What problems should be paid attention to in the use of components in the PCB proofing process?

by:A-TECH      2021-03-09
In the PCB circuit board proofing, the reasonable and effective use of components is an important guarantee for the performance and quality of the circuit board. So, what issues should be paid attention to when using components in the PCB proofing process? 1. Limit the output current to avoid the locking effect of the CMOS circuit: the locking effect means that there are parasitic PNP transistors and NPN transistors in the internal structure of the CMOS circuit, and they form a parasitic PNPN thyristor structure. . The common solution is to use a resistor to isolate each output terminal from its cable, and use two high-speed switching diodes to clamp to VDD (drain power) and VSS (source power) with the cable. . 2. Use a filter network: Sometimes a long input cable is needed between the CMOS circuit system and the mechanical contacts, which increases the possibility of electromagnetic interference, so you should consider using a filter network. 3. Forming an RC network: For the sensitive input terminals of bipolar devices, an RC network composed of a resistor with a larger resistance value and a capacitor of at least 100pF can be used to reduce the impact of electrostatic discharge. 4. Avoid floating input pins of CMOS devices: once the input pins are floating, the input potential will be in an unstable state, which will not only destroy the normal logical relationship of the circuit, but also easily cause electrostatic breakdown and external noise interference. The redundant input terminal should be dealt with separately according to the circuit function. The above are a few issues that engineers should pay attention to when using components in the PCB proofing process. I hope it will be helpful to our customers.
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