This study is based on the UC3845 controller, designed a flyback switching power supply, which has a wide input voltage range, high output voltage accuracy, and high load regulation. According to the characteristics of flyback switching power supply and UC3845, adding filter circuit, a feedback circuit, protection circuit, etc., develop a single-ended flyback switching power supply with adjustable output, stable and reliable, and high efficiency. According to the simulation results, it can be seen that the designed switching power supply has high output voltage accuracy, and the input voltage in the range of 200V∼240V, the accuracy of the output voltage is kept within 1.3%; the voltage adjustment is less than 1%, The output ripple factor is kept below 0.09%, and the output voltage is adjustable.