JP2007043871A - Constant-current circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To supply a constant-current to circuits provided to each cell of a battery pack with a smaller circuit scale than before. <P>SOLUTION: A reference voltage VBG of a band-gap reference 18 is converted into a constant current by a voltage-current conversion circuit 19. This constant current is made to return at a current mirror circuit 20, flows into a current mirror circuit 17, and is outputted to a reference voltage generating circuit 13, inside an overcharge detection circuit 12 of cells BC5-BC8 via transistors Q17-Q20. The constant current, outputted from the transistor Q21, is made to return at a current mirror circuit 21, flows into a current mirror circuit 16, and is outputted to the reference voltage generating circuit 13 that is inside the overcharge detection circuit 12 of cells BC1-BC4 via transistors Q12-Q15. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a constant current circuit that supplies a constant current to a circuit provided for each cell in an assembled battery configured by connecting a plurality of secondary battery cells in series.

  An assembled battery used as a battery of an electric vehicle (EV) or a hybrid electric vehicle (HV) requires a high voltage of about 100V to 400V, and thus has a configuration in which a large number of secondary batteries (cells) are connected in series. ing. For example, in the case of a 300V battery pack, 150 cells are connected in series for a lead battery (about 2V / cell), 250 cells are connected for a nickel metal hydride battery (1.2V / cell), and 80 cells are connected in series for a lithium ion battery (3.6V / cell). Has been.

Secondary batteries, particularly lithium-ion batteries, are vulnerable to overcharge and overdischarge, and if not used within the specified limit voltage range, there is a risk that the capacity will be significantly reduced or heat will be generated. Therefore, when using an assembled battery, constant voltage charge control is performed so that the voltage of the assembled battery is within a voltage range determined by a predetermined upper limit voltage and a lower limit voltage. In the assembled battery, the state of charge (SOC) and thus the voltage of each cell varies due to individual differences in capacity and self-discharge characteristics of each cell. (See Patent Documents 1 and 2).
Japanese Patent Laid-Open No. 2004-080909 (FIG. 2) Japanese Patent Laid-Open No. 2004-248348

  FIG. 2 shows a schematic configuration of the overcharge detection circuit of the assembled battery. The assembled battery 1 includes a positive terminal T1 of the cell BC1, a positive terminal of the cell BC2 (a negative terminal of the cell BC1) T2,..., A positive terminal of the cell BC8 (a negative terminal of the cell BC7) T8 and a cell BC8. Negative side terminal TG is provided. The overcharge detection circuit 2 of the cell BC1 is formed between a voltage line LN1 connected to the terminal T1 and a voltage line LN2 connected to the terminal T2, and includes a voltage detection circuit 3 including a series circuit of resistors R1 and R2, It comprises a reference voltage generation circuit 5 comprising a current circuit 4 and a trimming resistor R3, and a comparator 6 that compares the detected cell voltage with the reference voltage. The overcharge detection circuits 2 of the other cells BC2 to BC8 are similarly configured.

  However, in such a configuration, the constant current circuit 4 is required for each of the cells BC1 to BC8. The high-accuracy constant current circuit 4 often generates a constant current using a reference voltage generated by a bandgap reference. As a result, a band gap reference is required for each of the overcharge detection circuits 2 of the cells BC1 to BC8, and the chip area when configured as an IC increases, resulting in high costs.

  The present invention has been made in view of the above circumstances, and an object thereof is a constant current circuit capable of supplying a constant current to a circuit provided for each cell of an assembled battery with a circuit scale smaller than that of the prior art. Is to provide.

  According to the means described in claim 1, a constant current is supplied to the circuit provided for each cell constituting the assembled battery. That is, a reference current output circuit that outputs a constant current as a reference is provided in common, and an output current of the reference current output circuit is output to each of the circuits via a current mirror circuit. In this current mirror circuit, the voltage at which the emitter of the current input transistor into which the output current of the reference current output circuit flows and the emitter of the current output transistor provided corresponding to each of the above circuits is connected to one terminal of any cell. Commonly connected to the line.

  Thus, it is necessary to provide a reference current output circuit for each circuit (each cell) by forming the current mirror circuit and returning the output current of the reference current output circuit provided in common to each circuit described above. Thus, a constant current can be supplied to each circuit with a circuit scale that is significantly smaller than that of the prior art. Further, in the case of being configured as an IC, the chip area on which the constant current circuit is formed can be reduced, so that the cost can be greatly reduced.

  According to the means described in claim 2, the cell and the circuit provided for each cell are divided into n groups (n ≧ 2), and the current mirror circuit is provided for each group. Since the current transfer circuit passes the output current of the reference current output circuit to the current mirror circuit provided in each group, there is no need to provide a reference current output circuit for each group, and the circuit scale is further reduced compared to the conventional configuration. can do.

  According to the means described in claim 3, the cells constituting the secondary battery and the circuit provided for each cell are divided into n groups in order from the low potential side of the secondary battery, and each group is divided into the group. Since the current mirror circuit is provided using the low potential side terminal of the cell located on the lowest potential side as a common voltage line, the maximum voltage applied to the current output transistor is set to the total added voltage of the cells constituting each group. The following can be suppressed.

  According to the means described in claim 4, since the number of cells belonging to each group is the same, the cells constituting the assembled battery are evenly grouped, and the withstand voltage of the current output transistor can be lowered.

  According to the means described in claim 5, since the reference current output circuit converts the high-accuracy reference voltage generated by the bandgap reference into a current by the voltage-current conversion circuit, it can output a high-accuracy current. Since the current is turned back by the current mirror circuit, a highly accurate current can be supplied to each circuit provided for each cell.

  According to the means described in claim 6, since the circuit provided for each cell detects the overcharge or overdischarge of the cell using the reference voltage generated by the constant current output from the current mirror circuit. Thus, it is possible to perform charge / discharge monitoring with high accuracy while having a smaller circuit configuration than the conventional one.

Hereinafter, an embodiment of the present invention will be described with reference to FIG. In FIG. 1, the same components as those in FIG. 2 showing the prior art are denoted by the same reference numerals.
FIG. 1 shows the configuration of an overcharge detection circuit and a constant current circuit of an assembled battery. The assembled battery 1 is used as a battery for an electric vehicle (EV) or a hybrid electric vehicle (HV), and is composed of, for example, a lithium ion battery. The assembled battery 1 is composed of a plurality of cell groups connected in series, and each cell group is composed of eight cells BC1 to BC8 connected in series.

  The IC 11 that monitors and controls the state of charge (SOC) of the assembled battery 1 is used for each cell group, and performs charge / discharge control that detects the cell voltage and maintains the state of charge of each cell in an appropriate state. It is supposed to run. For this reason, the IC 11 is provided with an overcharge detection circuit 12 and an overdischarge detection circuit for each of the cells BC1 to BC8. The overdischarge detection circuit is not shown, but has the same configuration as the overcharge detection circuit 12.

  The overcharge detection circuit 12 includes a reference voltage generation circuit 13, a voltage detection circuit 3, and a comparator 6. For example, in the overcharge detection circuit 12 of the cell BC1, the reference voltage generation circuit 13 includes a current mirror circuit 14 including PNP transistors Q1 and Q2 whose emitters are connected to the voltage line LN1, a collector of the transistor Q2, and a voltage line LN2. And a trimming resistor R3 connected between the two. The voltage detection circuit 3 includes resistors R1 and R2 connected in series between a voltage line LN1 connected to the high potential side terminal of the cell BC1 and a voltage line LN2 connected to the low potential side terminal of the cell BC1.

  The comparator 6 (corresponding to the comparison circuit) is operated by the voltage of the cell BC1 between the voltage lines LN1 and LN2, and is output from the reference voltage output from the reference voltage generation circuit 13 and the voltage detection circuit 3. The overcharge detection signal OC1 is output by comparing the detection voltage (cell voltage). The overcharge detection circuits 12 of the other cells BC2 to BC8 are configured in the same manner, and output overcharge detection signals OC2 to OC8, respectively.

  In order for the reference voltage generation circuit 13 to generate a highly accurate reference voltage with small temperature fluctuations and voltage variations, it is necessary to flow a highly accurate current to the trimming resistor R3 via the current mirror circuit 14. Therefore, the IC 11 includes a constant current circuit 15 that supplies a highly accurate current to the overcharge detection circuits 12 of the cells BC1 to BC8.

  The constant current circuit 15 includes the overcharge detection circuits 12 of the cells BC1 to BC4 as one group, and the overcharge detection circuits 12 of the cells BC5 to BC8 as another group. For each of these groups, the current mirror circuit 16, 17 is provided. Furthermore, one bandgap reference 18 for outputting the reference voltage VBG, a voltage-current conversion circuit 19 for outputting a reference current corresponding to the reference voltage VBG, a current mirror circuit 20 for flowing this reference current to the current mirror circuit 17, A current mirror circuit 21 for supplying a current flowing through the current mirror circuit 17 to the current mirror circuit 18 and power supply circuits 22 and 23 are provided. Here, a reference current output circuit 26 is constituted by the band gap reference 18 and the voltage-current conversion circuit 19.

  The current mirror circuit 16 includes transistors Q11 to Q15 whose emitters are connected to the voltage line LN5 and whose bases are connected to each other. The voltage line LN5 to which the emitter is connected is connected to the low potential side terminal of the cell BC4 located on the lowest potential side among the cells BC1 to BC4 constituting one group. The collectors of the transistors Q12 to Q15 are connected to the collector of the transistor Q1 of the overcharge detection circuit 12 of the cells BC1 to BC4, respectively.

  Similarly, the current mirror circuit 17 includes transistors Q16 to Q21 whose emitters are connected to the voltage line GND and whose bases are connected to each other. The collectors of the transistors Q17 to Q20 are connected to the collector of the transistor Q1 of the overcharge detection circuit 12 of the cells BC5 to BC8, respectively. Here, the transistors Q11 and Q16 correspond to the current input transistors referred to in the present invention, and the transistors Q12 to Q15 and Q17 to Q20 correspond to the current output transistors referred to in the present invention.

  The power supply circuit 22 inputs an addition voltage of the cells BC1 to BC4 constituting one group, that is, a voltage between the voltage lines LN1 and LN5, and outputs a constant voltage, for example, 5V. The transistors Q22 and Q23 constituting the current mirror circuit 21 are connected between the output power supply line 24 of the power supply circuit 22 and the collectors of the transistors Q21 and Q11, respectively. Note that the current mirror circuit 21 and the transistor Q21 correspond to a current transfer circuit in the present invention.

  The band gap reference 18 inputs the addition voltage of the cells BC5 to BC8 constituting one group, that is, the voltage between the voltage lines LN5 and GND, and outputs the reference voltage VBG. The power supply circuit 23 also receives a voltage between the voltage lines LN5 and GND, and outputs a constant voltage, for example, 5 V between the power supply line 25 and the voltage line GND.

  The voltage-current conversion circuit 19 is connected between the transistor Q24 whose collector is grounded with respect to the voltage line GND, the transistor Q25 whose base is connected to the emitter of the transistor Q24, and the emitter of the transistor Q25 and the voltage line GND. And a current supply circuit (not shown) connected to the resistor R11 and the emitter of the transistor Q24. Transistors Q26 and Q27 constituting the current mirror circuit 20 are connected between the power line 25 and the collectors of the transistors Q25 and Q16, respectively.

Next, the operation of this embodiment will be described.
The lithium ion battery used for the assembled battery 1 has an excellent feature that the volume energy density and mass energy density are large and the cycle life is long. On the other hand, since it is vulnerable to overcharge and overdischarge, high-precision control is required to prevent overcharge / discharge. Therefore, the overcharge detection circuit 12 and the overdischarge detection circuit (not shown) provided for each of the cells BC1 to BC8 need to detect with high accuracy that each cell has been overcharged or overdischarged. .

  The reference voltage generation circuit 13 in the overcharge detection circuit 12 of each of the cells BC1 to BC8 generates a reference voltage by passing a constant current through the trimming resistor R3 via the current mirror circuit 14. The highly accurate reference voltage VBG generated by the bandgap reference 18 is converted into a constant current according to the reference voltage VBG by the voltage-current conversion circuit 19. The constant current is folded back by the current mirror circuit 20 and flows to the current mirror circuit 17, and the reference voltage generation circuit 13 in the overcharge detection circuit 12 of the cells BC 5 to BC 8 is passed through the transistors Q 17 to Q 20 of the current mirror circuit 17. Is output.

  The constant current output from the transistor Q21 of the current mirror circuit 17 is folded back by the current mirror circuit 21 and flows to the current mirror circuit 16, and the cells BC1 to BC4 of the cells BC1 to BC4 are passed through the transistors Q12 to Q15 of the current mirror circuit 16. This is output to the reference voltage generation circuit 13 in the overcharge detection circuit 12. In this case, the relationship between the reference voltage VBG and the current flowing through the trimming resistor R3 of the reference voltage generation circuit 13 is that the resistance value of the resistor R11 of the voltage-current conversion circuit 19 and the current mirror circuits 14, 16, 17, 20, and 21 It depends on the mirror ratio. It should be noted that the current shift caused by the variation in the resistance value and the mirror ratio, that is, the shift of the reference voltage output from the reference voltage generation circuit 13 can be reduced by laser trimming with respect to the trimming resistor R3.

  According to this embodiment, since it is not necessary to provide the band gap reference 18 for each of the overcharge detection circuits 12 of the cells BC1 to BC8, a conventional configuration in which a band gap reference is provided for each of the cells BC1 to BC8 (see FIG. 2). ), The circuit scale of the IC 11, that is, the chip area can be reduced while maintaining high current accuracy, and the manufacturing cost of the IC 11 can be greatly reduced. Further, since the current flowing through the current mirror circuit 17 is passed through the current mirror circuit 21 via the current mirror circuit 21, the IC 11 that controls eight cells may be provided with one band gap reference 18. The area reduction effect and the cost reduction effect are further increased.

  One cell group is composed of eight cells BC1 to BC8 connected in series. In this embodiment, these cells are arranged from the high potential side (from another perspective, from the low potential side) BC1 to BC4. , BC5 to BC8 (n = 2). For each group, current mirror circuits 16 and 17 are provided with the voltage lines LN5 and GND connected to the low potential side terminals T5 and TG of the cells BC4 and BC8 positioned on the lowest potential side as common voltage lines.

  Thereby, for example, the collector-emitter voltage VCE (Q12) of the transistor Q12 having the highest applied voltage among the transistors Q12 to Q15 constituting the current mirror circuit 16 is suppressed to (VBC1 + VBC2 + VBC3 + VBC4) ≈4 · VBC or less. Similarly, the collector-emitter voltages VCE (Q13), VCE (Q14), and VCE (Q15) of the transistors Q13, Q14, and Q15 are also suppressed to 3 · VBC, 2 · VBC, and VBC, respectively.

  Incidentally, when one current mirror circuit is provided for all the cells BC1 to BC8 using the voltage line GND as a common voltage line, the collector-emitter voltage VCE of the transistors corresponding to the cells BC1 to BC4 in the current mirror circuit. Are 8 · VBC to 5 · VBC, respectively. That is, by dividing the eight cells BC1 to BC8 constituting one cell group equally into two groups so that the number of cells is equal, the breakdown voltage of the transistors Q12 to Q15 constituting the current mirror circuit 16 is reduced to 1 / It can be lowered to 2 or less.

The present invention is not limited to the embodiment described above and shown in the drawings. For example, the present invention can be modified or expanded as follows.
In the above embodiment, eight cells BC1 to BC8 belonging to one cell group are divided into two groups (n = 2), and current mirror circuits 16 and 17 are provided for each group. A current mirror circuit may be provided for each group separately in n ≧ 3). In this case, it is preferable to make the number of cells belonging to each group equal.

  In the above embodiment, the band gap reference 18 and the voltage-current conversion circuit 19 are provided on the group side including the cells BC5 to BC8, and the current flowing through the current mirror circuit 17 is supplied to the current mirror circuit 16 via the current mirror circuit 21. However, instead of this, a band gap reference 18 and a voltage-current conversion circuit 19 are provided on the group side including the cells BC1 to BC4, and the current flowing through the current mirror circuit 16 is supplied to the current mirror circuit via the current mirror circuit. It is good also as a structure supplied to 17. Further, although the circuit scale is slightly larger, a configuration may be adopted in which the reference current output circuit 26 (the band gap reference 18 and the voltage-current conversion circuit 19) is provided for each group.

  Although the reference current output circuit 26 is composed of the band gap reference 18 and the voltage-current conversion circuit 19, for example, a constant current circuit, a Wilson constant current circuit, a self-bias that outputs a current determined from the forward voltage VF and the resistance value of the transistor. A constant current circuit of a system, a constant current circuit including a Zener diode and a voltage-current conversion circuit, or the like may be used.

Not only bipolar transistors but also semiconductor elements such as MOSFETs may be used. Further, a current mirror circuit using a PNP type (NPN type) transistor may be used instead of the current mirror circuit using an NPN type (PNP type) transistor.
The assembled battery 1 is not limited to a lithium ion battery, and may be a secondary battery such as a lead battery or a nickel metal hydride battery.

1 is a configuration diagram of an overcharge detection circuit and a constant current circuit of a battery pack showing an embodiment of the present invention Configuration diagram of an overcharge detection circuit for an assembled battery showing a conventional configuration

Explanation of symbols

1 is an assembled battery, 6 is a comparator (comparison circuit), 12 is an overcharge detection circuit, 13 is a reference voltage generation circuit, 15 is a constant current circuit, 16 and 17 are current mirror circuits, 18 is a band gap reference, and 19 is a voltage. -Current conversion circuit, 21 is a current mirror circuit (current transmission circuit), 26 is a reference current output circuit, BC1 to BC8 are cells, Q11 and Q16 are transistors (current input transistors), Q12 to Q15 and Q17 to Q20 are transistors ( Current output transistors), LN1 to LN8, and GND are voltage lines.

Claims (6)

A constant current circuit for supplying a constant current to a circuit provided for each cell of an assembled battery configured by connecting a plurality of secondary battery cells in series,
A reference current output circuit that outputs a constant current as a reference;
A current output transistor provided corresponding to the circuit for each cell and a current input transistor provided in common so that an output current of the reference current output circuit flows, and each of the emitters of the transistors is any of the above A constant current circuit comprising: a current mirror circuit connected in common to a voltage line connected to one terminal of the cell and having the bases of the transistors connected in common.   The cells constituting the secondary battery and the circuit provided for each cell are divided into n groups (n ≧ 2), and one terminal of any cell belonging to the group is used as a common voltage line for each group. 2. The constant current circuit according to claim 1, further comprising a current transmission circuit for providing an output current of the reference current output circuit to a current mirror circuit provided for each group. .   The cells constituting the secondary battery and the circuit provided for each cell are divided into n groups in order from the low potential side of the secondary battery, and for each group, the cell located on the lowest potential side in the group 3. The constant current circuit according to claim 2, wherein the current mirror circuit is provided with a low potential side terminal as a common voltage line.   4. The constant current circuit according to claim 2, wherein the number of cells belonging to each group is equal.   5. The constant current circuit according to claim 1, wherein the reference current output circuit includes a band gap reference and a voltage-current conversion circuit. The circuit provided for each cell includes a reference voltage generation circuit that generates a reference voltage corresponding to a constant current given from the current mirror circuit, and a comparison circuit that compares the reference voltage with the voltage of the cell. 6. The constant current circuit according to claim 1, further comprising an overcharge / discharge detection circuit.

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