Sensor circuit

Abstract

The present disclosure addresses the problem of providing a sensor circuit capable of detecting the output of a sensor with higher accuracy. This sensor circuit (10) comprises a conversion circuit (14) and a control circuit (3). The conversion circuit (14) converts the detection voltage (V1) detected by the sensor (8) into a predetermined output voltage (V2). The control circuit (3) controls the conversion circuit (14). The conversion circuit (14) has a switching circuit (4). The switching circuit (4) includes at least one switching element (Q7). The switching circuit (4) receives the detection voltage (V1) as an input voltage. The control circuit (3) controls the duty of a control signal for the at least one switching element (Q7) in accordance with the amplitude of the input voltage to the switching circuit (4).

Description

Sensor Circuit

[0001] The present disclosure generally relates to sensor circuits, and more particularly to a sensor circuit that detects an output of a sensor.

[0002] The physical quantity measuring device described in Patent Document 1 is exemplified. The physical quantity measuring device includes a circuit device (sensor circuit). The circuit device includes a temperature sensor, a voltage conversion circuit, a chopping modulation circuit, and an A / D conversion circuit.

[0003] In the circuit device included in the physical quantity measuring device described in Patent Document 1, there may be cases where it is desired to detect the output of the temperature sensor with higher accuracy.

[0004] Japanese Unexamined Patent Publication No. 2019-20204

[0005] An object of the present disclosure is to provide a sensor circuit capable of detecting an output of a sensor with higher accuracy.

[0006] A sensor circuit according to one aspect of the present disclosure includes a conversion circuit and a control circuit. The conversion circuit converts a detection voltage detected by a sensor into a predetermined output voltage. The control circuit controls the conversion circuit. The conversion circuit includes a switching circuit. The switching circuit includes at least one switching element. The switching circuit receives the detection voltage as an input voltage. The control circuit controls the duty of a control signal to the at least one switching element in accordance with the amplitude of the input voltage of the switching circuit.

[0007] Figure 1 is a circuit diagram showing an example of use of a power converter equipped with a sensor circuit according to Embodiment 1. Figure 2 is a circuit diagram showing a part of the above sensor circuit. Figure 3 is a block diagram of the control circuit in the above sensor circuit. Figure 4 is a graph showing the change in duty cycle for the above sensor circuit. Figure 5 is a waveform diagram showing the operation of the above sensor circuit. Figure 6 is an enlarged view of the corrected U-phase current waveform for the operation of the above sensor circuit. Figure 7 is another enlarged view of the corrected U-phase current waveform for the operation of the above sensor circuit. Figure 8 is a waveform diagram showing another operation of the above sensor circuit. Figure 9 is a waveform diagram showing yet another operation of the above sensor circuit. Figure 10 is a circuit diagram showing a part of a sensor circuit according to a modified example of Embodiment 1. Figure 11 is a waveform diagram showing the operation of a sensor circuit according to Embodiment 2. Figure 12 is an enlarged view of the corrected U-phase current waveform for the operation of the above sensor circuit. Figure 13 is another enlarged view of the corrected U-phase current waveform for the operation of the above sensor circuit. Figure 14 is a graph showing the change in duty cycle for a sensor circuit according to Embodiment 3. Figure 15 is a waveform diagram showing the operation of the sensor circuit described above. Figure 16 is a graph showing the change in duty cycle for the sensor circuit according to Embodiment 4. Figure 17 is a waveform diagram showing the operation of the sensor circuit described above. Figure 18 is a graph showing the change in duty cycle for the sensor circuit according to Embodiment 5. Figure 19 is a waveform diagram showing the operation of the sensor circuit described above. Figure 20 is a waveform diagram showing the operation of the sensor circuit according to Embodiment 6. Figure 21 is an enlarged view of the waveform in Figure 20.

[0008] The sensor circuits according to Embodiments 1 to 6 will be described below with reference to the drawings. The configurations described in each of the embodiments below are merely examples of the present disclosure. The present disclosure is not limited to each embodiment, and various modifications are possible depending on the design, etc., as long as the effects of the present disclosure can be achieved. Furthermore, the present disclosure can also be applied by appropriately combining at least some of the configurations of each of the embodiments and modified examples below.

[0009] (1) Embodiment 1 Hereinafter, a power conversion device A1 equipped with a sensor circuit 10 according to Embodiment 1 will be described with reference to Figures 1 to 9.

[0010] The power converter A1 is used in the motor drive system 100, for example, as shown in Figure 1. The motor drive system 100 includes the power converter A1 and an AC load B1. The AC load B1 is, for example, a three-phase servo motor.

[0011] (2) Power converter The power converter A1 comprises a three-phase inverter circuit 20, a sensor 8, and a sensor circuit 10.

[0012] The three-phase inverter circuit 20 converts DC power from a DC power source (not shown) into AC power and outputs the converted AC power to the AC load B1. The converted AC power is three-phase (U-phase, V-phase, and W-phase) AC power. The DC power source includes an AC / DC converter or a DC / DC converter.

[0013] The three-phase inverter circuit 20 includes a pair of input terminals 11 and 12, a capacitor C1, a U-phase switching circuit 21, a V-phase switching circuit 22, and a W-phase switching circuit 23.

[0014] The pair of input terminals 11 and 12 are electrically connected to a DC power supply. For example, input terminal 11 is electrically connected to the high-potential terminal of the DC power supply. Input terminal 12 is electrically connected to the low-potential terminal of the DC power supply (for example, the ground terminal).

[0015] Capacitor C1 is, for example, an electrolytic capacitor. Capacitor C1 is electrically connected between a pair of input terminals 11 and 12. For example, the high-potential terminal of capacitor C1 is electrically connected to input terminal 11. The low-potential terminal of capacitor C1 is electrically connected to input terminal 12.

[0016] The U-phase switching circuit 21 has two switching elements Q1 and Q2. Switching element Q1 and switching element Q2 are connected in series with each other.

[0017] Each of the two switching elements Q1 and Q2 is, for example, a normally-off MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor). Each of the two switching elements Q1 and Q2 includes a parasitic diode. Each of the two switching elements Q1 and Q2 has a first main terminal, a second main terminal, and a control terminal. For the sake of explanation, the first main terminal will be referred to as the drain terminal, the second main terminal as the source terminal, and the control terminal as the gate terminal.

[0018] The drain terminal of switching element Q1 is electrically connected to the high-potential terminal of capacitor C1. The gate terminal of switching element Q1 is electrically connected to the control circuit 3 in the sensor circuit 10, which will be described later. The source terminal of switching element Q1 is electrically connected to the drain terminal of switching element Q2.

[0019] The gate terminal of the switching element Q2 is electrically connected to the control circuit 3. The source terminal of the switching element Q2 is electrically connected to the low-potential terminal of the capacitor C1.

[0020] The connection point 210 of switching element Q1 and switching element Q2 is electrically connected to the U-phase terminal (not shown) of the AC load B1. The connection point 210 of switching element Q1 and switching element Q2 may be, for example, a connection point provided on the circuit between the source terminal of switching element Q1 and the drain terminal of switching element Q2, or it may be the source terminal of switching element Q1, or it may be the drain terminal of switching element Q2.

[0021] The V-phase switching circuit 22 has two switching elements Q3 and Q4. Switching element Q3 and switching element Q4 are connected in series with each other.

[0022] Each of the two switching elements Q3 and Q4 is, for example, a normally-off MOSFET. Each of the two switching elements Q3 and Q4 includes a parasitic diode. Each of the two switching elements Q3 and Q4 has a first main terminal, a second main terminal, and a control terminal. For the sake of explanation, the first main terminal will be referred to as the drain terminal, the second main terminal as the source terminal, and the control terminal as the gate terminal.

[0023] The drain terminal of switching element Q3 is electrically connected to the drain terminal of switching element Q1. The gate terminal of switching element Q3 is electrically connected to the control circuit 3. The source terminal of switching element Q3 is electrically connected to the drain terminal of switching element Q4.

[0024] The gate terminal of switching element Q4 is electrically connected to the control circuit 3. The source terminal of switching element Q4 is electrically connected to the source terminal of switching element Q2.

[0025] The connection point 220 of switching element Q3 and switching element Q4 is electrically connected to the V-phase terminal (not shown) of the AC load B1. The connection point 220 of switching element Q3 and switching element Q4 may be, for example, a connection point provided on the circuit between the source terminal of switching element Q3 and the drain terminal of switching element Q4, or it may be the source terminal of switching element Q3, or it may be the drain terminal of switching element Q4.

[0026] The W-phase switching circuit 23 has two switching elements Q5 and Q6. Switching element Q5 and switching element Q6 are connected in series with each other.

[0027] Each of the two switching elements Q5 and Q6 is, for example, a normally-off MOSFET. Each of the two switching elements Q5 and Q6 includes a parasitic diode. Each of the two switching elements Q5 and Q6 has a first main terminal, a second main terminal, and a control terminal. For the sake of explanation, the first main terminal will be referred to as the drain terminal, the second main terminal as the source terminal, and the control terminal as the gate terminal.

[0028] The drain terminal of switching element Q5 is electrically connected to the drain terminal of switching element Q3. The gate terminal of switching element Q5 is electrically connected to the control circuit 3. The source terminal of switching element Q5 is electrically connected to the drain terminal of switching element Q6.

[0029] The gate terminal of switching element Q6 is electrically connected to the control circuit 3. The source terminal of switching element Q6 is electrically connected to the source terminal of switching element Q4.

[0030] The connection point 230 of switching element Q5 and switching element Q6 is electrically connected to the W-phase terminal (not shown) of the AC load B1. The connection point 230 of switching element Q5 and switching element Q6 may be, for example, a connection point provided on the circuit between the source terminal of switching element Q5 and the drain terminal of switching element Q6, or it may be the source terminal of switching element Q5, or it may be the drain terminal of switching element Q6.

[0031] Sensor 8 detects the current corresponding to the AC power from the three-phase inverter circuit 20 as a detection voltage. Sensor 8 has, for example, three detection units 8a to 8c. Detection unit 8a includes, for example, a shunt resistor Ra (see Figure 2). Each of the two detection units 8b and 8c also includes a shunt resistor (not shown), similar to detection unit 8a.

[0032] The detection unit 8a is located on the circuit between the connection point 210 of the U-phase switching circuit 21 and the U-phase terminal of the AC load B1. Specifically, the first end of the detection unit 8a is electrically connected to the connection point 210. The second end of the detection unit 8a is electrically connected to the U-phase terminal of the AC load B1. The detection unit 8a detects the current Isa flowing from the U-phase switching circuit 21 to the AC load B1 (hereinafter referred to as "U-phase current") as a detection voltage V1 (see Figure 2).

[0033] The detection unit 8b is located on the circuit between the connection point 220 of the V-phase switching circuit 22 and the V-phase terminal of the AC load B1. Specifically, the first end of the detection unit 8b is electrically connected to the connection point 220. The second end of the detection unit 8b is electrically connected to the V-phase terminal of the AC load B1. The detection unit 8b detects the current Isb (hereinafter referred to as "V-phase current") flowing from the V-phase switching circuit 22 to the AC load B1 as a detection voltage.

[0034] The detection unit 8c is located on the circuit between the connection point 230 of the W-phase switching circuit 23 and the W-phase terminal of the AC load B1. Specifically, the first end of the detection unit 8c is electrically connected to the connection point 230. The second end of the detection unit 8c is electrically connected to the W-phase terminal of the AC load B1. The detection unit 8c detects the current Isc (hereinafter referred to as "W-phase current") flowing from the W-phase switching circuit 23 to the AC load B1 as a detection voltage.

[0035] (3) Sensor circuit The sensor circuit 10 comprises a conversion circuit 14 and a control circuit 3.

[0036] The conversion circuit 14 converts the detected voltage from the sensor 8 into a predetermined output voltage. The conversion circuit 14 includes an amplitude control circuit 1 and an offset superposition circuit 2.

[0037] The amplitude control circuit 1 receives input of three detection voltages detected by the sensor 8. In other words, the amplitude control circuit 1 accepts three detection voltages as input voltages. The amplitude control circuit 1 also controls the amplitude of each of the three detection voltages. The amplitude control circuit 1 includes a U-phase amplitude control unit 1a (see Figure 2), a V-phase amplitude control unit (not shown), and a W-phase amplitude control unit (not shown).

[0038] Note that the configurations of the U-phase amplitude control unit 1a, the V-phase amplitude control unit, and the W-phase amplitude control unit are the same, with only the detected voltage of the controlled object differing. Therefore, in the following, only the U-phase amplitude control unit 1a will be described, and the descriptions of the V-phase amplitude control unit and the W-phase amplitude control unit will be omitted.

[0039] The U-phase amplitude control unit 1a shown in FIG. 2 controls the amplitude of the detection voltage V₁ detected by the detection unit 8a to generate a predetermined output voltage V₂. The U-phase amplitude control unit 1a includes, for example, a switching circuit 4, an amplifier circuit 5, and a filter 6. The detection voltage V₁ is a voltage corresponding to the U-phase current Isa flowing through the shunt resistor Ra.

[0040] The switching circuit 4 is, for example, a half-bridge circuit. The switching circuit 4 includes two switching elements Q7 and Q8. The switching element Q7 and the switching element Q8 are connected in series with each other.

[0041] Each of the two switching elements Q7 and Q8 is, for example, a normally-off MOSFET. Each of the two switching elements Q7 and Q8 includes a parasitic diode. Each of the two switching elements Q7 and Q8 includes a first main terminal, a second main terminal, and a control terminal. For convenience of explanation, the first main terminal is hereinafter referred to as a drain terminal, the second main terminal is referred to as a source terminal, and the control terminal is referred to as a gate terminal.

[0042] The drain terminal of the switching element Q7 is electrically connected to the first terminal of the shunt resistor Ra. The gate terminal of the switching element Q7 is electrically connected to the control circuit 3. The source terminal of the switching element Q7 is electrically connected to the drain terminal of the switching element Q8.

[0043] The gate terminal of the switching element Q8 is electrically connected to the control circuit 3. The source terminal of the switching element Q8 is electrically connected to the second terminal of the shunt resistor Ra.

[0044] The amplifier circuit 5 amplifies the output voltage V₁₁ of the switching circuit 4. For example, the amplifier circuit 5 is an inverting amplifier circuit. The amplifier circuit 5 includes an operational amplifier 13 and two resistors R1 and R2.

[0045] A non-inverting input terminal of the operational amplifier 13 is electrically connected to the drain terminal of the switching element Q8 via the resistor R1. An inverting input terminal of the operational amplifier 13 is electrically connected to the source terminal of the switching element Q8. An output terminal of the operational amplifier 13 is electrically connected to the non-inverting input terminal of the operational amplifier 13 via the resistor R2. Further, the output terminal of the operational amplifier 13 is electrically connected to the filter 6.

[0046] The filter 6 removes noise contained in the output voltage V12 of the amplifier circuit 5 and outputs the output voltage V2. For example, the filter 6 is a low-pass filter. The filter 6 includes the resistor R3 and the capacitor C2. The capacitor C2 is, for example, an electrolytic capacitor.

[0047] A first end of the resistor R3 is electrically connected to the output terminal of the operational amplifier 13. A second end of the resistor R3 is electrically connected to a high potential side terminal of the capacitor C2. A low potential side terminal of the capacitor C2 is electrically connected to the inverting input terminal of the operational amplifier 13. The capacitor C2 is connected in parallel with the offset superimposing circuit 2 (see Fig. 1). Note that illustration of the offset superimposing circuit 2 is omitted in Fig. 2.

[0048] The U-phase amplitude control unit 1a controls (amplifies) the amplitude of the detection voltage V1 to generate the output voltage V2 based on the following formula (1). In other words, the control circuit 3 controls the duty of a second control signal S2 (see Fig. 3) described later so that the U-phase amplitude control unit 1a generates the output voltage V2 based on formula (1).

[0049]

[0050] Note that V2 in formula (1) represents the voltage value of the output voltage V2. R1 in formula (1) represents the resistance value of the resistor R1. R2 in formula (1) represents the resistance value of the resistor R2. D in formula (1) represents the duty of the second control signal S2. V1 in formula (1) represents the voltage value of the detection voltage V1.

[0051] For example, if the amplitude of the detected voltage V1 is 1V, the amplitude of the output voltage V2 is 1.65V. In other words, if the peak-to-peak value of the detected voltage V1 is 2V, the peak-to-peak value of the output voltage V2 is 3.3V. That is, the U-phase amplitude control unit 1a multiplies the voltage value of the detected voltage V1 by a correction value. In the above example, the correction value is 1.65.

[0052] The offset superposition circuit 2 shown in Figure 1 is electrically connected to the amplitude control circuit 1 (specifically, the U-phase amplitude control unit 1a, the V-phase amplitude control unit, and the W-phase amplitude control unit).

[0053] The offset superposition circuit 2 offsets the output voltage V2 of the U-phase amplitude control unit 1a so that the voltage level of the output voltage V2 of the U-phase amplitude control unit 1a becomes a positive value. The offset superposition circuit 2 also offsets the output voltage of the V-phase amplitude control unit so that the voltage level of the output voltage of the V-phase amplitude control unit becomes a positive value. The offset superposition circuit 2 also offsets the output voltage of the W-phase amplitude control unit so that the voltage level of the output voltage of the W-phase amplitude control unit becomes a positive value.

[0054] The control circuit 3 controls the three-phase inverter circuit 20. More specifically, the control circuit 3 outputs a first control signal S1 (see Figure 3) to the three-phase inverter circuit 20 for controlling the three-phase inverter circuit 20.

[0055] Furthermore, the control circuit 3 controls the conversion circuit 14. More specifically, the control circuit 3 outputs a second control signal S2 (see Figure 3) to the conversion circuit 14 for controlling the amplitude control circuit 1 (specifically, the switching circuit 4).

[0056] The control circuit 3 is implemented, for example, by a computer system having one or more processors and one or more memories. In other words, the functions of the control circuit 3 are realized when one or more processors execute a program stored in memory. The program may be pre-stored in memory, provided via a telecommunication line such as the Internet, or provided on a non-temporary recording medium such as a memory card.

[0057] The control circuit 3 is electrically connected to the offset superposition circuit 2. As shown in Figure 3, the control circuit 3 includes a sample-and-hold circuit 31, an AD conversion unit 32, a correction unit 33, a first conversion unit 34, a current control unit 35, a second conversion unit 36, a first PWM (Pulse Width Modulation) generation unit 37, a duty cycle calculation unit 38, and a second PWM generation unit 39.

[0058] The sample-and-hold circuit 31 accepts the output voltage converted by the conversion circuit 14 as input. More specifically, the sample-and-hold circuit 31 accepts the output voltage (for example, output voltage V2) that has been offset by the offset superposition circuit 2 as input.

[0059] Furthermore, the sample-and-hold circuit 31 holds a signal corresponding to the output voltage converted by the conversion circuit 14 (hereinafter referred to as the "sample-and-hold signal").

[0060] The AD conversion unit 32 performs AD conversion on the sample-and-hold signals (U-phase sample-and-hold signal, V-phase sample-and-hold signal, and W-phase sample-and-hold signal) held by the sample-and-hold circuit 31.

[0061] The correction unit 33 corrects the AD-converted sample-and-hold signal. More specifically, the correction unit 33 divides the signal level of the AD-converted sample-and-hold signal (i.e., the voltage value of the output voltage converted by the conversion circuit 14) by the correction value. This allows the control circuit 3 to accurately read the voltage value of the detection voltage V1 corresponding to, for example, the U-phase current Isa flowing through the shunt resistor Ra.

[0062] The first conversion unit 34 includes, for example, a three-phase to two-phase conversion unit and a dq conversion unit, and converts the three-phase phase currents (U-phase current, V-phase current, and W-phase current) of an abc reference coordinate system, where the U-phase is the a-phase, the V-phase is the b-phase, and the W-phase is the c-phase, into the d-axis current Id and q-axis current Iq of a dq rotating coordinate system. The first conversion unit 34 is electrically connected to the correction unit 33.

[0063] The current control unit 35 is configured, for example, to perform PI control. The current control unit 35 generates a reference value for the d-axis voltage to perform feedback control that brings the absolute value of the difference between the current value of the d-axis current Id and the reference value of the d-axis current Id closer to zero. The current control unit 35 also generates a reference value for the q-axis voltage to perform feedback control that brings the absolute value of the difference between the current value of the q-axis current Iq and the reference value of the q-axis current Iq closer to zero. The current control unit 35 is electrically connected to the first conversion unit 34.

[0064] The second conversion unit 36 ​​includes, for example, an inverse dq conversion unit and a two-phase to three-phase conversion unit, and converts the reference value of the d-axis voltage and the reference value of the q-axis voltage generated by the current control unit 35 into the target voltage of the U-phase, the target voltage of the V-phase, and the target voltage of the W-phase.

[0065] The first PWM generation unit 37 generates three first PWM signals based on the target voltages of the three phases (U phase, V phase, and W phase) converted by the second conversion unit 36. In this embodiment, the three first PWM signals correspond to the first control signal S1.

[0066] The three first PWM signals include a U-phase PWM signal, a V-phase PWM signal, and a W-phase PWM signal. The U-phase PWM signal is a PWM signal generated based on the U-phase target voltage converted by the second conversion unit 36. The V-phase PWM signal is a PWM signal generated based on the V-phase target voltage converted by the second conversion unit 36. The W-phase PWM signal is a PWM signal generated based on the W-phase target voltage converted by the second conversion unit 36.

[0067] The first PWM generation unit 37 outputs a U-phase PWM signal to the U-phase switching circuit 21 (see Figure 1). The first PWM generation unit 37 also outputs a V-phase PWM signal to the V-phase switching circuit 22 (see Figure 1). The first PWM generation unit 37 also outputs a W-phase PWM signal to the W-phase switching circuit 23 (see Figure 1).

[0068] The U-phase switching circuit 21 shown in Figure 1 controls two switching elements Q1 and Q2 in response to the U-phase PWM signal to perform switching operations. The V-phase switching circuit 22 controls two switching elements Q3 and Q4 in response to the V-phase PWM signal to perform switching operations. The W-phase switching circuit 23 controls two switching elements Q5 and Q6 in response to the W-phase PWM signal to perform switching operations. As a result, the power converter A1 can stably supply AC power from the three-phase inverter circuit 20 to the AC load B1.

[0069] The duty cycle calculation unit 38 shown in Figure 3 calculates the duty cycle of the second control signal S2 to the switching circuit 4 (see Figure 2) based on the current value of the q-axis current Iq converted by the first conversion unit 34 and the amplitude value of the output voltage V2 of the amplitude control circuit 1.

[0070] In this embodiment, the output voltage V2 of the amplitude control circuit 1 corresponds to the input voltage (detection voltage) V1 of the amplitude control circuit 1. In other words, the output voltage V2 of the amplitude control circuit 1 and the input voltage V1 of the amplitude control circuit 1 are proportionally related. For example, the voltage value of the output voltage V2 of the amplitude control circuit 1 is the value obtained by multiplying the voltage value of the input voltage V1 of the amplitude control circuit 1 by the correction value.

[0071] The second PWM generation unit 39 generates a second PWM signal based on the duty cycle calculated by the duty cycle calculation unit 38. In this embodiment, the second PWM signal corresponds to the second control signal S2.

[0072] Furthermore, the second PWM generation unit 39 outputs the generated second PWM signal (second control signal S2) to the amplitude control circuit 1 (see Figure 1).

[0073] The switching circuit 4 of the U-phase amplitude control unit 1a shown in Figure 2 controls two switching elements Q7 and Q8 in response to the second control signal S2 from the second PWM generation unit 39 (see Figure 3) to perform switching operations. The switching circuit of the V-phase amplitude control unit also performs switching operations in the same way as the switching circuit 4 of the U-phase amplitude control unit 1a. The switching circuit of the W-phase amplitude control unit also performs switching operations in the same way as the switching circuit 4 of the U-phase amplitude control unit 1a.

[0074] Incidentally, the control circuit 3 controls the duty cycle of the second control signal S2 to at least one of the switching elements Q7 and Q8 according to the amplitude of the input voltage V1 of the amplitude control circuit 1 (more specifically, the switching circuit 4) (see Figure 4).

[0075] For example, the control circuit 3 has a control mode for controlling the duty cycle (hereinafter simply referred to as "duty cycle") of the second control signal S2. As shown in Figure 4, the control mode includes a variable mode M1, a first fixed mode M2, and a second fixed mode M3. In this embodiment, the control mode is a type of operation in which the control circuit 3 operates by one or more processors in the control circuit 3 executing a program (software) stored in memory.

[0076] Variable mode M1 is a mode in which the duty cycle is changed. For example, as shown in Figure 4, variable mode M1 is a mode in which the duty cycle continuously decreases as the amplitude of the input voltage V1 of the switching circuit 4 increases.

[0077] The first fixed mode M2 ​​is a mode in which the duty cycle is fixed so that it remains constant, for example, the duty cycle is fixed so that it becomes a first specified value D1.

[0078] The second fixed mode M3 is a mode in which the duty cycle is fixed so that it remains constant. For example, the duty cycle is fixed so that it becomes a second specified value D2. The second specified value D2 is greater than the first specified value D1. In this embodiment, for example, the first specified value D1 is 0.1 and the second specified value D2 is 0.95.

[0079] The control circuit 3 shown in Figure 2 selects one of the following modes—variable mode M1, first fixed mode M2, and second fixed mode M3—according to the amplitude of the input voltage V1 of the switching circuit 4, and controls the duty cycle based on the selected mode. In other words, the control circuit 3 controls the duty cycle based on either the variable mode M1 or the fixed mode (first fixed mode M2 ​​or second fixed mode M3).

[0080] When variable mode M1 is selected as the control mode, the control circuit 3 increases the duty cycle as the amplitude of the input voltage V1 decreases, and decreases the duty cycle as the amplitude of the input voltage V1 increases, as shown in Figure 4, to set the amplitude of the output voltage V2 of the conversion circuit 14 to a predetermined voltage (1.65V in the example in Figure 4).

[0081] As a result, the waveforms K1 of the U-phase current before and after correction by the correction unit 33 (see Figure 3) are as shown in Figure 5. Figure 5 shows the waveforms of the simulation results. Also, waveform K2 in Figure 5 shows the waveforms of the U-phase current before and after correction by the correction unit in the comparative example sensor circuit. The comparative example sensor circuit does not have the amplitude control circuit 1 of the sensor circuit 10. Also, the waveforms in Figure 5 show the case where the resolution of the control circuit 3 (specifically, the AD conversion unit 32) is 12 bits.

[0082] In the comparative example sensor circuit, for example, when the amplitude of the U-phase current Isa is large, the corrected U-phase current waveform K2 becomes almost the same as the U-phase current waveform Isa, as shown in Figure 6. Similarly, in the sensor circuit 10 of Embodiment 1, for example, when the amplitude of the U-phase current Isa is large, the corrected U-phase current waveform K1 becomes almost the same as the U-phase current waveform Isa. In other words, in either sensor circuit, when the amplitude of the U-phase current Isa is large, the sensor output can be detected with high accuracy. Figure 6 is an enlarged view of the waveform shown at position P1 in Figure 5.

[0083] On the other hand, in the comparative example's sensor circuit, for example, when the amplitude of the U-phase current Isa is small, the corrected U-phase current waveform K2 becomes different from the waveform of the U-phase current Isa, as shown in Figure 7. In other words, in the comparative example's sensor circuit, when the amplitude of the U-phase current Isa is small, the sensor output cannot be detected with high accuracy. Note that Figure 7 is an enlarged view of the waveform shown at position P2 in Figure 5.

[0084] In contrast, in the sensor circuit 10 of Embodiment 1, for example, when the amplitude of the U-phase current Isa is small, the waveform K1 of the corrected U-phase current becomes almost the same as the waveform of the U-phase current Isa (see Figure 7). Therefore, in the sensor circuit 10 of Embodiment 1, the output of the sensor 8 can be detected with high accuracy even when the amplitude of the U-phase current Isa is small.

[0085] In the sensor circuit 10 of Embodiment 1, the amplitude control circuit 1 amplifies the amplitude of the detected voltage (e.g., detected voltage V1) detected by the sensor 8 to generate a predetermined output voltage (e.g., output voltage V2). In other words, the conversion circuit 14 amplifies the detected voltage V1 and converts it into the output voltage V2.

[0086] As a result, in the sensor circuit 10 of Embodiment 1, the input voltage range (so-called dynamic range) of the control circuit 3 (specifically, the AD conversion unit 32) can be widened, so that, for example, the accuracy of reading the voltage value of the detected voltage detected by the sensor 8 during AD conversion by the AD conversion unit 32 can be improved. In other words, in the sensor circuit 10 of Embodiment 1, the decrease in resolution per bit during AD conversion by the AD conversion unit 32 can be reduced. Note that "the input voltage range of the control circuit 3 (specifically, the AD conversion unit 32)" means the voltage range that can be appropriately converted when converting from analog to digital by the AD conversion unit 32.

[0087] On the other hand, since the comparative example's sensor circuit does not have an amplitude control circuit 1, the input voltage range of the AD conversion unit 32 is narrower than that of the sensor circuit 10 in embodiment 1, and the resolution per bit decreases. As a result, in the comparative example's sensor circuit, as shown in Figure 7, when the amplitude of the U-phase current Isa is small, the corrected U-phase current waveform K2 becomes coarse data, and the sensor output cannot be detected with high accuracy.

[0088] Therefore, the sensor circuit 10 of Embodiment 1 can detect the output of the sensor 8 with higher accuracy than the sensor circuit of the comparative example. In other words, the sensor circuit 10 of Embodiment 1 can detect the output of the sensor 8 with higher accuracy.

[0089] Furthermore, the control circuit 3 controls the duty cycle based on the first fixed mode M2 ​​when the amplitude of the input voltage V1 of the switching circuit 4 is greater than or equal to a predetermined value (hereinafter referred to as the "first predetermined value") E1 (see Figure 4). For example, when the first fixed mode M2 ​​is selected as the control mode, the control circuit 3 controls (fixes) the duty cycle so that it becomes the first specified value D1 (see Figures 4 and 8).

[0090] Furthermore, the control circuit 3 controls the duty cycle based on the second fixed mode M3 when the amplitude of the input voltage V1 of the switching circuit 4 is less than the second predetermined value E2 (see Figure 4). For example, when the second fixed mode M3 is selected as the control mode, the control circuit 3 controls (fixes) the duty cycle so that it becomes the second predetermined value D2 (see Figures 4 and 9). The second predetermined value E2 is smaller than the first predetermined value E1. In this embodiment, for example, the first predetermined value E1 is 1 and the second predetermined value E2 is 10.

[0091] (4) The effect sensor circuit 10 comprises a sensor 8, a conversion circuit 14, and a control circuit 3, the conversion circuit 14 having a switching circuit 4. The control circuit 3 controls the duty cycle of the second control signal S2 according to the amplitude of the input voltage V1 of the switching circuit 4. As a result, the sensor circuit 10 can detect the output of the sensor 8 with higher accuracy.

[0092] Furthermore, the conversion circuit 14 includes an amplification circuit 5 and a filter 6. This allows the sensor circuit 10 to broaden the input voltage range of the control circuit 3 (specifically, the AD conversion unit 32). As a result, the sensor circuit 10 can detect the output of the sensor 8 with even greater precision.

[0093] The control circuit 3 has two control modes: a variable mode M1 and a fixed mode (first fixed mode M2 ​​or second fixed mode M3). The control circuit 3 controls the duty cycle based on either the variable mode M1 or the fixed mode. As a result, the sensor circuit 10 can change the control of the duty cycle by selecting either the variable mode M1 or the fixed mode (first fixed mode M2 ​​or second fixed mode M3) when controlling the duty cycle. Therefore, the sensor circuit 10 can adjust the output of the output voltage (for example, output voltage V2) converted by the conversion circuit 14, enabling the sensor 8 to detect the output with even greater accuracy.

[0094] Variable mode M1 is a mode in which the duty cycle continuously decreases as the input voltage V1 of the switching circuit 4 increases. This allows the sensor circuit 10 to adjust the control of the duty cycle. Therefore, the sensor circuit 10 can further adjust the output of the output voltage (for example, output voltage V2) converted by the conversion circuit 14, making it possible to detect the output of the sensor 8 with even greater accuracy.

[0095] The control circuit 3 controls the duty cycle based on the first fixed mode M2 ​​when the amplitude of the input voltage V1 of the switching circuit 4 is greater than or equal to a first predetermined value E1. As a result, the sensor circuit 10 can stabilize the output of the output voltage (for example, output voltage V2) converted by the conversion circuit 14. Furthermore, the sensor circuit 10 can suppress the duty cycle from becoming excessively small. Therefore, the sensor circuit 10 can reduce the amount of current flowing through the amplitude control circuit 1, for example, thus achieving lower power consumption.

[0096] Furthermore, the control circuit 3 controls the duty cycle based on the second fixed mode M3 when the amplitude of the input voltage V1 of the switching circuit 4 is less than the second predetermined value E2. This allows the sensor circuit 10 to stabilize the output of the output voltage (for example, output voltage V2) converted by the conversion circuit 14. In addition, the sensor circuit 10 can suppress the duty cycle from becoming excessively large, thereby achieving lower power consumption.

[0097] (5) Modified Example: The switching circuit 4 shown in Figure 2 has two switching elements Q7 and Q8, but it may also have only one switching element Q7. In this case, instead of switching element Q8, a diode is electrically connected in series with switching element Q7 in the switching circuit 4.

[0098] Each of the multiple switching elements Q1 to Q8 includes a parasitic diode, but may not include one. In this case, for example, each of the multiple switching elements Q1 to Q8 includes an external diode, and the external diode is connected in antiparallel between the drain and source of each switching element Q1 to Q8.

[0099] Furthermore, each of the multiple switching elements Q1 to Q8 is a MOSFET, but they may also be, for example, a bipolar transistor, an IGBT (Insulated Gate Bipolar Transistor), or a GaN-based GIT (Gate Injection Transistor).

[0100] Furthermore, although the switching circuit 4 is a half-bridge circuit, it may also be a full-bridge circuit, as shown in Figure 10, for example. In this case, the switching circuit 4 has two additional switching elements Q9 and Q10 in addition to the two switching elements Q7 and Q8. Note that the offset superposition circuit 2 is not shown in Figure 10.

[0101] Each of the two switching elements Q9 and Q10 is, for example, a MOSFET. Each of the two switching elements Q9 and Q10 includes a parasitic diode. Each of the two switching elements Q9 and Q10 has a first main terminal, a second main terminal, and a control terminal. For the sake of explanation, the first main terminal will be referred to as the drain terminal, the second main terminal as the source terminal, and the control terminal as the gate terminal.

[0102] The drain terminal of switching element Q9 is electrically connected to the drain terminal of switching element Q7. The gate terminal of switching element Q9 is electrically connected to the control circuit 3. The source terminal of switching element Q9 is electrically connected to the drain terminal of switching element Q10. The drain terminal of switching element Q10 is electrically connected to the inverting input terminal of operational amplifier 13. The gate terminal of switching element Q10 is electrically connected to the control circuit 3. The source terminal of switching element Q10 is electrically connected to the source terminal of switching element Q8.

[0103] The sensor 8 includes a shunt resistor (for example, shunt resistor Ra), but it may also include something other than a shunt resistor, such as a current transformer or a Hall element.

[0104] Furthermore, while sensor 8 detects current, it may also detect voltage. In other words, the sensor 8 may detect current, voltage, temperature, etc.

[0105] Amplifier circuit 5 is an inverting amplifier circuit, but it may also be a boost chopper circuit or the like.

[0106] Filter 6 is an RC type low-pass filter, but it may also be an LC type low-pass filter, for example. Furthermore, filter 6 is not limited to a low-pass filter; it may be another type of filter (for example, a notch filter), or it may be just a capacitor.

[0107] The control circuit 3 controls the conversion circuit 14 and the three-phase inverter circuit 20, but it may also control only the conversion circuit 14. In this case, a control unit separate from the control circuit 3 controls the three-phase inverter circuit 20.

[0108] The conversion circuit 14 has an offset superposition circuit 2, but it does not have to have an offset superposition circuit 2. In this case, the control circuit 3 has an offset superposition circuit 2.

[0109] In this embodiment, the sensor circuit 10 includes an amplification circuit 5, but it does not have to include the amplification circuit 5. Also, in this embodiment, the sensor circuit 10 includes a filter 6, but it does not have to include the filter 6. Also, in this embodiment, the sensor circuit 10 does not include a sensor 8, but it may include a sensor 8.

[0110] The sensor circuit 10 is used in the motor drive system 100, but it may also be used in a system that includes other inverter circuits besides the three-phase inverter circuit 20 (for example, a system that includes a grid-connected inverter). Furthermore, the sensor circuit 10 is not limited to systems that include inverter circuits, but may also be used in a system that includes a DC / DC converter, for example.

[0111] (Embodiment 2) The sensor circuit 10 according to Embodiment 2 differs from the sensor circuit 10 according to Embodiment 1 in that the resolution of the control circuit 3 (specifically, the AD conversion unit 32) is 8 bits. Regarding the sensor circuit 10 according to Embodiment 2, components similar to those in the sensor circuit 10 according to Embodiment 1 are denoted by the same reference numerals and their description is omitted.

[0112] The sensor circuit 10 according to Embodiment 2 will be described below with reference to Figures 11 to 13.

[0113] When variable mode M1 is selected as the control mode, the control circuit 3 sets the amplitude of the output voltage V2 of the conversion circuit 14 to a predetermined voltage (see Figure 4).

[0114] As a result, the waveforms K1 of the U-phase current before and after correction by the correction unit 33 are as shown in Figure 11. Figure 11 shows the waveforms of the simulation results. Waveform K2 in Figure 11 shows the waveforms of the U-phase current before and after correction by the correction unit in the comparative example sensor circuit. Furthermore, the waveforms in Figure 11 represent the case where the resolution of the control circuit 3 (specifically, the AD conversion unit 32) is 8 bits.

[0115] In the comparative example sensor circuit, for example, when the amplitude of the U-phase current Isa is large, the corrected U-phase current waveform K2 becomes different from the waveform of the U-phase current Isa, as shown in Figure 12. In other words, in the comparative example sensor circuit, when the amplitude of the U-phase current Isa is large, the sensor output cannot be detected with high accuracy. Note that Figure 12 is an enlarged view of the waveform shown at position P3 in Figure 11.

[0116] Furthermore, in the comparative example's sensor circuit, for example, when the amplitude of the U-phase current Isa is small, the corrected U-phase current waveform K2 becomes different from the waveform of the U-phase current Isa, as shown in Figure 13. Rather, in the comparative example's sensor circuit, when the amplitude of the U-phase current Isa is small, the sensor output cannot be detected. Note that Figure 13 is an enlarged view of the waveform shown at position P4 in Figure 11.

[0117] On the other hand, in the sensor circuit 10 of Embodiment 2, for example, when the amplitude of the U-phase current Isa is large, the corrected U-phase current waveform K1 becomes approximately the same as the waveform of the U-phase current Isa, as shown in Figure 12.

[0118] Furthermore, in the sensor circuit 10 of Embodiment 2, for example, when the amplitude of the U-phase current Isa is small, the waveform K1 of the corrected U-phase current is different from the waveform of the U-phase current Isa, as shown in Figure 13. However, compared to the sensor circuit of the comparative example, the output of the sensor 8 can be detected.

[0119] Therefore, the sensor circuit 10 of Embodiment 2 can detect the output of sensor 8 with higher accuracy than the sensor circuit of the comparative example. In other words, the sensor circuit 10 of Embodiment 2 can also detect the output of sensor 8 with higher accuracy. Furthermore, the sensor circuit 10 of Embodiment 2 can detect the output of sensor 8 even when the resolution of the control circuit 3 is low.

[0120] (Embodiment 3) The sensor circuit 10 according to Embodiment 3 differs from the sensor circuit 10 according to Embodiment 1 (see Figure 4) in that the change in duty cycle is different in the variable mode M1, as shown in Figure 14, for example. Regarding the sensor circuit 10 according to Embodiment 3, components similar to those in the sensor circuit 10 according to Embodiment 1 are denoted by the same reference numerals and their descriptions are omitted.

[0121] The variable mode M1 in the sensor circuit 10 of Embodiment 3 is a mode in which the duty cycle continuously decreases as the amplitude of the input voltage V1 of the switching circuit 4 increases, similar to the variable mode M1 in the sensor circuit 10 of Embodiment 1. Furthermore, the duty cycle changes in a stepwise manner. In addition, the duty cycle changes to have multiple (four in the example of Figure 14) flat portions 7. Note that "flat portion 7" means the portion in which the duty cycle is constant.

[0122] When variable mode M1 is selected as the control mode, the control circuit 3 controls the duty cycle according to the amplitude of the input voltage V1 of the amplitude control circuit 1 (specifically, the switching circuit 4), as shown in Figure 14. In this case, the amplitude of the output voltage V2 of the conversion circuit 14 does not become a predetermined voltage (see Figure 14). In other words, the amplitude of the output voltage V2 of the conversion circuit 14 becomes various voltages (voltage values) depending on the amplitude of the input voltage V1.

[0123] As a result, the waveform of the U-phase current after correction by the correction unit 33 has approximately the same amplitude or peak-to-peak value as the waveform K1 of the corrected U-phase current in the sensor circuit 10 of Embodiment 1 (see Figure 5), as shown in Figure 15. Figure 15 shows the waveform of the simulation result. Furthermore, the waveform in Figure 15 represents the case where the resolution of the control circuit 3 (specifically, the AD conversion unit 32) is 12 bits.

[0124] Therefore, the sensor circuit 10 of Embodiment 3 can detect the output of the sensor 8 with higher accuracy than the sensor circuit of the comparative example. In other words, the sensor circuit 10 of Embodiment 3 can detect the output of the sensor 8 with higher accuracy.

[0125] (Embodiment 4) The sensor circuit 10 according to Embodiment 4 differs from the sensor circuit 10 according to Embodiment 3 (see Figure 14) in that the change in duty cycle is different in the variable mode M1, as shown in Figure 16, for example. Regarding the sensor circuit 10 according to Embodiment 4, components similar to those in the sensor circuit 10 according to Embodiment 3 are denoted by the same reference numerals and their descriptions are omitted.

[0126] In the sensor circuit 10 of Embodiment 4, the variable mode M1 is a mode in which the duty cycle decreases discontinuously as the amplitude of the input voltage V1 of the switching circuit 4 increases, as shown in Figure 16. For example, the duty cycle changes in a step-like manner. Furthermore, the duty cycle changes to have multiple (four in the example of Figure 16) flat sections 7 and multiple (four in the example of Figure 16) vertical sections 9. The "vertical section 9" refers to the part in which the duty cycle decreases sharply and changes perpendicular to the flat section 7. Also, "vertical" is not limited to cases where the angle between the vertical section 9 and the flat section 7 is 90 degrees, but also includes cases where the angle is in the range of 85 degrees or more and less than 95 degrees.

[0127] When variable mode M1 is selected as the control mode, the control circuit 3 controls the duty cycle according to the amplitude of the input voltage V1 of the amplitude control circuit 1 (specifically, the switching circuit 4), as shown in Figure 16.

[0128] As a result, the waveform of the U-phase current after correction by the correction unit 33 has approximately the same amplitude or peak-to-peak value as the waveform of the corrected U-phase current in the sensor circuit 10 of Embodiment 3 (see Figure 15), as shown in Figure 17. Figure 17 shows the waveform of the simulation result. Furthermore, the waveform in Figure 17 represents the case where the resolution of the control circuit 3 (specifically, the AD conversion unit 32) is 12 bits.

[0129] Therefore, the sensor circuit 10 of Embodiment 4 can detect the output of the sensor 8 with higher accuracy than the sensor circuit of the comparative example. In other words, the sensor circuit 10 of Embodiment 4 can detect the output of the sensor 8 with higher accuracy.

[0130] Furthermore, in the sensor circuit 10 of Embodiment 4, the duty cycle decreases discontinuously, so for example, when the duty cycle changes, the generation of noise in the q-axis current Iq can be reduced (see Figures 15 and 17). Therefore, in the sensor circuit 10 of Embodiment 4, the generation of surge current when the duty cycle changes can be reduced.

[0131] Furthermore, in the sensor circuit 10 of Embodiment 4, when the duty cycle changes, the occurrence of chattering in the two switching elements Q7 and Q8 can be reduced (see Figures 15 and 17). Therefore, in the sensor circuit 10 of Embodiment 4, the generation of switching noise when the duty cycle changes can be reduced.

[0132] (Embodiment 5) The sensor circuit 10 according to Embodiment 5 differs from the sensor circuit 10 according to Embodiment 4 (see Figure 16) in that the change in duty cycle is different in the variable mode M1, as shown in Figure 18, for example. Regarding the sensor circuit 10 according to Embodiment 5, components similar to those in the sensor circuit 10 according to Embodiment 4 are denoted by the same reference numerals and their description is omitted.

[0133] As shown in Figure 18, the variable mode M1 in the sensor circuit 10 of Embodiment 5 is a mode in which the duty cycle changes to have a hysteresis characteristic. In other words, the control circuit 3 controls the duty cycle so that the change in the duty cycle has a hysteresis characteristic.

[0134] When variable mode M1 is selected as the control mode, the control circuit 3 controls the duty cycle according to the amplitude of the input voltage V1 of the amplitude control circuit 1 (specifically, the switching circuit 4), as shown in Figure 18.

[0135] As a result, the waveform of the U-phase current after correction by the correction unit 33 has approximately the same amplitude or peak-to-peak value as the waveform of the corrected U-phase current in the sensor circuit 10 of Embodiment 4 (see Figure 17), as shown in Figure 19. Figure 19 shows the waveform of the simulation result. Furthermore, the waveform in Figure 19 represents the case where the resolution of the control circuit 3 (specifically, the AD conversion unit 32) is 12 bits.

[0136] Therefore, the sensor circuit 10 of Embodiment 5 can detect the output of the sensor 8 with higher accuracy than the sensor circuit of the comparative example. In other words, the sensor circuit 10 of Embodiment 5 can detect the output of the sensor 8 with higher accuracy.

[0137] Furthermore, in the sensor circuit 10 of Embodiment 5, the duty cycle changes in a manner that exhibits hysteresis characteristics. For example, when the duty cycle changes, the generation of noise in the q-axis current Iq can be further reduced (see Figures 17 and 19). Therefore, in the sensor circuit 10 of Embodiment 5, the generation of surge current when the duty cycle changes can be further reduced.

[0138] Furthermore, in the sensor circuit 10 of Embodiment 5, when the duty cycle changes, the occurrence of chattering in the two switching elements Q7 and Q8 can be further reduced (see Figures 17 and 19). Therefore, in the sensor circuit 10 of Embodiment 5, the generation of switching noise when the duty cycle changes can be further reduced.

[0139] (Embodiment 6) The sensor circuit 10 according to Embodiment 6 differs from the sensor circuit 10 according to Embodiment 5 in that the operation of the sample-and-hold circuit 31 is different. Regarding the sensor circuit 10 according to Embodiment 6, components similar to those in the sensor circuit 10 according to Embodiment 5 are denoted by the same reference numerals and their descriptions are omitted.

[0140] In the sensor circuit 10 of Embodiment 6, the sample-and-hold circuit 31 does not hold the sample-and-hold signal when the duty cycle changes (see Figure 21). That is, the sample-and-hold circuit 31 does not accept the output voltage converted by the conversion circuit 14 as input. In other words, the control circuit 3 applies a mask to the input of the sample-and-hold signal when the duty cycle changes.

[0141] As a result, in the sensor circuit 10 of Embodiment 6, for example, when the duty cycle changes, the generation of noise in the q-axis current Iq can be further reduced (see Figures 19 and 20). Therefore, in the sensor circuit 10 of Embodiment 6, when the duty cycle changes, the generation of surge current can be further reduced.

[0142] Furthermore, in the sensor circuit 10 of Embodiment 6, when the duty cycle changes, the generation of noise in the U-phase current after correction by the correction unit 33 can be reduced (see Figures 19 and 20). Therefore, the sensor circuit 10 of Embodiment 6 can detect the output of the sensor 8 with even higher accuracy. In other words, the sensor circuit 10 of Embodiment 6 can suppress false detection of the output of the sensor 8.

[0143] Figure 20 shows the waveform of the simulation result. The waveform in Figure 20 represents the case where the resolution of the control circuit 3 (specifically, the AD conversion unit 32) is 12 bits. Figure 21 is an enlarged view of the waveform shown at position P5 in Figure 20.

[0144] (Aspects) The following aspects are disclosed in this specification.

[0145] The sensor circuit (10) according to the first embodiment comprises a conversion circuit (14) and a control circuit (3). The conversion circuit (14) converts the detection voltage (V1) detected by the sensor (8) into a predetermined output voltage (V2). The control circuit (3) controls the conversion circuit (14). The conversion circuit (14) has a switching circuit (4). The switching circuit (4) includes at least one switching element (Q7; Q8). The switching circuit (4) accepts the detection voltage (V1) as an input voltage. The control circuit (3) controls the duty cycle of the control signal (S2) to at least one switching element (Q7; Q8) according to the amplitude of the input voltage to the switching circuit (4).

[0146] According to this embodiment, the output of the sensor (8) can be detected with higher accuracy.

[0147] The sensor circuit (10) according to the second embodiment further comprises, in the first embodiment, an amplification circuit (14), an amplification circuit (5), and a filter (6). The amplification circuit (5) amplifies the output (V11) of the switching circuit (4). The filter (6) removes noise contained in the output (V12) of the amplification circuit (5) and outputs an output voltage (V2).

[0148] According to this embodiment, the output of the sensor (8) can be detected with even higher accuracy.

[0149] The sensor circuit (10) according to the third embodiment, in the first or second embodiment, has a control circuit (3) that has a variable mode (M1) and fixed modes (M2; M3) as control modes for controlling the duty cycle. The variable mode (M1) is a mode that changes the duty cycle. The fixed modes (M2; M3) are modes that fix the duty cycle so that it remains constant. The control circuit (3) controls the duty cycle based on either the variable mode (M1) or the fixed modes (M2; M3).

[0150] According to this embodiment, the output of the sensor (8) can be detected with even greater accuracy.

[0151] In the fourth embodiment, the sensor circuit (10) is such that, in the third embodiment, the variable mode (M1) is a mode in which the duty cycle continuously decreases as the amplitude of the input voltage of the switching circuit (4) increases.

[0152] According to this embodiment, the output of the sensor (8) can be detected with even higher accuracy.

[0153] The sensor circuit (10) according to the fifth embodiment, in the third embodiment, is a variable mode (M1) in which the duty cycle decreases discontinuously as the amplitude of the input voltage of the switching circuit (4) increases.

[0154] According to this embodiment, the output of the sensor (8) can be detected with even greater precision. Furthermore, according to this embodiment, the generation of surge current when the duty cycle changes can be reduced. Furthermore, according to this embodiment, the generation of switching noise when the duty cycle changes can be reduced.

[0155] In the sixth embodiment, the sensor circuit (10) is configured such that, in the fifth embodiment, the control circuit (3) controls the duty cycle such that the change in the duty cycle has hysteresis characteristics.

[0156] According to this embodiment, the generation of surge current when the duty cycle changes can be further reduced. Furthermore, according to this embodiment, the generation of switching noise when the duty cycle changes can be further reduced.

[0157] The sensor circuit (10) according to the seventh embodiment, in any one of the first to sixth embodiments, has a control circuit (3) which includes a sample-and-hold circuit (31). The sample-and-hold circuit (31) receives an input of the output voltage (V2) converted by the conversion circuit (14). The sample-and-hold circuit (31) holds a signal corresponding to the output voltage (V2). When the duty cycle changes, the sample-and-hold circuit (31) does not hold a signal corresponding to the output voltage (V2).

[0158] According to this embodiment, the generation of surge current when the duty cycle changes can be further reduced. In addition, according to this embodiment, false detection of the output of the sensor (8) can be suppressed.

[0159] The sensor circuit (10) according to the eighth embodiment, in the third embodiment, includes a fixed mode (M2; M3) which comprises a first fixed mode (M2) and a second fixed mode (M3). The first fixed mode (M2) is a mode in which the duty cycle is fixed so that it becomes a first specified value (D1). The second fixed mode (M3) is a mode in which the duty cycle is fixed so that it becomes a second specified value (D2). The second specified value (D2) is greater than the first specified value (D1). The control circuit (3) controls the duty cycle based on the first fixed mode (M2) when the amplitude of the input voltage of the switching circuit (4) is greater than or equal to a predetermined value (E1).

[0160] According to this embodiment, the output of the output voltage (V2) converted by the conversion circuit (14) can be stabilized. Furthermore, according to this embodiment, power consumption can be reduced.

[0161] In the ninth embodiment, the sensor circuit (10), in the eighth embodiment, controls the duty cycle based on a second fixed mode (M3) when the amplitude of the input voltage of the switching circuit (4) is less than a second predetermined value (E2) which is smaller than a first predetermined value (E1) which is a predetermined value (E1).

[0162] According to this embodiment, the output voltage (V2) converted by the conversion circuit (14) can be stabilized. Furthermore, according to this embodiment, power consumption can be reduced even further.

[0163] 3 Control circuit 4 Switching circuit 5 Amplifier circuit 6 Filter 8 Sensor 10 Sensor circuit 14 Conversion circuit 31 Sample-and-hold circuit D1 First specified value D2 Second specified value E1 First predetermined value E2 Second predetermined value M1 Variable mode M2 ​​First fixed mode M3 Second fixed mode Q7 Switching element Q8 Switching element S2 Second control signal V1 Detected voltage V2 Output voltage V11 Output voltage (output of switching circuit) V12 Output voltage (output of amplifier circuit)

Claims

A conversion circuit that converts the detected voltage detected by the sensor into a predetermined output voltage, The system comprises a control circuit for controlling the aforementioned conversion circuit, The conversion circuit has a switching circuit that includes at least one switching element, The switching circuit receives the detected voltage as an input voltage, The control circuit controls the duty cycle of the control signal to the at least one switching element according to the amplitude of the input voltage of the switching circuit. Sensor circuit. 　 The aforementioned conversion circuit is An amplification circuit that amplifies the output of the switching circuit, The amplifier circuit further comprises a filter that removes noise contained in the output of the amplifier circuit and outputs the output voltage, The sensor circuit according to claim 1. 　 The aforementioned control circuit is The control modes for controlling the duty cycle include a variable mode for changing the duty cycle and a fixed mode for fixing the duty cycle so that it remains constant. The duty cycle is controlled based on either the variable mode or the fixed mode. The sensor circuit according to claim 1 or claim 2. 　 The variable mode is a mode in which the duty cycle continuously decreases as the amplitude of the input voltage of the switching circuit increases. The sensor circuit according to claim 3. 　 The variable mode is a mode in which the duty cycle decreases discontinuously as the amplitude of the input voltage of the switching circuit increases. The sensor circuit according to claim 3. 　 The control circuit controls the duty cycle such that the change in the duty cycle has hysteresis characteristics. The sensor circuit according to claim 5. 　 The aforementioned control circuit is The circuit includes a sample-and-hold circuit that receives the input of the output voltage converted by the conversion circuit and holds a signal corresponding to the output voltage, The sample-and-hold circuit does not hold the signal corresponding to the output voltage when the duty cycle changes. The sensor circuit according to any one of claims 1 to 6. 　 The aforementioned fixed mode is, A first fixed mode in which the duty cycle is fixed so that the duty cycle becomes a first specified value, A second fixed mode includes fixing the duty cycle such that the duty cycle becomes a second specified value greater than the first specified value, The control circuit controls the duty cycle based on the first fixed mode when the amplitude of the input voltage of the switching circuit is greater than or equal to a predetermined value. The sensor circuit according to claim 3. 　 The control circuit controls the duty cycle based on the second fixed mode when the amplitude of the input voltage of the switching circuit is less than a second predetermined value which is smaller than the first predetermined value which is a predetermined value. The sensor circuit according to claim 8.

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