Abstract:
An apparatus and its corresponding method for switching a light source are provided. The apparatus includes a light sensor, a decision device and a light source. The light sensor senses the ambient luminance and outputs a sensing signal to indicate whether the luminance is greater than a predetermined quantity. The decision device is connected to the light sensor. It receives a switching signal and outputs a lighting signal according to the sensing signal and the switching signal. The light source is coupled to the decision device and is activated whenever the lighting signal demands light.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims the priority benefit of Taiwan application serial no. 941 03013, filed on Feb. 1, 2005. All disclosure of the Taiwan application is incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention generally relates to an apparatus and method for switching a light source by using a light sensor. And especially to an apparatus and method for switching a light source by using a light sensor to judge whether or not a light source should be activated. 
   2. Description of Related Art 
   In the conventional keyboard of a mobile telephone, light emitting diode (i.e. LED) is generally utilized for the background light design. In addition, the lighting time and occasion are fixed regardless under sun light or in a dark room. However, when a user is in a sufficient light environment, it is not necessary to have the background light LED of the keyboard activated. Since the LED is not switched off at the time, the mobile telephone consumes a great amount of power. The communication time and standby period of the mobile telephone are therefore affected. Nowadays, due to the design trend of a mobile phone being light, thin and small, the volume and capacity of the battery can not be unlimitedly increased. The prior art fixed light emitting method is disadvantageous in the aspect of power consumption. 
   Accordingly, we need a better method to solve the above-mentioned problem so as to avoid power waste under the sufficient light environment. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide an apparatus and method for switching a light source. The present invention aims to disable the light source from emitting light under a sufficient light environment so to avoid power waste. When the present invention is utilized to the mobile telephone and other handy electrical devices, the power of the battery will be used with utmost efficiency without unnecessary waste. Further, the communication hours and the standby period can be extended so that to accord with the recent principle of light, thin, small and long standby period. Hence, the design flexibility and production practicability can be improved. When the present invention is applied to general light source, it also can achieve the advantages of saving electric power and lengthen the lifetime of light sources. 
   In order to achieve the above mentioned objects and other objects, the present invention provides an apparatus for switching a light source. The apparatus comprises a light sensor, a decision device and a light source. The light sensor senses the ambient luminance and outputs a sensing signal to indicate whether the luminance is greater than a predetermined value. The decision device is coupled to the light sensor, receives a switching signal and outputs a lighting signal according to the switching signal and the sensing signal. The light source is coupled to the decision device and decides whether or not to emit light according to the lighting signal. 
   In accordance with the above mentioned apparatus for switching a light source in a preferred embodiment of the present invention, when the sensing signal is at a logic high voltage, it means that the luminance is greater than the predetermined value. 
   In accordance with the above mentioned apparatus for switching a light source in the preferred embodiment of the present invention, the above mentioned light sensor further comprises a direct current voltage source, a ground and an ambient light sensor. Wherein, the voltage of the direct current voltage source is at a logic high voltage, the voltage of the ground is at a logic low voltage. The light sensor is coupled among the direct current voltage source, the ground and an output end of the light sensor; connects the direct current voltage source and the output end when the luminance is greater than the predetermined value so that the light sensor outputs the logic high voltage. Contrarily, the light sensor disconnects the direct current voltage source and the output end when the luminance is less than or equal to the predetermined value so that the light sensor outputs the logic low voltage. 
   In accordance with the above mentioned apparatus for switching a light source in a preferred embodiment of the present invention, when the luminance is greater than the predetermined value, the decision device outputs a lighting signal which indicates that the light source should not emit light. When the luminance is less than or equal to the predetermined value, the decision device directly outputs the switching signal as the lighting signal. 
   In accordance with the above mentioned apparatus for switching a light source in the preferred embodiment of the present invention, when the lighting signal is at the logic high voltage, it indicates that the light source should not emit light. 
   In accordance with the above mentioned apparatus for switching a light source in the preferred embodiment of the present invention, the above mentioned decision device further comprises a direct current voltage source and an analog switch. Wherein, the voltage of the direct current voltage source is at the logic high voltage. The analog switch is coupled between the direct current voltage source and the output end of the decision device; receives the lighting signal and the switching signal; connects the direct current voltage source and the output end when the luminance is greater than the predetermined value so that the decision device outputs the lighting signal with the logic high voltage; and connects the switching signal and the output end when the luminance is less than or equal to the predetermined value so that the decision device directly outputs the switching signal as the lighting signal. 
   In accordance with the above mentioned apparatus for switching a light source in the preferred embodiment of the present invention, the light source emits light when the lighting signal is at logic low voltage. 
   In accordance with the above mentioned apparatus for switching a light source in the preferred embodiment of the present invention, the above mentioned decision device further comprises a direct current voltage source, a switching device and a light emitting diode (i.e. LED). Wherein, voltage of the direct current voltage source is at the logic high voltage. The switching device is coupled to the direct current voltage source; receives the lighting signal; turned on when the lighting signal is at the logic low voltage; outputs the voltage of the direct current voltage source. The LED is coupled to the switching device and emits light when the output of the switching device is at logic high voltage. 
   In accordance with the above mentioned apparatus for switching a light source in the preferred embodiment of the present invention, the above mentioned switching device is a PMOS transistor. 
   In another view, the present invention provides a method for switching a light source. The method comprises the following steps: first, sense an ambient luminance; further, disable the light source from emitting light when the luminance is greater than a predetermined value; and decide whether or not the light source should emit light according to a switching signal when the luminance is less than or equal to the predetermined value. 
   In accordance with the description of the preferred embodiments in the present invention, the present invention utilizes the light sensor to sense ambient luminance. When there is sufficient ambient light, the light source will be switched off so to disable it from emitting light. Therefore, the present invention can eliminate unnecessary waste of energy and achieve the advantages of saving electric power and lengthen the lifetime of light sources. 
   The above is a brief description of some deficiencies in the prior art and advantages of the present invention. Other features, advantages and embodiments of the invention will be apparent to those skilled in the art from the following description, accompanying drawings and appended claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a drawing schematically showing a view of a circuit of an apparatus for switching a light source according to an embodiment of the present invention. 
       FIG. 2  is a drawing schematically showing a view of a flow chart of a method for switching a light source according to an embodiment of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The following is a preferred embodiment for describing an apparatus for switching a light source according to the present invention. 
     FIG. 1  is a drawing schematically showing a circuit diagram of an apparatus for switching a light source according to an embodiment of the present invention. Wherein, the circuit comprises a light sensor  101 , a decision device  102  and a light source  103 . In brief, the light sensor  101  senses the ambient luminance and outputs a sensing signal  104  to indicate whether the luminance is greater than a predetermined value. In the embodiment, the predetermined value is about 51 lux. The decision device  102  is coupled between the light sensor  101  and the light source  103 , receives a switching signal  105  and the sensing signal  104  and outputs a lighting signal  106  according to these two signals. The light source  103  is coupled to the decision device  102  to receive the lighting signal  106  and decides whether or not it emits light according to the lighting signal  106 . 
   The light sensor  101  comprises a direct current voltage source  130 , a ground  140 , an ambient light sensor  107  and a resistor  150 . The direct current voltage source  130  provides a voltage with a logic high voltage. The ground  140  provides a voltage with a logic low voltage. The ambient light sensor  107  is coupled among the direct current voltage source  130 , the ground  140  and the output end of the light sensor  101 . The ambient light sensor  107  senses the ambient luminance, connects the direct current voltage source  130  and the above mentioned output end when the luminance is greater than the predetermined value so that the light sensor  101  outputs the sensing signal  104  with the logic high voltage. When the sensed luminance is less than or equal to the predetermined value, the ambient light sensor  107  disconnects the direct current voltage source  130  and the output end so that the light sensor  101  outputs the sensing signal  104  with the logic low voltage. 
   The decision device  102  comprises direct current voltage sources  131  and  133 , an analog switch  108 , a ground  141  and a resistor  151 . The direct current voltage source  131  provides a voltage with a logic high voltage. The analog switch  108  is coupled between the direct current voltage source  131  and the output end of the decision device  102 ; receives the sensing signal  104  via the line  121 ; receives the switching signal  105  via the line  122 ; and decides the output voltage of the lighting signal  106 . Wherein, the switching signal  105  is from the user&#39;s interface, for example, a key of the keyboard of the mobile telephone, which the key is used to switch on the light source of the background light. When the luminance is greater than the above mentioned predetermined value, it means that the sensing signal  104  is at the logic high voltage. The analog switching  108  will connect the lines  120  and  123  so that the decision device  102  outputs the lighting signal  106  with logic high voltage. When the luminance is less than or equal to the predetermined value, it means that the sensing signal  104  is at the logic low voltage. The analog switching  108  will connect the lines  122  and  123  so that the decision device  102  directly outputs the switching signal  105  as the lighting signal  106 . 
   The light source  103  comprises a direct current voltage source  132 , a switching device  109 , an LED  110 , a ground  142  and resistors  152  and  153 . The direct current voltage source  132  provides a voltage with a logic high voltage. The switching device  109  is coupled between the direct current voltage source  132  and the LED  110  to receive the lighting signal  106 . When the lighting signal  106  is at the logic low voltage, the switching device  109  is turned on and outputs the logic high voltage from the direct current voltage source  132  so that the LED emits light. In the embodiment, the switching device  109  is a PMOS (p-channel metal oxide semiconductor) transistor which receives the lighting signal  106  with the gate. 
   Generally speaking, in a sufficient light environment, the ambient luminance is greater than the predetermined value. The sensing signal  104  will be at logic high voltage so that the light signal  106  of the output of the decision device  102  is also at logic high voltage. At this point, the PMOS transistor  109  will disable the direct current voltage source  132  and the LED  110 . No matter what voltage the switching signal  105  is at, the LED  110  will not emit light so power waste can be avoided. Whereas, when the light is insufficient, the ambient luminance will be less than or equal to the above mentioned predetermined value, the sensing signal  104  will be at logic low voltage. Accordingly, the decision device  102  directly outputs the switching signal  105  to the gate of the PMOS transistor  109 . Whether or not the LED emits light depends on the voltage of the switching signal  105 , which depends on the user&#39;s action. 
   In addition to the above mentioned apparatus for switching a light source, the present invention also provides a corresponding method for switching a light source which is described with an embodiment as follows. 
     FIG. 2  is a drawing schematically showing a flow chart of a method for switching a light source according to an embodiment of the present invention. First, step  202  senses the ambient luminance. Further, step  204  judges whether or not the luminance is greater than a predetermined value. In the embodiment, the predetermined value is about 51 lux. If the luminance is greater than the predetermined value, step  206  will be carried out to disable the light source from emitting light. Otherwise, step  208  is performed to decide whether or not the light source should emit light according to the switching signal from the user. 
   In summary, under a sufficient light environment, the apparatus and its corresponding method for switching a light source in the present invention disable the light source from emitting light so as to avoid power waste. When the present invention is utilized to a mobile telephone and other handy electrical devices, the power of the battery will be used with utmost efficiency without unnecessary waste. Further, the communication and standby period can be extended. The present invention accords with the recent principle of light, thin, small and long standby period. Therefore, the design flexibility and production practicability can be increased. When the present invention is utilized to general light source, it also can achieve the advantages of saving electric power and lengthen the lifetime of light sources. 
   The above description provides a full and complete description of the preferred embodiments of the present invention. Various modifications, alternate construction, and equivalent may be made by those skilled in the art without changing the scope or spirit of the invention. Accordingly, the above description and illustrations should not be construed as limiting the scope of the invention which is defined by the following claims.