In PCB proofing, rational and effective use of components is an important guarantee for the stability of PCB performance and quality. So, what problems should be paid attention to when using components in PCB proofing process? 1. PCB proofing limits the output current to avoid locking effect of CMOS circuit; Lock-in effect means that there are parasitic PNP transistors and NPN transistors in the internal structure of CMOS circuits, and they just form a parasitic PNPN thyristor structure. The common solution is to use a resistor to separate each output terminal from its cable, and use two high-speed switching diodes to clamp the cable to VDD (drain power supply) and VSS (source power supply). 2. PCB proofing uses 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. Therefore, a filter network should be considered.
3. PCB proofing forms RC network: For the sensitive input terminal of bipolar device, RC network composed of resistor with larger resistance value and capacitor with at least 100pF can reduce the influence of electrostatic discharge. 4. PCB proofing prevents the input pins of CMOS devices from hanging; This is because once the input pin is suspended, the input potential will be in an unstable state, which will not only destroy the normal logic relationship of the circuit, but also easily lead to electrostatic breakdown and external noise interference. The redundant input terminals should be treated separately according to the function of the circuit. These are some problems that should be paid attention to in the use of components in PCB proofing process. I wonder if it can help solve some of your little doubts. Usually, we need SMT placement when making boards. Every time we make a plate, the placement is a manufacturer, and after we buy components, it is also a manufacturer, which is very troublesome and wastes a lot of time.
