JP4771096B2 - Protection circuit - Google Patents

Description

  The present invention relates to a protection circuit for preventing overcurrent and overvoltage of a battery pack using a protection element in which a heating resistor and a fuse element are provided on a substrate.

  With the spread of mobile electronic devices such as mobile phones and laptop computers, the market for lithium ion batteries has expanded. In these mobile electronic devices, a battery pack in which 1 to 4 lithium ion batteries are connected in series is usually used as a power source. In such a battery pack, if the lithium ion battery is overcharged (i.e., overvoltage) during charging, there is a possibility of fire or smoke, and a protection circuit is provided to prevent this.

  This protection circuit needs to protect the battery from both overcurrent and overvoltage. Therefore, a protection circuit using a protection element in which a heating resistor and a fuse element are provided on a substrate and a detection element that detects an overvoltage and switches a current flowing through the protection element is used. In this protection circuit, the fuse element is blown in the event of an overcurrent, while in the event of an overvoltage, the sensing element abruptly passes a current through the heating resistor, causing the heating resistor to generate heat, and the heat causes the fuse element to blow. (Patent Document 1).

Japanese Patent No. 2790433

  In recent years, with the expansion of the market for mobile electronic devices used with large currents, battery packs with a rated voltage of about 10 in series exceeding the conventional rated voltage of 4 or less in series of lithium ion batteries are also used. It has become so.

  On the other hand, in the protection circuit for the battery pack described above, the voltage applied to the heating resistor of the protection element depends on the number of batteries in the battery pack. Therefore, in order to blow out the fuse element of the protection element reliably at the time of overcharge, a protection element provided with a heating resistor having an appropriate resistance value for each series of batteries must be lined up. Today, the voltage rating of packs has diversified from 4 or fewer lithium ion batteries to about 10 in series, and there has been a problem of cost increase or price increase due to multi-product production.

  For example, in the protection circuit 1X of FIG. 10 and the protection circuit 1Y of FIG. 11, the protection elements 2A and 2B are each composed of the heating resistor 3 and the fuse element 4 provided on the substrate, and the operable power is 10 to 20 W. Assuming that the maximum voltage of one battery 6 in the battery pack 5 is 4 V and that the voltage detection IC 8 and the FET 9 are provided as the detection means 7, the protection element 2 includes a battery constituting the battery pack 5. For every 6 serial numbers, the heating resistors 3 having the resistance values shown in Table 1 must be prepared.

If the protection circuit 1X of FIG. 10 is assembled using a 25Ω heating resistor corresponding to the battery pack 5 having a series number of 4 in the battery pack 5 having a series number of 10, the voltage detection IC 8 is connected during overcharge. By detecting the overvoltage at both ends of the battery pack 5, the gate potential of the FET 9 changes, and the power consumption W at the heating resistor 3 when a large current flows through the heating resistor 3 is:
W = V * V / R = 40 * 40/25 = 64W
As a result, the power becomes 64 W, greatly exceeding the operable range of 10 to 20 W. Therefore, before the fuse element 4 is melted, the heating resistor 3 is burned out.

  Thus, it is necessary to use a resistance value corresponding to the voltage of the battery pack 5 as the heating resistor 3 of the protection elements 2A and 2B.

  On the other hand, battery packs used in mobile electronic devices for high current applications require protective element fuse elements for large currents. From this point of view, there is a lineup of protective elements with fuse elements of various ratings. Therefore, the cost of the protection element or the price increase has been a problem.

  Therefore, the present invention provides a protection circuit that protects a battery pack from overcurrent and overvoltage using a protection element provided with a resistance heating element and a fuse element on a substrate, and a detection means, regardless of the current rating of the battery pack. Moreover, it aims at providing the protection circuit which can use a common protection element irrespective of the serial number of the batteries in a battery pack.

  In the protection circuit that protects a battery pack in which a plurality of secondary batteries are connected in series from overcurrent or overvoltage, when the protection circuit is activated by overvoltage, the protection element operates within the operable range of the protection element. In order to apply a voltage to the heating resistor of the element, (1) When overvoltage occurs, the voltage of a predetermined number of batteries is generated rather than the total number of batteries connected in series in the battery pack. It is effective to be applied to the resistor. (2) When detecting the overvoltage by the detection means, the voltage to be detected is not necessarily the voltage for the total number of batteries connected in series in the battery pack. It is not necessary to detect the voltage of a predetermined number of batteries connected in series, and in order to use a protective element with the same rating as a normal application in a large current application, Are arranged in multiple stages in parallel It found that Bayoi, has led to the completion of the present invention.

That is, the first aspect of the present invention is a protection circuit for protecting a battery pack in which secondary batteries are connected in series from overcurrent and overvoltage,
The protection circuit has a protection element provided with a heating resistor and a fuse element on a substrate, and detection means for detecting an overvoltage and switching a current flowing through the heating resistor,
As the fuse element melts during overcurrent,
When the current flowing through the heating resistor is switched on by the detecting means at the time of overvoltage, the voltage of a predetermined number of batteries in the battery pack is applied to the heating resistor so that the heating resistor generates heat and the fuse element is blown. A protection circuit is provided.

2nd this invention is a protection circuit which protects the battery pack with which the secondary battery was connected in series from overcurrent and overvoltage,
The protection circuit includes a protection element provided with a heating resistor and a fuse element on a substrate, and detection means for detecting an overvoltage between arbitrary batteries in the battery pack and switching a current flowing through the heating resistor,
As the fuse element melts during overcurrent,
Provided is a protection circuit in which the heating resistor is heated by the current flowing through the heating resistor being switched on by the detecting means at the time of overvoltage between the batteries, and the fuse element is blown. An aspect is provided in which a plurality of detection means for detecting an overvoltage between them are provided.

3rd this invention is a protection circuit which protects the battery pack with which the secondary battery was connected in series from overcurrent and overvoltage,
The protection circuit has a protection element provided with a heating resistor and a fuse element on a substrate, and detection means for detecting an overvoltage and switching a current flowing through the heating resistor,
Multiple protection elements are connected in parallel,
At the time of overcurrent, the fuse element melts in each protection element,
Provided is a protection circuit in which a current flowing through a heating resistor of each protection element is switched on by a detection means when an overvoltage occurs, whereby the heating resistor of each protection element generates heat and the fuse element is blown.

The fourth aspect of the present invention is a protection circuit for protecting a battery pack in which secondary batteries are connected in series from overcurrent and overvoltage,
The protection circuit includes a protection element provided with a heating resistor and a fuse element on a substrate, and detection means for detecting an overvoltage between arbitrary batteries in the battery pack and switching a current flowing through the heating resistor,
Multiple protection elements are connected in parallel,
At the time of overcurrent, the fuse element melts in each protection element,
When the current flowing in the heating resistor is switched on by the detecting means when the battery is overvoltaged, the voltage of a predetermined number of batteries in the battery pack is applied to the heating resistor of each protection element, and the heating resistor is Provided is a protection circuit that generates heat and blows a fuse element.

  Each of the first, second, third, and fourth aspects of the present invention is a protection circuit that protects a battery pack in which secondary batteries are connected in series from overcurrent and overvoltage, and includes a heating resistor on the substrate. It has a protection element provided with a fuse element and an overvoltage detection means.

  Among these, in the first protection circuit, when the detection means detects an overvoltage to switch on the current flowing through the heating resistor of the protection element, and the voltage is applied to the heating resistor of the protection element, the applied voltage is The voltage is not the voltage of all the batteries connected in series in the battery pack, but the voltage of a predetermined number of batteries connected in series in the battery pack. For this reason, a common heating resistor must be used for the protection element used in the protection circuit for battery packs with a large number of batteries in series and the protection element used in a protection circuit for battery packs with a low number of batteries in series. Can do. Therefore, it is possible to avoid the production of various types of protection elements and reduce the manufacturing cost of the protection circuit.

  In the second protection circuit, when the detection means detects an overvoltage to switch on the current flowing through the heating resistor of the protection element, and the voltage is applied to the heating resistor of the protection element, the detection voltage is This is not the voltage for the whole number of batteries connected in series, but the voltage between any batteries connected in series. For this reason, according to this protection circuit, an overvoltage in a battery pack having a high voltage rating can be detected by a voltage detection IC having a low voltage rating. Here, assuming that the detection voltage is the voltage between individual batteries among arbitrary batteries, it is possible to observe the state of charge according to the variation in characteristics of each individual battery in the battery pack. In this protection circuit, if a plurality of detection means are provided to detect overvoltage between different batteries in the battery pack, the battery pack as a whole has a voltage rating for detecting overvoltage because of the large number of batteries in series. Even when a high voltage detection IC does not exist, a protection circuit can be assembled using an existing voltage detection IC with a low voltage rating corresponding to a battery pack with a small number of batteries in series.

  In the third protection circuit, since the protection elements are connected in parallel, the fuse elements are connected in parallel. For this reason, the fuse element of the protection element can be shared by the protection circuit in which a large current flows in the battery pack and the protection circuit in which a small current flows in the battery pack, and the manufacturing cost of the protection element can be reduced.

  Since the fourth protection circuit has the characteristics of the first, second, and third protection circuits described above, the protection circuit is used for the heating resistor of the protection element used therein, the fuse element, and the like. Also, the detection means used in the protection circuit can be reduced in cost, and the entire protection circuit can be significantly reduced in cost.

  Hereinafter, the present invention will be described in detail with reference to the drawings. In each figure, the same numerals indicate the same or equivalent components.

  FIG. 1 shows a protection circuit 1A according to an embodiment of the first invention. The protection circuit 1A protects the battery pack 5 in which ten secondary batteries 6-1 to 6-10 are connected in series from overcurrent and overvoltage, and includes a protection element 2A and a detection means 7. .

  As described in Japanese Patent No. 2790433 (Patent Document 1), Japanese Patent Application Laid-Open No. 2000-285778, etc., the protective element 2A is provided with a heating resistor 3 and a fuse element 4 on a substrate. The fuse element 4 is blown by heating with energization.

  The detection means 7 comprises a voltage detection IC 8 and an FET 9. The voltage detection IC 8 detects the voltage across the battery pack 5 and outputs the detection signal to the gate of the FET 9.

  When an overcurrent is generated in the battery pack 5 by the protection circuit 1A, the fuse element 4 of the protection element 2A is blown, and when an overvoltage is generated in the battery pack 5, the gate potential of the FET 9 becomes equal to or higher than a predetermined potential and the switch is turned on. As a result, a current suddenly flows between the drain and source of the FET 9, so that a current suddenly flows through the heating resistor 3 of the protective element 1A, the heating resistor 3 generates heat, and the fuse element 4 is blown.

  Here, since the source side terminal of the FET 9 is connected between the batteries 6-4 to 6-5 in the battery pack 5, the voltage applied to the heating resistor 3 in the switched-on state is the connection voltage. It is a series voltage of four batteries determined by the position, and is not a voltage across the battery pack 5. Therefore, according to this protection circuit, ten batteries are connected in series using the heating resistor 3 suitable for the series voltage of the four batteries applied to the heating resistor 3 in the switched-on state. In addition, it is possible to cope with an overvoltage at both ends of the battery pack 5 and to reduce the cost of the protection circuit.

  In consideration of troubles due to short-circuit between batteries, it is preferable to apply as many series battery voltages as possible to the heating resistor 3 in the switch-on state. Therefore, in practice, the voltage of the battery having two or more in series may be applied to the heating resistor 3.

  FIG. 2 shows a protection circuit 1B according to an embodiment of the second invention. Similarly to the above-described protection circuit 1A, this protection circuit 1B also protects the battery pack 5 in which ten secondary batteries 6-1 to 6-10 are connected in series from overcurrent and overvoltage. It has the element 2A and the detection means 7. Even in this protection circuit 1B, the detection means 7 comprises a voltage detection IC 8 and an FET 9. The voltage detection IC 8 detects the voltage between the first battery 6-1 and the fourth battery 6-4. To be connected. By connecting the voltage detection IC 8 in this way, an overvoltage is generated in the battery pack 5 in which 10 batteries are connected in series using the voltage detection IC 8 suitable for detecting the series voltage of the four batteries. Can be prevented. In particular, in this protection circuit 1B, the voltage detection IC 8 is connected so as to detect the voltage between the individual batteries between the first battery 6-1 and the fourth battery 6-4. Therefore, even if individual batteries accommodated in the battery pack 5 have variations in characteristics, and even if there are variations in individual battery voltages during charging, overvoltage can be prevented for each battery.

  In the protection circuit 1B of FIG. 2, the resistor R is provided between the gate and the source of the FET 9 in order to switch on the N-channel TFT when the voltage detection IC 8 detects an overvoltage. This is because the gate potential of the FET 9 needs to be higher than the source potential to some extent.

  The protection circuit 1C in FIG. 3 detects the voltage between the first battery 6-1 and the fourth battery 6-4 using the voltage detection IC 8-1 in the same manner as the protection circuit 1B in FIG. Further, by connecting the voltage detection IC 8-2 between the remaining batteries 6-5 and the fourth battery 6-7, the voltage detection ICs are provided in two stages. When the overvoltage is detected by the voltage detection ICs 8-1 and 8-2, the fuse element 4 of the protection element 2A is melted to protect the battery pack 5 from overcharging.

  That is, if an overvoltage occurs between any one of the first battery 6-1 and the fourth battery 6-4, the gate of the FET 9-3 is detected by the voltage detection IC 8-1. The potential rises, the FET 9-3 is switched on, a current flows suddenly through the heating resistor 3 of the protective element, the heating element 3 generates heat, and the fuse element 4 is melted.

  On the other hand, if an overvoltage occurs between any of the fifth batteries 6-5 and the seventh battery 6-7, first, the FET 9-1 is detected by the voltage detection IC 8-2. The gate potential of the FET 9-1 becomes high, and a current suddenly flows between the drain and source of the FET 9-1, thereby lowering the gate potential of the FET 9-2. Since this FET 9-2 is a P-channel FET, it is switched on due to a drop in the gate potential, and a current flows rapidly between its drain and source. As a result, the gate potential of the FET 9-3 is raised, the FET 9-3 is switched on, a current suddenly flows through the heat generating resistor 3 of the protective element, the heat generating body 3 generates heat, and the fuse element 4 is blown. The diodes D-1 and D-2 are provided in order to prevent the potential from being lowered through another circuit when the gate potential of the FET 9-3 is raised.

  Therefore, according to the protection circuit 1C, for example, by using the voltage detection ICs 8-1 and 8-2 corresponding to the series number 4 or 3 of the batteries, an overvoltage occurring in the battery pack of the series number 10 is completely prevented. be able to. In other words, because the number of series of batteries is large, the entire battery pack has an existing voltage rating corresponding to a battery pack with a small number of series of batteries, even if there is no voltage detection IC with a high voltage rating for detecting overvoltage. A protection circuit can be assembled using a low voltage detection IC.

  FIG. 4 shows a protection circuit 1D according to an embodiment of the third aspect of the present invention corresponding to a battery pack for large current. In this protection circuit 1D, three protection elements 2A similar to those described above are provided in parallel. Therefore, when a large current flows in the normal energization state of the battery pack 5 and the protection element 2A is provided alone, even when the fuse element 4 is blown, the protection circuit 1D can protect the protection element 2A. Since the energization path branches into three in FIG. 3, the fuse element 4 can be prevented from fusing.

  On the other hand, at the time of overcurrent, the fuse element 4 of each protection element 2A is melted. Therefore, according to the protection circuit 1D, the protection element that allows a large current to flow through the battery pack and the protection circuit that allows a small current to flow through the battery pack can share the fuse element of the protection element. Cost can be reduced.

  In addition, when the fuse element 4 is blown by an overcurrent, for example, as shown in FIG. 5 or FIG. 6, a conduction path remains in the circuit as indicated by an arrow even after the fuse element 4 is blown. Become. Therefore, in order to prevent such a conduction path from remaining after the fuse element 4 is blown, it is preferable to connect a rectifying element to the heating resistor. Specifically, as in a protection circuit 1E shown in FIG. It is preferable to connect a diode to the protective element 2A or connect an FET to the protective element 2A as in the protective circuit 1F shown in FIG.

  The protection circuits of the first, second, and third aspects of the present invention are not limited to the illustrated modes. In addition, these features can be combined with any two or more, thereby making it possible to manufacture a protection circuit suitable for battery packs having various voltage ratings or current ratings at a lower cost. .

  For example, the protection circuit 1G shown in FIG. 9 is provided with three voltage detection ICs in accordance with the voltage detection ICs provided in two stages in the protection circuit 1C shown in FIG. ICs 8-1, 8-2, and 8-3 that are suitable for detecting the voltage of 2 to 4 batteries in series are used. Further, each of the voltage detection ICs 8-1, 8-2, 8-3 detects not only the voltage at both ends of the battery array detected by each, but also the voltage of each battery. Therefore, according to this protection circuit 1G, any of the three voltage detection ICs 8-1, 8-2, and 8-3 can be used when any of the ten batteries 6-1 to 6-10 is overcharged. Is detected, the FET 9-3 is switched on, and the series voltage of four batteries 6-1 to 6-4 is applied to each heating resistor 3 of the protective element 2A, and the heating resistor 3 generates heat. As a result, the fuse element 4 is melted. Thus, according to this protection circuit 1G, a good protection circuit for a battery pack having 10 battery series is assembled using a voltage detection IC and a protection element suitable for detecting a voltage having 2 to 4 battery series. be able to.

  In the protection circuit 1G, four protection elements 2A are connected in parallel. Therefore, even if each protection element 2A is for a normal rated current application, this protection circuit 1G is for a large current application.

  The protection circuit of the present invention is useful as a protection circuit for battery packs having various voltage ratings and current ratings, such as mobile phones, notebook computers, electric automobiles, and electric motorcycles.

4 is a protection circuit according to one embodiment of the present invention. It is a protection circuit of a different mode of the present invention. It is a protection circuit of a different mode of the present invention. It is a protection circuit of a different mode of the present invention. In the protection circuit of the different aspect of this invention, it is explanatory drawing of the conduction path when a fuse element fuses. In the protection circuit of the different aspect of this invention, it is explanatory drawing of the conduction path when a fuse element fuses. It is a protection circuit of a different mode of the present invention. It is a protection circuit of a different mode of the present invention. It is a protection circuit of a different mode of the present invention. It is explanatory drawing of the problem of the conventional protection circuit. It is explanatory drawing of the problem of the conventional protection circuit.

Explanation of symbols

1X, 1Y Conventional protection circuit 1A, 1B, 1C, 1D, 1E, 1F, 1G Example protection circuit 2A, 2B Protection element 3 Heating resistor 4 Fuse element 5 Battery pack 6, 6-1 to 6-10 Battery 7 Detection means 8, 8-1, 8-2, 8-3 Voltage detection IC
9, 9-1, 9-2, 9-3 FET

Claims (4)

A protection circuit for protecting a battery pack in which secondary batteries are connected in series from overcurrent and overvoltage,
The protection circuit detects overvoltages for the total number of secondary batteries connected in series in the protection element provided with the heating resistor and the fuse element on the substrate, and switches the current flowing through the heating resistor. Detecting means for
Multiple protection elements are connected in parallel,
At the time of overcurrent, the fuse element melts in each protection element,
A predetermined number of batteries connected in series smaller than the total number of secondary batteries connected in series in the battery pack by switching on the current flowing through the heating resistor of each protection element by the detection means at the time of overvoltage Is applied to the heating resistor of each protection element, the heating resistor of each protection element generates heat, and the fuse element is blown.   2. The protection circuit according to claim 1, wherein a rectifying element is connected to the heating resistor so that no conduction resistance remains through the heating resistor when the fuse element is blown incompletely due to overcurrent. A protection circuit for protecting a battery pack in which secondary batteries are connected in series from overcurrent and overvoltage,
Between the protection element in which the protection circuit is provided with the heating resistor and the fuse element on the substrate, and any battery connected in series in a number smaller than the total number of secondary batteries connected in series in the battery pack Detecting means for detecting the overvoltage of the heating resistor and switching the current flowing through the heating resistor,
Multiple protection elements are connected in parallel,
At the time of overcurrent, the fuse element melts in each protection element,
A predetermined number of batteries connected in series smaller than the total number of secondary batteries connected in series in the battery pack by switching on the current flowing in the heating resistor by the detecting means at the time of overvoltage between the batteries. Is applied to the heating resistor of each protection element, the heating resistor generates heat, and the fuse element is blown.   4. The protection circuit according to claim 3, wherein a rectifying element is connected to the heating resistor so that no conduction resistance remains through the heating resistor when the fuse element is blown incompletely due to overcurrent.

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