| 摘要 |
<P>PROBLEM TO BE SOLVED: To widen a dimming range of a light source load in a relatively simple configuration. <P>SOLUTION: In a first control mode, a control circuit 4 turns on/off a switching element 162 of a step-down chopper circuit 16 according to a predetermined oscillation frequency and on time such that a current flows through an inductor 163 without any quiescent intervals. In a second control mode, the control circuit 4 keeps the oscillation frequency of the switching element 162 substantially fixed, but changes the on time thereof. In a third control mode, the control circuit 4 keeps the on time of the switching element 162 substantially fixed, but changes the oscillation frequency thereof. The second control mode and the third control mode are assigned to a plurality of intervals into which a dimming ratio is divided. The control circuit 4 selects the first control mode to fully light a light source load 3, and when a dimming ratio is specified, selects one of the second control mode and the third control mode in accordance with the interval to which the dimming ratio corresponds, to dim the light source load 3. <P>COPYRIGHT: (C)2013,JPO&INPIT |
