JP2005080347A - Overcharge protection circuit of battery, packed battery and method of protecting overcharge of battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an overcharge protecting circuit, etc. of a battery which can protect the battery against overcharge without setting an overcharge detection voltage to low. <P>SOLUTION: A method of protecting the overcharge of the battery includes a step of monitoring a voltage of the battery, a step of interrupting charging to protect the battery against the overcharge when the voltage of the battery exceeds a predetermined overcharge detection voltage. The method further includes a step of measuring the battery voltage by an overcharge detector, a step of comparing the battery voltage with a first voltage value of the overcharge detection voltage set by a controller 5, a step of judging the overcharge when the battery voltage exceeding the first voltage value is detected, a step of interrupting the charging by the controller 5 for controlling the charging, a step of switching the overcharge detection voltage to a second voltage value lower than the first voltage value, and a step of returning the overcharge detection voltage from the second voltage value to the first voltage value by the controller 5 when the battery is discharged. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an overcharge protection circuit for preventing overcharge of a battery, a battery pack provided with an overcharge protection circuit, and a method for overcharge protection of a battery.

  A rechargeable secondary battery may deteriorate when overcharged, or may be in a dangerous state such as explosion or ignition. For this reason, in order to protect the battery from such overcharge, an overcharge protection circuit that monitors the voltage of the battery and interrupts charging when a predetermined overcharge detection voltage is exceeded may be built in the battery. When the battery voltage falls below the overcharge detection voltage, the overcharge protection circuit returns to the normal state and resumes charging.

  In addition, in order to prevent malfunction, the overcharge protection circuit does not stop charging immediately when the battery voltage exceeds the overcharge detection voltage, but sets a predetermined delay time in advance. Some are configured to detect overcharge only when the voltage continues to exceed the overcharge detection voltage.

  Furthermore, give hysteresis to the overcharge detection voltage, set a return voltage that is lower than the overcharge detection voltage to detect overcharge, and restore the charge when the battery voltage drops below this return voltage. There is also an overcharge protection circuit.

  However, in these methods, in the state where charging and discharging are repeated in a short time and the battery is overcharged, the overcharge protection circuit returns to the reset state because the battery voltage decreases while the charging is stopped and discharged. When charging is resumed, charging is possible during the delay time, so charging during the delay time is repeated and the battery cannot be protected despite overcharging. there were.

  Here, the state of overcharging while repeating charging and discharging in a short time is shown in the timing chart of FIG. 1, and the operation of the conventional charge protection circuit is shown in the flowchart of FIG. As shown in this figure, the overcharge detection voltage value is preset (step S'1). Here, if the battery voltage rises for some reason and exceeds the overcharge detection voltage value, and this state continues for a predetermined delay time or longer, the protection circuit is activated and the process proceeds from step S′2 to step S′3 for charging. Turn off the switch and shut off the circuit. Then, charging is stopped and no current flows, so the battery voltage is maintained and drops due to discharge. When the battery voltage drops to a predetermined overcharge recovery voltage value considering the hysteresis (step S'4), the charging switch is turned on to return to a chargeable state (step S'5). However, when charging and discharging are repeated in the vicinity of full charge, the above steps are repeated as shown in FIG. At this time, since the protection circuit does not work during the delay time in step S′2, if the charge / discharge is repeated in a short time, the battery voltage may gradually exceed the overcharge detection voltage value.

Also, from the viewpoint of protecting the battery, it is preferable to set the overcharge detection voltage as low as possible.However, if the overcharge detection voltage is set low, overcharge is detected by mistake even though it is in a normal state. As a result, the protection circuit may be activated to prevent full charge. Thus, it has been difficult to achieve both protection of the battery from overcharge and avoiding malfunction of charge protection.
Japanese Patent No. 2925241 Japanese Patent No. 2872365 Japanese Patent No. 3031969

  The present invention has been made to solve such problems. A main object of the present invention is to provide a battery overcharge protection circuit, a pack battery, and a battery overcharge protection method that can protect the battery from overcharge without setting the overcharge detection voltage low. .

  In order to achieve the above object, the battery overcharge protection circuit according to claim 1 of the present invention monitors the voltage of the battery, cuts off the charge when a predetermined overcharge detection voltage is exceeded, and prevents the battery from being overcharged. A battery overcharge protection circuit for protecting the battery, controls charging, and uses an overcharge detection voltage as a first voltage value and a second voltage value lower than the first voltage value. And a control unit for measuring the battery voltage and an overcharge detection unit for comparing the overcharge detection voltage set by the control unit, the first voltage as the overcharge detection voltage When the value is set and the overcharge detection unit detects a battery voltage exceeding the first voltage value, it is determined as overcharge, and the control unit cuts off the charge and detects overcharge. The voltage is switched from the first voltage value to the second voltage value.

  The battery overcharge protection circuit according to claim 2 of the present invention monitors the voltage of the battery and shuts off the charge when a predetermined overcharge detection voltage is exceeded to protect the battery from overcharge. A control unit for controlling charging and for setting a first voltage value and a second voltage value lower than the first voltage value as an overcharge detection voltage, the overcharge protection circuit; An overcharge detection unit for measuring a battery voltage and comparing the overcharge detection voltage set by the control unit with the first voltage value being set as the overcharge detection voltage. When the overcharge detection unit detects a battery voltage exceeding the first voltage value, it is determined as overcharge, and the control unit cuts off the charge, while the battery voltage exceeds the first voltage value. Count the number of times, and if it exceeds the predetermined number of times, overcharge detection voltage from the first voltage value And switches the second voltage value.

  Furthermore, the overcharge protection circuit for a battery according to claim 3 of the present invention is the overcharge protection circuit for a battery according to claim 1 or 2, wherein the overcharge detection unit is based on the second voltage value. If it is detected that the battery voltage has dropped below the lower third voltage value, it is determined that the battery has been discharged, and the control unit changes the overcharge detection voltage from the second voltage value to the first voltage value. It is characterized by controlling to return.

  According to a fourth aspect of the present invention, there is provided a battery pack comprising an overcharge protection circuit for monitoring the voltage of the battery and interrupting the charge to protect the battery from overcharge when a predetermined overcharge detection voltage is exceeded. A battery pack that controls charging and sets a first voltage value and a second voltage value lower than the first voltage value as an overcharge detection voltage, and a battery An overcharge detection unit for measuring a voltage and comparing the overcharge detection voltage set by the control unit, and in a state where the first voltage value is set as the overcharge detection voltage, When the overcharge detection unit detects a battery voltage exceeding the first voltage value, it is determined as overcharge, the control unit cuts off the charge, and the overcharge detection voltage is changed from the first voltage value to the second voltage value. It is characterized by switching to the voltage value.

  Furthermore, the battery overcharge protection method according to claim 5 of the present invention monitors the voltage of the battery and cuts off the charge when a predetermined overcharge detection voltage is exceeded to protect the battery from overcharge. In this protection method, the overcharge detection unit measures the battery voltage, compares the first voltage value set as the overcharge detection voltage with the battery voltage, and detects a battery voltage exceeding the first voltage value. When determining that the battery is overcharged, the control unit that controls the charge cuts off the charge and switches the overcharge detection voltage to a second voltage value lower than the first voltage value, and the battery is discharged. The control unit includes a step of returning the overcharge detection voltage from the second voltage value to the first voltage value.

  According to the present invention, a battery overcharge protection circuit, a battery pack, and a battery overcharge protection method that achieve both battery protection from overcharge and effective charging are realized. That is, by switching between the first voltage value and the second voltage value lower than the first voltage value as the overcharge detection voltage, the overcharge detection voltage is increased in the normal state, and erroneous detection of overcharge is suppressed. On the other hand, if the battery is overcharged by repeatedly charging and discharging in a short time, the overcharge detection voltage can be lowered to protect the battery. As described above, the present invention realizes a battery overcharge protection circuit, a battery pack, and a battery overcharge protection method with high practicality that protects the battery without impairing charging and achieves both safety and convenience. .

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the embodiment described below exemplifies a battery overcharge protection circuit, a pack battery, and a battery overcharge protection method for embodying the technical idea of the present invention. The charge protection circuit, battery pack, and battery overcharge protection method are not specified as follows.

  Further, the present specification by no means specifies the members shown in the claims to the members of the embodiments. In particular, the dimensions, materials, shapes, relative arrangements, and the like of the component parts described in the embodiments are not intended to limit the scope of the present invention unless otherwise specified, and are merely explanations. It's just an example. Note that the size, positional relationship, and the like of the members shown in each drawing may be exaggerated for clarity of explanation. Furthermore, in the following description, the same name and symbol indicate the same or the same members, and detailed description thereof will be omitted as appropriate. Furthermore, each element constituting the present invention may be configured such that a plurality of elements are constituted by the same member and the plurality of elements are shared by one member, and conversely, the function of one member is constituted by a plurality of members. It can also be realized by sharing.

(Embodiment 1)
The battery overcharge protection method according to Embodiment 1 of the present invention is shown in the flowchart of FIG. 4, and the manner in which the battery is protected from overcharge due to repeated charge and discharge by this method is shown in the timing chart of FIG. . FIG. 5 shows a block diagram of a battery pack provided with an overcharge protection circuit according to an embodiment of the present invention.

  The battery pack 1 shown in FIG. 5 generates a secondary battery 2, a charging switch 3 for charging the secondary battery, a discharging switch 4 for discharging, a control unit 5 for controlling them, and a delay time. A delay timer 6, an overcharge detector 7 for measuring the battery voltage of the secondary battery to detect overcharge, and a power supply unit 8 for driving them. The battery pack includes a positive terminal and a negative terminal as charge / discharge terminals. In addition, in this example, since description is advanced paying attention to an overcharge protection function, description and illustration of other protection functions such as an overdischarge protection function and an overcurrent protection function are omitted. Needless to say, these functions can be employed as appropriate in the battery pack according to the present embodiment.

  As the secondary battery 2, a lithium ion battery, a lithium polymer battery, or the like can be used. Although only one secondary battery is shown in FIG. 5, it goes without saying that two or more batteries can be connected in series or in parallel.

  The charging switch 3 and the discharging switch 4 are switches for turning on / off a circuit for charging and discharging a secondary battery, and a switching element such as a power MOSFET can be used.

  The control unit 5 controls ON / OFF of the charging switch 3 and the discharging switch 4, respectively. The control unit may be provided separately for charging and discharging. When charging the secondary battery, the control unit 5 controls charging by turning on / off the charging switch 3 while keeping the discharging switch 4 ON. Similarly, at the time of discharging, the charging switch 3 is kept ON, and ON / OFF of the discharging switch 4 is controlled.

  The overcharge detection unit 7 measures the battery voltage of the secondary battery 2 to detect overcharge, and notifies the control unit 5 of the overcharge. The control unit 5 controls ON / OFF of the charging switch 3 based on the notification from the overcharge detection unit 7. The delay timer 6 generates a delay time until the control unit 5 controls ON / OFF of the charging switch 3 after detecting overcharge. The delay timer 6 may be provided as a separate member or the same member as the control unit 5. The control unit 5 can be realized by hardware or software such as a predetermined gate array (FPGA and ASIC).

  With the above configuration, a battery overcharge protection circuit is realized. The operation of this overcharge protection circuit will be described based on the flowchart of FIG. 4 and the timing chart of FIG. First, in step S1, the control unit 5 sets the overcharge detection voltage to the first voltage value. The first voltage value is an overcharge detection voltage value that is normally set. For example, in the case of a lithium ion battery, the first voltage value is set to 4.35V. In general, the overcharge voltage of one lithium ion battery is 4.2 V, but is set slightly higher than this in consideration of the internal resistance of the battery.

  Next, in step S2, the battery voltage detected by the overcharge detection unit is compared with the first voltage value that is the overcharge detection voltage, and the time during which the battery voltage exceeds the first voltage value is continuously predetermined. Determine whether the delay time is exceeded. The reason for setting the delay time is to eliminate the case where the battery voltage exceeds the first voltage value in a pulsed manner or temporarily. For example, the delay time is set to 2 s. The delay time is counted by counting a delay timer. If the battery voltage falls below the first voltage value within the delay time, the delay timer is reset and timed again. At the same time, the process returns to step S2 through step S2-1 or step S2-2, and the protection circuit enters a standby state by looping. At this stage, since the overcharge detection voltage is set to the first voltage value, these steps have no effect.

  When the state exceeding the first voltage value for the delay time continues, it is determined that the battery is overcharged, and the process proceeds to step S3, where the charging switch is turned off to interrupt charging. Further, the overcharge detection voltage is set to the second voltage value. The second voltage value is set to a value lower than the first voltage value. For example, it is set to 4.25V for a first voltage value of 4.35V for a lithium ion battery. As a result, when the battery voltage rises again, it is determined that the battery is overcharged at a lower voltage and the charge is cut off, so that the secondary battery is reliably protected from overcharge.

  Furthermore, it transfers to step S4 and it is determined whether the battery voltage measured by an overcharge detection part fell rather than the overcharge return voltage value. The overcharge return voltage value is obtained by providing hysteresis to the overcharge detection voltage so that the charging switch does not chatter and turn on / off at high speed. Here, the overcharge return voltage value is a value obtained by subtracting the hysteresis from the overcharge detection voltage. For example, when the hysteresis is 0.1 V and the overcharge detection voltage is 4.25 V as the second voltage value, the overcharge return voltage value is set to 4.15 V. If the battery voltage has not dropped below this overcharge return voltage value, step S4 is looped and waits until the battery voltage drops. When it falls, it transfers to step S5, the switch for charge is set to ON, charge becomes possible, and charge is restarted in this Embodiment. Then, it returns to step S2-1.

  In step S2-1, it is determined whether the battery voltage is equal to or lower than a third voltage value. The third battery voltage value is a reference for determining whether or not the battery is sufficiently discharged, in other words, whether or not the overcharge detection voltage may be returned to the first voltage value. For example, in the case of a lithium ion battery, it is set to 3.6V. If the battery voltage is less than or equal to the third voltage value, it is determined that the battery has been sufficiently discharged, the process proceeds to step S2-2, the overcharge detection voltage is returned to the first voltage value, and the process proceeds to step S2. . Otherwise, the process proceeds to step S2 as it is without passing through step S2-2, and the overcharge detection voltage is held at the low second voltage value.

  Through the above procedure, the overcharge protection circuit detects an overcharge state and protects the battery in an optimum state. The time chart of FIG. 3 shows a state in which overcharging is effectively avoided while charging and discharging are repeated in a short time by the above procedure. First, when the battery voltage indicated by the bold dotted line in FIG. 3 rises for some reason and the delay time elapses beyond the overcharge detection voltage set to the first voltage value, the charging switch is turned off and charging is cut off. The battery voltage gradually drops because the current is not supplied. This is the same as in FIG. When the voltage becomes equal to or lower than the overcharge return voltage value considering the hysteresis, the charging switch is returned to ON. As a result, the battery voltage rises again, but the overcharge detection voltage is changed to the second voltage value lower than the first voltage value, so that charging is cut off before the battery voltage reaches a dangerous voltage. It will be. As a result, even if charging / discharging is repeated in a short time, the overcharge detection voltage is changed to a low voltage value, so the burden on the secondary battery is reduced and protected from overcharging.

(Embodiment 2)
Further, the timing for changing the overcharge detection voltage to a low voltage value is not limited to the method that is immediately performed when the battery voltage exceeds the overcharge detection voltage. For example, the overcharge detection voltage can be changed to a low voltage value when the battery voltage exceeds the overcharge detection voltage a predetermined number of times or more. An overcharge protection method according to Embodiment 2 of the present invention that employs this method will be described with reference to the flowchart of FIG. 6 and the timing chart of FIG. In FIG. 6, the same step numbers as those in the flowchart of FIG. 4 mean the same steps. First, in step S0, the number n of times when the battery voltage exceeds the overcharge detection voltage is reset to zero.

  In step S1, the overcharge detection voltage is set to the first voltage value. In step S2, when the battery voltage exceeds the first voltage value and the delay time has elapsed, the process proceeds to step S3-1. Here, charging is turned off by turning off the charging switch. Moreover, it transfers to step S3-2 and adds 1 to n. In step S3-3, it is determined whether n has exceeded a predetermined number k. The predetermined number of times can be arbitrarily set. For example, in the example of FIG. If n does not exceed k, the process proceeds to step S4 without changing the overcharge detection voltage, and loops until the battery voltage drops from the overcharge detection voltage by the amount of hysteresis. If n exceeds k, the process proceeds to step S3-4, the overcharge detection voltage is set to the second voltage value, the process proceeds to step S4, and the same operation as in FIG. 4 is repeated. In step S2-2, n is reset in step S2-3, and the process proceeds to step S2. As a result, the overcharge detection voltage is maintained up to a predetermined number of times to continue normal overcharge protection operation, and when the predetermined number of times is exceeded, the overcharge detection voltage is changed to a low value for the first time. Transition to a safer state of protection from charging. According to this method, since the overcharge detection voltage is not lowered when the battery voltage temporarily increases, the possibility of erroneous detection of overcharge with a low overcharge detection voltage value is avoided, and the overcharge detection voltage is In such a state, the risk of overcharging while repeating charging and discharging in a short time increases, so that the overcharge detection voltage can be lowered to avoid battery damage due to overcharging.

  The voltage values and the number of times described above are merely examples, and it goes without saying that optimum values are selected depending on the secondary battery to be used, usage conditions, and the like.

  The battery overcharge protection circuit, the battery pack, and the battery overcharge protection method of the present invention can be applied by being incorporated in a battery such as a mobile phone or a laptop computer.

It is a timing chart which shows the fluctuation | variation of the battery voltage by the conventional overcharge protection method. It is a flowchart which shows the conventional overcharge protection method. It is a timing chart which shows the fluctuation | variation of the battery voltage by the overcharge protection method which concerns on Embodiment 1 of this invention. It is a flowchart which shows the overcharge protection method which concerns on Embodiment 1 of this invention. It is a block diagram which shows the battery pack provided with the overcharge protection circuit which concerns on one embodiment of this invention. It is a flowchart which shows the overcharge protection method which concerns on Embodiment 2 of this invention. It is a timing chart which shows the fluctuation | variation of the battery voltage by the overcharge protection method which concerns on Embodiment 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Pack battery 2 ... Secondary battery 3 ... Switch for charge 4 ... Switch for discharge 5 ... Control part 6 ... Delay timer 7 ... Overcharge detection part 8 ... Power supply part

Claims (5)

A battery overcharge protection circuit for monitoring the voltage of the battery and cutting off the charge when a predetermined overcharge detection voltage is exceeded to protect the battery from overcharge,
A control unit for controlling charging and setting a first voltage value and a second voltage value lower than the first voltage value as an overcharge detection voltage;
An overcharge detection unit for measuring a battery voltage and comparing the overcharge detection voltage set by the control unit;
With
In a state where the first voltage value is set as the overcharge detection voltage, when the overcharge detection unit detects a battery voltage exceeding the first voltage value, the overcharge detection unit determines that it is overcharged, and the control unit An overcharge protection circuit that cuts off charging and switches an overcharge detection voltage from a first voltage value to a second voltage value. A battery overcharge protection circuit for monitoring the voltage of the battery and cutting off the charge when a predetermined overcharge detection voltage is exceeded to protect the battery from overcharge,
A control unit for controlling charging and setting a first voltage value and a second voltage value lower than the first voltage value as an overcharge detection voltage;
An overcharge detection unit for measuring a battery voltage and comparing the overcharge detection voltage set by the control unit;
With
In a state where the first voltage value is set as the overcharge detection voltage, when the overcharge detection unit detects a battery voltage exceeding the first voltage value, the overcharge detection unit determines that it is overcharged, and the control unit While charging is stopped, the number of times the battery voltage exceeds the first voltage value is counted, and when the predetermined number of times is exceeded, the overcharge detection voltage is switched from the first voltage value to the second voltage value. Overcharge protection circuit characterized by. An overcharge protection circuit for a battery according to claim 1 or 2,
When the overcharge detection unit detects that the battery voltage has dropped below a third voltage value lower than the second voltage value, the control unit determines that the battery has been discharged, and the control unit detects the overcharge detection voltage. Is controlled to return from the second voltage value to the first voltage value. A battery pack comprising an overcharge protection circuit for monitoring the voltage of the battery and cutting off the charge when a predetermined overcharge detection voltage is exceeded to protect the battery from overcharge,
A control unit for controlling charging and setting a first voltage value and a second voltage value lower than the first voltage value as an overcharge detection voltage;
An overcharge detection unit for measuring a battery voltage and comparing the overcharge detection voltage set by the control unit;
With
In a state where the first voltage value is set as the overcharge detection voltage, when the overcharge detection unit detects a battery voltage exceeding the first voltage value, the overcharge detection unit determines that it is overcharged, and the control unit A battery pack characterized by blocking charging and switching an overcharge detection voltage from a first voltage value to a second voltage value. A battery overcharge protection method that monitors battery voltage and cuts off charge when a predetermined overcharge detection voltage is exceeded to protect the battery from overcharge,
The overcharge detection unit measures the battery voltage, compares the battery voltage with the first voltage value set as the overcharge detection voltage, and detects a battery voltage exceeding the first voltage value, Determining and switching the overcharge detection voltage to a second voltage value lower than the first voltage value while the control unit that controls the charge cuts off the charge; and
When the battery is discharged, the control unit returns the overcharge detection voltage from the second voltage value to the first voltage value;
An overcharge protection method comprising:

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