Patent Application
20090072759
The present invention relates to a method for dimming multiple lamps and particularly to a method to control and adjust the luminosity of a plurality of light sources.
A conventional liquid crystal display (LCD) requires a backlight module to serve as the light source. The backlight module generally includes a plurality of lamp modules each consists of a plurality of cold cathode fluorescent lamps (CCFLs). The number of the lamp modules may increase or decrease depending on the size of the LCD. The conventional lamp activating circuit includes a pulse modulation unit to generate a duty cycle signal to control operation of a power switch unit, then to regulate the tube current flowing through the lamp module, thereby to adjust the luminosity of the CCFLs. While the conventional backlight module changes the luminosity of the lamp by altering the tube current through regulation of the duty cycle of the power switch, to dim the light has to reduce the tube current. But the tube current has a lower limit while the CCFL is functioning. If the tube current drops below the lower limit two ends of the CCFL will have uneven brightness. This uneven brightness becomes more serious as the tube current drops even more. Hence there is a limited range to adjust the luminosity by regulating the tube current. In some special applications (such as sailing on the sea or camping outdoors at night) too much brightness is not desirable. Hence there is a need to provide an improved method to extend the dimming range downwards so that the products used the lamp module can be adjusted to a lower luminosity to suit the special environments.
In view of the problems occurred to the conventional technique that have a lower limit to adjust the luminosity of a light source and a luminosity adjustment range not meeting the requirement of special environments, the primary object of the present invention is to provide a circuit structure to expand the luminosity adjustment range of the light source.
The present invention provides a method for dimming multiple lamps. The method includes: getting a brightness range of a lighting area which has at least two light sources, getting a dimming range of the light sources, setting the brightness of the lighting area, determining the dimming value of each light source, and defining different dimming values of at least two light sources. A luminosity adjustment upper limit and a luminosity adjustment lower limit of the individual light sources are obtained. After the brightness of the lighting area is set, the dimming value of each light source is determined to form the brightness of the lighting area through the two light sources of different brightness. A circuit is provided to implement the method, which includes: a dimming signal source, a duty voltage regulation unit and a switch unit coupled in parallel with the duty voltage regulation unit. The dimming signal source generates a dimming signal proportional to the dimming range of the light source. The duty voltage regulation unit receives the dimming signal and outputs a voltage regulation signal to a plurality of power transformation units which receive electric power from a power source. The voltage regulation signal controls the amount of power output from the power transformation units to the light sources. The switch unit is connected to the dimming signal source and sets a different cutoff voltage value for each power transformation unit. The voltage of the dimming signal and the cutoff voltage are compared. When the voltage of the dimming signal is lower than one cutoff voltage a corresponding power transformation unit is turned off. Thus the dimming signal regulates the amount of power output to the light source and at the same time also controls asynchronous ON/OFF of the power transformation units. Through the sum of multiple light sources the brightness of the lighting area can be set.
The foregoing, as well as additional objects, features and advantages of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.
The present invention provides a method for dimming multiple lamps and aims to control the brightness of a lighting area which has at least two light sources. The method includes steps A through D as follow: A. getting a brightness range of a lighting area; B. getting a dimming range and brightness of the light sources; C. setting the brightness of the lighting area; and D. determining the dimming value of each light source. Refer to
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Table 1 shows that due to the lighting sources 8a, 8b and 8c have a luminosity adjustment lower limit because of their operation condition restriction, their luminosity adjustment lower limit is set to 50%. The switch unit 5 also sets the cutoff voltage value of each power transformation unit 7 below the adjustment lower limit. Hence when the dimming signal is adjusted output power of the power transformation units A 7a, B 7b and C 7c also are regulated synchronously to adjust simultaneously the brightness of the light sources 8a, 8b and 8c. When the light sources 8a, 8b and 8c have reached the luminosity adjustment lower limit, and the dimming signal is adjusted further downwards; if the dimming signal is lower than the cutoff voltage value of each power transformation unit 7, the power transformation units A 7a, B 7b and C 7c and their corresponding light sources 8a, 8b and 8c are turned off sequentially so that the effective dimming range of the lighting area can reach 35% or 20% of the maximum luminosity. Another more complicated embodiment is shown in Table 2 below:
The embodiment shown in Table 2 is based on a set brightness base value. When the brightness of the lighting area is greater than or equal to the brightness base value, the dimming values of the lighting sources 8a, 8b and 8c are set equal, namely the dimming value of each power transformation unit 7 is adjusted simultaneously. When the brightness of the lighting area is smaller than the brightness base value (the embodiment shown in Table 2 sets the brightness base value at 60% of the dimming ratio of each light source 8), then the dimming values of the light sources 8a, 8b and 8c and the ON/OFF sequences thereof are adjusted asynchronously. Therefore the effective dimming range of the lighting area can be extended.
The embodiments set forth above serve only for illustrative purpose, and are not the limitation of the invention. The brightness of the light sources 8 can be equal to or greater than the luminosity adjustment lower limit. The light source 8 connected to the power transformation unit 7 may be a single or multiple light emitting diode, hot cathode lamp, CCFL or gas discharge lamp. Thus modifications of the disclosed embodiments of the invention as well as other embodiments thereof may occur to those skilled in the art. Accordingly, the appended claims are intended to cover all embodiments which do not depart from the spirit and scope of the invention.
