Converter whine

[davelectronic]

After having just picked up four DC to DC buck converters, one of the units has a whine under load. These converter are rated to 8 Amps, but I'm testing at just over 3 Amps load. Three of the modules seem fine, no problems. But the whining module also has a greater voltage drift than the other three under the same load. I'm not certain what's generating this whine in one of the modules.
Any help or ideas appreciated.
Thanks for reading.

[amyk]

Use a stethoscope to figure out where it's coming from. It's likely to be the inductor, in which case some varnish can fix it.

[cdev]

Some transformers - like a toroid, may emit a whine at twice the frequency they operate at, typically. On iron core transformers, varnish, "Glyptol" I think is one brand, are used to dampen transformer hum.

[cdev]

I've also used a fat straw as a substitute for a stethoscope for locating the source of sounds.

[Brumby]

+1 on the inductor probability.

Coils in such circuits create an oscillating magnetic field - which in turn will put a mechanical force on the conductors in the coil.  If they are not properly secured, they can physically move - even if microscopically - and create sound.

Running some thin liquid into the windings - such as varnish - which will penetrate and dry hard, will (hopefully) mechanically secure the conductors from moving and thus reduce (and possibly eliminate) the sound produced.

[Doctorandus_P]

It could be that an inductor / transformer is whining because a diode or transistor is defective, but still half working.

The fluctuating output voltage also is an indication of something being not as it should be.

So take your oscilloscope, put both a good and your suspicious circuit on your bench and start comparing waveforms.

[davelectronic]

Thank you for the help and replys. I don't have the use of a scope at the moment, the toroid wound inductor is free to move, no salastic holding it down. I will take a closer look to see where it's coming from. The slight voltage drift does seem to suggest a semiconductor might be involved.

[T3sl4co1l]

Can also be ceramic capacitors, specifically type 2 dielectric, which are somewhat piezoelectric.

Actually, most capacitors are electrostrictive at least (meaning, they expand in response to an electric field -- distinction is, electrostriction is proportional to E^2 and thus unsigned, doesn't matter the polarity or direction of E; while piezoelectricity is proportional and signed), though you may need a large voltage swing to see it.

Inductors are the most common noise source, because they see the most ripple in a converter.  The effect responsible is, guess what: magnetostriction.   (There is such a thing as "piezomagnetism" as well, but it's actually rather rare.)

Tim

[Le_Bassiste]

After having just picked up four DC to DC buck converters, one of the units has a whine under load. These converter are rated to 8 Amps, but I'm testing at just over 3 Amps load. Three of the modules seem fine, no problems. But the whining module also has a greater voltage drift than the other three under the same load. I'm not certain what's generating this whine in one of the modules.
Any help or ideas appreciated.
Thanks for reading.

considering that your converter is working at an in-audible high switching frequency, then the root cause for the whine (either in inductors/transformers, or in the ceramic capacitors) probably comes from
1. an unstable (audibly oscillating) controller chip, or
2. if the controller is stable, from the load that has audible fluctuation in power demand (typical example: graphics cards)

assuming that you are testing with a "clean" dc load, i'd suspect a faulty control loop compensation in the controller part of the module. more so, as it is "1 out of 4" and not all the modules singing, even more so as that particular animal has poor voltage regulation behavior.

[TrickyNekro]

I had to repair a power supply from a sat receiver some long time ago... It was a small electrolytic capacitor
in the feedback loop that sounded like a widow in bed

Coils can whine yes, but caps... caps never change...

It could have been of course a bad cap that caused wrong feedback and then the coils were whining yes,
it´s been years since that repair and I remember the cap. 

[davelectronic]

The load was a 50 watt halogen bulb,  as three modules are fine, I will take a closer look. I've only limited test equipment, so looking at wave forms are not doable for this. My only thoughts are this unit playing up with an RF load. I'm unsure of the way these converters will behave with an RF load anyway.
What I'm doing is dropping a hp 135 watt 19.50 Volts power brick to a more usable 12 to 13.80 Volt output supply. I've never used a buck converter on anything RF related, so all new idea to me.