Design of power supply circuit for IoT smart gateway

　　The gateway device uses 220V AC power supply, and the power module directly uses a stable brand switching power supply. The switching power supply outputs 5V voltage to supply the power demand of the weak current part of the board. The weak current part consists of three parts: core board, expansion board and RS485 interface board. The power supplies of these three parts are independently designed and isolated from each other to avoid mutual interference.

        The power supply on the core board is mainly 5V and 3.3V. The power consumption unit of the 5V power supply has low requirements for the power supply, and the 5V power supply provided by the switching power supply can be used directly. Since the core board is mounted on the expansion board, the core board does not have a separate power interface, so the power supply of the core board is also introduced from the 5V power interface on the expansion board. Switches and fuses are also introduced at the entrance of the 5V power interface on the expansion board to facilitate the switching and overcurrent protection of the equipment. The 3.3V power supply part uses LM1117-3V3 to stabilize the 5V power supply. The circuit schematic is shown in the figure.