How to select the right protection for the IO port of a smart controller PAC?

The selection of protection devices for the I/O ports of a PAC (Power Arrangement Controller) must be determined based on the port type, operating voltage, and potential threats. For digital I/O (24VDC), a TVS diode (SMBJ24CA) is selected for transient clamping, and a self-resetting fuse (SMD2920-150-30V) is connected in series for overcurrent protection. For analog I/O, a combination of a bidirectional TVS diode (SMBJ6.5CA) and an RC filter is used. High-speed I/O (such as encoders) requires a low-capacitance TVS diode (such as ESDLC5V0D3B) to maintain signal integrity.

For I/O in industrial environments that may be subject to surges, a gas discharge tube (2R090L-6×8) is added as a primary protection. When selecting protection devices, ensure that the breakdown voltage is 20% higher than the operating voltage and the peak pulse current is greater than the potential threat current. In terms of layout, the protection devices should be placed close to the connectors. Testing has verified that this selection scheme enables the I/O ports to pass IEC61000-4-2 ESD 8kV and IEC61000-4-5 Surge protection. 1kV test, lifespan greater than 100,000 insertion/removal cycles;