Current detection circuit

Abstract

Provided is a current detection circuit (50) that can accurately measure a current flowing to a load with a lower-cost configuration compared to the prior art. The current detection circuit is for a converter device (1) comprising: an inverter circuit (20) that is driven in accordance with a gate control signal (S1), generates a drive voltage by switching a DC voltage input from a power supply (10), and outputs the drive voltage to a load (30) having an inductance component; a current detection circuit that detects a return current returning from a first electrode of the power supply to a second electrode of the power supply via the inverter circuit; and a controller (40) that generates the gate control signal on the basis of the return current. The current detection circuit comprises: a first diode (51) having an anode connected to the second electrode of the power supply, and a cathode connected to the inverter circuit; and a series circuit (52) connected in parallel with the first diode, the series circuit being composed of a second diode (53) connected in a direction opposite to the first diode, and a resistor (54). The resistor detects a current detection voltage corresponding to the return current, and outputs the current detection voltage to the controller.

Description

Current Detection Circuit

[0001] The present disclosure relates to a current detection circuit.

[0002] Conventionally, in order to accurately control the drive amount of a load such as an actuator, a method for determining the drive amount of a load based on the current flowing through the load has been known. For example, Patent Document 1 discloses an inverter device in which a current detection circuit is connected between an output terminal of an inverter circuit and the load, and the current detection circuit is used to measure the current flowing through the load.

[0003] Japanese Patent Application Laid-Open No. 2001-309664

[0004] In recent years, there has been a demand for current detection circuits that can accurately measure the current flowing through a load with a low-cost configuration.

[0005] An object of the present disclosure is to provide a current detection circuit that can accurately measure the current flowing through a load with a configuration that is lower in cost than conventional techniques.

[0006] A current detection circuit according to one aspect of the present disclosure is a current detection circuit for a converter device including: an inverter circuit driven in response to a gate control signal, the inverter circuit switching a DC voltage input from a power supply to generate a drive voltage and outputting the drive voltage to a load having an inductance component; a current detection circuit detecting a feedback current returning from a first pole of the power supply via the inverter circuit to a second pole of the power supply; and a controller generating a gate control signal based on the feedback current, wherein the current detection circuit includes a first diode having an anode connected to the second pole of the power supply and a cathode connected to the inverter circuit, and a series circuit including a second diode connected in parallel with the first diode and connected in the opposite direction to the first diode, and a resistor, and the resistor detects a current detection voltage corresponding to the feedback current and outputs the voltage to the controller.

[0007] According to the present disclosure, it is possible to provide a current detection circuit that can accurately measure the current flowing through a load with a configuration that is lower in cost than conventional techniques.

[0008] 1 is a schematic diagram of a converter device according to a first embodiment. FIG. 2 is a timing chart of each signal waveform of the converter device shown in FIG. 1. FIG. 3 is a schematic diagram of a converter device as a comparative example to the converter device according to the first embodiment. FIG. 4 is a timing chart of each signal waveform of the converter device according to the comparative example. FIG. 5 is a timing chart of each signal waveform of the converter device shown in FIG. 7. FIG. 8 is a schematic diagram of a converter device according to a third embodiment. FIG. 9 is a timing chart of each signal waveform of the converter device shown in FIG.

[0009] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. However, the configurations described below are merely examples of the present disclosure, and the present disclosure is not limited to the following embodiments. The technology of the present disclosure is not limited to these embodiments, and various modifications, substitutions, additions, omissions, etc. are possible depending on the design, etc., as long as they do not deviate from the technical concept of the present disclosure.

[0010] Although the present disclosure has been fully described in connection with the preferred embodiments with reference to the accompanying drawings, various changes and modifications will be apparent to those skilled in the art, and such changes and modifications are to be understood as included within the scope of the present disclosure as defined by the appended claims unless they depart therefrom.

[0011] In the present disclosure, when describing comparative examples, modified examples, or multiple embodiments, differences from embodiment 1 will be mainly described. In this case, components in the comparative examples, modified examples, or other embodiments that are the same as or equivalent to those in embodiment 1 will be described using the same reference numerals. Furthermore, in the comparative examples, modified examples, or other embodiments, descriptions that overlap with embodiment 1 may be omitted.

[0012] In recent years, there has been a demand for a low-cost configuration that can accurately measure the current flowing through a load. For example, the inverter device disclosed in Patent Document 1 employs a configuration in which the output of a current detection circuit connected between the inverter circuit and the load is input to a control circuit that operates based on the potential on the ground side of the inverter circuit. In such a configuration, the potential difference between the potential of the output terminal of the inverter circuit and the potential on the ground side of the inverter circuit changes depending on the operating state of the inverter circuit. Therefore, the current detection circuit is required to be a circuit that is insulated from the path through which the current flows, but such a current detection circuit is expensive.

[0013] A current detection circuit according to the present disclosure is a circuit for a converter device, comprising an inverter circuit, a current detection circuit, and a controller. The inverter circuit is driven in response to a gate control signal and switches a DC voltage input from a power supply to generate a drive voltage and output the drive voltage to a load having an inductance component. The current detection circuit detects a feedback current that flows from a first pole of the power supply through the inverter circuit and returns to a second pole of the power supply. The controller generates a gate control signal based on the feedback current. The current detection circuit comprises a first diode having an anode connected to the second pole of the power supply and a cathode connected to the inverter circuit, and a series circuit including a second diode connected in the opposite direction to the first diode and a resistor. The series circuit is connected in parallel with the first diode. The resistor detects a current detection voltage corresponding to the feedback current and outputs the voltage to the controller.

[0014] With this configuration, the current detection circuit can be configured using simple circuit elements. The current detection circuit detects a current flowing from a first pole of a power supply to a load. That is, the current detection circuit detects a current flowing in one of two possible directions. A controller of a converter device including the current detection circuit can obtain the period during which current flows from the first pole to the load, allowing the controller to accurately measure the current flowing in the load. Therefore, the current detection circuit can accurately measure the current flowing in the load with a low-cost configuration.

[0015] (First embodiment) [1-1. Configuration] A converter device 1 according to a first embodiment of the present disclosure will be described with reference to Fig. 1 and Fig. 2. Fig. 1 shows a schematic diagram of the converter device 1 according to the first embodiment of the present disclosure.

[0016] As shown in FIG. 1 , the converter device 1 includes a power supply 10 , an inverter circuit 20 , an actuator 30 , a controller 40 , and a current detection circuit 50 .

[0017] The power supply 10 is a power supply that can apply a DC voltage of VCC to the inverter circuit 20. The power supply 10 includes a positive electrode and a negative electrode. The positive electrode is an example of a first electrode or a second electrode. The negative electrode is an example of a second electrode or a first electrode.

[0018] The inverter circuit 20 includes a plurality of MOSFETs Q1, Q2, Q3, and Q4, and inverters 21 and 22. MOSFETs are an example of switching elements. The inverter circuit 20 is driven in response to a gate control signal S1, including high and low signals, that is input to the gates of the MOSFETs Q1, Q2, Q3, and Q4. When driven in response to the gate control signal S1 output from the controller 40, the inverter circuit 20 switches the DC voltage input from the power supply 10 to generate a drive voltage and outputs the drive voltage to the actuator 30.

[0019] MOSFET Q1 and MOSFET Q2 are connected in series. The positive electrode of the power supply 10 is connected to one end of the current detection circuit 50 via the drain and source of MOSFET Q1 and the drain and source of MOSFET Q2. MOSFET Q3 and MOSFET Q4 are connected in series. The positive electrode of the power supply 10 is connected to one end of the current detection circuit 50 via the drain and source of MOSFET Q3 and the drain and source of MOSFET Q4. The series circuit of MOSFETs Q1 and Q2 and the series circuit of MOSFETs Q3 and Q4 are connected in parallel.

[0020] In the first embodiment, the gate control signal S1 is applied to the gate of the MOSFET Q1 and the gate of the MOSFET Q4. Alternatively, the gate control signal S1 is applied to the gate of the MOSFET Q2 via the inverter 21 and to the gate of the MOSFET Q3 via the inverter 22. The gate control signal S1 output from the controller 40 and an inverted signal obtained by inverting the gate control signal S1 by the inverter 21 or the inverter 22 constitute a pair of gate input signals having an inverted relationship with each other.

[0021] The actuator 30 is a load having an inductance component. The actuator 30 is, for example, a DC motor. The actuator 30 is connected between a connection point P1 between the source of the MOSFET Q1 and the drain of the MOSFET Q2, and a connection point P2 between the source of the MOSFET Q3 and the drain of the MOSFET Q4.

[0022] The controller 40 outputs a gate control signal S1 to control the driving of the inverter circuit 20 so that a current of a desired magnitude flows through the actuator 30. The controller 40 includes a microcontroller 41, a PWM modulator 42, and an AD converter 43.

[0023] The microcontroller 41 includes an arithmetic circuit and a storage device. The arithmetic circuit controls the overall operation of the microcontroller 41. The arithmetic circuit may either realize a predetermined function through cooperation between hardware resources and software, or realize a predetermined function using a dedicated hardware circuit. The arithmetic circuit includes a general-purpose processor such as a CPU or MPU that realizes a predetermined process or function by executing a program. The arithmetic circuit is configured to be able to communicate with the storage device. The arithmetic circuit realizes various functions of the microcontroller 41 by reading and executing arithmetic programs, etc. stored in the storage device.

[0024] The storage device is a storage medium that can store various information. This information includes programs and data. For example, the storage device stores an arithmetic program for implementing various functions according to the present embodiment. The storage device is implemented, for example, by a DRAM, an SRAM, a flash memory, a volatile or non-volatile semiconductor memory such as an SSD, an HDD, or other storage devices, or an appropriate combination thereof.

[0025] The microcontroller 41 transmits the duty ratio of the gate control signal S1 output from the PWM modulator 42 to the PWM modulator 42. Upon receiving the duty ratio, the PWM modulator 42 outputs a modulated signal having the received duty ratio as the gate control signal S1 to the inverter circuit 20. The PWM modulator 42 also outputs a timing signal indicating the timing of the gate control signal S1 to the microcontroller 41. The AD converter 43 converts the received analog signal into a digital signal and outputs it to the microcontroller 41. The microcontroller 41 determines the magnitude of the current flowing through the actuator 30 based on the received digital signal, and changes the duty ratio to be output to the PWM modulator 42 in accordance with the determination result.

[0026] The current detection circuit 50 is connected in series to the inverter circuit 20. In this embodiment, the current detection circuit 50 is disposed between the inverter circuit 20 and the negative electrode of the power supply 10. Specifically, one end of the current detection circuit 50 is connected to the connection point between the source of the MOSFET Q2 and the source of the MOSFET Q4. The other end of the current detection circuit 50 is connected to the negative electrode of the power supply 10.

[0027] The current detection circuit 50 includes a first diode 51, a series circuit 52, and an operational amplifier circuit 60. The series circuit 52 includes a second diode 53 and a current detection resistor 54 connected in series.

[0028] A first diode 51 has an anode connected to the negative terminal of power supply 10 and a cathode connected to the junction between the source of MOSFET Q2 and the source of MOSFET Q4.

[0029] The series circuit 52 is connected in parallel with the first diode 51. The second diode 53 is connected in the opposite direction to the first diode 51. That is, the second diode 53 has an anode connected to the connection point between the source of MOSFET Q2 and the source of MOSFET Q4, and a cathode connected to one end of a current detection resistor 54. The current detection resistor 54 has one end connected to the cathode of the second diode and the other end connected to the negative electrode of the power supply 10. The current detection resistor 54 detects and outputs a current flowing through the current detection resistor 54. For example, the current detection resistor 54 detects the current flowing through the current detection resistor 54 and outputs a voltage corresponding to the current to the controller 40.

[0030] The operational amplifier circuit 60 amplifies the voltage output from the current detection resistor 54 and outputs the amplified voltage to the AD converter 43. The operational amplifier circuit 60 includes an operational amplifier 61, resistors R1 and R2 connected to the non-inverting input terminal of the operational amplifier 61, and resistors R3 and R4 connected to the inverting input terminal of the operational amplifier 61. The non-inverting input terminal is connected to the connection point between the cathode of the second diode 53 and the current detection resistor 54 via resistor R1. The non-inverting input terminal is connected to the negative electrode of the power supply 10 via resistor R2. The inverting input terminal is connected to the negative electrode of the power supply 10 via resistor R3. The inverting input terminal is connected to the output terminal of the operational amplifier 61 via resistor R4.

[0031] [1-2. Operation] An outline of the operation of the converter device 1 according to the first embodiment will be described below. Fig. 2 shows a timing chart of each signal waveform of the converter device 1 shown in Fig. 1. S1 indicates the gate control signal S1. The gate control signal S1 has a cycle including a high period T1 and a low period T2. Q1 to Q4 indicate the on / off states of the MOSFETs Q1 to Q4, respectively.

[0032] The actuator voltage indicates the voltage applied to the actuator 30. I1 indicates the current flowing through MOSFET Q1. I2 indicates the current flowing through MOSFET Q2. I3 indicates the current flowing through MOSFET Q3. I4 indicates the current flowing through MOSFET Q4. I5 indicates the current flowing through the actuator 30 from connection point P1 to connection point P2. Current I5 is also referred to as the actuator current as appropriate. The actuator current includes a recurrent current flowing during period T1 and a regenerative current flowing during period T2, the details of which will be described later. I6 indicates the current flowing through the current detection resistor 54.

[0033] As described above, the PWM modulator 42 outputs the gate control signal S1, which includes high and low levels, to the inverter circuit 20.

[0034] First, the operation of each component of the converter device 1 during period T1 will be described. During period T1, the gate control signal S1 is high. During period T1, a high signal is input to the gates of MOSFETs Q1 and Q4, turning them on. Furthermore, a low signal is input to the gates of MOSFETs Q2 and Q3, turning them off. Therefore, during period T1, a feedback current I5 flowing from the positive electrode to the negative electrode of the power supply 10 flows via MOSFET Q1, actuator 30, MOSFET Q4, and current detection circuit 50.

[0035] The actuator voltage indicates the potential difference between connection points P1 and P2 caused by the DC voltage of the power supply 10. During period T1, connection point P1 is connected to the positive electrode of the power supply 10 via MOSFET Q1. Connection point P2 is connected to the negative electrode of the power supply 10 via MOSFET Q4 and current detection circuit 50. Therefore, a voltage of +VCC is applied between connection points P1 and P2. As a result, actuator current I5 flows from connection point P1 to connection point P2.

[0036] As described above, the actuator 30 has an inductance component. Therefore, the equivalent circuit of the actuator 30 can be expressed as a series circuit of a series resistance and an inductance. When a voltage of +VCC and a voltage of -VCC are applied to such an actuator 30 such that period T1 is greater than period T2, an actuator current I5 flows through the actuator 30 under certain conditions, as shown in FIG. 2.

[0037] For example, under conditions where the frequency of the modulation signal is such that the impedance of the inductance is sufficiently large relative to the resistance of the actuator 30, the value by which the current changes over time in the period of the modulation signal is small. Therefore, the current I5 is expressed as a value obtained by adding a predetermined amount of change to the offset current Ioffset due to the DC component, which is the average value of the voltage applied to the actuator 30. The offset current Ioffset is expressed by the following equation (1): Ioffset=VCC×((T1−T2) / (T1+T2)) / R (1)

[0038] For example, current I5 is expressed as a value obtained by adding the amount of change that increases at a gradient indicated by "(VCC-R x Ioffset) / L" during period T1. Current I5 is also expressed as a value obtained by adding the amount of change that decreases at a gradient indicated by "(-VCC-R x Ioffset) / L" during period T2. Note that the change in current is not precisely shown as a straight line, and fluctuates depending on the current flowing at that timing, but this fluctuation is small compared to the current value, so it is expressed as an approximately straight line.

[0039] 2, if the period T1 during which the gate control signal S1 is high is longer than the period T2 during which the gate control signal S1 is low, then during the period T1, power from the power supply 10 is stored in the inductance component and converted into heat by the series resistance component. Furthermore, during the period T2 described below, the power stored in the inductance component is regenerated to the power supply 10 and converted into heat by the series resistance component. Therefore, as described below, during the period T2, a regenerative current I5 flows through the actuator 30.

[0040] The regression current I5 flows to the current detection circuit 50 via the MOSFETs Q1 and Q4. The regression current I5 also flows to the negative terminal of the power supply 10 through the series circuit 52. That is, during the period T1, the regression current I5 flows through the second diode 53 and the current detection resistor 54. Therefore, during the period T1, the currents I1, I4, and I6 are equal to the current I5. The currents I2 and I3 are zero.

[0041] The current detection resistor 54 detects the current flowing through it and outputs a current detection voltage corresponding to the regression current I5 to the controller 40. In FIG. 2, Vr represents the current detection voltage output from the current detection resistor 54. The output current detection voltage Vr is amplified by the operational amplifier circuit 60 and input to the AD converter 43. In FIG. 2, Vad represents the amplified current detection voltage. The current detection voltage Vad is then AD converted by the AD converter 43 and input to the microcontroller 41. In this way, the microcontroller 41 can measure the current I5 flowing through the actuator during the period T1.

[0042] Next, the operation of each component of the converter device 1 during period T2 will be described. During period T2, the gate control signal S1 is low. During period T2, a low signal is input to the gates of MOSFETs Q1 and Q4, turning them off. Furthermore, a high signal is input to the gates of MOSFETs Q2 and Q3, turning them on.

[0043] During period T2, a regenerative current I5 flows through the actuator 30. The regenerative current I5 flows to the positive electrode of the power supply 10 via the current detection circuit 50, MOSFET Q2, actuator 30, and MOSFET Q3. Therefore, during period T2, the currents I2 and I3 are the inverse of the current I5. Furthermore, the currents I1, I4, and I6 are zero.

[0044] The regenerative current I5 flows through the first diode 51 in the current detection circuit 50. During the period T2, no current flows through the series circuit 52, so the current detection resistor 54 detects no current, and the current detection voltage Vad indicates zero.

[0045] As described above, in the first embodiment, the microcontroller 41 can measure the current I5 flowing through the actuator 30 during the period T1. Based on the timing signal acquired from the PWM modulator 42, the microcontroller 41 can determine the period T1 during which the regression current I5 flows and the period T2 during which the regenerative current I5 flows. The microcontroller 41 can accurately measure the regression current I5 by acquiring the output of the AD converter 43 during the period T1. Based on the regression current I5 and the duty ratio, the microcontroller 41 can calculate and acquire the current I5 flowing through the actuator 30, including the regression current I5 and the regenerative current I5. This allows the microcontroller 41 to accurately determine the current I5 flowing through the actuator 30 and, as a result, the amount of drive of the actuator 30. Furthermore, the microcontroller 41 can adjust the duty ratio according to the current I5 flowing through the actuator 30 so that a desired magnitude of the current I5 flows through the actuator 30.

[0046] Furthermore, the current detection voltage Vr output from the current detection resistor 54 according to the first embodiment is a positive value. Therefore, unlike the comparative example described below, the operational amplifier circuit 60 does not need to offset the current detection voltage Vr by a predetermined voltage. Because the current detection voltage Vr is not offset by a predetermined voltage, the operational amplifier circuit 60 can amplify the current detection voltage Vr by a larger factor than in the comparative example. Therefore, the converter device 1 including the current detection circuit 50 according to the present disclosure can improve the accuracy of AD conversion.

[0047] <Comparative Example> A comparative example to the converter device 1 in embodiment 1 will be described. Fig. 3 shows a schematic diagram of a converter device 1 that is a comparative example to the converter device 1 in embodiment 1. The converter device 1 in the comparative example differs from the converter device 1 in embodiment 1 in that the current detection circuit 50 in the comparative example is composed of only a current detection resistor 54. Furthermore, the converter device 1 in the comparative example applies an offset voltage Voff to the non-inverting input terminal via a resistor R5.

[0048] 4 shows a timing chart of each signal waveform of the converter device 1 according to the comparative example. In FIG. 4, the waveforms related to I6, Vr, and Vad are different from the waveforms shown in FIG.

[0049] In the converter device 1 according to the comparative example, when the gate control signal S1 is input to the inverter circuit 20, a current I5 flows through the actuator 30, similar to the converter device 1 according to the first embodiment. In the comparative example, the current detection circuit 50 has only the current detection resistor 54, and therefore both the feedback current I5 and the regenerative current I5 flow through the current detection resistor 54.

[0050] In the converter devices 1 according to the first embodiment and the comparative example, the voltage proportional to the current detected by the current detection resistor 54 is set to a very small value, for example, a maximum of approximately 100 mV, in order to suppress power loss due to the current detection resistor 54. The input voltage of the AD converter 43, which converts the current detection voltage Vr into digital data usable by the microcontroller 41 that executes control, is, for example, a maximum of 3.3 V. In this case, an operational amplifier circuit 60 having a 33-fold amplification factor can be inserted between the current detection resistor 54 and the AD converter 43.

[0051] As indicated by I5 in FIG. 4 , current flows in a fixed direction through the actuator 30. However, as indicated by I6 in FIG. 4 , the direction of current flowing through the current detection resistor 54 in the comparative example changes depending on the state of the gate control signal S1. Therefore, the voltage generated across the current detection resistor 54 takes on positive and negative values. The input voltage range of the AD converter 43 is generally 0 V to the maximum input voltage. To limit the input voltage to the AD converter 43 within this input voltage range, an offset voltage Voff is applied to the non-inverting input terminal of the operational amplifier 61 in the operational amplifier circuit 60 of the converter device 1 according to the comparative example via resistor R5. The offset voltage Voff can be set so that the output voltage Vad of the operational amplifier circuit 60 is half the maximum input voltage when the current detection voltage Vr is 0 V.

[0052] In this way, in the converter device 1 according to the comparative example, the offset voltage Voff is added to the current detection voltage Vr. Therefore, the gain of the operational amplifier circuit 60 is set to half the gain (e.g., approximately 16 times) compared to when the offset voltage Voff is not added, so that the current detection voltage Vr is half the input voltage range of the AD converter 43. Because the gain of the operational amplifier circuit 60 is halved, the accuracy of AD conversion by the AD converter 43 is halved.

[0053] In the converter device 1 according to the first embodiment, the current detection voltage Vr takes only positive values, as indicated by I6 in Fig. 2. Therefore, the converter device 1 according to the first embodiment does not need to superimpose the offset voltage Voff in the operational amplifier circuit 60. Therefore, the current detection circuit 50 of the converter device 1 according to the first embodiment can improve the accuracy of the AD conversion that occurs in the converter device 1 according to the comparative example.

[0054] [1-3. Effects] According to the current detection circuit 50 according to the first embodiment of the present disclosure, the following effects can be achieved.

[0055] The current detection circuit 50 is a circuit for the converter device 1, which includes an inverter circuit 20, a controller 40, and the inverter circuit 20. The inverter circuit 20 is driven in response to a gate control signal S1 and switches a DC voltage input from the power supply 10 to generate a drive voltage and output the drive voltage to a load 30 having an inductance component. The current detection circuit 50 detects a feedback current I5 that flows from a first pole of the power supply 10 through the inverter circuit 20 and returns to a second pole of the power supply 10. The controller 40 generates a gate control signal S1 based on the feedback current I5. The current detection circuit 50 includes a first diode 51 having an anode connected to the second pole of the power supply 10 and a cathode connected to the inverter circuit 20, and a series circuit 52 including a second diode 53 connected in the opposite direction to the first diode 51 and a resistor 54. The series circuit 52 is connected in parallel with the first diode 51. The resistor 54 detects a current detection voltage Vr corresponding to the feedback current I5 and outputs the voltage to the controller 40.

[0056] With this configuration, the current detection circuit 50 can be configured using simple circuit elements. Furthermore, the current detection circuit 50 detects a current detection voltage Vr corresponding to the current I5 based on the current I5 flowing from the first pole of the power supply 10 to the load 30. That is, the current detection circuit 50 detects a current flowing in one of two possible directions. The controller 40 of the converter device 1 equipped with the current detection circuit 50 can acquire the period during which the current I5 flows from the first pole to the load 30, allowing the controller 40 to accurately measure the current I5 flowing through the load 30. Therefore, the current detection circuit 50 can accurately measure the current I5 flowing through the load 30 with a low-cost configuration.

[0057] The current detection circuit 50 also includes an operational amplifier circuit 60 disposed between the resistor 54 and the controller 40, which amplifies the input current detection voltage and outputs the amplified current detection voltage to the controller 40. Because the current detection voltage from the current detection resistor 54 is only positive, this configuration eliminates the need for the current detection circuit 50 to apply an offset voltage to the operational amplifier 61 to make the voltage positive when output to the controller 40. Therefore, the current detection circuit 50 can improve the accuracy of AD conversion by the AD converter 43 in the controller 40, which converts the analog signal from the operational amplifier circuit 60 into a digital signal and outputs it. Therefore, the current detection circuit 50 can accurately measure the current I5 flowing through the load 30 with a low-cost configuration.

[0058] (Embodiment 2) [2-1. Configuration] An overview of the converter device 1 in embodiment 2 will be described. Fig. 5 shows a schematic diagram of the converter device 1 according to embodiment 2. Compared to the current detection circuit 50 of the converter device 1 according to embodiment 1, the current detection circuit 50 of the converter device 1 according to embodiment 2 further includes a low-pass filter 55. In embodiment 2, the low-pass filter 55 is disposed between the series circuit 52 and the operational amplifier circuit 60.

[0059] In the second embodiment, the low-pass filter 55 has one end connected to the connection point between the cathode of the second diode 53 and the current detection resistor 54, and the other end connected to the non-inverting input terminal of the operational amplifier 61 via the resistor R1.

[0060] [2-2. Operation] Hereinafter, an outline of the operation of the converter device 1 according to the second embodiment will be described.

[0061] The low-pass filter 55 smoothes the current detection voltage Vr output from the current detection resistor 54 by low-pass filtering components below a predetermined cutoff frequency, and outputs the smoothed current detection voltage Vr to the operational amplifier circuit 60. The operational amplifier circuit 60 amplifies the smoothed current detection signal and outputs it to the controller 40.

[0062] FIG. 6 shows a timing chart of each signal waveform of the converter device 1 shown in FIG. 5. In FIG. 6, Vsm represents the current detection voltage smoothed by the low-pass filter 55. For example, Vsm represents the average voltage obtained by smoothing the current detection voltage Vr output from the current detection resistor 54. The average voltage represents the voltage corresponding to the average value of the current I5 flowing through the actuator 30 during the period T1, i.e., the average value of the regression current I5. The smoothed current detection voltage Vsm output from the low-pass filter is amplified by the operational amplifier circuit 60 and input to the AD converter 43 and then to the microcontroller 41. In FIG. 6, Vad represents the amplified, smoothed current detection voltage.

[0063] In the converter device 1 according to the first embodiment, the operational amplifier circuit 60 is required to amplify the current detection waveform generated based on the current detection resistor 54 without distortion. Therefore, the frequency bandwidth of the operational amplifier 61 is generally required to be at least 10 times the frequency of the modulation signal period (e.g., the PWM period). For example, if the PWM period frequency is set to 100 kHz, the operational amplifier 61 is required to have a frequency bandwidth of approximately 1 MHz while maintaining an amplification factor of 33. Therefore, the converter device 1 according to the first embodiment is required to include an operational amplifier 61 that can operate at high speed, which is more expensive than an operational amplifier that does not operate at high speed.

[0064] In the converter device 1 according to the second embodiment, the low-pass filter 55 removes high-frequency components of the modulation signal period from the current detection voltage, and the resulting average value is input to the operational amplifier circuit 60. Therefore, the operational amplifier 61 does not need to have a wide frequency bandwidth. Therefore, the converter device 1 can perform current detection using an operational amplifier 61 that is slower than the operational amplifier 61 included in the converter device 1 according to the first embodiment.

[0065] In the converter device 1 according to the second embodiment, the microcontroller 41 can measure the average value of the current flowing through the current detection resistor 54. Therefore, the microcontroller 41 can acquire the output of the AD converter 43 without matching the timing of acquiring the output of the AD converter 43 with the timing signal output from the PWM modulator 42. This eliminates the need for the microcontroller 41 to acquire the timing signal from the PWM modulator 42. Furthermore, because a voltage from which high-frequency components have been removed is input to the AD converter 43, the converter device 1 can detect the current using a slow AD converter 43 with a long conversion time.

[0066] In the second embodiment, the average value of the current measured by the microcontroller 41 indicates the average value of the current I5 flowing during the period T1 of the current I5 flowing through the actuator 30. Therefore, the microcontroller 41 can correct the acquired average value of the current to the value of the current flowing through the actuator 30 by dividing the output value of the AD converter 43 by the duty ratio, that is, by the ratio of the period T1 to one cycle. Therefore, the microcontroller 41 can obtain the average value of the current I5 flowing through the actuator 30 based on the average value of the current I5 flowing through the actuator 30 during the period T1.

[0067] [2-3. Effects] According to the current detection circuit 50 according to the second embodiment of the present disclosure, the following effects can be achieved.

[0068] The current detection circuit 50 is a circuit for the converter device 1, which includes an inverter circuit 20, a controller 40, and the inverter circuit 20. The inverter circuit 20 is driven in response to a gate control signal S1 and switches a DC voltage input from the power supply 10 to generate a drive voltage and output the drive voltage to a load 30 having an inductance component. The current detection circuit 50 detects a feedback current I5 that flows from a first pole of the power supply 10 through the inverter circuit 20 and returns to a second pole of the power supply 10. The controller 40 generates a gate control signal S1 based on the feedback current I5. The current detection circuit 50 includes a first diode 51 having an anode connected to the second pole of the power supply 10 and a cathode connected to the inverter circuit 20, and a series circuit 52 including a second diode 53 connected in the opposite direction to the first diode 51 and a resistor 54. The series circuit 52 is connected in parallel with the first diode 51. The resistor 54 detects a current detection voltage Vr corresponding to the feedback current I5 and outputs the voltage to the controller 40. The current detection circuit 50 further includes a low-pass filter 55 disposed between the resistor 54 and the controller 40, which low-pass filters the current detection voltage and outputs the filtered voltage to the controller.

[0069] With this configuration, the low-pass filter 55 outputs the average voltage Vsm, which is the current detection voltage Vr that may fluctuate with the same period as the gate control signal S1, with high-frequency components removed. Therefore, the controller 40 of the converter device 1 including the current detection circuit 50 does not need to acquire the output from the current detection circuit 50 at the specified timing of the gate control signal S1. As a result, the controller 40 can accurately acquire the current I5 flowing through the load 30 with simple control.

[0070] The current detection circuit 50 also includes an operational amplifier circuit 60 disposed between the low-pass filter 55 and the controller 40, which amplifies the input current detection voltage Vr and outputs the amplified current detection voltage Vr to the controller 40. Because the low-pass filter 55 outputs an average voltage Vsm, from which high-frequency components have been removed, this configuration eliminates the need for the operational amplifier circuit 60 to include an operational amplifier 61 with a wide frequency bandwidth. Therefore, the current detection circuit 50 can perform current detection using an operational amplifier 61 that is slower than the current detection circuit 50 according to the first embodiment. Therefore, the current detection circuit 50 can accurately measure the current I5 flowing through the load 30 with a low-cost configuration.

[0071] (Third Embodiment) [3-1. Configuration] An overview of the converter device 1 according to the third embodiment will be described. FIG. 7 shows a schematic diagram of the converter device 1 according to the third embodiment. Compared to the current detection circuit 50 of the converter device 1 according to the second embodiment, the current detection circuit 50 of the converter device 1 according to the third embodiment includes a current detection resistor 57 and a low-pass filter 58. The first diode 51 and the current detection resistor 57 connected in series form a series circuit 56. In the third embodiment, the current detection resistor 57 has a resistance value equivalent to that of the current detection resistor 54. The current detection resistor 54 is an example of a first resistor. The current detection resistor 57 is an example of a second resistor. The series circuit 52 is an example of a first series circuit. The series circuit 56 is an example of a second series circuit.

[0072] The series circuits 52 and 56 are connected in parallel to each other. The first diode 51 has a cathode connected to the connection point between the source of the MOSFET Q2 and the source of the MOSFET Q4, and an anode connected to one end of a current detection resistor 57. The current detection resistor 57 has one end connected to the anode of the first diode and the other end connected to the negative pole of the power supply 10. The current detection resistor 57 detects and outputs a current flowing through the current detection resistor 57. For example, the current detection resistor 57 detects the current flowing through the current detection resistor 57 and outputs a voltage corresponding to the current to the controller 40.

[0073] In the third embodiment, the low-pass filter 58 is disposed between the series circuit 56 and the operational amplifier circuit 60. The low-pass filter 58 has one end connected to the connection point between the anode of the first diode and the current detection resistor 57, and the other end connected to the inverting input terminal of the operational amplifier 61 via a resistor R6, which will be described later.

[0074] In the third embodiment, an operational amplifier circuit 60 includes an operational amplifier 61, resistors R1 and R2 connected to the non-inverting input terminal of the operational amplifier 61, and resistors R4 and R6 connected to the inverting input terminal of the operational amplifier 61. The non-inverting input terminal is connected to the connection point between the cathode of the second diode 53 and the current detection resistor 54 via the resistor R1 and a low-pass filter 55. The non-inverting input terminal is connected to the negative electrode of the power supply 10 via the resistor R2. The inverting input terminal is connected to the connection point between the anode of the first diode 51 and the current detection resistor 57 via the resistor R6 and a low-pass filter 58. The inverting input terminal is connected to the output terminal of the operational amplifier 61 via the resistor R4.

[0075] [3-2. Operation] Hereinafter, an outline of the operation of the converter device 1 according to the third embodiment will be described.

[0076] In the converter device 1 according to the third embodiment, when a regression current I5 flows through the actuator 30, the regression current I5 flows through the series circuit 52. The current detection resistor 54 detects the regression current I5 flowing through the current detection resistor 54 and outputs a current detection voltage. The current detection voltage from the current detection resistor 54 is input to the non-inverting input terminal of the operational amplifier 61 via the low-pass filter 55.

[0077] Furthermore, when regenerative current I5 flows through actuator 30, regenerative current I5 flows through series circuit 56. Current detection resistor 57 detects regenerative current I5 flowing through current detection resistor 57 and outputs a current detection voltage. The current detection voltage from current detection resistor 57 is input to the inverting input terminal of operational amplifier 61 via low-pass filter 58. Low-pass filter 58 smoothes the current detection voltage output from current detection resistor 57 by low-pass filtering components below a predetermined cutoff frequency, and outputs the smoothed voltage to operational amplifier circuit 60.

[0078] In the converter device 1 according to the third embodiment, the operational amplifier circuit 60 is configured to operate as a differential amplifier circuit. Therefore, the operational amplifier circuit 60 subtracts the smoothed current detection voltage input to its inverting input terminal from the smoothed current detection voltage input to its non-inverting input terminal, amplifies the subtracted value, and outputs the amplified value to the AD converter 43.

[0079] Fig. 8 shows a timing chart of each signal waveform of the converter device 1 shown in Fig. 7. In Fig. 8, V+ indicates the current detection voltage smoothed by the low-pass filter 55. For example, V+ indicates an average voltage obtained by smoothing the current detection voltage output from the current detection resistor 54. The average voltage V+ indicates a voltage corresponding to the average value of the current I5 flowing through the actuator 30 during the period T1, i.e., the average value of the regression current I5.

[0080] In Figure 8, V- indicates the current detection voltage smoothed by the low-pass filter 58. For example, V- indicates an average voltage obtained by smoothing the current detection voltage output from the current detection resistor 57. The average voltage V- indicates a voltage corresponding to the average value of the current I5 flowing through the actuator 30 during the period T2, that is, the average value of the regenerative current I5. V+ is an example of a first average voltage. V- is an example of a second average voltage.

[0081] 8, Vad indicates a voltage obtained by subtracting the average voltage V- output from the low-pass filter 58 from the average voltage V+ output from the low-pass filter 55 and amplifying the result using the operational amplifier circuit 60. For example, Vad indicates a voltage calculated by the following equation (2). α indicates the amplification factor of the operational amplifier circuit 60. Vad=((V+)-(V-))×α (2)

[0082] 8, in the third embodiment, V+ indicates a positive value and V- indicates a negative value. Therefore, Vad indicates a value obtained by amplifying the sum of the absolute values ​​of V+ and V-. Therefore, Vad indicates an average voltage corresponding to the current I5 flowing through the actuator 30, including the regression current I5 and the regenerative current I5.

[0083] Regardless of the duty ratio, the microcontroller 41 can use the value acquired from the AD converter 43 as a value corresponding to the current I5 flowing through the actuator 30. Therefore, according to the converter device 1 of the third embodiment, the processing load on the microcontroller 41 is reduced.

[0084] [3-3. Effects] According to the current detection circuit 50 according to the third embodiment of the present disclosure, the following effects can be achieved.

[0085] The current detection circuit 50 is a circuit for the converter device 1, which includes an inverter circuit 20, a controller 40, and the inverter circuit 20. The inverter circuit 20 is driven in response to a gate control signal S1 and switches a DC voltage input from the power supply 10 to generate a drive voltage and output the drive voltage to a load 30 having an inductance component. The current detection circuit 50 detects a feedback current I5 that flows from a first pole of the power supply 10 through the inverter circuit 20 and returns to a second pole of the power supply 10. The controller 40 generates a gate control signal S1 based on the feedback current I5. The current detection circuit 50 includes a first diode 51 having an anode connected to the second pole of the power supply 10 and a cathode connected to the inverter circuit 20, and a series circuit 52 including a second diode 53 connected in the opposite direction to the first diode 51 and a resistor 54. The series circuit 52 is connected in parallel with the first diode 51. The resistor 54 detects a current detection voltage Vr corresponding to the feedback current I5 and outputs the voltage to the controller 40. The resistor 54 is a first resistor 54, and the series circuit 52 is a first series circuit 52. The current detection circuit 50 further detects a regenerative current I5 flowing from the load 30 via the inverter circuit 20 to the first pole of the power supply 10. The first diode 51 and the second resistor 57 form a second series circuit 56 connected in parallel with the first series circuit 52. The second resistor 57 detects a current detection voltage corresponding to the regenerative current I5 and outputs it to the controller 40. The current detection circuit 50 further includes a differential amplifier circuit 60 that outputs the difference between the current detection voltage from the first resistor 54 and the current detection voltage from the second resistor 57 to the controller 40.

[0086] With this configuration, the current detection circuit 50 can detect the regenerative current I5 flowing from the load 30 to the first pole of the power supply 10, in addition to the feedback current I5 flowing from the first pole of the power supply 10 to the load 30. Therefore, the current detection circuit 50 can output a current detection voltage corresponding to the current I5 flowing through the load 30, regardless of whether the gate control signal S1 indicates a high or low value. The controller 40 of the converter device 1 equipped with the current detection circuit 50 can measure the current I5 flowing through the load using the value obtained from the current detection circuit 50 without considering the duty ratio of the gate control signal S1. Therefore, the controller 40 can accurately obtain the current I5 flowing through the load 30 with simple control.

[0087] The current detection circuit 50 also includes a first low-pass filter 55 and a second low-pass filter 58. The first low-pass filter 55 low-pass filters the current detection voltage from the first resistor 54 and outputs the result to the differential amplifier circuit 60. The second low-pass filter 58 low-pass filters the current detection voltage from the second resistor 57 and outputs the result to the differential amplifier circuit 60. With this configuration, the current detection circuit 50 can output the average value of the current detection voltage corresponding to the current I5 flowing through the load 30, regardless of whether the gate control signal S1 indicates a high or low value. Therefore, the current detection circuit 50 can accurately measure the current I5 flowing through the load 30 with a low-cost configuration.

[0088] (Modification) In the current detection circuit 50 according to the first embodiment described above, the operational amplifier circuit 60 is connected between the series circuit 52 and the controller 40, but the current detection circuit 50 is not limited to a configuration that includes the operational amplifier circuit 60. For example, the current detection circuit 50 may be configured to input the current detection voltage Vr output from the current detection resistor 54 to the AD converter 43.

[0089] In the current detection circuit 50 according to the third embodiment described above, the low-pass filters 55 and 58 are connected between the series circuits 52 and 56 and the operational amplifier circuit 60, but the current detection circuit 50 is not limited to a form including the low-pass filters 55 and 58.

[0090] 7 may be configured not to include the low-pass filters 55 and 58, as in the current detection circuit 50 according to the first embodiment. In this case, the operational amplifier circuit 60 outputs the difference between the output from the current detection resistor 54 and the output from the current detection resistor 57 to the controller 40. For example, the output from the current detection resistor 54 is a current detection voltage corresponding to the current value of the regression current I5. For example, the output from the current detection resistor 57 is a current detection voltage corresponding to the current value of the regenerative current I5.

[0091] In the converter device 1 described above, the current detection circuit 50 is disposed between the inverter circuit 20 and the negative electrode of the power supply 10, but the location of the current detection circuit 50 is not limited to this. For example, the current detection circuit 50 may be disposed between the inverter circuit 20 and the positive electrode of the power supply 10.

[0092] (Summary of Aspects) As is clear from the above description, the present disclosure includes the following aspects. In the following, reference numerals are given in parentheses only to clarify the correspondence with the embodiments.

[0093] (Aspect 1) A current detection circuit (50) according to the present disclosure is a current detection circuit for a converter device (1) including: an inverter circuit (20) driven in response to a gate control signal (S1), the inverter circuit switching a DC voltage input from a power source (10) to generate a drive voltage and outputting the drive voltage to a load (30) having an inductance component; a current detection circuit detecting a feedback current returning from a first pole of the power source via the inverter circuit to a second pole of the power source; and a controller (40) generating a gate control signal based on the feedback current, wherein the current detection circuit includes: a first diode (51) having an anode connected to the second pole of the power source and a cathode connected to the inverter circuit; and a series circuit (52) connected in parallel with the first diode, the second diode (53) being connected in the opposite direction to the first diode, and a resistor (54), the resistor detecting a current detection voltage corresponding to the feedback current and outputting the voltage to the controller.

[0094] (Aspect 2) The current detection circuit (50) of aspect 1 may further include a low-pass filter (55) disposed between the resistor (54) and the controller (40), which low-pass filters the current detection voltage and outputs it to the controller.

[0095] (Aspect 3) The current detection circuit (50) of aspect 1 may further include an operational amplifier circuit (60) disposed between the resistor (54) and the controller (40), which amplifies the input current detection voltage and outputs it to the controller.

[0096] (Aspect 4) The current detection circuit (50) of aspect 2 may further include an operational amplifier circuit (60) disposed between the low-pass filter (55) and the controller (40), which amplifies the input current detection voltage and outputs it to the controller.

[0097] (Aspect 5) In the current detection circuit (50) of aspect 1, the resistor (54) is a first resistor (54), and the series circuit (52) is a first series circuit (52), the current detection circuit further detects a regenerative current flowing from the load (30) to a first pole of the power supply (10) via the inverter circuit (20), a second series circuit (56) connected in parallel with the first series circuit and constituting a second series circuit of the first diode (51) and a second resistor (57), the second resistor detects a current detection voltage corresponding to the regenerative current and outputs it to the controller (40), and the current detection circuit may further include a differential amplifier circuit (60) that outputs the difference between the current detection voltage from the first resistor and the current detection voltage from the second resistor to the controller.

[0098] (Aspect 6) The current detection circuit (50) of aspect 5 may further include a first low-pass filter (55) that low-pass filters the current detection voltage from the first resistor (54) and outputs it to the differential amplifier circuit (60), and a second low-pass filter (58) that low-pass filters the current detection voltage from the second resistor (57) and outputs it to the differential amplifier circuit.

[0099] As used herein, terms such as "first," "second," etc. are used for descriptive purposes only and should not be understood as expressing or implying relative importance or ranking of technical features. Features qualified as "first" and "second" expressly or imply the inclusion of one or more of that feature.

[0100] The converter device 1 described in the present disclosure is realized by the cooperation of hardware resources, such as a processor and a memory, and software (computer program).

[0101] According to the present disclosure, a current detection circuit that can accurately measure the current flowing through a load can be provided with a configuration that is lower cost than conventional techniques, and therefore can be suitably used in this type of industrial field.

Claims

1. A current detection circuit for a converter device comprising: an inverter circuit driven in response to a gate control signal, the inverter circuit switching a DC voltage input from a power supply to generate a drive voltage and outputting it to a load having an inductance component; a current detection circuit detecting a feedback current returning from a first pole of the power supply via the inverter circuit to a second pole of the power supply; and a controller generating a gate control signal based on the feedback current, wherein the current detection circuit comprises: a first diode having an anode connected to the second pole of the power supply and a cathode connected to the inverter circuit; and a series circuit consisting of a resistor and a second diode connected in parallel with the first diode and connected in the opposite direction to the first diode, the resistor detecting a current detection voltage corresponding to the feedback current and outputting it to the controller.

2. The current detection circuit according to claim 1, further comprising a low-pass filter disposed between said resistor and said controller, said low-pass filtering said current detection voltage and outputting the filtered voltage to said controller.

3. The current detection circuit according to claim 1, further comprising an operational amplifier circuit disposed between said resistor and said controller, said operational amplifier circuit amplifying said input current detection voltage and outputting the amplified voltage to said controller.

4. The current detection circuit according to claim 2, further comprising an operational amplifier circuit disposed between said low-pass filter and said controller, said operational amplifier circuit amplifying said input current detection voltage and outputting the amplified voltage to said controller.

5. The current detection circuit according to claim 1, wherein the resistor is a first resistor, the series circuit is a first series circuit, the current detection circuit further detects a regenerative current flowing from the load through the inverter circuit to a first pole of the power supply, and a second series circuit is connected in parallel with the first series circuit and forms a second series circuit of the first diode and a second resistor, the second resistor detects a current detection voltage corresponding to the regenerative current and outputs it to the controller, and the current detection circuit further comprises a differential amplifier circuit that outputs a difference between the current detection voltage from the first resistor and the current detection voltage from the second resistor to the controller.

6. The current detection circuit according to claim 5, further comprising: a first low-pass filter that low-pass filters the current detection voltage from the first resistor and outputs the result to the differential amplifier circuit; and a second low-pass filter that low-pass filters the current detection voltage from the second resistor and outputs the result to the differential amplifier circuit.

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