Abstract:
Disclosed are a load/charger detection circuit, a battery management system comprising the same and a driving method thereof. The load/charger detection circuit includes a current source; a current mirror connected to the current source to copy a current of the current mirror; at least two resistors connected between a first terminal providing a corresponding voltage to a charger or a load and a power supply; and a zener diode connected between the first terminal and the current mirror.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2012-0149899 filed in the Korean Intellectual Property Office on Dec. 20, 2012, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     (a) Field of the Invention 
     The present invention relates to a load/charger detection circuit, a battery management system comprising the same and a driving method thereof. 
     (b) Description of the Related Art 
     A battery serves to charge electrical energy and supply the charged electrical energy to various electronic devices. Particularly, a secondary battery (cell) may recharge electrical energy to be used. The secondary battery may be implemented by stacking a plurality of cells in order to increase output. The secondary battery including a plurality of cells may perform a charging operation as well as a discharging operation. In order to efficiently manage the charging operation and the discharging operation, a battery management system (hereinafter referred to as ‘BMS’) is mounted in the secondary battery. 
     When a load is connected to the secondary battery, the BMS detects the connection of the load and controls an operation of supplying a charged voltage of the secondary battery to the load. Further, when a charger is connected to the secondary battery, the BMS detects the connection of the charger and controls an operation of supplying a current from the charger to the secondary battery. 
     In order to detect the connection of the load or the connection of the charger, the BMS includes a detection circuit. The detection circuit generally includes a comparator and a reference voltage. However, when the comparator and the reference voltage are used, power consumption is high so that the problem may be caused when taking into account the characteristics of the battery valuing the power consumption. Particularly, even when the load or the charger is not connected, the power consumption is increased due to the comparator and the reference voltage. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in an effort to provide a load/charger detection circuit, a battery management system comprising the same and a driving method thereof having advantages of reducing power consumption. 
     A load/charger detection circuit according to an exemplary embodiment of the present invention is provided. The load/charger detection circuit may include a current source; a current mirror connected to the current source to copy a current of the current mirror; at least two resistors connected between a first terminal providing a corresponding voltage to a charger or a load and a power supply; and a zener diode connected between the first terminal and the current mirror. 
     The load/charger detection circuit may further include a first inverter including an input terminal connected to a contact point between the at least two resistors; and a second inverter including an input terminal connected to a contact point between the current source and the current mirror. 
     An output of the first inverter may be a signal indicating that the charger is connected, and an output of the second inverter is a signal indicating that the load is connected. 
     The load/charger detection circuit may further include a resistor connected between the first terminal and the zener diode. 
     The current mirror may include a first transistor including a first terminal and a control terminal connected to the zener diode; and a second transistor including a control terminal connected to the control terminal of the first transistor, a first terminal connected to the current source, and a second terminal connected to a second terminal of the first transistor. 
     A voltage of the first terminal when the load is connected may be greater than a voltage of the first terminal when the charger is connected. 
     A battery management system according to another exemplary embodiment of the present invention is provided. The battery management system may include a first terminal providing a corresponding first voltage when a load or a charger is connected; a load/charger detector receiving the first voltage through the first terminal, providing a first signal when the load is connected, and providing a second signal when the charger is connected; and a controller controlling such that discharging is performed from a battery cell to the load according to the first signal, and controlling such that charging is performed from the charger to the battery cell according to the second signal, wherein the load/charger detector may include at least two resistors coupled to each other in series between a voltage source and the first terminal; a current mirror connected to a current source to copy a current of the current mirror; and a zener diode connected between the first terminal and the current mirror, and wherein the first signal may correspond to a voltage of a first contract point between the current source and the current mirror, and the second signal may correspond to a voltage of a second contact point between the at least two resistors. 
     A voltage of the first terminal when the load is connected may be greater than a voltage of the first terminal when the charger is connected. 
     The load/charger detector may include a first inverter including an input connected to the first contact point and outputting the second signal; and a second inverter including an input connected to the second contact point and outputting the first signal. 
     The load or the charger may be connected between a first end of the battery cell and the first terminal, and a charging switch switching according to the second signal and a discharging switch switching according to the first signal may be connected between the first terminal and a second end of the battery cell. 
     A method of driving a battery management system according to another exemplary embodiment of the present invention is provided. The method of driving a battery management system may include providing a current source; providing a current mirror connected to the current source to copy a current of the current mirror; providing a first terminal providing a first voltage when a charger is connected and providing a second voltage greater than the first voltage when a load is connected; providing at least two resistors coupled to each other in series between a voltage source and the first terminal; providing a first signal to a contact point between the at least two resistors by stopping the current mirror when the charger is connected; providing a second signal to a contact point between the current source and the current mirror by operating the current mirror when the load is connected; and charging or discharging a battery cell according to the first signal and the second signal. 
     The charging or discharging of the battery cell may include charging the battery cell according to the first signal; and discharging the battery cell according to the second signal. 
     The method of claim may further include providing a zener diode between the first terminal and the current mirror, wherein the zener diode may generate a breakdown voltage when the load is connected. 
     The method may further include providing a first inverter inverting the first signal; and providing a second inverter inverting the second signal, wherein an output signal of the first inverter may indicate that the charger is connected and an output signal of the second inverter may indicate that the load is connected. 
     According to an exemplary embodiment of the present invention, power consumption can be reduced using a low current source without a separate comparator and reference voltage. 
     Further, according to the exemplary embodiment of the present invention, even when the load or the charger is not connected, only a current of the low current source flows so that the power consumption can be reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a circuit diagram illustrating a BMS and peripheral devices thereof according to an exemplary embodiment of the present invention. 
         FIG. 2  is a circuit diagram illustrating a BMS and peripheral devices thereof where a charger is substituted for the load of  FIG. 1 . 
         FIG. 3  is a circuit diagram illustrating a load/charger detector according to an exemplary embodiment of the present invention. 
         FIG. 4  is a circuit diagram illustrating an operation of a circuit of  FIG. 3  when the load is connected to cells (i.e., a case of  FIG. 2 ). 
         FIG. 5  is a circuit diagram illustrating an operation of the circuit of  FIG. 3  when the load is connected to cells (i.e., a case of  FIG. 1 ). 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     In the following detailed description, only certain exemplary embodiments of the present invention have been shown and described, simply by way of illustration. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not restrictive. Like reference numerals designate like elements throughout the specification. 
     Throughout this specification and the claims that follow, when it is described that an element is “connected” to another element, the element may be “directly connected” to the other element or “electrically connected” to the other element through a third element. In addition, unless explicitly described to the contrary, the word “comprise” and variations such as “comprises” or “comprising”, will be understood to imply the inclusion of stated elements but not the exclusion of any other elements. 
     Hereinafter, a load/charger detection circuit, a BMS comprising the same and a driving method thereof according to an exemplary embodiment of the present invention will be described with reference to the accompanying drawings. 
       FIG. 1  is a circuit diagram illustrating a BMS  100  and peripheral devices of the BMS  100  according to an exemplary embodiment of the present invention. The peripheral devices of the BMS  100  includes a plurality of cells  200 , a load  300 , filter  400 , a charging transistor TRc, a discharging transistor TRd, a plurality of bleeding resistors R 1  to R 16 , and a current sensing resistor Rcs, and is connected to the BMS  100 . 
     The cells  200  are coupled to each other in series, and each cell is charged with a predetermined voltage. Since the cells  200  are charged with the predetermined voltage, respectively, Vc 1 , Vc 2 , Vc 3  . . . , and V 15  are illustrated in  FIG. 1 . Voltages of the cells  200  are input to cell terminals C 0  to C 16  of the BMS  10  through the bleeding resistors R 1  to R 16 , respectively. 
     The bleeding resistors R 0  to R 16  are connected between the cells  200  and the cell terminals C 0  to C 16  of the BMS  100 , respectively. That is, the bleeding resistor R 0  is connected between one terminal (ground) of the first cell V 0  and the cell terminal C 0 , and the bleeding resistor R 1  is connected between a contact point of the first cell V 0  and the second cell V 1  and the cell terminal C 1 . Further, the bleeding resistor R 2  is connected between a contact point of the second cell V 1  and the third cell V 2  and the cell terminal C 2 . The BMS  100  receives voltage information of the cell V 0  to V 15  through the cell terminals C 0  to C 16 . That is, the difference in voltages between the cell terminal C 0  and the cell terminal C 1  corresponds to a voltage of the first cell V 0 , and the difference in the voltages between the cell terminal C 1  and a cell terminal C 2  corresponds to a voltage of the second cell V 1 . The bleeding resistors R 0  to R 16  may be used to detect voltages of the respective cells and may be used to balance the cell voltages. Although  FIG. 1  illustrates that the bleeding resistors R 0  to R 16  are not included inside the BMS  100 , the bleeding resistors R 0  to R 16  may be included inside the BMS  100 . In addition, the number of the cells  200  may be changed in  FIG. 1 . In this case, the number of bleeding resistors and the number of cell terminals may be changed. 
     The current sensing resistor (Rcs) is connected between the discharging transistor TRd and a ground, and the BMS  100  receives charging current information or discharging current information through a current terminal CS. 
     The filter  400  includes a diode DI, a resistor RI, and a capacitor CI, which is a low pass filter (LPF) for removing high frequency component (noise component) in a total voltage (V 0 +V 1 + . . . +V 15 ). The total voltage of the cells passing through the filter  400  is input to a terminal Vcc of the BMS  100 . 
     The load  300  may include various electronic devices serving as a target to which power charged in the cell  400  is supplied. As shown in  FIG. 1 , when the load  300  is connected to the BMS  100 , a discharging operation is performed. Further, as will be illustrated in  FIG. 2 , when a charging operation is performed, a charger  300 ′ is provided as substitution for the load  300 . 
     A drain of the charging transistor TRc is connected with a source of the discharging transistor TRd. A source of the charging transistor TRc is connected with the load  300  and a drain of the discharging transistor TRd is connected with the sensing resistor Rcs. A gate of the charging transistor TRc is connected with a charging terminal CHG of the BMS  100 , and a gate of the discharging transistor TRc is connected with a discharging terminal DSG of the BMS  100 , and switching of the discharging transistor TRc and the discharging transistor TRd are controlled by the BMS  100 . When the cells  200  are charged, the charging transistor TRc is turned-on. When the cells  200  are discharged, the discharging transistor TRd is turned-on. Although the charging transistor TRc and the discharging transistor TRd are illustrated as N-type MOSFET in  FIG. 1 , other transistor such as a P-type MOSFET or a BJT capable of performing switch operation may be used. In addition, although  FIG. 1  illustrates that the charging transistor TRc and the discharging transistor TRd are not included inside the BMS  100 , the charging transistor TRc and the transistor TRd may be included inside the BMS  100 . 
     Meanwhile, before the charging or discharging operation, that is, when the load  300  or the charger  300 ′ is connected, the charging transistor TRc and the discharging transistor TRd maintain the turning-off state. 
     Further, a contact point between the source the load  300  and the source of the charging transistor TRc is connected to the detection terminal DET, and the detection terminal DET of the BMS  100  is used to detect the connected state of the load  300  or the charger  300 ′. 
     As shown in  FIG. 1 , the BMS  100  according to the exemplary embodiment of the present invention includes a controller  120 , a load/charger detector  140 , and various terminals. 
     The controller  120  receives voltage information of the cells V 0  to V 15  through the cell terminals C 0  to C 16 , and receives total voltage information of the cells V 0  to V 15  through a terminal Vcc. Further, the controller  120  receives the charging current or discharging current information through a current terminal CS. In addition, the controller  120  outputs a control signal for switching the charging transistor TRc through the charging terminal CHG, and outputs a control signal for switching the transistor TRd through the discharging terminal DSG. 
     As illustrated above, the controller  120  according to the exemplary embodiment of the present invention turns-off the charging transistor TRc and the discharging transistor TRd before performing the discharging or charging operation. That is, the controller  120  turns-off the charging transistor TRc and the discharging transistor TRd at an initial time when the load  300  or the charger  300 ′ (see  FIG. 2 ) is connected. Moreover, the controller  120  detects the connection of the load  300 , and turns-on the discharging transistor TRd and turns-off the charging transistor TRd in order to perform the discharging operation. The controller  120  detects the connection of the charger  300 ′, and turns-on the discharging transistor TRd and turns-off the charging transistor TRd in order to perform the charging operation. In the meanwhile, the controller  120  may turn-on both of the charging transistor TRc and the discharging transistor TRd during the discharging operation or the charging operation in order to increase the efficiency of the battery. 
     Furthermore, the load/charger detector  140  according to the exemplary embodiment of the present invention receives a detection voltage Vdet through the detection terminal DET, and outputs a lode signal Sload and a charger signal Schg to the controller  120  according to the received detection voltage Vdet. When the load  140  is connected, the load/charger detector  140  transmits the load signal Sload including a detection result. When the charger  300 ′ is connected, the load/charger detector  140  transmits the charger signal Schg including the detection result. In this case, the controller  120  controls the charging transistor TRd and the discharging transistor TRc according to the load signal Sload and the charger signal Schg received from the load/charger detector  140 . 
       FIG. 2  is a circuit diagram illustrating the BMS and peripheral devices thereof where the charger  300 ′ is substituted for the load  300  of  FIG. 1 . A circuit of  FIG. 2  is the same as the circuit of  FIG. 1  except that the load  300  is substituted by the charger  300 ′. In this manner, a case where the charging operation is performed illustrated when the charger  300 ′ is connected. In this case, so as to perform the charging operation, a voltage Vchg across the charger  300 ′ is greater than a total voltage Vcc of the cells  200 . 
     The load/charger detector  140  according to the exemplary embodiment of the present invention is a circuit arrangement for reducing the power consumption, and the following is a detail description thereof. 
       FIG. 3  is a circuit diagram illustrating a load/charger detector  140  according to an exemplary embodiment of the present invention. 
     As shown in  FIG. 3 , the load/charger detector  140  according to the exemplary embodiment of the present invention includes a voltage source VDD, a current source I, resistors R 31 , R 32 , and R 33 , transistors TR 31  and TR 32 , a zener diode ZD, and inverters INV 1  and INV 2 . 
     The resistors R 31  and R 32  are coupled to each other in series between the voltage source VDD and the detection terminal DET, and an input of the inverter INV 1  is connected with a contact point between the resistors R 31  and R 32 . In this case, an output of the inverter INV 1  becomes the charger signal Schg. 
     One terminal of the resistor R 33  is connected with the detection terminal DET, and the other terminal of the resistor R 33  is connected with a cathode of the zener diode ZD. An anode of the zener diode ZD is connected with a drain of the transistor TR 31 . In  FIG. 3 , a breakdown voltage of the zener diode ZD is represented as Vzd. 
     A gate and the drain of the transistor TR 31  are connected with each other, and a source of the transistor TR 31  is connected with a ground. The gate of the transistor TR 31  and a gate of the transistor TR 32  are connected with each other, and a source of transistor TR 32  is connected with the ground. The drain of the transistor TR 32  is connected with the current source I. In  FIG. 3 , a gate-source voltage of the transistor TR 31  is represented as Vgs. In this case, the transistor TR 31  and the transistor TR 32  constitutes a current mirror, and a drain current of the transistor TR 31  is copied to a current (K*I) being K times of the current source I is copied in by the current mirror. The K is determined by a width between the transistor TR 31  and the transistor TR 32 . 
     Further, an input of the inverter INV 2  is connected with a contact point between the current source and the transistor TR 32 , and an output of the inverter INV 2  becomes the load signal Sload. 
     Hereinafter, a method of detecting connection of the load or the charger by the load/charger detector  140  as illustrated in  FIG. 3  will be described. 
     First, the following is a description of a method of detecting the connection of the charger to generate the charger signal Schg by the load/charger detector  140  when the charger  300 ′ is connected with the cells  200  as illustrated in  FIG. 2 . 
       FIG. 4  illustrates an operation of the circuit of  FIG. 3  when the load is connected to a cell (i.e., a case of  FIG. 2 ). 
     As illustrated previously, when the charger is connected, a charging transistor TRc and a discharging transistor TRd are turned-off. Accordingly, as shown in  FIG. 4 , a detection voltage Vdet being a voltage of a detection terminal DET is a value obtained by subtracting a voltage Vchg across a charger from a total voltage Vcc of a plurality of cells  200 . As described earlier, since the voltage Vchg across the charger is greater than the total voltage Vcc of the cells  200 , the detection voltage Vdet has a negative value. 
     When the detection voltage Vdet has the negative value, a breakdown voltage is not generated from the zener diode ZD so that the transistors TR 31  and TR 32  do not act as a current mirror. Accordingly, due to voltage division of a resistor R 31  and a resistor R 32 , an input of an inverter INV 1  becomes low level (Low). Further, an output of the inverter INV 1  becomes high level (High). That is, the charger signal Schg becomes high level (High). 
     Meanwhile, since the current mirror does not operate, the input of the inverter INV 2  becomes the high level (High) but an output of inverter INV 2  becomes the low level (Low). That is, the load signal Schg becomes low level (Low). 
     In this manner, when the charger  300 ′ is connected with the cells  200 , a load/charger detector  140  outputs the charger signal Schg of high level and the load signal Sload of low level. When the controller  120  receives the charger signal Schg of high level, the controller  120  detects connection of the charger and turns-on a charging transistor TRd for a charging operation. 
     Next, as illustrated in  FIG. 1 , the following is a description of a method of detecting connection of the load to generate the load signal Sload by the load/charger detector  140  when the load  300  is connected to the cells  200 . 
       FIG. 5  is a circuit diagram illustrating an operation of the circuit of  FIG. 3  when the load is connected to the cells  200  (i.e., a case of  FIG. 1 ). 
     As described above, when the load is connected, the charging transistor TRc and the discharging transistor TRd are turned-off. Accordingly, as shown in  FIG. 4 , the detection voltage Vdet being a voltage of the detection terminal DET becomes the total voltage Vcc of the cells  200 . Thus, the detection voltage Vdet is remarkably greater than a voltage Vcc-Vchg when the charger is connected. 
     When the detection voltage Vdet becomes the Vcc voltage, the input of the inverter INV 1  becomes the high level (High) by voltage division of the resistors R 31  and R 32 . In addition, the output of the inverter INV 1  becomes the low level Low. That is, the charger signal Schg becomes low level (Low). 
     Further, the Vcc being the detection voltage Vdet is greater than a breakdown voltage Vzd of the zener diode+gate-source voltage Vgs of the transistor TR 31 , the transistors TR 31  and TR 32  act as a current mirror. When the current mirror operates, the input of the inverter INV 2  becomes low level (Low) and the output of the inverter INV 2  becomes high level (High). That is, the load signal Schg becomes high level (High). 
     In this manner, when the load  300  is connected to the cells  200 , the load/charger detector  140  outputs the charger signal Schg of low level and the load signal Sload of high level. When the controller  120  receives the load signal Sload of high level, the controller  120  detects that the load is connected and turns-on the charging transistor TRc for the discharging operation. 
     Since the load/charger detector  140  according to the exemplary embodiment of the present invention as describe above does not use a separate comparator and reference voltage but uses a current source I having a low current, power consumption may be reduced. In addition, in the load/charger detector  140  according to the exemplary embodiment of the present invention, when the detection terminal DET is open (i.e., the load or the charger is not connected), only the current source I flows so that the power consumption can be further reduced. 
     While this invention has been described in connection with what is presently considered to be practical 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.