This module converts ac power into dc power for CPU memory, and is the energy supply center of the whole PLC system. Its quality directly affects the function and reliability of PLC. At present, most of the PLC using high quality switching stabilized power supply, compared with the ordinary power supply, PLC power work stability is good, strong anti-interference ability. In addition to the internal circuit, the power supply of some machines also provides 24VDC stabilized power supply for external sensors, so as to avoid external faults caused by unqualified external power supply.