Power brick "sound".... - Page 1
Forum section: electronics / beginners

author: Mo3tasm
author_rank: Contributor
timestamp: January 18, 2014, 10:52:04 pm
content: hello, i use this adapter for my lap (http://image.dhgate.com/albu_225988577_00/1.0x0.jpg)The thing is, recently i started to hear buzzing, humming, a near 60 Hz tone, whatever..., it's a bit frustrating because when i tried to look it up i found people call it different names without knowing what it actually is...The sound is clear when the adapter is idle, and it might indicate that it is "yet to be" faulty, actually i don't care about the adapter, what i care about is...What is the physics behind this?...

author: joblessalex
author_rank: Contributor
timestamp: January 18, 2014, 11:29:51 pm
content: If it is a high pitch squeal then that is the windings of the transformer acting like a speaker as they charge and discharge at the switching frequency which is in the audio range. When current is drawn, more power is pushed through the coil and it should get louder. Look up how switchmode supplies work to learn more. If it's 60hz, I have no idea where it's coming from....

author: con-f-use
author_rank: Unknown
timestamp: January 18, 2014, 11:39:37 pm
content: 50/60 Hz is the frequency of the main power grid. This adapter does likely not ground the chassis of your laptop. Thus the mains can couple to your speaker output and you hear the 60Hz humm. Try grounding the metal outer parts of your laptop. If the hum goes away, you know what the problem was.

author: Mo3tasm
author_rank: Contributor
timestamp: January 18, 2014, 11:42:32 pm
content: hmmmm, the sound source is the adapter itself, but that's right, i don't have proper grounding in my building...

author: amyk
author_rank: Super Contributor
timestamp: January 19, 2014, 11:42:33 am
content: The sound could be coming from the input choke, since mains frequency AC passes through it.

author: SeanB
author_rank: Super Contributor
timestamp: January 19, 2014, 11:47:22 am
content: Could also be the input capacitor failing and the converter regulating the output with a superimposed 100/120Hz noise on the normal switching cycle magnetostriction of the ferrite transformer core. If it is 50/60Hz then the one diode of the bridge rectifier on the input has failed open.

author: NadAngel
author_rank: Contributor
timestamp: January 19, 2014, 12:20:08 pm
content: The physical cause of audible noise in electronic components is caused by magnetostriction and electrostriction. The lather is in some cases called piezoelectric effect. Usually the sound is caused by an inductor (transformer) or a ceramic capacitor.

author: Mo3tasm
author_rank: Contributor
timestamp: January 19, 2014, 03:48:17 pm
content: Thank you all, you've been very helpful...

author: con-f-use
author_rank: Unknown
timestamp: January 19, 2014, 04:26:28 pm
content: Quote from: NadAngel on January 19, 2014, 12:20:08 pmAlthough those kind of noises are usually not loud. Capacitors usually have a resonant frequency in the kHz range. They certainly won't produce a 60Hz hum.

author: NadAngel
author_rank: Contributor
timestamp: January 19, 2014, 05:03:15 pm
content: Quote from: con-f-use on January 19, 2014, 04:26:28 pmYou are probably right, but I have came across situations of ringing ceramic capacitors on light loads when the controller was in burst mode.

author: djococaud
author_rank: Regular Contributor
timestamp: January 21, 2014, 09:23:21 am
content: Some times ago, I had a laptop power brick that sounded 50Hz as well (it was more an arcing sound).I opened it up, and figured out that a bad solder on the IEC connector was causing small arcs on the PCB...I resoldered it once but it didn't take long before it failed again... I threw it away and bought a new one...