| 摘要 |
This light-dimming device (10) has a switch unit (3), a control unit (4), and a power-supply unit (5). The switch unit (3) comprises switching elements (7). The power-supply unit (5) contains a capacitor (14) that is charged by a constant-voltage circuit (13). The control unit (4) comprises a driver circuit (8), a zero-crossing detection circuit (9), a detection circuit (21), and a control circuit (11). Power is supplied to the control unit (4) by the aforementioned capacitor (14). The driver circuit (8) drives the switching elements (7) in accordance with a PWM signal (S1). After a zero-crossing is detected by the zero-crossing detection circuit (9) and the voltage (V2) across the terminals of the capacitor (14) becomes greater than or equal to a threshold, the control circuit (11) starts generating the pulses that constitute the PWM signal (S1) and turn the switching elements (7) on. |
