iron on a patch of super glue?

Jim.

"those eye-stinging fumes " from heated superglue are cyanide gas, that can be dangerous.

CrossRoads:
"those eye-stinging fumes " from heated superglue are cyanide gas, that can be dangerous.

I’m surpised I’m still here to mention it then! I can’t remember the exact job I was doing, but it was a regular occurence.

Jim.