In my circuit I use a R-78E3.3-0.5 to generate the 3.3V supply voltage for a microcontroller from a 24V rail. The total load draws about 10mA. I'm using a 47uF decoupling capacitor at the regulator output and some smaller decoupling capacitors at the supply pins of the uC which already reduce the noise quite a bit.

However there is still a significant amount of noise left which I would like to further reduce and thought about using a second stage LC filter for that purpose (a first stage LC filter is included in the R-78E3.3-0.5 if I understand correctly). I'm getting a switching noise at 570kHz (consistent with the R-78E3.3-0.5 datasheet) and a ripple noise at around 7.7kHz as can be seen in my oscilloscope measurement (channel 1 (yellow) is the same signal measured at full range).

[![Supply Voltage measurement][1]][1]

However all instructions I can find talk about attenuating the switching noise with a LC filter set at a cutoff frequency of around 1/10 the switching frequency which would be 57kHz in my case. That would surely help with some of the noise but the ripple at 7.7kHz would be largely untouched, right? However a LC filter with a cutoff frequency of 1/10 * 7.7kHz would require a really large inductor.

So my questions are:
1. Am I overall on the right track to tackle this problem?
2. Is perhaps the R-78E3.3-0.5 a bad choice in my application because I only draw 10mA of its potential 500mA. Would the R-78E3.3-0.5 produce a higher (and thus easier to attenuate) ripple frequency in an application with a higher load?
3. Is it common to attenuate low ripple frequencies like my 7.7kHz from a switching regulator?

Thanks in advance for any help, hints and tips. Have a great day!


  [1]: https://i.sstatic.net/Zv4IK.png