1. Field of the Invention
The present invention generally relates to apparatus for controlling light emitting devices, and more particularly to apparatus for driving light emitting diodes with different spectrums by a feedback control system to produce different stable colors.
2. Description of the Prior Art
For the advantages of less volume, less input power, longer life and lower cost, light-emitting diodes (LEDs) are replacing conventional lighting devices, and novel applications thereof are emerging. For example, various colors could be generated by independently controlling the illuminance (or intensity) of two (or more) LEDs with distinct spectrum (or color) and mixing the color optically.
The LED is composed of N-type semiconductor and P-type semiconductor. The resistance of the interface (or node) between the N-type semiconductor and P-type semiconductor is susceptible to ambient temperature, and subsequently, the illuminance of the LED is likely to be affected by the resistance change. Specifically, the varying ambient temperature may result in an over-heated and over-lighted LED with high output, or alternately may result in an under-lighted LED with insufficient output. For example, in the constant-voltage driving mode when the ambient temperature rises, the interface resistance decreases, causing high operation power and heat for the LED and thus disadvantageously shortens the life of the LED; on the other hand, when the ambient temperature falls, the increased interface resistance causes low operating power for the LED, which renders the LED useless for its insufficient illuminance. Alternatively, in the constant-current driving mode, when the ambient temperature rises, the decreased interface resistance causes low operating power of the LED, which renders the LED useless for insufficient illuminance; and when the ambient temperature falls, the increased interface resistance causes high operating power and heat of the LED, which disadvantageously shortens the life of the LED. Further, the LEDs with different spectrums are susceptible to the ambient temperature with different degrees. Accordingly, it is difficult to precisely arrive at a required color by mixing the different spectrums.
For the foregoing reasons, a need has arisen to propose apparatus for controlling the LEDs that is capable of reducing the temperature affect on the LEDs, protecting to lengthen the life of the LEDs, stabilizing the output illuminance of the LEDs, and precisely mixing the colors of the LEDs.
In view of the foregoing, it is an object of the present invention to provide apparatus for controlling the LEDs, that is capable of reducing the temperature effects on the operating (or input) power of light emitting devices (such as LEDs), and reducing the unstable input voltage/current effects on the operating power of the light emitting devices. Accordingly, the present invention could protect and lengthen the life of the light emitting devices, stabilize the output illuminance of each light emitting device, and precisely mix the colors of the light emitting devices.
According to the object, the present invention provides apparatus for driving light emitting devices with different colors. The input powers of the light emitting devices are measured by power measuring devices, returned by feedback controllers to control the power input to the light emitting devices, and then individually configured by controlling the luminance of different spectrums, thus obtaining the desired colors.
The LEDs 12A and 12B are influenced by input DC (i.e., direct current), voltage VDC and ambient temperature Ta. The equivalent circuits of the LEDs 12A and 12B are shown in the figure, in which gain Gvi represents the function between the current flowing through the LEDs (12A and 12B) and the input DC voltage, and gain Gai represents the function between the current flowing through the LEDs (12A and 12B) and the ambient temperature.
The input DC voltages VDC to the LEDs 12A and 12B are provided by AC-to-DC (or AC/DC) converters (or adapters) 14A and 14B respectively. The AC/DC converters 14A and 14B convert the AC (i.e., alternating current) voltage Vac (such as the power voltage provided from indoor power outlet) into the DC voltage VDC.
The apparatus 100 according to the present embodiment includes two power measuring devices (or detectors) 16A and 16B, which are electrically coupled to the LEDs 12A and 12B for measuring the input power P of the LEDs 12A and 12B respectively. In the embodiment, taking the power measuring device 16A for example, a current measuring device 160A is coupled (in series) to one node of the LED 12A for measuring the current I of the LED 12A; and a voltage measuring device 162A is coupled (in parallel) to another node of the LED 12A for receiving and measuring the DC voltage VDC. The detected current I from the current measuring device 160A and the detected DC voltage VDC from the voltage measuring device 162A are inputted to a multiplier 164A whose resultant product represents the power P. With respect to another power measuring device 16B, the operation of its current measuring device 160B, voltage measuring device 162B, and multiplier 164B is the same as the power measuring device 16A. In the embodiment, the power measuring principle P=V×I is used in constructing the power measuring devices 16A and 16B.
The measured powers P from the power measuring devices 16A and 16B are inputted to the feedback controller 18A and 18B respectively, which generate output signals that further control the AC/DC converter 14A and 14B. For example, when the rising/falling ambient temperature changes the input power P of the LEDs 12A and 12B, the feedback controller 18A and 18B change their output signals according to a predetermined reference power Pset, and further control a digital variable resistor in the AC/DC converter 14A and 14B in order to change the generated DC voltage VDC and the current flowing through the LEDs (12A and 12B), thereby maintaining the input power, the output illuminance, and spectrum (or color) of the LEDs 12A and 12B. Therefore, the apparatus 100 could maintain the specific mixed color.
In the embodiment, taking the feedback controller 18A for example, a substractor 180A is coupled to receive the predetermined reference power Pset and the detected power P from the power measuring device 16A, and the resultant difference is inputted to a controller 182A, which controls the AC/DC converter 14A according to the resultant difference, until the power of the LED 12A is equal to the predetermined reference power Pset. For example, when the resultant difference is negative, the AC/DC converter 14A is controlled (by the controller 182A) to lower the DC voltage VDC; alternately, when the resultant difference is positive, the AC/DC converter 14A is controlled to raise the DC voltage VDC. The controller 182A may be a circuit, or a program-controlled controller (such as a microprocessor). With respect to another feedback controller 18B, the operation of its substractor 180B and controller 182B is the same as the feedback controller 18A. In other embodiments, the substractors 180A and 180B could be omitted, and the detected power P from the power measuring devices 16A and 16B are inputted into an individual or shared controller, which directly generates corresponding output via, for example, a look-up table, to the AC/DC converter 14A and 14B according to power P. In the present embodiment, the predetermined reference powers Pset of the feedback controllers 18A and 18B may be distinct or the same. The aforementioned predetermined reference powers Pset are fixed; however they could be dynamically adjusted at different time (or interval) by the controller (or other device) to change the illuminance of the LEDs 12A and 12B according to different applications, thereafter mixing the light to obtain dynamic color lighting.
The primary difference between the present embodiment and the embodiment of
In the present embodiment, each of the current measuring devices 160A and 160B and the voltage measuring devices 162A and 162B includes a signal processor that is capable of converting the detected switching current I and the direct voltage VDC into a continuous signal representing the average value, which is then respectively inputted to the multiplier 164A to generate the average input power P of the LEDs 12A and 12B. The measured powers P from the power measuring devices 16A and 16B are fed back to the feedback controller 19A and 19B respectively. Ta king the feedback controller 19A for example, a substractor 190A is coupled to it to receive a predetermined reference power Pset and the detected power P from the power measuring device 16A, and the resultant difference is inputted to a controller 192A, which generates a duty cycle control signal D to control the switch 191A and the light emitting of the LED 12A, thereby maintaining the input power, the output illuminance, and spectrum (or color) of the LED 12A. The apparatus 200 is then subjected to light mixing to obtain the desired color stably. With respect to another feedback controller 19B, the operation of its substractor 190B, switch 191B, and controller 192B is the same as the feedback controller 19A.
Similar to the previous embodiment, the controllers 192A and 192B may be circuits, or program-controlled controllers (such as microprocessors). The substractors 190A and 190B could be omitted, and the detected power P from the power measuring devices 16A and 16B are inputted into an individual or shared controller, which directly generates corresponding duty cycle control signals via, for example, a look-up table, to the switches 191A and 191B according to power P.
The primary difference between the present embodiment and the embodiment of
The embodiments discussed above are capable of reducing the temperature effects and the unstable input voltage/current effects on the operating (or input) power of the light emitting devices. Accordingly, the present invention could protect and lengthen the life of the light emitting devices, stabilize the output illuminance of the light emitting devices, and precisely mix the colors of the light emitting devices.
Although the 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.
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97102667 A | Jan 2008 | TW | national |
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20090189540 A1 | Jul 2009 | US |