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  #16   Spotlight this post!  
Unread 11-01-2017, 07:08 PM
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Re: Screaming VRM !?!?

Quote:
Originally Posted by IndySam View Post
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.
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Unread 11-02-2017, 08:13 AM
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Re: Screaming VRM !?!?

Quote:
Originally Posted by GeeTwo View Post
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.
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Unread 11-03-2017, 05:54 PM
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Re: Screaming VRM !?!?

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.
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Unread 11-10-2017, 02:34 PM
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Re: Screaming VRM !?!?

Guys,
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.
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