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?