| 摘要 |
A direct-current dimmer switch with low noise. A direct-current switch is turned on relatively slowly to avoid noise generation. Input capacitance of the direct-current switch device works in conjunction with a switch input series resistor to avoid a sharp turn-on characteristic. A set-point is compared against a voltage ramp to generate a pulse provided to the switch input. Essentially the full voltage is supplied to the load during the pulse. In one embodiment, a field-effect transistor with a low series resistance is used as the direct-current switching device. The ramp is generated by an integrator that is turned off at zero crossings of the alternating input line voltage to re-set the integrator. In a further embodiment a detector, such as a passive infra-red detector, is used to turn on the dimmer switch at a pre-set level.
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