I found this interesting article on SMPS EMI noise and reduction: http://www.eet-china.com/ARTICLES/2000DEC/2000DEC08_AMD_AN8.PDF?SOURCES=DOWNLOAD
It's the basic stuff (basically X1 and Y1 caps everywhere).
Which raises the question: how much power does one need to be handling to worry about all that?
In my case I'm making a 220VAC to 5VDC, 1A supply with the Viper22 IC, which already reduces EMI by slightly varying the switching frequency. At such small power, do I need any or all of:
Or better yet: at what power levels do any/all of these start mattering enough be completely necessary?
I've seen many ATX power supplies, which easily do 200W+, have jumper wires instead of an EMI choke. This is, of course, to reduce costs. But how do they get away with it? Is it because I'm not in USA and not subject to FCC rules? Are the FCC rules too strict, or the chinese SMPS too ****ty?
It's the basic stuff (basically X1 and Y1 caps everywhere).
Which raises the question: how much power does one need to be handling to worry about all that?
In my case I'm making a 220VAC to 5VDC, 1A supply with the Viper22 IC, which already reduces EMI by slightly varying the switching frequency. At such small power, do I need any or all of:
- X1 Capacitors between live and neutral, before the EMI choke
- The EMI choke
- X1 Capacitors between live and neutral, after the EMI choke ("reduces differential mode noise")
- Y1 capacitors between live and earth and between neutral and earth ("reduces common mode noise")
- Y1 capacitor between non-isolated GND and the isolated GND
- Transformer shielding
Or better yet: at what power levels do any/all of these start mattering enough be completely necessary?
I've seen many ATX power supplies, which easily do 200W+, have jumper wires instead of an EMI choke. This is, of course, to reduce costs. But how do they get away with it? Is it because I'm not in USA and not subject to FCC rules? Are the FCC rules too strict, or the chinese SMPS too ****ty?
