| 摘要 |
PURPOSE:To carry out continuous light adjustment and stepwise light adjustment by determining the minimum light output level of a lighting load at a certain level, and by continuously determining the levels between the minimum level and a maximum level through a light adjustment setting part. CONSTITUTION:A maximum level of a terminal voltage of a condenser C5 is determined by a partial pressure ratio between a resistance R9 and resistances R15, R16 provided on a second light adjustment control circuit 4. Since the partial pressure ratio is determined based on the open/closed conditions of switches SW1, SW2 that form a second light adjustment setting part 6, the maximum level of the terminal voltage of the condenser C5 is varied according to the open/closed conditions of the switches SW1, SW2. As a result, when the resistances R15, R16 are properly determined, an output voltage V0 of a first light adjustment control circuit 3 is determined in such a way that the maximum level is varied according to the set condition of the second light adjustment setting part 6, while it is proportional to the ON-duty of a first light adjustment setting part 5. Regardless of stages the light adjustment stage thus set is in, the minimum level of the light output level of the lighting load 2 can be made stable. |
