Abstract:
An analog switch and a battery pack using the same are provided. The analog switch can compensate for temperature dependence of voltages measured from a battery cell before applying the measured voltages to an analog-to-digital (A/D) converter. In an embodiment of the analog switch, a first diode is coupled in a backward direction from a flying capacitor, which is coupled to the A/D converter, to correspond to a second diode packaged therewith as a single set. The first diode is positioned in a battery cell voltage input path to store battery cell voltage values in the flying capacitor, while the second diode suppresses a temperature-related difference caused by the first diode to voltages measured from the battery cell.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims priority to and the benefit of U.S. Provisional Application No. 61/303,602, filed in the United States Patent and Trademark Office on Feb. 11, 2010, the entire content of which is incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Field 
     Aspects of embodiments according to the present invention relate to a battery pack. 
     2. Description of Related Art 
     In general, a portable electronic apparatus, such as a portable notebook computer or a portable electrical device, includes a rechargeable battery pack. The battery pack may include a plurality of battery cells, a voltage sensing and balancing circuit for sensing voltages of the respective battery cells and for maintaining voltage balance, and a controller for controlling charging and discharging operations of the respective battery cells. 
     In a battery pack mounted in a special device such as a handheld electrical device, some of battery cells constituting the battery pack are coupled to a voltage sensing and balancing circuit and measured. However, since the voltage sensing and balancing circuit has only a limited number of input ports, it may be that not all of the battery cells can be coupled to the voltage sensing and balancing circuit. Generally, the battery cells are directly coupled to an analog-to-digital (A/D) converter provided within the controller to transfer voltages thereof. 
     SUMMARY 
     Aspects of embodiments according to the present invention are directed to a battery pack that can compensate for temperature dependence of voltages measured from a battery cell and applying the same to an analog-to-digital converter. 
     An embodiment of the present invention provides for a battery pack including a first diode coupled in a backward direction from a flying capacitor, which is coupled to an analog-to-digital (A/D) converter, to correspond to a second diode packaged therewith as a single set. The first diode is positioned in a battery cell voltage input path to store battery cell voltage values in the flying capacitor. The second diode thereby suppresses a difference between voltages measured from battery cells depending on temperature characteristics of the first and second diodes. 
     An embodiment of the present invention also provides a battery pack including first and second diodes having the same temperature characteristics by packaging the first and second diodes as a single set. 
     An embodiment of the present invention also provides a battery pack including a first diode coupled in a backward direction to correspond to a second diode packaged therewith as a single set, the first diode preventing surge current from a voltage supply in a voltage input path from a flying capacitor to an A/D converter. 
     In the battery pack according to embodiments of the present invention, a first diode is coupled in a backward direction from a flying capacitor, which is coupled to an A/D converter, to correspond to a second diode packaged therewith as a single set. The first diode is positioned in a battery cell voltage input path to store battery cell voltage values in the flying capacitor, thereby suppressing a difference between voltages measured from battery cells depending on temperature characteristics of the first and second diodes. 
     In addition, in an embodiment of the battery pack according to embodiments of the present invention, a first diode is coupled in a backward direction to correspond to a second diode packaged therewith as a single set, the first diode for preventing surge current from a voltage supply in a voltage input path from a flying capacitor to an A/D converter, thereby suppressing a difference between voltages measured from battery cells depending on temperature characteristics of the first and second diodes. 
     According to an exemplary embodiment of the present invention, an analog switch is provided. The analog switch includes first and second inputs, an output, a flying capacitor, and first and second diodes. The first input is configured to couple to a first terminal of a battery. The second input is configured to couple to a second terminal of the battery. The output is configured to couple to an analog-to-digital (A/D) converter. The flying capacitor has a first terminal coupled to the first input and a second terminal coupled to the second input. The first diode includes an anode coupled to the second input and a cathode coupled to the second terminal of the flying capacitor. The second diode includes an anode coupled to a first capacitor for storing a supply voltage, and a cathode coupled to the second terminal of the flying capacitor. 
     The first diode and the second diode may have substantially the same temperature characteristics. 
     The analog switch may further include third and fourth inputs. The third input is configured to receive a first control signal for controlling voltage sensing of the battery. The fourth input is configured to receive a second control signal for controlling voltage transfer to the A/D converter. 
     The flying capacitor may be configured to store a voltage corresponding to a sum of a voltage between the first and second terminals of the battery and a forward voltage of the first diode in response to the first control signal. 
     The flying capacitor may be configured to transfer a voltage corresponding to a sum of the voltage between the first and second terminals of the battery, the forward voltage of the first diode, and the supply voltage minus a reverse voltage of the second diode to the A/D converter in response to the second control signal. 
     The forward voltage of the first diode may be substantially the same in magnitude as the reverse voltage of the second diode. 
     The analog switch may further include first through third transistors. The first transistor includes a first electrode coupled to ground, a second electrode, and a control electrode coupled to the third input. The second transistor includes a first electrode coupled to the first input, a second electrode coupled to the first terminal of the flying capacitor, and a control electrode coupled to the second electrode of the first transistor. The third transistor includes a first electrode coupled to the cathode of the first diode, a second electrode coupled to the second terminal of the flying capacitor, and a control electrode coupled to the second electrode of the first transistor. 
     The analog switch may further include a first voltage divider. The first voltage divider includes first and second resistors. The first resistor is coupled between the control electrode of the first transistor and the third input. The second resistor is coupled between the control electrode of the first transistor and the first electrode of the first transistor. 
     The analog switch may further include fourth and fifth transistors. The fourth transistor includes a first electrode coupled to ground, a second electrode, and a control electrode coupled to the fourth input. The fifth transistor includes a first electrode coupled to the first terminal of the flying capacitor, a second electrode coupled to the output, and a control electrode coupled to the second electrode of the fourth transistor. 
     The analog switch may further include a second voltage divider. The second voltage divider includes third and fourth resistors. The third resistor is coupled between the control electrode of the fourth transistor and the fourth input. The fourth resistor is coupled between the control electrode of the fourth transistor and the first electrode of the fourth transistor. 
     The analog switch may further include a second capacitor coupled to the first input. 
     The first and second diodes may be in a same package. 
     According to another exemplary embodiment of the present invention, a battery pack is provided. The batter pack includes a plurality of first battery cells, a voltage sensing and balancing circuit, a second battery cell, a controller, and an analog switch. The plurality of first battery cells is coupled to each other. The voltage sensing and balancing circuit includes a plurality of input terminals, and is configured to sense voltages and to maintain voltage balance of the plurality of first battery cells. The second battery cell is coupled to the plurality of first battery cells. The controller includes an analog-to-digital (A/D) converter and is configured to control charging and discharging of the battery cells. The analog switch is configured to sense and store a voltage of the second battery cell and to transfer the voltage to the A/D converter of the controller. The analog switch includes a flying capacitor and first and second diodes. The flying capacitor has a first terminal coupled to a first terminal of the second battery cell and a second terminal coupled to a second terminal of the second battery cell. The first diode includes an anode coupled to the second terminal of the second battery cell and a cathode coupled to the second terminal of the flying capacitor. The second diode includes an anode coupled to a capacitor for storing a supply voltage, and a cathode coupled to the second terminal of the flying capacitor. 
     The first and second diodes may have substantially the same temperature characteristics. 
     The battery pack may further include discharging and charging terminals, a negative electrode terminal, and a communications terminal. The discharging terminal is configured to discharge the battery cells. The charging terminal is configured to charge the battery cells. The negative electrode terminal is coupled to a negative terminal of the battery cells. The communications terminal is configured for single wire communication with an external device. 
     The battery pack may further include an overcharge preventing member between the battery cells and the charging terminal. 
     The overcharge preventing member may include a fuse. 
     The overcharge preventing member may include a heat resistor and a switch controlled by the controller. 
     The first and second diodes may be in a same package. 
     According to yet another exemplary embodiment of the present invention, a battery pack is provided. The battery pack includes a plurality of battery cells, a voltage sensing circuit, a flying capacitor, and a controller. The plurality of battery cells includes first through (N−1)th battery cells and an Nth battery cell. The voltage sensing circuit is configured to sense voltages of the first through (N−1)th battery cells. The flying capacitor is configured to sense a voltage of the Nth battery cell. The controller is configured to control storage of the Nth battery cell voltage in the flying capacitor and to control reading of the Nth battery cell voltage from the flying capacitor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, together with the specification illustrate exemplary embodiments of the present invention, and, together with the description, serve to explain the principles of aspects of the present invention. 
         FIG. 1  a block diagram illustrating the structure of a battery pack according to an aspect of the present invention; 
         FIG. 2  is a circuit diagram illustrating the structure of an analog switch of the battery pack illustrated in  FIG. 1 ; and 
         FIGS. 3 and 4  are circuit diagrams illustrating the operation of the analog switch of the battery pack illustrated in  FIG. 1 . 
     
    
    
     DESCRIPTION OF SOME OF THE REFERENCE CHARACTERS IN THE DRAWINGS 
     
       
         
               
               
             
           
               
                   
               
             
             
               
                 100: Battery pack 
                   
               
               
                 110: Battery cell 
                 120: Voltage sensing and balancing 
               
               
                   
                 circuit 
               
               
                 130: Controller 
                 141: Discharging terminal 
               
               
                 142: Charging terminal 
                 143: Communication terminal 
               
               
                 144: Negative electrode terminal 
                 151: Fuse 
               
               
                 152: Heat resistor 
                 153: Switch 
               
               
                 160: Analog switch 
                 161a, 161b: Voltage dividing resistor 
               
               
                 164: Balancing resistor 
                 165: Balancing switch 
               
               
                 166: Current sensing resistor 
                 167: Thermal sensor 
               
               
                   
               
             
          
         
       
     
     DETAILED DESCRIPTION 
     Exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that it can be practiced or carried out by one skilled in the art. In addition, when an element is referred to as being “connected to” or “coupled to” another element, it can be directly connected to the another element or be indirectly connected to the another element with one or more intervening elements interposed therebetween. Hereinafter, like reference numerals refer to like elements. 
     Hereinafter, a structure of a battery pack according to an embodiment of the present invention will be described. 
       FIG. 1  a block diagram illustrating a structure of a battery pack according to an embodiment of the present invention, and  FIG. 2  is a circuit diagram illustrating a structure of an analog switch of the battery pack illustrated in  FIG. 1 . 
     Referring to  FIG. 1 , the battery pack  100  according to the illustrated embodiment includes a plurality of rechargeable battery cells  110  coupled in series to each other, a voltage sensing and balancing circuit  120  for performing voltage sensing and balancing operations of the battery cells  110 , and a controller  130 . 
     Here, each of the respective battery cells  110  may be a lithium ion battery chargeable to a voltage of approximately 4.2 V, but embodiments of the present invention are not limited thereto. The voltage sensing and balancing circuit  120  may include various types of analog front ends manufactured for use with lithium ion batteries, but embodiments of the present invention are not limited thereto. In addition, the controller  130  may include various types of microcomputers manufactured for use with lithium ion batteries, but embodiments of the present invention are not limited thereto. 
     Further, the voltage sensing and balancing circuit  120  supplies power to the controller  130  and provides an analog-to-digital (A/D) converter of the controller  130  with data in the form of voltages detected from, for example, four battery cells  110 . The controller  130  provides charge/discharge control signals and a balancing control signal corresponding to the data processed by a program (for example, a predetermined program) or algorithm (for example, data corresponding to the voltages detected from the battery cells  110 ) to the voltage sensing and balancing circuit  120 . 
     The battery pack  100  includes a discharging terminal  141  for discharging the battery cells  110 , a charging terminal  142  for charging the battery cells  110 , a communication terminal  143  used for single wire communication with an external device, and a negative electrode terminal  144  for charging or discharging the battery cells  110 . 
     Here, the discharging terminal  141  and the charging terminal  142  are electrically coupled to positive electrodes of the battery cells  110 , the negative electrode terminal  144  is electrically coupled to negative electrodes of the battery cells  110 , and the communication terminal  143  is electrically coupled to the controller  130 , respectively. 
     In addition, the battery pack  100  may further include a fuse  151  coupled between the battery cells  110  and the charging terminal  142  to prevent overcharging the battery cells  110 . Referring to  FIG. 1 , the fuse  151  further includes a heat resistor  152  and a switch  153 . The switch  153  may be turned on or off by the control signals of the controller  130 . In the illustrated embodiment, the fuse  151  is used as the overcharge preventing member, but embodiments of the invention are not limited thereto. In other embodiments, for example, the overcharge preventing member may include a plurality of field effect transistors. 
     The battery pack  100  according to the illustrated embodiment includes five battery cells  110  coupled in series with each other. The voltage sensing and balancing circuit  120  in the illustrated embodiment of  FIG. 1 , however, is designed to detect voltages of only four battery cells  110 . In other words, the voltage detected from the fifth battery cell  110  cannot be detected without changing circuits, such as currently developed voltage sensing and balancing circuits. 
     To enable the voltage detection from the fifth battery cell  110 , the battery pack  100  according to the illustrated embodiment further includes an analog switch  160 . The analog switch  160  is coupled in parallel between positive and negative electrodes of the fifth battery cell  110 . The analog switch  160  stores a voltage of the fifth battery cell  110  and transfers the same to an A/D converter (not shown) of the controller  130 . 
     Referring to  FIG. 2 , the analog switch  160  includes a first transistor T 1  coupled to the controller  130  to perform a switching operation along with a second transistor T 2 , a third transistor T 3 , and a fourth transistor T 4  that are driven by the first transistor T 1 . In addition, the analog switch  160  includes a fifth transistor T 5  coupled to the controller  130  to perform a switching operation, and a sixth transistor T 6  that is driven by the fifth transistor T 5 . 
     The first transistor T 1  receives a first switching signal SW 1  from the controller  130 . Here, a first resistor R 1  is coupled between a control electrode of the first transistor T 1  and the controller  130 , and a second resistor R 2  is coupled between the control electrode of the first transistor T 1  and a first electrode of the first transistor T 1 . In addition, the first electrode of the first transistor is coupled to ground. Accordingly, the first switching signal SW 1  is divided by the first resistor R 1  and the second resistor R 2  to then be applied to the control electrode of the first transistor T 1 . 
     A control electrode of the second transistor T 2  is coupled to a second electrode of the first transistor T 1  through a third resistor R 3 . Therefore, the second transistor T 2  is turned on in response to a signal to the control electrode of the second transistor T 2  when the first transistor T 1  is turned on. Further, a fourth resistor R 4  is coupled between the control electrode of the second transistor T 2  and the first electrode of the second transistor T 2 . The first electrode of the second transistor T 2  is coupled to a positive terminal V 5  of the fifth battery cell  110 . In addition, a second electrode of the second transistor T 2  is coupled to a flying capacitor Cf, and applies a voltage of the positive terminal V 5  to the flying capacitor Cf when the second transistor T 2  is turned on. 
     A control electrode of the third transistor T 3  is coupled to the second electrode of the first transistor T 1  through the third resistor R 3 . Therefore, the third transistor T 3  is also turned on when the first transistor T 1  is turned on. A first electrode of the third transistor T 3  is coupled to the positive terminal V 5  of the fifth battery cell  110 . Here, the voltage of the positive terminal V 5  is stored through a first capacitor C 1 , to then be applied to the third transistor T 3 . In addition, a second electrode of the third transistor T 3  is coupled to the fourth transistor T 4  via a fifth resistor R 5  and a first diode D 1 . Here, the first diode D 1  prevents a current from flowing from the flying capacitor Cf through the fourth transistor T 4 . 
     A control electrode of the fourth transistor T 4  is coupled to the second electrode of the first transistor T 1  through a second diode D 2 . In addition, a first electrode of the fourth transistor T 4  is coupled to the control electrode of the fourth transistor T 4  through a sixth resistor R 6 . Therefore, if a current flows through the sixth resistor R 6 , the fourth transistor T 4  is turned on. In addition, a potential of a node coupled between the first diode D 1  and the sixth resistor R 6  is applied to the flying capacitor Cf through the fourth transistor T 4 . Meanwhile, the second diode D 2  cuts off a surge current applied through the ground. 
     A first electrode of the flying capacitor Cf is coupled to the second electrode of the second transistor T 2  and a first electrode of the sixth transistor T 6 . In addition, a second electrode of the flying capacitor Cf is coupled to a second electrode of the fourth transistor T 4 . Accordingly, the second electrode of the flying capacitor is coupled to a negative terminal V 4  of the fifth battery cell  110  through the first diode D 1  and the fourth transistor T 4 . Therefore, a voltage corresponding to the sum of the voltage of the fifth battery cell  110  and a driving voltage of the first diode D 1  is applied to the flying capacitor Cf. 
     In addition, the second electrode of the flying capacitor Cf is coupled to a third capacitor C 3  through a third diode D 3 . The third capacitor C 3  is coupled to a voltage supply Vd through an eleventh resistor R 11  and stores a voltage of the voltage supply Vd. An anode of the third diode D 3  is coupled to the third capacitor C 3 , and a cathode is coupled to the second electrode of the flying capacitor Cf. Accordingly, the voltage Vd stored in the third capacitor C 3  and a reverse driving voltage of the third diode D 3  are applied to the second electrode of the flying capacitor. 
     Therefore, the forward driving voltage of the first diode D 1  coupled to the second electrode of the flying capacitor Cf is offset by the reverse driving voltage of the third diode D 3 . In this way, a driving voltage difference dependent on the temperature characteristic of the first diode D 1  can be eliminated. In addition, in order to make the third diode D 3  and the first diode D 1  demonstrate the same temperature characteristics, the first diode D 1  and the third diode D 3  may be packaged as a single set. For example, the first and third diodes D 1  and D 3  may be in the same package. 
     A control electrode of the fifth transistor T 5  is coupled to the controller  130  through a seventh resistor R 7 . In addition, an eighth resistor R 8  is coupled between the control electrode of the fifth transistor T 5  and the first electrode of the fifth transistor T 5 . Further, a first electrode of the fifth transistor T 5  is coupled to ground. Accordingly, a second switching signal SW 2  is divided by the seventh resistor R 7  and a eighth resistor R 8  to then be applied to the control electrode of the fifth transistor T 5 . 
     The control electrode of the sixth transistor T 6  is coupled to a second electrode of the fifth transistor T 5  through a ninth resistor R 9 . In addition, the control electrode of the sixth transistor T 6  is coupled to the first electrode of the sixth transistor T 6  through a tenth resistor R 10  and a second capacitor C 2  coupled in parallel to each other. The tenth resistor R 10  and the second capacitor C 2  increase a gate-source voltage of the sixth transistor T 6  with a transient time, thereby preventing the sixth transistor T 6  from being turned on at the same time with the second transistor T 2  and the fourth transistor T 4 . 
     A second electrode of the sixth transistor T 6  is coupled to parallel branches of a thirteenth resistor R 13  and a fourth capacitor C 4  through a twelfth resistor R 12 . The fourth capacitor C 4  is coupled between the twelfth resistor R 12  and ground to store the voltage applied from the sixth transistor T 6 , and applies the same to an A/D converter (A/D) of the controller  130 . The thirteenth resistor R 13  and the fourth capacitor C 4  allow the voltage applied from the sixth transistor T 6  to be applied to the A/D converter (A/D) with a transient time. 
     A fourth diode D 4  having an anode coupled to the thirteenth resistor R 13  and a cathode coupled to a voltage supply Vd cuts off a surge current applied from the voltage supply Vd. A fifth diode D 5  is coupled in parallel to both terminals of the thirteenth resistor R 13 . An anode of the fifth diode D 5  is coupled to ground, and a cathode thereof is coupled to the anode of the fourth diode D 4 , thereby compensating for a driving voltage of the fourth diode D 4  when the surge current is applied. In such a manner, temperature dependence of the driving voltage of the fourth diode D 4  can be offset. Further, in order to make the fifth diode D 5  and the fourth diode D 4  demonstrate the same temperature characteristics, the fourth diode D 4  and the fifth diode D 5  may be packaged as a single set. 
     In addition, referring to  FIG. 1 , voltage dividing resistors  161   a  and  161   b  are coupled between a discharging terminal  141  and a negative electrode terminal  144 , and the voltage dividing resistors  161   a  and  161   b  output the overall voltage of the battery pack  100  to the controller  130 . 
     Hereinafter, the operation of the analog switch of the battery pack according to embodiments of the present invention will be described. 
       FIGS. 3 and 4  are circuit diagrams illustrating the operation of the analog switch of the battery pack illustrated in  FIG. 1 . 
     Referring to  FIG. 3 , a voltage of the fifth battery cell  110  is stored in the flying capacitor Cf of the analog switch  160 , as indicated by line {circle around ( 1 )}. First, when a first switching signal SW 1  is applied, a voltage of the second resistor R 2  is applied to the control electrode of the first transistor T 1  to turn on the first transistor T 1 . The current flowing through the first and second electrodes of the first transistor T 1  allows a voltage to be applied to control electrodes of the second transistor T 2  and the third transistor T 3  and turn on the second and third transistors T 2  and T 3 . 
     As a result, a potential of the positive terminal V 5  of the fifth battery cell  110  is transferred to the first electrode of the flying capacitor Cf through the second transistor T 2  along the line {circle around ( 1 )}. In addition, a potential of the negative terminal V 4  of the fifth battery cell  110  reaches the second electrode of the flying capacitor Cf along the first diode D 1  and the fourth transistor T 4 . Therefore, a voltage corresponding to ((V 5 −V 4 )+Vd 1 ) is stored across the flying capacitor Cf. Here, the (V 5 −V 4 ) is a voltage of the fifth battery cell  110 , and Vd 1  is a forward driving voltage of the first diode D 1 . 
     Referring to  FIG. 4 , the voltage of the fifth battery cell  110  stored in the flying capacitor Cf of the analog switch  160  is transferred to the A/D converter, as indicated by line {circle around ( 2 )}. First, when a second switching signal SW 2  is applied, the fifth transistor T 5  is turned on. The current flowing through the first and second electrodes of the fifth transistor T 5  allows a voltage to be applied to the sixth transistor T 6  to turn on the sixth transistor T 6 . Here, the sixth transistor T 6  is turned on with a transition time according to the time constant of the tenth resistor R 10  and the second capacitor C 2 . 
     As the sixth transistor T 6  is turned on, a potential of the first electrode of the flying capacitor Cf is transferred to the twelfth resistor R 12  to then become ((V 5 −V 4 )+Vd 1 )+(Vd−Vd 3 ). Here, Vd is a voltage of the voltage supply Vd, which is stored in the third capacitor C 3 , and Vd 3  is a reverse driving voltage of the third diode D 3 . If the reverse driving voltage of the third diode D 3  is equal to the forward driving voltage Vd 1  of the first diode D 1 , the potential of the first electrode of the flying capacitor Cf is ((V 5 −V 4 )+Vd). Thus, the term associated with the diode driving voltage is removed. In addition, the potential is divided by the twelfth resistor R 12  and the thirteenth resistor R 13 , and the voltage of the thirteenth resistor R 13  is finally transferred to the A/D converter. Here, the thirteenth resistor R 13  and the fourth capacitor C 4  apply the voltage to the A/D converter with a transient time. 
     Meanwhile, the fourth diode D 4  prevents a surge current from being applied from the voltage supply Vd, and the fifth diode D 5  offsets a forward driving voltage of the fourth diode D 4 . Accordingly, temperature dependence of voltages measured from a battery cell can be compensated for and the voltages can be applied to the A/D converter in a stable manner. 
     Although arrangements and actuation mechanisms in the battery pack according to the present invention have been illustrated through particular embodiments, it should be understood that many variations and modifications may be made in those embodiments within the scope of the present invention by selectively combining all or some of the illustrated embodiments herein described. 
     While the present invention has been described in connection with certain exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, and equivalents thereof.