Abstract: The converter used in the power supply has problems of low voltage gain, high voltage stress of power tube, non-electrical isolation and complex control. In order to solve the above problems, a mine cascaded converter with wide input voltage range is designed to meet the requirements of AC127-1 140 V power supply voltage level of coal mine. The cascaded converter can adapt to AC70-1 400 V voltage input. The converter adopts 3-way Buck converter and LLC converter in series to improve the voltage gain of the converter. Capacitor series voltage divider is used to reduce the voltage stress of power tube. Buck converter adopts input voltage feedforward compensation to reduce the influence of input voltage fluctuation. At the same time, Buck converter improves converter stability through output voltage closed-loop PI regulation. LLC converter has the performance of input and output electrical isolation. Pulse frequency modulation technology is used to perform closed-loop PI regulation on the output voltage. Then the power tube is driven by a voltage controlled oscillator with frequency conversion to adjust the resonant frequency of the converter, thus stabilizing the output voltage. The simulation and experimental results show that when the input voltage is AC70-1 400 V, the load effect of the converter is less than 5% and the output voltage deviation is less than 5%. These results meet the requirements of MT/T 408-1995 DC stabilized power supply for coal mine.