The entire disclosure of Taiwan, R.O.C. Patent Application No. 096146430, filed Jun. 12, 2007, is incorporated herein by reference.
1. Field of the Invention
The present invention generally relates to a constant power driving-and-controlling method for lighting elements, and more particularly to a constant power feedback control method for stably driving lighting elements so as to vanish the disturbance of the application that may occur. In conditions such as the changing environment temperature, the unstable power source, or the differences of the electrical characteristics of the lighting elements by different production lots, the effects on the input power of the lighting elements may cause disturbance, for example, the illumination of the lighting elements may become too high or too low, or the lighting elements may be damaged.
2. Description of the Prior Art
Because of the many advantages of LEDs such as small volume, low input power, long lifetime, low cost and so on, the conventional lighting devices are replaced by LEDs gradually; moreover, a lot of new applications of LEDs are also produced.
Each LED is composed of an N type semiconductor and a P type semiconductor. The resistance of P-N junction (node) between the N type semiconductor and the P type semiconductor is very sensitive to the environment temperature. Therefore, the environment temperature influences the output illumination of the LED. When the environment temperature changes, the input power of the LED may become too high, causing excessive output illumination of the LED and thus overheating the LED Alternatively, the input power of the LED may become too low, causing the insufficient output illumination of the LED. For example, when the environment temperature increases, the resistance of P-N junction decreases, it is easy to cause the LED to have a high operating power and thus result in the overheated LED and the LED becomes overheated, then the lifetime of the LED is shortened. When the environment temperature decreases, the resistance of P-N junction increases, giving the LED a low operating power, resulting in insufficient output illumination of the LED to reach the required illumination. Furthermore, for different types of LEDs or the LEDs produced in different times, the resistances vary because of the material and process differences. Even when the LEDs are driven by a constant current, the output illumination of the LEDs could also vary due to different production lots. The excessive or insufficient illumination of the LEDs causes disturbances in the application.
Accordingly, a need has arisen to propose a novel constant power driving-and-controlling method for LEDs, so as to reduce the effects of the environment temperature on the input power of the LEDs, protect and extend the lifetime of the LEDs, and moreover, to stabilize the output illumination regardless of the effects of the environment temperature and the difference of the electrical characteristics of the LEDs.
The present invention has been made in order to provide a constant power driving-and-controlling method for lighting elements so as to reduce the effects of the environment temperature on the input power of the lighting elements, and reduce the effects of the unstable input voltage or current on the input power of the lighting elements. In addition to protecting the lighting elements and extend the lifetime of the lighting elements, the present invention also stabilizes the output illumination of the lighting elements.
In order to achieve the above object, the present invention provides a constant power driving-and-controlling method for lighting elements so as to stably drive solid state lighting elements. Measuring the input power of lighting elements by a power measuring device then controlling the input power of the lighting elements by a feedback controller, the goal to stabilize the input power of the lighting elements and to eliminate the effects of the environment temperature and the difference of the electrical characteristics of the lighting elements on the input power is achieved.
The detailed description of the present invention will be discussed in the following embodiments, which are not intended to limit the scope of the present invention, but can be adapted for other applications.
The DC input voltage VDC of LEDs 12 is provided by an AC/DC converter (adapter) 14. The AC/DC converter 14 is used to transform an AC voltage Vac, for example, an AC voltage of city electrical power to a DC electrical power source which has a DC voltage VDC.
In this embodiment, the constant power driving-and-controlling method 100 for lighting elements includes a power measuring device (sensor) 16, the power measuring device 16 is connected to LEDs 12 respectively to measure the input power P of each LED 12. In this embodiment, a current measuring device 160 is (serially) connected to the input ends of LEDs 12 for measuring the current I of LEDs 12; a voltage measuring device 162 is (parallel) connected to the input ends of LEDs 12 for measuring the DC voltage VDC. The current I measured by the current measuring device 160 and the DC voltage VDC measured by the voltage measuring device 162 are both input to the multiplier 164 for multiplying the current by the input voltage so as to get the input power P of LEDs. The multiplier 164 of this embodiment is based on the theory P=V×I.
The power P measured by the power measuring device 16 is fed back returned to a controller 18, a output signal of the controller 18 is used to control the AC/DC converter 14. For example, when the environment temperature changes; the input power P changes. The feedback controller 18 changes the output signal according to a pre-set power value Pset so as to change the DC voltage VDC and the current passing through the LEDs, and stabilize the input power of the LED 12 by controlling a adjustable element (variable resistance) of the AC/DC converter 14. Whereby, the constant power driving-and-controlling apparatus 100 is able to make the output illumination of the LED stabilized in different environment temperatures.
Further included in this embodiment is a substrater 180 for obtaining a difference value between the pre-set reference power value Pset and the power P measured by the power measuring device 16. The difference value is inputted to a controller 182 for controlling the output DC voltage VDC of the AC/DC converter 14 according to the difference value, until the power P of LEDs 12 equals the pre-set reference power value Pset. For example, when the difference value is negative, the AC/DC converter 14 would undergo controlling to decrease the DC voltage VDC; on the contrary, when the difference value is positive, the AC/DC converter 14 would be controlled to increase the DC voltage VDC. The controller 182 can be a circuit or a controller controlled by software such as a microprocessor. In other embodiments, the power P measured by the power measuring device 16 is directly input to the controller without the substrater 180. According to the power P, a corresponding output for the AC/DC converter 14 is directly produced, for example, by a table. Although the pre-set reference power value Pset mentioned-above is a fix value, it is also possible to dynamically adjust the pre-set reference power value Pset by a controller or other elements according to different applications so as to adjust the input power of the LEDs for adjusting the output illumination.
In this embodiment, the current measuring device 160 and the voltage measuring device 162 include a signal processor respectively. The signal processors transform the switching of the DC current I measured and the DC voltage VDC measured to continuous average signals respectively. Then the continuous average signals are both input to the multiplier 164 for multiplying the average current by the average voltage so as to get the average input power P. The average power P measured by the power measuring device 16 is fed back to a feedback controller 19 respectively.
The feedback controller 19 includes a substrater 190 for accquiring a difference value between the pre-set reference power value Pset and the power P measured by the power measuring device 16. The difference value is inputted to a controller 192, then a duty cycle controlling signal D is produced according to the difference value to control the switch device 191 and the lighting of the LEDs 12. Whereby, the input power of the LEDs is stabilized, and the output illumination becomes stable because of the constant power driving-and-controlling method 200 for lighting elements.
Similar to the foregoing embodiments, the controller 192 can be a circuit or a controller which is controlled by software such as a microprocessor. The power P measured by the power measuring device 16 can be directly inputted to the controller without the substrater 190. According to the power P, a corresponding duty cycle controlling signal for the switch device 191 is directly produced, for example, by a table.
What is different from the embodiment shown in
Using the embodiments of the present invention described above, it is possible to reduce the impact of the environment temperature on the input power of the lighting elements, reduce the effects of the unstable input voltage and current on the input power of the lighting elements, and eliminate the disturbance of application such as excessive or insufficient illumination of the lighting elements, or damages to the lighting elements due to changing electrical characteristics of the lighting elements from different production lots, which might have effects on the input power of the lighting elements. Whereby protect the lighting elements and extend the lifetime of the lighting elements, moreover, stabilize the output illumination of the lighting elements.
Although specific embodiments have been illustrated and described, it will be appreciated by those skilled in the art that various modifications may be made without departing from the scope of the present invention, which is intended to be limited solely by the appended claims.
Number | Date | Country | Kind |
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096146430 | Dec 2007 | TW | national |