JP2000277174A - Cell voltage detection circuit and battery voltage detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure necessary voltage detection accuracy by providing a current conversion circuit that has an amplifier and a resistor forming a feedback loop and converts a cell voltage into a current, and an output resistor of which one end is connected to the negative terminal of a battery pack, and the other end is connected to the output of the current conversion circuit, and with which the voltage is detected as the cell voltage. SOLUTION: A feedback loop is formed so that a measurement cell voltage Vc equals a voltage between both ends of a current detection resistor R1. A source current Is flowing through the current detection resistor R1 becomes a drain current Id as it is because the gate current Ig of a P-channel FET is nearly zero. Therefore, the drain current Id flows through an output resistor R2 connected to the negative terminal of a battery pack, a voltage proportional to the cell voltage is generated across it, and the voltage is output on the basis of the negative terminal of the battery pack. In this case, provided that the resistance value of resistor R1 equals that of the resistor R2, the cell voltage is output as the voltage on the basis of the negative terminal of the battery pack.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cell voltage detecting circuit and a battery voltage detecting device, and more particularly to a cell voltage detecting circuit for detecting a cell voltage of an assembled battery having cells connected in series, and the cell voltage detecting circuit. The present invention relates to a battery voltage detection device provided with a circuit.

[0002]

2. Description of the Related Art Conventionally, as a method of monitoring the state of a battery pack, a method of measuring the voltage of a cell (cell) has been used. In particular, in a lithium-ion battery that has recently been used, it is required to accurately detect a cell voltage in order to protect against overcharge and overdischarge. As a method of detecting a cell voltage of a lithium ion battery, a method of converting a cell voltage of each cell using a differential amplifier with reference to a minus terminal of the assembled battery is generally used.

For example, a low-power dedicated IC incorporating a high-precision differential amplifier and a comparator is used in a cell voltage detection circuit of a three-series or four-series cell battery used as a power supply for a notebook personal computer or the like. Used. Also,
For other uses of the assembled battery, such as a power supply for an electric vehicle, an assembled battery having about 8 to 10 cells in series has been proposed and is being put to practical use. In this case, a cell voltage detection circuit using a differential amplifier is also used as in the above-described battery pack for a notebook personal computer.

FIG. 6 shows an example of a conventional cell voltage detection circuit in the case where a battery pack is composed of lithium-ion batteries in series of eight cells. In this cell voltage detection circuit, each terminal of the lithium ion batteries from cell 1 to cell 8 has a voltage dividing resistor (FIG. 6).
And the voltage is connected to the input of the differential amplifier, and the voltage division ratio is amplified by the differential amplifier to be the output voltage of each measurement cell.

Conventionally, the voltage division by the cell voltage detection circuit is performed in such a manner that the voltage rises up to about 35 V in a lithium ion battery when the cells 8 are connected in series. This is because the voltage is exceeded.

FIG. 7 shows a conventional example of a differential amplifier (differential amplifier 1 to differential amplifier 8 in FIG. 6) used in the cell voltage detection circuit shown in FIG. As shown in FIG. 7, the conventional differential amplifier includes two operational amplifiers and a plurality of high-precision resistors.

[0007]

However, in the conventional cell voltage detection circuit shown in FIGS. 6 and 7, a plurality of high-precision resistors are required to secure the voltage detection accuracy. However, there is a problem that the cost of the device becomes high and the required accuracy of voltage detection may not be satisfied.

That is, as shown in FIG. 7, if the offset voltage of the operational amplifier used for the differential amplifier is Voff, the voltage of the plus terminal of the measuring cell is Vp, and the voltage of the minus terminal of the measuring cell is Vm, the output is The voltage Vout can be expressed by the following equation 1.

[0009]

(Equation 1)

The following Table 1 shows the resistance of the cell voltage detection circuit.
It is assumed that a resistor having a resistance value shown in FIG.

[0011]

[Table 1]

The error of the resistance value shown in Table 1 is set to 0.1%, and the offset voltage Voff of the operational amplifier is set to + -1.8 m.
Assuming V, the worst value of each resistance and offset voltage Voff is as shown in Table 2 below.

[0013]

[Table 2]

When the cell voltage is 4.35 V, the worst value of the error of the output voltage Vout when the worst value shown in Table 2 is obtained is calculated as shown in Table 3 below.

[0015]

[Table 3]

As shown in Table 3, even if a very high-precision and cost-effective 0.1% resistor is used, the error is large on the uppermost cell (cell 8) side and reaches a maximum of 130 mV or more. In a lithium ion battery, the voltage detection accuracy during overcharge must be detected at less than ± 50 mV in practical use and safety standards. Therefore, the required accuracy cannot be satisfied when the worst value is considered. .

The reason why the required accuracy cannot be satisfied even when a high-precision resistor is used is that the number of resistors affecting the error is as large as eight, and the error becomes large considering the worst value described above. It is in. To reduce the number of resistors,
The accuracy can be improved by directly inputting the signal to the differential amplifier without dividing the input voltage. However, as described above, the signal is directly input to the operational amplifier due to the withstand voltage of the operational amplifier used for the differential amplifier. It is not possible.

In order to satisfy the required accuracy, it is conceivable to adjust the resistance value one by one using a variable resistor. However, man-hours and costs required for the adjustment and environmental changes such as vibration and temperature change are considered. In consideration of the stability of the battery pack, it is not suitable for mass production as a cell voltage detection circuit of an assembled battery for an electric vehicle.

Another solution to satisfy the required accuracy is to use an insulated amplifier to connect a ground (GND).
It is also conceivable to use a special multiplexer or operational amplifier with high withstand voltage, but the use of an insulated amplifier or multiplexer with high withstand voltage is expensive. There is a problem from the viewpoint of power consumption and cost because the power consumption is increased due to the necessity.

In view of the above, it is an object of the present invention to provide a low-cost cell voltage detection circuit which can secure required voltage detection accuracy without using a high-precision resistor, and consumes less power.

[0021]

According to a first aspect of the present invention, there is provided a cell voltage detecting circuit for detecting a cell voltage of an assembled battery having cells connected in series. Having a formed amplifier and a resistor, a current conversion circuit for converting the cell voltage to a current,
One end is connected to the minus terminal of the battery pack, the other end is connected to the output of the conversion circuit, and an output resistor whose both ends voltage is detected as the cell voltage is provided.

According to a second aspect of the present invention, in the current conversion circuit according to the first aspect, an operational amplifier having a positive-phase input terminal connected to a negative terminal of the measurement cell, and a gate connected to an output terminal of the operational amplifier. A P-channel FET (P-channel field-effect transistor) having a drain connected to the other end of the output resistor, one end connected to a plus terminal of the measurement cell, and the other end connected to an opposite-phase input terminal of the operational amplifier; And a current detection resistor connected to the source of the P-channel FET.

According to a third aspect of the present invention, a PNP transistor or a Darlington-connected PNP transistor is used in place of the P-channel FET according to the second aspect.

According to a fourth aspect of the present invention, in the first aspect of the present invention, a cell voltage of a cell connected to the negative terminal of the battery pack is output by a non-inverting amplifier having an amplification factor of one. The voltage of the upper cell is output by a differential amplifier having an amplification factor of 1.

The invention according to claim 5 is the invention according to claims 1 to 4.
In the invention described in any one of the above, the operational amplifier is configured such that a positive power supply terminal and a negative power supply terminal of the operational amplifier receive a cell voltage of each cell as input so that operation power is supplied within the withstand voltage range. And connected to the output of a non-inverting amplifier having an amplification factor of 1.

According to a sixth aspect of the present invention, there is provided a battery voltage detecting device including the cell voltage detecting circuit according to any one of the first to fifth aspects.

According to the first aspect of the present invention, the cell voltage is converted to a current by the current conversion circuit having the amplifier and the resistance forming the feedback loop and output to the output resistance connected to the minus terminal of the battery pack. There are only two resistors that affect accuracy, a resistor for converting the cell voltage of the current conversion circuit into a current and an output resistor connected to the minus terminal of the battery pack. Therefore, the accuracy of the cell voltage detection circuit can be secured without using a highly accurate resistor.

According to the second aspect of the present invention, as shown in FIG.
A feedback loop is formed, and the cell voltage Vc becomes equal to the voltage across the current detection resistor. The current (source current Is) flowing through this current detection resistor is a P-channel FET
Since the gate current Ig is almost zero, the drain current Id is used as it is. Accordingly, the drain current Id flows through the output resistance connected to the negative terminal of the battery pack, and a voltage proportional to the cell voltage is generated, and the voltage is output based on the negative terminal of the battery pack. Here, assuming that the resistance value of the current detection resistor is equal to the resistance value of the output resistance, the cell voltage is output at a voltage based on the minus terminal of the assembled battery as shown in the following equation 2.

[0029]

(Equation 2)

According to the third aspect of the present invention, the P
Instead of a channel FET, a PNP transistor having a large DC current amplification factor h _fe or a Darlington-connected PN
By using a P-transistor, the current flowing through the base is extremely small, and it can be considered that the emitter current is equal to the collector current. Therefore, the cell voltage detection circuit can be constituted by an inexpensive transistor without using a relatively expensive P-channel FET.

According to the fourth aspect of the present invention, only the cell voltage detecting circuit according to any one of the first to third aspects has a cell connected to the negative terminal of the assembled battery (the lowest cell of the assembled battery) and one higher level thereof. Since the cell voltage of the cell on the side cannot be output properly, a normal non-inverting amplifier is used for the lowest cell and a normal differential amplifier is used for the cell on the next higher level.
That is, for example, in the cell voltage detection circuit shown in FIG. 1, the plus terminal of the measurement cell is connected to the positive power supply terminal (plus power supply) of the operational amplifier and the current detection resistor, and the current detection resistor and the output resistance are connected to each other. Since the same voltage is generated as that of the measuring cell, the voltage of the plus terminal of the measuring cell must be at least twice the cell voltage to be detected. However,
In the lowest cell, since the voltage of the plus terminal and the detected cell voltage are the same, the cell voltage of the measurement cell cannot be output normally. In addition, the voltage of the plus terminal is (the voltage of the lowest cell + the voltage of the measurement cell) even in the cell one level higher than the lowest, so that the normal operation is performed only when the voltage of the measurement cell is lower than the voltage of the lowest cell. Cannot output. Therefore, by using a non-inverting amplifier for the voltage of the lowest cell and using a differential amplifier for the next higher cell, the cell voltage of the lower cell and the cell one higher than the lowest cell is calculated. It is possible to detect properly.

According to a fifth aspect of the present invention, a non-inverting amplifier having an amplification factor of 1 and having a positive power supply terminal and a negative power supply terminal input with a cell voltage of each cell so that operating power is supplied within a withstand voltage range of the operational amplifier. , The voltage from the non-inverting amplifier can be appropriately selected and the operational amplifier can be operated within the withstand voltage range even if the withstand voltage of the operational amplifier used is low.

According to the sixth aspect of the present invention, since the cell voltage detecting circuit according to any one of the first to fifth aspects is provided, a battery voltage detecting device satisfying the required accuracy can be realized. it can.

[0034]

BEST MODE FOR CARRYING OUT THE INVENTION A cell voltage detecting circuit (hereinafter, referred to as a voltage detecting circuit) according to the present invention is used as a voltage detecting circuit for detecting a cell voltage of an assembled battery for an electric vehicle in which lithium-ion batteries 8 are connected in series. An embodiment to which the present invention is applied will be described. In this embodiment, the voltage detection circuit of the present invention except for the invention described in claim 3 is applied.

As shown in FIG. 2, in the voltage detection circuit according to the present embodiment, the lowest cell 1
Is output from the non-inverting amplifier IC1 having an amplification factor of 1, and the cell voltage of the cell 2 is output from a differential amplifier IC2B having an amplification factor of 1.
Is output. On the other hand, the voltage detection circuits described in claims 1 and 2 are applied to cell voltage detection of cells 3 to 8. The cell voltages of the cells 1 to 8 are output with reference to the negative terminal (GND) of the battery pack (cell output 1 to cell output 8 in FIG. 2).

The operational amplifier used in this voltage circuit has a total of 1
In this embodiment, eight ICs each including two operational amplifiers in one package are used. Therefore, the two operational amplifiers included in the package have a common positive power supply (positive power supply terminal + V _CC ) and a common negative power supply (negative power supply terminal -V _EE ).

The circuit on the left half side of FIG. 2 is a non-inverting amplifier having an amplification factor of 1. If this part is described in detail with respect to the voltage detection circuit for the cell 3, the minus terminal of the cell 3 is connected to one end of the resistor RI. The other end of the resistor RI is connected to the positive-phase input terminal of the operational amplifier IC3A, branched therefrom and connected to one end of the capacitor CI, and the other end of the capacitor CI is connected to the plus terminal of the cell 3. . One end of a resistor RF is connected to the opposite-phase input terminal of the operational amplifier IC3A, and the other end of the resistor RF is connected to the output terminal of the operational amplifier IC3A. A capacitor CC is inserted between the positive power supply terminal and the negative power supply terminal of the operational amplifier IC3A. The positive power supply terminal of the operational amplifier IC3A is connected to the output terminal of the operational amplifier IC4A, and the negative power supply terminal of the operational amplifier IC3A is connected to the output terminal of the operational amplifier IC1 via a resistor RC.

Accordingly, the minus terminals of the cells 3 to 8 are connected to the plus input terminal of the operational amplifier, and the output of each operational amplifier has the same potential as the minus terminal of each cell. In the cells 1 and 2, the plus terminal of each cell is connected to the plus input terminal of the operational amplifier, and the output of each operational amplifier has the same potential as the plus terminal of each cell. In this part, the resistor RI and the capacitor CI are RC filters for removing noise.

The voltage detection circuit for the cell 1 will be described in detail. The minus terminal of the cell 1 is connected to GND, branched therefrom and connected to one end of a capacitor CI, and the other end of the capacitor CI is connected to a non-amplifier having a gain of 1. An inverting input terminal and one end of an operational amplifier IC1 as an inverting amplifier are connected to the other end of the resistor RI connected to the plus terminal of the cell 1.
Further, a capacitor CC is inserted between the positive power supply terminal and the negative power supply terminal of the operational amplifier IC1. Therefore, cell 1
Is output from the output of the operational amplifier IC1 to the cell 1 as it is.
(The output of cell 1 in FIG. 2). As shown in Table 4 below, the operational amplifier IC1
Is connected to the output terminal of the operational amplifier IC3A via a resistor RC, and the negative power supply terminal of the operational amplifier IC1 is connected to GND.

Next, the voltage detection circuit for the cell 2 will be described in detail.
One end of I is connected, the other end of the capacitor CI is connected to the positive-phase input terminal of the operational amplifier IC2A, and the other end of the resistor RI whose one end is connected to the plus terminal of the cell 2. Further, a capacitor CC is inserted between the positive power supply terminal and the negative power supply terminal of the operational amplifier IC2A, and a resistor RF is inserted between the negative phase input terminal and the output terminal. The positive power supply terminal of the operational amplifier IC2A is connected to the output terminal of the operational amplifier IC4A via the resistor RC, and the negative power supply terminal of the operational amplifier IC2A is connected to the output terminal of the operational amplifier IC1.

One end of a resistor R3 is connected to the output terminal of the operational amplifier IC2A, and the other end of the resistor R3 has an amplification factor of 1.
Is connected to the positive-phase input terminal of an operational amplifier IC2B as a differential amplifier and the other end of a resistor R4 having one end connected to GND. One end of the opposite-phase input terminal of the operational amplifier IC2B is connected to the other end of the resistor R2 connected to the output terminal of the operational amplifier IC2B and one end of the resistor R1.
The other end of the resistor R1 is connected to the other end of the resistor RF, one end of which is connected to the opposite-phase input terminal of the operational amplifier IC1.

Accordingly, the voltage of the cell 2 is controlled by the operational amplifier IC
2A is connected to a differential amplifier formed by an operational amplifier IC2B and resistors R1 to R4, and the output from the operational amplifier IC1 is used as an input to a negative-phase input terminal. , The cell voltage of cell 2 is output to the cell 2 output terminal (cell 2 output of FIG. 2).

Next, the right half of the voltage detection circuit for the cell 3 will be described in detail. The operational amplifier IC3B as an amplifier forming a feedback loop and the output terminal and the gate of the P-channel FET Q1 are connected to each other. One end is a P-channel FET at the phase input terminal
The other end of the feedback resistor RF connected to the source of Q1 is connected.

One end of the positive-phase input terminal of the operational amplifier IC3B is connected to a resistor R having one end connected to the output terminal of the operational amplifier IC3A.
I is connected to the other end. The other end of the output resistor RO, one end of which is connected to GND, is connected to the drain of the P-channel FET Q1. The output resistor RO branches off therefrom and extends to the output terminal of the cell 3 (the output of the cell 3 in FIG. 2). Further, P
One end of a current detection resistor RD is connected to the source of the channel FET Q1, and the other end of the current detection resistor RD is connected to the output terminal of an operational amplifier (non-inverting amplifier) IC4A.

The voltage detection circuit including the current conversion circuit of the cell 3 is basically the same as the voltage detection circuit shown in FIG. What is different is that the negative-phase input terminal of the operational amplifier IC3B is connected to the output from the operational amplifier (non-inverting amplifier) IC4A of the upper cell, and the positive-phase input terminal of the operational amplifier IC3B is different in operation. Only the point connected to the output of the amplifier (non-inverting amplifier) IC3A. In each case, the same potential as that in FIG. 1 is input to the operational amplifier IC3B, and the voltage of the cell 3 is output based on the minus terminal of the battery pack. There is no difference in what is done.

The output circuits of the cells 4 to 8 have the same configuration as the output circuit of the cell 3, and each cell voltage is output based on the minus terminal (GND) of the battery pack. However, since only the cell 8 has the highest rank, the operational amplifiers IC8A and IC8B
Is connected to the positive terminal of the battery pack.

In order to reduce the voltage applied to the power supply terminals of the operational amplifiers, the positive power supply terminal and the negative power supply terminal of each operational amplifier are connected as shown in Table 4 below. Have been.

[0048]

[Table 4]

The operational amplifier used in the present voltage detection circuit operates from a single power supply to a power supply voltage of +3 V, and the voltage of the positive-phase input terminal and the negative-phase input terminal ranges from GND to a positive power supply voltage of −1.5 V. A general-purpose product that is operable and has a standard offset voltage Voff of 2 mV, a maximum of 7 mV, and a current consumption of 1.6 mA was used. Further, the current detection resistor RD and the output resistor RO
Means that the resistance value is 47 kΩ and the accuracy is 0.25%. Further, the resistance RI is set as a constant of the RC filter.
Was set to 47 kΩ and the capacitor CI was set to 0.47 μF. The resistor RC and the capacitor CC are a decoupling resistor and a capacitor for stably operating the operational amplifier.

(Characteristic Test) Next, an error characteristic test, a current consumption characteristic test, and a frequency response characteristic test performed to confirm the characteristics of the voltage detection circuit of the present embodiment will be described in order.

In the error characteristic test, the environmental temperature of the present voltage detection circuit was set to -40 ° C., 25 ° C., and + 80 ° C., and the voltage of the assembled battery was changed from 15 V (1.875 V / cell) to 37 V.
(4.625 V / cell), the error characteristics between the cell voltage and the output voltage were measured. Figure 3 shows the measurement results.
Shown in As shown in FIG. 3, even when the environmental temperature and the voltage of the battery pack are changed, the maximum error between the cell voltage and the output voltage is 6 mV, which is sufficiently accurate as a voltage detection circuit of the battery pack for electric vehicles. It was recognized that.

In the current consumption characteristic test, the ambient temperature of the present voltage detection circuit was set to -40 ° C., 25 ° C., and + 80 ° C., and the voltage of the assembled battery was changed from 15 V (1.875 V / cell) to 37 V.
(4.625 V / cell), the current consumption of the present voltage detection circuit was measured. FIG. 4 shows the results of the measurement, in which the horizontal axis represents the voltage (V) of the assembled battery and the vertical axis represents the current consumption (mA).
This is shown. As shown in FIG. 4, the current consumption of the present voltage detection circuit was a sufficiently small value of 5 mA or less at the maximum.

In the frequency response characteristic test, an AC current having a frequency of 0.1 Hz to 10000 Hz (10 KHz) was applied to each cell, and an AC voltage component appearing at the output was measured. FIG. 6 shows the frequency response characteristics. As shown in FIG. 6, an attenuation rate of −40 db or more was obtained at a frequency of 1 kHz, and it was confirmed that the present voltage detection circuit has sufficient characteristics with respect to noise.

As described above, in the voltage detection circuit according to the present embodiment, the current detection resistance RD and the output resistance RO have an accuracy of 0.2.
Although 5% was used, the maximum error between the cell voltage and the output voltage was 6 mV even when the environmental temperature and the voltage of the assembled battery were changed, as shown in the test results of the error characteristic test,
Sufficient accuracy can be secured as a voltage detection circuit for an assembled battery for an electric vehicle. Moreover, since there is no need to use a variable resistor as in the prior art, and the stability is high and the error is small even when the environmental temperature changes, it is suitable for mass production as a voltage detection circuit for an assembled battery for an electric vehicle.

Further, in the present voltage detection circuit, since a resistor with an accuracy of 0.25% is used instead of a resistor with a high accuracy of 0.1%,
The cost of the cell voltage detection circuit can be reduced. In addition, the circuit configuration does not require a special and expensive multiplexer or operational amplifier having a high withstand voltage as in the prior art.

Further, in the present voltage detecting circuit, as shown in the test result of the current consumption characteristic test, the maximum current consumption is 5 m.
A cell voltage detection circuit of A or less can be realized. Therefore, it is possible to provide a voltage detection circuit that consumes very little power compared to the case where an insulated lamp is used as in the related art.

Further, in this voltage circuit, the non-inverting amplifier IC1 is used to detect the cell voltage of the cell 1, and the differential amplifier IC2B is used to detect the cell voltage of the cell 2. The cell voltage of the cell 2 on the one upper side can be properly detected. Note that in the present voltage detection circuit, even if the cell voltage of the cell 3 is theoretically detected, normal output cannot be performed unless the sum of the voltage of the lowest cell 1 and the voltage of the cell 2 is larger than the voltage of the measurement cell. It is assumed that the cell voltage of the cell 3 can be detected as long as the cell balance is not extremely bad.

Also, in the present voltage detection circuit, as shown in Table 4, only the sum voltage of the two cells is applied between the plus power supply and the minus power supply terminals of each operational amplifier. It is possible to use an amplifier.

Further, as shown in the test results of the frequency response characteristic test, the present voltage detection circuit has excellent characteristics with respect to noise.

In this embodiment, the P channel FE
T has been described, but the P channel F
Instead of ET, a PNP transistor having a large DC current amplification factor h _fe or a PNP transistor connected in Darlington can be used. In this case, those skilled in the art should be able to connect the base, collector and emitter terminals of a PNP transistor or a Darlington-connected PNP transistor instead of the gate, source and drain terminals of the P-channel FET. Is self-evident. In this way, the relatively expensive P-channel F
Since the voltage detection circuit can be manufactured at a lower cost than when ET is used, the cost of the voltage detection circuit can be further reduced.

[0061]

As described above, according to the first aspect of the present invention, the resistance of the current conversion circuit for converting the cell voltage into the current and the output resistance connected to the minus terminal of the battery pack are described. Since there are only two resistors that affect the accuracy, it is possible to obtain an effect that the accuracy of the cell voltage detection circuit can be secured without using a high-precision resistor.

According to the second aspect of the present invention, since the gate current Ig of the P-channel FET is substantially zero, it becomes the drain current Id as it is, and the resistance value of the current detection resistor is equal to the resistance value of the output resistance. Since the voltage is output at a voltage with reference to the negative terminal of the battery pack, an advantage is obtained in that the accuracy of the cell voltage detection circuit can be secured without using a high-precision resistor, as in claim 1. Can be.

According to the third aspect of the present invention, the cell voltage detection circuit can be constituted by inexpensive transistors without using relatively expensive P-channel FETs.
The effect that a low-cost cell voltage detection circuit can be realized can be obtained.

According to the fourth aspect of the present invention, since the non-inverting amplifier is used for the lowermost cell and the differential amplifier is used for the next higher cell, the lowermost cell of the assembled battery and its lower cell are used. It is possible to obtain an effect that the cell voltage of the cell on the one upper side can be properly detected.

According to the fifth aspect of the present invention, the positive power supply terminal and the negative power supply terminal have an amplification factor of 1 with the cell voltage of each cell as an input so that the operating power is supplied within the withstand voltage range of the operational amplifier. Is connected to the output of the non-inverting amplifier, so that even if the withstand voltage of the operational amplifier used is low, the voltage from the non-inverting amplifier is appropriately selected to operate the operational amplifier within the withstand voltage range. Can be obtained.

According to the sixth aspect of the present invention,
Since the cell voltage detecting circuit according to any one of claims 1 to 5 is provided, an effect that a battery voltage detecting device satisfying required accuracy can be realized can be obtained.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a current conversion circuit for explaining the operation of the invention described in claim 2;

FIG. 2 is a circuit diagram showing a cell voltage detection circuit according to an embodiment to which the present invention is applied.

FIG. 3 is a characteristic diagram showing an error characteristic of the cell voltage detection circuit according to the embodiment to which the present invention is applied.

FIG. 4 is a characteristic diagram showing current consumption characteristics of the cell voltage detection circuit according to the embodiment to which the present invention is applied.

FIG. 5 is a characteristic diagram showing a frequency response characteristic of the cell voltage detection circuit according to the embodiment to which the present invention is applied.

FIG. 6 is a configuration diagram showing a circuit configuration of a conventional cell voltage detection circuit.

FIG. 7 is a circuit diagram showing details of a differential amplifier of the cell voltage detection circuit shown in FIG. 6;

[Explanation of symbols]

RI, RF, RC, RD, RO, R1, R2, R3, R
4, R5, R6, R7, R8 Resistance CI, CC capacitor Q1, Q2, Q3, Q4, Q5, Q6 P channel F
ET IC1, IC2A, IC2B, IC3A, IC3B, I
C4A, IC4B, IC5A, IC5B, IC6A, I
C6B, IC7A, IC7B, IC8A, IC8B Operational amplifier

Claims (6)

[Claims] 1. A cell voltage detecting circuit for detecting a cell voltage of an assembled battery having cells connected in series, comprising: an amplifier having a feedback loop formed therein; and a resistor, wherein the current for converting the cell voltage into a current is provided. A converter circuit, one end of which is connected to the negative terminal of the battery pack, the other end of which is connected to the output of the converter circuit, and an output resistor whose both-ends voltage is detected as the cell voltage. Cell voltage detection circuit. 2. The current conversion circuit includes: an operational amplifier having a positive-phase input terminal connected to a negative terminal of a measurement cell; a gate connected to an output terminal of the operational amplifier; and a drain connected to the other end of the output resistor. Connected P channel FE
T, one end of which is connected to the positive terminal of the measuring cell, and the other end of which is connected to the opposite-phase input terminal of the operational amplifier and the P-channel FE.
The cell voltage detection circuit according to claim 1, further comprising: a current detection resistor connected to a source of T. 3. In place of the P-channel FET, PN
3. The cell voltage detection circuit according to claim 2, wherein a P-type transistor or a Darlington-connected PNP-type transistor is used. 4. A cell voltage of a cell connected to a negative terminal of the battery pack is output by a non-inverting amplifier having an amplification factor of 1,
2. The cell voltage detection circuit according to claim 1, wherein the cell voltage of the cell on the upper side of the cell is output by a differential amplifier having an amplification factor of one. 5. An operational amplifier, wherein a positive power supply terminal and a negative power supply terminal of the operational amplifier have an amplification factor of 1 with a cell voltage of each cell as an input so that operating power is supplied within the withstand voltage range.
5. The cell voltage detection circuit according to claim 1, wherein the cell voltage detection circuit is connected to an output of the non-inverting amplifier. 6. A battery voltage detection device comprising the cell voltage detection circuit according to claim 1.