Abstract:
An apparatus for prolonging lamp lifetime by reducing luminance of a least one lamp ( 5 ) in phases includes an image signal outputting unit ( 1 ), a scaler ( 2 ), and a Microprogrammed Control Unit (MCU) ( 4 ). The MCU further includes a CPU ( 41 ), a timer ( 42 ), and a memory ( 43 ). The image signal outputting unit outputs image signals to the scaler. The MCU detects in real-time statuses of the image signals being input to the scaler. The timer records each elapsed time “Tn” during which no image signal is input to the scaler. The CPU compares the elapsed time “Tn” with preset times stored in the memory, and sends a control signal to the scaler according to the comparison result. The scaler generates PWM waves with a corresponding duty cycle according to the control signal, in order to control the luminance of the lamp. A related method for prolonging lamp lifetime is also provided.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to apparatuses and methods that can prolong the lifetime of at least one electric lamp, and particularly to an apparatus and method which can prolong the lifetime of at least one Liquid Crystal Display (“LCD”) backlight lamp.  
         [0003]     2. Related Art of the Invention  
         [0004]     Images displayed by an LCD are produced by many liquid crystal molecules which do not emit light themselves. Rather, in a typical LCD, one or more high intensity lamps in a backlight module of the LCD illuminate the liquid crystal molecules. For example, one or more cold cathode fluorescent lamps may be employed. The high intensity lamps gradually age over time, which can result in a yellow display. To avoid yellowing and to prolong the lifetime of the lamps, users can adjust the luminance of the lamps to a reduced level, and/or simply turn off the lamps when the LCD is not actually being used.  
         [0005]     The technology of prolonging the lifetime of lamps includes power management by way of an associated computer. If no input from a user is received by the computer over a short period of time, the computer automatically shuts off the lamps. Nowadays, computer manufacturers provide shortcut keying to facilitate users in turning off the lamps. In particular, when a user wants to shut off the lamps for a short moment, the user need only press the shortcut keys provided by the computer manufacturer.  
         [0006]     However, turning off the lamps in a very short time also wears out the lamps. The sharp changes of current passing through the lamps damage the fluorescent powder of the lamps, and can age the lamps prematurely.  
         [0007]     Thus there is a need for an apparatus and method which can not only shut off lamps when they are not needed, but also avoid the sharp changes of current passing through the lamps.  
       SUMMARY OF THE INVENTION  
       [0008]     Accordingly, a main objective of the present invention is to provide an apparatus and method which can reduce the unneeded luminance of at least one lamp in phases and prolong the lifetime of the lamp.  
         [0009]     To accomplish the above objective, an apparatus for prolonging lamp lifetime (“the apparatus”) is provided herein. The apparatus is connected to at least one lamp in order to control its illumination. The apparatus comprises an image signal outputting unit, a scaler, an inverter, and a Microprogrammed Control Unit (MCU). The image signal outputting unit is for outputting image signals to the scaler. The scaler is for receiving the image signals from the image signal outputting unit, and generating Pulse Width Modulation (PWM) waves with different duty cycles. Such PWM waves are inverted to alternating current with a different intensity to adjust the current of a lamp, and therefore control the luminance of the lamp. The MCU comprises a Central Processing Unit (CPU), a timer, and a memory. The timer is used for recording an elapsed time during which no image signal is input to the scaler. The memory is used for storing a plurality of preset times and preset percentages. Each preset percentage indicates a ratio of corresponding reduced luminance of the lamp to normal luminance of the lamp. The CPU is used for detecting statuses of the image signals being input to the scaler, obtaining the elapsed time recorded by the timer, comparing the elapsed time with the preset times stored in the memory, and generating control signals to control the scaler. The control signals control the scaler to generate PWM waves with corresponding duty cycles, and PWM waves with a corresponding duty cycle adjust the luminance of the lamp to a corresponding intensity. Such adjustment may be recovering the lamp to a normal luminance, or reducing the luminance to a preset percentage of the normal luminance.  
         [0010]     Further, the present invention provides a method for prolonging lamp lifetime, the method comprising the steps of: (a) detecting in real time statuses of image signals being input to a scaler; (b) starting a timer to record an elapsed time during which no image signal is being input to the scaler; and (c) reducing luminance of a lamp in phases.  
         [0011]     Step (c) comprises: (c1) determining in real time whether the elapsed time timed by the timer reaches a preset time; (c2) controlling the scaler to generate PWM waves with a corresponding duty cycle if the elapsed time reaches the preset time, wherein the PWM waves are used for reducing the luminance of the lamp to a preset percentage of normal luminance; (c3) maintaining the lamp at a current luminance and continuing to record the elapsed time if the elapsed time has not reached any particular time; and (c4) continuing to detect in real time the statuses of the image signals being input to the scaler.  
         [0012]     These and other objects, advantages and novel features of the present invention will be drawn from the following detailed description of a preferred embodiment and method in conjunction with the attached drawings, in which: 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a block diagram of hardware infrastructure of an apparatus for prolonging lamp lifetime in accordance with a preferred embodiment of the present invention;  
         [0014]      FIG. 2  is a flowchart of a preferred method for operating the apparatus of  FIG. 1 ;  
         [0015]      FIG. 3  is a flowchart of details of one step of  FIG. 2 , namely reducing the luminance of a lamp in phases; and  
         [0016]      FIG. 4  is a graph of luminance of a lamp varying according to elapsed time of a timer of the apparatus of  FIG. 1 , showing the luminance of the lamp being reduced in three phases according to the preferred method of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]      FIG. 1  is a block diagram of hardware infrastructure of an apparatus for prolonging lamp lifetime (hereinafter “the apparatus”) in accordance with the preferred embodiment. The apparatus is connected to one or more lamps  5  in order to control their illumination. For simplicity, only one lamp  5  is shown in  FIG. 1 , and only one lamp  5  will be described hereinafter. Nevertheless, the description is not to be construed as limiting the invention to any particular number of lamps  5 . The apparatus comprises an image signal outputting unit  1 , a scaler  2 , an inverter  3 , and a Microprogrammed Control Unit (MCU)  4 . The image signal outputting unit  1  is used for outputting image signals to the scaler  2 . The scaler  2  is for receiving the image signals from the image signal outputting unit  1 , and generating Pulse Width Modulation (PWM) waves with different duty cycles. In the preferred embodiment, such PWM waves are then inverted to alternating current with a different intensity, in order to adjust the current of the lamp  5  and therefore control the luminance of the lamp  5 . The MCU  4  is used for detecting statuses of the image signals being input to the scaler  2 , and for controlling the scaler  2  to generate PWM waves with different duty cycles according to the statuses of the image signals being input to the scaler  2 . The MCU  4  comprises a Central Processing Unit (CPU)  41 , a timer  42 , a memory  43 , and a plurality of input/output (I/O) ports  44 .  
         [0018]     Both the timer  42  and the memory  43  are connected to and controlled by the CPU  41 . The timer  42  is used for recording an elapsed time T during which no image signal is input to the scaler  2 . The memory  42  may be a RAM (random-access memory), a ROM (read-only memory), or any other nonvolatile memory such as a PROM (programmable read-only memory), an EPROM (erasable and programmable read-only memory), an EEPROM (electrically erasable programmable read-only memory) or a Flash memory. The memory  42  is for storing a plurality of preset times and preset percentages. Each preset percentage corresponds to a respective preset time. The number of preset percentages equals the number of phases in which the luminance of the lamp  5  is to be reduced. For example, if the luminance of the lamp  5  is to be reduced in N phases, the memory  42  stores N preset times (T 1 , T 2 , Tn) and N corresponding percentages (X 1  %, X 2 %, . . . , Xn %). Each preset percentage indicates a ratio of a corresponding reduced luminance of the lamp  5  to a normal luminance of the lamp  5 . Generally, the preset times (T 1 , T 2 , . . . , Tn) sequentially increase in value, while the preset percentages (X 1  %, X 2 %, . . . , Xn %) sequentially decrease in value. That is, T 1 &lt;T 2 &lt; . . . &lt;Tn, and X 1 %&gt;X 2 %&gt; . . . &gt;Xn %. When the elapsed time T recorded in the timer  41  reaches T 1 , the luminance of the lamp  5  is reduced to X 1 % of the normal luminance. When the elapsed time T reaches T 2 , the luminance of the lamp  5  is reduced to X 2 % of the normal luminance. Finally, when the elapsed time T reaches Tn, the luminance of the lamp  5  is reduced to Xn % of the normal luminance.  
         [0019]     The CPU  41  is used for detecting the statuses of the image signals being input to the scaler  2 , obtaining the elapsed time T recorded in the timer  41 , comparing the elapsed time T with the preset times stored in the memory  43 , and generating various control signals to control the scaler  2 . Each time the CPU  41  generates a control signal, the scaler  2  generates PWM waves with a particular duty cycle accordingly. The PWM waves are used to adjust the luminance of the lamp  5  to a corresponding intensity, such as recovering the luminance to the normal luminance, or reducing the luminance to a preset percentage of the normal luminance. According to the preferred embodiment, if the CPU  41  determines that no image signals are being input to the scaler  2 , the CPU starts the timer  42  to record an elapsed time T during which no image signal is input to the scaler  2 . If the elapsed time T reaches a preset time, the CPU  41  generates and sends a control signal (hereinafter referred to as “Control Signal I”) to the scaler  2 . The scaler  2  generates PWM waves with a duty cycle according to the Control Signal I, and adjusts the luminance of the lamp  5  to a corresponding preset percentage of the normal luminance. If the elapsed time T does not reach any preset time, the scaler  2  generates PWM waves having an unchanged duty cycle, thereby maintaining the luminance of the lamp  5  at the current luminance. If the CPU  41  determines that image signals are being input to the scaler  2  when the timer  42  is recording the elapsed time T, the CPU  41  generates another control signal (hereinafter referred to as “Control Signal II”) to the scaler  2 . The scaler  2  generates PWM waves with a corresponding duty cycle according to the Control Signal II, and recovers the luminance of the lamp  5  from a current luminance to the normal luminance.  
         [0020]     The I/O ports  44  are used for connecting the lamp  5  to the CPU  41 , and for enabling the CPU  41  to turn on and turn off the lamp  5 . The inverter  3  is used for inverting PWM waves to alternating current having a certain intensity, in order to control the luminance of the lamp  5 .  
         [0021]      FIG. 2  is flowchart of a preferred method for operating the apparatus. In step S 200 , the MCU  4  detects statuses of the image signals being input to the scaler  2 . In step S 201 , the CPU  41  determines whether there are image signals being input to the scaler  2 . If there are image signals being input to the scaler  2 , in step S 202 , the scaler  2  generates PWM waves with an unchanged duty cycle. This maintains the lamp  5  at the normal luminance, and the procedure is ended. If no image signal is being input to the scaler  2 , in step S 203 , the CPU  41  starts the timer  42  to record an elapsed time T during which no image signal is input to the scaler  2 . In step S 204 , the MCU  4  and the scaler  2  cooperate to reduce the luminance of the lamp  5  in phases (described in detail below in relation to  FIG. 3 ), whereupon the procedure is ended.  
         [0022]      FIG. 3  is a flowchart of details of step S 204  of  FIG. 2 , namely reducing the luminance of the lamp  5  in phases. In step S 300 , the MCU  4  detects in real time statuses of the image signals being input to the scaler  2  while the timer  42  is recording the elapsed time T. In step S 301 , the CPU  41  determines in real time whether there are image signals being input to the scaler  2 , according to the statuses of the image signals being input to the scaler  2 . If no image signal is being input to the scaler  2 , in step S 302 , the timer  42  continues recording the elapsed time T. In step S 303 , the CPU  41  compares in real time the elapsed time T with preset times stored in the memory  43 , and determines whether the elapsed time T has reached a particular preset time Tn. If the elapsed time T has reached the preset time Tn, in step S 304 , the CPU  41  generates a Control Signal I, and the scaler  2  generates PWM waves with a duty cycle according to the Control Signal I. The PWM waves are inverted to alternating current with a certain intensity by the inverter  3 . The luminance of the lamp  5  is thereby reduced to Xn % of the normal luminance, whereupon the procedure returns to step S 300  described above. If the elapsed time T has not reached the preset time Tn, then in step S 305 , the scaler  2  generates PWM waves having an unchanged duty cycle. This maintains the lamp  5  at its current luminance, whereupon the procedure returns to step S 300 .  
         [0023]     If the CPU  41  determines that there are image signals being input to the scaler  2  when the timer  42  is recording the elapsed time T, then in step S 306 , the CPU  41  generates a Control Signal II, and the scaler  2  generates PWM waves having a duty cycle according to the Control Signal II. The PWM waves are inverted to alternating current, and the luminance of the lamp  5  is recovered to the normal luminance. In step S 307 , the CPU  41  stops the timer  42  recording the elapsed time T, and initializes the timer  42  to zero.  
         [0024]      FIG. 4  is a graph of luminance variation of the lamp  5  when the luminance of the lamp  5  is reduced in three phases I, II, III. During all three phases I, II, III, it is assumed that the MCU  4  does not detect any image signal being input to the scaler  2 . In phase I, once the elapsed time T recorded by the timer  42  reaches a preset time T 1 , the luminance of the lamp  5  is reduced to X 1 % of the normal luminance. In phase II, once the elapsed time T recorded by the timer  42  reaches a preset time T 2 , the luminance of the lamp  5  is reduced to X 2 % of the normal luminance. In phase III, once the elapsed time T recorded by the timer  42  reaches a preset time T 3 , the luminance of the lamp  5  is reduced to X 3 % of the normal luminance. Generally, X 3 % is set to be zero. Once the luminance of the lamp  5  is reduced to zero at the end of phase III, the lamp  5  is maintained in a dormant state, which prolongs the lifetime of the lamp  5 . If, during any of the phases I, II, III, the MCU  4  detects any image signal being input to the scaler  2 , then the luminance of the lamp  5  is immediately recovered to the normal luminance, and the current process of phased reduction of the luminance of the lamp  5  is canceled.  
         [0025]     Although the present invention has been specifically described on the basic of a preferred embodiment and a preferred method, the invention is not to be construed as being limited thereto. Various changes and modifications may be made to the embodiment and method without departing from the scope and the spirit of the invention.