| 摘要 |
This light-dimming device (10) comprises first and second terminals (1 and 2), a switch unit (3) comprising switching elements (7) connected between said first and second terminals (1 and 2), an adjustment unit (6) that can change the conduction angle of the switch unit (3), a control unit (4) that controls the switch unit (3), and a power-supply unit (5) that supplies power to the control unit (4). The control unit (4) comprises a zero-crossing detection circuit (9) that detects zero crossings of an AC voltage (Va), a control circuit (11) that generates a PWM signal having a duty cycle corresponding to the conduction angle obtained from the adjustment unit (6), and a driver circuit (8) that uses said PWM signal to drive the switching elements (7). The control unit (4) turns the switching elements (7) on and then off during a change period that starts at the beginning of a half cycle of the AC voltage and is shorter than said half cycle. The control circuit (11) starts generating the pulses constituting the PWM signal when a prescribed length of time that is shorter than the aforementioned change period has elapsed from a zero crossing of the AC voltage (Va). |
