Patent Description:
As a current detection device using an operational amplifier, there has been known a current detection device that includes a shunt resistor, an operational amplifier, a low-pass filter, and an operator (for example, Patent Document <NUM>). The shunt resistor is connected in series to a path through which a current flows. The operational amplifier amplifies a voltage across the shunt resistor at a predetermined amplification factor. The low-pass filter averages output voltages from the operational amplifier. The operator operates a current flowing through the path based on the voltage output from the low-pass filter. In this current detection device, a power supply voltage of the operational amplifier is set to be higher than a power supply voltage of the operator, and the low-pass filter averages the output voltages from the operational amplifier so as to be a value lower than the power supply voltage of the operator. <CIT> discloses a current measurement device with electrical isolation comprising an input signal connected to an electrical shunt, an output of an output signal, and signal transfer means with electrical isolation receiving the input signal and supplying said output signal. The transfer means comprise at least one signal transformer having at least one primary winding to receive a primary signal representative of said input signal, switching means to switch the input signal and supply the latter to said primary winding, and electrically isolated control means of the switching means comprising a control input receiving control signals during switching periods. A trip unit and an electrical circuit breaker comprises one such current measurement device and a processing unit processing electrical protection functions.

In the current detection device of Patent Document <NUM>, by configuring the power supply voltage of the operational amplifier to be higher than the power supply voltage of the operator, the output voltage range of the operational amplifier is expanded to enhance detection accuracy of the current. That is, the current detection device of Patent Document <NUM> includes a plurality of types of power supplies having voltages at different heights to enhance the detection accuracy of the current. This causes a problem of difficulty in increasing the detection accuracy of the current without disposing the plurality of types of power supplies having the voltages at different heights.

A problem solved by the present invention is to provide a current detection device and a current detection method that allow increasing detection accuracy of a current without disposing a plurality of types of power supplies having voltages at different heights.

The dependent claims contain advantageous embodiments of the present invention. Aspects of the present invention concern a shunt resistor, a first circuit, a second circuit a constant current circuit, and an arithmetic circuit. The shunt resistor is connected in series to a path through which a current flows. The first circuit converts a voltage across the shunt resistor into a predetermined differential voltage. To the second circuit, the predetermined differential voltage is input from the first circuit via a pair of wirings. The second circuit amplifies the predetermined differential voltage. The constant current circuit is connected between the pair of wirings. The arithmetic circuit operates a current flowing through the path based on the voltage amplified by the second circuit. Thus, the present invention solves the above-described problem.

According to the present invention, since an output voltage range of the differential amplifier circuit can be adjusted by the constant current circuit, the present invention allows increasing detection accuracy of a current without disposing a plurality of types of power supplies having voltages at different heights.

The following describes embodiments of the present invention with reference to the drawings.

<FIG> is a block diagram of a current detection device <NUM> according to an embodiment. The current detection device <NUM> is, for example, disposed in an electric vehicle including a motor as a traveling driving source. The electric vehicle includes an inverter to drive the motor, and the current detection device <NUM> measures a value of a current (hereinafter referred to as a current value) flowing from the inverter to the motor. Note that a device in which the current detection device <NUM> is disposed is not especially limited, and may be other than the electric vehicle. The type of the current measured by the current detection device <NUM> is not limited to the current flowing from the inverter to the motor, and the current detection device <NUM> may measure another current value.

As illustrated in <FIG>, the current detection device <NUM> includes three substrates from a substrate <NUM> to a substrate <NUM>. Each substrate includes, for example, an element, a component, or a circuit described later.

The substrate <NUM> and the substrate <NUM> are connected with a pair of connection bodies <NUM>. The connection bodies <NUM> include a connection body 54a and a connection body 54b. The substrate <NUM> and the substrate <NUM> are connected with a pair of connection bodies <NUM>. The connection bodies <NUM> include a connection body 55a and a connection body 55b. The connection body <NUM> and the connection body <NUM> only need to be wiring bodies that can connect between the substrates, and the length, the material, the configuration, and the like of the connection body are not specifically limited in this embodiment. As the connection body <NUM> and the connection body <NUM>, for example, harness connectors are used.

The current detection device <NUM> includes a shunt resistor <NUM>, an insulation circuit <NUM>, a differential amplifier circuit <NUM>, a constant current circuit <NUM>, and an arithmetic circuit <NUM>. Hereinafter, the element, the component, and the circuit constituting the current detection device <NUM> will be described.

The shunt resistor <NUM> is disposed in the substrate <NUM>. The shunt resistor <NUM> is connected in series to a path through which a current If flows and is a resistor for current detection for detecting the current If. The shunt resistor <NUM> functions as a detection unit for detecting the current If. In <FIG>, the current If flows from the top to the bottom of the drawing. A voltage across the shunt resistor <NUM> is applied to the insulation circuit <NUM> via the connection bodies <NUM>. Note that the resistance value, the structure, the magnitude, and the like of the shunt resistor <NUM> are not especially limited, and the shunt resistor <NUM> is selected according to the device in which the current detection device <NUM> is disposed.

The insulation circuit <NUM> is disposed in the substrate <NUM>. To the insulation circuit <NUM>, a voltage across the shunt resistor <NUM> is input via the connection bodies <NUM>. Input resistors <NUM>, <NUM> are disposed between the connection bodies <NUM> and the insulation circuit <NUM>. The input resistor <NUM> is connected in series between the connection body 54a and the insulation circuit <NUM>, and the input resistor <NUM> is connected in series between the connection body 54b and the insulation circuit <NUM>.

The insulation circuit <NUM> converts the voltage across the shunt resistor <NUM> into a predetermined differential voltage. In the example of <FIG>, the insulation circuit <NUM> generates the predetermined differential voltage based on the voltage across the shunt resistor <NUM> input from the substrate <NUM> via the connection bodies <NUM>. The insulation circuit <NUM> outputs the differential voltage to the differential amplifier circuit <NUM> via the connection bodies <NUM>. At the differential voltage, the voltage of the connection body 55a is higher than the voltage of the connection body 55b.

As illustrated in <FIG>, the insulation circuit <NUM> includes a modulation unit <NUM> and a demodulation unit <NUM>. The modulation unit <NUM> is electrically insulated from the demodulation unit <NUM>, and the insulation circuit <NUM> has a configuration that cannot transmit a direct current signal between the modulation unit <NUM> and the demodulation unit <NUM>.

The modulation unit <NUM> includes a modulation circuit that modulates the voltage across the shunt resistor <NUM> to predetermined signals. The modulation circuit generates a modulation signal according to the current If. The signal modulated by the modulation circuit is transmitted to the demodulation unit <NUM>.

The demodulation unit <NUM> includes a demodulation circuit that generates a differential voltage based on the signal transmitted from the modulation unit <NUM>. The demodulation circuit outputs the generated differential voltage. Since the modulation unit <NUM> is insulated from the demodulation unit <NUM>, the demodulation unit <NUM> can generate a differential voltage not affected by the voltage across the shunt resistor <NUM>. That is, the insulation circuit <NUM> can generate a differential voltage as a minute signal regardless of the height of the voltage across the shunt resistor <NUM>.

In this embodiment, the signal transmitted from the modulation unit <NUM> to the demodulation unit <NUM> is an alternating current signal, and the modulation unit <NUM> is AC coupled to the demodulation unit <NUM> by a capacitor <NUM> (AC coupling). The alternating-current component in the voltage based on the voltage across the shunt resistor <NUM> is transmitted to the demodulation unit <NUM> from the modulation unit <NUM> via the capacitor <NUM>.

For example, the modulation unit <NUM> performs modulation to a predetermined alternating current signal based on the voltage across the shunt resistor <NUM>. The modulated alternating current signal is transmitted to the demodulation unit <NUM>. The demodulation unit <NUM> converts the alternating current signal into a direct current signal and generates the differential voltage based on the direct current signal. The differential voltage generated by the demodulation unit <NUM> is output to the differential amplifier circuit <NUM> via the connection bodies <NUM>. Note that as the modulation circuit of the modulation unit <NUM> and the demodulation circuit of the demodulation unit <NUM>, a modulation circuit and a demodulation circuit that have been known as of the filing of the present application and can transmit the alternating current signal by the AC coupling are applicable, respectively. Additionally, while <FIG> representatively illustrates one capacitor <NUM>, the number of capacitors <NUM> can be changed according to the respective circuit configurations of the modulation circuit of the modulation unit <NUM> and the demodulation circuit of the demodulation unit <NUM>.

The differential amplifier circuit <NUM> is disposed in the substrate <NUM>. To the differential amplifier circuit <NUM>, a differential voltage is input via the connection bodies <NUM>. The differential amplifier circuit <NUM> includes an operational amplifier <NUM> that amplifies the input differential voltage at a predetermined amplification factor. The operational amplifier <NUM> operates at a power supply voltage V1 (for example, <NUM> V). The differential amplifier circuit <NUM> outputs the amplified voltage to the arithmetic circuit <NUM>. The amplification factor of the differential amplifier circuit <NUM> is configured according to a resistor R1 to a resistor R4. Note that as the differential amplifier circuit <NUM>, a differential amplifier circuit known as of the filing of the present application is applicable.

As illustrated in <FIG>, in the substrate <NUM>, a constant current circuit <NUM> is disposed between the connection bodies <NUM> and the differential amplifier circuit <NUM>. In the substrate <NUM>, a pair of differential wirings electrically conductive to the connection bodies <NUM> are disposed. The differential voltage output from the insulation circuit <NUM> is input to the differential amplifier circuit <NUM> via the connection bodies <NUM> and the differential wirings. The constant current circuit <NUM> flows a constant current between the differential wirings.

As the constant current circuit <NUM>, a resistor <NUM> that connects the differential wirings is used. In view of this, by changing the resistance value of the resistor <NUM>, a current flowing between the differential wirings can be changed. Expressed in another way, by changing the resistance value of the resistor <NUM>, a voltage between an input terminal 31a and an input terminal 31b of the differential amplifier circuit <NUM> can be changed. The resistor <NUM> is a resistor for current adjustment that adjusts the current flowing between the differential wirings. Additionally, with the differential voltage, noise immunity between the insulation circuit <NUM> and the differential amplifier circuit <NUM> can be improved.

The arithmetic circuit <NUM> is a computer for measuring the current If. The arithmetic circuit <NUM> includes a Read Only Memory (ROM) that stores a program for operating a current value, a Central Processing Unit (CPU) that executes the program stored in the ROM, and a Random Access Memory (RAM) that functions as an accessible storage device. The arithmetic circuit <NUM> operates at the power supply voltage V1 (for example, <NUM> V) similarly to the operational amplifier <NUM>. To the arithmetic circuit <NUM>, the voltage amplified by the differential amplifier circuit <NUM> is input. The arithmetic circuit <NUM> executes the program stored in the ROM to operate a current value (a digital value) corresponding to the current If based on the voltage from the differential amplifier circuit <NUM>. In other words, the arithmetic circuit <NUM> generates a digital signal from an analog signal.

Here, with reference to <FIG> and <FIG>, the detection voltage characteristic of the arithmetic circuit <NUM> will be described. <FIG> is characteristics of detection voltages detected by the arithmetic circuit <NUM> relative to currents flowing through the shunt resistor <NUM> when a current flowing through the constant current circuit <NUM> is changed. In <FIG>, the horizontal axis indicates the current If (unit: [A]) flowing through the shunt resistor <NUM>, and the vertical axis indicates the detection voltage (unit: [V]) detected by the arithmetic circuit <NUM>. In <FIG>, Ic1 to Ic5 indicate current values flowed by the constant current circuit <NUM>. The current values increase in the order of Ic1 to Ic5.

The arithmetic circuit <NUM> operates the current value corresponding to the current If based on the detection voltage illustrated in <FIG>. As illustrated in <FIG>, the current If and the detection voltage of the arithmetic circuit <NUM> are in a proportional relation. In view of this, the arithmetic circuit <NUM> operates the current value to be low as the detection voltage lowers. On the other hand, the arithmetic circuit <NUM> operates the current value to be high as the detection voltage increases.

Here, using <FIG>, the relationship between operation accuracy of the arithmetic circuit <NUM> and the output voltage of the differential amplifier circuit <NUM> will be described. The operation accuracy of the arithmetic circuit <NUM> is determined by the inclination of the detection voltage with respect to the current If illustrated in <FIG>. When the inclination of the detection voltage is large, the arithmetic circuit <NUM> operates the current value from the wide detection voltage range compared with the case of the small inclination of the detection voltage. In view of this, from the aspect of detection accuracy of the current detection device <NUM>, as the detection voltage range of the arithmetic circuit <NUM> widens, that is, as the output voltage range of the differential amplifier circuit <NUM> widens, the operation accuracy of the arithmetic circuit <NUM> can be enhanced. Expressed in another way, as the maximum output voltage of the differential amplifier circuit <NUM> is close to the power supply voltage V1 of the arithmetic circuit <NUM>, the operation accuracy of the arithmetic circuit <NUM> can be enhanced.

The current detection device <NUM> according to the embodiment can change the characteristic of the detection voltage of the arithmetic circuit <NUM> to the current If according to the current flowing in the constant current circuit <NUM>. As illustrated in <FIG>, the smaller the current flowing in the constant current circuit <NUM> is, the larger the inclination of the detection voltage V to the current If becomes. This indicates that the smaller the current flowing in the constant current circuit <NUM> is, the larger the differential voltage input to the differential amplifier circuit <NUM> becomes and the maximum output voltage of the differential amplifier circuit <NUM> becomes high. That is, the smaller the current flowing in the constant current circuit <NUM> is, the maximum output voltage of the differential amplifier circuit <NUM> can be approached to the power supply voltage V1 of the arithmetic circuit <NUM> and the operation accuracy of the arithmetic circuit <NUM> can be enhanced.

<FIG> is characteristics of detection voltages detected by the arithmetic circuit <NUM> relative to currents flowing through the shunt resistor <NUM> when a resistance value of the resistor <NUM> is changed. In <FIG>, the horizontal axis indicates current If flowing in the shunt resistor <NUM>, and the vertical axis indicates the detection voltage detected by the arithmetic circuit <NUM>. In <FIG>, Rc1 to Rc5 indicate the resistance values of the resistor <NUM>. The resistance values decrease in the order from Rc1 to Rc5.

As in this embodiment, with the use of the resistor <NUM> as the constant current circuit <NUM>, according to the resistance value of the resistor <NUM>, the characteristic of the detection voltage of the arithmetic circuit <NUM> relative to the current If can be changed. As illustrated in <FIG>, the larger the resistance value of the resistor <NUM> is, the smaller the current flowing in the constant current circuit <NUM> becomes and the larger the inclination of the detection voltage V relative to the current If becomes. The explanation of <FIG> is referred for the relationship between the current flowing through the constant current circuit <NUM> and the output voltage of the differential amplifier circuit <NUM>. That is, in the current detection device <NUM> according to the embodiment, as the resistance value of the resistor <NUM> becomes large, the maximum output voltage of the differential amplifier circuit <NUM> can be approached to the power supply voltage V1 of the arithmetic circuit <NUM> and the operation accuracy of the arithmetic circuit <NUM> can be enhanced.

As described above, the current detection device <NUM> according to the embodiment includes the shunt resistor <NUM>, the insulation circuit <NUM>, the differential amplifier circuit <NUM>, the constant current circuit <NUM>, and the arithmetic circuit <NUM>. The shunt resistor <NUM> is connected in series to the path through which the current If flows. The insulation circuit <NUM> converts the voltage across the shunt resistor <NUM> into the predetermined differential voltage. To the differential amplifier circuit <NUM>, a differential voltage is input from the insulation circuit <NUM> via the pair of connection bodies <NUM>, and the differential amplifier circuit <NUM> amplifies the input differential voltage. The constant current circuit <NUM> is connected between the pair of connection bodies <NUM>. The arithmetic circuit <NUM> operates the current If flowing through the path based on the voltage amplified by the differential amplifier circuit <NUM>. Since the constant current circuit <NUM> can adjust the output voltage range of the differential amplifier circuit <NUM>, the power supply voltage V1 of the differential amplifier circuit <NUM> can be adjusted to the power supply voltage V1 of the arithmetic circuit <NUM>. Consequently, the detection accuracy of the current can be enhanced without disposing a plurality of types of power supplies having voltages at different heights. Additionally, the number of components can be reduced and a cost can be reduced. Furthermore, the use of the differential amplifier circuit <NUM> allows improving noise immunity compared with the use of a single-ended amplifier circuit.

In this embodiment, the shunt resistor <NUM> is disposed in the substrate <NUM>, the insulation circuit <NUM> is disposed in the substrate <NUM>, and the differential amplifier circuit <NUM>, the constant current circuit <NUM>, and the arithmetic circuit <NUM> are disposed in the substrate <NUM>. Separating them into the plurality of substrates allows enhancing a degree of freedom of the layout of the current detection device <NUM>. Additionally, for ensuring an insulating property, since the insulation circuit <NUM>, which requires a certain distance in the circuit, is disposed in the independent substrate, compared with a case of constituting the current detection device <NUM> by one substrate, the insulating property in the insulation circuit <NUM> is easily ensured.

Furthermore, in this embodiment, the constant current circuit <NUM> is configured by the resistor <NUM> connected between the pair of connection bodies <NUM>. Since this allows adjusting the output voltage range of the differential amplifier circuit <NUM> by the resistance value of the resistor <NUM>, while the power supply voltage V1 of the differential amplifier circuit <NUM> is adjusted to the power supply voltage V1 of the arithmetic circuit <NUM>, the operation accuracy of the arithmetic circuit <NUM> can be enhanced.

In addition, in this embodiment, the insulation circuit <NUM> includes the modulation unit <NUM> and the demodulation unit <NUM>, and the modulation unit <NUM> is insulated from the demodulation unit <NUM>. The modulation unit <NUM> generates the modulation signal produced by modulating the voltage across the shunt resistor <NUM>, and the demodulation unit <NUM> demodulates the modulation signal modulated by the modulation unit <NUM> to generate the predetermined differential voltage. Since the modulation unit <NUM> is electrically insulated from the demodulation unit <NUM>, the power supply voltage of the differential amplifier circuit <NUM> can be a voltage independent from the voltage applied to the shunt resistor <NUM>. As a result, the power supply voltage V1 of the differential amplifier circuit <NUM> can be adjusted to the power supply voltage V1 of the arithmetic circuit <NUM>.

Additionally, in this embodiment, the insulation circuit <NUM> includes the capacitor <NUM>, and the modulation unit <NUM> is AC coupled to the demodulation unit <NUM> by the capacitor <NUM>. The modulation unit <NUM> transmits the alternating current signal to the demodulation unit <NUM> via the capacitor <NUM>, and the demodulation unit <NUM> generates the predetermined differential voltage based on the alternating current signal input via the capacitor <NUM>. Since the demodulation unit <NUM> can operate at a voltage independent from the voltage applied to the shunt resistor <NUM>, the insulation circuit <NUM> can generate the differential voltage according to the power supply voltage V1 of the differential amplifier circuit <NUM>.

For example, in the above-described embodiment, an example of the current detection device <NUM> configured by the three substrates from the substrate <NUM> to the substrate <NUM> has been described, but the current detection device <NUM> may be configured by two substrates, a substrate <NUM> (not illustrated) and a substrate <NUM> (not illustrated). In this case, the shunt resistor <NUM> and the insulation circuit <NUM> are disposed in the substrate <NUM>, and the differential amplifier circuit <NUM>, the constant current circuit <NUM>, and the arithmetic circuit <NUM> are disposed in the substrate <NUM>. A pair of connection bodies <NUM> (not illustrated) connect between the substrate <NUM> and the substrate <NUM>. Similar to the above-described embodiment, separating them into the plurality of substrates allows enhancing a degree of freedom of the layout of the current detection device <NUM>. Additionally, since the insulation circuit <NUM> is disposed in the substrate different from the substrate in which the differential amplifier circuit <NUM> and the arithmetic circuit <NUM> are disposed, compared with the case of the current detection device <NUM> being configured of one substrate, the insulating property in the insulation circuit <NUM> is easily ensured.

For example, while the alternating current signal is described as an example of the signal transmitted from the modulation unit <NUM> to the demodulation unit <NUM> in the above-described embodiment, the signal transmitted from the modulation unit <NUM> to the demodulation unit <NUM> is not limited to this.

For example, in a current detection device according to a modification, the insulation circuit <NUM> includes an insulation transformer. The modulation unit <NUM> is configured of a primary side coil in the insulation transformer, and the demodulation unit <NUM> is configured of a secondary side coil in the insulation transformer. The primary side coil includes a modulation circuit that flows the current according to the current If to the primary side coil. The secondary side coil includes a demodulation circuit that generates the differential voltage according to the current flowing through the secondary side coil. When the current flows to the primary side coil by the modulation circuit, a magnetic field occurs around the primary side coil. In the secondary side coil, a current flows by the magnetic field generated in the primary side coil and the demodulation circuit generates the differential voltage according to the current flowing in the secondary side coil. While the modulation unit <NUM> is electrically insulated from the demodulation unit <NUM>, the insulation circuit <NUM> may transmit the signal from the modulation unit <NUM> to the demodulation unit <NUM> by the principle of electromagnetic induction.

As another example, for example, in a current detection device according to a modification, the insulation circuit <NUM> includes a photocoupler that converts an electrical signal into an optical signal and converts the optical signal into an electrical signal again. The modulation unit <NUM> is configured of a light-emitting element that converts an electrical signal into an optical signal in the photocoupler, and the demodulation unit <NUM> is configured of a light-receiving element that converts an optical signal into an electrical signal in the photocoupler. The light-emitting element includes a modulation circuit that flows a current according to the current If to the light-emitting element. The light-receiving element includes a demodulation circuit that generates a differential voltage according to a current flowing through the light-receiving element. When the currents flows through the light-emitting element by the modulation circuit, the light-emitting element emits light according to the current. In the light-receiving element, the current flows according to the light emission of the light-emitting element, and the demodulation circuit generates the differential voltage according to the current flowing through the light-receiving element. The insulation circuit <NUM> may transmit the optical signal from the modulation unit <NUM> to the demodulation unit <NUM> with the modulation unit <NUM> electrically insulated from the demodulation unit <NUM>.

In the above-described embodiment, the resistor <NUM> connected between the connection bodies <NUM> has been described as an example of the constant current circuit <NUM>, the circuit configuration of the constant current circuit <NUM> is not limited to the resistor. For example, the constant current circuit <NUM> may be configured of a circuit using a transistor (such as a current mirror circuit). Additionally, the resistor <NUM> is not limited to the resistor whose resistance value is fixed, and may be a variable resistor whose resistance value is changeable.

While in the above-described embodiment, from the aspect of the output voltage range of the differential amplifier circuit <NUM>, it has been described that as the current flowing through the constant current circuit <NUM> decreases, the operation accuracy of the arithmetic circuit <NUM> is enhanced. However, from the aspect of noise immunity, as the current flowing through the constant current circuit <NUM> increases, the operation accuracy of the arithmetic circuit <NUM> is enhanced. That is, the larger the current flowing through the constant current circuit <NUM> is, the more noise immunity of the differential wiring of the differential amplifier circuit <NUM> can be achieved. Accordingly, a possibility of generating an error in the output voltage of the differential amplifier circuit <NUM> due to a noise can be reduced. Consequently, the operation accuracy of the arithmetic circuit <NUM> can be increased. In the present invention, from the aspect of the output voltage range of the differential amplifier circuit <NUM> and noise immunity, the current flowing through the constant current circuit <NUM> is preferably set.

Claim 1:
A current detection device comprising:
a shunt resistor (<NUM>) connected in series to a path through which a current (If) flows;
a first circuit (<NUM>) that is configured to convert a voltage across the shunt resistor (<NUM>) into a differential voltage;
a second circuit (<NUM>) that is configured to amplify an input differential voltage at a predetermined amplification factor, the input differential voltage being input from the first circuit via a pair of wirings;
a modulation unit (<NUM>) and a demodulation unit (<NUM>);
a resistor (<NUM>) connected between the pair of wirings; and
an arithmetic circuit (<NUM>) that operates the current flowing through the path based on the voltage amplified by the second circuit (<NUM>),
wherein the first circuit (<NUM>) includes the modulation unit (<NUM>),
the modulation unit (<NUM>) generates a modulation signal produced by modulating the voltage across the shunt resistor (<NUM>) and is insulated from the demodulation unit (<NUM>),
the resistor (<NUM>) is a resistor for current adjustment that adjusts the output voltage of the second circuit (<NUM>),
the larger the resistance value of the resistor (<NUM>) is, the larger the inclination of a detection voltage of the arithmetic circuit (<NUM>) relative to the current flowing through the shunt resistor becomes, characterized in that:
the first circuit (<NUM>) includes the demodulation unit (<NUM>),
the demodulation unit (<NUM>) is configured to demodulate the modulation signal to generate the differential voltage.