Ringing noise from Power supply

Thread Starter

beera beer beera beera

Joined Dec 16, 2016
Dear All,

We have 12V SMPS which will again convert to 5V (Display purpose) and 3.3V (for microconteoller). Power supply and block diagram of systems look as below.

I am getting ringing noise at 12V supply which is impacting 3.3V and 5V supply also, see the waveforms for reference. I tried by adding small ceramic cap in between , still there is no use. Can anyone tell what I can do more???? (Waveform measured by decreasing the GND lead of oscilloscope).


Waveforms at Waveform-1:- Time scale with 500uS and 100uS respectively.


Waveform at Waveform-2:- Time scale with 500uS and 100uS respectively.




Joined Jun 19, 2015
What is the ripple voltage you are seeing (I can't tell the scale)?

You could look at using a pi-filter (two capacitors and an inductor) for the +ve supply line, and possibly a common mode choke for both lines (this is generally what I've used to reduce noise on power supplies - although mainly for CE testing purposes).


Joined Mar 10, 2018
100 mV of noise not atypical. However if you need to suppress it
even further prior suggestion is good. Also consider using polymer
tantalum as bulk cap along with ceramic, .1 uF or there about.

Troubleshooting wise disconnect 5V loads, then do same for 3.3,
to see what the origin is of the noise.

Regards, Dana.


Joined Mar 10, 2018
When you are working with noise, trying to suppress, a handy method
is using a DSO scope on infinite persistence, looking at supply rail. That
way you will get pk-pk value. Each time you change a component trying
to reduce noise do not forget to clear the screen so that it starts "fresh"
displaying the results for the new component.

Regards, Dana/