JP2014163809A - Current detection circuit and charging/discharging circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current detection circuit capable of performing stable current detection for performing charging/discharging control by correcting the voltage fluctuation of a rectifying element due to temperature change and a charging/discharging circuit.SOLUTION: A current detection circuit includes: an FET 15 as current control means which performs the ON/OFF operation of currents flowing through a circuit; voltage detection means constituted by a rectifying element D1 which detects a voltage to be generated in the FET during the ON operation of the FET 15 and a resistor R1 as a current adjustment element; voltage amplification means for amplifying the voltage from the voltage detection means; and output means constituted by resistors R2 and R3 for outputting the voltage amplified by the voltage amplification means to a control part which controls the FET 15 and a rectifying element D2. The rectifying elements D1 and D2 of the voltage detection means and the output means have voltage change characteristics with which a voltage changes in accordance with the size of currents and the change of temperature, and currents flowing through the rectifying elements are set by the resistance of the voltage detection means and output means such that the rate of the voltage fluctuation of the rectifying elements D2 and D1 due to the change of temperature becomes predetermined times determined by the gain of the voltage amplification means.

Description

  The present invention relates to a current detection circuit and a charge / discharge circuit, and in particular, a current detection circuit capable of detecting a current flowing in a circuit for performing charge / discharge control of a battery or the like without being affected by temperature, and The present invention relates to a charge / discharge circuit.

  A charging / discharging circuit that controls charging and discharging of a battery or the like detects current flowing through the battery and the load, and controls charging / discharging based on the detected current. Conventionally, a current flowing through a load or the like is measured from a voltage value generated by a current flowing through the shunt resistor by inserting a shunt resistor into the circuit. However, since power is consumed by the shunt resistor in this case, there is a problem that power efficiency is lost and the shunt resistor generates heat. For example, Patent Literature 1 and Patent Literature 2 disclose a charge / discharge circuit that detects a current flowing through a circuit from a voltage value of an FET (Field Effect Transistor) that controls an output current without using a shunt resistor.

  According to FIG. 1 of Patent Document 1, a charging switch circuit 39 that controls charging composed of a sense FET 29 and a power FET 30 connected in parallel and a discharging switch circuit that controls discharging composed of a sense FET 27 and a power FET 28 connected in parallel. 38, and sense resistors 19 and 20 for detecting a current value are connected in series to the drain sides of the sense FETs 27 and 29, respectively. The voltages at both ends of the resistor and both ends of the sense FETs 27 and 29 are measured, and the measured voltages are subjected to arithmetic processing to detect the charge / discharge current.

  Further, according to FIG. 1 of Patent Document 2, the overcurrent protection circuit includes first and second reference FETs Q3 and Q4 having the same temperature characteristics and source-gate voltage characteristics as the charge FET Q1 and the discharge FET Q2, respectively. It consists of an overvoltage detection comparator. The first and second reference FETs Q3 and Q4 are supplied with current from a reference current circuit. The on-resistances Ron1, Ron2 of the charge FET Q1 and the discharge FET Q2 and the on-resistances Ron3, Ron4 of the first and second reference FETs Q3, Q4 have a relationship of (Ron3 + Ron4) ÷ (Ron1 + Ron2) = K (constant).

  The voltage between the sources of the charge FET Q1 and the discharge FET Q2 is input to one input terminal of the overvoltage detection comparator, and the voltage between the sources of the first reference FET Q3 and the second reference FET Q4 is input to the other input terminal. Entered. When the voltage between the sources of the charge FET Q1 and the discharge FET Q2 becomes larger than the voltage between the sources of the first reference FET Q3 and the second reference FET Q4, the overvoltage detection comparator detects the overcurrent state as an overcurrent state. The discharge FET Q2 is turned off to protect the secondary battery from overcurrent. Further, since the FETs Q1, Q2, Q3, and Q4 have the same temperature characteristics, it is possible to detect an overcurrent state without being affected by a temperature change.

JP 2007-195351 A JP 2009-1331020 A

  For example, as disclosed in Patent Document 2, detection of a current flowing through a load in charge / discharge control is performed by detecting a voltage value generated in an FET that controls an output current.

  In this case, the voltage at the drain of the FET is input to a device such as an operational amplifier (operational amplifier). For example, when the FET is in an OFF state, the voltage at the drain of the FET may become a high voltage. For this reason, in order to avoid the input of a high voltage from the FET, it is necessary to provide a protection circuit using a diode at the input of a device such as an operational amplifier. FIG. 6 is a diagram showing a configuration of a conventional discharge circuit having a current detection circuit provided with a protection circuit using a diode. FIG. 6 shows a discharge circuit that supplies power from the battery to the load and controls the discharge of the battery to the load. As shown in FIG. 6, the conventional discharge circuit 30 includes a current detection unit 31 that detects a current flowing from the battery 20 to the load 21, a discharge control unit 12 that controls a current flowing through the load 21, and one of the batteries 20. The FET 15 is inserted between one terminal of the terminal and the load 21 and performs ON / OFF operation of current. The battery 20 is connected to the discharge circuit 30 via terminals T1 and T2 and supplies power, and the discharge circuit 30 supplies power to the load via terminals T3 and T4.

  The current detection circuit 31 as the current detection unit 31 includes an operational amplifier 8, resistors R1, R2, R3, and a diode D1. One end of the resistor R1 of the current detection circuit 31 is connected to the reference voltage source, and the other end is connected to the non-inverting input (+) terminal of the operational amplifier 8 and the anode side of the diode D1. Further, the cathode side of the diode D1 and the drain of the FET 15 are connected. The resistor R2 and the resistor R3 connected in series are connected to the output terminal of the operational amplifier 8. Furthermore, the connection point of the inverting input (−) terminal of the operational amplifier 8 and the resistors R2 and R3 is connected. Thus, the operational amplifier 8 of the current detection circuit 31 forms a non-inverting amplifier circuit. The resistance value of the resistor R2 is R2, and the resistance value of the resistor R3 is R3.

  The current detection circuit 31 having these configurations is G = 1 + (R3 / R2), where G is the gain of the operational amplifier 8. Further, the voltage across the FET 15 (the voltage between the drain and the source) when the FET 15 is ON is Vdf, and the voltage across the diode D1 is Vd1.

  When the output voltage of the operational amplifier 8 is Vo, Vo = G × (Vdf + Vd1). That is, the input voltage (Vdf + Vd1) of the operational amplifier 8 is multiplied by G and output. When the temperature changes in this state, the diode has a voltage change characteristic depending on the temperature, so that the voltage between the anode and the cathode in the forward direction changes. When the voltage across the diode D1 changes by ΔVd1 due to the temperature change, if the output voltage of the operational amplifier 8 at this time is Vo ′, then Vo ′ = G × (Vdf + (Vd1 + ΔVd1)). For this reason, the fluctuation (Vo'-Vo) of the output voltage of the operational amplifier 8 due to the temperature change becomes Vo'-Vo = G * [Delta] Vd1, and the voltage change [Delta] Vd1 due to the diode D1 is multiplied by G times.

  For this reason, when the temperature changes, even if the voltage value of the FET 15 that detects the current flowing through the circuit is the same, the voltage across the diode D1 changes depending on the temperature. It will fluctuate. In particular, when the device uses an amplifier circuit using an operational amplifier, the fluctuation amount of the input voltage value is multiplied by the gain by the operational amplifier, and the voltage fluctuation value multiplied by the gain is output. For this reason, the accuracy of detection of the current flowing through the circuit is lowered due to the voltage fluctuation of the diode D1 due to temperature.

  FIG. 7 is a graph showing changes in the voltage output from the operational amplifier with respect to the current flowing through the FET shown in FIG. 6 in each temperature state of the diode D1. The temperature state of the diode D1 is high temperature, normal temperature, and low temperature. The FET current is calculated from the measured voltage with the resistance value between the drain and the source when the FET 15 is ON being constant.

  As shown in FIG. 7, the change in voltage with respect to the FET current when the diode D1 is at a high temperature has a small rate of change in voltage even when the FET current increases. On the other hand, the change in voltage with respect to the FET current when the diode D1 is at a low temperature has a large rate of change in voltage as the FET current increases. Further, the voltage with respect to the FET current when the diode D1 is in the normal temperature state is approximately an intermediate value between the high temperature and the low temperature. For this reason, the voltage output from the operational amplifier 8 fluctuates even if the current flowing through the FET 15 is the same value in each temperature state of the diode D1.

  For this reason, it is necessary to correct the output voltage of the operational amplifier in order to eliminate the fluctuation of the voltage output from the operational amplifier in each temperature state of the diode D1.

  For example, when the voltage fluctuation output from the operational amplifier 8 is corrected by a microcomputer, a circuit for detecting the temperature of the diode D1 is required. FIG. 8 is a diagram showing a configuration of a discharge circuit in which a temperature detection unit for detecting the temperature of the diode D1 is provided in the discharge circuit shown in FIG. Note that the same components as those of the discharge circuit including the current detection circuit shown in FIG. 6 are denoted by the same reference numerals, and detailed description thereof is omitted.

  As shown in FIG. 8, the temperature detection unit 37 of the discharge circuit 35 includes a temperature measurement sensor and outputs a signal to the discharge control unit 36. The discharge controller 36 can detect the temperature by a signal from a temperature measurement sensor. Further, the discharge control unit 36 has a built-in microcomputer.

  In the memory of the microcomputer, a data table or the like for correcting the change in voltage of the diode with respect to the detected temperature is prepared in advance. The data table is configured to correct the detected temperature so as to correspond to the voltage change of the diode at room temperature. The microcomputer of the discharge controller 36 converts the measured temperature and the output voltage of the operational amplifier 8 into an output voltage at normal temperature by referring to the data table and corrects it.

  As a result, the magnitude of the current flowing through the FET 15 is converted into a voltage at normal temperature, and thus is not affected by voltage fluctuation due to the temperature of the diode. However, since the output voltage is corrected to the normal temperature voltage, the output voltage at the maximum current (Imax) of the FET current does not reach the maximum measurable voltage (Vmax) as shown in FIG. The voltage becomes a measurement voltage range by temperature correction shown in FIG. For this reason, the resolution of the measured current value is lowered, and the measurement accuracy is lowered.

  In addition, the charge / discharge circuit 35 provided with the temperature detection unit 37 increases the number of parts, and the discharge control unit 36 requires a microcomputer for performing arithmetic processing, and the circuit configuration is complicated. In addition, a data table for correcting a voltage change with respect to the detected temperature by a microcomputer is required. In particular, since a diode has nonlinear characteristics, it takes time to create a data table. Further, when a rectifying element other than a diode is used in the protection circuit of the current detection circuit 31, it is necessary to create a data table that matches the characteristics of the used rectifying element.

  Therefore, the present invention provides a current detection circuit and a charge / discharge circuit that can correct voltage fluctuations of the rectifying element due to temperature change and thereby stably perform current detection for charge / discharge control. The purpose is to do.

  To achieve the above object, a current detection circuit according to the present invention is a current detection circuit that detects a current flowing through a circuit by converting the current into a voltage, and includes a current control unit that performs an ON / OFF operation of the current flowing through the circuit, A voltage detection means for detecting a voltage generated in the current control means when the current control means is ON; a voltage amplification means for amplifying the voltage from the voltage detection means; and a voltage amplified by the voltage amplification means Output means for outputting to a control unit for controlling the control means, the voltage detecting means has a rectifying element and a current adjusting element, and the output means includes a resistor and the same rectifying element as the voltage detecting means. The voltage detecting means and the rectifying element of the output means have voltage change characteristics depending on current and temperature, and a ratio of voltage fluctuations of the output means and the rectifying element of the voltage detecting means due to temperature change is Above The current flowing through the rectifying element of the voltage detecting means and the output means is set by the current adjusting element of the voltage detecting means and the resistance of the output means so as to be a constant multiple determined by the gain (gain) of the pressure amplifying means. It is characterized by that.

  In the current detection circuit of the present invention, the rectifying element of the voltage detection means protects the voltage amplification means so that an excessive voltage from the current control means is not input.

  The rectifying element of the current detection circuit of the present invention is any one of a diode, a transistor, a thyristor, or a solar cell.

  The voltage amplifying means of the current detection circuit of the present invention comprises an operational amplifier, the current control means comprises an FET, and the voltage detection means comprises a resistor R1 having a resistance value R1 and a diode D1 as a rectifying element, One end of the resistor R1 is connected to the reference voltage source, the other end is connected to the non-inverting input (+) terminal of the operational amplifier and the anode side of the diode D1, and the cathode side of the diode D1 and the drain of the FET are connected. The output means includes a resistor R2 having a resistance value R2, a resistor R3 having a resistance value R3, and a diode D2 as a rectifying element. The output terminal of the operational amplifier has the resistor R2 connected in series with the output means and the resistor R2 A resistor R3 and the diode D2 are connected in order, and the inverting input (−) terminal of the operational amplifier is connected to the resistor R2 and the resistor R3. And the voltage variation value ΔVd2 due to the temperature of the diode D2 is 1+ (resistance value R2 / resistance value R3) times the voltage variation value ΔVd1 due to the temperature of the diode D1. The magnitude of the current flowing through the diode D1 is set by the resistor R1 of the voltage detecting means, and the magnitude of the current flowing through the diode D2 of the output means is set by the resistors R2 and R3 of the output means. It is characterized by.

  The charging / discharging circuit of the present invention is a charging / discharging circuit that performs charging and / or discharging, a current detecting circuit that detects a current for controlling charging and / or discharging, and a current detecting circuit from the current detecting circuit. A charge / discharge control circuit that controls charging and / or discharging according to a signal, wherein the current detection circuit performs an ON / OFF operation of a current flowing in the charging / discharging circuit; and the current control unit performs an ON operation. Voltage detecting means for detecting the voltage generated in the current control means at the time, voltage amplifying means for amplifying the voltage from the voltage detecting means, and control for controlling the current control means with the voltage amplified by the voltage amplifying means Output means for outputting to the unit, the voltage detection means has a rectifier element and a current adjustment element, the output means has a resistor and a rectifier element, and the voltage detection means and the output means Rectifier element It has a voltage change characteristic depending on the current and temperature, and the ratio of the voltage fluctuation of the rectifying element of the output means and the voltage detection means due to the temperature change is a fixed multiple determined by the gain of the voltage amplification means. The current flowing through the rectifying element of the voltage detecting means and the output means is set by the current adjusting element of the voltage detecting means and the resistance of the output means.

  According to the present invention, by using a rectifying element such as a diode having a voltage change characteristic in which a voltage changes depending on the magnitude of the current and the temperature, the voltage fluctuation of the rectifying element due to a temperature change can be corrected. Thereby, the current detection for performing charge / discharge control can be performed stably.

  Further, the output current value can be easily obtained with high accuracy with respect to the temperature change without narrowing the range in which the current detection is measured as a voltage.

  Further, the rectifying element constituting the voltage detecting means for detecting the voltage generated in the FET as the current control means and the rectifying element constituting the output means for outputting the voltage of the voltage amplifying means to the control unit have the same characteristics. Can be used. For this reason, the circuit configuration can be simplified. For example, since the diode has non-linear characteristics, the diode D2 having the same characteristic as the output means can be used for the diode D1 of the voltage detecting means.

  Further, since the current flowing through the load or the like is detected by the FET that controls the ON / OFF of the current, a current detection circuit such as a shunt resistor becomes unnecessary.

It is a figure which shows the structure of the charging / discharging circuit containing the current detection circuit which concerns on this invention. It is a figure which shows the structure of the discharge circuit and current detection circuit of the charging / discharging circuit shown in FIG. It is the figure which comprised the operational amplifier of the current detection circuit by the inverting amplifier circuit. It is a graph which shows the relationship of the voltage change amount of the diodes D1 and D2 with respect to a temperature change, and the voltage change amount of the diode D1 and the diode D2. It is a graph which shows the output voltage of the operational amplifier with respect to FET current in correction | amendment of the voltage fluctuation of the diode by a temperature change. It is a figure which shows the structure of the conventional discharge circuit which has a current detection circuit provided with the protection circuit by a diode. It is a graph which shows the change of the voltage output from the operational amplifier with respect to the electric current which flows into FET in each temperature state of a diode. It is a figure which shows the structure of the discharge circuit which provided the temperature detection part which detects the temperature of a diode in the charging / discharging circuit shown in FIG.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for implementing a current detection circuit and a charge / discharge circuit according to the present invention will be described with reference to the drawings. Note that the current detection circuit and the charge / discharge circuit according to the present invention use a rectifying element such as a diode having a voltage change characteristic in which a voltage changes according to a change in the magnitude of the current and a temperature to detect the current flowing in the load, and the temperature. By correcting the voltage fluctuation of the rectifying element due to the change, the current detection for performing the charge / discharge control is stably performed without being influenced by the temperature.

  FIG. 1 is a diagram showing a configuration of a charge / discharge circuit including a current detection circuit according to the present invention. The same components as those of the discharge circuit having the current detection circuit shown in FIG. 6 will be described using the same reference numerals.

  As shown in FIG. 1, the charging / discharging circuit 1 includes a discharging circuit 2 that supplies power from a battery 20 to a load 21, and a charging circuit 3 that supplies power from an external power supply 22 to the battery 20.

  The discharge circuit 2 includes a current detection unit 6 that detects a current flowing from the battery 20 to the load 21, a discharge control unit 12 that controls a current flowing through the load 21, and one terminal of the load 21 and a negative electrode terminal of the battery 20. And the FET 15 for performing ON / OFF operation of current. The battery 20 is connected to the discharge circuit 2 via terminals T1 and T2 and supplies power, and the discharge circuit 2 supplies power to the load 21 via terminals T3 and T4.

  The charging circuit 3 includes a current detection unit 6 that detects a current flowing from the external power supply 22 that outputs direct current to the battery 20, a charge control unit 13 that controls a current flowing through the battery 20, and a negative terminal of the external power supply 22. And an FET 16 which is inserted between the negative terminals of the battery 20 and performs ON / OFF operation of current. The external power supply 22 is connected to the charging circuit 3 through terminals T5 and T6 to supply power, and the charging circuit 3 supplies power to the battery 20 through terminals T7 and T8 to perform charging.

  As shown in FIG. 1, the discharge circuit 2 and the current detection unit 6 of the charge circuit 3 are the same circuit. Hereinafter, the discharge circuit 2 and the current detection unit 6 of the charge / discharge circuit 1 of FIG. State. FIG. 2 is a diagram showing the configuration of the discharge circuit 2 and the current detection unit 6 of the charge / discharge circuit 1 shown in FIG.

  As shown in FIG. 2, the current detection circuit 6 as the current detection unit 6 includes an operational amplifier 8 as voltage amplification means, and forms a non-inverting amplification circuit. The resistor R1 as a current adjustment element on the non-inverting input (+) terminal side of the operational amplifier 8 has one terminal connected to the reference voltage source, and the other terminal connected to one terminal (anode) of the diode D1. It is connected. The resistor R1 as the current adjusting element adjusts the magnitude of the current flowing through the diode D1, and is not limited to the resistor but may function as a current source such as a transistor. The other terminal (cathode) of the diode D1 is connected to the drain side of the FET 15 as current control means. A current flows through the diode D1 via the resistor R1. The diode D1 serves to prevent a high voltage from the drain when the FET 15 is OFF from being input to the non-inverting input (+) terminal of the operational amplifier 8, and forms a protection circuit. The non-inverting input (+) terminal of the operational amplifier 8 is connected to the connection point between the resistor R1 and the diode D1. Thus, the voltage at the drain terminal of the FET 15 and the voltage generated at the diode D1 are input to the non-inverting input (+) terminal of the operational amplifier 8. The resistor R1 and the diode D1 as the rectifying element constitute voltage detecting means.

  Further, a resistor R2, a resistor R3, and a diode D2 are connected in series to the output terminal of the operational amplifier 8. The cathode side of the diode D2 is connected to GND. The resistor R2, the resistor R3, and the diode D2 as a rectifying element constitute output means. The inverting input (−) terminal of the operational amplifier 8 is connected to a connection point between the resistor R2 and the resistor R3 connected to the output terminal of the operational amplifier 8. The inverting input (−) terminal of the operational amplifier 8 receives a voltage obtained by adding the voltage generated at the resistor R2 due to the voltage at the output terminal of the operational amplifier 8 and the voltage generated at the diode D2. The voltage at the output terminal of the operational amplifier 8 is input to the discharge controller 12.

  The both-end voltage of the FET 15 in the ON state is a voltage proportional to the current flowing through the FET 15, that is, the current flowing through the load 21. This is because the FET 15 in the ON state has a constant drain-source resistance value, and the voltage across the FET 15 becomes a voltage proportional to the magnitude of the current flowing through the load 21.

  As described above, in the current detection circuit 6, the voltage across the FET 15 is input to the operational amplifier 8 and amplified, and the operational amplifier 8 outputs a voltage having a magnitude proportional to the current flowing through the load 21. For this reason, the current flowing through the load 21 can be detected from the output voltage value of the operational amplifier 8.

  In the current detection circuit shown in FIG. 2, the operational amplifier constitutes a non-inverting amplifier circuit, but the operational amplifier of the current detection circuit can also be constituted by an inverting amplifier circuit. FIG. 3 is a diagram in which the operational amplifier of the current detection circuit is configured by an inverting amplifier circuit. As shown in FIG. 3, the operational amplifier 8 of the current detection circuit 25 forms an inverting amplifier circuit. The resistor R1 as a current adjustment element on the non-inverting input (+) terminal side of the operational amplifier 8 has one terminal connected to the reference voltage source, and the other terminal connected to one terminal (anode) of the diode D1. It is connected. The resistor R1 as the current adjusting element adjusts the magnitude of the current flowing through the diode D1, and is not limited to the resistor but may function as a current source such as a transistor. The other terminal (cathode) of the diode D1 is connected to GND. A current flows through the diode D1 via the resistor R1. The non-inverting input (+) terminal of the operational amplifier 8 is connected to the connection point between the resistor R1 and the diode D1.

  On the other hand, a resistor R2, a resistor R3, and a diode D2 are connected in series to the output terminal of the operational amplifier 8. The cathode side of the diode D2 is connected to the drain side of the FET 15 as current control means. The inverting input (−) terminal of the operational amplifier 8 is connected to a connection point between the resistor R2 and the resistor R3 connected to the output terminal of the operational amplifier 8. The inverting input (−) terminal of the operational amplifier 8 receives a voltage obtained by adding the voltage generated at the resistor R3 due to the voltage at the output terminal of the operational amplifier 8, the voltage generated at the diode D2, and the voltage at the drain terminal of the FET 15. The voltage at the output terminal of the operational amplifier 8 is input to the discharge controller 12.

  The discharge controller 12 shown in FIGS. 1, 2, and 3 is a circuit that controls the discharge current that flows from the battery 20 to the load 21, and controls the FET 15 based on the signal from the current detector 6 for discharge. That is, the discharge controller 12 controls the ON / OFF state of the FET 15 from the output voltage of the operational amplifier 8. For example, control is performed so that the current flowing through the load 21 is kept constant. In addition, the discharge control unit 12 controls the FET 15 to be in an OFF state when the current value of the load 21 is excessively large or when the current value becomes excessive due to a short circuit.

  On the other hand, the charging control unit 13 of the charging circuit 3 shown in FIG. 1 is a circuit that controls the charging current that flows from the external power source 22 to the battery 20, and controls the FET 16 based on the signal from the charging current detection unit 6. . That is, the charging control unit 13 controls the ON / OFF state of the FET 16 from the output voltage of the operational amplifier 8. For example, control is performed so that the current flowing through the battery 20 is kept constant. In addition, the charge control unit 13 controls the FET 16 to be in an OFF state when the current value to the battery 20 is excessively large due to a decrease in current or an excessive current value due to a short circuit. When the current for charging the battery 20 becomes less than a predetermined value, the FET 16 is turned off to stop the charging of the battery 20.

  A circuit setting for correcting voltage fluctuation of the rectifying element due to temperature change by the current detection circuit according to the present invention will be described below with reference to FIG.

  The resistance value of the resistor R1 is R1, the resistance value of the resistor R2 is R2, and the resistance value of the resistor R3 is R3. Further, the voltage across the diode D1 is Vd1 (shown by an arrow in FIG. 2), the voltage across the diode D2 is Vd2 (shown by an arrow in FIG. 2), and the voltage across the FET 15 (drain-source voltage) is Vdf (FIG. 2). Is indicated by an arrow).

Assuming that the gain of the operational amplifier 8 shown in FIG. 2 is G = 1 + (R3 / R2) and the voltages of the diodes D1 and D2 do not vary depending on the temperature, the output voltage Vo of the operational amplifier 8 is expressed by Expression (1).
Vo = G × (Vdf + Vd1−Vd2) + Vd2 (1)
Next, assuming that the voltage of the diode D1 changes by ΔVd1 and the voltage of the diode D1 changes by ΔVd2 due to temperature, the output voltage Vo ′ of the operational amplifier 8 is expressed by Expression (2).
Vo ′ = G × {Vdf + (Vd1 + ΔVd1) − (Vd2 + ΔVd2)} + (Vd2 + ΔVd2) (2)
The fluctuation amount (Vo′−Vo) of the output voltage of the operational amplifier 8 due to the temperature change is expressed by Expression (3).
Vo′−Vo = G × (ΔVd1−ΔVd2) + ΔVd2 (3)
In the equation (3), when ΔVd1 = ΔVd2, the output voltage fluctuation amount is ΔVd2.

For this reason, in order to set the variation amount of the output voltage to Vo′−Vo = 0, the following expression must be established from the expression (3). A relational expression between ΔVd1 and ΔVd2 when Vo′−Vo = 0 is expressed by Expression (4).
ΔVd2 = {G / (G−1)} × ΔVd1 (4)
However, G / (G-1) = 1 + (R2 / R3)
Therefore, when the voltage fluctuation value ΔVd2 due to the temperature of the diode D2 is 1+ (R2 / R3) times the voltage fluctuation value ΔVd1 due to the temperature of the diode D1 from the equation (4), Vo′−Vo = 0, that is, depending on the temperature. The output voltage does not fluctuate and is not affected by temperature changes.

  In addition, the temperature-voltage characteristics of the diode vary depending on the value of the current flowing through the diode. That is, when the current flowing through the diode is small, the voltage change with respect to temperature increases, and when the current flowing through the diode is large, the voltage change with temperature decreases. Using this diode characteristic, a current that flows so that the temperature-voltage characteristic is 1+ (R2 / R3) times that of the diode D1 is set in the diode D2.

  As described above, when the operational amplifier shown in FIG. 2 is a non-inverting amplifier, the voltage fluctuation value ΔVd2 due to the temperature of the diode D2 is 1+ (R2 / R3) times the voltage fluctuation value ΔVd1 due to the temperature of the diode D1. At this time, Vo′−Vo = 0, that is, the output voltage does not fluctuate due to temperature and is not affected by temperature change. In the case where the operational amplifier shown in FIG. 3 is an inverting amplifier, similarly to the case where the operational amplifier is a non-inverting amplifier, the voltage fluctuation value ΔVd2 due to the temperature of the diode D2 is 1+ of the voltage fluctuation value ΔVd1 due to the temperature of the diode D1. When (R2 / R3) times, Vo′−Vo = 0, that is, the output voltage does not fluctuate due to temperature and is not affected by temperature change.

  The setting of the current flowing through the diode will be described below with reference to FIG. FIG. 4 is a graph showing the relationship between the voltage change amount of the diodes D1 and D2 and the voltage change amount of the diode D1 and the diode D2 with respect to the temperature change. As shown in FIG. 4, when the voltage change amount of the diode D1 at the diode temperature Tp1 is ΔVd1, the voltage change of the diode D2 is set so that ΔVd2 becomes ΔVd1 × (1+ (R2 / R3)). A large current is passed through the diode D1 to reduce the voltage change with respect to the temperature, and a small current is passed through the diode D2 to increase the voltage change with respect to the temperature.

  More specifically, the resistance value is determined as follows. Since the temperature-voltage characteristics of the diode vary depending on the value of the current flowing through the diode, the current flowing through the diode D1 is determined by the value of the resistor R1 in the circuit shown in FIG. Further, the current flowing through the diode D2 is determined by the values of the resistors R2 and R3. In order to determine the resistance value, first, a necessary amplification factor of the operational amplifier 8 is determined. The amplification factor of the operational amplifier 8 is determined from the maximum value of the detection voltage of the FET 15, the voltage that can be input to the discharge control unit 12, and the like. The ratio between R2 and R3 is determined from the amplification factor.

  Further, the current values flowing through the diode D2 and the diode D1 are selected so as to satisfy the diode temperature voltage change shown in FIG. The value of R1 is determined from the current value passed through the diode D1, and the values of R2 and R3 are determined from the current value passed through the diode D2.

  FIG. 5 shows the output voltage of the operational amplifier with respect to the FET current in the correction of the voltage fluctuation of the diode due to the temperature change in the current detection circuit according to the present invention described above. 5 indicates the output voltage of the operational amplifier due to the FET current by the current detection circuit illustrated in FIG. 2, and the dotted line illustrated in FIG. 5 indicates the output voltage of the operational amplifier due to the FET current at each temperature illustrated in FIG. As shown in FIG. 5, when the FET current is the maximum value (Imax shown in FIG. 5), the output voltage reaches the maximum voltage that can be measured (Vmax shown in FIG. 5). The resolution is also improved.

  As described above, the current detection circuit of the present invention uses a diode as a rectifying element having a voltage change characteristic depending on current and temperature, and the ratio of the voltage fluctuation due to the temperature change of the diode connected to the input and output of the operational amplifier is high. By setting the current that flows in the diode of the input circuit and output circuit with a resistor so that it becomes a fixed multiple determined by the gain (gain) of the operational amplifier, the detection of the current flowing in the circuit is stabilized without being affected by temperature. Can be done.

  Although the embodiment using a diode as a rectifying element has been described above, the diode is suitable as a rectifying element of a current detection circuit because it is easy to handle and has voltage change characteristics depending on current and temperature. Note that the rectifying element may be a transistor, a thyristor, or a solar cell in addition to the diode. Since the diode has non-linear characteristics, the circuit configuration can be simplified by using the diode D2 having the same characteristics as the diode D1. For example, when a diode D1 is used for the input circuit of the operational amplifier and a transistor is used instead of the diode D2 for the output circuit of the operational amplifier, the characteristics of the transistor are the same as the characteristics of the diode because the characteristics of the diode and the transistor are different. Circuit is required, and the circuit configuration is complicated. For this reason, the same rectifying element is desirable.

  As described above, according to the present invention, by using a rectifying element such as a diode having a characteristic that the voltage changes depending on the magnitude of the current and the temperature, the voltage fluctuation of the rectifying element due to the temperature change is corrected. Accordingly, current detection for performing charge / discharge control can be stably performed.

  Further, the output current value can be easily obtained with high accuracy with respect to the temperature change without narrowing the range in which the current detection is measured as a voltage.

  Further, the rectifying element constituting the voltage detecting means for detecting the voltage generated in the FET as the current control means and the rectifying element constituting the output means for outputting the voltage of the voltage amplifying means to the control unit have the same characteristics. Can be used. For this reason, the circuit configuration can be simplified. For example, since the diode has non-linear characteristics, the diode D2 having the same characteristic as the output means can be used for the diode D1 of the voltage detecting means.

  Further, since the detection of the current flowing through the load (sensor) and the ON / OFF control of the current are performed by the same FET, a current detection circuit such as a shunt resistor becomes unnecessary.

  The present invention can be embodied in many forms without departing from its essential characteristics. Therefore, it is needless to say that the above-described embodiment is exclusively for description and does not limit the present invention.

1 Charging / Discharging Circuit 2, 30, 35 Discharging Circuit 3 Charging Circuit
6, 25, 31 Current detection unit (current detection circuit)
8 Operational amplifier 12, 36 Discharge control unit 13 Charge control unit
15, 16 FET
20 Battery 21 Load 22 External power supply 37 Temperature detection part D1, D2 Diode R1, R2, R3 Resistance

Claims (5)

A current detection circuit that detects a current flowing in a circuit by converting it into a voltage,
Current control means for performing ON / OFF operation of current flowing in the circuit, voltage detection means for detecting a voltage generated in the current control means when the current control means is ON, and amplifying the voltage from the voltage detection means Voltage amplifying means, and output means for outputting the voltage amplified by the voltage amplifying means to a control unit that controls the current control means,
The voltage detecting means has a rectifying element and a current adjusting element,
The output means has the same rectifying element as the resistor and the voltage detection means,
The rectifying elements of the voltage detection means and the output means have voltage change characteristics depending on current and temperature,
Rectification of the voltage detection means and the output means so that a ratio of voltage fluctuations of the rectifying elements of the output means and the voltage detection means due to temperature changes is a constant multiple determined by a gain of the voltage amplification means. A current detection circuit characterized in that a current flowing through an element is set by a current adjustment element of the voltage detection means and a resistance of the output means.   2. The current detection circuit according to claim 1, wherein the rectifying element of the voltage detection unit protects the voltage amplification unit so that an excessive voltage from the current control unit is not input.   The current detection circuit according to claim 1, wherein the rectifying element is any one of a diode, a transistor, a thyristor, and a solar cell. The voltage amplification means comprises an operational amplifier, the current control means comprises an FET,
The voltage detection means includes a resistor R1 as a current adjusting element and a diode D1 as a rectifying element. One end of the resistor R1 is connected to a reference voltage source, and the other end is a non-inverting input (+) terminal of the operational amplifier. Connected to the anode side of the diode D1, the cathode side of the diode D1 and the drain of the FET are connected,
The output means includes a resistor R2 having a resistance value R2, a resistor R3 having a resistance value R3, and a diode D2 as a rectifying element. The output terminal of the operational amplifier has the resistor R2 and the resistor connected in series to the output means. R3 and the diode D2 are connected in order, and the connection point of the resistor R2 and the resistor R3 is connected to the inverting input (−) terminal of the operational amplifier,
The voltage fluctuation value ΔVd2 due to the temperature of the diode D2 is 1+ (resistance value R2 / resistance value R3) times the voltage fluctuation value ΔVd1 due to the temperature of the diode D1. The magnitude of the flowing current is set by the resistor R1 of the voltage detecting means, and the magnitude of the current flowing through the diode D2 of the output means is set by the resistors R2 and R3 of the output means. The current detection circuit according to claim 1. A charge / discharge circuit for charging and / or discharging,
A current detection circuit for detecting a current for controlling charging and / or discharging;
A charge / discharge control circuit that controls charging and / or discharging according to a signal from the current detection circuit;
The current detection circuit includes a current control unit that performs an ON / OFF operation of a current flowing in the charge / discharge circuit, a voltage detection unit that detects a voltage generated in the current control unit when the current control unit is in an ON operation, Voltage amplifying means for amplifying the voltage from the voltage detecting means, and output means for outputting the voltage amplified by the voltage amplifying means to a control unit for controlling the current control means,
The voltage detecting means has a rectifying element and a current adjusting element,
The output means includes a resistor and a rectifying element,
The rectifying elements of the voltage detection means and the output means have voltage change characteristics depending on current and temperature,
Rectification of the voltage detection means and the output means so that a ratio of voltage fluctuations of the rectifying elements of the output means and the voltage detection means due to temperature changes is a constant multiple determined by a gain of the voltage amplification means. A charge / discharge circuit characterized in that a current flowing through an element is set by a current adjusting element of the voltage detecting means and a resistance of the output means.

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