Patent ID: 7969132
Filing Date: 2011-06-28
Classification: H02M

Abstract:
1. A switching power supply unit, wherein said switching power supply unit selects a first signal whose pulse frequency is modulated according to a voltage supplied to a load or a second signal whose pulse width is modulated according to a voltage supplied to said load, switches on/off a semiconductor switch using the selected signal, and supplies a direct-current voltage converted into a predetermined voltage level to said load, said switching power supply unit comprising: a frequency determining unit that determines whether or not the frequency of said first signal exceeds a predetermined value; and a selection unit that selects said first or second signal according to the determination result of said frequency determining unit, wherein said first signal is a binary signal having first and second levels; said semiconductor switch is switched on corresponding to a period of said first level; said frequency determining unit determines whether or not a period of said second level in one cycle of said first signal is equal to or less than a predetermined time period; and said selection unit selects said second signal when said period of said second level is equal to or less than the predetermined time period in a state where said first signal is selected.