Patent Publication Number: US-2004056533-A1

Title: Power supply circuit

Description:
[0001] This Application claims priority to Taiwan Patent Application No. 091121847 filed Sep. 24, 2002.  
       FIELD OF INVENTION  
       [0002] The present invention relates to a power supply circuit of an electrical apparatus, such as projectors and LCD monitors. When the electrical apparatus switches to a power saving mode, a battery, instead of an AC/DC converter, is used as a DC power supply to reduce power consumption.  
       BACKGROUND OF THE INVENTION  
       [0003] A power supply, indispensable for any electrical apparatus, is used to covert an alternating current (AC) signal transmitted from a power plant to a direct current (DC) signal which can be utilized by the electrical apparatus. As FIG. 1 shows, a conventional electrical apparatus  100  includes a power supply circuit  113  and an electrical device  117 . An AC signal  101  flows into the power supply circuit  113  via an input terminal  103  and is converted to a DC signal  107  by an AC/DC converter  115  of the power supply circuit  113 . The DC signal  107  is then outputted, via an output terminal  105 , to the electrical device  117  as a power resource for use. However, there is always power consumption during the conversion. To pass the strict safety regulations, a conventional power supply circuit  113  needs to be re-designed to decrease the power consumption caused when the electrical apparatus  100  is in a power saving mode.  
       SUMMARY OF THE INVENTION  
       [0004] The present invention provides a power supply circuit having a battery, an AC/DC converter, a control circuit and two switches. One switch is connected to an input terminal of the power supply circuit, the AC/DC converter and the control circuit. The other switch is connected to the battery, the control circuit and an output terminal of the power supply circuit. When going into a power saving mode, an electrical device connected to the power supply circuit of the present invention sends a control signal to inform the control circuit. After receiving the control signal, the control circuit respectively turns off the switch connected to the input terminal and turns on the switch connected to the battery. Accordingly, there is no AC signal allowed to flow into the AC/DC converter and the DC power of the electrical device is supplied by the battery. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0005] The present invention will be clearly understood by referring to the detailed description as well as the attached figures:  
     [0006]FIG. 1 illustrates a power supply circuit of an electrical apparatus of the prior art;  
     [0007]FIG. 2 illustrates the power supply circuit of the present invention as the electrical apparatus is in a normal mode in accordance with the present invention; and  
     [0008]FIG. 3 illustrates the power supply circuit of the present invention as the electrical apparatus is in a power saving mode in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION  
     [0009] The present invention provides an electrical apparatus with a power supply circuit and an electrical device. The power supply circuit is configured to selectively supply a first and a second DC signal inputted as a power resource to the electrical device. The electrical device is configured to execute specific function(s). As FIG. 2 shows, the power supply circuit  113  includes an input terminal  103 , an output terminal  105 , a first switch  121 , a second switch  123 , an AC/DC converter  115 , a battery  200  and a control circuit  300 . The input terminal  103  is configured to input an AC signal  101  transmitted from a power plant. The output terminal  105  is configured to selectively output a DC signal  107 . The first switch  121  has a first end  120 , which is connected to the input terminal  103 , and a second end  122 . The AC/DC converter  115  has an input terminal connected to the second end  122  of the first switch  121 , and has an output terminal connected to the output terminal  105  of the power supply circuit  113 . The second switch  123  has a first end  124 , which is connected to the output terminal  105  of the power supply circuit  113 , and a second end  126 . The battery  200  is connected to the second end  126  of the second switch  123 . The control circuit  300  is configured to control the first switch  121  and the second switch  123 . When being in a normal mode, the electrical device  117  sends a first control signal  111  to the control circuit  300 . In response to the first control signal  111 , the control circuit  300  turns on the first switch  121  to electrically connect the input terminal  103  to the AC/DC converter  115 , and also turns off the second switch  123  to electrically disconnect the battery  200  and the output terminal  105 . Therefore, the AC signal  101  can flow inwards and then be converted to the first DC signal  107  by the AC/DC converter  115 .  
     [0010] On the other hand, as FIG. 3 shows, when being in a particular mode, the electrical device  117  of an electrical apparatus  400  sends a second control signal  119  to the control circuit  300 . In response to the second control signal  119 , the control circuit  300  turns off the first switch  121  to electrically disconnect the input terminal  103  and the AC/DC converter  115 , and also turns on the second switch  123  to electrically connect the battery  200  to the output terminal  105 . Hence, the power resource of the electrical device  117  now switches to the second DC signal  109  supplied by the battery  200  to the output terminal  105  of the power supply circuit  113 .  
     [0011] The electrical apparatus  400  in FIG. 3 may be a project or a monitor. When users stop using the electrical apparatus  400  for a while, the electrical apparatus  400  will enter a power saving mode automatically. The power consumption of the power saving mode is required to be low by safety regulations. When the control circuit  300  receives the second control signal  119 , the battery  200  directly supplies the second DC signal  109  to the electrical device  117  without undesired power consumption generated by the AC/DC converter  115 . Therefore, the aforementioned particular mode can be regarded as a power saving mode.  
     [0012] The above description of the preferred embodiments is expected to clearly expound the characteristics of the present invention but not expected to restrict the scope of the present invention. Those skilled in the art will readily observe that numerous modifications and alterations of the apparatus may be made while retaining the teaching of the invention. Accordingly, the above disclosure should be construed as limited only by the bounds of the claims.