This paper introduced a design of the low volltage large current switching powersupply,it took the PWM control chip UC3825 as the core.It expounded the design scheme of the main circuit and control circuit topology structure of main circuit design,and designed a soft start-up and overcomepaction over-current protection circuit,application feedback method and pulse width modulation techniques to realize the stable output voltage,current,and developed a 15 V/1 200 A prototype.