JP2006246585A - Battery protection circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a battery protection circuit, capable of eliminating a required charging voltage detection function required on the charger side and a plurality of charging voltage output function, by controlling the charging voltage in the inside of a battery pack. <P>SOLUTION: A charging control IC11 monitors a battery voltage VBATT of a lithium ion battery 10, by measuring the terminal voltage of the lithium ion battery 10 connected between a VDD terminal and a GND terminal, and controls the gate/source voltage VGS of a transistor Q2 on the basis of the measured results. Furthermore, the charging control IC11 makes the gate/source voltage VGS of the transistor Q2 changes, increases the drain/source resistance RDS of the transistor Q2, and increases the drain/source voltage VDS of the transistor Q2 so as to keep the value of the battery voltage VBATT constant (V1). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a battery protection circuit, and more particularly to a charge voltage control type battery protection circuit built in a lithium ion battery pack that is charged by a constant voltage and constant current method (hereinafter referred to as CCCV).

  FIG. 7 shows a circuit diagram of an example of a conventional battery protection circuit. In the figure, a circuit portion comprising a charging control IC 15, field effect transistors (FETs) Q 1 and Q 2, a resistor R, and a thermistor (TH) is a battery protection circuit for the lithium ion battery 10, and a charger including a charging circuit 16. Connected. In the charging control IC 15, the control voltage applied to the gate of the transistor Q <b> 2 is a binary level of high or low level, and the charging current is controlled by controlling the internal resistance of Q <b> 2.

  The battery protection circuit portion shown in FIG. 7 and the lithium ion battery 10 constitute the battery pack 21 or 23 of FIG. 8, and the charging circuit 16 of FIG. 7 constitutes the charger 25 of FIG. . In FIG. 8, the type A battery pack 21 has a connection terminal 22 and a battery type detection terminal S, whereas the type B battery pack 23 has a connection terminal 24. It does not have a terminal for type detection. The battery packs 21 and 23 are connected to the connection terminals 22 and 24 and the connection terminal 26 of the charger 25, whereby the batteries in the battery packs 21 and 23 are charged by the charger 25.

  Here, the battery packs 21 and 23 are internally connected to GND, OPEN, etc. for each battery pack type, so that the battery pack type is detected on the charger side and a voltage output corresponding to the battery pack type is output. It has become. Further, the charger 25 is configured to detect the presence or absence of the battery pack type detection protrusion S of the connected battery pack by the detection SW 27, whereby the charger 25 outputs a voltage output corresponding to the type of the battery pack. Designed to be In FIG. 8, since the battery pack 21 has the battery pack type detection protrusion S, the charger 25 recognizes that the connected battery pack 21 is type A, and outputs a voltage corresponding to the type A. The battery pack 23 that does not have the battery pack type detection protrusion S is recognized as the type B and outputs a voltage corresponding to the type B.

  In addition, the battery pack device includes a detection resistor, a control circuit, and a control FET, detects the charging current and charging voltage of the battery cell via the detection resistor, and has a potential corresponding to the charging current or charging voltage by the control circuit. A battery pack device that generates a control signal and supplies the control signal to the gate electrode of the control FET that opens and closes the charging path to control the opening and closing of the control FET and variably control the on-resistance of the control FET It is known (see, for example, Patent Document 1). According to this conventional battery pack device, the configuration is particularly suitable for charging a lithium ion battery.

  In addition, when performing constant current constant voltage charging for the secondary battery via the charging circuit, current limiting means for limiting the charging current by a control signal inserted between the secondary battery and the charging circuit; A charging device having a voltage monitoring unit that monitors a terminal voltage of a battery and outputs a control signal with a predetermined threshold as a reference is also conventionally known (for example, see Patent Document 2). In this charging device, even if the secondary battery is in an overcharged state, monitoring the terminal voltage of the secondary battery and starting the current limiting means prevents excessive current from flowing in the secondary battery or the charging circuit. Can be prevented.

JP 2000-0669689 A JP 2001-275271 A

  However, in the conventional battery protection circuit, since the battery pack voltage cannot be controlled on the battery pack side, a mechanism for notifying the charger side of the required charge voltage on the charger side is required. Further, in the conventional battery protection circuit, since the battery charging voltage cannot be controlled on the battery pack side, a mechanism for outputting all the charging voltages required by the battery pack on the charger side is required.

  In the conventional charger-battery pack relationship, the charger has the function of setting the output of the charging voltage. Therefore, it is necessary for the charger to support multiple types of battery packs, and when multiple types of charging voltages are required for the multiple types of battery packs, the battery pack side requires the charger side. It was necessary to have a function of notifying a charging voltage, a function of identifying a plurality of types of battery packs on the charger side, and a function of generating a plurality of types of charging voltages.

  Further, since the battery pack device described in Patent Document 1 includes a switching regulator, the charging voltage / charging current of the battery cell may be controlled by the switching regulator, and both the charging current and the charging voltage are controlled. Because of this, the configuration is complicated. Furthermore, Patent Document 2 discloses a configuration for controlling the charging current, but does not disclose a configuration for controlling the charging voltage.

  The present invention has been made in view of the above points, and by controlling the charging voltage inside the battery pack, the required charging voltage detection function of the battery pack, which is necessary on the charger side, and a plurality of charging voltage output functions are provided. An object is to provide a battery protection circuit that can be eliminated.

  Another object of the present invention is to provide a battery protection circuit that can realize cost reduction and space saving of a battery pack.

  In order to achieve the above object, the first invention is a battery protection circuit that is charged with a constant current when the battery voltage is lower than a predetermined constant voltage, and charged with a constant voltage when the battery voltage is higher than a predetermined voltage. The battery voltage measuring means for measuring the battery voltage of the battery, and the charging voltage to the battery is controlled only during the period when the battery voltage measured by the battery voltage measuring means reaches a constant voltage and is charged at a constant voltage. And charging voltage control means for maintaining the battery voltage at a constant voltage.

  In the present invention, since no control is performed in the constant current charging mode, and the charging voltage control is performed on the external output side of the charger after the constant voltage charging mode, the charger side Can eliminate the function of detecting the charging voltage and eliminates the need for a voltage detecting resistor required in the constant current charging mode.

  In order to achieve the above object, according to a second aspect, the charging voltage control means of the first aspect is a variable resistor whose resistance value is variably controlled according to the battery voltage measured by the battery voltage measuring means. It has the element.

  In order to achieve the above object, the third invention is the charge voltage control means of the first invention, a field effect transistor having a drain and a source connected between the charger and the battery, and a battery voltage measurement. And a control circuit that varies the drain-source resistance of the field effect transistor by controlling the gate voltage of the field effect transistor so that the battery voltage measured by the means becomes a constant voltage. And

  Further, in order to achieve the above object, the fourth invention is charged with a constant current when the battery voltage of the battery in the battery pack connected to the charger is smaller than a predetermined voltage predetermined by the charger, A protection circuit for a battery that is charged with a constant voltage when the voltage exceeds a certain voltage, a battery voltage measuring means for measuring the battery voltage of the battery, a variable resistance element whose resistance value is variable by a control voltage, and a battery voltage measuring means The battery voltage is kept constant by generating a control voltage according to the battery voltage and varying the resistance value of the variable resistance element only during the period when the battery voltage measured in step 1 reaches a constant voltage and charging is performed at a constant voltage. And a control circuit for maintaining the voltage, and the battery pack includes a battery voltage measuring means, a variable resistance element, and a control circuit.

  In this invention, since the necessary charging voltage is generated in the battery pack, the battery pack has a function of notifying the charger side of the necessary charging voltage, a function of detecting the necessary charging voltage on the charger side, and the battery pack. Therefore, it is not necessary to provide a function for generating a plurality of charging voltages, and it is only necessary to prepare one type of CCCV output on the charger side, and it is not necessary to have a plurality of types of CCCV outputs.

  In order to achieve the above object, according to a fifth aspect of the present invention, in the variable resistance element according to the fourth aspect of the present invention, a control voltage from a control circuit is applied to a gate, and the drain and source are predetermined terminals of a charger and a battery. The voltage drop due to the current flowing through the battery and the drain-source resistance of the field effect transistor so that the battery voltage measured by the battery voltage measuring means becomes a constant voltage. The analog voltage that controls the drain-source resistance is generated as a control voltage and applied to the gate so that the sum of the voltage and the battery voltage is approximately equal to the output voltage of the charger. And Here, the battery voltage measuring means and the control circuit are constituted by an integrated circuit for charge control.

  According to the present invention, the function of detecting the charging voltage required by the battery on the charger side is deleted by controlling the charging voltage with a circuit outside the charger. Since only the CCCV output needs to be prepared and there is no need to have a plurality of CCCV outputs, the circuit scale of the charger can be reduced, and the battery pack side containing the battery has an electrical signal terminal for notifying the charger, Since the physical mechanism for detection by the detection SW of the charger can be deleted, the cost and space saving of the battery pack can be reduced.

  FIG. 1 shows a circuit diagram of an embodiment of a battery protection circuit according to the present invention. FIG. 2 is a characteristic diagram of the VDS voltage, battery voltage VBATT, and battery current IBATT of the field effect transistor (FET) Q2 in FIG. In FIG. 1, a charge control IC 11 has a VDD terminal and a GND terminal connected to a positive terminal and a negative terminal of a lithium ion battery 10, and a DOUT terminal is an FET (field effect transistor; hereinafter simply abbreviated as a transistor). ) Connected to the gate of Q1, the COUT terminal is connected to the gate of the transistor Q2, and the VSS terminal is connected to the negative terminal of the lithium ion battery 10 via the resistor R.

  The transistor Q1 has a source connected to the negative terminal of the lithium ion battery 10, a drain connected to the drain of the transistor Q2, and a magnetic diode connected between the drain and source. The source of the transistor Q2 is connected to the VSS terminal of the charging control IC 11 via a resistor R, and a magnetic diode is connected between the drain and source. TH is a thermistor. This battery protection circuit is connected to a charger (not shown).

  Thereby, the charge control IC 11 monitors the battery voltage VBATT of the lithium ion battery 10 by measuring the terminal voltage of the lithium ion battery 10 connected between the VDD terminal and the GND terminal, and based on the measurement result, The gate-source voltage VGS of the transistor Q2 is controlled, and the drain-source voltage VDS of the transistor Q2 is controlled. Here, the charge control IC 11 according to the present embodiment is characterized in that a constant charge voltage V1 is obtained as an analog voltage as will be described later from the voltage applied from the COUT terminal to the gate of the transistor Q2. . Note that the circuit operations of the transistors Q1 and Q2 are well known to those skilled in the art and are not directly related to the present invention, and thus detailed description thereof is omitted.

  Next, operations of the charging control IC 11 and the transistor Q2 in the present embodiment will be described. In the following description, for CCCV charging required by the battery pack, the current value in the CC region at the initial stage of charging is CC = I1, and the charging voltage value in the CV region in the latter stage of charging is CV = V1. In addition, as shown in FIG. 2, the CCCV charging is performed in two areas, namely, the CC area in the initial stage of charging and the CV area in the latter stage of charging. The latter-stage CV region will be described as region B.

  Further, the output characteristics of the charge control IC 11 used in this embodiment are as shown in FIG. 3, and the output voltage Vo needs to be Vo> V1 and the output current Io (droop characteristic) = I1. . As will be described later in the description, the CCCV charging in the present embodiment does not control the charging voltage / charging current on the protection circuit side of the battery pack in the region A, but the output of the charging control IC 11. This is because in the region B, the output voltage Vo of the charging control IC 11 is dropped in the protection circuit and charged at a constant voltage value V1.

  Next, an operation that is a new part of the charging control IC 11 that realizes charging voltage control inside the battery pack in the present embodiment will be described. Since components other than the charging control IC 11 do not perform a functional operation, there is no change from the conventional one. The charging control IC 11 monitors the battery voltage VBATT of the lithium ion battery 10 by measuring the voltage between VDD and GND. In the CC area (VBATT <V1) which is the area A, the charging voltage / current control is performed. Nothing is performed, and charging is performed depending on the output characteristics of a charger (not shown) to be connected.

  That is, after the start of charging, in the region A until the battery voltage VBATT reaches the set voltage V1, it operates in the constant current charging mode with the current value I1 of the charging current as shown in FIG. The battery voltage VBATT of the battery 10 gradually increases toward the set voltage V1 as indicated by II in FIG.

  Next, the operation of the charging control IC 11 when charging proceeds and the charging shifts to the region B will be described. When the battery voltage VBATT of the lithium ion battery 10 reaches V1, the charging control IC 11 shifts to the region B and operates in the constant voltage charging mode of the set voltage V1, and the battery voltage VBATT of the lithium ion battery 10 is shown in FIG. At I and as shown in FIG. 3, a constant voltage V1 is obtained, and the charging current gradually decreases as indicated by II in FIG.

  The charge voltage is controlled by controlling the drain-source resistance RDS of the transistor Q2 by controlling the output voltage (VGS) of the COUT pin of the charge control IC 11 connected to the gate of the transistor Q2. Since the drain-source resistance RDS control is almost the same as controlling the drain-source voltage VDS, the battery voltage VBATT is controlled so that VBATT becomes a constant value of V1.

  At this time, the VGS-RDS characteristic of the transistor Q2 generally has a characteristic that the drain-source resistance RDS rapidly increases as the drain-source voltage VGS decreases as shown in FIG. As shown in FIG. 6, when the gate-source voltage VGS decreases, the drain-source voltage VDS increases rapidly. However, the characteristic diagram of FIG. 5 shows a general VGS-VDS characteristic when the current Io flowing through the transistor Q2 is constant.

  Next, the control of the gate-source voltage VGS of the charging control IC 11 in the region B will be described in detail with reference to FIG. 6A shows an equivalent circuit diagram of the battery protection circuit of FIG. 1 at a certain point where the charging control IC 11 controls the charging voltage in the region B. FIG. In FIG. 6A, for easy understanding of the operation, the transistor Q2 in FIG. 1 is represented by a resistor R2, and the transistor Q1 and the charge control IC 11 are not described. In addition, the voltage and current of each part in FIG.

Output characteristics of the charger 12: Vo = 5.0V, Io = 0.6A
Battery pack required charging specification: V1 = 4.5V, I1 = 0.6A
The state of the battery 10 at a certain point in the region B shown in FIG.
VBATT = 4.5V, IBATT = 0.5A
Next, taking FIG. 6A and FIG. 6B as an example, a method for controlling VBATT of the charging control IC 11 will be described. If the charging voltage / current control is not performed in the protection circuit after the charging is in the region B and the battery voltage VBATT becomes V1, the battery voltage is charged according to the output characteristics of the charger 12 (not shown in FIG. 1). The battery voltage becomes larger than V1.

  Therefore, the charge control IC 11 changes the gate-source voltage VGS of the transistor Q2, increases the drain-source resistance RDS of the transistor Q2, and increases the drain-source voltage VDS of the transistor Q2. The value of the voltage VBATT is controlled to be constant at V1. At this time, the transistor Q1 is turned on, and its drain-source resistance RDS is set to the minimum value.

  For example, in the example shown in FIG. 6, the value of V1 to be controlled is 4.5V. Here, the output voltage Vo of the charger 12 at an arbitrary point Io = 0.5A in the region B is 5.0V as shown in FIG. 6B, so that RDS = 1Ω. If VGS is controlled, the voltage drop value VDS at R2 in FIG. 6A is 0.5V, and the value of VBATT is 4.5V, which is a value obtained by subtracting VDS = 0.5V from Vo = 5.0V. It will be possible to control.

  Here, CCCV charging at a unique voltage value set by the charging control IC 11 becomes possible by continuing the above-described operation of keeping VBATT = V1 corresponding to changes in VBATT, Vo, and Io. That is, in the circuit according to the present embodiment, if the charging voltage V1 is lower than the output voltage Vo of the charger 12, CCCV charging with the unique charging voltage V1 set by the charging control IC 11 is possible. That is, in the circuit of the present embodiment, if the charging voltage V1 is lower than Vo, CCCV charging with the unique charging voltage V1 set by the charging control IC 11 is possible.

  As described above, according to the present embodiment, the configuration of the charging control IC, which has conventionally only operated as a battery protection function, is changed without adding / changing parts as compared with the conventional battery protection circuit. By causing the transistor Q2 to perform the charging voltage control operation, the CCCV charging with the voltage set by the charging control IC 11 can be performed on the lithium ion battery 10 only by the circuit in the battery pack.

  For this reason, even if a battery pack supports multiple types of battery packs and the battery pack requires a plurality of charging voltages, the charger side has a CCCV output that outputs at a higher voltage than the required voltage. Charging is performed by generating a unique charging voltage necessary for each of the internal protection circuits of the individual battery packs.

  For this reason, there is no need to switch the charging voltage on the charger side according to the charging voltage required on the charger side. The effect that the function of generating a voltage is not necessary is obtained. Therefore, only one type of CCCV output needs to be prepared on the charger side, and since there is no need to have a plurality of CCCV outputs, the circuit scale of the charger is reduced, and the charging voltage required for the battery pack on the charger side is reduced. Since it is not necessary to detect, a physical mechanism such as a detection signal terminal having a required voltage and a detection SW can be eliminated, so that cost and space can be reduced.

  Further, in the present embodiment, it is possible to design a new battery pack that can be charged with a conventional charger only by a design change on the battery pack side without a design change on the charger side. In addition, the battery pack side can eliminate the electrical signal terminal for notifying the charger and the physical mechanism for detection by the detection SW of the charger, so that the cost and space saving of the battery pack can be reduced. .

It is a circuit diagram of one embodiment of the present invention. It is a figure which shows the charging current and charging voltage of FIG. FIG. 2 is an output characteristic diagram of the charging control IC in FIG. 1. It is a characteristic view of an example of the gate-source voltage versus the drain-source resistance of the field effect transistor. It is a characteristic view of an example of the voltage between the gate source of the field effect transistor versus the drain source voltage. FIG. 2 is an equivalent circuit diagram and a characteristic diagram for explaining a method of controlling VBATT by the charging control IC in FIG. 1. It is a circuit diagram of an example of the conventional battery protection circuit. It is connection explanatory drawing of an example of the battery pack and charger of the conventional battery protection circuit.

Explanation of symbols

10 Lithium ion battery 11 Charge control IC
12 Charger Q1, Q2 Field Effect Transistor (FET)
R, R2 resistance

Claims (6)

A battery protection circuit that is charged with a constant current when the battery voltage is smaller than a predetermined voltage, and charged with a constant voltage when the battery voltage is greater than or equal to the predetermined voltage,
Battery voltage measuring means for measuring the battery voltage of the battery;
Only when the battery voltage measured by the battery voltage measuring means reaches the constant voltage and charging is performed at the constant voltage, the battery voltage is controlled by controlling the charging voltage to the battery. And a charging voltage control means for maintaining the battery protection circuit.   2. The battery protection circuit according to claim 1, wherein the charging voltage control means includes a variable resistance element whose resistance value is variably controlled according to the battery voltage measured by the battery voltage measuring means.   The charging voltage control means includes a field effect transistor having a drain and a source connected between a charger and the battery, and the battery voltage measured by the battery voltage measuring means is the constant voltage. 2. The battery protection circuit according to claim 1, further comprising a control circuit that varies a drain-source resistance of the field effect transistor by controlling a gate voltage of the field effect transistor. Protection of a battery that is charged with a constant current when the battery voltage of the battery in the battery pack connected to the charger is smaller than a predetermined voltage determined by the charger, and charged with a constant voltage when the battery voltage is higher than the predetermined voltage A circuit,
Battery voltage measuring means for measuring the battery voltage of the battery;
A variable resistance element whose resistance value is variable by a control voltage;
The resistance of the variable resistance element is generated by generating the control voltage according to the battery voltage only in a period in which the battery voltage measured by the battery voltage measuring means reaches the constant voltage and charging is performed at the constant voltage. And a control circuit for maintaining the battery voltage at the constant voltage by varying a value, and the battery voltage measuring means, the variable resistance element, and the control circuit are included in the battery pack. Battery protection circuit.   The variable resistance element is a field effect transistor in which the control voltage from the control circuit is applied to a gate, and a drain and a source of the variable resistance element are connected to a predetermined terminal of the charger and the battery. The sum of the battery voltage and the voltage drop due to the current flowing through the battery and the drain-source resistance of the field effect transistor so that the battery voltage measured by the battery voltage measuring means becomes the constant voltage. 5. The battery according to claim 4, wherein an analog voltage for controlling the drain-source resistance is generated as the control voltage and applied to the gate so that the voltage is substantially equal to the output voltage of the charger. Protection circuit. 6. The battery protection circuit according to claim 4, wherein the battery voltage measuring means and the control circuit are configured by an integrated circuit for charge control.

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