Abstract:
A battery pack with a charge control function includes a charge protection circuit and a charge control circuit. The charge control circuit turns a discharge control switch on or off to control a discharge current which flows from a secondary battery to a load and also turns a charge control switch on or off to control a charge current which flows from a charger to the secondary battery. When an abnormal voltage is input, the charge control circuit turns the charge control switch on or off to stop the charging of the secondary battery through the charger.

Description:
This application claims priority to prior Japanese application JP 2003-84326, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION  
     The present invention relates to battery packs and, more particularly, relates to a battery pack with a charge control function, the battery pack having the charge control function and a charge protection function therein. 
     Rechargeable batteries (secondary batteries), particularly, lithium-ion batteries each requires a protection circuit (charge protection IC) for detecting an overdischarge mode and an overcharge mode to protect the present secondary battery from the overdischarge mode and the overcharge mode because the lithium-ion battery is weak in overdischarging and overcharging. Each protection circuit (charge protection IC) has an overdischarge preventive mechanism and an overcharge preventive mechanism. The protection circuits (charge protection ICs) include a protection circuit for further detecting an overcurrent mode in the discharge mode of the corresponding secondary battery to protect the battery from the overcurrent mode. This protection circuit (charge protection IC) includes an overdischarge preventive mechanism, an overcharge preventive mechanism, and an overcurrent preventive mechanism. A conventional secondary-battery protection circuit (charge protection IC) will now be described hereinbelow. The protection circuit includes an overdischarge preventive mechanism and an overcharge preventive mechanism. 
     A battery unit having the above-mentioned protection circuit (charge protection IC) is called a “battery pack”. When a secondary battery enters the overdischarge mode, it is necessary to stop the discharging of the secondary battery and charge the secondary battery using a charger. The charger includes an adapter and a charge control circuit (charge control IC). In other words, the conventional battery pack includes only the protection circuit (charge protection IC) and the charger has the charge control circuit (charge control IC). 
       FIG. 1  shows a conventional battery module  800 ′ including a charge protection IC  200  and a charge control IC  600 . Referring to  FIG. 1 , the battery module  800 ′ has a discharging positive terminal  801 , a negative terminal  802 , and a charging positive terminal  803 . A load  400  is arranged between the discharging positive terminal  801  and the negative terminal  802 . An adapter  700  serving as a commercial charger is arranged between the charging positive terminal  803  and the negative terminal  802 . The negative terminal  802  is called a ground terminal (GND). 
     The battery module  800 ′ includes: a secondary battery  300 ; the charge protection IC  200 ; the charge control IC  600 ; peripheral devices (a power transistor Tr, a diode D, and a current-detecting resistor R); a first field-effect transistor FET 1  functioning as a discharge control switch; and a second field-effect transistor FET 2  operating as a charge control switch. 
     The charge protection IC  200  is connected between the discharging positive terminal  801  and a negative electrode of the secondary battery  300 . The charge control IC  600  and the peripheral devices are arranged between the charging positive terminal  803  and the positive electrode of the secondary battery  300 . According to the arrangement, the charger comprising only the adapter  700  can be used. 
     A conventional battery pack  100 ′ and a conventional charger  500 ′ will now be described hereinbelow with reference to  FIGS. 2 and 3 .  FIG. 2  is a block diagram showing the conventional battery pack and a protection circuit (charge protection IC) included therein.  FIG. 3  is a block diagram showing the conventional charger and a charge control circuit (charge control IC) included therein. 
     The conventional battery pack  100 ′ will now be described with reference to  FIG. 2 . This kind of battery pack is disclosed as a rechargeable power supply circuit in Japanese Patent No. 2872365. The conventional battery pack  100 ′ will be described on the basis of the description of the above patent. In the patent document, the structure of control means is not schematically shown in accompanying drawings. In the following description, the structure of the control means is estimated by analogy with the specification of the patent. The structure of the control means will be described with reference to the drawings. 
     Referring to  FIG. 2 , the battery pack  100 ′ has a positive terminal  101  and a negative terminal  102 . Each of the positive and negative terminals  101  and  102  is called an external connection terminal. The load  400  or the charger  500 ′ is arranged between the positive terminal  101  and the negative terminal  102 . The charger  500 ′ will be described later. 
     Referring to  FIG. 2 , the battery pack  100 ′ has the secondary battery  300  including at least one lithium-ion battery (unit cell)  301 . The secondary battery  300  generates a battery voltage Vcc(ba). The protection circuit (charge protection IC)  200  is connected in parallel to the secondary battery  300 . The major features of the protection circuit  200  are an overdischarge protecting function and an overcharge protecting function. The protection circuit  200  includes an overdischarge control circuit  210  serving as the overdischarge protecting function and an overcharge control circuit  220  serving as the overcharge protecting function. 
     An overdischarge-detecting threshold voltage Vth(od) is predetermined in the overdischarge control circuit  210 . The overdischarge control circuit  210  compares the battery voltage Vcc(ba) with the threshold voltage Vth(od). If the battery voltage Vcc(ba) is lower than the threshold voltage Vth(od), the overdischarge control circuit  210  determines an overdischarge mode and generates an overdischarge detection signal at a logical low level. The overdischarge control circuit  210  includes: a zener diode for generating an overdischarge-detecting reference voltage corresponding to the overdischarge-detecting threshold voltage Vth(od); an overdischarge resistive voltage-dividing circuit for dividing the battery voltage Vcc(ba), the circuit comprising a bleeder resistor in series; an overdischarge-detecting comparator for comparing an overdischarge divided-voltage, generated from the overdischarge resistive voltage-dividing circuit, with the overdischarge-detecting reference voltage; and an overdischarge hysteresis circuit arranged between an output terminal and a noninverting input terminal of the overdischarge-detecting comparator. The above components of the overdischarge control circuit  210  are not shown in  FIG. 2 . 
     When the overdischarge divided-voltage is lower than the overdischarge-detecting reference voltage, namely, the battery voltage Vcc(ba) is lower than the overdischarge-detecting threshold voltage Vth(od), the overdischarge-detecting comparator outputs an overdischarge detection signal at a logical low level. On the other hand, when the battery voltage Vcc(ba) is higher than an overdischarge return voltage (Vth(od)+Vhy(od)), the overdischarge-detecting comparator outputs an overdischarge-protection cancel signal at a logical high level. The overdischarge return voltage is obtained by adding the overdischarge-detecting threshold voltage Vth(od) to an overdischarge hysteresis voltage Vhy(od), which is defined by the overdischarge hysteresis circuit. 
     Similarly, an overcharge-detecting threshold voltage Vth(oc) is predetermined in the overcharge control circuit  220 . The overcharge control circuit  220  compares the battery voltage Vcc(ba) with the threshold voltage Vth(oc). When the battery voltage Vcc(ba) is higher than the threshold voltage Vth(oc), the overcharge control circuit  220  determines an overcharge mode and outputs an overcharge detection signal at a logical low level. The overcharge control circuit  220  includes: a zener diode for generating an overcharge-detecting reference voltage corresponding to the overcharge-detecting threshold voltage Vth(oc); an overcharge resistive voltage-dividing circuit for dividing the battery voltage Vcc(ba), the circuit comprising a bleeder resistor in series; an overcharge-detecting comparator for comparing an overcharge divided-voltage, generated from the overcharge resistive voltage-dividing circuit, with the overcharge-detecting reference voltage; and an overcharge hysteresis circuit arranged between an output terminal and a noninverting input terminal of the overcharge-detecting comparator. The above components of the overcharge control circuit  220  are not shown in  FIG. 2 . 
     When the overcharge divided-voltage is higher than the overcharge-detecting reference voltage, namely, the battery voltage Vcc(ba) is higher than the overcharge-detecting threshold voltage Vth(oc), the overcharge-detecting comparator outputs an overcharge detection signal at a logical low level. On the other hand, when the battery voltage Vcc(ba) is lower than an overcharge return voltage (Vth(oc)−Vhy(oc)), the overcharge-detecting comparator outputs an overcharge-protection cancel signal at a logical high level. The overcharge return voltage is obtained by subtracting an overcharge hysteresis voltage Vhy(oc), defined by the overcharge hysteresis circuit, from the overcharge-detecting threshold voltage Vth(oc). 
     The first and second field-effect transistors FET 1  and FET 2  are connected in series between the negative electrode of the secondary battery  300  and the negative terminal  102 . The first field-effect transistor FET 1  operates as a discharge control switch. The second field-effect transistor FET 2  functions as a charge control switch. 
     When the logical low level overdischarge detection signal is supplied from the overdischarge control circuit  210  to the gate of the first field-effect transistor FET 1 , the first field-effect transistor FET 1  is turned off. On the other hand, when the logical high level overdischarge-protection cancel signal is supplied from the overdischarge control circuit  210  to the gate of the first field-effect transistor FET 1 , the first field-effect transistor FET 1  is turned on. Similarly, when the logical low level overcharge detection signal is supplied from the overcharge control circuit  220  to the gate of the second field-effect transistor FET 2 , the second field-effect transistor FET 2  is turned off. When the logical high level overcharge-protection cancel signal is supplied from the overcharge control circuit  220  to the gate of the second field-effect transistor FET 2 , the second field-effect transistor FET 2  is turned on. 
     As described in the foregoing patent, the first field-effect transistor FET 1  has a parasitic diode Dp 1 . The parasitic diode Dp 1  is arranged such that the forward direction thereof corresponds to the charging direction of the secondary battery  300 . The second field-effect transistor FET 2  has a parasitic diode Dp 2 . The parasitic diode Dp 2  is arranged such that the forward direction thereof corresponds to the discharging direction of the secondary battery  300 . Therefore, if the first field-effect transistor FET 1  is turned off, the secondary battery  300  can be charged through the parasitic diode Dp 1 . If the second field-effect transistor FET 2  is turned off, the secondary battery  300  can be discharged through the parasitic diode Dp 2 . 
     The charger  500 ′ will now be described hereinbelow with reference to  FIG. 3 . The charger  500 ′ has a positive terminal  501  and a negative terminal  502 . The positive terminal  501  and the negative terminal  502  of the charger  500 ′ are connected to the positive terminal  101  and the negative terminal  102  of the battery pack  100 ′, respectively. 
     Referring to  FIG. 3 , the charger  500 ′ includes the adapter  700 . The adapter  700  generates an adapter voltage Vcc(ad). The charge control circuit (charge control IC)  600  is connected in parallel to the adapter  700  through the power transistor Tr, the diode D, and the current-detecting resistor R. The major features of the charge control circuit  600  are a constant-current charging function, a constant-voltage charging function, and a primary overvoltage detecting function. The charge control circuit  600  includes: a constant-current control circuit  610  having the constant-current charging function; a constant-voltage control circuit  620  having the constant-voltage charging function; and a primary overvoltage detection circuit  630  having the primary overvoltage detecting function. 
     The constant-current control circuit  610  controls the power transistor Tr so as to keep the potential difference across the current-detecting resistor R at a predetermined value in order to charge the battery pack  100 ′ at a constant current. The constant-voltage control circuit  620  detects the battery voltage Vcc(ba) of the secondary battery  300  and controls the power transistor Tr so that the battery voltage Vcc(ba) does not exceed a predetermined voltage in order to charge the battery pack  100 ′. The primary overvoltage detection circuit  630  detects the primary (adapter) voltage Vcc(ad). If the primary voltage Vcc(ad) is an overvoltage, the primary overvoltage detection circuit  630  turns the power transistor Tr off, thus stopping charging. 
     The power transistor Tr, the diode D, and the current-detecting resistor R are arranged in series in that order between the positive electrode of the adapter  700  and the positive terminal  501 . 
     As mentioned above, the conventional battery pack  100 ′ includes only the charge protection IC  200  and the conventional charger  500 ′ includes the charge control IC  600 . Namely, the conventional charger  500 ′ exclusively charges the battery pack  100 ′. In other words, a commercial charger is not available as the charger  500 ′. To use a commercial charger, namely, to use the charger including only the adapter  700 , the charge control IC  600  and the peripheral devices may be built in the battery pack. 
     For conventional battery protection, the following features are provided. A battery is prevented from igniting in the overcharge mode. The battery is prevented from deteriorating. Further, the battery is prevented from deteriorating and heating in the discharge mode. Even for a unit cell, the safety thereof has been pursued. Thus, the unit cell hardly ignites. In actuality, however, there are many requests to prevent batteries from deteriorating. 
     Referring to  FIG. 2 , the above-mentioned conventional battery module  800 ′ requires the power transistor Tr and the second field-effect transistor FET 2 , which serves as a charge control switch. Namely, the battery module  800 ′ requires the two devices in order to control the charging operation. Since the power transistor Tr is included in the charger and the second field-effect transistor FET 2  is built in the battery pack, the manufacturing cost is high. Moreover, since the charger is concerned with the charge control and the battery pack is concerned with the charge protection, controlling functional mechanisms for battery protection (the charge control function and the charge protection function) is complicated. 
     Since the above two devices generate heat, it is hard to perform the above-mentioned control. 
     SUMMARY OF THE INVENTION  
     It is an object of the present invention to provide a secondary-battery charge control circuit capable of overcoming the above-mentioned disadvantages and exhibiting a battery protecting function with a simple arrangement at low cost. 
     According to the present invention, a battery pack having a charge control function includes: a charge protection circuit for turning a discharge control switch on or off to control a discharge current which flows from a secondary battery to a load and turning a charge control switch on or off to control a charge current which flows from a charger to the secondary battery; and a charge control circuit having a function of turning the charge control switch on or off to stop the charging of the secondary battery through the charger when an abnormal voltage is input. 
     The discharge control switch includes a discharge control field-effect transistor having a gate serving as a control terminal. The charge control switch includes a charge control field-effect transistor having a gate serving as a control terminal. 
     The discharge control field-effect transistor controls an overdischarge control circuit included in the charge protection circuit. The charge control field-effect transistor controls an overcharge control circuit included in the charge protection circuit and also controls the charge control circuit. 
     For the characteristics of the charge control field-effect transistor, a gate voltage of the charge control field-effect transistor is controlled to adjust a drain current thereof so that the one charge control field-effect transistor performs both charge control and overcharge control. 
     The charge protection circuit includes a temperature detection unit. 
     The temperature detection unit detects a temperature in discharge control through the discharge control switch and detects a temperature in the charge control through the charge control switch. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         FIG. 1  is a block diagram showing the structure of a conventional battery module; 
         FIG. 2  is a block diagram showing the arrangement of a conventional battery pack and a protection circuit (charge protection IC) provided therefor; 
         FIG. 3  is a block diagram showing the arrangement of a conventional charger and a charge control circuit (charge control IC) provided therefor; and 
         FIG. 4  is a block diagram showing the structure of a battery pack with a charge control function according to an embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
     A secondary-battery charge control circuit according to an embodiment of the present invention will now be described hereinbelow with reference to  FIG. 4 . Referring to  FIG. 4 , a charge control IC  600  and a charge protection IC  200  in a battery pack  100  are the same as those in  FIG. 1 . In  FIG. 4 , therefore, components having the same functions as those in the components in  FIG. 1  are designated by the same reference numerals. The explanation of the respective components is omitted to simplify the description. In the foregoing related art, the parasitic diode Dp 1  is connected to the first field-effect transistor FET 1  such that the forward direction of the parasitic diode Dp 1  corresponds to the charging direction of the secondary battery and the parasitic diode Dp 2  is connected to the second field-effect transistor FET 2  such that the forward direction of the parasitic diode Dp 2  corresponds to the discharging direction of the secondary battery. According to the present embodiment, the respective parasitic diodes are similarly arranged but they are not shown in  FIG. 4 . 
     Referring to  FIG. 4 , the battery pack  100  has: a battery protection IC  20  including the charge control IC  600 , the charge protection IC  200 , and a temperature detection unit  50 ; a secondary battery (lithium-ion cell)  70 ; a charge control transistor (FET)  30 ; and a discharge control transistor (FET)  40 . The charge control FET  30  and the discharge control FET  40  are connected in series between a negative electrode of the secondary battery  70  and a negative terminal of the charger  500 . 
     The major features of the charge protection IC  200  are an overdischarge protecting function and an overcharge protecting function. The charge protection IC  200  includes an overdischarge control circuit  210  having the overdischarge protecting function and an overcharge control circuit  220  having the overcharge protecting function. The structure of the charge protection IC  200  is the same as that shown in  FIG. 2 . The respective functions of the charge protection IC  200  have been described in detail in the explanation regarding the foregoing related art. In the present embodiment, therefore, the detailed description of the circuit  200  is omitted. 
     The charge control IC  600  has a constant-current control circuit  610  having a constant-current charging function, a constant-voltage control circuit  620  having a constant-voltage charging function, and a primary overvoltage detection circuit  630  having a primary overvoltage detecting function. The structure of the charge control IC  600  is the same as that shown in  FIG. 3 . 
     The discharge control FET  40  operates only as a discharge control switch. The charge control FET  30  operates as a charge control switch and also functions as follows. 
     The constant-current control circuit  610  controls the charge control FET  30  so that the potential difference across a current-detecting resistor R is kept at a predetermined value. The constant-voltage control circuit  620  detects a battery voltage Vcc(ba) of the secondary battery  70  and controls the charge control FET  30  so that the battery voltage Vcc(ba) does not exceed a predetermined voltage. 
     In response to a control signal generated from the constant-voltage control circuit  620 , a current flowing through the charge control FET  30  is controlled. In order to perform a desired constant-current control, the characteristics of the charge control FET  30  have to be determined. For example, in the constant-current control, a voltage of the control signal generated from the constant-voltage control circuit  620  is set so that a drain current of the charge control FET  30  indicates a predetermined value. Constant-voltage control is similarly performed. 
     When the primary voltage Vcc(ad) is an overvoltage, the primary overvoltage detection circuit  630  detects a primary (adapter) voltage Vcc(ad), so that the charge control FET  30  is turned off. Thus, the charging operation is interrupted. In the charge interruption control, in a manner similar to the foregoing constant-current control and overcharge control, the characteristics of the transistor and the voltage of the control signal generated from the overvoltage detection circuit have to be set so that the transistor accurately performs the above-mentioned operation. 
     On the other hand, in the overcharge control, the characteristics of the charge control FET  30  have to be determined so that when a logical low level overcharge detection signal is supplied from the overcharge control circuit  220  to the gate of the charge control FET  30 , the charge control FET  30  is turned off. In other words, in both of the constant-current control and the overcharge control, it is necessary to set the characteristics of the transistor and the voltage of the control signal so that the charge control FET  30  performs the above-mentioned operation with accuracy. 
     The charge control FET  30  corresponds to the power transistor Tr included in the charger  500 ′ in  FIG. 3 . In other words, the main features of the battery pack  100  with the charge control function according to the present invention are that the charge control FET  30  has a function of being controlled by the overcharge control circuit  220  and a function of being controlled by the charge control IC  600  to interrupt a current supplied to the charger  500 . According to the present invention, in the above-mentioned arrangement, the one charge control FET  30  as a charge control device can perform both the charge control and the overcharge control. 
     When the charge control transistor (FET) and the discharge control transistor (FET) are built in the IC, for example, a multichip IC is used, a temperature detection level is improved, resulting in higher level of safety. According to this arrangement, a temperature is detected in the charge control and a temperature is also detected in the discharge control, so that charging and discharging can be controlled. 
     As obviously understood from the above description, according to the present invention, in the battery pack with the charge control function, the charge control FET has the function of controlling the overcharge control circuit and the function of performing the constant-current control and the constant-voltage control of the charge control IC. Consequently, both of the charge control and the overcharge control can be achieved by the one charge control FET serving as a charge control device. Moreover, the arrangement is simplified, resulting in the reduction of the manufacturing cost. 
     According to the present embodiment, the temperature detection unit (thermistor) having a temperature detecting function is built in the battery pack. Although an external thermistor is conventionally attached to the battery pack, the arrangement according to the present invention does not require the external thermistor. 
     According to the present invention, the device (transistor) generating heat is only one. In the related conventional arrangement, two external devices (transistors) generating heat adversely affect on the control. Thus, as compared to the conventional arrangement, the adverse effect caused by the heat can be reduced.