Electronics > Power/Renewable Energy/EV's

Power supply noise issue , how to remove it?

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electronic_artist_:

Attached is the circuit diagram of my power supply. it converts input 12V DC into 5V DC and then 3.3V DC with linear regulator.
Red circled is power supply 5v and 3.3v power

So current situation is, whatever noise is there on 12V input voltage shows up on 5V and 3.3V. How do i filter this ? how do i improve my design to get clean 5V and 3.3V even with a noisy 12V input. If i use clean power supply 12v, i am getting best results.But i cant give 12V clean power supply to everyone. Customers can pick up any noisy power supply and it should work with my design.

below i am attaching two waveform, Yellow is 12V , Blue is 5V and Pink is 3.3V.

If you look at the waveforms, the noise appearing on 12V is carried on to the 3.3V. i was assuming LDO will at least attenuate it more but, it is very high.

how do i get rid of this, what ill have to change or add in my design to improve it?

David Hess:
Start by using a single point ground to remove ground loops.

electronic_artist_:
hi,
thanks for pointing out. But on my PCB i have full solid ground with proper vias ground stitching.
still it will have effect?

David Hess:

--- Quote from: electronic_artist_ on July 25, 2019, 01:27:51 am ---But on my PCB i have full solid ground with proper vias ground stitching.  Still it will have effect?

--- End quote ---

A solid ground plane is not a perfect solution but that means the cause is elsewhere.

To check for common mode noise, connect one oscilloscope probe with the probe tip and ground at the same spot.  If this is a problem, then a common mode choke between the adapter and switching input may be needed.

Beyond that, LCR filters may be needed at inputs and outputs.

ogden:
It looks like probing problem. Are you even using scope probe ground clips? Seems like you don't. Note that frequency of noise bursts is exactly 100Hz, could be external noise leaking into your measurements. Start with single channel probing, make sure you are probing properly. You can find SMPS probing techniques on youtube and web. Just one of search hits: https://www.cui.com/blog/how-to-measure-ripple-and-transient-in-power-supplies   https://youtu.be/VLzcV9Sxt5Q?t=1

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