Patent Application
20100188006
This application relates generally to LED lighting, and more particularly to LED lighting for applications requiring dimming and/or color mixing capabilities.
Conventional silicon controlled rectifier (SCR) dimmers designed for incandescent lamps generally employ a technique that removes a single, continuous section of the input alternating current (AC) waveform during both the positive and negative portions of the cycle, proportional to the desired intensity (
AC LEDs, such as the Acriche manufactured by Seoul Semiconductor of Seoul, South Korea, use a semiconductor chip composed of an LED array electrically wired at the semiconductor or package level in series, in at least two anti-parallel strings, or as a rectification circuit. Although AC LEDs offer the advantages of simplicity, cost-effectiveness, and negligible power conversion losses, they react adversely to SCR dimmers. The typical AC LED draws less than fifty milliamps, which is below the minimum current level, known as the “holding current,” required for most SCRs to maintain an “on” state. In addition, the non-linear current/voltage (I-V) response of LEDs disconnects the direct proportionality of input waveform to output luminous intensity. Both of these characteristics cause SCR dimmers to be overwhelmingly unresponsive to user input and connected LEDs to illuminate intermittently throughout operation.
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.
This Summary is an overview of some of the teachings of the present application and not intended to be an exclusive or exhaustive treatment of the present subject matter. Further details about the present subject matter are found in the detailed description and appended claims. Other aspects will be apparent to persons skilled in the art upon reading and understanding the following detailed description and viewing the drawings that form a part thereof, each of which are not to be taken in a limiting sense. The scope of the present invention is defined by the appended claims and their equivalents.
a-2d compares the waveforms of a SCR dimmer versus the AC LED dimmer.
In
c shows the sinusoidal AC waveform overlaid with the pulse-width modulated control signal.
A specialized fixture connector would be required for a multi-channel circuit, with a pin for the input voltage and a pin for the return voltage of each light source group [407]. In a three channel system, an example of an appropriate connector would be the 26725-405 from Leviton of Little Neck, N.Y., USA.
The invention has several inherent advantages: The direct current series switch does not require a minimum current level, or “holding current”, to respond correctly to the control signal, enabling the system to be used with solid-state light sources (LEDs). 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. Finally, the high frequency (i.e. >2 kHz) of the modulation results in the users perception of consistent intensity and smooth transitions.
The potential applications for the invention are many and varied. A system using a single channel could be used in any commercial or residential lighting application requiring the ability to dim LEDs. Systems utilizing multiple channels have the additional ability to be used in color-mixing applications (allowing the user to create custom colors) or to customize color temperatures, such as cool and warm whites. Both single and multi-channel light source systems could be used to provide variable intensity and/or color in such lighting applications as restaurants, theme parks, museums, hotels, and retail.
This application claims the benefit of U.S. Provisional Application No. 61/206,123, filed on 28 Jan., 2009, under 35 U.S.C. §119(e), which is hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61206123 | Jan 2009 | US |
