What problems should be paid attention to in PCB filter technology?

PCB manufacturers, PCB designers and PCBA manufacturers explain to you what problems should be paid attention to in PCB filter technology?

Filtering technology is an effective measure to suppress interference, especially in dealing with conducted interference and some radiated interference of switching power supply EMI signal. So, what problems should PCB manufacturers pay attention to regarding PCB filtering technology?

1. Differential mode interference and common mode interference

The conducted interference signals on any power line can be represented by differential mode and common mode interference signals.

In general, the differential mode interference has small amplitude, low frequency and small interference; Common mode interference has large amplitude and high frequency, and can also generate radiation through the wire, resulting in large interference. Therefore, to weaken conducted interference, EMI signal shall be controlled below the limit level specified in relevant EMC standards. In addition to suppressing interference sources, the most effective method is to add EMI filters to the input and output circuits of the switching source. For the high-frequency EMI signals generated by switching power supply, as long as the PCB factory selects the corresponding decoupling circuit or EMI filter with simple network structure, it is not difficult to meet the filtering effect in line with EMC standards.

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2. Transient disturbance

The transient interference will cause the output voltage fluctuation of the monolithic switching power supply; When the transient voltage is superimposed on the DC input voltage VI after rectification and filtering, making VI exceed the drain source breakdown voltage V (BR) DS of the internal power switch, TOPSwitch chip will also be damaged, so suppression measures must be taken. The power line filter can protect the power supply. The common mode capacitor between the line and the ground is an effective device to suppress this transient interference, which bypasses the interference to the chassis and away from the internal circuit. When the capacity of this capacitor is limited by the leakage current and cannot be too large, the common mode choke must provide greater protection. The common mode choke is usually wound around a ferrite core with high permeability, and its typical inductance is 15~20mH.

3. Inhibition of conduction

There is no problem when a lot of equipment are tested for electromagnetic compatibility, but when the two equipment are connected, they cannot meet the requirements of electromagnetic compatibility. That is, the cable plays the role of receiving and radiating antenna. The only measure is to add a filter, cut off the path of electromagnetic interference propagation along the signal line or power line, and form a complete electromagnetic interference protection together with shielding. Filtering technology can be used to suppress interference sources, eliminate coupling, or improve the resistance of the receiving circuit.

These are the problems that PCB filter technology should pay attention to. PCB manufacturers hope they can help you. PCB manufacturers, PCB designers and PCBA manufacturers explain to you what problems should be paid attention to in PCB filter technology?