Screaming VRM !?!?

Has anyone experienced obnoxiously loud noises coming out of their Voltage Regulator Modules? When a single 12 volt led light ring is plugged into the VRM, either 2A or 500mA, it (the VRM) emits a painful high frequency whistle. Even weirder, when other 12v loads are plugged in (i.e. Radio), the noise stops.

Any ideas?

This sounds like coil whine. I just want to confirm:

Even weirder, when other 12v loads are plugged in (i.e. Radio), the noise stops.

Do you mean that plugging in the radio WHILE keeping the LED ring plugged in eliminates the noise? Or do you take the LED ring out and then put the radio in?

Also, does the LED ring light up when you plug it in? If not, I would suspect a short circuit in the LED ring. Try testing the resistance across the LED ring with a multimeter. In the forward direction, it should be in the order of 100-1000 ohms I think. In the reverse direction it should be very large (megaohms). If that is not the case, you probably have a bad LED ring, potentially a short.

I have this same problem. Even when it is not powering anything it whines. It started suddenly too. Gets pretty annoying at 1 am.

I believe that is a normal and expected behavior.

Can’t tell if you are being sarcastic, but we do not have this problem.

This is not normal expected behavior from a VRM.

Our VRM does this too, not sure why. I took a video of it happening:

Does anyone know how to fix this?

You can get a high pitched whine from frequency switching devices if the switching frequency is low enough to be audible (20 to 20,000 Hz), especially at low loads.

Errr… yes it is. The old blue PDBs will do it too with the right load.

A single ring light alone will cause the VRM to emit a high frequency noise?
We had a large ring light light last year and did not get a noise like this.

I think there are two different “expected” being thrown around here. Correct me if I’m wrong but the expected you’re using seems to be in reference to the intended behavior of the device. The expected that those who are saying coil whine can be expected are not using it in this way. What they are saying is that although not intended, you have to expect to some extent that coil whine could be present in the board. I would also have to agree with cgmv123 on the statement that coil whine is a normal behavior. Take for instance the GTX 970. At launch A huge number of units have massive issues with coil whine, to the point where is was actually quite normal. After a little bit the issues stopped happening because Nvidia stopped selling its reference models and board partners started tweaking mainly power delivery stuff in the firmware which made the cards sold after have much less coil whine. This issue was most prevalent among people who bought lesser quality power supplies because lesser quality power can be a large factor of coil whine.

This helps explain my view and makes more sense.

My team just found one of these “Blue PDBs” last night putting together an off season project.

Does it whistle when you power it up? We always joked about it because everyone noticed it standing near the old bots.

Just be glad that you’re young enough to still hear it.

Take it from us old guys protect your hearing always.

Hearing protection works! Even though my job for a decade involved riding ships and detonating 1.8lb TNT charges just to measure the sound a couple of months a year [no joking], in my mid-50s I can still hear a rodent repeller at 5 to 10 feet.

I know this isn’t the point of this thread, but I’ve always found it upsetting how little FIRST focuses on hearing protection. Between the loud noises made by manufacturing machinery, the noises from robots, and the extra loud music in the pits, we are at risk of hearing loss if we don’t take precautions. Some teams take it upon themselves to hand out earplugs, but it’s hard to convince team members to wear them when it makes it hard to communicate during the competitions and FIRST doesn’t require them. My team requires hearing protection while manufacturing parts on the robot in the shop, but we don’t have a rule for competitions. IMO FIRST either needs to lower the noise level at competitions or require hearing protection the same way they require eye protection. It’s not going to be a popular move, but I think it’s a necessary one.

Are the whines or whistles happening only at low or no load conditions? If one LED light causes it to make noise, does it still make noise with 2 or 3 plugged in? Do you have an oscilloscope you can connect across the output of the VRM when it is making the noise?

Regardless of the switching frequency of the regulator, some switching regulators will go into a dis-continuous mode of operation when the load is very low. You will then get sub-harmonics of the switching frequency showing up (Fs/2, Fs/3,…) which may be more audible. I have had some switching regulators that made a crackling sound at low loads when it alternated between the continuous and dis-continuous modes.

The whistle is normal for all devices that use a coil. The VRM uses a common technique called ‘boost/buck’ power supply design. Essentially, a voltage is switched on and off using a PWM generator to regulate the average output of the device. This rapidly switched signal uses a coil of wire to help filter out the switching signal so that output is nearly pure DC voltage. If the wires in the coli are not secure, they will vibrate with the input signal. The coil is also wound on a metal (usually powdered iron or ferrite) core and if that is not secure, it will also vibrate. The switching frequency is generally well above the hearing pass band but the vibrating parts are producing something that you can hear. A simply technique is usually employed during manufacture. Either a tab of hot glue or paraffin is dribbled over the structure to hold the wire and core in place. Without the ability to vibrate, no noise will be heard.
In larger coils and transformers, the manufacturer will usually dip the device into a vat of varnish to secure all the core parts and the windings. In low frequency devices like audio transformers and power line devices, moving windings and cores can actually cause significant distortions.