Motor drive unit

Abstract

To provide a motor drive device that can drive a stepping motor with high precision. [Solution] The motor drive device drives a stepping motor having a first coil and a second coil connected unipolar for each phase, and includes a differential amplifier circuit comprising first and second switching elements connected to one end of the first and second coils, first and second shunt resistors with one end connected to the first and second switching elements and the other end grounded, an operational amplifier whose non-inverting input terminal is connected to a first node between one end of the first shunt resistor and the first switching element and whose inverting input terminal is connected to a second node between one end of the second shunt resistor and the second switching element, and a control unit that controls the rotation of the stepping motor by turning the first switching element and the second switching element on and off according to the output voltage of the differential amplifier circuit.

Description

[Technical Field]

[0001] This invention relates to a motor drive device. [Background technology]

[0002] For example, Patent Document 1 describes the drive process for a unipolar drive type stepping motor. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2021-78320 [Overview of the project] [Problems that the invention aims to solve]

[0004] Patent Document 1 describes a method in which the current flowing through the coil of a unipolar stepping motor is detected by a shunt resistor commonly connected between each FET (Field Effect Transistor) at both ends of the coil and the ground point, and the FETs are switched and controlled according to the detected value. However, since the direction of the current flowing from the power supply to the shunt resistor is opposite to the direction of the regenerative current flowing from the ground point, it is difficult to continuously detect the current.

[0005] The present invention has been made in view of the above problems, and aims to provide an inexpensive and low-noise motor drive device that continuously detects the current flowing through the coil in a unipolar drive stepping motor and drives the unipolar drive stepping motor using a vector control method. [Means for solving the problem]

[0006] The motor drive device of the present invention is a motor drive device for driving a stepping motor having a first coil and a second coil connected unipolar for each phase, and comprises a first switching element connected to one end of the first coil, a second switching element connected to one end of the second coil, a differential amplifier circuit comprising a first shunt resistor with one end connected to the first switching element and the other end grounded, a second shunt resistor with one end connected to the second switching element and the other end grounded, an operational amplifier whose non-inverting input terminal is connected to a first node between the one end of the first shunt resistor and the first switching element and whose inverting input terminal is connected to a second node between the one end of the second shunt resistor and the second switching element, and a control unit that controls the rotation of the stepping motor by turning the first switching element and the second switching element on and off according to the output voltage of the differential amplifier circuit. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide an inexpensive and low-noise motor drive device that continuously detects the current flowing through the coil in a unipolar drive stepping motor and drives the unipolar drive stepping motor using a vector control method. Furthermore, compared to a bipolar drive system, the drive circuit of the unipolar drive stepping motor M is simpler and less expensive. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic diagram showing the drive system of a unipolar stepping motor. [Figure 2] Figure 2 is a diagram illustrating the forward and reverse operation of a drive unit for a unipolar stepping motor. [Figure 3] Figure 3 is a diagram illustrating the forward and reverse operation of a drive unit for a unipolar stepping motor. [Figure 4] Figure 4 is a waveform diagram showing the output current in the forward and reverse directions. [Figure 5] Figure 5 is a diagram showing an example of a detection circuit. [Figure 6] Figure 6 is a diagram showing another example of a detection circuit. [Figure 7] Figure 7 is a diagram showing an example of a control circuit. [Figure 8] Figure 8 is a diagram showing the configuration of a comparative example drive device. [Figure 9] Figure 9(a) shows the detection voltage of the detection circuit in the embodiment, and Figure 9(b) shows the detection voltage of the detection circuit in the comparative example. [Modes for carrying out the invention]

[0009] (Unipolar drive stepping motor) Figure 1 is a schematic diagram showing the drive system of a unipolar drive stepping motor M. The stepping motor M has a rotor R and forward and reverse A-phase coils La and B-phase coils Lb provided on the stator. In this specification, unless otherwise specified, the stepping motor M refers to a unipolar drive stepping motor.

[0010] The center taps C of coils La and Lb are connected to the positive terminal side of the DC power supply E. One end of forward and reverse switching elements SW1a and SW2a are connected to both ends of coil La, and one end of forward and reverse switching elements SW1b and SW2b are connected to both ends of coil Lb, respectively. The other ends of switching elements SW1a, SW2a, SW1b, and SW2b are grounded. For example, MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) are used as switching elements SW1a, SW2a, SW1b, and SW2b. Switching elements SW1a, SW2a, SW1b, and SW2b are, for example, bipolar transistors, with freewheeling diodes connected in parallel to each other.

[0011] Pulse signals are input to the control terminals of the switching elements SW1a, SW2a, SW1b, and SW2b according to a predetermined unipolar driving method, respectively. As a result, the switching elements SW1a, SW2a, SW1b, and SW2b in the forward and reverse directions are turned on and off, and currents from the power supply E and regenerative currents alternately flow through the coils La and Lb on the time axis.

[0012] (Configuration of the driving device) FIG. 2 and FIG. 3 are configuration diagrams showing the operations in the forward direction (A phase) and the reverse direction ( / A phase) in the driving device 1 of the stepping motor M with the unipolar driving method. The driving device 1 is an example of a motor driving device. The driving device 1 includes coils L1, L2, switching elements SW1, SW2, freewheeling diodes D1, D2, shunt resistors Rs1, Rs2, a detection circuit 10, and a control circuit 11.

[0013] The coils L1 and L2 are unipolar-connected and correspond to the coils La in the forward direction (A phase) and the reverse direction ( / A phase) of the above-described stepping motor M. Note that the coils L1 and L2 may be the coils Lb in the forward direction (B phase) and the reverse direction ( / B phase). The connection point (center tap) between the coils L1 and L2 is directly connected to the power supply line Vcc.

[0014] FIG. 2 shows a case where the forward switching element SW1 is in the on state and the reverse switching element SW2 is in the off state, and FIG. 3 shows a case where the forward switching element SW1 changes from the on state to the off state and the reverse switching element SW2 is in the off state. The switching element SW1 is an example of a first switching element, and the switching element SW2 is an example of a second switching element.

[0015] Figure 4 is a waveform diagram showing the output current in the forward direction (A phase) and reverse direction ( / A phase). The thick waveform is the output current waveform in the state shown in Figure 2, and the current at a given moment is indicated by the sign Ip in the enlarged section M. The thin waveform is the output current waveform in the state shown in Figure 3, and the current at a given moment is indicated by the sign In in the enlarged section M. Switching elements SW1 and SW2 are switched on and off so that the forward and reverse output currents alternately become positive and negative at each periodic period #1 to #3. For example, in periods #1 and #3, switching element SW1 is switched on and off, and switching element SW2 is off. Also, in period #2, switching element SW2 is switched on and off, and switching element SW1 is off. This switching operation generates electromagnetic induction and causes current to flow. In this example, the operation in periods #1 and #3 is given, but in period #2, only the forward and reverse directions are reversed in the circuit, and the operation is the same.

[0016] The switching elements SW1 and SW2 are, for example, N-type MOSFETs, but N-type bipolar transistors may be used instead of MOSFETs. One end (drain) of switching element SW1 is connected to one end of coil L1, and one end of switching element SW2 is connected to one end of coil L2. Furthermore, the switching elements SW1 and SW2 are, for example, N-type bipolar transistors, and freewheeling diodes D1 and D2 are connected in parallel to each other. Note that if the switching elements SW1 and SW2 are N-type MOSFETs, the body diode performs the same role as the freewheeling diodes D1 and D2.

[0017] Shunt resistor Rs1 is an example of a first shunt resistor, and shunt resistor Rs2 is an example of a second shunt resistor. One end of shunt resistor Rs1 is connected to the other end (source) of switching element SW1, and the other end of shunt resistor Rs1 is grounded. One end of shunt resistor Rs2 is connected to the other end (source) of switching element SW2, and the other end of shunt resistor Rs2 is grounded. The other ends of switching elements SW1 and SW2 are directly connected to the ground line GND.

[0018] A detection node N1 is provided between one end of shunt resistor Rs1 and the other end of switching element SW1, and a detection node N2 is provided between one end of shunt resistor Rs2 and the other end of switching element SW2. A potential for current detection is applied to detection nodes N1 and N2 by shunt resistors Rs1 and Rs2, with the ground potential as the reference. Detection nodes N1 and N2 are connected to the detection circuit 10. Note that detection node N1 is an example of a first node, and detection node N2 is an example of a second node.

[0019] The control terminals (gates) of the switching elements SW1 and SW2 are connected to the control circuit 11. The control circuit 11 controls the switching elements SW1 and SW2 by outputting control signals CTL1 and CTL2 to the switching elements SW1 and SW2, thereby switching them on and off.

[0020] As shown in Figure 2, when switching element SW1 is ON and switching element SW2 is OFF, a current I1 flows through the forward coil L1 from the power line Vcc towards the ground line GND. At this time, the voltage at detection node N1 (hereinafter referred to as detection node voltage Vin+) is the product of the current I1 and the resistance value of the shunt resistor Rs1 (referred to as Rs1). This detection node voltage Vin+ (=I1 × Rs1) is applied to the detection circuit 10. As indicated by the arrow, the detection node voltage Vin+ is a voltage that makes the terminal of the shunt resistor Rs1 on the detection node N1 side high potential and the terminal of the shunt resistor Rs1 on the ground line GND side low potential.

[0021] Furthermore, as shown in Figure 3, when the switching element SW1 changes from the ON state to the OFF state, electromagnetic induction occurs in the coil L2 on the reverse side, causing a regenerative current I2 to flow from the ground line GND towards the power line Vcc. At this time, the voltage at the detection node N2 (hereinafter referred to as the detection node voltage Vin-) is the product of the current I2 and the resistance value of the shunt resistor Rs2 (referred to as Rs2). This detection node voltage Vin- (=I2 × Rs2) is applied to the detection circuit 10. As indicated by the arrow, the detection node voltage Vin- is a voltage that makes the terminal on the ground line GND side of the shunt resistor Rs2 a high potential and the terminal on the detection node N2 side of the shunt resistor Rs2 a low potential. The detection circuit 10 detects the magnitudes of the detection node voltages Vin+ and Vin- as the detection voltage Vout and outputs it to the control circuit 11.

[0022] The control circuit 11 is an example of a control unit. The control circuit 11 outputs control signals CTL1 and CTL2 to switching elements SW1 and SW2 in response to the detected voltage Vout output from the detection circuit 10. The control circuit 11 controls the rotation of the stepping motor M by turning the switching elements SW1 and SW2 on and off.

[0023] In this manner, the drive unit 1 causes currents to flow in opposite directions through coils L1 and L2 each time the switching elements SW1 and SW2 are switched on or off. The detection circuit 10 detects the detection voltage Vout based on the detection node voltages Vin+ and Vin- applied from detection nodes N1 and N2.

[0024] (Configuration of the detection circuit) Figure 5 is a diagram showing an example of the detection circuit 10. The detection circuit 10 is an example of a differential amplifier circuit and includes input terminals T1, T2, a voltage divider circuit 100, a voltage follower 101, an operational amplifier U2, and resistors R1 to R4.

[0025] The operational amplifier U2 is powered by being connected to the power line Vcc and the ground line GND. Resistors R1 to R3 are examples of the first to third resistors, respectively. Resistor R1 is connected between input terminal T1 and the non-inverting input terminal (+) of the operational amplifier U2. Resistor R2 is connected between input terminal T2 and the inverting input terminal (-) of the operational amplifier U2. Detection node voltages Vin+ and Vin- are applied to input terminals T1 and T2 from detection nodes N1 and N2, respectively. Resistor R3 is connected between node N3, which is between the inverting input terminal of the operational amplifier U2 and resistor R2, and the output terminal of the operational amplifier U2. The detection voltage Vout is output from the output terminal of the operational amplifier U2. Note that node N3 is an example of a third node.

[0026] The voltage divider circuit 100, the voltage follower 101, and the resistor R4 apply a bias voltage Vbias to the non-inverting input terminal of the operational amplifier U2. The resistor R4 is an example of a fourth resistor.

[0027] The voltage divider circuit 100 divides the power supply voltage to generate divided voltages. The voltage divider circuit 100 has resistors R5 and R6 connected in series between the power supply line Vcc and the ground line GND. Resistor R5 is connected to the power supply line Vcc side, and resistor R6 is connected to the ground line GND side. The divided voltages are output from the output node Nout at the connection point of resistors R5 and R6. The divided voltages substantially coincide with the bias voltage Vbias.

[0028] The voltage follower 101 has an operational amplifier U1 that stabilizes the bias voltage Vbias. The operational amplifier U1 is powered by being connected to the power supply line Vcc and the ground line GND. The voltage follower 101 is connected between node N4, which is between the non-inverting input terminal of the operational amplifier U2 and the resistor R1, and the output node Nout of the voltage divider circuit 100. The bias voltage Vbias is applied to the non-inverting input terminal of the operational amplifier U1 from the output node Nout of the voltage divider circuit 100. The inverting input terminal and output terminal of the operational amplifier U1 are directly connected to each other. Note that node N4 is an example of a fourth node.

[0029] Resistor R4 is an example of a fourth resistor. Resistor R4 is connected between the output terminal of the voltage follower 101 and the fourth node. As a result, the operational amplifier U2 can operate as an operational amplifier.

[0030] In the detection circuit 10 of this example, the non-inverting input terminal of the operational amplifier U2 is connected to input terminal T1 via resistor R1, and the inverting input terminal of the operational amplifier U2 is connected to input terminal T2 via resistor R2. Therefore, the potential V+ at the non-inverting input terminal of the operational amplifier U2 is a value corresponding to the current I1 in the direction from the power line Vcc to the ground line GND when the switching element SW1 is in the ON state. Also, since the switching element SW2 is in the OFF state, the voltage of the ground line GND is effectively applied to the inverting input terminal of the operational amplifier U2 from the detection node N2.

[0031] On the other hand, when switching element SW1 changes from the ON state to the OFF state and switching element SW2 is OFF, electromagnetic induction occurs in coil L2 due to transformer coupling, and a regenerative current I2 flows from the ground line GND towards the power line Vcc. The potential V- at the inverting input terminal of op-amp U2 is a value corresponding to the regenerative current I2. Also, since switching element SW1 is OFF, the voltage of the ground line GND is effectively applied to the non-inverting input terminal of op-amp U2 from detection node N1.

[0032] Therefore, the detection circuit 10 can detect detection node voltages Vin+ and Vin-, which correspond to the currents I1 and regenerative current I2, which have different directions, as a continuous detection voltage Vout.

[0033] Furthermore, the detection circuit 10 in this example is equipped with a voltage follower 101. The voltage follower 101 is a non-inverting amplifier circuit with a gain of 1, configured with an operational amplifier U1. By converting the impedance with the voltage follower 101, the bias voltage Vbias can be stabilized even when, for example, the input impedance of the detection voltage Vout is not very high.

[0034] Next, we will discuss the gain of the operational amplifier U2. In this example, the resistance values ​​of the resistors R1 to R6 are R1 to R6, respectively. Also, the potential at the non-inverting input terminal of the operational amplifier U2 is V + The potential at the inverting input terminal of the operational amplifier U2 is set to V - Let's assume that the potential of the output node Nout of the voltage divider circuit 100 is the bias voltage Vbias.

[0035]

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[0036] Potential V + This is expressed as equation (1) above, based on the superposition principle. The input impedance of op-amp U2 is theoretically infinite, so the current flowing through resistor R2 and the current flowing through resistor R3 are equal. Here, the output impedance of op-amp U2 is considered to be 0. Note that an imaginary short is established in op-amp U2, so V - =V + It will be considered as such.

[0037]

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[0038] Furthermore, according to Kirchhoff's laws, equation (2) above holds true.

[0039]

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[0040] From equation (2), the detected voltage Vout is expressed as equation (3) above.

[0041]

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[0042] Assuming that R1=R2 and R4=R3 hold true, the detected voltage Vout can be expressed as equation (4) above from equations (1) and (3). As a result, the gain on the non-inverting input terminal side of op-amp U2 is (+R3 / R2), and the gain on the inverting input terminal side of op-amp U2 is (-R3 / R2). In addition, the detected voltage Vout is offset by the bias voltage Vbias.

[0043]

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[0044] Furthermore, the bias voltage Vbias is expressed by equation (5) above.

[0045] (Configuration of other detection circuits) Figure 6 is a diagram showing another example of the detection circuit 10. The detection circuit 10 is an example of a differential amplifier circuit and has input terminals T1 and T2, a voltage divider circuit 100, an operational amplifier U2, and resistors R1 to R3. In Figure 6, components common to Figure 5 are denoted by the same reference numerals, and their descriptions are omitted.

[0046] The detection circuit 10 does not have a voltage follower 101, and the output node Nout of the voltage divider circuit 100 is directly connected to node N4. Therefore, in this example, it is possible to reduce the number of operational amplifiers U1 compared to the example in Figure 5. This reduces cost and mounting area.

[0047] Furthermore, in the detection circuit 10 of this example, the non-inverting input terminal of the operational amplifier U2 is connected to the input terminal T1 via the resistor R1, and the inverting input terminal of the operational amplifier U2 is connected to the input terminal T2 via the resistor R2. Therefore, the detection circuit 10 can detect the detection node voltages Vin+ and Vin- corresponding to the current I1 and regenerative current I2 as a continuous detection voltage Vout.

[0048] Next, we will discuss the gain of the operational amplifier U2. In this example, the resistance values ​​of the resistors R1-R3, R5, and R6 are R1-R3, R5, and R6, respectively. Also, the potential at the non-inverting input terminal of the operational amplifier U2 is V + The potential at the inverting input terminal of the operational amplifier U2 is set to V - Let's assume that the potential of the power line Vcc is Vcc.

[0049]

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[0050] The detected voltage Vout is expressed by equation (6) above.

[0051]

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[0052]

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[0053] Also, potential V + This is expressed as equation (7) above, based on the superposition principle. Here, the operator " / / " indicates the resistance value of a parallel connection; for example, in the case of parallel connection of resistors R5 and R6, the resistance value is expressed by equation (8).

[0054]

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[0055] In Equation (7), the potential V in+ has a gain represented by the above Equation (9) by setting R1 = R2 and R5 / / R6 = R3 so that the gain becomes the gain of differential amplification.

[0056]

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[0057] Also, from Equations (6) and (7), the gain of the potential Vcc is calculated as in the above Equation (10a). Here, it is also assumed that R1 = R2 and R5 / / R6 = R3.

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[0058] Equation (10b) above is obtained from Equation (10a).

[0059]

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[0060] Based on the gains of Equations (9) and (10b), the above Equation (11) is obtained from Equations (6) and (7). Therefore, the gain of the potential V in+ is (+R3 / R2), and the gain of the potential V in- is (-R3 / R2).

[0061] (Configuration of the control circuit) FIG. 7 is a configuration diagram showing an example of the control circuit 11. The control circuit 11 is an example of a control unit, and as an example, it vector-controls the rotation of the stepping motor M. The control circuit 11 includes a rotation angle detector 110, a dq coordinate converter 111, an αβ coordinate converter 112, a PWM (Pulse Width Modulation) controller 113, a field PI (Proportional Integral) controller 114, a torque PI controller 115, and adders 116 and 117. Note that the symbol X refers to the circuit portion of the above switching elements SW1, SW2 and shunt resistors Rs1, Rs2.

[0062] The rotation angle detector 110 detects the rotation angle θ of the rotor R (see Figure 1) from the rotation angle sensor 12 provided on the stepping motor M. The rotation angle sensor 12 is, for example, a resolver, but is not limited to this. The rotation angle θ is output to the dq coordinate converter 111 and the αβ coordinate converter 112.

[0063] The detection circuit 10 detects the current values ​​Iα and Iβ of the two-phase (A-phase and B-phase) coils L1 and L2 of the stepping motor M as a detection voltage Vout, as described above. The dq coordinate converter 111 converts the current values ​​Iα and Iβ into the d-axis component current value Id and the q-axis component current value Iq based on the rotation angle θ.

[0064] The adder 116 calculates the difference between the command value of the field command and the current value Id. The adder 116 outputs the difference to the field PI controller 114. The field PI controller 114 calculates the d-axis component Vd of the target voltage by performing PI control based on the difference.

[0065] The adder 117 calculates the difference between the torque command value and the current value Iq. The adder 117 outputs the difference to the torque PI controller 115. The torque PI controller 115 calculates the q-axis component Vq of the target voltage by performing PI control based on the difference. The torque command and field command are input from an external application that utilizes the stepping motor M.

[0066] The αβ coordinate converter 112 converts the d-axis component Vd and q-axis component Vq of the target voltage into target voltage values ​​Vα and Vβ for each phase based on the rotation angle θ. The PWM controller 113 performs PWM control on each of the two phase switching elements SW1 and SW2 based on the target voltage values ​​Vα and Vβ. For each phase, the PWM controller 113 generates pulsed control signals CTL1 and CTL2 by PWM control and outputs them to the switching elements SW1 and SW2, respectively. The duty cycle of the control signals CTL1 and CTL2 is controlled according to the target voltage values ​​Vα and Vβ.

[0067] In this way, the control circuit 11 turns the switching elements SW1 and SW2 on and off by vector control according to the detected voltage Vout output by the detection circuit 10. As described above, the detection circuit 10 is capable of continuous voltage detection, so the accuracy of the vector control is improved compared to the following comparative example.

[0068] (Comparative example) Figure 8 is a diagram showing the configuration of a comparative example drive device 1a. In Figure 8, components common to Figures 2 and 3 are denoted by the same reference numerals, and their descriptions are omitted. The drive device 1a has a common shunt resistor Rs instead of the shunt resistors Rs1 and Rs2 for each switching element SW1 and SW2. The potentials across the shunt resistor Rs are defined as the detection node voltages Vin+ and Vin-.

[0069] The other ends (sources) of switching elements SW1 and SW2 are connected at node Nc. The shunt resistor Rs is connected between node Nc and the ground line GND. Both ends of the shunt resistor Rs are connected to the detection circuit 10a, and regardless of the on / off state of switching elements SW1 and SW2, the detection node voltages Vin+ and Vin- are always applied to the detection circuit 10a from both ends of the shunt resistor Rs.

[0070] The detection node voltages Vin+ and Vin- are applied to the inverting and non-inverting input terminals of the operational amplifier (not shown) of the detection circuit 10a, respectively. However, as described above, since the shunt resistor Rs is connected between node Nc, where the currents flowing through coils L1 and L2 merge, and the ground line GND, it is not possible to detect the forward (A phase) and reverse ( / A phase) currents individually.

[0071] Figure 9(a) shows the detection voltage Vout of the detection circuit 10 in the embodiment, and Figure 9(b) shows the detection voltage Vout of the detection circuit 10a in the comparative example. The horizontal axis represents time, and the vertical axis represents the detection voltage Vout of the detection circuits 10 and 10a.

[0072] In this embodiment, detection node voltages Vin+ and Vin-, generated by forward (A phase) and reverse ( / A phase) currents flowing in opposite directions, are applied to the non-inverting and inverting input terminals of the operational amplifier U2 of the detection circuit 10, respectively. Therefore, the detection circuit 10 can process the forward (A phase) and reverse ( / A phase) currents separately and continuously output a detection voltage Vout.

[0073] On the other hand, in the comparative example, the detection node voltages Vin+ and Vin- are applied to the non-inverting and inverting input terminals of the operational amplifier of the detection circuit 10a, respectively, regardless of the direction of the current flowing through the shunt resistor Rs. Therefore, the control circuit 11 needs to discretely acquire the peak value of the detection voltage Vout and use it for vector control, and cannot use a continuous detection voltage Vout, thus requiring advanced control.

[0074] Thus, with the drive device 1 of the embodiment, the current flowing through coils L1 and L2 in the stepping motor M can be continuously detected, making it easy to drive using a vector control method. Therefore, compared to general constant current drive methods, torque ripple is reduced, which suppresses noise, and the circuit configuration is simplified, resulting in reduced costs.

[0075] Although embodiments of the present invention have been described in detail above, the present invention is not limited to these specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention as described in the claims. [Explanation of symbols]

[0076] 1. Drive unit 10,10a Detection circuit 11 Control circuits 100 voltage divider circuit 101 Voltage Follower Rs, Rs1, Rs2 shunt resistors R1~R6 Resistor elements L1, L2 coils SW1, SW2 switching elements U1, U2 operational amplifiers M Stepping Motor

Claims

1. In a motor drive device for driving a stepping motor having a first coil and a second coil connected unipolarly for each phase, A first switching element connected to one end of the first coil, A second switching element connected to one end of the second coil, A first shunt resistor, one end of which is connected to the first switching element and the other end of which is grounded, A second shunt resistor, one end of which is connected to the second switching element and the other end of which is grounded, A differential amplifier circuit comprising an operational amplifier whose non-inverting input terminal is connected to a first node between one end of the first shunt resistor and the first switching element, and whose inverting input terminal is connected to a second node between one end of the second shunt resistor and the second switching element, The control unit controls the rotation of the stepping motor by switching the first switching element and the second switching element on and off according to the output voltage of the differential amplifier circuit. Motor drive device.

2. The differential amplifier circuit is A first resistor element connected between the first node and the non-inverting input terminal, A second resistive element connected between the second node and the inverting input terminal, A third node between the inverting input terminal and the second resistor element, and a third resistor element connected between the output terminal of the operational amplifier, It has a voltage divider circuit that generates divided voltages by dividing the power supply voltage, The output node of the voltage divider circuit, which outputs the divided voltage, is directly connected to the fourth node between the non-inverting input terminal and the first resistive element. A motor drive device as described in claim 1.

3. The differential amplifier circuit is A first resistor element connected between the first node and the non-inverting input terminal, A second resistive element connected between the second node and the inverting input terminal, A third node between the inverting input terminal and the second resistor element, and a third resistor element connected between the output terminal of the operational amplifier, A voltage divider circuit generates divided voltages by dividing the power supply voltage, A voltage follower connected between the fourth node between the non-inverting input terminal and the first resistive element and the output node of the voltage divider circuit from which the divided voltage is output, The voltage follower has an output terminal and a fourth resistor connected between it and the fourth node, A motor drive device according to claim 1 or 2.

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