Abstract:
A power conversion device includes a DC-to-DC conversion circuit that receives and processes a DC power input and supplies a DC output of a predetermined voltage level, an output connector receiving the DC output and having power terminals to transmit the DC output and a plurality of level-selecting terminals, a terminal device having counterpart power terminals and a plurality of counterpart level-selecting terminals, which engage the power terminals and the level-selecting terminals of the output connector, respectively, a feedback circuit coupled to the DC-to-DC conversion circuit and connected to each level-selecting terminal by a resistor having a predetermined resistance to provide a feedback signal to the DC-to-DC conversion circuit which in turn changes the voltage level of the DC output, and a display circuit, which is coupled to the output connector to display the voltage level of the DC output at the power terminals of the output connector.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates generally to a power conversion device, which can be made in the form of an adaptor, and in particular to a power converter comprising an output voltage level indicating device for indication and easy reading of selectable output levels of voltage.  
         [0003]     2. Description of the Prior Art  
         [0004]     Portable electronic appliances, such as mobile phone and notebook computer, play an important role in the modern world in doing business and society activities. Such portable appliances are often powered by built-in power sources, which must be constantly recharged in order to maintain operability of the portable appliances. Also, external powering is also available for most of the portable appliances, such as wall outlet, automobile electrical system including cigarette lighter socket and electrical socket regularly available in airplanes. Often the external powering must be converted by for example a conversion circuit made in the form of an adaptor before it can be supplied to the portable appliances.  
         [0005]     However, the portable appliances are often operated with different working voltages and for such a reason, the general consumers that own and use two or more different portable appliance must regularly bring two or more adaptors corresponding to those portable appliances. This complicates the use of the portable appliances and is very troublesome to the consumers. U.S. Pat. No. 6,628,535, issued to the present inventor, teaches a power conversion device that provides variable output voltage levels to different appliances or loads. The power conversion device of the &#39;535 patent comprises an output to which a terminal connector is selectively coupled. The terminal connector comprises a circuit comprised of resistors that generates a feedback signal to a control circuit of the power conversion device, inducing a corresponding voltage level at the output of the conversion device.  
         [0006]     Such a conventional power conversion device works well in supplying voltage of different levels to electronic appliances that operates with different working voltages. It, however, is still unclear to a user what voltage level is being output by the power conversion device when the device is powering an electronic appliance. This may cause problem to the user.  
         [0007]     Thus, the present invention is aimed to provide a power conversion device that overcomes the drawback of the conventional devices.  
       SUMMARY OF THE INVENTION  
       [0008]     An object of the present invention is to provide a power conversion device that selectively supplies output voltage of different levels to different electronic appliances and comprising indicating device that shows or indicates the output voltage level that is being supplied.  
         [0009]     Another object of the present invention is to provide a multi-output power conversion device comprising an indicating device that displays or indicates an output level for each output.  
         [0010]     To achieve the above objects, in accordance with the present invention, there is provided a power conversion device comprising a DC-to-DC conversion circuit that receives and processes a DC power input and supplies a DC output of a predetermined voltage level, an output connector receiving the DC output and having power terminals to transmit the DC output and a plurality of level-selecting terminals, a terminal device having counterpart power terminals and a plurality of counterpart level-selecting terminals, which engage the power terminals and the level-selecting terminals of the output connector, respectively, a feedback circuit coupled to the DC-to-DC conversion circuit and connected to each level-selecting terminal by a resistor having a predetermined resistance to provide a feedback signal to the DC-to-DC conversion circuit which in turn changes the voltage level of the DC output, and a display circuit, which is coupled to the output connector to display the voltage level of the DC output at the power terminals of the output connector. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The present invention will be apparent to those skilled in the art by reading the following description of preferred embodiments thereof, with reference to the attached drawings, in which:  
         [0012]      FIG. 1  is a perspective view of a power conversion device constructed in accordance with a preferred embodiment of the present invention with connection cables detached therefrom;  
         [0013]      FIG. 2  is a block diagram of a control circuit of the power conversion device of the present invention;  
         [0014]      FIG. 3  is a first embodiment of a voltage level indicating circuit in accordance with the present invention;  
         [0015]      FIG. 4  is a second embodiment of the voltage level indicating circuit in accordance with the present invention;  
         [0016]      FIG. 5  is a third embodiment of the voltage level indicating circuit in accordance with the present invention;  
         [0017]      FIG. 6  is a perspective view of a power conversion device constructed in accordance with another preferred embodiment of the present invention with connection cables detached therefrom; and  
         [0018]      FIG. 7  is a block diagram of a control circuit of the power conversion device illustrated in  FIG. 6 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]     With reference to the drawings and in particular to  FIG. 1 , a power conversion device constructed in accordance with the present invention, generally designated with reference numeral  100 , comprises a casing  1  that forms an input socket  11  with which a plug  21  of a power cord  22  is engageable. The power cord  22  has a proximal end forming the plug  21  and a remote end forming a plug connector  23  that is compatible to and engageable with a standard cigarette lighter socket provided in an automobile (both not shown). Thus, power from an electrical system of an automobile can be supplied by the power cord  22  to the power conversion device  100  of the present invention. The plug connector  23  can be configured to mate with a power socket provided in an airplane.  
         [0020]     The power conversion device  100  is provided with an alternative power cord  25  having opposite ends forming a plug  24  that is engageable with the input socket  11  of the casing  1  and a plug  26  for selective engagement with an electrical main, such as a wall outlet (not shown). Preferably, the plug  26  is of a universal design that is compatible with different types of wall outlet around the worlds, such as wall outlets of 110 and 220 volts.  
         [0021]     The casing  1  forms first and second output sockets  3 ,  4 , both supplying direct current outputs. Two extension cables  32 ,  42  are provided to respectively connect an electronic appliance (not shown) to the first and second output sockets  3 ,  4 . The first extension cable  32  has opposite ends forming a device-side plug  31  and an appliance-side connector  33 , respectively. The device-side plug  31  is engageable with the first output socket  3  and the appliance-side connector  33  is engageable with a first level-selecting terminal device  34 , which provides output voltage of V 1 +, V 1 − that is variable (to be further discussed hereinafter) to an electronic appliance powered by the power conversion device  100  via the first extension cable  32 . Preferably, the first extension cable  32  is releasably stowed in a cable-winding device (not labeled) to avoid entangling of the cable.  
         [0022]     Similarly, the second extension cable  42  has opposite ends forming a device-side plug  41  and an appliance-side connector  43 , respectively. The device-side plug  41  is engageable with the second output socket  4  and the appliance-side connector  43  is engageable with a second level-selecting terminal device  44 , which provides output voltage of V 2 +, V 2 − that is variable (to be further discussed hereinafter) to an electronic appliance powered by the power conversion device  100  via the second extension cable  42 . Preferably, the second extension cable  42  is releasably stowed in a cable-winding device (not labeled) to avoid entangling of the cable.  
         [0023]     The casing  1  further forms a third output socket  5  for powering an electronic appliance via a third extension cable  52 . The third extension cable  52  has opposite ends, respectively forming a device-side plug  51  that is engageable with the third output socket  5  and an appliance-side USB (Universal Serial Bus) plug  53  that supplies a constant direct current output of voltage V 3 +, V 3 − of for example 5 volts. Such a constant output can be used to power small-load appliance (not shown). Preferably, the third extension cable  52  is releasably stowed in a cable-winding device (not labeled) to avoid entangling of the cable.  
         [0024]     The casing  1  has a top face (not labeled) on which display means is formed to indicate/display the output voltage level of each level-selecting terminal device  34 ,  44 . For example, the display means may comprise a set of first indicators D 11 -D 16  associated with, and preferably adjacent to, the first output socket  3  for indicating/displaying the voltage output V 1 +, V 1 −, and set of second indicators D 21 -D 26  associated with, and preferably adjacent to, the second output socket  4  for indicating/displaying the voltage output V 2 +, V 2 −. A further indicator D 3  is arranged on the top face of the casing  1  for indicating normal/abnormal condition of the output voltage V 3 +, V 3 −. A power indicator D 4  is also provided on the top face of the casing  1  to indicate normal/abnormal input of power from an external power source through the input socket  11 .  
         [0025]     Also referring to  FIG. 2 , which shows a block diagram of a control circuit of the power conversion device  1 , the input socket  11  comprises direct current input terminals DC+, DC− and alternate current input terminals AC 1 , AC 2 , which are arranged to respectively receive electrical current from the plug  21  of the power cord  22  (DC input) and the plug  24  of the alternative power cord  25  (AC input) when the plugs  21 ,  24  are alternately inserted into the input socket  11 . The DC input terminals DC+, DC− are directly coupled to lines L 1 , L 2  of the control circuit, while the AC input terminals AC 1 , AC 2  are coupled to the lines L 1 , L 2  via a AC-to-DC conversion circuit  12 , which converts the AC input from the power cord  25  into DC power that is then applied to the line L 1 , L 2 . Indicator D 4  shows normal operation of power receiving through the power cords  22 ,  25 .  
         [0026]     The control circuit comprises first, second, and third DC-to-DC conversion circuits  35 ,  45 ,  54 , respectively associated with the first, second, and third output sockets  3 ,  4 ,  5 , all connected to the line L 1 , L 2  to receive power from the input socket  11 . With the device-side plug  31 ,  41 ,  51  of each extension cable  32 ,  42 ,  52  received in the associated output socket  3 ,  4 ,  5 , the first, second, and third DC-to-DC conversion circuits  35 ,  45 ,  54  are respectively and electrically connected to the first, second, and third appliance-side connectors  33 ,  43 ,  53 .  
         [0027]     The first appliance-side connector  33  comprises primary, power terminals V 10 +, V 10 − coupled to the first DC-to-DC conversion circuit  35 . A first resistor network  36  and a first feedback circuit  37 , which are connected in series, are connected between the first appliance-side connector  33  and the first DC-to-DC conversion circuit  35  in parallel to the connection between the primary terminals V 10 +, V 10 − and the first DC-to-DC conversion circuit  35 . The first feedback circuit  37  provides a first feedback signal Sfb 1  to the first DC-to-DC conversion circuit  35 . The first resistor network  36  is comprised of resistors R 11 , R 12 , R 13 , and R 14 , which are in turn connected to secondary, level-selecting terminals V 11 , V 12 , V 13 , and V 14  of the first appliance-side connector  33 . A first voltage display circuit  38  is connected to the secondary, level-selecting terminals V 11 , V 12 , V 13 , and V 14  of the first resistor network  36 .  
         [0028]     The first level-selecting terminal device  34  is comprised of primary and secondary terminals V′ 10 +, V′ 10 −, V′ 11 , V′ 12 , V′ 13 , and V′ 14 , which respectively engage the primary and secondary terminals V 10 +, V 10 −, V 11 , V 12 , V 13 , and V 14  of the first appliance-side connector  33 , when the first level-selecting terminal device  34  mates the first appliance-side connector  33 . By selective use of different jump connection between the secondary terminals V′ 11 , V′ 12 , V′ 13 , and V′ 14  and the primary terminal V′ 10 −, a different resistance is observed in the first resistor network  36 , which changes the first feedback signal Sfb 1  and thereby changes the output level of voltage at the output V 1 +, V 1 − of the first level-selecting terminal device  34 . The output level of voltage at output V 1 +, V 1 − is displayed on the first voltage display device  38 .  
         [0029]     Similarly, the second appliance-side connector  43  comprises primary, power terminals V 20 +, V 20 − coupled to second DC-to-DC conversion circuit  45 . A second resistor network  46  and a second feedback circuit  47 , which are connected in series, are connected between the second appliance-side connector  43  and the second DC-to-DC conversion circuit  45  in parallel to the connection between the primary terminals V 20 +, V 20 − and the second DC-to-DC conversion circuit  45 . The second feedback circuit  47  provides a second feedback signal Sfb 2  to the second DC-to-DC conversion circuit  45 . The second resistor network  46  is comprised of resistors R 21 , R 22 , R 23 , and R 24 , which are in turn connected to secondary, level-selecting terminals V 21 , V 22 , V 23 , and V 24  of the second appliance-side connector  43 . A second voltage display circuit  48  is connected to the secondary, level-selecting terminals V 21 , V 22 , V 23 , and V 24  of the second resistor network  46 .  
         [0030]     The second level-selecting terminal device  44  is comprised of primary and secondary terminals V′ 20 +, V′ 20 −, V′ 21 , V′ 22 , V′ 23 , and V′ 24 , which respectively engage the primary and secondary terminals V 20 +, V 20 −, V 21 , V 22 , V 23 , and V 24  of the second appliance-side connector  43 , when the second level-selecting terminal device  44  mates the second appliance-side connector  43 . By selective use of different jump connection between the secondary terminals V′ 21 , V′ 22 , V′ 23 , and V′ 24  and the primary terminal V′ 20 −, a different resistance is observed in the second resistor network  46 , which changes the second feedback signal Sfb 2  and thereby changes the output level of voltage at the output V 2 +, V 2 − of the second level-selecting terminal device  44 . The output level of voltage at output V 2 +, V 2 − is displayed on the second voltage display device  48 .  
         [0031]     Also referring to  FIG. 3 , a first example of the first voltage display device  38  comprises a circuit  38   a  comprising operational amplifiers  381 ,  382 ,  383 ,  384  each having a first input connected to the level-selecting terminals V 11 , V 12 , V 13 , and V 14  of the first resistor network  36  whereby each operational amplifier  381 ,  382 ,  383 ,  384  and the associated resistor R 11 , R 12 , R 13 , R 14  forms a comparison circuit. Each operational amplifier  381 ,  382 ,  383 ,  384  has a second input connected to a power source of +5V. Each operational amplifier  381 ,  382 ,  383 ,  384  has an output coupled to and applying an output signal to a decoding circuit  385 , which in turn generates output signals applied to and driving the indicators D 11 -D 16 . Thus, the indicators D 11 -D 16  shows to a user of the power conversion device  100  of the voltage level at the output V 1 +, V 1 −.  
         [0032]     The circuit  38   a  may also be applied to the second voltage display device  48  and thus no further description of the detailed structure of the second voltage display device  48  will be given hereinafter.  
         [0033]     Also referring to  FIG. 4 , a second example of the first voltage display device  38  comprises a circuit  38   b  comprising transistors  386 ,  387 ,  388 ,  389  respectively connected to the level-selecting terminals V 11 , V 12 , V 13 , and V 14  of the first resistor network  36 . Each transistor  386 ,  387 ,  388 ,  389  generates an output signal associated with ON/OFF state thereof and applies the output signal to a decoding circuit  390 , which in turn generates output signals applied to and driving the indicators D 11 -D 16 . Thus, the indicators D 11 -D 16  shows to a user of the power conversion device  100  of the voltage level at the output V 1 +, V 1 −. Again, the second voltage display circuit  48  may incorporate the circuit  38   b.    
         [0034]     Also referring to  FIG. 5 , a third example of the first voltage display device  38  comprises a circuit  38   c  comprising operational amplifiers  391 ,  392 ,  393 ,  394  each having a first input commonly connected to the primary terminal V 10 + whereby the operational amplifiers. Each operational amplifier  391 ,  392 ,  393 ,  394  has an output coupled to and applying an output signal to a decoding circuit  395 , which in turn generates output signals applied to and driving the indicators D 11 -D 16 . Thus, the indicators D 11 -D 16  shows to a user of the power conversion device  100  of the voltage level at the output V 1 +, V 1 −. Again, the second voltage display circuit  48  may incorporate the circuit  38   c.    
         [0035]     Also referring to  FIG. 6 , a power conversion device constructed in accordance with another embodiment of the present invention, generally designated with reference numeral  100   a , is shown. The power conversion device  100   a  is substantially identical to the power conversion device  100  with reference to  FIGS. 1 and 2 , except that the first and second voltage display devices  38 ,  48  comprise a liquid crystal display device  61 . The outputs of the first and second level-selecting terminal device  34 ,  44  are alternately displayed in the liquid crystal display  61 . Alternatively, a manual switch is provided to allow a user to selectively display the outputs of the first and second level-selecting terminal device  34 ,  44 .  
         [0036]     A block diagram of a control circuit of the power conversion device  100   a  is shown in  FIG. 7 , which is substantially identical to the control circuit of the power conversion device  100 , except that a microprocessor  62  is coupled, via any known interface, to the first and second resistor networks  36 ,  46 , as well as the third DC-to-DC conversion circuit  54  to detect voltage level at the associated outputs. The microprocessor  62  controls the liquid crystal display  61  to display the voltage levels. The first and second voltage display circuits  38 ,  48  of the power conversion device  100  are thus omitted here.  
         [0037]     Although the present invention has been described with reference to the preferred embodiments thereof, it is apparent to those skilled in the art that a variety of modifications and changes may be made without departing from the scope of the present invention intended to be defined by the appended claims.