Overvoltage detection circuit capable of improving accuracy of battery performance evaluation

Abstract

To provide an overvoltage detection circuit capable of improving the accuracy of battery performance evaluation.SOLUTION: A charging current supplied from a constant-current power supply 1 passes through a current detection circuit 2 and a switch 3 and applies an overvoltage to a charging battery 4. The level shift amplification circuit 5 inputs a signal obtained by the switching operation of the charging battery 4 to the analog-digital conversion circuit 7. The microcomputer 8 controls the switch 3 to temporarily stop the charging current supplied to the battery. The level shift amplification circuit 5 receives the reference voltage from the reference voltage generation circuit 6, lowers the DC voltage of the input electromotive force voltage of the charging battery 4, and amplifies the electromotive force voltage of the charging battery 4 to a predetermined level.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an apparatus for evaluating the performance of a rechargeable battery. [Background technology]

[0002] When batteries are connected in series to be used as a power source, the lifespan of the batteries will be shortened unless the characteristics of each battery are matched. Therefore, it is necessary to understand the characteristics of each battery and select them accordingly. Originally, to evaluate the performance of a rechargeable battery, the cumulative amount of electricity from a full charge to a full discharge was calculated, and performance was evaluated based on the obtained value, which took time to understand the battery characteristics.

[0003] To solve this problem, a method for instantaneously measuring battery performance is known in which an overvoltage is applied to the electromotive force of the battery, and the flowing current is detected to calculate the internal resistance of the battery (see Patent Document 1).

[0004] This instantaneous battery performance measurement method detects the electromotive force by instantaneously stopping the charging operation while applying an overvoltage to the rechargeable battery and measuring the voltage obtained from the battery. However, the voltage difference between the applied overvoltage and the electromotive force is small, at only a few tens of millivolts, and in the case of a rechargeable lithium-ion battery, the voltage changes from about 2.7 V to about 4.2 V after charging begins under an overvoltage condition, which poses the problem of requiring a highly accurate detection circuit to cover a wide voltage range above 4.2 V. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-056999 Summary of the Invention [Problem to be solved by the invention]

[0006] Although Patent Document 1 does not specifically disclose the measurement circuit, a circuit block diagram that can be read from Patent Document 1 is shown in Figure 5, and an attempt will be made to explain its operation. As shown in Figure 5, charging current supplied from constant current power supply 1 passes through switch 3 to charge rechargeable battery 4. Microcomputer 8 controls switch 3 to temporarily suspend the supply of charging current to the battery. Analog-to-digital conversion circuit 7 measures the voltage just before and after the current is halted, and inputs the measured voltage to microcomputer 8. Microcomputer 8 then inputs the voltage detected by analog-to-digital conversion circuit 7 and calculates the battery's internal resistance, thereby evaluating the performance of the battery being measured.

[0007] Due to the characteristics of batteries, the potential difference between the charging voltage and the electromotive force is small, and in the case of a lithium-ion battery, when charging begins after a full discharge, the potential of the battery being charged rises to about 2.7V in a short period of time, but then gradually increases over time to about 4.2V, when the battery is fully charged.

[0008] Battery performance is evaluated by its internal resistance, which is a small value of a few milliohms. Therefore, to evaluate battery performance with an accuracy of about 2%, it is necessary to monitor a voltage of about several tens of millivolts with a five-digit accuracy when the voltage changes by about 1.5 V, which requires a high-performance detection circuit. As described above, in order to perform charging operations when evaluating the performance of rechargeable batteries, in the case of lithium-ion batteries, monitoring at approximately 2.7 V to 4.2 V is required, and the resulting electromotive force is small, at several tens of mV, making it difficult to evaluate with high accuracy.

[0009] In view of the above circumstances, an object of the present invention is to provide an overvoltage detection circuit that can improve the accuracy of battery performance evaluation. [Means for solving the problem]

[0010] To achieve the above object, the overvoltage detection circuit of the present invention includes a constant current power supply circuit that charges a rechargeable battery, a current detection circuit connected upstream of the battery charged by the constant current power supply circuit and that detects the current value charging the battery, a switch that stops the charging operation when the battery is being charged, a level shift amplifier circuit that amplifies the signal obtained from the switch operation by an amplification factor of 1x or more and DC-shifts the DC level of the signal obtained from the switch operation, and an analog-to-digital conversion circuit that detects the output signal level of the level shift amplifier circuit, thereby improving the accuracy of battery performance evaluation. Here, DC-shifting the DC level of a signal means DC-shifting the DC component using, for example, an operational amplifier, etc. In the case of other clamp circuits or bias circuits other than an operational amplifier, the DC component is blocked by a capacitor and a new DC component is applied, and the difference is the amount of shift.

[0011] The overvoltage detection circuit of the present invention converts the DC level of the input signal and amplifies the amplitude of the input signal. By installing this level shift amplifier circuit in the front stage of the analog-to-digital conversion circuit, the detection accuracy can be improved. In other words, by providing a level shift amplifier circuit in front of the analog-to-digital conversion circuit, the amplitude level can be amplified, the dynamic range of the analog-to-digital conversion circuit can be expanded, and the accuracy of battery performance evaluation can be improved.

[0012] An analog-to-digital conversion circuit is used to detect the amplified amplitude level, and a microcomputer or FPGA (Field Programmable Gate Array) can be suitably used to determine the output value of the analog-to-digital conversion circuit. Note that if the output value of the analog-to-digital conversion circuit is determined as High or Low, a comparator is sufficient, but in the case of a microcomputer, battery performance can be evaluated in percentage (%).

[0013] In the amount of shift in the level shift amplifier circuit of the overvoltage detection circuit of the present invention, it is preferable that a voltage lower than the nominal voltage of the battery is set to a value below the lower limit reference voltage of the analog-digital conversion circuit, and that the battery voltage is not measured, and that the amount of shift in the level shift amplifier circuit is set to a value that causes the voltage output by the constant current power supply circuit to vary gradually over time and exceed the lower limit reference voltage of the analog-digital conversion circuit. Here, the nominal voltage of a battery is a value established as a guideline for the voltage across the terminals that can be obtained when the battery is used under normal conditions, and a fully charged battery will have a terminal voltage (initial voltage) that is higher than the nominal voltage. On the other hand, if the battery has been used for a long time and has been charged and discharged many times, the internal resistance of the battery will increase, and the terminal voltage will drop significantly below the nominal battery capacity when a load is connected. In the case of lithium-ion batteries, the operating voltage range is 3.7V to 3.8V, and when charging from an empty battery, the voltage fluctuates to approximately 2.7V to 4.3V. Therefore, there is no point in monitoring voltages below 2.7V, so a level shift circuit is used to keep them outside the range so that they are not measured.

[0014] Preferably, the overvoltage detection circuit of the present invention further comprises a computer, which controls the switch, inputs the output signal of the analog-to-digital conversion circuit, and inputs the output signal of the current detection circuit, and determines the timing for reading the signal by the analog-to-digital conversion circuit.

[0015] In the overvoltage detection circuit of the present invention, it is preferable that the timing of reading by the analog-to-digital conversion circuit is based on the output signal voltage of the analog-to-digital conversion circuit and the current value detected by the current detection circuit immediately after the charging current is stopped by the switch.

[0016] In the overvoltage detection circuit of the present invention, when the computer determines that the battery is fully charged, or when the charging current output by the constant current power supply circuit decreases and the computer determines that the battery is fully charged, it preferably outputs a stop signal to the constant current power supply circuit and stops the operation of evaluating battery performance. [Effects of the Invention]

[0017] The overvoltage detection circuit of the present invention has the effect of improving sensitivity by using a level shift amplifier circuit, thereby enabling highly accurate evaluation of battery performance without using a high-performance device. [Brief explanation of the drawings]

[0018] [Figure 1] Functional block diagram of an overvoltage detection circuit that can improve the accuracy of battery performance evaluation in Example 1. [Figure 2] Level shift amplifier circuit diagram [Figure 3] Computer operation flow diagram [Figure 4] Functional block diagram of an overvoltage detection circuit that can improve the accuracy of battery performance evaluation in Example 2. [Figure 5] Functional block diagram of a prior art circuit DETAILED DESCRIPTION OF THE INVENTION

[0019] An example of an embodiment of the present invention will be described in detail below with reference to the drawings. Note that the scope of the present invention is not limited to the following examples and illustrated examples, and many modifications and variations are possible. [Example]

[0020] FIG. 1 shows a block diagram of an overvoltage detection circuit capable of improving the accuracy of battery performance evaluation according to the first embodiment. As shown in Figure 1, the charging current supplied from a constant current power supply 1 passes through a current detection circuit 2 and a switch 3 to charge a rechargeable battery 4. A level shift amplifier circuit 5 inputs the signal obtained by the switching operation of the rechargeable battery 4 to an analog-to-digital conversion circuit 7. A microcomputer 8 controls (ON / OFF control) the switch 3 to temporarily suspend the charging current supplied to the battery. It also detects the current charging the battery from the current detection circuit 2. The level shift amplifier circuit 5 inputs a reference voltage from a reference voltage generation circuit 6, and reduces the DC voltage of the input electromotive force voltage of the rechargeable battery 4, while amplifying the electromotive force voltage of the rechargeable battery 4 to a predetermined level. Here, electromotive force voltage (or simply electromotive force) refers to the voltage that the battery currently has. In a discharged state, the battery gradually discharges, so it is not the original electromotive force. Therefore, it refers to the voltage value when the charging operation is stopped from the charging state of the battery. However, because a chemical reaction occurs inside the battery, it changes over time, so it is the voltage value when it has stopped and settled down.

[0021] The signal output from the level shift amplifier circuit 5 is input to the analog-to-digital conversion circuit 7, which measures the voltage immediately before charging was stopped and the voltage after charging has stopped based on the current value detected by the current detection circuit 2, and inputs this to the microcomputer 8. The microcomputer 8 inputs the voltage detected by the analog-to-digital conversion circuit 7 and calculates the internal resistance of the battery, thereby evaluating the performance of the battery being measured.

[0022] Here, a specific circuit diagram of the level shift amplifier circuit 5 and the reference voltage generating circuit 6 is shown in FIG. As shown in Figure 2, the battery voltage output from current detection circuit 2 is divided by R1 and R2 and input to amplifier 9b, where it is amplified by R3 and R4 to obtain a doubled signal. The 3.3V power supply voltage is divided by R5 and R6 to approximately 2.7V and input to amplifier 9a. Since amplifier 9a is a voltage follower, the divided voltage is input to the - (negative) terminal of amplifier 9b, and the signal input to the + (positive) terminal of amplifier 9b undergoes a DC level shift. Here, the amplification factor of amplifier 9b (op-amp) can be changed by changing the resistance values ​​(R1 and R2, R3 and R4). In the circuit shown in Figure 2, R1 and R4, and R2 and R3 have the same resistance values ​​(R1 = R4, R2 = R3), resulting in a differential amplifier with an amplification factor of 2 (R3 / R4 = 20 / 10 = 2), which is often used primarily to reduce common-mode noise in transmission systems. When the amplification factor is equal (1x), it is called a difference amplifier, and all resistance values ​​are the same (R1 = R2 = R3 = R4), and the output is equal to the difference between the inputs. Amplifier 9b is composed of an op-amp, but it can also be composed of a transistor. In recent years, 3.3V has become the mainstream power supply voltage for semiconductors, etc., in consideration of power consumption savings. 5V is also commonly used, but the power-hungry microcomputers and FPGAs are now operating at 3.3V or less, so this voltage is suitable for these.

[0023] When the reference voltage for shifting the DC component is set to 2.7 V in this way, the charging voltage of 4.2 V at full charge is level-shifted to 1.5 V. When the gain of the level shift amplifier circuit 5 is set to 2 times, the charging voltage at full charge is amplified to 3.0 V. The battery voltage here changes from 2.7 V to 4.2 V. By using this level shift amplifier circuit, the voltage can be shifted from 1.5 V to 3.0 V, making it possible to shift the DC level of the signal in a DC manner.

[0024] These operations double the amplitude of the input signal to the analog-digital conversion circuit 7, widening the range from approximately 2.7V to 4.2V, which was previously only available with a potential difference of 1.5V, to 3.0V, which is double the range. Therefore, the overvoltage detection circuit of the present invention can achieve four times the accuracy of the conventional circuit.

[0025] FIG. 3 shows an operational flow diagram of a computer (also called a microcomputer). As shown in FIG. 3, first, a signal to supply a charging current to the constant current power supply circuit is output (step S01). The battery voltage and charging current are detected (step S02), and when the charging current value and battery voltage fall within a predetermined range (step S03), battery performance is evaluated (step S04). The evaluation result is output, and a signal to stop the constant current power supply circuit is output (step S05). This stops the charging operation to the battery. If the charging current value and battery voltage do not fall within a predetermined range, a signal to stop the constant current power supply circuit is output (step S05), which stops the charging operation to the battery. The electromotive force of a battery refers to the potential that appears when an overvoltage is applied to the battery and the charge is stopped, so it is the voltage when the charging current becomes 0, i.e., immediately after the charging operation is stopped. [Example]

[0026] FIG. 4 shows a block diagram of an overvoltage detection circuit according to the second embodiment. The overvoltage detection circuit of the second embodiment differs from the overvoltage detection circuit of the first embodiment described above in that there is no control signal from the microcomputer 8 to the constant current power supply 1, but otherwise has the same configuration as the first embodiment.

[0027] The control signal from microcomputer 8 to constant current power supply 1 has the role of stopping the charging operation, but since the charging current is a constant current source and can be set in advance, there is no particular need to specify this if you are only evaluating battery performance. The present invention improves the accuracy of battery performance evaluation by detecting the actual current flowing. [Industrial Applicability]

[0028] The present invention is useful in devices for evaluating the performance of rechargeable batteries. [Explanation of symbols]

[0029] 1 Constant current power supply 2 Current detection circuit 3 Switch 4 Rechargeable battery 5 Level shift amplifier circuit 6 Reference voltage generation circuit 7 Analog-to-Digital Conversion Circuit 8 Microcomputer 9a, 9b Amplifier R1~R6 resistor

Claims

1. a constant current power supply circuit for charging a rechargeable battery; a current detection circuit connected in front of the battery to detect the current value charging the battery, and a switch to stop the charging operation when charging the battery; a level shift amplifier circuit that amplifies a signal obtained from a switching operation of the switch by an amplification factor of 1x or more and DC-shifts a DC level of the signal obtained from the switching operation; an analog-to-digital conversion circuit that detects the output signal level of the level shift amplifier circuit; and an overvoltage detection circuit for improving the accuracy of performance evaluation of the battery.

2. In the amount of shift in the level shift amplifier circuit, 2. The overvoltage detection circuit according to claim 1, wherein the voltage lower than the nominal voltage of the battery is set to a value lower than a lower limit reference voltage of the analog-to-digital conversion circuit.

3. further comprising a computer; The computer Controlling the switch 2. The overvoltage detection circuit according to claim 1, wherein the output signal of the analog-to-digital conversion circuit and the output signal of the current detection circuit are input to determine the timing of reading by the analog-to-digital conversion circuit.

4. The timing of reading by the analog-to-digital conversion circuit is as follows:

4. The overvoltage detection circuit according to claim 3, wherein the overvoltage detection circuit is read based on the output signal voltage of the analog-to-digital conversion circuit immediately after the charging current is stopped by the switch and the current value detected by the current detection circuit.

5. The computer If the battery is determined to be fully charged, or When the charging current output by the constant current power supply circuit decreases and it is determined that the battery is fully charged, 5. The overvoltage detection circuit according to claim 4, wherein a stop signal is output to said constant current power supply circuit to stop the performance evaluation operation of said battery.

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