When the small relay on the PCB frequently disconnects the large current, arc discharge will occur, which will cause strong electromagnetic interference, which not only affects the CPU, but also causes the decoder and driver to generate incorrect signals and instructions, causing a series of problems. The following are some solutions to electromagnetic interference caused by frequent actions of small relays on PCB multilayer circuit boards:
1) Improve Chip Anti-Interference Ability:
PCB multi-layer circuit board CPU is replaced with super anti-interference chip. The ceramic chip decoupling capacitor should be installed between the CPU and the power port of the decoder, and the grounding terminal should be as close to the chip as possible, and the shorter pin is much better.
2) Inhibition of Interference Sources:
The relay drive amplifier adopts a Darlington IC module with continuous current function (such as ULN2004A), which can effectively eliminate the interference caused by the back electromotive force when the coil is cut off. In addition, choosing a suitable relay on the PCB multilayer circuit board or plating a layer of copper foil with a medium thickness on the PCB can also effectively prevent electromagnetic interference.
Compared with the size of the pad, the opening length or width of the PCB multi-layer circuit board template is reduced by 10% to 30%, so as to achieve the purpose of reducing the amount of solder paste deposition. The shape of the template opening is in a certain selected form (such as triangle, teardrop, etc.) to reduce the amount of solder paste deposited on the narrow pitch pad. Choose a compromised template thickness to make it suitable for both narrow-pitch pads and non-narrow-pitch pads, so that different pads require different template thicknesses.
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