Figure 9-1 A Typical CPU (PLC Controller) System Block Diagram

The PLC system is usually connected to an external 24-V DC power supply to provide power to the controller unit, backplane, and I/O modules. Input protection circuits are required to protect the PLC from faults such as overvoltage, undervoltage, and overload. Because input supply connectors are screw type, there can always be a possibility of reverse supply connections. Protection circuits must block the reverse polarity to protect the PLC from possible negative voltages. At the same time, every PLC is tested for electrostatic discharge (ESD) according to IEC 61000-4-2, burst pulses (EFT) according to IEC 61000- 4-4, energy single pulse (surge) according to IEC 61000-4-5, voltage drops and interruptions. Figure 9-1 shows a system block diagram of PLC controller unit along with the input protection socket. The TPS2663x devices offer a plug and play input protection solution for such applications. For more information about this end equipment, refer to the TI application site on Programmable Logic Controller (PLC), DCS & PAC: CPU (PLC Controller).

Figure 9-2 24-V, 2-A eFuse Input Protection Circuit for Industrial PLC, CNC CPU