| 摘要 |
PROBLEM TO BE SOLVED: To perform successful adjustment of brightness for the lighting system using LED or HID lamp as the light source. SOLUTION: A switching circuit of a constant current power supply 10 is provided with a basic waveform SW 11 for outputting a current pulse of the basic peak value IB and a difference waveform SW 12 for outputting a current pulse of the difference peak valueΔI. A comparator 23 of the constant current control circuit 2 obtainsΔI by comparing, depending on the value of brightness 20, the desired preset peak value IS outputted from the preset peak value generator 21 with the basic peak value IB stored in a memory 22, and a driver 24 drives the basic waveform SW 11 and difference waveform SW12 using the value IB stored in the memory 22 and the valueΔI from the comparator 23. Accordingly, IB from the basic waveform SW 11 andΔI from the difference waveform SW 12 are combined and a current pulse which supplies a load current IL depending on the desired value of brightness 20 may be outputted.
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