JP4719972B2 - Charge / discharge current measuring device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a charge / discharge current measuring device for measuring a charging current and a discharging current of a secondary battery used as a power source of a portable electronic device, and particularly when calculating a remaining capacity of a secondary battery of a portable electronic device. The present invention relates to a charge / discharge current measuring device used.
[0002]
[Prior art]
As a battery remaining amount display device for calculating the remaining capacity of a secondary battery used as a power source of a portable electronic device, a device disclosed in, for example, Japanese Patent Laid-Open No. 6-176798 (Patent No. 2932872) has been disclosed. is there. FIG. 3 is a block diagram showing the battery remaining amount display device.
[0003]
The charge / discharge current of the secondary battery 101 flows through the current detection resistor 102 connected in series with the secondary battery 101. The charging / discharging current detection means 103 includes a charging current detection operational amplifier 131 that receives a minute voltage generated at both ends of the current detection resistor 102 and a discharge current detection operational amplifier 132. The voltage drop detection unit 104 monitors a voltage drop of the secondary battery 101 as the discharge progresses.
[0004]
When a charger (not shown) is connected to the terminal 113, the electric quantity calculating means 106 calculates the electric quantity by multiplying the charging current value output from the operational amplifier 131 by a predetermined time, and further, this electric quantity is the magnitude of the charging current. And the charging efficiency determined by the temperature information output from the temperature detection means 105 are multiplied to obtain a final charge electricity amount, which is output as a signal to the electricity amount integration means 110. The charging completion detection unit 107 resets the signal output when the charging current signal is input from the operational amplifier 131. Reference numeral 112 denotes a microcomputer, which constitutes a circuit corresponding to the electric quantity calculation means 106, the charging completion detection means 107, the discharge electric quantity integration means 108, the capacity storage means 109, and the electric quantity integration means 110.
[0005]
When a portable device (not shown) is connected to the terminal 113, the discharge electricity amount integrating means 108 integrates the discharge electricity amount every predetermined time. The electric quantity integrating means 110 adds the charged electric quantity output as a signal from the electric quantity calculating means 106 every predetermined time and subtracts the discharged electric quantity, thereby depending on the ratio to the stored value of the capacity storage means 109. Determine the remaining capacity value. The display unit 111 displays the remaining capacity in a stepwise manner based on the remaining amount information determined by the electricity amount integrating unit 110.
[0006]
In this conventional device, a battery remaining amount display device with high remaining amount display accuracy can be configured by storing the accurate latest capacity of the battery, but on the charge / discharge current detection means 103, two operational amplifiers for charging and discharging are provided. Since 131 and 132 were used, there was a problem in cost.
[0007]
In addition, in order to know the remaining capacity of the secondary battery, the power source of the portable electronic device usually needs to measure a current from about several mA to several A, and the current detection resistor 102 for that purpose is used as the secondary battery. In consideration of the efficiency of the battery, a resistor having a small resistance value, for example, a resistance of about several tens [mΩ] is used. Therefore, the voltage across the detection resistor is 100 [μV] to 100 [mV] (1: 1000). When the minimum value of the detected current is about several milliamps [mA], even if the gain of the detection amplifier is 200 times, the output value is a small value of about 20 [mV]. That is, when a general general-purpose operational amplifier is used for the operational amplifiers 131 and 132 and the power supply is set to 0 [V] −Vdd [V], the output voltage range becomes narrower than the power supply voltage range. ] Measured values near cannot be output accurately. Thus, in consideration of the efficiency of the secondary battery, when a special operational amplifier called rail-to-rail is used in order to enable output in the power supply voltage range, there is a problem in terms of cost.
[0008]
Furthermore, in the capacity remaining amount measuring method using the current integration method, the offset voltage of the current detection means becomes an error factor of the measured current value. Therefore, a method of using a high-precision operational amplifier with a small offset voltage, a method of adjusting the offset voltage of the operational amplifier to zero when manufacturing the battery pack, or measuring the operational amplifier offset voltage in advance and measuring the current value using a microcomputer It is conceivable to subtract the offset voltage from. However, in any case, there is a problem that the cost of the conventional apparatus is increased.
[0009]
As another conventional example, a method for measuring charge / discharge current of a secondary battery for power storage that accurately measures and evaluates the remaining capacity of the secondary battery with an inexpensive measurement circuit configuration is known (Japanese Patent Laid-Open No. 8-17478). . FIG. 4 is a block diagram showing the battery remaining amount measuring circuit.
[0010]
This method is the same as the former one in that the charge / discharge current flowing from the charge / discharge circuit 202 to the secondary battery 201 is converted into a voltage value by the shunt resistor 204, but information from the charge / discharge switching device 203 is used. This is different in that the polarity inversion circuit 206 is operated based on the above and a signal having the same polarity is always input to the isolation amplifier 208. The voltage measuring device 209 amplifies the output value of the insulation amplifier 208, and the arithmetic unit 210 converts the voltage measurement value of the voltage measuring device 209 into a current absolute value and calculates. At this time, under the control of the control device 207, the absolute value of the current is switched between the positive direction and the negative direction according to the charging and discharging conditions.
[0011]
The integrating device 211 is connected to the output side of the computing device 210, and the integrating device 211 integrates the current value. If the rated capacity value of the secondary battery 201 is set in advance at the time of completion of full charge, the remaining capacity of the secondary battery 201 is obtained by this integration.
[0012]
[Problems to be solved by the invention]
If this method for measuring the charge / discharge current of a secondary battery for power storage is applied to the power source of a portable electronic device, the cost can be reduced because only one detection amplifier is required to measure the remaining capacity of the secondary battery. There is. However, as with the former prior art, the offset voltage of the current detection means not only causes an error in the measured current value, but also increases the cost when considering the power efficiency of the portable electronic device. There was a problem that it was not easy.
[0013]
An object of the present invention is to provide a charge / discharge current measuring apparatus capable of measuring with high accuracy at low cost.
[0014]
[Means for Solving the Problems]
In order to achieve the above object, there is provided a charge / discharge current measuring device for measuring a charge current and a discharge current of a secondary battery used as a power source of a portable electronic device. The discharge current measuring device, which is connected secondary batteries in series, a current detection resistor for converting a charging and discharging current of it to the small voltage signal, said current detecting said polarity of resistance occurring the small voltage signal secondary with batteries can be switched to a predetermined polarity direction depending on whether the charge state or discharging state, said a switching means capable of disconnecting the current detection resistor from the subsequent circuit, the small voltage that is constant polarity by said switching means an operational amplifier means for amplifying by a gain setting for the desired signal, and an offset adjusting means for dropping to the ground as well as short-circuiting the input to the operational amplifier means when the offset adjustment of the operational amplifier means, the level adjustment signal supplied It is such that the output voltage level of the operational amplifier means is readable voltage value according to the level adjustment signal, Le for adjusting the level shift amount And Rushifuto amount adjusting means, the arithmetic output voltage of the amplifying means and the analog-to-digital conversion means for converting into a digital signal, the level adjustment to be supplied to the level shift amount adjusting means according to the set gain to the operational amplifier means storage means for storing a level shift amount of size corresponding to the signal, the polarity switching and disconnecting in said switching means, the gain setting in the operational amplification means, and operation for instructing the adjustment at the level shift amount adjusting means Means. This charge-discharge current measuring device, after the adjustment setting processing of the level shift amount, executing the remaining capacity calculation by current measurement, charging current and discharging current of the secondary battery of the portable electronic device is measured with high precision Alternatively, the remaining capacity of the secondary battery can be calculated with high accuracy .
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing a configuration of a charge / discharge current measuring apparatus according to the present invention.
[0016]
In the figure, reference numeral 1 denotes a current detection resistor that is connected in series with the secondary battery 2 and converts the charge / discharge current into a minute voltage. When the secondary battery 2 is connected to a load such as a charger or a portable electronic device (not shown), a charging current or a discharging current flows in the current detection resistor 1 in the direction shown in the drawing.
[0017]
Reference numeral 3 denotes an input polarity inverting circuit, in which a minute voltage signal generated at both ends of the current detection resistor 1 is always switched to a constant polarity direction depending on whether it is in a charged state or a discharged state, or a minute voltage signal generated at both ends of the current detection resistor 1. Switching means for separating the voltage signal from the subsequent operational amplifier circuit is configured. The input polarity inversion circuit in the figure shows the state of charge.
[0018]
Reference numeral 5 denotes an operational amplifier circuit, which comprises an operational amplifier 6, a gain switching circuit 7, and a plurality of resistors R1 and R2. Here, the resistance value of the resistor indicated by R1 is R1, and the resistance value of the resistor indicated by R2 is R2. The operational amplifier circuit 5 is connected to the first output terminal 31 and the second output terminal 32 of the input polarity inverting circuit 3, both of which are connected to the positive and negative input terminals of the operational amplifier 6 through the resistor R 1 with a constant polarity direction. A very small voltage signal is supplied. In order to switch the gain of the operational amplifier 6, the gain switching circuit 7 is composed of a series circuit of a resistor R 1 and a switch 8.
[0019]
Here, the gain switching circuit 7 is switched in two steps of 20 times and 220 times as described below, but may be in three steps or more.
Since the input polarity inverting circuit 3 is specifically composed of an analog switch, there is an ON resistance, which causes a gain error of the operational amplifier circuit 5. In order to reduce the influence of the on-resistance, the resistance value R1 of the gain setting resistor of the operational amplifier circuit 5 may be increased. However, when an integrated circuit is formed, there are restrictions in terms of chip area and cost. For example, the resistance value R1 is set to 100 [kΩ] and the resistance value R2 is set to 1 [MΩ].
[0020]
When the gain switching circuit 7 selects a low gain, the switch 8 is switched to the open state to obtain the following equation (1):
(2.R2) / R1 = 20 (1)
The gain of the operational amplifier circuit 5 can be 20 times.
[0021]
When the high gain is selected by the gain switching circuit 7, the switch 8 is switched to a short circuit state. Then, from the following equation (2),
2 · {1 + 1 / (1/10)} · (R2 / R1) = 220 (2)
The gain of the operational amplifier circuit 5 is 220 times.
[0022]
Reference numeral 9 denotes an offset adjustment circuit of the operational amplifier circuit 5, which is composed of a pair of switches for short-circuiting the positive and negative input terminals of the operational amplifier 6 and dropping them to the ground in the offset adjustment state.
[0023]
Reference numeral 10 denotes a level shift amount adjustment circuit that can adjust the level shift amount of the output voltage of the operational amplifier circuit 5. The level shift amount adjustment circuit 10 is supplied with a first reference potential V1 and a level adjustment signal from a CPU described later.
[0024]
Reference numeral 11 denotes an analog-digital conversion circuit (hereinafter referred to as an AD conversion circuit) that converts the output signal Vout of the operational amplifier circuit 5 into a digital quantity. The AD converter circuit 11 is supplied with a second reference potential V2.
[0025]
Reference numeral 12 denotes a CPU that captures an output signal of the AD conversion circuit 11. A non-volatile memory 13 for recording the level shift amount of the level shift amount adjusting circuit 10 for a desired gain of the operational amplifier circuit 5 and a memory 14 for temporarily storing other necessary data are connected. Yes.
[0026]
The operation of the charge / discharge current measuring apparatus configured as described above will be described.
First, before executing the current detection process or the remaining capacity calculation process, the level shift amount adjustment setting process is performed only once as follows.
[0027]
In the level shift amount adjustment setting process, both ends of the current detection resistor 1 and the input of the operational amplifier circuit 5 are separated by the input polarity inverting circuit 3, the input of the operational amplifier circuit 5 is short-circuited by the offset adjustment circuit 9, and Drop it to the ground. The operational amplifier circuit 5 is set to a desired gain by the gain switching circuit 7, and the level shift amount adjusting circuit 10 performs adjustment so that the output value of the operational amplifier circuit 5 at that time becomes a readable voltage value. After the adjustment is completed, the adjustment value of the level shift amount adjusted and set with respect to the set gain value of the operational amplifier circuit 5 is stored in the nonvolatile memory 13.
[0028]
In the offset amount measurement process, the CPU 12 switches the input polarity inverting circuit 3 to disconnect the both ends of the current detection resistor 1 from the input of the operational amplifier circuit 5 and uses the offset adjustment circuit 9 to input the operational amplifier circuit 5. And the positive and negative input terminals of the operational amplifier 6 are dropped to the ground. The CPU 12 sets the gain of the operational amplifier circuit 5 to a desired value by using the switch 8 of the gain switching circuit 7.
[0029]
Further, the CPU 12 reads the level shift amount corresponding to the set gain value from the nonvolatile memory 13 and sets the read level shift amount using the level shift amount adjustment circuit 10. In this state, the output of the AD conversion circuit 11 is read into the CPU 12, and the value is stored in the memory 14 as an offset amount.
[0030]
The offset amount obtained in this way is a value obtained by adding the level shift amount set by the level shift amount adjustment circuit 10 and the offset amount calculated by the operational amplifier circuit 5 and converted by the AD conversion circuit 11. It has become. Therefore, in the current measurement process described below, the offset amount including the temperature drift component in the operational amplifier circuit 5 and the AD conversion circuit 11 is canceled by subtracting the offset amount stored in the memory 14 from the measured value. . This offset amount measurement process is performed at an appropriate timing during the current measurement process described below.
[0031]
In the current measurement process, the CPU 12 outputs and switches the polarity inversion signal to the input polarity inversion circuit 3 depending on whether it is in the charge state or the discharge state, and the minute voltage signal generated at both ends of the current detection resistor 1 is always in the constant polarity direction. To do. Further, the CPU 12 controls the gain switching circuit 7 with a gain switching signal corresponding to the magnitude of the current value, and sets the magnitude of the gain of the operational amplifier circuit 5. Further, the CPU 12 reads the level shift amount corresponding to the set gain value from the nonvolatile memory 13 and outputs a level adjustment signal to the level shift amount adjustment circuit 10 to set the read level shift amount Vshift.
[0032]
Thereafter, the CPU 12 reads the output signal from the AD conversion circuit 11, subtracts the offset amount stored in the memory 14 from the read value, and sets the subtraction result as the current measurement value. This current measurement process is performed at regular time intervals.
[0033]
By the way, in the charging / discharging current measuring apparatus mentioned above, the current detection resistor 1 is arrange | positioned in series with the charging / discharging path | route of the secondary battery 2, and converts charging / discharging electric current into a minute voltage. In a portable electronic device, the generated power in such a current detection resistor 1 becomes a loss, and thus the resistance value Rcs is normally set to a small value of about several tens [mΩ]. The operational amplifier 6 of the operational amplifier circuit 5 is a differential amplifier circuit using a general-purpose operational amplifier, and its input offset voltage is about ± 5 [mV] at the maximum. Since the measurement current for measuring the remaining amount of the secondary battery 2 ranges from several [mA] to 5, 6 [A], the operational amplifier 6 constituting the operational amplifier circuit 5 has a wide dynamic range of 1: 1000. Needed.
[0034]
Here, when the gain of the operational amplifier circuit 5 is set to 20 times, the input offset voltage is generated up to ± 0.1 [V], and when the gain is 220 times, up to ± 1.1 [V ]appear. On the other hand, the power source for driving the operational amplifier 6 is a single power source when it is assumed to be an IC and its voltage value is assumed to be 3 [V]. When a general-purpose operational amplifier is used, its output range is slightly narrower than the power supply voltage, and the actual output offset voltage is 0.05 [V] to 0.1 [V] when the gain is 20 times. Is between 0.05 [V] and 1.1 [V] when 2 is 20 times. That is, when the output offset voltage is going to take a negative value, a region where measurement itself is impossible occurs.
[0035]
Therefore, the level shift amount adjustment circuit 10 determines the level shift amount by the output voltage Vshift according to the level adjustment signal. That is, the level shift amount is set so that the output of the operational amplifier circuit 5 becomes about 0.1 [V] when the gain is 20 times and the input voltage is zero regardless of the offset voltage of the operational amplifier 8. It is adjusted. In this case, when the output offset voltage is −0.1 [V], the output voltage Vshift is 0.2 [V], and when the output offset voltage is +0.1 [V], the output voltage Vshift is 0 [V]. It is necessary to do. Therefore, the output voltage Vshift range of the level shift amount is 0 [V] to 0.2 [V].
[0036]
Next, when the gain is 220 times, the level shift amount is set so that the output of the operational amplifier circuit 5 becomes about 1.1 [V] when the input voltage is zero regardless of the magnitude of the offset voltage of the operational amplifier 6. It is adjusted. In this case, when the output offset voltage is −1.1 [V], the output voltage Vshift is 2.2 [V], and when the output offset voltage is +1.1 [V], the output voltage Vshift is 0 [V]. It is necessary to do. Therefore, the output voltage Vshift range of the level shift amount is 0 [V] to 2.2 [V].
[0037]
As described above, since the level shift amount adjustment circuit 10 is commonly used regardless of the magnitude of the gain, the output voltage Vshift range may be 0 [V] to 2.2 [V]. .
[0038]
Next, a specific configuration of the level shift amount adjustment circuit 10 will be described. FIG. 2 is a block diagram showing the configuration of the level shift amount adjusting circuit.
The level shift amount adjustment circuit is turned on / off by the decoder 16 having a 3-bit signal input terminal, resistors R1 to R7 for dividing the reference potential (2.2 [V]) into eight, and eight outputs of the decoder 16. The switches SW1 to SW8 and the output amplifier 17 are configured. The resistors R1 to R7 are selected by a 3-bit signal input from the CPU 12 to the decoder 16, and can output a voltage value obtained by dividing the reference potential into eight.
[0039]
Here, since the purpose of the level shift amount adjustment is to eliminate the region that cannot be measured, it is not necessary to increase the setting resolution so much. This is because the offset of the measurement system can be canceled by subtracting the offset amount measured in the offset amount measurement process on the program.
[0040]
The level shift amount adjusting circuit in FIG. 2 outputs a voltage divided by a step width of 0.314 [V] in the range of 0 [V] to 2.2 [V], and the gain is set to 20 times. Even if the input offset voltage is zero, the level shift amount can only be set to 0.314 [V]. However, as will be described later, the dynamic range can be secured even in that case.
[0041]
Next, when the charge / discharge current is measured by switching the gain, the specific magnitude of the current value for switching the gain will be considered.
For example, the resistance value Rcs of the current detection resistor 1 is set to 20 [mΩ], and the width of the detected current value is set to 5 [mA] to 5 [A]. Then, the voltage across the current detection resistor 1 to be detected has a fluctuation range of 100 [μV] to 0.1 [V]. Therefore, when the detected current value is small, that is, when the detected voltage value is small, the gain of the operational amplifier circuit 5 is increased by 220 times. Conversely, when the detected current value is large and the detected voltage value is large, the operational amplifier circuit 5 is increased. The gain is set to 20 times.
[0042]
Now, assuming that the detected current value is small, if the input offset voltage of the operational amplifier 6 is Voffset, the output voltage Vout of the operational amplifier circuit 5 is expressed by the following equation (3).
[0043]
Vout = I · Rcs · 220 + Vshift−220 · Voffset (3)
Here, I is the charge / discharge current of the secondary battery 2, and Vshift is the output voltage of the level shift amount adjustment circuit 10.
[0044]
The level shift amount Vshift to be set in the operational amplifier circuit 5 varies depending on the magnitude of the input offset voltage Voffset, and is set so that the value of (Vshift−220 · Voffset) is approximately 1.1 [V]. . Therefore, the above equation (3) can be rewritten as the following equation (4).
[0045]
Vout = I · Rcs · 220 + about 1.1 (4)
In the offset amount measurement process, since the charging / discharging current I of the secondary battery 2 is zero, Vout is about 1.1 [V]. Therefore this value, keep the C PU12 to the memory 14 via the AD converter 11.
[0046]
In the current measurement process, a voltage value Vout corresponding to the magnitude of the charge / discharge current I is input to the CPU 12. Therefore, by taking out about 1.1 [V] stored in the offset amount measurement process from the memory 14 and performing a subtraction process, the first term of the equation (4) corresponding to the current measurement value can be obtained.
[0047]
Here, at the minimum detectable current value (= 5 [mA]), the output voltage Vout of the operational amplifier circuit 5 is 22 [mV] + about 1.1 [V]. This output voltage value Vout is input to the CPU 12 via the AD conversion circuit 11. Therefore, 22 [mV] corresponding to the actual current measurement value can be obtained by subtracting the offset voltage value (about 1.1 [V]) stored in the memory 14 from the output voltage Vout.
[0048]
The AD conversion circuit 11 is assumed to be a 10-bit successive approximation type circuit, for example, and the reference voltage is set to 3 [V]. Therefore, the resolution per bit is 2. It is 93 [mV], and the digital value is 7 to 8 bits with respect to the minimum detected current value, which can be measured.
[0049]
When the detected current value is large, the maximum current value that can be measured can be calculated from the following inequality (5).
Vout = I · Rcs · 220 + about 1.1 <about 2.8 (5)
Here, the value on the right side of inequality (5) represents the maximum output voltage value of the operational amplifier 6 when the power supply voltage is 3 [V]. From this, the maximum measured current value is about 380 [mA]. This means that when the charge / discharge current is 5 [mA] to 380 [mA], the gain is measured 220 times, and when the charge / discharge current is 380 [mA] or more, the gain is switched to 20 times and measured. I know it ’s good.
[0050]
When the gain of the operational amplifier circuit 5 is 20 times, the output voltage value Vout of the operational amplifier circuit 5 is expressed by the following equation (6).
Vout = I · Rcs · 20 + Vshift− 20 · Voffset (6)
The value of the level shift amount Vshift to be set in the operational amplifier circuit 5 varies depending on the magnitude of the input offset voltage Voffset, and is set so that the value of (Vshift- 20 · Voffset) is approximately 0.1 [V]. . It is preferable to set the value of the level shift amount Vshift in this way in order to optimize the dynamic range. However, the level shift amount adjustment circuit 10 is commonly used between the two gains, and the output step size is 0.314 [V]. Therefore, the value of (Vshift- 20 · Voffset) is about 0.364 [V] (= 0.314 + 0.05) at the maximum. At this time, equation (6) is rewritten to the following equation (7), and the dynamic range becomes the worst.
[0051]
Vout = I · Rcs · 20 + about 0.364 (7)
Further, the maximum measurable current value is obtained from the following equation (8).
Vout = I · Rcs · 20 + about 0.364 <about 2.8 (8)
From this equation (8), the maximum measured current value is 6.09 [A], which is 5 [A] or more of the specification. The minimum measured current value can be calculated from the resolution (= 2.93 [mA] / bit) of the AD conversion circuit 11 when the value of the first term of the equation (8) is within an error of 1%. That is,
(2. 93/2) / ( I · Rcs · 20) <1% ... (9)
Therefore, if Rcs is calculated with 20 [mΩ], I> 370 [mA]. Therefore, when the current value decreases to 370 [mA] or less, the gain may be switched from 20 times to 220 times. Here, the hysteresis width at the time of gain switching is about (380-370) = 10 [mA].
[0052]
In the charge / discharge current measuring apparatus of the present invention, the charge / discharge current value is further multiplied by the activation time interval of the current measurement process by multiplying the measured charge / discharge current value, and the charge / discharge electric quantity is obtained for each current measurement process. It is also possible to measure the remaining capacity of the battery.
[0053]
【The invention's effect】
As described above, the charge / discharge current measuring device of the present invention uses the input polarity reversing means to always switch the input voltage signal in a constant polarity direction to the operational amplification means regardless of whether it is in a charged state or a discharged state. Since the input is made, only one operational amplifier for current detection can be provided, and the cost can be reduced.
[0054]
Further, by biasing the operating point of the operational amplifier means using the level shift amount adjusting means, it is possible to accurately measure the charge / discharge current even if the offset voltage of the general-purpose operational amplifier exists. In addition, since the current can be accurately measured without using a rail-to-rail output operational amplifier that enables output in the power supply voltage range, the cost of the apparatus can be further reduced.
[0055]
Furthermore, since the charge / discharge current measuring device of the present invention is configured to appropriately detect the offset voltage and level shift amount of the operational amplifier and subtract from the current measurement value, it is possible to reduce the detection circuit offset at low cost using a general-purpose operational amplifier. High-precision measurement that is not affected by temperature drift is possible.
[0056]
In addition, since the gain switching current value has a hysteresis characteristic, frequent switching can be prevented even when the current is measured near the switching point, and the program processing time can be shortened.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of the present invention.
FIG. 2 is a block diagram showing a configuration of level shift amount adjusting means.
FIG. 3 is a block diagram showing a configuration of a conventional battery remaining amount display device.
FIG. 4 is a block diagram showing a configuration of a conventional charge / discharge measuring apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Current detection resistor 2 Secondary battery 3 Input polarity inversion circuit 5 Operation amplification circuit 6 Operational amplifier 7 Gain switching circuit 8 Switch 9 Offset adjustment circuit 10 Level shift amount adjustment circuit 11 Analog digital conversion circuit 12 CPU
13 Nonvolatile memory 14 Memory

Claims (5)

In a charging / discharging current measuring device for measuring charging current and discharging current of a secondary battery used as a power source for portable electronic devices,
Said connected secondary batteries in series, a current detection resistor for converting a charging and discharging current of it to the small voltage signal,
The polarity of the minute voltage signal generated in the current detection resistor can be switched in a fixed polarity direction depending on whether the secondary battery is in a charged state or a discharged state , and the current detection resistor can be disconnected from the subsequent circuit. Switching means;
An operational amplifier means for amplifying set to a desired gain the small voltage signal constant polarity by said switching means,
An offset adjusting means for short-circuiting the input to the operational amplifying means at the time of offset adjustment of the operational amplifying means and dropping it to the ground;
Level shift amount adjusting means for adjusting the level shift amount so that the level adjustment signal is supplied and the output voltage level of the operational amplifier means becomes a readable voltage value according to the level adjustment signal ;
Analog-digital conversion means for converting the output voltage of the operational amplification means into a digital signal;
Storage means for storing a level shift amount of a magnitude corresponding to the level adjustment signal supplied to the level shift amount adjustment means according to a gain set in the operational amplification means;
Arithmetic means for instructing polarity switching and disconnection at the switching means , gain setting at the operational amplification means , and adjustment at the level shift amount adjusting means ,
A charge / discharge current measuring apparatus comprising:   The charge / discharge current measuring apparatus according to claim 1, wherein the storage unit is a nonvolatile memory. In a state of disconnecting the said operational amplifier means and said current detecting resistor, said operational amplifier means input connected to the ground as well as shorting of the operational amplifier means to a becomes the voltage value that can be output voltage read of their wherein the level shift amount adjusting means adjusts the level Cie shift amount, the charge and discharge current measuring device according to claim 2, wherein the adjustment value of the level shift amount, characterized in that stored in the nonvolatile memory.   The charge / discharge current measuring apparatus according to claim 1, wherein the operational amplification means includes gain switching means. 5. The charge / discharge current measuring apparatus according to claim 4, wherein the gain switching means has a hysteresis in a magnitude of a current value serving as a reference when switching the gain.

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