Switching Power Supply Design Needs to Pay Attention to 22 Points
1. The PCB area ofthe noise circuit node is minimized; for example, the drain and collector of the switch, the nodes of the primary and secondary windings, etc.
2. Keep the input and output terminals away from noise components such as transformer package, transformer core, heat sink of switch tube, etc.
3. Keep noise components(such as unshielded transformer cords, unshielded transformer cores, and switch tubes, etc.) away from the edge of the enclosure because the edge of the enclosure is likely to be close to the ground wire under normal operation.
4. If the transformer is not shielded by electric field, keep the shield and heat sink away from the transformer.
5. Minimize the area of the current loop: secondary(output) rectifier, primary switching power device, gate (base) drive line, auxiliary rectifier.
6. Do not mix the gate (base) drive feedback loop with the primary or auxiliary rectifier circuit.
7. Adjust the optimized damping resistance so that it does not produce a ringing sound during the dead time of the switch.
8. Prevent EMI filter inductor saturation.
9. Keep the components of the corner node and the secondary circuit away from the shield of the primary circuit or the heat sink of the switch.
10 Keep the node and component body that oscillates the primary circuit away from the shield or heat sink.
11. Place the high frequency input EMI filter close to the input cable or connector end.
12. Keep the EMI filter of the high frequency output close to the output wire terminals.
13. Keep a distance between the copper foil of the PCB opposite the EMI filter and the component body.
14. Place some resistors on the line of the rectifier of the auxiliary winding.
15. Connect the damping resistor in parallel with the coil of the magnet.
16. Connect the damping resistor in parallel across the output RF filter.
17. Allow 1nF/500V ceramic capacitors or a series of resistors to be connected between the static and auxiliary windings of the primary of the transformer during PCB design.
18. Keep the EMI filter away from the power transformer; especially avoid positioning at the end of the package.
19. Where the PCB area is sufficient, the position of the shield winding and the position of the RC damper can be left on the PCB, and the RC damper can be connected across the shield winding.
20. If space permits, place a small radial lead capacitor(Miller capacitor, 10 picofarads /1 kV capacitor) between the drain and gate of the switching power FET.
21. Space allows a small RC damper to be placed at the DC output.
22. Do not put the AC socket against the heat sink of the primary switch.