Power supply noise, how can I get rid of it?
Power supply noise, how can I get rid of it?
(OP)
Hi guys,
I have a 300kHz RF amplifier working (see thread248-366918: Signal generator curent source 1MHz / 1A for info), but my small TRACOPower +15/-15Vdc SMPS is coupling a terrible 2 MHz noise up to 3-4Vpeak all over the circuit nodes (from PS, input and output).
The schematic is something like: 220AC - 24Vdc SMPS Carlo Gavazzi - +15/-15dc SMPS TracoPower - RF amplifier
The noise dissapears when I use a "good" lab source. If I supply with the lab source to the TRACOPower +15/-15 source it cames back again, so I guess the main problem is the Traco, not the Carlo Gavazzi 24Vdc source.
I thought of being switching induced glitches and prepared a LC filter for both PS outputs (4.7mH 0,1uF) that has quite high attenuation at that noise freq.
My surprise is that with the filter at the output the noise remains excatly equal, as if there were any filter there.
Even sensing just with the GND clamp of the probe at the output I see this noise. This seems to me to be a emmited EMI problem.
Any idea or help will be welcomed cause don´t know how to follow on, and would want to be able to use my "portable" source (that for the power given was not cheap!).
Regards





RE: Power supply noise, how can I get rid of it?
RE: Power supply noise, how can I get rid of it?
RE: Power supply noise, how can I get rid of it?
I will try also a common mode inductor to see if I can get a even cleaner DC rail.
is this common practice to follow with COTS switched sources?
it surprises me a little that I bought a supply from a known supplier to avoid problems, and finish reparing its problems...
btw, some radiation also, seen the difference if I put the source 1m away, but nothing comparing the common mode glitches.
Thanks!
RE: Power supply noise, how can I get rid of it?
You may need to experiment with adding a common mode filter to the 230VAC input of your supply to see if that also helps. If you keep the output ferrite bead then another thing to try may be to put a small capacitor on each of the +15, -15, and gnd wires to the chassis before the ferrite bead/choke you put on the output. Try values of 100pf to 2200pf. This will provide a easier path for the noise currents to circulate without traveling into your RF amplifer to find a path.
RE: Power supply noise, how can I get rid of it?
small rf by pass caps work too.
If you attempt to useL/C filters there is no attenuation, as you discovered.
RE: Power supply noise, how can I get rid of it?
Other issues appearing now, may comeback soon
Thanks!