High power DC power filter, which is a passive network structure, is suitable for both AC and DC power supply, and has bidirectional suppression performance. Inserting it between the AC network and the power supply is equivalent to adding a blocking barrier between the EMI noise of the two. Such a simple passive filter plays a bi-directional role in suppressing noise, thus it is widely used in various electronic devices.

For common-mode interference current, the magnetic field produced by the two coils is in the same direction, and the common-mode choke coil shows a larger impedance, thus playing the role of attenuating the interference signal; for the differential-mode signal (in this case, the low-frequency power supply current), the magnetic field generated by the two coils cancels, so it does not affect the power transmission function of the circuit.

Power filter is designed for the characteristics of electromagnetic disturbance at power port. Generally, it is a frequency selective two-port network composed of inductance, capacitance, resistance or ferrite devices. In fact, it is a kind of filter, which is called reflective filter according to its working principle.

It can provide high series impedance and low parallel impedance in the filter stopband, which seriously mismatches the impedance of noise source and load impedance, thus transmitting undesired frequency components back to the noise source.

When choosing power filter, we should consider three main indicators: first, voltage and current, secondly, insertion loss, and secondly, structure size.

Because the filter is usually encapsulated, the environmental characteristics are not the main problem. However, the temperature characteristics of all encapsulation materials and filter capacitors have a certain impact on the environmental characteristics of power filter.

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