As un energia conversione dispositivo lavoro in il commutazione stato, il tensione e corrente cambiamento velocità di il commutazione alimentazione alimentazione è molto alto, e il interferenza intensità generato è relativamente grande; il interferenza sorgenti sono principalmente concentrato durante il potenza commutazione periodo e il radiatore e alto-livello trasformatore connesso a esso. Confrontato con digitale Il posizione del circuito interferenza sorgente è relativamente chiaro; il commutazione frequenza è non alto (da decine di kilohertz a diversi megahertz), e il principale forme di interferenza are conduzione interferenza e campo vicino interferenza; while stampato circuito scheda (PCB) cablaggio è di solito manualmente cablato, esso ha maggiore arbitrarietà, che aumenta il difficoltà di estrazione PCB distribuzione parametri e stima campo vicino interferenza.
All'interno 1MHZ - principalmente differenziale modalità interferenza, che può essere risolto da crescente il X condensatore
1MHZ---5MHZ---differenziale mode and common mode mixed, use the input terminal and a series of X capacitors to filter out the differential interference and analyze which kind of interference exceeds the standard and solve it; 5M---the above are principalmente common interference , using the method of suppressing co-touching. per il caso messa a terra, using a magnetico anello on il terra filo per 2 giri sarà grande attenuare il interferenza sopra 10MHZ (diudiu2006); for 25--30MHZ, you can use a larger Y capacitor to the ground and wrap rame skin outside the transformer , Change PCBLAYOUT, connect a small magnetic ring with double wires in parallel in front of the output line, at least 10 turns, and connect an RC filter at both ends of the output rectifier tube.
30---50MHZ is generalmente caused by the high-speed turn-on and turn-off of MOS tubes. It can be solved by increscente the MOS drive resistance, using 1N4007 slow tubes for the RCD buffer circuit, and using 1N4007 slow tubes for the VCC supply voltage.
100---200MHZ is general caused by the reverse recovery current of the output rectifier, you can string magnetic beads on the rectifier
Between 100MHz and 200MHz, most of them are PFC MOSFETs and PFC diodes. Now MOSFETs and PFC diodes are effective, and the horizontal direction can basically solve the problem, but the vertical direction is very helpless.
The radiation of switching power supply generally only affects the frequency band below 100M. It is also possible to add a corresponding absorption circuit on the MOS and the diode, but the efficiency will be reduced.
Misure a prevenire EMI quando progettazione commutazione alimentazione alimentazione
1. Minimize the PCB copper foil area of the noisy circuit nodes; such as the drain and collector of the switch tube, the nodes of the primary and secondary windings, etc.
2. Keep the input and output terminals away from noisy components, such as transformer wire packs, transformer cores, heat sinks of switching tubes, and so on.
3. Keep noisy components (such as unshielded transformer wire wraps, unshielded transformer cores, and switching tubes, etc.) away from the edge of the case, because the edge of the case is likely to be close to the outside ground wire under normal operation.
4. If il trasformatore non uso elettrico campo schermatura, mantenere il schermo e calore dissipatore via da il trasformatore.
5. Minimize the area of the following current loops: 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 switching circuit or auxiliary rectification circuit.
7. Adjust the optimal damping resistor value so that it does not produce ringing sound during the dead time of the switch.
8. Prevent EMI filter inductor saturation.
9. Keep the turning node and the components of the secondary circuit away from the shield of the primary circuit or the heat sink of the switch tube.
10. Keep swing nodes and component bodies of the primary circuit away from shields or heat sinks.
11. Make the EMI filter for high-frequency input close to the input cable or connector end.
12. Keep the EMI filter for high frequency output close to the output wire terminals.
13. Keep a certain distance between the copper foil of the PCB opposite the EMI filter and the component body.
14. Put alcuni resistori in il linea di il raddrizzatore per il ausiliario bobina.
15. Connect the damping resistor in parallel on the coil of the magnetic rod.
16. Connect damping resistors in parallel across the output RF filter.
17. It is allowed to put 1nF/500V ceramic capacitors or a series of resistors in the PCB design, and connect them between the primary static end of the transformer and the auxiliary winding.
18. Keep the EMI filter away from the power transformer; especially avoid positioning at the end of the winding.
19. If the PCB area is sufficient, the pins for the shield winding and the position for the RC damper can be left on the PCB, and the RC damper can be connected across the two ends of the shield winding.
20. If space permits, place a small radial lead capacitor (Miller, 10 pF/1 kV) between the drain and gate of the switching power MOSFET.
21. Luogo a small RC smorzatore on il DC uscita se spazio permessi.
22. Do not put the AC socket close to the heat sink of the primary switching tube.
