Voltage detection circuit, charge / discharge control device, and storage battery device

Abstract

Provided is a voltage detection circuit (101) that does not decrease in detection accuracy even if a cell imbalance occurs, the voltage detection circuit (101) comprising: a leakage resistance circuit (BR) that divides a battery voltage into a divided voltage (VD1) and a divided voltage (VD2); a comparator (C2) that receives the divided voltage (VD1) and a reference voltage and outputs a signal indicating normal or overcharge; a switch (M3) which is connected in parallel to the resistor unit (R2) and which is turned on when overcharged; a comparator (C1) that receives the divided voltage (VD2) and a reference voltage and outputs a signal indicating a normal or low voltage; a switch (M1) that is connected between the high-voltage side of the resistor unit (R3) and the input unit of the comparator (C1) and that is turned on at a low voltage; and a switch (M2) that is connected between the low-voltage side of the resistor unit (R3) and the input unit of the comparator (C1), and that is turned off at a low voltage. The invention further provides a charging and discharging control circuit and a storage battery device.

Description

Technical Field

[0001] The present invention relates to a voltage detection circuit, a charge / discharge control device, and a battery device. Background Art

[0002] Secondary batteries such as lithium-ion batteries are used in a wide range of fields as power sources for mobile devices, power tools, transportation equipment, etc. In devices that require a high voltage, a battery pack in which a plurality of battery cells are connected in series is used. To safely use the battery pack, a protection circuit that monitors overcharging and overdischarging (low voltage) of each battery cell is connected to the battery pack to prevent imbalance due to individual differences in the battery cells.

[0003] To detect overcharging and the like, most of the protection circuits have a comparator that compares the divided battery voltage with a reference voltage. In such a case, the detection voltage has a "hysteresis" different from the release voltage to prevent unstable operation when the battery voltage fluctuates.

[0004] For example, an overcharging and overdischarging prevention circuit that can provide hysteresis for overcharging detection and overdischarging detection and achieve balance among individual battery cells during overcharge / discharge has been proposed (see Patent Document 1).

[0005] [Prior Art Documents]

[0006] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Laid-Open No. 5-49181 Summary of the Invention

[0008] [Problems to be Solved by the Invention]

[0009] In one aspect of the present invention, an object is to provide a voltage detection circuit that can be miniaturized, can provide hysteresis for overcharging detection and overdischarging detection, and does not reduce the overcharging detection accuracy even when cell imbalance occurs.

[0010] [Means for Solving the Problems]

[0011] The voltage detection circuit in one embodiment of the present invention detects the respective battery voltages in order to perform charge / discharge control on a plurality of battery cells together.

[0012] The voltage detection circuit includes:

[0013] A leakage resistance circuit in which a plurality of resistance portions are connected in series, and divides the battery voltage into a first divided voltage and a second divided voltage;

[0014] A comparator for overcharge detection is input with the first divided voltage and the reference voltage of the leakage resistance circuit, and outputs an output signal indicating a normal state or an overcharge state;

[0015] An overcharge switch is connected in parallel with the first resistor portion in the leakage resistance circuit, is turned off in the normal state, and is turned on in the overcharge state;

[0016] A comparator for low voltage detection is input with the second divided voltage and the reference voltage of the leakage resistance circuit, and outputs an output signal indicating the normal state or the low voltage state;

[0017] A first low voltage switch is connected between the high voltage side of the second resistor portion in the leakage resistance circuit and the input portion of the comparator for low voltage detection that has the first divided voltage, is turned off in the normal state, and is turned on in the low voltage state; and

[0018] A second low voltage switch is connected between the low voltage side of the second resistor portion in the leakage resistance circuit and the input portion of the comparator for low voltage detection, is turned on in the normal state, and is turned off in the low voltage state,

[0019] The voltage detection circuit is connected in parallel for each of the battery cells, and a plurality of the leakage resistance circuits are connected in series.

[0020] A charge and discharge control circuit in an embodiment of the present invention includes:

[0021] The above-described voltage detection circuit, which is connected in parallel with the plurality of battery cells respectively; and

[0022] A control unit that controls a plurality of the voltage detection circuits together,

[0023] The control unit controls the overcharge switch, the first low voltage switch, and the second low voltage switch respectively based on the output signal of the comparator for overcharge detection and the output signal of the comparator for low voltage detection.

[0024] A storage battery device in an embodiment of the present invention includes:

[0025] The above-described charge and discharge control circuit;

[0026] A storage battery pack on which the plurality of battery cells connected in series are mounted; and

[0027] A charge control field effect transistor, which is connected in parallel with the storage battery pack between external terminals.

[0028] [Effects of the Invention]

[0029] According to one aspect of the present invention, there can be provided a voltage detection circuit that can achieve miniaturization, has hysteresis in overcharge detection and overdischarge detection, and does not reduce the overcharge detection accuracy even when cell imbalance occurs. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a circuit diagram showing a battery device and a charge / discharge control circuit in an embodiment of the present invention.

[0031] Figure 2 is a circuit diagram showing a voltage detection circuit in an embodiment of the present invention.

[0032] Figure 3 is a circuit diagram showing a conventional voltage detection circuit.

[0033] DESCRIPTION OF SYMBOLS

[0034] 1: Battery device

[0035] 10: Charge / discharge control device

[0036] 20: Battery pack

[0037] 21, 22, 23, 24: Battery cells

[0038] 30: SCP

[0039] 31, 32: Fuses

[0040] 33: Resistance element

[0041] 40: Charge control FET

[0042] 100: Voltage detection unit

[0043] 101, 102, 103, 104: Voltage detection circuits

[0044] 110: Control unit

[0045] BR: Leakage resistance circuit

[0046] C1: Low voltage detection comparator

[0047] C2: Overcharge detection comparator

[0048] CO: Output terminal

[0049] EB+, EB-: External terminals

[0050] M1: Low voltage switch (first low voltage switch)

[0051] M2: Low voltage switch (second low voltage switch)

[0052] M3: Overcharge switch

[0053] R1, R4, R5: Resistance parts

[0054] R2: Resistance part (first resistance part)

[0055] R3: Resistance part (second resistance part)

[0056] T1, T2, T3: Terminals

[0057] VC1, VC2, VC3, VC4: Input parts

[0058] VD1, VD2, VD3: Divided voltages

[0059] VDD: Power supply terminal

[0060] VR: Reference voltage source

[0061] VSS: Ground terminal Detailed implementation mode

[0062] The present invention is based on the following insight: In the circuit structure described in Patent Document 1, if it is necessary to make the detection of overcharge and overdischarge have hysteresis, two switches are required respectively, so the number of transistors as the switches increases, and the wiring becomes complicated, making it difficult to miniaturize.

[0063] When it is set to a simple circuit structure with one switch each in the detection of overcharge and overdischarge as shown in Figure 3 , the details will be described later. Sometimes, due to cell imbalance, the overcharge detection voltage changes and the detection accuracy of overcharge decreases. Especially in a protection circuit called "secondary protection", it is important to cut off the circuit under overcharge. Even if the detection accuracy is improved by other parts, the detection accuracy of overcharge will decrease due to cell imbalance, and it is not foolproof.

[0064] Therefore, in one embodiment of the present invention, a circuit structure is provided that can achieve miniaturization, can make the overcharge detection and overdischarge detection have hysteresis, and the overcharge detection accuracy will not decrease even if cell imbalance occurs.

[0065] Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

[0066] In addition, in the drawings, the same reference numerals may be given to the same structural parts, and repeated descriptions may be omitted.

[0067] Figure 1 It is a circuit diagram showing a battery device and a charge / discharge control circuit in one embodiment of the present invention.

[0068] The battery device 1 is a power supply device that can safely use battery cells of lithium-ion batteries connected in series, and has a protection integrated circuit (IC) called "secondary protection" that can stop charging. The battery device 1 includes a charge and discharge control device 10 as the protection IC, a battery pack 20 in which four battery cells 21 to 24 are connected in series, a self-control protector (SCP) 30, a charge control field effect transistor (FET) 40, an external terminal EB+, and an external terminal EB-.

[0069] When charging the battery device 1, a charging device is connected between the external terminal EB+ and the external terminal EB-. In addition, when using the battery device 1, a load device is connected between the external terminal EB+ and the external terminal EB-.

[0070] The charge and discharge control device 10 detects the battery voltages of the battery cells 21 to 24 of the battery pack 20 respectively, and controls the charge and discharge according to the detected battery voltages.

[0071] If any one of the battery cells 21 to 24 becomes in an overcharged state, the charge and discharge control device 10 controls to stop charging the battery pack 20. In addition, if any one of the battery cells 21 to 24 becomes in a low voltage state (over-discharged state), the charge and discharge control device 10 controls to stop other functions and stop discharging from the battery pack 20.

[0072] Here, the "overcharged state" means that the battery voltage of any one of the battery cells 21 to 24 exceeds a specified overcharge detection voltage, and the time when the battery voltage exceeds the overcharge detection voltage exceeds a specified time. In addition, when the battery voltage drops below the overcharge release voltage within the specified time, it returns to the "normal state". Furthermore, an "overcharge hysteresis voltage" (= overcharge detection voltage - overcharge release voltage) is set by making the overcharge release voltage lower than the overcharge detection voltage to make the operation stable, so as to prevent the operation from becoming unstable when the battery voltage fluctuates near the overcharge detection voltage. Specifically, it is set that the overcharge detection voltage is 4.6V, the overcharge release voltage is 4.3V, etc.

[0073] The so-called "low voltage state" refers to a state in which the battery voltage of any one of the battery cells 21 to 24 drops below a specified low voltage detection voltage, and the time during which the battery voltage is lower than the low voltage detection voltage continues for a specified time or more. In addition, when the battery voltage rises above the recovery voltage within the specified time, it returns to the "normal state". Furthermore, a "low voltage hysteresis voltage" (= recovery voltage - low voltage detection voltage) is set such that the recovery voltage is higher than the low voltage detection voltage to stabilize the operation, so as to prevent the operation from becoming unstable when the battery voltage fluctuates near the low voltage detection voltage. Specifically, the low voltage detection voltage is set to 2.5V and the recovery voltage is set to 2.7V, etc.

[0074] The so-called "normal state" refers to a state in which the battery voltages of all of the battery cells 21 to 24 are below the overcharge detection voltage and above the low voltage detection voltage.

[0075] In addition, as other functions, there are no particular restrictions, and they can be appropriately selected according to the purpose. For example, in the case where the load device is a notebook computer and the charge and discharge control device 10 includes a constant voltage circuit that supplies a constant voltage to the real-time clock circuit of its external circuit, the constant voltage circuit corresponds to other functions.

[0076] The charge and discharge control device 10 includes a voltage detection unit 100, a control unit 110, a power supply terminal VDD, a ground terminal VSS, input units VC1 to VC4, and an output terminal CO. The battery cells 21 to 24 of the battery pack 20 are connected to the power supply terminal VDD, the input units VC1 to VC4, and the ground terminal VSS of the charge and discharge control device 10 in a manner that allows the battery voltages of the battery cells 21 to 24 to be detected separately.

[0077] The positive electrode side of the battery pack 20 is connected to the external terminal EB+, and the negative electrode side is connected to the external terminal EB-. An SCP 30, which is a fuse circuit for cutting off the charging path during charging, is connected between the external terminal EB+ and the positive electrode side of the battery pack 20. The terminal T1 of the SCP 30 is connected to the battery pack 20, and the terminal T2 of the SCP 30 is connected to the external terminal EB+.

[0078] The SCP 30 has a fuse 31 and a fuse 32 connected in series between the terminal T1 and the terminal T2, and a resistance element 33 is connected between the connection portion of the fuses 31 and 32 and the terminal T3.

[0079] When an overcurrent state occurs, fuses 31 and 32 are blown to cut off the circuit. Additionally, when an overcharge state occurs, the charge control FET 40 conducts, and the resistance element 33 that serves as a heater is energized. Fuses 31 and 32 are blown by the heat generated from the resistance element 33, thereby cutting off the circuit.

[0080] In addition, in the present embodiment, the resistance element 33 is provided as a single one, but it may also be multiple.

[0081] The gate terminal of the charge control FET 40 is connected to the output terminal CO of the charge-discharge control device 10. The charge control FET 40 conducts / turns off based on the control signal from the charge-discharge control device 10, and is off in the normal state and on in the overcharge state.

[0082] Therefore, as an operation of the charge-discharge control device 10, the charge control FET 40 is pre-set to be off in the normal state. When an overcharge state occurs during charging, the charge control FET 40 is turned on to energize the resistance element 33, and fuses 31 and 32 are blown by the heat to stop charging. Additionally, when a low voltage state occurs, the charge-discharge control device 10 stops other functions and stops discharging from the battery pack 20.

[0083] Next, the voltage detection unit 100 and the control unit 110 of the charge-discharge control device 10 will be described in detail.

[0084] In order to detect the battery voltages of the battery cells 21 to 24 respectively, the voltage detection unit 100 includes voltage detection circuits 101 to 104 connected to the positive electrode side and the negative electrode side of each battery cell.

[0085] The voltage detection circuits 101 to 104 are all formed in the same manner. Therefore, the voltage detection circuit 101 will be described below, and the descriptions of the voltage detection circuits 102 to 104 will be omitted.

[0086] Figure 2 It is a circuit diagram showing a voltage detection circuit in an embodiment of the present invention.

[0087] As Figure 2 shown, the voltage detection circuit 101 includes a leakage resistance circuit BR, a reference voltage source VR, a low voltage detection comparator C1, a low voltage switch M1, a low voltage switch M2, an overcharge detection comparator C2, and an overcharge switch M3.

[0088] The leakage resistance circuit BR is a voltage dividing circuit, and is connected in series from the positive electrode to the negative electrode of the battery cell 21 in the order of a plurality of resistance parts R1, R2, R3, R4, and R5.

[0089] In addition, each resistor section can be formed by a single resistor element or multiple resistor elements. Further, a fuse element may be included in each resistor section to enable adjustment of the resistance value, and the detection accuracy is mostly improved by trimming the fuse element.

[0090] The leakage resistance circuit BR divides the battery voltage of the battery cell 21 into a divided voltage VD1 (first divided voltage), a divided voltage VD2 (second divided voltage), and a divided voltage VD3.

[0091] The divided voltage VD1 is output from the connection portion of the resistor section R2 and the resistor section R3, and is input to the first input portion of the low-voltage detection comparator C1 via the low-voltage switch M1.

[0092] The divided voltage VD2 is output from the connection portion of the resistor section R3 and the resistor section R4, and is input to the first input portion of the low-voltage detection comparator C1 via the low-voltage switch M2.

[0093] The divided voltage VD3 is output from the connection portion of the resistor section R4 and the resistor section R5, and is input to the first input portion of the overcharge detection comparator C2.

[0094] The reference voltage source VR outputs the generated reference voltage VREF to the second input portion of the low-voltage detection comparator C1 and the second input portion of the overcharge detection comparator C2, respectively.

[0095] The low-voltage detection comparator C1 inputs the divided voltage VD1 or the divided voltage VD2 to the first input portion, and inputs the reference voltage VREF to the second input portion. Then, the low-voltage detection comparator C1 compares any one of the divided voltages with the reference voltage VREF, and outputs an output signal of H level or L level corresponding to the result to the control unit 110, thereby detecting the low voltage of the battery cell 21.

[0096] The low-voltage switches M1 and M2 can generate a "low-voltage hysteresis voltage", and the overcharge detection accuracy will not be reduced even if any one of the battery cells is in a low-voltage state.

[0097] First, the case where the low-voltage switches M1 and M2 generate a "low-voltage hysteresis voltage" will be described.

[0098] The low-voltage switch M1 is a transistor, and is connected between the high-voltage side of the resistor section R3, which is the second resistor section in the leakage resistance circuit BR, and the first input portion of the low-voltage detection comparator C1. The gate terminal of the low-voltage switch M1 is connected to the control unit 110, and is turned off in the normal state and turned on in the low-voltage state according to the control signal from the control unit 110.

[0099] The low-voltage switch M2 is a transistor and is connected between the low-voltage side of the resistor part R3 in the leakage resistance circuit BR and the first input part of the low-voltage detection comparator C1. The gate terminal of the low-voltage switch M2 is connected to the control unit 110 and is turned on in the normal state and turned off in the low-voltage state according to the control signal from the control unit 110.

[0100] Therefore, by turning on and off the low-voltage switch M1 and the low-voltage switch M2, the divided voltage VD1 is input to the first input part of the low-voltage detection comparator C1 in the low-voltage state, and the divided voltage VD2 is input in the normal state, thus generating a "low-voltage hysteresis voltage".

[0101] The overcharge detection comparator C2 compares the divided voltage VD3 input to the first input part with the reference voltage VREF input to the second input part, and outputs an output signal of H level or L level corresponding to the result to the control unit 110, thereby detecting the overcharge of the battery cell 21.

[0102] The overcharge switch M3 is a transistor and is connected in parallel with the resistor part R2 as the first resistor part. The gate terminal of the overcharge switch M3 is connected to the control unit 110 and is turned off in the normal state and turned on in the overcharge state according to the control signal from the control unit 110.

[0103] Therefore, by turning on and off the overcharge switch M3, a voltage drop occurs in the resistor part R2 in the normal state, and no voltage drop occurs in the overcharge state, thus generating an "overcharge hysteresis voltage". Thus, an "overcharge hysteresis voltage" can be generated by one switch, and miniaturization can be achieved without leading to complex wiring.

[0104] In addition, in the entire voltage detection unit 100, as Figure 1 shown, the leakage resistance circuits BR are respectively provided in the battery cells 21 to 24, and the four leakage resistance circuits are connected in series.

[0105] Based on the output signal of any one of the voltage detection circuits 101 to 104, the control unit 110 outputs a control signal that turns on / off the charge control FET 40, the low-voltage switch M1, the low-voltage switch M2, and the overcharge switch M3 in all the voltage detection circuits 101 to 104 at once.

[0106] Specifically, if all of the battery cells 21 to 24 are in the normal state, the control unit 110 turns off the low-voltage switch M1, turns on the low-voltage switch M2, and turns off the overcharge switch M3 for all the voltage detection circuits 101 to 104.

[0107] Further, if any one of battery cells 21 to 24 is in a low voltage state, the control unit 110 turns on the low voltage switch M1, turns off the low voltage switch M2, and turns off the overcharge switch M3 for all the voltage detection circuits 101 to 104.

[0108] Furthermore, if any one of battery cells 21 to 24 is in an overcharge state, the control unit 110 turns on the low voltage switch M1, turns off the low voltage switch M2, and turns on the overcharge switch M3 for all the voltage detection circuits 101 to 104.

[0109] And, for example, consider a case of "cell imbalance" where battery cells 21 to 23 are in a normal state and only battery cell 24 changes from the normal state to a low voltage state. In this case, in order to control the low voltage state, the control unit 110 turns on the low voltage switch M1, turns off the low voltage switch M2, and keeps the overcharge switch M3 off for all the voltage detection circuits 101 to 104.

[0110] Even in the case of such cell imbalance, the overcharge detection voltage VCU (which is a standard value and thus not shown in the figure) of the voltage detection circuits 101 to 104 is the same value in the normal state and the low voltage state.

[0111] Specifically, if the resistance values of the resistor parts R1, R2, R3, R4, and R5 are set to r1, r2, r3, r4, and r5 in sequence, it is as follows.

[0112] In the normal state, the low voltage switch M1 is off, the low voltage switch M2 is on, and the overcharge switch M3 is off. Therefore, the overcharge detection voltage VCU becomes the following formula (1).

[0113] VCU = ((r1 + r2 + r3 + r4 + r5) / r5) × VREF ··· (1)

[0114] In the low voltage state, the low voltage switch M1 is on, the low voltage switch M2 is off, and the overcharge switch M3 is off. Therefore, the overcharge detection voltage VCU becomes the following formula (2).

[0115] VCU = ((r1 + r2 + r3 + r4 + r5) / r5) × VREF ··· (2)

[0116] Therefore, as shown in the aforementioned formulas (1) and (2), even when cell imbalance occurs, the overcharge detection voltage VCU in one embodiment of the present invention does not change in the normal state and the low voltage state, so the overcharge detection accuracy will not decrease. That is, it is unlikely that one battery cell becomes in the low voltage state while other battery cells are in the overcharged state, but the battery storage device 1 can accurately cut off the circuit in the overcharged state through the charge and discharge control device 10 including the voltage detection circuits 101 to 104.

[0117] Hereinafter, in order to compare with one embodiment of the present invention, a previous voltage detection circuit will be described.

[0118] Figure 3 It is a circuit diagram showing the previous voltage detection circuit.

[0119] As Figure 3 shown, in the previous voltage detection circuit, in the voltage detection circuit 101 which is one embodiment of the present invention, the low voltage switch M4 is connected in parallel with the resistor part R3 instead of the low voltage switches M1 and M2, and other than that, it is the same as the voltage detection circuit 101.

[0120] The low voltage switch M4 is a transistor, and generates a "low voltage hysteresis voltage" by being off in the normal state and on in the low voltage state.

[0121] In such a previous voltage detection circuit, the overcharge detection voltage VCU changes in the normal state and the low voltage state due to cell imbalance. Specifically, as described below.

[0122] In the normal state, the overcharge switch M3 is off and the low voltage switch M4 is on, so the overcharge detection voltage VCU becomes the following formula (3).

[0123] VCU = ((r1 + r2 + r4 + r5) / r5) × VREF ··· (3)

[0124] In the low voltage state, the overcharge switch M3 is off and the low voltage switch M4 is off, so the overcharge detection voltage VCU becomes the following formula (4).

[0125] VCU = ((r1 + r2 + r3 + r4 + r5) / r5) × VREF ··· (4)

[0126] Therefore, as shown in the aforementioned formulas (3) and (4), when cell imbalance occurs, the overcharge detection voltage VCU in the previous voltage detection circuit changes between the normal state and the low voltage state, and the overcharge detection accuracy decreases. Especially in a charge-discharge control device called "secondary protection", it is important to cut off the circuit in the overcharge state. Even if the detection accuracy is improved by trimming using a fuse element as described above, the overcharge detection accuracy will still decrease due to cell imbalance, and it is not foolproof.

[0127] Therefore, in one embodiment of the present invention, by configuring the low voltage switches M1 and M2 as described below Figure 2 to replace the low voltage switch M4, the overcharge detection voltage does not change between the normal state and the low voltage state, and the overcharge detection accuracy will not decrease even if cell imbalance occurs.

[0128] As described above, the voltage detection circuit in one embodiment of the present invention is a circuit that detects the respective battery voltages in order to perform charge-discharge control on multiple battery cells together. The voltage detection circuit has a leakage resistance circuit, and a plurality of resistance parts are connected in series in the leakage resistance circuit to divide the battery voltage into a first divided voltage and a second divided voltage. In addition, the voltage detection circuit further has: an overcharge detection comparator, which is input with the first divided voltage and a reference voltage and outputs a signal indicating the normal state or the overcharge state; and an overcharge switch, which is connected in parallel with the first resistance part and is off in the normal state and on in the overcharge state. Furthermore, the voltage detection circuit further has a low voltage detection comparator, which is input with the second divided voltage and a reference voltage and outputs a signal indicating the normal state or the low voltage state. Moreover, the voltage detection circuit further has: a first low voltage switch, which is connected between the high voltage side of the second resistance part and the input part of the low voltage detection comparator and is off in the normal state and on in the low voltage state; and a second low voltage switch, which is connected between the low voltage side of the second resistance part and the input part of the low voltage detection comparator and is on in the normal state and off in the low voltage state. And the voltage detection circuit is respectively connected in parallel with multiple battery cells, and a plurality of leakage resistance circuits are connected in series.

[0129] Thereby, the voltage detection circuit can be miniaturized, and hysteresis can be provided for overcharge detection and over-discharge detection, and the overcharge detection accuracy will not decrease even if cell imbalance occurs.

[0130] In this embodiment, the secondary protection of a lithium-ion battery is taken as an example for illustration, but it is not limited thereto, and it can be applied as long as it is a device using a circuit for voltage detection.

[0131] In addition, in order to control the charge and discharge of the battery pack based on the output signals from the respective comparators, the control unit may also include various circuits such as a delay circuit and an oscillation circuit.

[0132] In addition, in the above-described embodiment, the resistance portion of the leakage resistance circuit is provided with five, but it is not limited thereto, and it is sufficient if it has at least a first resistance portion and a second resistance portion.

[0133] Furthermore, in the above-described embodiment, the number of battery cells is four, but it is not limited thereto, and it is sufficient if it is plural.

[0134] Moreover, various switches are described as N-type metal oxide semiconductor (NMOS) transistors in the drawings, but it is not limited thereto, and any element having an on / off function may be used. For example, considering the conductivity type of the semiconductor substrate, the substrate bias effect, etc., various switches may be P-type metal oxide semiconductor (PMOS) transistors, or may be junction FETs.

Claims

1. A voltage detection circuit for detecting the voltage of each battery in order to control the charge and discharge of a plurality of battery cells at once, wherein the voltage detection circuit is characterized by: a leakage resistance circuit having a plurality of resistance parts connected in series, and dividing the battery voltage into a first divided voltage and a second divided voltage; an overcharge detection comparator, to which the first divided voltage of the leakage resistance circuit and a reference voltage are input, and outputs an output signal indicating a normal state or an overcharge state; an overcharge switch connected in parallel with the first resistor section in the leakage resistor circuit, being turned off in the normal state and turned on in the overcharge state; a low voltage detection comparator, to which the second divided voltage of the leakage resistance circuit and the reference voltage are input, and outputs an output signal indicating the normal state or the low voltage state; A first low voltage switch connected between the high voltage side of the second resistor section in the leakage resistor circuit and the input section of the low voltage detection comparator to which the first divided voltage is input, and is turned off in the normal state and turned on in the low voltage state; as well as A second low voltage switch is connected between the low voltage side of the second resistor section in the leakage resistor circuit and the input section of the low voltage detection comparator, is turned on in the normal state, and is turned off in the low voltage state. The voltage detection circuits are connected in parallel to the respective battery cells, and a plurality of the leakage resistance circuits are connected in series.

2. A charge and discharge control circuit, characterized in that: have: The voltage detection circuit as claimed in claim 1, connected in parallel with the plurality of battery cells respectively; and The control unit controls the plurality of voltage detection circuits at once. The control unit controls the overcharge switch, the first low voltage switch, and the second low voltage switch based on an output signal of the overcharge detection comparator and an output signal of the low voltage detection comparator.

3. A battery device, characterized in that: have: The charge and discharge control circuit as claimed in claim 2; a battery pack equipped with the plurality of battery cells connected in series; and The charge control field effect transistor is connected in parallel with the battery pack between the external terminal pair.

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