1769-PA2 PLC Power Supply for use with Compact I/O Module, 70 x 118 x 87 mm. The 1769-PA2, -PB2, -PA4, -PB4, -PS120 essential power supply modules provide 5V DC and 24V DC power for Compact I/O modules. A power supply module must be included in each bank of Compact I/O modules, unless the modules are connected directly to a MicroLogix 800/1500 base unit. Up to eight I/O modules can be installed on either side of the power supply, for a maximum of 16 modules, within the load capacity of the power supply, allowing you to boost the functionality of your control system.