Secondary battery protection circuit, secondary battery protection device, and battery pack

Abstract

A secondary battery protection circuit protects a secondary battery using charge control and discharge control switching elements inserted between a positive electrode terminal of the secondary battery and a high potential terminal of a charger. The secondary battery protection circuit includes: a first voltage detection circuit that detects whether a battery voltage is less than a first threshold value; a switching circuit that outputs a high potential voltage of the charger when the detection is detected, and outputs a battery voltage when the detection is not detected; a booster circuit for boosting and outputting the battery voltage using the output voltage of the switching circuit; and a drive circuit that performs control such that, when the detection is detected, the output voltage of the booster circuit is output only to the control terminal of the charge control switching element, thereby turning on only the switching element, and, when the detection is not detected, the output voltage of the booster circuit is output only to the control terminal of the charge control switching element. The output voltage of the booster circuit is output to each control terminal of the charge control and discharge control switching elements, so that the switching elements are turned on together.

Description

Technical Field

[0001] The present invention relates to a secondary battery protection circuit, a secondary battery protection device and a battery pack. Background Art

[0002] The secondary battery protection circuit involved in the known prior art example 1 is a circuit that controls the on / off state of a pair of N-channel charge and discharge control MOS field effect transistors (hereinafter, "field effect transistor" is referred to as "FET", and "charge and discharge control MOSFET" is referred to as "charge and discharge control FET". Here, "charge and discharge control FET" includes "charge control FET" and "discharge control FET".) inserted in series in a current path between the positive electrode of the secondary battery and the positive terminal of the high potential side power supply terminal connected to the load and the charger. The voltage supplied from the secondary battery is boosted and supplied by a charge pump, thereby controlling the on / off state of the pair of charge and discharge control FETs.

[0003] However, the secondary battery protection circuit according to the first conventional example cannot perform a boosting operation at a secondary battery voltage near zero volts, which is lower than the minimum operating voltage of the charge pump, and a voltage for turning on the charge control FET cannot be supplied to the gate, so that charging cannot occur.

[0004] In order to solve this problem, a secondary battery protection circuit according to a conventional example 2 is known that uses the following method: when the battery voltage is near zero volts, the secondary battery protection circuit is provided with a high potential voltage (positive electrode voltage) VP of the charger that is switched to the gate voltage Vg of the charge control FET. + The switch can turn on the charge control FET even when the secondary battery is near zero volts (for example, refer to Patent Document 1).

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent No. 6614388 Summary of the invention

[0008] Problems to be solved by the invention

[0009] In the secondary battery protection circuit involved in the conventional example 2, it is assumed that when charging the secondary battery near zero volts, the charger starts charging with a constant current called "CC charging". Here, in order to charge the secondary battery near zero volts, it is necessary to generate a gate-source voltage Vgs in the charging control FET so that the current supplied by the charger flows. In this case, the gate-source voltage of the charging control FET required to drive the supply current of the charger is set to the threshold voltage Vth, and the source voltage of the charging control FET is set to Vs, and the condition for driving the supply current of the charger is expressed by the following formula.

[0010] Vg=Charger voltage (≈positive electrode voltage VP + )

[0011] Vs = battery voltage VB + (≈ power supply voltage VDD)

[0012] Therefore, the positive voltage VP + Becomes the charger voltage VP + , expressed by the following formula.

[0013] Vgs>Vth

[0014] That is, the following formula is obtained.

[0015] VP + >VDD+Vth

[0016] There is a charger voltage VP + The larger the voltage at the positive terminal (VP + ) and the positive terminal of the battery, the greater the heat loss associated with charging. In particular, this may become a bottleneck when charging with a large current from a low battery voltage state in order to shorten the charging time. Therefore, it is preferred to charge with a lower charger voltage.

[0017] The object of the present invention is to provide a secondary battery protection circuit, a secondary battery protection device having the secondary battery protection circuit, and a battery pack having the secondary battery protection circuit, which can reduce heat loss compared with the prior art by charging the secondary battery near zero volts with a charger voltage lower than before.

[0018] Means for solving problems

[0019] The secondary battery protection circuit of the present invention is a secondary battery protection circuit that uses a charging control switch element and a discharging control switch element that are inserted between the positive terminal of the secondary battery and the high potential terminal of the load and the charger and are connected in series with each other to protect the secondary battery, and comprises:

[0020] A first voltage detection circuit, detecting whether the battery voltage of the secondary battery is less than a specified first threshold;

[0021] a switch circuit that outputs an output voltage as a high potential voltage of the charger when a voltage less than the first threshold is detected, and outputs an output voltage as a battery voltage when a voltage less than the first threshold is not detected;

[0022] a boost circuit, using the output voltage of the switch circuit to boost the battery voltage and output the boosted voltage; and

[0023] The driving circuit is controlled so that when it is detected that the voltage is less than the first threshold value, the output voltage of the boost circuit is output only to the control terminal of the charge control switch element, thereby only the charge control switch element is turned on. On the other hand, when it is not detected that the voltage is less than the first threshold value, the output voltage of the boost circuit is output to the control terminals of the charge control switch element and the discharge control switch element, thereby both the charge control switch element and the discharge control switch element are turned on.

[0024] Effects of the Invention

[0025] Therefore, according to the secondary battery protection circuit and the like according to the present invention, by charging the secondary battery near zero volts at a charger voltage lower than conventional ones, it is possible to reduce heat loss compared to the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 1 is a circuit diagram showing a configuration example of the battery pack BP1 and its peripheral circuits according to the first embodiment of the present invention.

[0027] Figure 2 Yes means Figure 1 A block diagram of a configuration example of a switching circuit 3 and a boost circuit 6.

[0028] Figure 3 1 is a timing chart showing various voltages after a charger is connected in the secondary battery protection circuit according to the second conventional example.

[0029] Figure 4 It means in Figure 1 1 is a timing diagram of various voltages in the secondary battery protection circuit 16 after the charger is connected.

[0030] Figure 5A 1 is a circuit diagram showing a configuration example of a battery pack BP2 and its peripheral circuits according to the second embodiment of the present invention.

[0031] Figure 5B Yes means Figure 5A A block diagram of a configuration example of a switching circuit 3 and a boost circuit 6.

[0032] Figure 6 This is a circuit diagram showing a configuration example of a battery pack BP3 and its peripheral circuits according to the third embodiment of the present invention.

[0033] Figure 7 1 is a circuit diagram showing a configuration example of a battery pack BP4 and its peripheral circuits according to a fourth embodiment of the present invention.

[0034] Fig. 8A This is a circuit diagram showing a configuration example of a battery pack BP5 and its peripheral circuits according to a fifth embodiment of the present invention.

[0035] Figure 8B This is a circuit diagram showing a configuration example of a battery pack BP6 and its peripheral circuits according to a sixth embodiment of the present invention. DETAILED DESCRIPTION

[0036] Hereinafter, embodiments and modifications of the present invention will be described with reference to the drawings. In addition, the same or similar components are denoted by the same reference numerals.

[0037] (Implementation Method 1)

[0038] Figure 1 1 is a circuit diagram showing a configuration example of the battery pack BP1 and its peripheral circuits according to the first embodiment of the present invention.

[0039] exist Figure 1 In the embodiment, the battery pack BP1 is composed of a secondary battery B1 having a positive terminal 21 and a negative terminal 22, a secondary battery protection device 20, a positive terminal 13, and a negative terminal 12. Here, a parallel circuit of a system load RL and a charger CH1 is connected between the positive terminal 13 and the negative terminal 12. That is, a high potential terminal of the charger CH1 is connected to the positive terminal 13, and a low potential terminal of the charger CH1 is connected to the negative terminal 12. In addition, the negative terminal 22 of the secondary battery B1 has a ground voltage VSS and is connected to the negative terminal 12. The secondary battery B1 has a battery voltage (power supply voltage) VDD as a potential difference between its positive and negative electrodes.

[0040] The secondary battery protection device 20 is provided with a secondary battery protection circuit 16, a charge control FET (CFET) 14 which is, for example, an N-channel MOSFET and has a body diode 10, and a discharge control FET (DFET) 15 which is, for example, an N-channel MOSFET and has a body diode 11. Here, the charge control FET 14 and the discharge control FET 15 are connected in series with each other, and the series circuit is connected between the positive terminal 21 and the positive terminal 13. The secondary battery protection circuit 16 is provided with an overdischarge detection circuit 2, a switch circuit 3 including a control circuit 3A, a boost circuit 6 including a control circuit 6A, and a drive circuit 7.

[0041] The overdischarge detection circuit 2 generates a detection signal S2 as a comparison result signal by comparing the battery voltage VDD with a predetermined overdischarge detection threshold value Vthe. Here, when the battery voltage VDD is lower than the overdischarge detection threshold value Vthe, the overdischarge detection circuit 2 outputs an L-level detection signal S2 indicating "overdischarge is detected" to the drive circuit 7 and the control circuit 3A. On the other hand, when the battery voltage VDD is higher than the overdischarge detection threshold value Vthe, the overdischarge detection circuit 2 outputs an H-level detection signal S2 indicating "overdischarge is not detected" to the drive circuit 7 and the control circuit 3A. Here, the overdischarge detection threshold value Vthe is set to, for example, the discharge termination voltage or a voltage slightly lower than the discharge termination voltage.

[0042] The switch circuit 3 includes a control circuit 3A and switches 4 and 5. The control circuit 3A of the switch circuit 3 turns off the switch 4 and turns on the switch 5 in response to the detection signal S2 at the H level, thereby outputting the battery voltage VDD as the output voltage VSW to the boost circuit 6. On the other hand, the control circuit 3A of the switch circuit 3 turns on the switch 4 and turns off the switch 5 in response to the detection signal S2 at the L level, thereby outputting the positive electrode voltage VP as the charger voltage of the positive terminal 13. + The voltage is output to the boost circuit 6 as the output voltage VSW.

[0043] The boost circuit 6 operates using the output voltage VSW from the switch circuit 3 as a power supply voltage, and generates a boosted voltage VCP (=VDD+VSW) based on the battery voltage VDD and the output terminal VSW.

[0044] The drive circuit 7 controls the on or off state of the charge control FET 14 and the discharge control FET 15 using the boosted voltage VCP based on the detection signal S2. Here, the drive circuit 7 outputs the control signals COUT and DOUT of the H level (=VCP) to the gates (control terminals) of the charge control FET 14 and the discharge control FET 15, respectively, based on the detection signal S2 of the H level, thereby turning on both the charge control FET 14 and the discharge control FET 15. On the other hand, the drive circuit 7 outputs the control signal COUT of the H level (=VCP) to the gate of the charge control FET 14 and the control signal DOUT of the L level (=VSS) to the gate of the discharge control FET 15, thereby turning on the charge control FET 14 and turning off the discharge control FET 15.

[0045] Figure 2 Yes means Figure 1 A block diagram of a configuration example of a switching circuit 3 and a boost circuit 6.

[0046] exist Figure 2 In the embodiment, the switch circuit 3 is composed of a control circuit 3A and switches 4 and 5, and operates as described above. The boost circuit 6 is a general charge pump circuit, and is composed of a control circuit 6A, four switches 6a to 6d, and a boost capacitor C1. In the boost circuit 6, the output voltage VSW from the switch circuit 3 is supplied as a power supply voltage of the control circuit 6A, and is output as a boost voltage VCP to the drive circuit 7 via switches 6a and 6b. The battery voltage VDD is grounded via switches 6c and 6d. Here, the connection point of the switch 6a and the switch 6b is connected to the connection point of the switch 6c and the switch 6d via the boost capacitor C1.

[0047] In the booster circuit 6 configured as described above, the control circuit 6A controls the operation of the booster circuit 6 according to a predetermined clock so that the following operation is repeatedly performed:

[0048] (1) by turning on switch 6a, turning off switch 6b, turning off switch 6c, and turning on switch 6d, capacitor C1 is charged with an electric charge corresponding to the voltage difference between output voltage VSW and ground voltage VSS; and

[0049] (2) By turning off the switch 6 a , turning on the switch 6 b , turning on the switch 6 c , and turning off the switch 6 d , a boosted voltage VCP (=VDD+VSW) is generated and output to the drive circuit 7 .

[0050] In the switch circuit 3, when the battery voltage VDD is above the over-discharge detection threshold value Vthe, in response to the detection signal S2 of the H level from the over-discharge detection circuit 2, the switch 5 is turned on and the switch 4 is turned off, and the positive electrode voltage VDD of the positive terminal 21 is supplied to the boost circuit 6 as the output voltage VSW via the switch 5. Since the output voltage VSW is connected to the battery voltage VDD as described above, VCP=VDD+VDD.

[0051] On the other hand, when the battery voltage VDD is lower than the over-discharge detection threshold Vthe, in response to the L-level detection signal S2 from the over-discharge detection circuit 2, the switch 5 is turned off and the switch 4 is turned on, and the positive electrode voltage VP of the positive terminal 13 is + The output voltage VSW is supplied to the boost circuit 6 via the switch 4. At this time, since the output voltage VSW is electrically connected to the positive terminal 13 as described above, the boost voltage VCP=VDD+VP + .

[0052] Next, a method of charging the zero-volt battery according to the present embodiment and output voltage conditions of the charger CH1 that enables charging will be described.

[0053] (A) When the battery voltage VDD is higher than the predetermined over-discharge detection threshold value Vthe, the over-discharge detection circuit 2 is in the "over-discharge not detected" state and outputs the detection signal S2 at the H level. Therefore, the switch 5 of the switch circuit 3 is turned on and the switch 4 is turned off, thereby outputting the battery voltage VDD as the output voltage VSW to the boost circuit 6. That is, VSW = VDD. Therefore, regardless of whether the charger CH1 is connected or not, the boost voltage VCP generated by the boost circuit 6 is expressed by the following formula.

[0054] VCP=VDD+VSW=VDD+VDD=2×VDD

[0055] At this time, the drive circuit 7 outputs the control signals COUT and DOUT of the H level (=VCP) to the gates of the charge control FET 14 and the discharge control FET 15, respectively, so that both the charge control FET 14 and the discharge control FET 15 are turned on.

[0056] (B) On the other hand, when a zero-volt battery is charged, that is, when the battery voltage VDD is lower than the over-discharge detection threshold Vthe, the over-discharge detection circuit 2 is in the "over-discharge detected" state and outputs the detection signal S2 of the L level. Therefore, the drive circuit 7 outputs the control signal DOUT of the L level (=VSS) to the gate of the discharge control FET 15, thereby turning off the discharge control FET 15. The switch circuit 3 turns off the switch 5 and turns on the switch 4, and the charger voltage VP+ It is output as output voltage VSW. That is, VSW = VP + .

[0057] When the charger CH1 is not connected, the discharge control FET 15 is turned off, and the discharge path from the secondary battery B1 is cut off. Therefore, the positive electrode voltage VP of the positive electrode terminal 13 is + The system load RL pulls down the voltage VSS to the ground voltage VSS. That is, VSW=VSS (=0V). Here, since the boost circuit 6 uses the output voltage VSW as the power supply voltage, in this case, no boosting operation is performed, and the boost voltage VCP that drives the charge control FET 14 to turn on is not supplied to the drive circuit 7, so the charge control FET 14 is driven to turn off.

[0058] On the other hand, when the charger CH1 is connected, the positive electrode voltage VP + This is equal to the output voltage of charger CH1. Therefore, the charger output voltage VP + =VSW. The boost circuit 6 performs a boost operation using the output voltage VSW as the power supply voltage, and the drive circuit 7 outputs a control signal COUT of the H level (=VCP) to the gate of the charge control FET 14 to turn on the charge control FET 14, thereby turning on the charge path to charge the zero-volt battery. Here, the boost voltage VCP generated by the boost operation of the boost circuit 6 is expressed by the following formula.

[0059] VCP=VDD+VSW=VDD+VP +

[0060] Here, if the gate-source voltage of the charge control FET 14 is Vgs and the gate-source voltage of the charge control FET 14 required to drive the supply current of the charger CH1 is Vth, the difference voltage (Vg-Vs) between the gate voltage Vg and the source voltage Vs of the charge control FET 14 is expressed by the following formula.

[0061] Vg-Vs

[0062] =COUT-VDD

[0063] =(VDD+VP + )-VDD

[0064] =VP +

[0065] Here, the condition for charging is Vgs ≥ Vth, that is, P + ≥Vth.

[0066] Figure 3 1 is a timing chart showing the voltages after the charger is connected in the secondary battery protection circuit according to the prior art example 2. Figure 4 It means in Figure 1 The timing diagram of each voltage after the charger is connected in the secondary battery protection circuit 16. Figure 3 as well as Figure 4 , describing the timing diagram for charging the zero-volt battery in the conventional example 2 and the first embodiment.

[0067] In the secondary battery protection circuit according to the conventional example 2, when a charger is connected to a secondary battery near zero volts, a potential difference is generated between the positive terminal 13 and the negative terminal 12 until a voltage that satisfies the output voltage condition of the charger for enabling charging is generated. Specifically, the gate-source voltage Vgs of the charge control FET 14 is expressed by the following equation.

[0068] Vgs=COUT-VDD

[0069] Here, the voltage COUT of the control signal is expressed by the following formula ( Figure 3 ).

[0070] COUT=VP +

[0071] Therefore, it becomes the following formula.

[0072] Vgs=VP + -VDD

[0073] If the gate-source voltage of the charge control FET 14 required to drive the supply current of the charger CH1 is Vth, the condition for charging is Vgs ≥ Vth, so VP + - VDD ≥ Vth, which becomes VP + ≥VDD+Vth( Figure 3 ).

[0074] In the secondary battery protection circuit 16 according to the first embodiment, when the gate-source voltage of the charge control FET 14 is Vgs and the gate-source voltage of the charge control FET 14 required to drive the supply current of the charger CH1 is Vth, it is expressed by the following equation.

[0075] COUT=VCP=VDD+VSW=VDD+VP +

[0076] Therefore, it is expressed by the following formula.

[0077] Vgs=COUT-VDD=(VDD+P + )-VDD=P+

[0078] Here, the condition for charging is Vgs>Vth, that is, P+≥Vth ( Figure 4 ).from Figure 4 It can be seen that, unlike the conventional example 2, since it does not depend on the battery voltage VDD, as a result, charging is performed with a charger voltage lower than that of the conventional example 2. On the other hand, if the forward voltage of the body diode 11 of the discharge control FET 15 is Vf and the drain-source voltage of the charge control FET is Vds, the charge start condition when the VDD voltage rises as charging progresses is expressed by the following equation.

[0079] VP + ≥VDD+Vds+Vf

[0080] In order to meet this condition, the charger CH1 makes the positive electrode voltage VP + Rise to perform CC charging. Figure 3 In the prior art example 2, immediately after the charging starts, as the battery voltage VDD rises, the positive electrode voltage VP + In contrast, Figure 4 In the first embodiment, after charging starts, there is a positive electrode voltage VP for a predetermined period of time. + During the time period when the voltage does not rise, charging can be maintained at a charger voltage lower than that of the second conventional example.

[0081] As described above, according to Embodiment 1, Figure 4 It is understood that by charging the secondary battery B1 near zero volts at a charger voltage lower than that of conventional technology, heat loss can be reduced compared to the conventional technology.

[0082] (Implementation Method 2)

[0083] Figure 5A 1 is a circuit diagram showing a configuration example of a battery pack BP2 and its peripheral circuits according to a second embodiment of the present invention. Figure 5B Yes means Figure 5A A block diagram of a configuration example of a switching circuit 3 and a boost circuit 6. Figure 5A The battery pack BP2 with Figure 1 The battery pack BP1 is different from the battery pack BP1 in the following points.

[0084] (1) A secondary battery protection circuit 16A is provided in place of the secondary battery protection circuit 16 , and the secondary battery protection circuit 16A further includes the voltage detection circuit 1 .

[0085] (2) A secondary battery protection device 20A is provided in place of the secondary battery protection device 20, and the secondary battery protection device 20A includes the secondary battery protection circuit 16A.

[0086] (3) The booster circuit 6 includes the control circuit 6B instead of the control circuit 6A.

[0087] The differences are described below.

[0088] exist Figure 5A In the circuit, the voltage detection circuit 1 converts the positive voltage VP + The positive electrode voltage VP is compared with the predetermined voltage threshold Vthd, and a detection signal S1 is generated as a comparison result signal. + When the voltage is equal to or higher than the voltage threshold Vthd, the voltage detection circuit 1 determines that the boost circuit 6 is in a normal operating state and outputs the detection signal S1 of the H level to the drive circuit 7. + When the voltage is lower than the predetermined voltage threshold Vthd, the voltage detection circuit 1 determines that the booster circuit 6 is not in a normal operating state and outputs an L-level detection signal S1 to the drive circuit 7. Here, the voltage threshold Vthd is set higher than the minimum operating voltage of the booster circuit 6.

[0089] In addition, Figure 5A as well as Figure 5B In the embodiment, the control circuit 6B of the boost circuit 6 operates the boost circuit 6 in response to the detection signal S1 of the H level from the voltage detection circuit 1, but stops the boosting operation of the boost circuit 6 in response to the detection signal S2 of the H level (over-discharge detection signal) and the detection signal S1 of the L level from the over-discharge detection circuit 2. In addition, the detection signal S1 from the voltage detection circuit 1 is also output to the drive circuit 7 to notify the boost circuit 6 of the stop of the boosting operation.

[0090] Hereinafter, the effects of the second embodiment having the above-described structure further including the “voltage detection circuit 1” will be described.

[0091] If the over-discharge detection circuit 2 detects the "over-discharge" state of the secondary battery B1, the discharge control FET 15 is driven to be off, and the discharge from the secondary battery B1 stops. Then, the positive electrode voltage VP + With negative voltage VP － The voltage between is pulled down to 0V by the system load RL. At this time, if the charger CH1 is connected, the positive voltage VP + At this time, in order to charge the zero-volt battery, the switch 5 of the switch circuit 3 is turned off and the switch 4 is turned on, and the positive electrode voltage VP is used as +When the output voltage VSW of the booster circuit 6 is supplied as the power supply voltage, if the positive voltage VP + If the booster circuit 6 is activated during the period from 0 V to the minimum operating voltage of the booster circuit 6 (not during the period in which the booster circuit 6 can operate normally), it is assumed that a malfunction or a through current may occur depending on the structure of the booster circuit 6 .

[0092] Therefore, in the second embodiment, when the positive electrode voltage VP + When the voltage is lower than the minimum operating voltage of the booster circuit 6 (not in the normal operating state of the booster circuit 6), the booster circuit 6 is controlled to stop. + When the voltage is lower than the minimum operating voltage of the boost circuit 6, the boost circuit 6 is started to prevent malfunction of the boost circuit 6 or generation of a through current. In addition, when a charger CH1 that outputs an abnormally low voltage due to a fault is connected and a voltage lower than the minimum operating voltage of the boost circuit 6 is stably applied to the positive terminal 13, the voltage detection circuit 1 is in a "not detected" state, outputs an L-level detection signal S1, and stops the boost circuit 6, thereby preventing malfunction of the boost circuit 6 or generation of a through current.

[0093] The secondary battery protection circuit 16A according to the second embodiment has the same operational effects as those of the secondary battery protection circuit 16 according to the first embodiment.

[0094] (Implementation method 3)

[0095] Figure 6 This is a circuit diagram showing a configuration example of a battery pack BP3 and its peripheral circuits according to the third embodiment of the present invention. Figure 6 The battery pack BP3 with Figure 2 The battery pack BP2 is different from the battery pack BP2 in the following points.

[0096] (1) The secondary battery protection circuit 16A is replaced with the secondary battery protection circuit 16B, and the secondary battery protection circuit 16B further includes the clamp circuit 8 .

[0097] (2) A secondary battery protection device 20B is provided in place of the secondary battery protection device 20A, and the secondary battery protection device 20B includes the secondary battery protection circuit 16B.

[0098] The differences are described below.

[0099] exist Figure 6 In the clamp circuit 8, the positive voltage VP + With negative voltage VP －The voltage between (=VSS) is clamped to a fixed clamp voltage VCL which is lower than the withstand voltage of the switches 4 and 5 and the booster circuit 6 and is output to one end of the switch 4 of the switch circuit 3.

[0100] Next, the effects of further including the “clamp circuit 8 ” in the third embodiment configured as described above will be described.

[0101] exist Figure 1 or Figure 5A middle,

[0102] (1) The over-discharge detection circuit 2 detects that the battery voltage VDD is lower than the over-discharge threshold Vthe and outputs a detection signal S2 at an L level.

[0103] (2) Thus, when the switch 5 of the switch circuit 3 is turned off and the switch 4 is turned on, the positive voltage VP + When the output voltage VSW is output,

[0104] (3) A charger CH1 that outputs a voltage greater than a voltage threshold Vthd to the positive terminal 13 is connected.

[0105] (4) The voltage detection circuit 1 detects the connection of the charger CH1.

[0106] (5) While the boost circuit 6 is performing the boost operation, the drive circuit 7 outputs the control signal COUT of the H level (= VCP) to the gate of the charge control FET 14, turning on the charge control FET 14 and charging the secondary battery B1 near zero volts.

[0107] (6) Charger CH1 fails for some reason.

[0108] (7) If the output voltage changes sharply and a high voltage is output to P + , the output voltage VSW becomes a higher voltage.

[0109] (8) That is, it is assumed that a high voltage exceeding the withstand voltage is applied to the switches 4 and 5 and the booster circuit 6 connected to the output voltage VSW, and the switches 4 and 5 and the booster circuit 6 are destroyed.

[0110] To solve this problem, it is conceivable to form the switches 4 and 5 and the booster circuit 6 using high-voltage components, but this has disadvantages of increasing the area, increasing the number of masks used in the manufacturing process of the semiconductor manufacturing device, and increasing the lead time.

[0111] As described above, according to the third embodiment, by further providing the clamp circuit 8 , it is possible to avoid the switches 4 , 5 and the booster circuit 6 from being destroyed.

[0112] In addition, the secondary battery B1 is usually used at 4.2V or less, so when the secondary battery protection circuit 16B is formed by a semiconductor integrated circuit (IC), the protection circuit IC connected only to the battery voltage generally uses components of a 5V process. Therefore, by setting the clamp voltage VCL from the clamp circuit 8 to 5V or less, the secondary battery protection circuit 16B including the switches 4, 5 and the boost circuit 6 can be formed by low-voltage components of a 5V process generally used in the protection circuit IC. Therefore, the advantages of area saving, reduction in the number of masks, and shortened lead time can be obtained.

[0113] The secondary battery protection circuit 16B according to the third embodiment has the same operational effects as the secondary battery protection circuits 16 and 16A according to the first and second embodiments.

[0114] In the above Figure 6 In the third embodiment, the voltage detection circuit 1 may be deleted (a variation of the third embodiment).

[0115] (Implementation 4)

[0116] Figure 7 1 is a circuit diagram showing a configuration example of a battery pack BP4 and its peripheral circuits according to a fourth embodiment of the present invention. Figure 7 The battery pack BP4 with Figure 6 The battery pack BP3 has the following differences compared to the battery pack BP3.

[0117] (1) The secondary battery protection circuit 16B is replaced with the secondary battery protection circuit 16C in which the insertion position of the clamp circuit 8 is changed. The clamp circuit 8 is inserted between the positive electrode terminal 13 and the voltage detection circuit 1 and one end of the switch 4 of the switch circuit 3 .

[0118] (2) A secondary battery protection device 20C is provided in place of the secondary battery protection device 20B, and the secondary battery protection device 20C includes the secondary battery protection circuit 16C.

[0119] The differences are described below.

[0120] exist Figure 7 In the clamp circuit 8, the positive voltage VP + With negative voltage VP －The voltage between the switching circuit 3 and the boost circuit 6 is clamped to clamp the voltage between the switching circuit 3 and the boost circuit 6, and a fixed clamp voltage VCL which is lower than the withstand voltage of the switches 4, 5 and the boost circuit 6 is output to one end of the switch 4 of the switch circuit 3 and the voltage detection circuit 1. When the clamp voltage VCL is higher than the voltage threshold Vthd, the voltage detection circuit 1 generates an H-level detection signal S1 and outputs it to the drive circuit 7. On the other hand, when the clamp voltage VCL is lower than the voltage threshold Vthd, the voltage detection circuit 1 generates an L-level detection signal S1 and outputs it to the drive circuit 7.

[0121] According to the above-structured embodiment 4, Figure 7 As shown, by configuring the voltage detection circuit 1 at the rear stage of the clamp circuit 8 and monitoring the clamp voltage VCL from the clamp circuit 8, the voltage detection circuit 1 can be constructed with a low withstand voltage of 5V, which can achieve the advantages of saving area, reducing the number of masks and shortening the lead time.

[0122] The secondary battery protection circuit 16C according to the fourth embodiment has the same operational effects as the secondary battery protection circuits 16 and 16A to 16B according to the first to third embodiments.

[0123] (Implementation 5)

[0124] Fig. 8A This is a circuit diagram showing a configuration example of a battery pack BP5 and its peripheral circuits according to a fifth embodiment of the present invention. Fig. 8A The battery pack BP5 with Figure 7 The battery pack BP4 is different in the following points.

[0125] (1) A secondary battery protection circuit 16D is provided in place of the secondary battery protection circuit 16C, and the secondary battery protection circuit 16D further includes a voltage detection circuit 17. The voltage detection circuit 17 is inserted between the positive electrode terminal 13 and the clamp circuit 8 and the voltage detection circuit 1.

[0126] (2) A secondary battery protection device 20D including the secondary battery protection circuit 16D is provided instead of the secondary battery protection device 20C.

[0127] The differences are described below.

[0128] exist Fig. 8A The voltage detection circuit 17 monitors the positive electrode voltage VP as the charger voltage. + The charger voltage monitoring circuit has a voltage threshold Vthf set higher than the voltage threshold Vthd of the voltage detection circuit 1. The voltage detection circuit 17 detects the positive electrode voltage VP +The voltage is compared with the voltage threshold Vthf to detect a so-called "high voltage", and a detection signal S17 is generated as a comparison result signal as follows.

[0129] (A) At positive voltage VP + When the voltage is equal to or higher than the voltage threshold value Vthf, the voltage detection circuit 17 generates a detection signal S17 of the H level (=VCL) and outputs it to the voltage detection circuit 1.

[0130] (B) On the other hand, at the positive voltage VP + When the voltage is lower than the voltage threshold Vthf, the voltage detection circuit 17 generates a detection signal S17 of an L level (=VSS) and outputs the detection signal S17 to the voltage detection circuit 1.

[0131] The voltage detection circuit 1 generates a detection signal S1 at an L level (= VSS) in response to the detection signal S17 at an H level and outputs it to the drive circuit 7 and the control circuit 6B of the boost circuit 6. On the other hand, the voltage detection circuit 1 generates a detection signal S1 at an H level (= VCL) in response to the detection signal S17 at an L level and outputs it to the drive circuit 7 and the control circuit 6B of the boost circuit 6 when the positive voltage VP+ is equal to or higher than the voltage threshold Vthd. + When the voltage is lower than the voltage threshold Vthd, a detection signal S1 of an L level (=VSS) is generated and output to the drive circuit 7 and the control circuit 6B of the booster circuit 6 .

[0132] Next, the operation and effects of the voltage detection circuit 17 according to the fifth embodiment will be described below.

[0133] In the prior art example 2 and the first to fourth embodiments, when the charger CH1 outputting a relatively high voltage is connected between the positive terminal 13 and the negative terminal 12 of the secondary battery B1 at a voltage near zero volts, the positive terminal VP + Since the potential difference between the (charger voltage) and the battery voltage VDD is large, there is a problem that an inrush current flows into the secondary battery B1, causing damage to the secondary battery B1 or ignition. In order to solve this problem, a voltage detection circuit 17 is further provided.

[0134] exist Fig. 8AIn the embodiment, the voltage detection circuit 17 is further provided. When the charger CH1 outputting a relatively high voltage higher than the voltage threshold value Vthf is connected between the positive terminal 13 and the negative terminal 12, the voltage detection circuit 17 generates a detection signal S17 of an H level (=VCL) and outputs it to the voltage detection circuit 1. The voltage detection circuit 1 generates a detection signal S1 of an L level (=VSS) in response to the detection signal S17 of an H level and outputs it to the drive circuit 7 and the control circuit 6B of the booster circuit 6. Therefore, since the booster circuit 6 does not perform the boosting operation, the drive circuit 7 outputs the control signal COUT of an L level to the gate of the charge control FET 14, and thus the charge control FET 14 is turned off to cut off the charging path. As a result, since the charging of the secondary battery B1 near zero volts is not started, the inrush current does not flow into the secondary battery B1, and damage or ignition of the secondary battery B1 can be avoided.

[0135] The secondary battery protection circuit 16D according to the fifth embodiment has the same operational effects as the secondary battery protection circuits 16 and 16A to 16C according to the first to fourth embodiments.

[0136] (Implementation 6)

[0137] Figure 8B This is a circuit diagram showing a configuration example of a battery pack BP6 and its peripheral circuits according to a sixth embodiment of the present invention. Figure 8B The battery pack BP6 with Fig. 8A The battery pack BP5 has the following differences compared to the BP5.

[0138] (1) The voltage detection circuit 17 detects the clamp voltage VCL from the clamp circuit 8 instead of the positive voltage VP + .

[0139] (2) A secondary battery protection device 20E including the secondary battery protection circuit 16E is provided instead of the secondary battery protection device 20D including the secondary battery protection circuit 16D.

[0140] The differences are described below.

[0141] exist Figure 8B In the embodiment, the voltage detection circuit 17 monitors the positive voltage VP from the clamp circuit 8 via the clamp voltage VCL. + The charger voltage monitoring circuit has a voltage threshold Vthf set higher than the voltage threshold Vthd of the voltage detection circuit 1. At this time, in order to enable the voltage detection circuit 17 to detect the positive electrode voltage VP based on the clamp voltage VCL from the clamp circuit 8, +When the voltage threshold Vthf is reached or higher, the clamp voltage from the clamp circuit 8 is set higher than Vthf. The voltage detection circuit 17 detects a so-called "high voltage" by comparing the clamp voltage VCL with the voltage threshold Vthf, and generates a detection signal S17 as a comparison result signal as follows.

[0142] (A) When the clamp voltage VCL becomes equal to or higher than the voltage threshold value Vthf, the voltage detection circuit 17 generates the detection signal S17 of the H level (=VCL) and outputs it to the voltage detection circuit 1.

[0143] (B) On the other hand, when the clamp voltage VCL is lower than the voltage threshold Vthf, the voltage detection circuit 17 generates the detection signal S17 of the L level (=VSS) and outputs it to the voltage detection circuit 1.

[0144] The secondary battery protection circuit 16E according to the sixth embodiment configured as described above has the same operational effects as the secondary battery protection circuit 16D according to the fifth embodiment except for the detection voltage of the voltage detection circuit 17 .

[0145] (Variation Example)

[0146] In the above embodiment, the overdischarge detection circuit 2 detects overdischarge of the secondary battery B1, but the present invention is not limited thereto, and for example, a reduction in the battery voltage of the positive terminal 21 of the secondary battery B1 may be detected by an increase in the current consumption of the secondary battery B1, etc. That is, the overdischarge detection threshold Vthe may also be another threshold for detecting a voltage reduction.

[0147] In the above embodiments, the secondary battery protection circuit, the secondary battery protection device and the battery pack are described, but the present invention is not limited thereto and can constitute a control circuit or a control method for the secondary battery protection circuit, or can perform various modifications such as combining part or all of other embodiments in a certain embodiment.

[0148] For example, the charge control FET 14 and the discharge control FET 15 may be arranged in such a manner that their arrangement positions are replaced with each other.

[0149] In the above embodiment, the charge control FET 14 and the discharge control FET 15 are used, but the present invention is not limited thereto, and other types of switching elements such as bipolar transistors (having a control terminal as a base) may be used.

[0150] Explanation of symbols

[0151] 1 voltage detection circuit; 2 over-discharge detection circuit; 3 switch circuit; 3A control circuit; 4, 5 switches; 6 boost circuit; 6A, 6B control circuit; 6a~6d switches; 7 drive circuit; 8 clamp circuit; 9 control circuit; 10, 11 body diode; 12 negative terminal; 13 positive terminal; 14 charge control FET; 15 discharge control FET; 16, 16A~16E secondary battery protection circuit; 17 voltage detection circuit; 20, 20A~20E secondary battery protection device; 21 positive terminal; 22 negative terminal; B1 secondary battery; BP1~BP6 battery pack; C1 capacitor; CH1 charger; RL system load.

Claims

1. A secondary battery protection circuit, which protects the secondary battery by using a charge control switch element and a discharge control switch element which are inserted between the positive terminal of the secondary battery and the high potential terminal of the load and the charger and are connected in series with each other, the secondary battery protection circuit comprising: A first voltage detection circuit, detecting whether the battery voltage of the secondary battery is less than a specified first threshold; a switch circuit that outputs an output voltage as a high potential voltage of the charger when a voltage less than the first threshold is detected, and outputs an output voltage as a battery voltage when a voltage less than the first threshold is not detected; A boost circuit, using the output voltage of the switch circuit to boost the battery voltage and output it; as well as The driving circuit performs control so that when it is detected that the voltage is less than the first threshold value, the output voltage of the boost circuit is output only to the control terminal of the charge control switch element, thereby only the charge control switch element is turned on; on the other hand, when it is not detected that the voltage is less than the first threshold value, the output voltage of the boost circuit is output to the control terminals of the charge control switch element and the discharge control switch element, thereby both the charge control switch element and the discharge control switch element are turned on.

2. The secondary battery protection circuit according to claim 1, wherein: The secondary battery protection circuit further comprises: a second voltage detection circuit for detecting that the voltage at the high potential terminal of the charger is equal to or greater than a predetermined second threshold value, indicating that the boost circuit is in a normal operating state, wherein the second threshold value is higher than a minimum operating voltage of the boost circuit; When the boost circuit is detected to be in a state where it can operate normally, the second voltage detection circuit operates the boost circuit. On the other hand, when a voltage less than the first threshold is detected and it is not in a state where the boost circuit can operate normally, the second voltage detection circuit stops the operation of the boost circuit.

3. The secondary battery protection circuit according to claim 1 or 2, wherein: The secondary battery protection circuit further comprises: The clamp circuit clamps the high potential voltage of the charger to a predetermined clamp voltage, and outputs the clamp voltage to the switch circuit instead of the high potential voltage of the charger.

4. The secondary battery protection circuit according to claim 2, wherein: The secondary battery protection circuit further comprises: The clamp circuit clamps the high potential voltage of the charger to a predetermined clamp voltage, and outputs the clamp voltage to the switch circuit and the second voltage detection circuit instead of the high potential voltage of the charger.

5. The secondary battery protection circuit according to claim 2 or 4, wherein: The secondary battery protection circuit further comprises: a third voltage detection circuit for detecting that the voltage of the high potential terminal of the charger is a high voltage equal to or higher than a predetermined third threshold value, wherein the third threshold value is higher than the second threshold value; The third voltage detection circuit stops the operation of the boost circuit when detecting the high voltage.

6. The secondary battery protection circuit according to claim 4, wherein: The secondary battery protection circuit further comprises: A third voltage detection circuit detects that the clamp voltage is a high voltage greater than a third threshold value, wherein the third threshold value is higher than the second threshold value. The third voltage detection circuit stops the operation of the boost circuit when detecting the high voltage.

7. A secondary battery protection device, comprising: The secondary battery protection circuit as claimed in claim 1 or 2; The charging control switch element; and The discharge controls the switching element.

8. A battery pack comprising: The secondary battery protection circuit as claimed in claim 1 or 2; the secondary battery; The charging control switch element; and The discharge controls the switching element.

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