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

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

In PCB circuit board proofing, rational and effective use of components is an important guarantee for circuit board performance and quality stability. So, what problems should be paid attention to in the use of components in the PCB circuit board proofing process?

1. Limit the output current to avoid the lock-in effect of the CMOS circuit: the lock-in effect refers to the existence of parasitic PNP transistors and NPN transistors on the internal structure of the CMOS circuit, and a parasitic PNPN thyristor structure is formed between them. . A common solution is to separate each output from its cable with a resistor, and to clamp the cable to VDD (drain supply) and VSS (source supply) with two high-speed switching diodes .

2. Use a filter network: Sometimes a long input cable is required between the CMOS circuit system and the mechanical contact, which increases the possibility of electromagnetic interference, and the use of a filter network should be considered.

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 influence of electrostatic discharge.

4. Avoid suspending the input pins of CMOS devices: This is because once the input pins are 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 cause electrostatic breakdown, external noise interference and other phenomena. The redundant input terminals should be dealt with separately according to the function of the circuit.


Post time: Mar-29-2022