A novel power supply apparatus (10) includes a microcontroller (102) and a plurality of voltage converters (104). If the voltage converters (104) are in a boost mode and a plurality of duty cycles of the voltage converters (104) calculated by the microcontroller (102) are less than 0.5, the microcontroller (102) is configured to limit at least one of the duty cycles of the voltage converters (104) to 0.5. If the voltage converters (104) are in a buck mode and the duty cycles of the voltage converters (104) calculated by the microcontroller (102) are greater than 0.5, the microcontroller (102) is configured to limit at least one of the duty cycles of the voltage converters (104) to 0.5.