JP4612174B2 - Battery current measurement circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a battery current measurement circuit that can measure the current of a battery, particularly a secondary battery, used as a drive source for various electronic devices while minimizing a voltage drop associated with current measurement.
[0002]
[Prior art]
In portable electronic devices such as mobile phones and notebook personal computers, rechargeable secondary batteries are used as power sources. Further, in an electronic device using a commercial power source as a drive source, a rechargeable secondary battery is used as a power source for storing and supplying electric energy.
[0003]
In order to maintain the performance of the secondary battery over a long period of time and use it stably, it is desirable to manage the charging and discharging of the secondary battery. This charge / discharge management is performed, for example, by using a current detection resistor inserted in series in the charge / discharge path of the battery, and measuring the charge / discharge current from the voltage drop that occurs across the current detection resistor. Is called.
[0004]
[Problems to be solved by the invention]
However, when the current detection resistor is inserted in the charge / discharge path of the battery and the charge / discharge current is measured, the voltage drop in the current detection resistor cannot be ignored.
For example, in a mobile phone, it is necessary to supply a maximum current of about 2 A to the electronic circuit main body from a secondary battery that is a driving source. In a notebook personal computer, a maximum current of about 5 A is supplied. There is a need to. In this case, even if a current detection resistor having a resistance of 20 to 50 mΩ is used, a voltage drop of 40 to 100 mV or 100 to 250 mV occurs. Such a voltage drop becomes a factor that lowers the voltage supplied from the secondary battery to the electronic circuit main body such as a notebook personal computer, and as a result shortens the battery life of the secondary battery.
[0005]
The present invention has been made in view of the above problems, and a battery current measuring circuit having a simple configuration capable of suppressing a voltage drop accompanying measurement of a charging / discharging current of a battery and enabling a long-time operation of an electronic device using the battery. The purpose is to provide.
[0006]
[Means for Solving the Problems]
Battery current measuring circuit according to the present invention described in claim 1 in order to achieve the above object, a semiconductor for controlling turning on and off the charging and discharging currents of the connected in series to one electrode in the secondary battery of the secondary battery A switch , and voltage / current pressure conversion means for obtaining a charging current and / or a discharging current of the secondary battery from a voltage drop generated between both ends of the semiconductor switching element ,
The voltage / current pressure converting means includes a voltage drop measuring means for measuring a voltage across the semiconductor switch, a temperature measuring means for measuring the temperature of the semiconductor switch, and a voltage measured by the voltage drop measuring means as a current value. Storage means storing a temperature characteristic indicating a relationship between a conversion coefficient for conversion and the temperature of the semiconductor switch, and a conversion coefficient obtained from the storage means according to the temperature of the semiconductor switch measured by the temperature measurement means Using an arithmetic circuit that converts the voltage measured by the voltage drop measuring means into a current value,
Further, characteristic correction means for correcting the temperature characteristic of the conversion coefficient stored in the storage means according to the temperature of the semiconductor switch detected when charging the secondary battery with a constant current and the voltage across the semiconductor switch.
It is characterized by providing .
[0007]
With such a configuration, it is possible to measure the battery current without using a current detection resistor by measuring the voltage drop that occurs across the semiconductor switch. A battery current measuring circuit that solves the problem and enables the electronic device to operate for a long time using a battery is provided.
Here, it is preferable to use a field effect transistor having a low on-resistance as the semiconductor switch, and in this case, it is possible to realize conduction / cutoff control with low power.
[0008]
In particular, the voltage / current converting means includes a voltage drop measuring means for measuring a voltage across the semiconductor switch, a temperature measuring means for measuring the temperature of the semiconductor switch, and a voltage measured by the voltage drop measuring means is converted into a current value. Storage means for storing a conversion coefficient for performing the voltage drop measurement means using the conversion coefficient stored in the storage means according to the temperature of the semiconductor switch measured by the temperature measurement means. Since it is constituted by an arithmetic circuit that converts it into a current value, it is possible to easily convert a voltage drop generated in the semiconductor switch into a current value of a battery current.
[0009]
A preferred embodiment of the present invention, as the semiconductor switch, using a first semiconductor switch for controlling the charging of the secondary battery, and a second semiconductor switch for controlling the discharge of the secondary battery, in the voltage drop measurement unit It is configured to measure the voltage across the first or second semiconductor switches. That is, the first and second semiconductor switches that control charging and discharging of the secondary battery are used as current detection elements.
[0010]
Further, a characteristic correction for correcting the temperature characteristic of the conversion coefficient stored in the storage means according to the temperature of the semiconductor switch detected when charging the secondary battery at a constant current and the voltage across the semiconductor switch. Since the means is provided, even if the on-resistance of the semiconductor switch changes depending on the temperature, the battery current can be accurately measured by correcting the conversion coefficient in accordance with the temperature.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below in detail with reference to the drawings.
FIG. 1 is a schematic configuration diagram of a battery current measuring circuit for a secondary battery according to an embodiment of the present invention.
In FIG. 1, 11 is a positive power supply terminal of the battery pack 6 provided with the secondary battery B11, and 12 is its negative power supply terminal. The pair of power supply terminals 11 and 12 are connected to an electronic device (not shown). The secondary battery B11 is formed by, for example, connecting a plurality of secondary battery cells B11a to B11d in series, and charging / discharging is performed via the pair of power supply terminals 11 and 12. In the charge / discharge path of the secondary battery B11, in particular, between the positive electrode B11p of the secondary battery B11 and the positive power supply terminal 11, the first and second field effect transistors Tr12 that control the charge / discharge are provided. , Tr11 are inserted in series.
[0012]
Each of the field effect transistors Tr11 and Tr12 is a P-channel type, and is provided in series with the drains D1 and D2 connected to each other. Thus, the first field effect transistor Tr11 in which the source S1 is connected to the positive power supply terminal 11 functions as a switching element that controls the charging of the secondary battery B11, and the source S2 is connected to the secondary battery B11. The second field effect transistor Tr12 connected to the plus electrode B11p functions as a switch element that controls the discharge of the secondary battery B11.
[0013]
These first and second field effect transistors Tr11 and Tr12 detect the battery voltage of each of the secondary battery cells B11a to B11d to detect the overcharge and overdischarge of the secondary battery B11. Are received and controlled by the gates G1 and G2, respectively. Specifically, at the time of charging / discharging of the secondary battery B11, the field effect transistors Tr11 and Tr12 are both set to a conductive state. When the secondary battery B11 is charged, when the overcharge is detected by the protection circuit 14, the protection circuit 14 controls the cutoff of the first field effect transistor Tr11 and stops the charging. Further, when the secondary battery B11 is discharged, when the terminal voltage of the secondary battery cells B11a to B11d drops to a preset monitoring voltage (discharge prohibition voltage), the protection circuit 14 detects this and detects the second voltage. The field effect transistor Tr12 is controlled to be cut off to stop the discharge.
[0014]
Basically, as described above, the first field-effect transistor Tr11 that controls the charging of the secondary battery B11 and the second field-effect transistor Tr12 that controls the discharging of the secondary battery B11 in the charging / discharging path of the secondary battery B11. The battery current measuring circuit included in the battery pack 6 including the above is characterized in that the first and second field effect transistors Tr11 and Tr12 are used for measuring the charging / discharging current of the secondary battery B11 as they are. It is in the point used as an element of current detection.
[0015]
That is, this battery current measuring circuit detects a voltage drop generated between both ends of the first and second field effect transistors Tr11 and Tr12 connected in series, which is a switching element for controlling charging / discharging of the secondary battery B11. And a microcontroller (voltage / current conversion means) 15 for obtaining a charge / discharge current of the secondary battery B11 from a voltage drop detected by the differential amplifier 13.
[0016]
The microcontroller 15 includes a first analog / digital converter (abbreviated as AD converter) 16 for digitally converting the voltage drop detected by the differential amplifier 13 and an electric field detected by the temperature sensor 21. A third AD converter 18 that digitally converts the case temperature of the effect transistors Tr11 and 12 and a second AD converter 17 that digitally converts the battery voltage (on the positive electrode B11p side) of the secondary battery B11 are provided. Further, the microcontroller 15 converts the voltage drop generated between the both ends of the first and second field effect transistors Tr11 and Tr12 into the charge / discharge current of the secondary battery B11, specifically, the first and Based on the storage circuit 19 that stores the characteristics of the second field effect transistors Tr11 and Tr12 and the conversion coefficient stored in the storage circuit 19, the charging (charging voltage) of the secondary battery B11 is obtained from the output (voltage drop) of the AD converter 16. And an arithmetic circuit 20 for calculating a discharge current. The information on the charging / discharging current of the secondary battery B11 obtained by the arithmetic circuit 20 is transmitted via the communication port 20c, and the charge amount and battery voltage of the secondary battery B11, which will be described later, and further the state of charge / discharge The information is output to an electronic device (not shown) together with information.
[0017]
Here, the differential amplifier 13, the protection circuit 14, the microcontroller 15 and the temperature sensor 21 are configured to operate by being driven by an independent power source Vcc, respectively, but receive power supply from the secondary battery B11. It can also be configured to operate.
Next, the operation and action of the battery current measuring circuit configured as described above will be described.
[0018]
The secondary battery B11 is charged by supplying electric power from an external power supply device (not shown) through the pair of power supply terminals 11 and 12 described above, and the secondary battery B11 is discharged by the pair of power supply terminals 11 and 12. This is done by supplying power to an external electronic device (not shown). The charge / discharge current Idc at that time flows through the first and second field effect transistors Tr11 and Tr12. At this time, since the field effect transistors Tr11 and Tr12 connected in series have at least an on-resistance Rds, a voltage drop due to the charge / discharge current Idc occurs between both ends of the field effect transistors Tr11 and Tr12. However, the direction in which the current Idc flows is opposite between charging and discharging, and therefore the polarity of the voltage drop is also different. The differential amplifier 13 detects a voltage drop Vdc generated between both ends of the field effect transistors Tr11 and Tr12 due to the charging current Idc, and the detected voltage value Vdc is the first AD as described above. The signal is given to the arithmetic circuit 20 via the converter 16.
[0019]
Note that the gain and DC offset of the differential amplifier 13 are set so that the output voltage range thereof matches the analog input voltage range of the first AD converter 16. Regarding DC offset, in order to detect the voltage drop at the time of charging and discharging, respectively, the output voltage is set so that the output voltage becomes the middle point potential within the output voltage range when the voltage drop is zero (0). Is done. The gain of the differential amplifier 13 may be set according to the maximum voltage drop determined by the on-resistance of the field effect transistors Tr11 and Tr12 and the maximum value of the charge / discharge current and the analog input voltage range of the AD converter 16. .
[0020]
By the way, in order to obtain the charge / discharge current Idc from the voltage drop Vdc measured as described above, it is necessary to know the on-resistances of the field effect transistors Tr11 and Tr12.
Incidentally, the on-resistance Rds of the field effect transistor changes depending on the case temperature Tc of the field effect transistor. The on-resistance Rds of the field effect transistor is the reciprocal of its mutual conductance, and therefore depends on the gate-source potential difference Vgs of the field effect transistor. The on-resistance Rds of the field-effect transistor is substantially independent of the case temperature Tc and hardly depends on the drain current Id as illustrated in FIG. 2 when the gate-source potential difference Vgs is constant. It shows a linear change (the drain current Id is equal to the charge / discharge current Idc). Therefore, if the gate-source potential difference Vgs of the field effect transistor and its case temperature Tc are clear, the on-resistance Rds is obtained from the relationship between the gate-source potential difference Vgs of the field effect transistor and the case temperature Tc. It becomes possible.
[0021]
For example, a thermistor may be used as the temperature sensor 21 that detects the case temperature of the field effect transistors Tr11 and Tr12.
Further, regarding the gate-source potential difference Vgs of the field effect transistors Tr11 and Tr12, these field effect transistors Tr11 and Tr12 are of P-channel type, and the gates G1 and G2 have a negative potential with respect to the sources S1 and S2. In general, a ground potential is applied to cause conduction, so that the voltage applied to the sources S1 and S2 may be detected as the source-gate voltage Vgs. Here, the source S2 is connected to the positive electrode B11p of the secondary battery, and the voltage drop between the sources S1 and S2 is extremely smaller than the secondary battery voltage Vb. It may be regarded as the inter-voltage Vgs.
[0022]
At this time, since the two field effect transistors Tr11 and Tr12 are both conductive and have the same characteristics, it is considered that a voltage drop of (Vdc / 2) occurs for each field effect transistor. You can do that.
Accordingly, the storage circuit 19 stores in advance the operation characteristics including the above-described change characteristic of the on-resistance Rds with respect to the case temperature Tc of the field effect transistors Tr11 and Tr12, using the case temperature Tc and the gate-source potential difference Vgs as parameters. Has been. Therefore, the arithmetic circuit 20 determines the positive electrode voltage of the secondary battery B11 obtained through the second AD converter 17 and the field effect transistors Tr11 and Tr12 obtained through the third AD converter 18. The memory circuit 19 is searched according to the case temperature Tc, and the on-resistance Rds corresponding to the case temperature Tc and the gate-source potential difference Vgs is obtained from the memory circuit 19.
[0023]
Then, the on-resistance Rds is used as a conversion coefficient, and the secondary current flowing through the field effect transistors Tr11 and Tr12 from the voltage (voltage drop) Vdc across the field effect transistors Tr11 and Tr12 obtained via the AD converter 16 is obtained. The charge / discharge current Idc of the battery B11 is Idc = Vdc / (2 × Rds)
Is to be calculated as
[0024]
In the arithmetic circuit 20, the charging current Idc obtained as described above may be integrated over a predetermined period T to obtain the charge / discharge amount of the secondary battery B11.
By the way, in order to further improve the current measurement accuracy, the following may be performed. That is, in this case, the secondary battery B11 is charged with a constant current (for example, 1.0 A) from the external power source (not shown) through the first and second field transistors Tr11 and Tr12, and the voltage drop Vdc at this time is charged. And the case temperature Tc are measured to correct the characteristic stored in the storage circuit 19 as described above (the change characteristic of the on-resistance Rds with respect to the case temperature Tc). That is, in this case, since the current value itself flowing through the first and second field transistors Tr11 and Tr12 is known, the on-resistance Rds of the field transistors Tr11 and Tr12 is determined from the voltage drop Vdc and the case temperature Tc at that time. Can be calculated backwards. Therefore, if the characteristic stored in the memory circuit 19 is corrected using the on-resistance Rds of the field transistors Tr11 and Tr12 obtained by back calculation, the charging of the secondary battery B11 is performed using the corrected characteristic as described above. It becomes possible to obtain the charging / discharging current at the time of discharging with higher accuracy.
[0025]
Further, the correction of the on-resistance Rds with respect to the case temperature Tc by the above-described constant current charging is performed as two points of correction for one constant current (for example, 1.0 A) and another constant current (for example, 2.0 A). Also good. By performing the correction with the two charging currents, the offset of the differential amplifier 13 and the first AD converter 16 can be easily corrected.
Thus, according to the battery current measuring circuit configured as described above, it is generated between both ends of the field effect transistors Tr11 and Tr12 inserted in series in the charge / discharge path in order to control the charge / discharge of the secondary battery B11. By measuring the voltage drop Vdc, the field effect transistors Tr11 and Tr12 can be effectively used as current measurement elements, and the charge / discharge current of the secondary battery B11 can be measured. In addition, the electric field effect transistors Tr11 and Tr12 stored in the memory circuit 19 and the on-resistance Rds of the field effect transistors Tr11 and Tr12 obtained from the case temperature Tc and the gate-source potential difference Vgs are used as the conversion coefficient to convert the electric field. Since the charge / discharge current Idc is obtained from the voltage Vdc across the effect transistors Tr11 and Tr12, current measurement can be performed easily and with high accuracy. In particular, since it is not necessary to insert a current measuring resistor in the charging / discharging path of the secondary battery B11 as in the prior art, it is possible to suppress generation of a useless voltage drop, and the voltage that can be supplied by the secondary battery B11. Can be effectively utilized, and a great effect can be obtained in practical use, such as extending its operating life.
[0026]
The present invention is not limited to the embodiment described above. For example, in the embodiment, the charge / discharge current of the two field effect transistors connected in series is measured from the voltage drop across the transistors Tr11 and Tr12, but the charge / discharge current is measured from the voltage drop of one of the field effect transistors. Anyway. Further, here, the charge / discharge circuit that controls the charging and discharging of the secondary battery B11 using the two field effect transistors Tr11 and Tr12 is described as an example, but the charging of the secondary battery B11 by one field effect transistor is described. Alternatively, the present invention can be similarly applied to a charge / discharge circuit configured to control discharge. Further, in the embodiment, the case where the charge / discharge current of the secondary battery B11 is measured has been described, but it is needless to say that the present invention can also be applied to the case where the discharge current of the primary battery is measured.
[0027]
Furthermore, the present invention can be similarly applied to the case where the above-described switch elements (field effect transistors Tr11, Tr12) are inserted in series on the negative electrode side of the secondary battery B11, and an N-channel field effect transistor is used as the switch element. May be. Further, it is not always necessary to use the two field effect transistors Tr11 and Tr12 having the same characteristics. However, in this case, it is necessary to store the characteristics of the field effect transistors Tr11 and Tr12 in the storage circuit 19, respectively. In addition, the present invention can be variously modified and implemented without departing from the scope of the invention.
[0028]
【The invention's effect】
As described above, according to the battery current measuring circuit of the present invention, the charge / discharge current of the battery is measured from the voltage drop in the semiconductor switch that controls the charge and / or discharge of the battery. A voltage drop due to current detection can be suppressed without the need for a voltage detector. Therefore, it is possible to obtain an effect that the electronic device can be operated for a long time by the battery.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of a battery current measuring circuit according to an embodiment of the present invention.
FIG. 2 is a change characteristic diagram of an on-resistance Rds with respect to a case temperature Tc of a field effect transistor.
[Explanation of symbols]
B11 Secondary battery Tr11, Tr12 Field effect transistor (semiconductor switch)
13 differential amplifier 14 protection circuit 16 first AD converter 17 second AD converter 18 third AD converter 19 storage circuit 20 arithmetic circuit 21 temperature sensor

Claims (3)

A semiconductor switch connected in series to one electrode of the secondary battery on-off control the charging and discharging currents of the secondary battery, the charging from the voltage drop generated across the semiconductor switching element of the secondary battery Voltage / current pressure conversion means for obtaining current and / or discharge current ,
The voltage / current pressure converting means includes a voltage drop measuring means for measuring a voltage across the semiconductor switch, a temperature measuring means for measuring the temperature of the semiconductor switch, and a voltage measured by the voltage drop measuring means as a current value. Storage means storing a temperature characteristic indicating a relationship between a conversion coefficient for conversion and the temperature of the semiconductor switch, and a conversion coefficient obtained from the storage means according to the temperature of the semiconductor switch measured by the temperature measurement means Using an arithmetic circuit that converts the voltage measured by the voltage drop measuring means into a current value,
Further, characteristic correction means for correcting the temperature characteristic of the conversion coefficient stored in the storage means according to the temperature of the semiconductor switch detected when charging the secondary battery with a constant current and the voltage across the semiconductor switch.
Battery current measuring circuit, characterized in that it comprises a.   The battery current measuring circuit according to claim 1, wherein the semiconductor switch includes a field effect transistor. The semiconductor switch comprises a first semiconductor switch that controls charging of the secondary battery, and a second semiconductor switch that controls discharging of the secondary battery,
The battery current measuring circuit according to claim 1 , wherein the voltage drop measuring means measures a voltage across the first or second semiconductor switch.

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