Patent ID: 7759917

Claim:
A power supply unit comprising: a first power supply circuit for converting an input voltage into a predetermined output voltage, said first power supply circuit having a power conversion efficiency that is high for a light load but decreases with the magnitude of said load; and a second power supply circuit for converting said input voltage into an output voltage, said second power supply circuit having an output end connected to the output end of said first power supply circuit and having a power conversion efficiency that is lower than said high efficiency of said first power supply circuit for a light load but increases with the magnitude of said load and exceeds that of said first power supply circuit when said load exceeds a threshold, wherein said first and second power supply circuits are switchable depending on the magnitude of the power to be supplied from said power supply circuits to said load, said first and second power supply circuits are in operation simultaneously to supply their power for a common overlapping period when switching is made between said first and second power supply circuits, and said switching is carried out in advance prior to an actual increase or decrease in load based on a prediction that the power to be supplied from said first and second power supply circuits to said load would increase or decrease via said threshold.