Solutions to electromagnetic compatibility issues in power supplies
From the three elements of electromagnetic compatibility, to solve the electromagnetic compatibility of switching power supplies, we can start from three aspects.
1) Reduce interference signals generated by interference sources;
2) Cut off the propagation path of interference signals;
3) Enhance the anti-interference ability of the affected body.
When solving the internal electromagnetic compatibility of switching power supplies, the above three methods can be comprehensively applied, based on cost-effectiveness ratio and ease of implementation. The external interference generated by switching power supplies, such as harmonic currents in power lines, conducted interference in power lines, electromagnetic radiation interference, etc., can only be solved by reducing the interference source. On the one hand, it can enhance the design of input output filtering circuits, improve the performance of active power factor correction (APFC) circuits, reduce the voltage and current change rate of switch tubes and rectifier freewheeling diodes, and adopt various soft switching circuit topologies and control methods. On the other hand, strengthen the shielding effect of the casing, improve the gap leakage of the casing, and carry out good grounding treatment. And for external anti-interference capabilities such as surges and lightning strikes, the lightning protection capabilities of AC input and DC output ports should be optimized. Usually, for 1.2/50 μ Open circuit voltage and 8/20 μ The combined lightning strike waveform of short circuit current can be solved by combining zinc oxide varistors and gas discharge tubes due to their small energy. For electrostatic discharge, usually in the small signal circuits of communication and control ports, TVS tubes and corresponding grounding protection are used, the electrical distance between the signal circuit and the casing is increased, or anti-static interference devices are selected to solve the problem. The fast transient signal contains a wide spectrum and is easily transmitted into the control circuit in a common mode manner. The same anti-static method is used to reduce the distributed capacitance of the common mode inductance and strengthen the common mode signal filtering of the input circuit (such as adding a common mode capacitor or inserting a loss type ferrite magnetic ring, etc.) to improve the system's anti-interference performance.
