Solution to the problem of excessive power supply radiation
Within 1MHz:
Differential mode interference is the main 1.Increase X capacitance; 2.Add differential mode inductor; 3.Small power supply can be handled by PI-type filter (it is recommended that electrolytic capacitors close to the transformer can be chosen to be larger).
1M-5MHz:
Differential mode common-mode mixing, using the input and a series of X capacitors to filter out the differential touch interference and analyse which kind of interference exceeds the standard and solve it;
5MHz:
Above to common touch interference is mainly, using the method of suppressing common touch. For the shell grounded, in the ground line with a magnetic ring around 2 circles will be more than 10MHZ interference has a greater attenuation (diudiu2006); for 25 - 30MHZ but can be used to increase the Y capacitance to the ground, in the transformer outside the bread copper, change the PCBLAYOUT, the output line in front of the connection of a two-wire and winding of a small magnetic ring, a minimum of 10 turns around the output rectifier tube ends and the RC filter.
1M-5MHZ:
Differential mode common-mode mixing, using the input side in parallel with a series of X capacitors to filter out the differential interference and analyze which interference exceeds the standard and to solve the problem, 1. For the differential mode interference exceeds the standard can be adjusted to X capacitance, add differential mode inductors, differential mode inductance; 2. For the common-mode interference exceeds the standard can be added to the common-mode inductance, the choice of a reasonable amount of inductance to inhibit; 3. You can change the characteristics of the rectifier diode to deal with a pair of fast diodes, such as FR107 a pair of ordinary rectifier diodes 1N4007.
Above 5MHz:
The common touch interference is the main one, and the method of suppressing the common touch is used.
For the shell grounded, in the ground line with a magnetic ring string around 2-3 turns will be more than 10MHz interference has a greater attenuation effect; can choose to stick copper foil immediately after the core of the transformer, copper foil closed loop. Deal with the back-end output rectifier absorption circuit and the size of the primary large circuit shunt capacitance.
For 20M-30MHz:
1. For a class of products can be used to adjust the Y2 capacitance to ground or change the Y2 capacitor position;
2. Adjust the Y1 capacitance position and parameter value between the primary and secondary sides;
3. Wrap copper foil on the outside of the transformer; add shielding layer to the innermost layer of the transformer; adjust the arrangement of the windings of the transformer.
4. Change the PCB Layout;
5. In front of the output line, connect a small common mode inductor with two wires parallel wound;
6. Output rectifier in parallel with both ends of the RC filter and adjust the reasonable parameters;
7. Add BEADCORE between the transformer and the MOSFET;
8. Add a small capacitor to the input voltage pin of the transformer.
9. Can be used to increase the MOS drive resistance.,,
