Electromagnetic compatibility design in PCB circuits

　　Once electrostatic discharge occurs, it should be bypassed as soon as possible, and do not directly invade the internal circuit. For example, if the internal circuit is shielded by a metal chassis, the chassis should be well grounded, and the grounding resistance should be as small as possible, so that the discharge current can flow into the ground from the outer chassis, and the disturbance caused by the discharge of surrounding objects can also be imported into the ground, without affecting the internal circuit. For a metal chassis, the circuits in the chassis are grounded through I/O cables and power cables. When electrostatic discharge occurs on the chassis, the potential of the chassis increases, but the potential of the internal circuits is kept near the ground potential due to grounding. At this time, there is a large potential difference between the chassis and the circuit. This causes a secondary arc between the chassis and the circuit. Cause damage to the circuit. Secondary arcing can be avoided by increasing the distance between the circuit and the enclosure. When the distance between the circuit and the enclosure cannot be increased, a grounded metal baffle can be added between the enclosure and the circuit to block the arc. If the circuit is connected to the case, it should only be connected through one point. Prevent current from flowing through the circuit. The connection point between the circuit board and the chassis should be at the cable entrance. For a plastic chassis, there is no grounding problem.