Abstract:
Apparatus for producing an output voltage V o  to power an electronic device is disclosed herein. According to the preferred embodiment, the apparatus comprises a power supply ( 100 ) having two or more first connection elements ( 108 ) in which some or all of the first connection elements ( 108 ) are in series with different respective resistive loads ( 103 ) and circuitry for maintaining the first connection elements ( 108 ) at different voltages, and a connector assembly ( 200 ) arranged to be coupled between the power supply ( 100 ) and the electronic device. The connector assembly ( 200 ) includes at least two second connection elements ( 204 ) for connection to respective ones of the first connection elements ( 108 ) and electrically connectable to the electronic device and also includes selection means, in the form of an electrical wire ( 203 ), for modifying the voltage difference between the first connection elements ( 108 ) to which the second connection elements ( 204 ) are connected, whereby the connector assembly ( 200 ) draws a selected voltage from the power supply ( 100 ) and passes the selected voltage V o  to the electronic device.

Description:
BACKGROUND AND FIELD OF THE INVENTION  
       [0001]     This invention relates to apparatus for producing an output voltage suitable to power an electronic device.  
         [0002]     Electronic devices such as laptop computers, cellular phones, digital camcorders and portable music players are typically powered from an external power source such as line current or the electrical systems of automobiles. Alternatively, the electronic devices may be powered from an internal rechargeable battery.  
         [0003]     To power an electronic device externally or to recharge an internal battery of the electronic device, the manufacturer provides an external power supply which may be a switching power supply commonly known as an AC adapter that may weigh close to a pound and may be about six inches long, three inches wide and about two inches high.  
         [0004]     The external power supply therefore contribute substantially to the weight of the electronic device since a user would need to carry the external power supply with him to permit the charging of the internal battery and/or powering the device from an electrical wall socket. Furthermore, with a wide range of portable electronic devices available in the market with different power requirements, it may be necessary for a user of these different electronic devices to carry more than one AC adapter.  
         [0005]     Some manufacturers propose to resolve the problem by introducing a universal power supply which enables selection of a specific voltage, for example within the range of 3V-24V. This alleviates the need to carry several power adapters to power different electronic devices. The selection of the voltage is normally done via a multi-position switch that in turn controls a voltage converter in the universal power supply to generate an output voltage in accordance with the switch setting. This accommodates the different voltage/power requirements for different devices.  
         [0006]     However, there is another incompatibility problem which is faced by the user of such electronic devices. Different electronic devices may use different input sockets with different dimensions and thus such an universal power supply may further comprise a number of different interface connectors to match the power supply&#39;s output plug to the input sockets of these electronic devices. These different interface connectors come in different shapes and sizes and are offered by many manufacturers, such as the range of “Adaptaplugs” offered by Radioshack Corporation of Fort Worth, Tex., USA.  
         [0007]     To use such a universal power supply, the user selects the required voltage rating and attaches an appropriate interface connector to the output plug of the power supply and then connects the power supply to the electronic device via the interface connector. Thus, the proper use of the universal power supply depends on user&#39;s proper selection of the correct voltage requirement in addition to choosing the correct interface connector. The possibility of the user incorrectly or accidentally selecting a voltage unsuitable for a corresponding electronic device&#39;s voltage requirement is real and this often results in damage to the device&#39;s internal electrical circuitry. There is also a possibility of the user mis-matching the polarity of the interface connector which may also result in electrical damage to the electronic device.  
         [0008]     To reduce the chances of damaging the electronic device, some manufacturers incorporate resistor circuitry in the interface connector, for example the range of connectors called “PowerTips” from Targus Inc. of Anaheim, Calif., USA, in which the patentee of the present application understands to be licensed from Comarco Wireless Technologies (patent no. U.S. Pat. No. 6,091,611). The resistor circuitry built into the connector replaces the manual selection of the desired voltage since the resistor circuitry controls the voltage/current supplied to the electronic device. As such, a plurality of interface connectors unique in their physical dimension and resistor circuitry to provide a pre-determined voltage is available which corresponds to the different input socket dimensions and voltage requirements of different electronic devices. This obviates the need for a power converter and a multi-position switch within the universal power supply.  
         [0009]     Although such a voltage selection means greatly reduces the possibility of the user selecting an incorrect voltage, it necessitates the manufacturer producing a vast number of interface connectors to accommodate different types of electronic devices. Suppose, for example, that ten different types of interface connectors are required to fit the input sockets of fifty different laptop computers. Suppose further that the input voltages required by these fifty laptop computers are different, say 12V, 15V and 18V. This means that the manufacture needs to have a corresponding number of resistive circuits in the connector to regulate the output voltages. Consequently, the permutations of connectors required to support each of these fifty laptop computers would be thirty. This possibly raises production costs which may ultimately be borne by the end user of such power supplies.  
         [0010]     It is an object of the present invention to provide an apparatus for producing an output voltage which alleviates the disadvantage of the prior art and/or to provide the public with a useful choice.  
       SUMMARY OF THE INVENTION  
       [0011]     The invention, in general terms, relates to a power supply arranged to output different voltages and a connector assembly having selection means arranged to select a suitable output voltage to power an electronic device.  
         [0012]     In a first aspect of the invention, there is provided apparatus for producing an output voltage to power an electronic device, the apparatus comprising a power supply comprising two or more first connection elements in which some or all of the first connection elements are in series with different respective resistive loads and circuitry for maintaining the first connection elements at different voltages, and a connector assembly arranged to be coupled between the power supply and the electronic device; the connector assembly having at least two second connection elements for connection to respective ones of the first connection elements and electrically connectable to the electronic device, the connector assembly further having selection means for modifying the voltage difference between the first connection elements to which the second connection elements are connected, whereby the connector assembly draws a selected voltage from the power supply and passes the selected voltage to the electronic device.  
         [0013]     An advantage of the described embodiment of the invention is that the user of the apparatus needs only to select the corresponding connector assembly for a particular model of electronic device for connection between the power supply and the electronic device. This reduces the possibility of the user selecting a wrong voltage. In this way, the apparatus is programmed to output a voltage in accordance with the selection means of the connector assembly.  
         [0014]     According to a second aspect of the invention, there is provided a power supply comprising two or more first connection elements and circuitry for maintaining the first connection elements at different voltages, the power supply being arranged to be coupled to a connector assembly having at least two second connection elements for connection to respective ones of the first connection elements of the power supply and electrically connectable to an electronic device, the connector assembly further having selection means for modifying the voltage difference between the first connection elements to which the second connection elements are connected, whereby the connector assembly draws a selected voltage from the power supply and passes the selected voltage to the electronic device.  
         [0015]     According to a third aspect of the invention, there is provided a connector assembly arranged to be coupled between a power supply and an electronic device, the power supply comprising two or more first connection elements and circuitry for maintaining the first connection elements at different voltages, the connector assembly comprising at least two second connection elements for connection to respective ones of the first connection elements of the power supply and electrically connectable to the electronic device, and selection means for modifying the voltage difference between the first connection elements of the power supply to which the second connection elements are connected, whereby the connector assembly draws a selected voltage from the power supply and passes the selected voltage to the electronic device.  
         [0016]     Preferably, the power supply comprises more than two first connection elements and the selection means includes one or more auxiliary connection elements which are connectable to selected ones of the first connection elements to vary the voltage difference between the first connection elements to which the second connection elements are attached. Typically, the auxiliary elements are electrically connected to each other.  
         [0017]     The sides of the resistive loads away from the first connection elements may be mutually connected to a point in a voltage divider circuit such that upon connection of the auxiliary connection elements to selected ones of the first connection elements, the voltage at the point in the voltage divider is held substantially constant and the voltage difference is varied between the first connection elements to which the second connection elements are attached.  
         [0018]     Preferably, the second connection elements of the connector assembly are electrically connectable to the electronic device via an electric cable. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]     An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings in which,  
         [0020]      FIG. 1  is a schematic diagram of a power supply arranged to output an output voltage and a connector assembly for selecting the output voltage according to the preferred embodiment of the invention;  
         [0021]      FIG. 2  illustrates a perspective exploded view of the connector assembly of  FIG. 1 ;  
         [0022]      FIG. 3  is a table showing various output voltages which can be selected by the connector assembly of  FIG. 2 ; and  
         [0023]     FIGS.  4  to  25  illustrate schematic diagrams of the connector assembly of  FIG. 2  depicting different wiring in the connector assembly for selecting the output voltage of the power supply.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0024]      FIG. 1  is a circuit diagram illustrating apparatus arranged to generate an output voltage V o  suitable for powering an electronic device according to the preferred embodiment of the invention and which comprises a power supply  100  and a connector assembly  200  for automatically selecting the output voltage V o .  
         [0025]     The power supply  100  comprises a voltage converter  101  in the form of a conventional buck converter  101  which will be familiar to a person skilled in the art. The voltage converter  101  converts power from an internal eight cells battery  102  to an output voltage V o , which is less than the cumulative voltage of the battery  102 . Typically, the output voltage is in the range of 3V to 24V DC.  
         [0026]     This arrangement is similar to the power supply  100  proposed in a patent application PCT/SG02/00031 by the applicant of the present invention except that the power supply  100  further comprises a resistive network  103  which forms a divider circuit and a regulation circuit formed by a comparator and a pulse width modulator (PWM)  106 .  
         [0027]     The power supply  100  regulates the output voltage V o  by dividing down the output voltage V o  using the resistive divider  103  which comprises a plurality of resistive elements for providing a plurality of electrical loads to vary the output voltage V o . In a basic form, the resistive divider  103  comprises resistors R 1  and R 2  connected as shown in  FIG. 1 . Node  104  of the resistive divider  103  is coupled to a negative (−ve) input of the comparator which, in this embodiment, is in the form of an error amplifier U 1 . A positive (+ve) terminal of the error amplifier U 1  is tied to a stable voltage reference  105  which in this embodiment is 2.5V (half of 5.0V reference). The voltage at node  104  of the resistive divider  103  is thus compared with the voltage reference  105  and if the voltage converter  101  is outputting the output voltage V o  correctly, the −ve and +ve inputs of the error amplifier U 1  would be substantially at a same voltage, typically within a few mVolts. The error amplifier U 1  is stabilised by a feedback network which comprises R 6  and C 2 .  
         [0028]     The error amplifier U 1  produces an analog output voltage V e  or error signal which is converted to a digital signal by the PWM  106  as shown in  FIG. 1   a. The PWM    106  compares the output of the error amplifier V e  to a sawtooth ramp signal  108  which is typically 1V in amplitude at 100 Hz frequency. The output  107  of the PWM  106  is “high” whenever the ramp input amplitude  108  is lower than that of the error signal V e  and is “low” whenever the ramp input amplitude  108  is higher than V e , thus creating a pulsed waveform as shown in  FIG. 1   a. In this way, the error signal V   e  is converted to a digital signal (PWM&#39;s output  107 ) of fixed frequency with a duty ratio D which can vary linearly between 0 and 100%.  
         [0029]     The PWM&#39;s output  107  is applied to an input of a driver U 2  having an output  109  connected to a “Gate” terminal of a power MOSFET Q 1 . The driver U 2  provides level translation and drives the MOSFET Q 1  to turn the MOSFET ON or OFF depending on the state of the PWM output  107 . In this embodiment, MOSFET Q 1  is turned ON whenever the PWM output  107  is a “high” and is OFF if the PWM output  107  is a “low”.  
         [0030]     The MOSFET Q 1 , diode D 1 , Inductor L 1  and capacitor C 1  form the buck converter  101  as described earlier, which receives an input from the battery, and outputs a corresponding voltage at the output of the power supply  100  (which is V o ).  
         [0031]     It would be apparent to a skilled man in the relevant art that the input voltage of the buck converter  101  V i , output voltage V o  and the switching duty ratio D of the buck converter  101  are related by the equation V o =V i *D. Therefore, by varying the duty ratio D between 0 to 100%, the output voltage V o  can be varied from zero to the maximum voltage of the batteries  102 . If the output voltage V o  increases for any reason, for example due to reduction in the current drawn by the load, the error signal V e  decreases. This causes the duty ratio D to reduce since the OFF state of the PWM output will increase. With the duty ratio D reduced, V o  would be adjusted accordingly since, as mentioned, V o =V i *D until an equilibrium condition is reached. In this way, the output voltage is regulated to a present voltage appropriate to the requirement of the electronic device to which the power supply  100  is connected.  
         [0032]     The circuitry encompassing the PWM, error amplifier U 1  and the stable voltage reference  105  can be provided in an integrated circuit such as UC3843 available from Texas Instrument.  
         [0033]     Respective outputs of the buck converter  101  are also coupled to two first connection elements  205  of an input connector  110  for coupling to the connector assembly  200 . These two first connection elements  205  are used to carry an electrical current to the connector assembly  200  and subsequently used to power an electronic device.  
         [0034]     The gain of the error amplifier U 1  is very high, preferably 10,000, and thus the two inputs of the error amplifier are maintained in an equilibrium condition.  
         [0035]     Therefore the −ve input is held substantially to be at 2.5V as is the +ve input. To maintain a balance voltage between the two inputs (+ve and −ve) of the error amplifier U 1 , a current, I R12 , of 2.5V/2.04 k through R 1  is necessary to maintain 2.5 volts at the negative (−ve) input of the error amplifier U 1 . This current I R12  develops a voltage of 12.5 volts (i.e. I R12 *R 2 ) across R 2 . The output voltage V o  would thus be 2.5V+12.5V=15.0V, approximately.  
         [0036]     The arrangement allows the power supply  100  to output a fixed output voltage in accordance with the values of R 1 , R 2  and the voltage reference  105 . To adjust or manipulate the output voltage V o  to output a plurality of voltages, the resistive divider  103  further comprises a plurality of resistors, R 3  to R 5 , with one terminal of the resistors R 3  to R 5  coupled to the node  104  and the other terminal of the resistors R 3  to R 5  coupled to three first connection elements of the input connector  110 , as shown in  FIG. 1 . The input connector  110  is arranged to be connected to a corresponding interface connector  201  of the connector assembly  200 .  
         [0037]      FIG. 2  shows a perspective view of the connector assembly  200  with an interface connector  201  disassembled from a connector housing  202 . The connector housing  202  may be molded around the connector  201  during production. The connector assembly  202  comprises selection means to select at least one of the resistors R 3  to R 5  and in this embodiment, the selection means is in the form of an electrical wire  203  and  FIG. 2  shows two wires  203  being used. The connector assembly  200  also comprises second connection elements  204  for connection to respective ones of the first connection elements  205  of the power supply  100  and in this embodiment, the second connection elements  204  are in the form of pins  1  to  6 . The electrical wires  203  connects any one of pins  4  to  6  of the connector assembly  200  to pin  1  or pin  3  which corresponds to 0V and 5V respectively at the power supply end. The number of pins  1  to  6  would typically correspond to the number of first connection elements  205  in the input connector  110  of the power supply  100  and in this case there are six pins to six connection elements  205 . The pins  1  to  6  are inserted into the interface connector  201  which is then coupled to the connector  110  of the power supply  100  such that each pin  1  to  6  is electrically connected to the corresponding first connection elements  205  of the input connector  110 .  
         [0038]     Two of the pins,  1  and  2 , and the corresponding wires  203   a  are connected to the buck converter  101  via two first connection elements  205  to carry the output current, typically 3 amps, from the power supply  100 . Since the node  104  is maintained at +2.5V by the error amplifier U 1 , connecting any one of resistors R 3 , R 4  or R 5  to 0V or 5V will increase or decrease the output voltage V o  by a predetermined amount. Each resistor R 3  to R 5  is thus selected so that when any of these resistors are connected as described above, R 1  draws current from the voltage converter to develop a corresponding voltage drop across R 2 .  
         [0039]     For example, the value of R 3  is chosen to be 25.5K so that the current through it, 2.5/25.5K, develops an extra 1 volt across resistor R 2 , raising the output voltage to 4 volts if pin  6  is connected to pin  1  which is 0V. Conversely, if pin  6  is connected to pin  3  which is at 5V, the same current 2.5/25.5K flows into node  104  so that the current is subtracted from the current through R 2  to maintain equilibrium, causing V 0  to fall by 1 volt.  
         [0040]     Because the resistors R 3 , R 4  and R 5  can each be connected in one of three states, that is, to +5 volts, to 0 volts, or unconnected, the resistor values are weighted according to a ternary scale  3   0 ,  3   1 ,  3   2 . Accordingly, resistors R 4  and R 5  are selected to be 8.50K and 2.83K respectively so that their effect on the output voltage is 3V and 9V respectively.  FIG. 3  shows a table depicting how the connections of the resistors R 3  to R 5  affect the output voltage V o  of the power supply  100 .  
         [0041]     Therefore, different connector assemblies  200  are configured by connecting the electrical wire or wires  203  between pins  4  to  6  and pins  1  and  3  depending on what is the required voltage output V o . FIGS.  4  to  25  shows how the pins  1  to  6  are connected schematically to “switch” between the different voltages available for selection as shown in the table in  FIG. 3 . For example if a user requires the power supply  100  to output 10V, then he would need to select the connector assembly  200  which has the configuration of  FIG. 11 . This means that pins  5  and  6  are connected to pin  1 , and pin  4  is connected to pin  3 . When the connector assembly  200  is coupled to the connection elements  205  of the power supply  100 , this translates to resistors R 3  and R 4  being connected to 0V whereas R 5  is connected to 5V. On the other hand, if a user requires 15V then he would need to select the connector assembly  200  of  FIG. 16  with none of the pins connected.  
         [0042]     The connection between the pins  1  to  6  is carried out during the manufacturing process and is thus transparent to the user. The user would also be provided with a chart which has the model numbers of each available connector assembly  200  since it would not be feasible for the user to inspect the connection to know whether that is the connector assembly  200  he requires.  
         [0043]     The connector assembly  200  also comprises an electric cable or cord  206  (see  FIG. 2 ) arranged to carry the current wires  203   a  and terminated with an output connector  207  that mates with an input socket of the electronic device being powered by the power supply  100 . Various off-the-shelf application specific connectors  207  may be used so that the connector assembly  200  is able to mate with any particular electronic device. In this way, the design of the connector assembly  200  is simplified.  
         [0044]     In use, the chart that is available to a purchaser of the power supply  100  will depict the different types of electronic devices and their corresponding model or type of connector assembly  200  to use. The wire or wires  203  are already pre-connected according to model to output voltages associated with respective electronic devices and are thus transparent to the user.  
         [0045]     The interface connector  201  of the connector assembly  200  is then connected to the power supply  100  whereas the output connector  207  of the connector assembly  200  is connected to the input socket of the electronic device. When power is applied to the power supply  100 , the voltage is automatically regulated by the resistive network  103  as described earlier, and depending on the configuration of the pins  1  to  6 , a corresponding voltage V o  will be output by the power supply  100 .  
         [0046]     Using the connector assembly  200  obviates the need of the user to manually select the required voltage output V o  and thus reduces the possibility of selecting an incorrect output voltage. The connector assembly allows an easy method of switching between different output voltages V o  so that the correct voltage is used to power an electronic device. If the output connector  207  of the connector assembly  200  is adapted to fit into the input socket of the electronic device, this also obviates chances of using interface sockets with the wrong polarity.  
         [0047]     On the other hand, the output connector  207  of the connector assembly  200  may be generic and readily available from connector manufacturers such that it may be used to interface the connector assembly  200  and the input socket of the electronic device. This will also reduce the number of connector assemblies  200  required to support the different electronic devices available since the permutations is reduced and the production cost would also be lowered as the interface sockets can be separately bought depending on the requirements of the user.  
         [0048]     Such a method can be applied to any power supply circuitry in order to enhance the universal feature in a power supply to various electronic devices. Such power supplies include, but are not limited to, switching power supply (AC adapters) and portable battery packs.  
         [0049]     The described embodiment should not be construed as limitative. For example, the stable voltage reference  105  may use other voltage values other than 2.5V. This would be dependent on the desired output voltage V o  since the output voltage is a function of this voltage reference  105  as described earlier.  
         [0050]     In this embodiment, the power supply  100  uses the power supply proposed in PCT/SG02/00031 as an example which uses an electric cell to provide an output voltage. However, it should be apparent that other types of power supplies, for example a typical power adapter, may be modified to include the resistive network as described in the preferred embodiment so that such adapters may be used with the connector assembly  200 .  
         [0051]     The number of pins  1  to  6  in the connector assembly  200  may be varied according to application. For example, instead of six pins, fewer pins may be used if the power supply requires to output only a small range of output voltages V o . In a further example, one more pin can be added as a ground since certain connectors  207  contain an extra connection for grounding purposes to counteract chances of an electrostatic surge.  
         [0052]     Having now fully described the invention, it should be apparent to one of ordinary skill in the art that many modifications can be made hereto without departing from the scope as claimed.