switching power supply noise reduction

[tantudaisu]

I have a small electronic device with speaker. Device is powered by standard, general purpose impulsive AC/AD power adapter (12V, 1A). When I first powered it up, I heard a switching noise from speaker. Then I tried my Lab power supply, there were no angry switching noise. So I decided to investigate how can switching noise could be reduced. I connected oscilloscope's ground to my devices PCB board and noise disappeared, I even cant measure noise frequency, when disconnected GND noise appeared again. Can anybody explain whats the effect, and how can I solve noise problem? Does it contain with common mode or diff mode noise?


--- tantudaisu ---

 

[emontllo]

Is it a low frequency noise or high frequency? You may connect a microphone to the oscilloscope to detect the noise frequency.
According to your explanation the noise could be caused for 50Hz/60Hz noise coupling that disappears when the circuit is referenced to Earth. In order to measure noise, you could operate your oscilloscope with earth connection disconnected or using an isolation transformer.
When the frequency of the noise, origin and coupling are known we will be able to find a solution!

 

[tpetar]

Probably is bad designed or bad maked switching power supply which emitting rf interference.


Read this articles:

https://www.miketyka.com/2012/01/filtering-emi-from-switching-power-supplies/

https://www.scribd.com/doc/52614278/all-about-emi-epmag

 

[goldsmith]

Dear tantudaisu
Hi
I'm agree with Tpetar too . but can you tell us more about noises ? is that really suffering ? can you measure switching frequency ? ( it's PWM ) .
The problem can be solved by using a differential filter simply !
Best Wishes
Goldsmith

 

[atripathi]

Connecting Scope GND to PCB is leading to reduction in noise, this simply means that connecting earth to PCB gnd is providing low impedance path to high frequency noise. You need to check your layout based on this: Possible noise sources and which may get impacted due to connection to earth. It's difficult comment without looking at circuit.