Secondary battery protection circuit, battery pack, battery system, and secondary battery protection methods

Abstract

This invention provides a secondary battery protection circuit, a battery pack, a battery system, and a secondary battery protection method. The secondary battery protection circuit utilizes a charging control transistor, connected in series between the electrodes of the secondary battery and the terminals of the load and charger, to cut off the charging path, thereby protecting the secondary battery from overcharging. It also utilizes a discharge control transistor, connected in series between the electrodes and terminals, to cut off the discharge path, thereby protecting the secondary battery from over-discharge. The secondary battery protection circuit includes: a potential difference detection circuit that outputs a potential difference detection signal based on the potential difference between the electrodes and terminals; and a potential difference control circuit that, in the event of overcharging detected by the overcharge detection circuit or over-discharge detected by the over-discharge detection circuit, feeds back the potential difference detection signal to the control terminal of the charging control transistor or the discharging control transistor to control the potential difference.

Description

Technical Field

[0001] This disclosure relates to secondary battery protection circuits, battery packs, battery systems, and methods for protecting secondary batteries. Background Technology

[0002] Previously, a battery pack was known to have a built-in secondary battery protection integrated circuit, which protected the secondary battery from over-discharge by cutting off a transistor that was connected in series with the negative terminal of the secondary battery and the negative terminal of the load or charger connected to ground (for example, see Patent Document 1).

[0003] However, in a structure that connects multiple battery packs, each with a secondary battery and a protection circuit, in parallel, excessive current may be generated between the secondary batteries of the parallel-connected battery packs when recovering from a protection operation state against overcharge or over-discharge.

[0004] Patent Document 1: Japanese Patent Application Publication No. 2019-106870 Summary of the Invention

[0005] This disclosure provides a secondary battery protection circuit, battery pack, battery system, and secondary battery protection method capable of suppressing excessive current flowing between secondary batteries in a structure where secondary batteries are connected in parallel.

[0006] One aspect of this disclosure provides a secondary battery protection circuit that uses a charging control transistor connected in series between the electrodes of the secondary battery and the terminals of a load and a charger to cut off the charging path, thereby protecting the secondary battery from overcharging. Similarly, a discharge control transistor connected in series between the electrodes and the terminals cuts off the discharge path, thereby protecting the secondary battery from over-discharging.

[0007] The secondary battery protection circuit has the following features:

[0008] An overcharge detection circuit that detects overcharging of the secondary battery;

[0009] An over-discharge detection circuit that detects over-discharge of the secondary battery;

[0010] A potential difference detection circuit that outputs a potential difference detection signal based on the potential difference between the electrode and the terminal; and

[0011] A potential difference control circuit, which, when overcharging is detected by the overcharge detection circuit or over-discharge is detected by the over-discharge detection circuit, feeds back the potential difference detection signal to the control terminal of the charging control transistor or the discharging control transistor to control the potential difference.

[0012] According to one aspect of this disclosure, in a structure where secondary batteries are connected in parallel, excessive current flowing between the secondary batteries can be suppressed. Attached Figure Description

[0013] Figure 1 This is a diagram illustrating a structural example of the battery system according to the first embodiment.

[0014] Figure 2 This is an example of a secondary battery protection circuit with a comparison method applied to the secondary battery protection circuits of both battery packs, showing the waveforms of both battery packs recovering from an overcharged state.

[0015] Figure 3 This is a diagram illustrating a structural example of a secondary battery protection circuit according to the first embodiment.

[0016] Figure 4 This is an example of a structure in which the secondary battery protection circuit of the first embodiment is applied to the secondary battery protection circuits of each of the two battery packs, and the waveforms of the two battery packs recovering from an overcharged state are shown.

[0017] Figure 5 This is an example of a secondary battery protection circuit in which a comparison method is applied to the secondary battery protection circuits of both battery packs, showing the waveform of one battery pack recovering from an overcharged state.

[0018] Figure 6 This is an example of a structure in which the secondary battery protection circuit of the first embodiment is applied to the secondary battery protection circuits of both battery packs, showing the waveform of one battery pack recovering from an overcharged state.

[0019] Figure 7 This is an example of a secondary battery protection circuit with a comparison method applied to the secondary battery protection circuits of both battery packs, showing the waveforms of both battery packs recovering from an over-discharge state.

[0020] Figure 8 This is a diagram illustrating a structural example of the battery protection circuit according to the first embodiment.

[0021] Figure 9 This is an example of a structure in which the secondary battery protection circuit of the first embodiment is applied to the secondary battery protection circuits of each of the two battery packs, and the waveforms of the two battery packs recovering from the over-discharge state are shown.

[0022] Figure 10 This is an example of a secondary battery protection circuit with a comparison method applied to the secondary battery protection circuits of both battery packs, showing the waveform of one battery pack recovering from an over-discharge state.

[0023] Figure 11 This is an example of a structure in which the secondary battery protection circuit of the first embodiment is applied to the secondary battery protection circuits of both battery packs, showing the waveform of one battery pack recovering from an over-discharge state.

[0024] Figure 12 This is a diagram showing a more detailed structural example of the secondary battery protection circuit of the first embodiment.

[0025] Figure 13 This is a diagram illustrating an example of the startup conditions for a differential amplifier.

[0026] Figure 14 This diagram illustrates the operation of a differential amplifier that controls the charging control transistor during an overcharge state.

[0027] Figure 15 This diagram illustrates the operation of a differential amplifier that controls the discharge control transistor in an over-discharge state.

[0028] Figure 16 This is a diagram illustrating the state transitions of the secondary battery protection circuit according to the first embodiment.

[0029] Figure 17 This is a diagram showing a more detailed structural example of the secondary battery protection circuit of the second embodiment.

[0030] Figure 18 This diagram illustrates the operation of a differential amplifier that controls the charging control transistor during an overcharge state.

[0031] Figure 19 This diagram illustrates the operation of a differential amplifier that controls the discharge control transistor in an over-discharge state.

[0032] Symbol Explanation

[0033] 1. Charging control transistor;

[0034] 2. Discharge control transistor;

[0035] 3. Switching circuit;

[0036] 10, 10A, 10B Battery protection circuit;

[0037] 20. First potential difference control circuit;

[0038] 21. Differential amplifier;

[0039] 22. Charging control circuit;

[0040] 23 First switching circuit;

[0041] 30 Second potential difference control circuit;

[0042] 31. Differential amplifier;

[0043] 32. Discharge control circuit;

[0044] 33 Second switching circuit;

[0045] 41. Overcharge detection circuit;

[0046] 42. Overcharge recovery detection circuit;

[0047] 43. Over-discharge detection circuit;

[0048] 44. Over-discharge recovery detection circuit;

[0049] 45. Overcurrent detection circuit;

[0050] 46. ​​Control circuit;

[0051] 50 Charger connection detection circuit;

[0052] 70 Secondary batteries;

[0053] 80 Battery protection device;

[0054] 100 and 200 battery packs;

[0055] 301 Battery System. Detailed Implementation

[0056] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings.

[0057] <First Implementation Method>

[0058] Figure 1 This is a diagram illustrating a structural example of the battery system according to the first embodiment. Figure 1 This illustrates a structural example of connecting the load 90 and the charger 91 to the battery system 301 of the first embodiment. Figure 1 The battery system 301 shown has multiple (two in this example) battery packs 100 and 200 connected in parallel. Battery pack 200 has the same structure as battery pack 100, therefore, the description of the structure of battery pack 200 is omitted by referring to the description of battery pack 100.

[0059] The battery pack 100 has a built-in secondary battery 70 and a battery protection device 80.

[0060] The secondary battery 70 is an example of a rechargeable battery. The secondary battery 70 supplies power to a load 90 connected to terminals PP and PM. The secondary battery 70 can be charged by a charger 91 connected to terminals PP and PM. Specific examples of the secondary battery 70 include lithium-ion batteries and lithium polymer batteries. Battery packs 100 and 200 can be internally mounted in the load 90 or externally mounted.

[0061] Load 90 is an example of a load powered by the secondary battery 70 of battery packs 100 and 200. Specific examples of load 90 include electronic devices such as mobile phones, smartphones, and tablets. Load 90 is not limited to these devices.

[0062] The battery protection device 80 is an example of a secondary battery protection device that operates using a secondary battery 70 as a power source. It protects the secondary battery 70 from overcharging and over-discharging by controlling the charging and discharging of the secondary battery 70. The battery protection device 80 includes: terminals PP, PM, BP, and BM, a switching circuit 3, and a battery protection circuit 10.

[0063] Terminal PP is an example of a positive terminal of the load, connecting the high-potential power supply terminal of the load 90 and the charger 91. Terminal PM is an example of a negative terminal of the load, connecting the low-potential power supply terminal of the load 90 and the charger 91. Terminal BP is an example of a positive terminal of the battery, connected to the positive terminal 71 of the secondary battery 70. Terminal BM is an example of a negative terminal of the battery, connected to the negative terminal 72 of the secondary battery 70.

[0064] Terminals BP and PP are connected via positive current path 9a. Positive current path 9a is the power path between terminals BP and PP, allowing charging or discharging current to flow. Positive current path 9a is an example of the charging / discharging current path between the positive terminal 71 of the secondary battery 70 and terminal PP.

[0065] Terminals BM and PM are connected via negative current path 9b. Negative current path 9b is the current path between terminals BM and PM, allowing charging or discharging current to flow. Negative current path 9b is an example of the charging / discharging current path between the negative terminal 72 of the secondary battery 70 and terminal PM.

[0066] The switching circuit 3 is connected in series to the negative current path 9b between terminals BM and PM. The switching circuit 3, for example, includes a charging control transistor 1 and a discharging control transistor 2, and is a series circuit in which the charging control transistor 1 and the discharging control transistor 2 are connected in series. The charging control transistor 1 is an example of a charging path cutting-off portion that cuts off the charging path of the secondary battery 70, and the discharging control transistor 2 is an example of a discharging path cutting-off portion that cuts off the discharging path of the secondary battery 70. Figure 1In this case, charging control transistor 1 cuts off the current path 9b that supplies charging current to the secondary battery 70, and discharging control transistor 2 cuts off the current path 9b that supplies discharging current to the secondary battery 70. Transistors 1 and 2 are switching elements that switch the current path 9b on / off, and are connected in series to the current path 9b. Transistors 1 and 2 are, for example, N-channel MOSFETs (Metal Oxide Semiconductor Field Effect Transistors).

[0067] The charging control transistor 1 has a parasitic diode 1a between its drain and source, which is forward-biased in the direction opposite to the charging current of the secondary battery 70. The charging control transistor 1 is connected in series with the switching element in the current path 9b such that the forward direction of the parasitic diode 1a of the charging control transistor 1 is consistent with the direction of the discharge current of the secondary battery 70.

[0068] The discharge control transistor 2 has a parasitic diode 2a between its drain and source, which is forward-biased in the direction opposite to the discharge current of the secondary battery 70. The discharge control transistor 2 is connected in series with the switching element in the current path 9b such that the forward direction of the parasitic diode 2a of the discharge control transistor 2 is consistent with the direction of the charging current of the secondary battery 70.

[0069] Battery protection circuit 10 is an example of a secondary battery protection circuit. Battery protection circuit 10 operates powered by secondary battery 70. Battery protection circuit 10 is, for example, an integrated circuit (IC) that operates based on the battery voltage (also called "cell voltage") between the positive terminal 71 and the negative terminal 72 of secondary battery 70.

[0070] The battery protection circuit 10 protects the secondary battery 70 from over-discharge and other abnormalities by controlling the switching circuit 3. For example, the battery protection circuit 10 protects the secondary battery 70 from abnormal charging (e.g., overcharging, overcurrent in the charging direction (charging overcurrent)) by turning off the charging control transistor 1. On the other hand, the battery protection circuit 10 protects the secondary battery 70 from abnormal discharging (e.g., over-discharge, overcurrent in the discharging direction (discharging overcurrent)) by turning off the discharging control transistor 2.

[0071] The battery protection circuit 10 includes, for example, a charging control terminal (terminal CO), a discharging control terminal (terminal DO), a monitoring terminal (terminal VM), a power supply terminal (terminal VDD), and a ground terminal (terminal VSS). These terminals are external connection terminals used to connect the internal circuitry of the battery protection circuit 10 to the outside of the battery protection circuit 10.

[0072] Terminal CO is connected to the gate (control terminal) of charging control transistor 1, outputting a signal that turns charging control transistor 1 on and off. Terminal DO is connected to the gate (control terminal) of discharging control transistor 2, outputting a signal that turns discharging control transistor 2 on and off.

[0073] Terminal VM is used to monitor the potential of terminal PM and is connected to terminal PM. Terminal VM is used, for example, in the detection circuit within battery protection circuit 10 to monitor the presence or absence of connection of load 90 or charger 91, and is connected to the negative-side current path 9b between transistors 1 and 2 and terminal PM.

[0074] Terminal VDD is the power supply terminal of battery protection circuit 10, connected to the positive terminal 71 of secondary battery 70 and the positive current path 9a. Terminal VSS is the ground terminal of battery protection circuit 10, connected to the negative terminal 72 of secondary battery 70 and the negative current path 9b. Terminal VSS is connected to the negative current path 9b between transistors 1 and 2 and terminal BM.

[0075] Battery protection circuit 10 monitors the power supply voltage Vd between terminals VDD and VSS. When battery protection circuit 10 detects a power supply voltage Vd higher than a predetermined overcharge detection voltage VDET1, it turns off the charging control transistor 1. When battery protection circuit 10 detects a power supply voltage Vd lower than a predetermined overcharge recovery voltage VRET1, it turns on the charging control transistor 1. When battery protection circuit 10 detects a power supply voltage Vd lower than a predetermined over-discharge detection voltage VDET2, it turns off the discharge control transistor 2. When battery protection circuit 10 detects a power supply voltage Vd higher than a predetermined over-discharge recovery voltage VRET2, it turns on the discharge control transistor 2.

[0076] Next, the operation of battery packs 100 and 200 on both sides when recovering from overcharged state will be explained.

[0077] Furthermore, for ease of explanation, in battery pack 100, the battery protection circuit 10, charging control transistor 1, and discharging control transistor 2 are defined as IC1, SW1, and SW2, respectively. Similarly, in battery pack 200, the battery protection circuit 10, charging control transistor 1, and discharging control transistor 2 are defined as IC2, SW3, and SW4, respectively. Additionally, in battery pack 100, Bat1 and B1- represent the secondary battery 70 and terminal BM of battery pack 100, respectively. In battery pack 200, Bat2 and B2- represent the secondary battery 70 and terminal BM of battery pack 200, respectively.

[0078] Figure 2This is a diagram illustrating the waveforms of battery packs 100 and 200 recovering from an overcharged state when a comparative battery protection circuit is applied to the respective battery protection circuits 10 of both battery packs 100 and 200. Furthermore, Figure 2 This indicates the waveform with terminal PP as the 0-volt reference.

[0079] When the secondary batteries 70 of both battery packs 100 and 200 are overcharged, and a power supply voltage Vd higher than the predetermined overcharge detection voltage VDET1 is detected, IC1 disconnects SW1 and IC2 disconnects SW3.

[0080] When restoring battery packs 100 and 200 from an overcharged state to their normal state, the secondary battery 70 of battery pack 100 needs to be discharged via diode 1a of SW1, and the secondary battery 70 of battery pack 200 needs to be discharged via diode 1a of SW3. In the overcharged state, with both SW1 and SW3 disconnected, each secondary battery 70 can be discharged via each diode 1a. However, when the battery voltage decreases and the secondary battery 70 of battery pack 200 recovers from overcharge first, only SW3 is turned on. Discharge only begins for the recovered secondary battery 70 of battery pack 200; the secondary battery 70 of battery pack 100 in the overcharged state cannot be discharged via diode 1a of SW1.

[0081] Further discharge occurs, and when the output voltage of battery pack 200 decreases, the secondary battery 70 of battery pack 100, which is in an overcharged state, can also be discharged via diode 1a of SW1. Consequently, when the voltage of the secondary battery 70 of battery pack 100 also decreases, and IC1 detects a power supply voltage Vd lower than the overcharge recovery voltage VRET1, IC1 disconnects SW1, and the secondary battery 70 of battery pack 100 recovers from overcharge.

[0082] At this point, a potential difference exists between the battery voltage of the first-recovered battery pack 200 and the battery voltage of the second-recovered battery pack 100 due to diode discharge. Therefore, at the time point of overcharge recovery of battery pack 100, an excessive current Ip1 is generated between battery pack 100 and battery pack 200. For example, when the total resistance between the batteries is set to 50mΩ and the forward voltage VF of the diode is set to 0.7V, the current Ip1 flowing from terminal PM of battery pack 200 to terminal PM of battery pack 100 is approximately 14A.

[0083] on the other hand, Figure 3 This is a diagram showing a structural example of the battery protection circuit 10A according to the first embodiment. Figure 4This is a diagram illustrating the waveforms of the battery packs 100 and 200 recovering from an overcharged state when the battery protection circuit 10A of the first embodiment is applied to the battery protection circuits 10 of each of the battery packs 100 and 200. Furthermore, Figure 4 This indicates the waveform with terminal PP set to a 0-volt reference.

[0084] The battery protection circuit 10A controls the charging control transistor 1 in the saturation region to maintain a constant potential difference between terminal B1- and terminal PM in the direction of discharge current flow until the power supply voltage Vd returns to a state lower than the overcharge recovery voltage VRET1 after exceeding the overcharge detection voltage VDET1. Therefore, when battery pack 100 recovers from an overcharged state after battery pack 200 recovers from an overcharged state, the voltage difference between battery packs 200 and 100 can be reduced, thus suppressing the inter-cell current Ip1 during recovery. For example, when the total inter-cell resistance is set to 50mΩ and the constant potential difference controlled by differential amplifier 21 is set to 50mV, the current value of Ip1 is suppressed to approximately 1A.

[0085] When an overcharge state is detected where the power supply voltage Vd is higher than the overcharge detection voltage VDET1, the battery protection circuit 10A maintains the difference between the potential of terminal VM and the potential of terminal VSS at a constant value (e.g., 50mV) while allowing current in the discharge direction to flow through the charging control transistor 1. This promotes the discharge of the secondary battery 70.

[0086] Figure 5 This is a diagram illustrating the waveform of one battery pack 100 recovering from an overcharged state when a comparative battery protection circuit is applied to the battery protection circuit 10 of each of the battery packs 100 and 200. Furthermore, Figure 5 This indicates the waveform with terminal PP set to a 0-volt reference.

[0087] When only the secondary battery 70 of the battery pack 100 is overcharged, and a power supply voltage Vd higher than the predetermined overcharge detection voltage VDET1 is detected, IC1 will disconnect SW1 (IC2 will keep SW3 on).

[0088] When restoring the battery pack 100 from an overcharged state to its normal state, the secondary battery 70 of the battery pack 100 needs to be discharged via diode 1a of SW1. Similar to the recovery from an overcharged state, the output voltage of the battery pack 200 is lower than the battery voltage of the battery pack 100 by the amount of the diode's forward voltage. If the power supply voltage Vd of the battery pack 100 is lower than the overcharge recovery voltage VRET1, then the battery pack 100 recovers.

[0089] Therefore, when battery pack 100 recovers from overcharge, the potential difference of the diode discharge is between battery pack 100 and battery pack 200. As a result, an excessive current Ip1 is generated between the battery packs at the time of overcharge recovery.

[0090] on the other hand, Figure 6 This is a diagram illustrating the waveform of one battery pack 100 recovering from an overcharged state in a configuration where the battery protection circuit 10A of the first embodiment is applied to the battery protection circuits 10 of both battery packs 100 and 200. Furthermore, Figure 6 This indicates the waveform with terminal PP set to a 0-volt reference.

[0091] The battery protection circuit 10A of the battery pack 100 controls the charging control transistor 1 in the saturation region to keep the potential difference between terminals BM and PM constant in the direction of discharge current flow until the power supply voltage Vd returns to a state lower than the overcharge recovery voltage VRET1 after exceeding the overcharge detection voltage VDET1. Therefore, when the battery pack 100 recovers from an overcharged state, the voltage difference between the batteries in the battery pack 200 and the battery pack 100 can be reduced, thus suppressing the inter-battery current Ip1 during recovery.

[0092] Next, the operation of battery packs 100 and 200 on both sides when recovering from over-discharge will be explained.

[0093] Figure 7 This is a diagram illustrating the waveforms of battery packs 100 and 200 recovering from an over-discharge state when a comparative battery protection circuit is applied to the respective battery protection circuits 10 of both battery packs 100 and 200. Furthermore, Figure 7 This indicates the waveform with terminal PP set to a 0-volt reference.

[0094] When the secondary batteries 70 of both battery packs 100 and 200 are over-discharged, and a power supply voltage Vd lower than the predetermined over-discharge detection voltage VDET2 is detected, IC1 disconnects SW2 and IC2 disconnects SW4.

[0095] When restoring battery packs 100 and 200 from an over-discharged state to their normal state, the secondary battery 70 of battery pack 100 needs to be charged via diode 2a of SW2, and the secondary battery 70 of battery pack 200 needs to be charged via diode 2a of SW4. In the over-discharged state, with both SW2 and SW4 disconnected, each secondary battery 70 can be charged via each diode 2a. However, when the battery voltage rises and the secondary battery 70 of battery pack 200 recovers from over-discharge first, only SW4 is turned on. Only the recovered secondary battery 70 of battery pack 200 is charged; the secondary battery 70 of battery pack 100 in the over-discharged state cannot be charged via diode 2a of SW2.

[0096] As charging continues, when the output voltage of battery pack 200 rises, the secondary battery 70 of battery pack 100, which is in an over-discharged state, can also be charged via diode 1a of SW2. Consequently, the voltage of the secondary battery 70 of battery pack 100 also rises. When IC1 detects a power supply voltage Vd higher than the over-discharge recovery voltage VRET2, IC1 disconnects SW2, and the secondary battery 70 of battery pack 100 recovers from over-discharge. Even when connected to charger 91, the output voltage of the battery pack rises.

[0097] At this point, a potential difference exists between the battery voltage of the first-recovered battery pack 200 and the battery voltage of the second-recovered battery pack 100 due to the diode discharge. Therefore, at the point of recovery from over-discharge in battery pack 100, an excessive current Ip2 is generated between battery pack 100 and battery pack 200. For example, when the total resistance between the batteries is set to 50mΩ and the forward voltage VF of the diode is set to 0.7V, the current Ip2 flowing from terminal PM of battery pack 100 to terminal PM of battery pack 200 is approximately 14A.

[0098] on the other hand, Figure 8 This is a diagram showing a structural example of the battery protection circuit 10A according to the first embodiment. Figure 9 This is a diagram illustrating the waveforms of the battery packs 100 and 200 recovering from an over-discharge state when the battery protection circuit 10A of the first embodiment is applied to the battery protection circuits 10 of each of the battery packs 100 and 200. Furthermore, Figure 9 This indicates the waveform with terminal PP set to a 0-volt reference.

[0099] The battery protection circuit 10A controls the discharge control transistor 2 in the saturation region to ensure that the potential difference between terminals B1- and PM remains constant in the direction of charging current flow until the power supply voltage Vd returns to a state higher than the over-discharge recovery voltage VRET2 after it has fallen below the over-discharge detection voltage VDET2. Therefore, when battery pack 100 recovers from an over-discharge state after battery pack 200 has recovered from an over-discharge state, the voltage difference between battery packs 200 and 100 can be reduced, thus suppressing the inter-cell current Ip2 during recovery. For example, when the total inter-cell resistance is set to 50mΩ and the constant potential difference controlled by the differential amplifier 31 is set to 50mV, the current Ip2 is suppressed to approximately 1A.

[0100] When the battery protection circuit 10A detects an over-discharge state where the power supply voltage Vd is lower than the over-discharge detection voltage VDET2, it maintains the difference between the potential of terminal VSS and the potential of terminal VM at a constant value (e.g., 50mV) while allowing current in the charging direction to flow through the discharge control transistor 2. This promotes the charging of the secondary battery 70.

[0101] Figure 10 This is a diagram illustrating the waveform of one battery pack 100 recovering from an over-discharge state when a comparative battery protection circuit is applied to the battery protection circuit 10 of each of the battery packs 100 and 200. Furthermore, Figure 10 This indicates the waveform with terminal PP set to a 0-volt reference.

[0102] When only the secondary battery 70 of the battery pack 100 is over-discharged, and a power supply voltage Vd lower than the predetermined over-discharge detection voltage VDET2 is detected, IC1 will disconnect SW2 (IC2 will keep SW4 on).

[0103] When restoring the battery pack 100 from an over-discharged state to its normal state, the secondary battery 70 of the battery pack 100 needs to be charged via diode 2a of SW2. Similar to the recovery from an over-discharged state, the output voltage of the battery pack 200 is higher than the battery voltage of the battery pack 100 by the forward voltage of the diode. If the power supply voltage Vd of the battery pack 100 is higher than the over-discharge recovery voltage VRET2, then the battery pack 100 recovers.

[0104] Therefore, when battery pack 100 recovers from over-discharge, the potential difference of the diode discharge is between battery pack 100 and battery pack 200. As a result, an excessive current Ip2 is generated between the battery packs at the time of over-discharge recovery.

[0105] on the other hand, Figure 11This is a diagram illustrating the waveform of one battery pack 100 recovering from an over-discharge state when the battery protection circuit 10A of the first embodiment is applied to the battery protection circuit 10 of each of the battery packs 100 and 200. Furthermore, Figure 11 This indicates the waveform with terminal PP set to a 0-volt reference.

[0106] The battery protection circuit 10A of the battery pack 100 controls the discharge control transistor 2 in the saturation region to maintain a constant potential difference between terminals BM and PM in the direction of charging current flow until the power supply voltage Vd returns to a state higher than the over-discharge recovery voltage VRET2 after it falls below the over-discharge detection voltage VDET2. Therefore, when the battery pack 100 recovers from an over-discharge state, the voltage difference between the batteries in the battery pack 200 and the battery pack 100 can be reduced, thus suppressing the inter-battery current Ip2 during recovery.

[0107] Figure 12 This is a diagram showing a more detailed structural example of the battery protection circuit 10A according to the first embodiment. The battery protection circuit 10A includes: an overcharge detection circuit 41, an overcharge recovery detection circuit 42, an over-discharge detection circuit 43, an over-discharge recovery detection circuit 44, and an overcurrent detection circuit 45.

[0108] When the overcharge detection circuit 41 detects a power supply voltage Vd higher than a predetermined overcharge detection voltage VDET1, it outputs an overcharge detection signal indicating that an overcharge voltage Vd higher than the overcharge detection voltage VDET1 has been detected. Similarly, when the overcharge recovery detection circuit 42 detects a power supply voltage Vd lower than a predetermined overcharge recovery voltage VRET1, it outputs an overcharge recovery detection signal indicating that an overcharge recovery voltage Vd lower than the overcharge recovery voltage VRET1 has been detected. The overcharge detection voltage VDET1 is a threshold voltage for overcharge detection, and the overcharge recovery voltage VRET1 is a threshold voltage for overcharge recovery detection. The overcharge recovery voltage VRET1 is set to a voltage value lower than the overcharge detection voltage VDET1.

[0109] When the over-discharge detection circuit 43 detects a power supply voltage Vd lower than the predetermined over-discharge detection voltage VDET2, it outputs an over-discharge detection signal indicating that a power supply voltage Vd lower than the over-discharge detection voltage VDET2 has been detected. Similarly, when the over-discharge recovery detection circuit 44 detects a power supply voltage Vd higher than the predetermined over-discharge recovery voltage VRET2, it outputs an over-discharge recovery detection signal indicating that a power supply voltage Vd higher than the over-discharge recovery voltage VRET2 has been detected. The over-discharge detection voltage VDET2 is a threshold voltage for over-discharge detection, and the over-discharge recovery voltage VRET2 is a threshold voltage for over-discharge recovery detection. The over-discharge recovery voltage VRET2 is set to a voltage value higher than the over-discharge detection voltage VDET2.

[0110] The overcurrent detection circuit 45 monitors the voltage between terminal VM and terminal VSS, i.e., the monitoring voltage VI, and detects the overcurrent flowing between terminal PM and terminal BM.

[0111] The overcurrent detection circuit 45 includes a discharge overcurrent detection circuit that outputs a discharge overcurrent detection signal indicating that a discharge overcurrent has been detected when a monitoring voltage VI higher than a predetermined discharge overcurrent detection voltage VDET3 is detected. The overcurrent detection circuit 45 also includes a discharge overcurrent recovery detection circuit that outputs a discharge overcurrent recovery detection signal indicating that no discharge overcurrent has flowed when a monitoring voltage VI lower than a predetermined discharge overcurrent recovery voltage VRET3 is detected. The discharge overcurrent detection voltage VDET3 is a threshold voltage for discharge overcurrent detection, and the discharge overcurrent recovery voltage VRET3 is a threshold voltage for discharge overcurrent recovery detection.

[0112] The overcurrent detection circuit 45 includes: a charging overcurrent detection circuit, which outputs a charging overcurrent detection signal indicating that a charging overcurrent has been detected when a monitoring voltage VI lower than a predetermined charging overcurrent detection voltage VDET4 is detected. The overcurrent detection circuit 45 also includes a charging overcurrent recovery detection circuit, which outputs a charging overcurrent recovery detection signal indicating that no charging overcurrent has flowed when a monitoring voltage VI higher than a predetermined charging overcurrent recovery voltage VRET4 is detected. The charging overcurrent detection voltage VDET4 is a threshold voltage for charging overcurrent detection, and the charging overcurrent recovery voltage VRET4 is a threshold voltage for charging overcurrent recovery detection.

[0113] The battery protection circuit 10A includes: a differential amplifier 21, a differential amplifier 31, a first potential difference control circuit 20, and a second potential difference control circuit 30.

[0114] Differential amplifier 21 is an example of a first potential difference detection circuit, which outputs a first potential difference detection signal b1 based on the potential difference Δ1 between terminals BM and PM (between terminals VSS and VM). Differential amplifier 31 is an example of a second potential difference detection circuit, which outputs a second potential difference detection signal b2 based on the potential difference Δ2 between terminals BM and PM (between terminals VSS and VM).

[0115] When overcharging is detected by the overcharge detection circuit 41, the first potential difference control circuit 20 feeds back the first potential difference detection signal b1 to the control terminal of the charging control transistor 1, thereby controlling the potential difference Δ1 by allowing the current in the direction of discharge of the secondary battery 70 to flow through the charging control transistor 1. Thus, as described above, in the overcharge state, the potential difference Δ1 can be controlled to a value lower than the forward voltage of the diode 1a, thereby suppressing the excessive current Ip1 during recovery.

[0116] When over-discharge is detected by the over-discharge detection circuit 43, the second potential difference control circuit 30 feeds back the second potential difference detection signal b2 to the control terminal of the discharge control transistor 2, thereby controlling the potential difference Δ2 by causing the current in the direction of charging the secondary battery 70 to flow through the discharge control transistor 2. Thus, as described above, in the over-discharge state, the potential difference Δ2 can be controlled to a value lower than the forward voltage of the diode 2a, thereby suppressing the excessive current Ip2 during recovery.

[0117] The battery protection circuit 10A includes a charging control circuit 22 and a first switching circuit 23. When overcharging is not detected by the overcharge detection circuit 41, the charging control circuit 22 outputs a charging control signal a1 to the control terminal of the charging control transistor 1. When overcharging is detected by the overcharge detection circuit 41, the first switching circuit 23 switches the signal output to the control terminal of the charging control transistor 1 from the charging control signal a1 to a first potential difference detection signal b1. Therefore, when no overcharging is detected, the charging control circuit 22 can control the charging control transistor 1 to be turned on or off via the charging control signal a1.

[0118] When the overcharge recovery detection circuit 42 detects the recovery of overcharge, the first switching circuit 23 switches the signal output to the control terminal of the charging control transistor 1 from the first potential difference detection signal b1 to the charging control signal a1. Thus, during recovery from overcharge, the charging control circuit 22 can control the charging control transistor 1 to be turned on or off via the charging control signal a1.

[0119] When the overcurrent detection circuit 45 detects a charging overcurrent, the first switching circuit 23 outputs a charging control signal a1 to the control terminal of the charging control transistor 1, causing the charging control transistor 1 to turn off. Thus, the charging control circuit 22 can cut off the charging overcurrent using the charging control signal a1.

[0120] The battery protection circuit 10A includes a discharge control circuit 32 and a second switching circuit 33. When over-discharge is not detected by the over-discharge detection circuit 43, the discharge control circuit 32 outputs a discharge control signal a2 to the control terminal of the discharge control transistor 2. When over-discharge is detected by the over-discharge detection circuit 43, the second switching circuit 33 switches the signal output to the control terminal of the discharge control transistor 2 from the discharge control signal a2 to the second potential difference detection signal b2. Therefore, when no over-discharge is detected, the discharge control circuit 32 can control the discharge control transistor 2 to be turned on or off via the discharge control signal a2.

[0121] When the over-discharge recovery detection circuit 44 detects the recovery of over-discharge, the second switching circuit 33 switches the signal output to the control terminal of the discharge control transistor 2 from the second potential difference detection signal b2 to the discharge control signal a2. Thus, during recovery from over-discharge, the discharge control circuit 32 can control the discharge control transistor 2 to be turned on or off via the discharge control signal a2.

[0122] When the overcurrent detection circuit 45 detects a discharge overcurrent, the second switching circuit 33 outputs a discharge control signal a2 to the control terminal of the discharge control transistor 2, causing the discharge control transistor 2 to turn off. Thus, the discharge control circuit 32 can cut off the discharge overcurrent through the discharge control signal a2.

[0123] The battery protection circuit 10A includes: a charger connection detection circuit 50 that detects the connection of the charger 91; and a control circuit 46 connected to the charger connection detection circuit 50. The charger connection detection circuit 50 includes, for example, a resistor 51, a switch 52, and a monitoring circuit 53. When over-discharge is detected by the over-discharge detection circuit 43, the control circuit 46 turns on the switch 52 according to the output of the discharge control circuit 32, thereby pulling the terminal VM up to the potential of the terminal VDD via the resistor 51. Therefore, if there is an open circuit between the terminals PP and PM, the potential of the terminal VM is fixed at the potential of the terminal VDD. When the charger 91 is connected between the terminals PP and PM, the potential of the terminal VM is lower than the potential of the terminal VDD by the output voltage of the charger 91. The charger connection detection circuit 50 monitors this potential change at the terminal VM via the monitoring circuit 53, thereby detecting whether the charger 91 is connected.

[0124] When the charger connection detection circuit 50 detects the connection of the charger 91 and the over-discharge recovery detection circuit 44 detects over-discharge recovery, the control circuit 46 disconnects the switch 52, thereby releasing the pull-up from terminal VM to terminal VDD.

[0125] The monitoring circuit 53 has an input section that can be pulled up to the potential of the terminal VDD via the switch 52. The monitoring circuit 53 is, for example, a CMOS (Complementary Metal Oxide Semiconductor) inverter circuit.

[0126] When charger 91 is connected between terminals PP and PM, the potential of terminal VM drops below the potential of terminal VSS. Consequently, the input of the CMOS inverter in monitoring circuit 53 changes from high to low, and the output of the CMOS inverter in monitoring circuit 53 changes from low to high. Control circuit 46 detects the connection of charger 91 by detecting the change in the output of the CMOS inverter in monitoring circuit 53 from low to high.

[0127] Next, the operation of differential amplifiers 21 and 31 will be explained in more detail.

[0128] Figure 13 This diagram illustrates an example of the activation conditions for a differential amplifier. In the state where no charging or discharging abnormalities are detected (normal state), differential amplifiers 21 and 31 are both unused (off state). In the state where overcharging is detected (overcharge state), differential amplifier 31 is unused (off state), and differential amplifier 21 is used (on state). In this overcharge state, the potential difference Δ1 between terminals BM and PM is controlled by feedback from differential amplifier 21. In over-discharge state 1 (over-discharge is detected, and a charger connection or output from another battery pack is detected), differential amplifier 21 is unused (off state), and differential amplifier 31 is used (on state). In over-discharge state 1, the potential difference Δ2 between terminals BM and PM is controlled by feedback from differential amplifier 31. In over-discharge state 2 (over-discharge is detected in all parallel-connected battery packs (standby state)), both differential amplifiers 21 and 31 are unused (off state).

[0129] Figure 14 This diagram illustrates the operation of a differential amplifier that controls the charging control transistor in an overcharged state. The differential amplifier 21 includes: a non-inverting input connected to terminal VM (terminal PM); an inverting input connected to a potential that is a constant voltage Va (e.g., +50mV) higher than terminal VSS (terminal BM); and an output connected to terminal CO, which is connected to the control terminal of the charging control transistor 1.

[0130] With this structure, when the differential amplifier 21 wants to reach a potential higher than (terminal BM + constant voltage Va), it increases the output voltage applied to the control terminal of the charging control transistor 1. As a result, the input and output impedance of the charging control transistor 1, which operates in the saturation region, is reduced, thus enabling the application of negative feedback that lowers the potential of terminal PM. Therefore, the differential amplifier 21 can control the potential difference between terminals PM and BM to a constant voltage Va while allowing current to flow through the charging control transistor 1 in the direction of discharge of the secondary battery 70 (from terminal PM to terminal BM).

[0131] On the other hand, when the differential amplifier 21 is at a potential lower than (terminal BM + constant voltage Va), it reduces the output voltage applied to the control terminal of the charging control transistor 1, thereby increasing the input and output impedance of the charging control transistor 1. As a result, the charging control transistor 1 switches to the off state. Therefore, the differential amplifier 21 can cut off the current in the direction of charging the secondary battery 70 (from terminal BM to terminal PM) by turning off the charging control transistor 1.

[0132] Figure 15 This diagram illustrates the operation of a differential amplifier that controls the discharge control transistor in an over-discharge state. The differential amplifier 31 includes: a non-inverting input connected to terminal VSS (terminal BM); an inverting input connected to a potential that is a constant voltage Vb (e.g., +50mV) higher than terminal VM (terminal PM); and an output connected to terminal DO, which is connected to the control terminal of the discharge control transistor 2.

[0133] With this structure, when terminal PM is to reach a potential lower than (terminal BM - constant voltage Vb), the differential amplifier 31 increases the output voltage applied to the control terminal of the discharge control transistor 2. This reduces the input and output impedance of the discharge control transistor 2, which operates in the saturation region, thus enabling the application of negative feedback that raises the potential of terminal PM. Therefore, the differential amplifier 31 can control the potential difference between terminals BM and PM to a constant voltage Vb while allowing current to flow through the discharge control transistor 2 in the direction of charging the secondary battery 70 (from terminal BM to terminal PM).

[0134] On the other hand, when the differential amplifier 31 has a potential higher than (terminal BM - constant voltage Vb), it reduces the output voltage applied to the control terminal of the discharge control transistor 2, thus increasing the input and output impedance of the discharge control transistor 2. As a result, the discharge control transistor 2 switches to the off state. Therefore, the differential amplifier 31 can cut off the current in the direction of discharging the secondary battery 70 (from terminal PM to terminal BM) by turning off the discharge control transistor 2.

[0135] Figure 16 This is a diagram illustrating the state transitions of the secondary battery protection circuit according to the first embodiment. (Refer to...) Figure 12 ,right Figure 16 Please provide an explanation.

[0136] The normal state is one where no overcharge or over-discharge is detected. In this state, the charging control circuit 22 selects the charging control signal a1 as the signal to be output to terminal CO via the first switching circuit 23, outputting a high-level charging control signal a1 that turns on the charging control transistor 1 to terminal CO. Conversely, in the normal state, the discharging control circuit 32 selects the discharging control signal a2 as the signal to be output to terminal DO via the second switching circuit 33, outputting a high-level discharging control signal a2 that turns on the discharging control transistor 2 to terminal DO.

[0137] Under normal conditions, when overcharging is detected by the overcharge detection circuit 41 (when an overcharge detection signal is output), the operation state of the battery protection circuit 10A changes from the normal state to the overcharge state. The overcharge state is the state in which overcharging is detected by the overcharge detection circuit 41 (the state in which an overcharge detection signal is output). In the overcharge state, the charging control circuit 22 selects the first potential difference detection signal b1 as the signal to be output to the terminal CO through the first switching circuit 23, and outputs the first potential difference detection signal b1, which causes the charging control transistor 1 to operate in the saturation region, to the terminal CO. On the other hand, in the overcharge state, the discharge control circuit 32 performs the same operation as in the normal state.

[0138] In the overcharged state, when the overcharge recovery detection circuit 42 detects overcharge recovery (when the overcharge recovery detection signal is output), the operation state of the battery protection circuit 10A returns from the overcharged state to the normal state.

[0139] Under normal conditions, when over-discharge is detected by the over-discharge detection circuit 43 (when an over-discharge detection signal is output), the operation state of the battery protection circuit 10A changes from the normal state to the over-discharge state. The over-discharge state is the state in which over-discharge is detected by the over-discharge detection circuit 43 (the state in which an over-discharge detection signal is output). In the over-discharge state, the discharge control circuit 32 selects the second potential difference detection signal b2 as the signal to be output to the terminal DO through the second switching circuit 33, and outputs the second potential difference detection signal b2, which causes the discharge control transistor 2 to operate in the saturation region, to the terminal DO. On the other hand, in the over-discharge state, the charging control circuit 22 performs the same operation as in the normal state. In addition, in the over-discharge state, the control circuit 46 turns on the switch 52 of the charger connection detection circuit 50, thereby pulling the terminal VM up to the potential of the terminal VDD.

[0140] When transitioning to an over-discharge state, the charger 91 should be disconnected at that transition time. Therefore, the battery protection circuit 10A switches to standby mode and shuts down the over-discharge recovery detection circuit 44. For example, in an over-discharge state, if the charger 91 is not detected by the charger connection detection circuit 50 for a predetermined time or longer, the operation state of the battery protection circuit 10A changes from the over-discharge state to the standby state.

[0141] In standby mode, the discharge control circuit 32 selects the discharge control signal a2 as the signal to be output to terminal DO through the second switching circuit 33, and outputs the low-level discharge control signal a2, which turns off the discharge control transistor 2, to terminal DO. On the other hand, in standby mode, the charging control circuit 22 performs the same operation as in the over-discharge state.

[0142] In standby mode, when the charger connection detection circuit 50 detects the connection of the charger 91, the standby mode is deactivated, the over-discharge recovery detection circuit 44 is activated, and the operating state of the battery protection circuit 10A changes from standby mode to over-discharge mode. During this transition, the second potential difference control circuit 30 and the over-discharge recovery detection circuit 44 operate. Thus, in the over-discharge mode, feedback operation based on the second potential difference detection signal b2 within the saturation region of the discharge control transistor 2 is possible, and over-discharge recovery detection is also possible. When over-discharge recovery is detected by the over-discharge recovery detection circuit 44 (when an over-discharge recovery detection signal is output), the operating state of the battery protection circuit 10A returns to normal operation from the over-discharge mode.

[0143] <Second Implementation Method>

[0144] Figure 17 This is a diagram showing a more detailed structural example of the battery protection circuit 10B according to the second embodiment. The difference between the battery protection circuit 10B of the second embodiment and the battery protection circuit 10A of the first embodiment is that the secondary battery 70 is protected by a charging control transistor 1 and a discharging control transistor 2 connected in series to the current path 9a. In the second embodiment, descriptions of structures and effects identical to those of the first embodiment are omitted by referring to the above description.

[0145] In the second embodiment, transistors 1 and 2 are, for example, P-channel MOSFETs. The battery protection circuit 10B includes, for example, a charging control terminal (terminal CO), a discharging control terminal (terminal DO), a monitoring terminal (terminal VP), a power supply terminal (terminal VDD), and a ground terminal (terminal VSS).

[0146] Terminal VP is used to monitor the potential of terminal PP and is connected to terminal PP. For example, terminal VP is used in the charger connection detection circuit 50 within the battery protection circuit 10B to monitor the connection of load 90 or charger 91, and is connected to the positive current path 9a between transistors 1 and 2 and terminal PP.

[0147] The overcurrent detection circuit 45 monitors the voltage between terminal VP and terminal VDD, i.e., the monitoring voltage VI, and detects the overcurrent flowing between terminal PP and terminal BP.

[0148] The state where the discharge of the secondary battery 70 is stopped by cutting off the discharge control transistor 2 and the terminal VP is pulled down to the terminal VSS by turning on the switch 52 is defined as the pull-down state pd. In the pull-down state pd, the potential of the terminal VP decreases to the potential of the terminal VSS due to the turning on of the switch 52. In this pull-down state pd, when the charger 91 is connected between the terminal PP and the terminal PM, the potential of the terminal VP rises above the potential of the terminal VDD. Therefore, when the charger connection detection circuit 50 detects that the potential of the terminal VP has risen to a level higher than the predetermined reference potential Vvp in the pull-down state pd through the monitoring circuit 53, it can determine that the charger 91 is connected.

[0149] Figure 18 This diagram illustrates the operation of a differential amplifier that controls the charging control transistor in an overcharged state. The differential amplifier 21 includes: a non-inverting input connected to terminal VP (terminal PP); an inverting input connected to a potential that is a constant voltage Va (e.g., +50mV) lower than terminal VDD (terminal BP); and an output connected to terminal CO, which is connected to the control terminal of the charging control transistor 1.

[0150] With this structure, when terminal PP is about to reach a potential lower than (terminal BP - constant voltage Va), the differential amplifier 21 reduces the output voltage applied to the control terminal of the charging control transistor 1. This reduces the input and output impedance of the charging control transistor 1, which operates in the saturation region, thus enabling the application of negative feedback that raises the potential of terminal PP. Therefore, the differential amplifier 21 can control the potential difference between terminals BP and PP to a constant voltage Va while allowing current to flow through the charging control transistor 1 in the direction of discharge of the secondary battery 70 (from terminal BP to terminal PP).

[0151] On the other hand, when the differential amplifier 21 has a potential higher than (terminal BP - constant voltage Va), it causes the output voltage applied to the control terminal of the charging control transistor 1 to rise, thus increasing the input and output impedance of the charging control transistor 1. As a result, the charging control transistor 1 switches to the off state. Therefore, the differential amplifier 21 can cut off the current in the direction of charging the secondary battery 70 (from terminal PP to terminal BP) by turning off the charging control transistor 1.

[0152] Figure 19 This diagram illustrates the operation of a differential amplifier that controls the discharge control transistor in an over-discharge state. The differential amplifier 31 includes: an inverting input connected to terminal VDD (terminal BP); a non-inverting input connected to a potential that is a constant voltage Vb (e.g., +50mV) lower than terminal VP (terminal PP); and an output connected to terminal DO, which is connected to the control terminal of the discharge control transistor 2.

[0153] With this structure, when terminal PP is about to reach a potential higher than (terminal BP + constant voltage Vb), the differential amplifier 31 reduces the output voltage applied to the control terminal of the discharge control transistor 2. This reduces the input and output impedance of the discharge control transistor 2, which operates in the saturation region, thus enabling the application of negative feedback to lower the potential of terminal PP. Therefore, the differential amplifier 31 can control the potential difference between terminals PP and BP to a constant voltage Vb while allowing current to flow through the discharge control transistor 2 in the direction of charging the secondary battery 70 (from terminal PP to terminal BP).

[0154] On the other hand, when terminal PP is at a potential lower than (terminal BP + constant voltage Vb), differential amplifier 31 increases the output voltage applied to the control terminal of discharge control transistor 2, thus increasing the input and output impedance of discharge control transistor 2. As a result, discharge control transistor 2 switches to the off state. Therefore, differential amplifier 31 can cut off the current in the direction of discharging the secondary battery 70 (from terminal BP to terminal PP) by turning off discharge control transistor 2.

[0155] The above description illustrates the secondary battery protection circuit, battery pack, battery system, and secondary battery protection method through various embodiments. However, the present invention is not limited to the above embodiments. Various modifications and improvements, such as combinations, substitutions, and other variations, are possible within the scope of the present invention.

[0156] Additionally, for example, the positions of the charging control transistor 1 and the discharging control transistor 2 can be interchanged relative to their positions shown in the figure. Furthermore, the switching circuit 3 can also be integrated into the battery protection circuit 10.

Claims

1. A secondary battery protection circuit, comprising: using a charging control transistor connected in series between the electrodes of the secondary battery and the terminals of a load and a charger to cut off the charging path, thereby protecting the secondary battery from overcharging; and using a discharge control transistor connected in series between the electrodes and the terminals to cut off the discharge path, thereby protecting the secondary battery from over-discharging, characterized in that... The secondary battery protection circuit has the following features: An overcharge detection circuit that detects overcharging of the secondary battery; An over-discharge detection circuit that detects over-discharge of the secondary battery; A potential difference detection circuit outputs a potential difference detection signal based on the potential difference between the electrode and the terminal; as well as A potential difference control circuit, which, when overcharging is detected by the overcharge detection circuit, feeds back the potential difference detection signal to the control terminal of the charging control transistor to control the potential difference; and, when over-discharge is detected by the over-discharge detection circuit, feeds back the potential difference detection signal to the control terminal of the discharge control transistor to control the potential difference.

2. The secondary battery protection circuit according to claim 1, characterized in that, If the overcharge is detected by the overcharge detection circuit, the potential difference control circuit feeds back the potential difference detection signal to the control terminal of the charging control transistor, so as to control the potential difference by causing the current in the direction of the secondary battery discharge to flow through the charging control transistor.

3. The secondary battery protection circuit according to claim 2, characterized in that, The secondary battery protection circuit has the following features: A charging control circuit that, when the overcharge is not detected by the overcharge detection circuit, outputs a charging control signal to the control terminal of the charging control transistor to control the charging control transistor. as well as The first switching circuit, when the overcharge detection circuit detects the overcharge, switches the signal output to the control terminal of the charging control transistor from the charging control signal to the potential difference detection signal.

4. The secondary battery protection circuit according to claim 3, characterized in that, The secondary battery protection circuit includes: an overcharge recovery detection circuit, which detects the recovery from overcharge. When the overcharge recovery detection circuit detects the recovery of the overcharge, the first switching circuit switches the signal output to the control terminal of the charging control transistor from the potential difference detection signal to the charging control signal.

5. The secondary battery protection circuit according to claim 3 or 4, characterized in that, The secondary battery protection circuit includes: a charging overcurrent detection circuit, which detects the charging overcurrent of the secondary battery. When the charging overcurrent is detected by the charging overcurrent detection circuit, the first switching circuit outputs a charging control signal to the control terminal of the charging control transistor to turn off the charging control transistor.

6. The secondary battery protection circuit according to claim 1, characterized in that, If the over-discharge is detected by the over-discharge detection circuit, the potential difference control circuit feeds back the potential difference detection signal to the control terminal of the discharge control transistor, so as to control the potential difference by causing the current in the direction of charging the secondary battery to flow through the discharge control transistor.

7. The secondary battery protection circuit according to claim 6, characterized in that, The secondary battery protection circuit includes: a discharge control circuit, which outputs a discharge control signal to the control terminal of the discharge control transistor to control the discharge control transistor when the over-discharge is not detected by the over-discharge detection circuit; as well as The second switching circuit, when the over-discharge detection circuit detects the over-discharge, switches the signal output to the control terminal of the discharge control transistor from the discharge control signal to the potential difference detection signal.

8. The secondary battery protection circuit according to claim 7, characterized in that, The secondary battery protection circuit includes: an over-discharge recovery detection circuit, which detects the recovery from the over-discharge. When the over-discharge recovery detection circuit detects the recovery of the over-discharge, the second switching circuit switches the signal output to the control terminal of the discharge control transistor from the potential difference detection signal to the discharge control signal.

9. The secondary battery protection circuit according to claim 8, characterized in that, The secondary battery protection circuit includes: a charger connection detection circuit that detects the connection of the charger. When the charger connection detection circuit detects a connection to the charger, the potential difference control circuit and the over-discharge recovery detection circuit activate.

10. The secondary battery protection circuit according to claim 9, characterized in that, The charger connection detection circuit includes a CMOS inverter circuit.

11. The secondary battery protection circuit according to any one of claims 7 to 10, characterized in that, The secondary battery protection circuit includes: a discharge overcurrent detection circuit, which detects the discharge overcurrent of the secondary battery. When the discharge overcurrent is detected by the discharge overcurrent detection circuit, the second switching circuit outputs a discharge control signal to the control terminal of the discharge control transistor to turn off the discharge control transistor.

12. A battery pack, characterized in that, have: The secondary battery protection circuit according to any one of claims 1 to 11; The secondary battery; The charging control transistor; and The discharge control transistor.

13. A battery system, characterized in that, have: Multiple battery packs connected in parallel, The battery pack is the battery pack according to claim 12.

14. A method for protecting a secondary battery, comprising using a charging control transistor connected in series between the electrodes of the secondary battery and the terminals of a load and a charger to cut off the charging path, thereby protecting the secondary battery from overcharging, and using a discharge control transistor connected in series between the electrodes and the terminals to cut off the discharge path, thereby protecting the secondary battery from over-discharging, characterized in that... Detect overcharging of the secondary battery. Detect over-discharge of the secondary battery. Based on the potential difference between the electrode and the terminal, a potential difference detection signal is output. In the event of overcharging, the potential difference detection signal is fed back to the control terminal of the charging control transistor to control the potential difference; in the event of over-discharging, the potential difference detection signal is fed back to the control terminal of the discharging control transistor to control the potential difference.

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