Cell balance circuit

Abstract

To provide a cell balance circuit capable of efficiently and safely cancelling variations in charge voltage of a plurality of cells constituting a cell group.SOLUTION: A cell balance circuit regulates a voltage of each cell in a cell group consisting of a plurality of cells connected in series and comprises: a limit circuit including a resistor of which one end is connected to a positive electrode terminal or a negative electrode terminal of each cell included in the cell group and a capacitive element to which the other end of the resistor is connected; a switch circuit including a plurality of switches configured to short-circuit the positive electrode terminal and the negative electrode terminal of each cell included in the cell group; a control circuit which controls the switch circuit; and a temperature detection section which detects a temperature in a periphery of the control circuit. The control circuit controls the switch circuit in accordance with the temperature that is detected by the temperature detection section.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a cell balance circuit.

Background Art

[0002] Cells of a rechargeable secondary battery may be a group of cells connected in series, which may form a DC power supply. In this case, while the charging and discharging are repeated, the cells constituting the cell group gradually develop a deviation in charging voltage from other cells. When the charging voltages of the plurality of cells constituting the cell group are different, overcharging occurs in some cells and undercharging occurs in other cells. As a result, problems such as shortening of the cell life and reduction in the utilization efficiency of the DC power supply provided by the cell group may occur. A cell balance circuit has been proposed to adjust the charging voltages of the plurality of cells included in the cell group to be uniform (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a cell balance circuit, in order to efficiently eliminate the variation in charging voltage among a plurality of cells in a short time, it is preferable to increase the cell balance current. However, if the resistance value of the filter resistor is made too small, the cell balance current may become too large depending on the ambient temperature, and as a result, the risk of the battery monitoring IC reaching the destruction temperature increases. Thus, in a conventional cell balance circuit, it has been an issue to efficiently and safely eliminate the variation in charging voltage of a plurality of cells.

[0005] In order to solve the above problems, an object of the present invention is to provide a cell balance circuit capable of efficiently and safely eliminating variations in charging voltages of a plurality of cells constituting a cell group.

Means for Solving the Problems

[0006] The cell balance circuit according to the present invention is a cell balance circuit for adjusting the voltage of each of the cells in a cell group composed of a plurality of cells connected in series. The cell balance circuit includes a resistor having one end connected to the positive electrode terminal or the negative electrode terminal of each cell included in the cell group, a limiting circuit including a capacitive element connected to the other end of the resistor, a switch circuit including a plurality of switches configured to be able to short-circuit the positive electrode terminal and the negative electrode terminal of each cell included in the cell group, a control circuit for controlling the switch circuit, and a temperature detection unit for detecting the temperature around the control circuit. The control circuit is characterized in that it controls the switch circuit according to the temperature detected by the temperature detection unit.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Modes for Carrying Out the Invention

[0008] Hereinafter, each embodiment for implementing the present invention will be described with reference to the drawings. The same or similar parts are denoted by the same or similar reference numerals, and redundant descriptions are omitted. Note that various plan views and cross-sectional views may be drawn at dimensional ratios different from those of the actual product in the horizontal plane and cross-section for ease of understanding. Also, in the plan view and the cross-sectional view, they may be illustrated at different dimensional ratios for ease of understanding and ease of illustration.

[0009] [First Embodiment] With reference to FIGS. 1 to 2, the cell balance circuit 1 of the first embodiment will be described. This cell balance circuit 1 is a circuit for monitoring the charging state of a cell group composed of a plurality of cells CL (for example, three cells CL1 to CL3) connected in series, and controlling charging / discharging to each cell CL so that the charging voltages of the plurality of cells CL are equalized. It is roughly composed of a battery monitoring IC 10, a limiting circuit 20, and a temperature detection element 30.

[0010] The battery monitoring IC 10 is, for example, an IC chip in which a control circuit 11, switch elements SW1 to 3, connection terminals 12 to 15, and a temperature signal input terminal 16 are mounted on one chip. The control circuit 11 controls the on / off of the switch elements SW1 to SW3 by outputting switch control signals CBAL1 to CBAL3 according to the information on the charging voltage of each cell CL. Thereby, control is performed such that discharge is performed from a cell CL with a relatively high charging voltage to a cell CL with a relatively low charging voltage, and the charging voltages among the plurality of cells CL are made uniform (equalized).

[0011] The control circuit 11 of this first embodiment executes on / off control of the switch elements SW1 to SW3 in consideration of the temperature detection result of the temperature detection element 30 in addition to the charging voltage of each cell CL as described above. As will be described later, the control circuit 11 controls the duty ratio of the switch elements SW1 to SW3 according to the temperature detected by the temperature detection element 30. The control circuit 11 sets the duty ratio of the switch elements SW1 to SW3 so that the temperature T around the control circuit 11 becomes the set temperature Tn.

[0012] The switch elements SW1 to SW3 each have a function of switching the short - circuiting / opening of the adjacent connection terminals 12 to 15, thereby enabling the connection of the positive - electrode terminal and the negative - electrode terminal of each cell CL, and are composed of, for example, MOSFETs (Metal - Oxide - Semiconductor Field Effect Transistors) or IGBTs (Insulated - Gate Bipolar Transistors). One end of the filter resistors R1 to R4 constituting the limiting circuit 20 is connected to the connection terminals 12 to 15, and filter capacitors C1 to C3 constituting the limiting circuit 20 are connected between the adjacent connection terminals 12 to 15. The limiting circuit 20 includes filter resistors R1 to R4 (resistors) whose other ends are connected to the positive - electrode terminal or the negative - electrode terminal of each cell CL included in the cell group, and filter capacitors C1 to C3 (capacitive elements) connected to one end of the filter resistors R1 to R4. The filter resistors R1 to R4 have a role of limiting the cell - balance current flowing from the cell CL, and the filter capacitors C1 to C3 have a role of suppressing the fluctuation of the charging voltage of the cell CL.

[0013] The temperature - sensing element 30 is arranged near the control circuit 11 in the battery monitoring IC10 and is connected to the temperature - signal input terminal 16. The temperature - sensing element 30 can be, for example, a thermistor, senses the temperature around the control circuit 11, and inputs a sensing current corresponding to the temperature to the control circuit 11 via the temperature - signal input terminal 16. The control circuit 11 compares the detected temperature T around the control circuit 11 with the set temperature Tn and changes the switch - control signals CBAL1 to 3 according to the comparison result.

[0014] When the charging voltage of each cell CL and the temperature around the control circuit 11 are detected, the control circuit 11 controls the on / off of the switch elements SW1 to SW3 so that the charging voltages among the plurality of cells CL are equalized and according to the detected temperature. Specifically, the control circuit 11 performs the on / off switching and duty - ratio setting of the switch elements SW1 to SW3 according to the detected charging voltage and the temperature around the control circuit 11, and executes the on / off control of the switches SW1 to SW3 according to the set duty ratio.

[0015] As shown in FIG. 2, when the temperature T around the detected control circuit 11 is lower than the set temperature Tn, the duty ratios of the respective switch elements SW1 to SW3 are set to high values, for example, 100%. On the other hand, when the temperature T around the control circuit 11 exceeds the set temperature Tn, the duty ratio is set to, for example, 20%, 10%, etc. according to the difference from the set temperature Tn. As the temperature T around the control circuit 11 approaches the breakdown temperature Tb, the duty ratio is set to a low value. Thereby, it is possible to prevent the temperature T around the control circuit 11 from reaching the breakdown temperature Tb. Further, by appropriately setting the duty ratio, the temperature T around the control circuit 11 is maintained at a value near the set temperature Tn. Thereby, fluctuations in the resistance value of the filter resistor R are also suppressed, and the temperature of the control circuit 11 is maintained near the set temperature Tn, which is sufficiently lower than the breakdown temperature Tb, so that the cell balance current can be passed as much as possible.

[0016] Referring to FIG. 5, the cell balance circuit 1C according to the comparative example will be described. The cell balance circuit 1C of this comparative example has no temperature detection element 30, and the switch control signals CBAL1 to 3 are changed only according to the charging voltage of the cell CL regardless of the ambient temperature T. In this case, as shown in FIG. 6, when the ambient temperature of the control circuit 11 is low, even if the resistance value of the filter resistor R is small and the cell balance current increases as a result, the control circuit 11 does not reach the breakdown temperature at which the IC is destroyed.

[0017] However, as shown in FIG. 7, when the ambient temperature of the control circuit 11 is high, if the resistance value of the filter resistor R becomes small and the cell balance current increases as a result, there is a high risk that the control circuit 11 will reach the breakdown temperature and the control circuit 11 will be destroyed. In order to prevent such a situation, it is necessary to set the filter resistor R to a larger value. In that case, however, a sufficient cell balance current cannot be passed, and the time required to execute the cell balance operation becomes long.

[0018] In this regard, in the cell balance circuit 1 of the first embodiment, the control circuit 11 controls the duty ratios of the switch elements SW1 to SW3 based on the temperature T around the control circuit 11 detected by the temperature detection element 30 so that the temperature T is near the set temperature Tn. Therefore, it is possible to flow a sufficiently large cell balance current that can avoid the temperature of the control circuit 11 reaching the breakdown temperature, so that the cell balance operation can be efficiently executed in a short time. Note that instead of controlling the duty ratios of the switch elements SW1 to SW3 according to the temperature T, the control circuit 11 can also control the on-periods of the switch elements and control the amount of the cell balance current.

[0019] [Second Embodiment] Next, with reference to FIG. 3, the cell balance circuit 1A of the second embodiment will be described. For the same components as those in the first embodiment (FIG. 1), the same reference numerals are given in FIG. 3, so redundant descriptions will be omitted below.

[0020] The cell balance circuit 1 of the first embodiment includes a temperature detection element 30 near the control circuit 11 separately from the battery monitoring IC 10. The cell balance circuit 1 of the second embodiment includes a temperature detection element 18 inside the battery monitoring IC 10 instead of the temperature detection element 30. This temperature detection element 18 is, for example, a diode for temperature measurement, is arranged near the control circuit 11, and is configured to flow a detection current according to the detected temperature. The control circuit 11 changes the switch control signals CBAL1 to 3 in the same manner as in the first embodiment according to the magnitude of this detection current.

[0021] According to this second embodiment, the temperature detection element 18 can be formed as one chip inside the battery monitoring IC 10. Therefore, a more compact cell balance circuit can be obtained compared to the first embodiment.

[0022] [Third Embodiment] Next, referring to FIG. 4, the cell balance circuit 1B of the third embodiment will be described. For the same components as those in the first / second embodiments (FIGS. 1 and 3), the same reference numerals are given in FIG. 4, and thus redundant descriptions will be omitted below.

[0023] The cell balance circuit 1 of this third embodiment includes a temperature detection element 18 inside the battery monitoring IC 10 in addition to the temperature detection element 30 installed outside the battery monitoring IC 10. This temperature detection element 18 is, for example, a temperature measurement diode as in the second embodiment, is arranged near the control circuit 11, and is configured to pass a detection current according to the detected temperature. The control circuit 11 changes the switch control signals CBAL1 to 3 in the same manner as in the first embodiment according to the detection signals of the temperature detection element 30 and the temperature detection element 18.

[0024] According to this third embodiment, the temperature detection elements 30 and 18 are arranged both outside and inside the battery monitoring IC 10, and the control of the switch elements SW1 to 3 can be executed according to the two temperature detection results. According to this embodiment, the temperatures inside and outside the battery monitoring IC 10 can be detected, and the switch elements SW1 to 3 can be controlled by reflecting the temperature difference information and the like, so that the cell balance operation can be executed more efficiently in a short time.

[0025] The present invention is not limited to the above-described embodiments, and various modifications can be made and implemented without departing from the gist of the present invention. And all of them are included in the technical idea of the present invention.

Explanation of Reference Numerals

[0026] 1, 1A, 1B, 1C... cell balance circuit CL (CL1 to 3)... cell 10... battery monitoring IC 11... control circuit 12 to 15... connection terminals SW1 to SW3... switch elements 16... temperature signal input terminal 18, 30... Temperature detection element 20... Limiting circuit R1~R4... Filter resistors C1~C3... Filter capacitances

Claims

1. In a cell balance circuit for adjusting the voltage of each of the cells in a cell group composed of a plurality of serially connected cells, a limiting circuit including a resistor having one end connected to the positive terminal or the negative terminal of each cell included in the cell group, and a capacitive element connected to the other end of the resistor; a switch circuit including a plurality of switches configured to connect the positive terminal and the negative terminal of each cell included in the cell group; a control circuit for controlling the switch circuit; a temperature detection unit for detecting the temperature around the control circuit is provided, and the control circuit controls the switch circuit according to the temperature detected by the temperature detection unit. A cell balance circuit characterized by the above.

2. The temperature detection unit is a thermistor provided around the control circuit, and the control circuit includes a temperature detection terminal to which a temperature detection signal related to the temperature detected by the thermistor is input. The cell balance circuit according to claim 1.

3. The control circuit is a temperature measurement diode provided in the vicinity of the control circuit, and the temperature measurement diode and the control circuit are provided inside the same chip. The cell balance circuit according to claim 1 or 2.

4. The control circuit controls the duty ratio of the switch circuit according to the temperature detected by the temperature detection unit. The cell balance circuit according to claim 1.

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