In view of the flaws of the auxiliary power supply of the battery charger, frequency converter,and photovoltaic inverter of three-phase AC input electric vehicles, an auxiliary power supply based on dual switch flyback has thus been designed, which utilizes UC2844A current type PWM control chips to realize the isolated output of the four circuit voltages, further stabilizing the 5 volt output by LDO chips. The test results show that the auxiliary power supply can output 80 W rated design power with small ripple waves, with its efficiency up to 84%. A stable output of four circuit voltages can be realized via the DC input of 100~800 V wide range of voltage. It is a reliable, low-cost, and widely used high-performance auxiliary power supply.