The utility model discloses a non -isolated auxiliary power circuit based on exchange 380V input voltage, it includes half -wave rectification filter circuit, serial -type stabilivolt reduction voltage circuit, non -isolated closed loop BUCK circuit, half -wave rectifier circuit's input is connected with interchange 380V input voltage, its output is connected with serial -type stabilivolt reduction voltage circuit, output connection to the non -isolated closed loop BUCK circuit of serial -type stabilivolt reduction voltage circuit, alternating voltage changes the DC voltage after through half -wave rectification filter circuit into, pass through the secondary steady voltage of serial -type stabilivolt reduction voltage circuit and non -isolated closed loop BUCK circuit again, it presses to export the galvanic current after the step -down, switching power supply control chip U1's internal integration oscillator, high voltage MOS pipe, current foldback circuit etc. Adopt efficient switching power supply BUCK structure, automatically restarting, short -circuit protection function have, make the utility model discloses it is small, can low heat generation effectively fall, raise the efficiency, export reliable and stable DC voltage.