Take stock of the measures taken to prevent EMI when designing switching power supplies.
1. Minimize the area of PCB copper foil at the nodes of noisy circuits; e.g., the drain and collector of switching tubes, the nodes of primary and secondary windings, and so on.
2, so that the input and output terminals away from the noise components, such as transformer wire packs, transformer cores, switching tube heat sinks, and so on.
3, so that the noise components (such as unshielded transformer wire packs, unshielded transformer cores, and switching tubes, etc.) away from the edge of the enclosure, because under normal operation the edge of the enclosure is likely to be close to the outside grounding wire.
4, If the transformer does not use electric field shielding, keep the shield and heat sink away from the transformer.
5, minimize the area of the following current loops: secondary (output) rectifiers, primary switching power devices, gate (base) drive lines, and auxiliary rectifiers.
6, do not mix the gate (base) drive return loop with the primary switching circuit or auxiliary rectifier circuit.
7. Adjust and optimize the value of the damping resistor so that it does not produce a ringing noise during the dead time of the switch.
8. Prevent saturation of the EMI filter inductor.
9. Keep corner nodes and secondary circuit components away from the primary circuit shield or switching tube heat sink.
10. Keep the nodes and components of the primary circuit's swing body away from the shield or heat sink.
11. Keep high frequency input EMI filters close to the input cable or connector terminals.
12. Keep the high frequency output EMI filter close to the output wire terminals.
13. Keep a distance between the copper foil of the PCB board opposite the EMI filter and the component body.
14. Put some resistors on the line of the rectifier of the auxiliary coil.
15. Connect damping resistors in parallel on the magnetic bar coil.
16. Connect damping resistors in parallel at both ends of the output RF filter.
17. Allow for a 1nF/500V ceramic capacitor or a series of resistors across the static end of the transformer's primary and auxiliary windings in the PCB design.
18. Keep the EMI filter away from the power transformer; in particular, avoid positioning it at the end of the winding.
19. In the case of sufficient PCB area, can be left on the PCB to put the shielding windings with the feet and put the RC damper position, RC damper can be connected across the shielding windings at both ends.
20. If space permits, in the switching power FET drain and gate between a small diameter to the lead capacitor (Miller capacitance, 10 picofarads / 1 kV capacitance).
21. Put a small RC damper on the DC output if space permits.
22. Do not place the AC socket against the heat sink of the primary switching tube.
