the switch power supply introduce into 50HZ/220V noise

[kimjin]

i used the switch power supply,but the power source introduced the 50HZ/220V noise onto my circuit board,the signal is overide by the noise when measuring the signal using the scope,how can i remove the 50HZ/220V noise?
i have used the 100uf decouple capacitor,but it doesn't work.

 

[VVV]

It's hard to believe that a switching power supply introduced 50Hz ripple. Either the P/S is defective, or something else is going on.

Check the power supply with just a load resistor that draws as much current as your circuit. Measure with the scope the ripple across that resistor. It should be at the P/S switching frequency, in the kHz range, but less than 1%.

If that checks OK, then verify your circuit, especially the grounds. My feel is that something is missing a ground, perhaps even the point where you ground your scope probe.

Check the probe ground lead. It happened to me many times to find it was broken.

 

[goodboy_pl]

ALSO check if power supply is not unstable.
Sometimes due to a specific load smps goes unstable and produce noise in both outputs and input main which could produce unwanted EMI.
it is possible to test for the situation by fully resistive load equal to your circuit power requirement.

BEST!

 

[stephen_h]

Check your load characteristics! If your loading is also switching load, care should be taken on control of the feedback loop of error-amp.

 

[cyberblak]

Hi,

If you mesure a very high voltage at 50Hz with the scope, that probably means that the probe's ground is defective... Better cheching it out first.

cyberblak