Що є заходи до запобігання EMI in the design of switching power supply
As an energy conversion device working in the switching state, the voltage and current change rate of the switching power supply is very high, and the interference intensity generated is relatively large; the interference sources are mainly concentrated in the power switching period and the radiator and high-level transformer connected to it. Порівняння з цифровим The position of the circuit interference source is relatively clear; the switching frequency is not high (from tens of kilohertz to sкілька мегагерц), and the main forms of interference are conduction interference and near-field interference; while printed circuit board (PCB) wiring is usually manually wired, It has greater arbitrariness, which increases the complexy of extracting PCB distribution параметри і оцінка ближнє поле перешкоди.
Within 1MHZ - mainly differential mode interference, which can be solved by increasing the X capacitor
1MHZ---5MHZ---differential mode and common mode mixed, use the input terminal and a series of X конденсатори to filter out the differential interference and analyze which kind of interference exceeds the standard and solve it; 5M---the above are mainly common interference , using the method of of over-touching. For the case grounded, using a magnetic ring on the the ground wire for 2 turns will greatly attenuate the interference above 10MHZ (diudiu2006); for 25--30MHZ, you can use a larger Y конденсатор to the ground and wrap мідь шкіра 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 підключення an RC filter at both ends of the output випрямляч трубка.
30---50MHZ is generally caused by the high-speed turn-on and turn-off of MOS tubes. It can can be solved by increasing 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 generally caused by the reverse recovery current of the output rectifier, you can string magnetic beads on the випрямляч
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 випромінювання of switching power supply generally only impacts 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.
Міри до запобігання EMI коли проектування комутація живлення живлення
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 обмоток, 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 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) 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 some resistors in the line of the випрямляч for the допоміжний котушка.
15. Connect the демпфірування резистор in parallel on the котушка of the магніт стрижень.
16. Підключення демпфірування резистори вхід паралель поперек вихід РЧ фільтр.
17. It is is allowed to put 1nF/500V ceramic конденсатори or a series of resistors in the PCB design, and connect them between the primary static end of the transformer and the auxiliary обмотка.
18. Keep the EMI filter away from the power transformer; особливо avoid positioning at the end of the обмотка.
19. When 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. Простір дозвіл місце a малий радіальний свинець конденсатор (Miller, 10 pF/1 kV cap) between the drain and gate of the switching power FET.
21. Place a small RC damper on the DC output if space permits.
22. Do not put the AC socket close to the heat sink of the the primary switching tube.
