The utility model discloses a miniature circuit breaker flyback switching power supply circuit, AC input voltage inputs high -frequency transformer's primary winding behind input rectification filter circuit, alternating voltage swashs the back through turning over, the last high -frequency voltage of auxiliary winding obtains output voltage VCC behind the output Rectifier filter circuit rectifying and wave -filtering, work as VCC voltage rises, the voltage that the high input constant voltage constant current output transform chip fin DRAIN of sharp formula was turned over in the primary winding of transformer input also can rise, integrateed 900V's MOS pipe of the high input constant voltage constant current output transform chip of formula turn over to swash, the rising of the high input constant voltage constant current output transform chip MOS intraduct control voltage of the sharp formula of turning over, turn over and swash the average efficiency control that the high input constant voltage constant current output transform chip of formula passes through self -adaptation PWMPFM, the switch of control MOS pipe, messenger's duty cycle reduces, thereby realize the steady voltage mesh, otherwise, when VCC reduces, it is stable too, thereby realize constant voltage / constant current mesh.