Relying only on the optimal design PCB board PCB layout to improve defense capabilities are very limited , in order to ensure that the entire system has a good PCB protection, external PCB protection devices is essential. The actual choice of different PCB protection programs according to specific needs . Typical PCB protection devices mainly in the following categories:
( 1 ) RC components . Each signal line access by resistive and capacitive components of the way , you can play a PCB shielding effect. Series resistance can be suppressed peak current moment , the parallel capacitance to ground is able to limit the peak voltage of the moment .
( 2 ) clamping diodes. Through two diodes Transient Voltage positive and negative can be clamped between a certain range , coupled with the effect of series resistance provides power to the load , and thus play a positive and negative polarity of PCB protection.
( 3 ) Zener diode . Although zener diodes are not designed specifically for PCB applications, but its operating characteristics determines that it has some positive and negative polarity PCB protection. Its disadvantage yes. N junction is small, it can not withstand the high peak currents , in addition, it produces parasitic capacitance is large, it is possible to affect the normal operation of the circuit.
( 4 ) transient voltage suppressor. Also known as Transient Voltage Suppressors TVS tube , a solid-state diode is designed for PCB protection . TVS tube is the most important feature short response time , the leakage current is very small, is the ideal protection devices.
( 5 ) gas discharge tube (GDT). Using a gas discharge tube having an airtight glass or ceramic as the shell . As the inner tube filled with neon gas or argon stability , to maintain a certain insulating state. Advantage of the gas discharge tube insulation resistance, parasitic capacitance is very small, self-healing , but the drawback is the response rate and life expectancy are not ideal , and electrical properties will gradually decay with time.
