| 摘要 |
The disclosed invention directs the current path of the light source through a signal rectifier and series switch, which is controlled by the pulse width modulation (PWM) generator based on the input intensity level. The direct current series switch (i.e. MOSFET) does not require a minimum current level, or “holding current”, to respond correctly to the control signal. The modulated control signal continues over the entire cycle period, which ensures accurate duty cycle control regardless of the minimum forward voltage bias, or “turn on voltage”, of the light source. In addition, accurate duty cycle control allows the possibility of non-linear dimming curves to compensate for human factors or characteristics of the light source. The high frequency (i.e. >2 kHz) of the modulation results in the users perception of consistent intensity and smooth transitions. The disclosed invention addresses the principle issues associated with dimming AC LED technology, while maintaining compatibility with traditional incandescent sources, by providing accurate duty cycle control independent of I-V characteristics of the light source and not requiring a “holding current”. The disclosed invention can adjust the intensity of any LED device that reacts to a significant portion of the ON and OFF time periods created by the modulation of the input power.
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