Patent ID: 7639516
Filing Date: 2009-12-29
Classification: H02M

Abstract:
1. A switching power source device comprising: a power source; an inductor; a switching element that performs a switching operation, and, when switched on, connects said inductor to said power source to let a switching current flow to said inductor; a transformer that transforms energy stored in said inductor as said switching current flows through said transformer, and supplies said transformed energy to a load; a detector that detects a status of said load; a mode switching unit that sets a low power-consumption operation mode by setting a frequency at which said switching element is switched on lower than a frequency in a normal mode or stopping said switching element from being switched on, when said detector detects that said load is lighter than a predetermined reference value; and an ON-duration adjusting unit that changes an ON duration of said switching element according to an input voltage from said power source by changing in said reference value according to said input voltage from said power source, in such a way that a load current flowing to said load is constant at a transition from said normal mode to said low power-consumption operation mode, irrespective of a value of said input voltage from said power source.