Motor drive unit

Abstract

To provide a motor drive unit for driving a brushless motor capable of improving motor operating efficiency.SOLUTION: A motor drive unit 20 in an embodiment is configured to drive a motor 10. The motor drive unit 20 includes a drive unit 24, a control unit 30, and a temperature detection unit 34. The temperature detection unit 34 is configured to detect the temperature of multiple switching elements Q1 to Q6. The control unit 30 is configured to control the magnitude of the drive current so that the slew rate of multiple switching elements Q1 to Q6 is constant regardless of temperature depending on the temperature detected by the temperature detection unit 34.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a motor drive device that drives a brushless motor. [Background technology]

[0002] It is known that in a motor drive device that drives a brushless motor by turning on and off a switching element, the output from the motor changes with temperature because the characteristics of the switching element (e.g., threshold voltage) change with temperature. Therefore, for example, Patent Document 1 below proposes a technique for changing the duty ratio of a PWM signal depending on temperature in order to suppress fluctuations in motor torque depending on temperature. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2012-254682 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, as a result of detailed study by the inventors, it was found that the technology of the above-mentioned Patent Document 1 can prevent torque from fluctuating according to temperature, but the operation efficiency of the motor is not improved. In the technology of the above-mentioned Patent Document 1, the slew rate of the switching element is not adjusted, so the timing at which voltage is applied to the motor is unstable. As a result, it is necessary to set the dead time under the worst conditions to avoid the occurrence of through current, and the operation efficiency of the motor decreases due to the relatively long dead time.

[0005] One aspect of the present disclosure is to enable improvement of the operating efficiency of a motor in a motor drive device that drives a brushless motor. [Means for solving the problem]

[0006] One aspect of the present disclosure is a motor drive device (20) configured to drive a brushless motor (10). The motor drive device includes a drive unit (24), a control unit (30), and a temperature detection unit (34).

[0007] The drive unit has a plurality of switching elements (Q1, Q2, Q3, Q4, Q5, Q6) and is configured to supply power to the brushless motor using the plurality of switching elements. The control unit is configured to control a magnitude of a drive current for driving the plurality of switching elements. The temperature detection unit is configured to detect temperatures of the plurality of switching elements. The control unit is configured to control a magnitude of the drive current in response to the temperature detected by the temperature detection unit so that the slew rate of the plurality of switching elements is constant regardless of temperature.

[0008] With this configuration, the control unit controls the slew rate to be constant regardless of temperature, so the timing at which voltage is applied to the motor can be made roughly constant. This makes it possible to set a shorter dead time in a motor drive device that drives a brushless motor, thereby improving the operating efficiency of the motor. [Brief description of the drawings]

[0009] [Figure 1] FIG. 2 is a block diagram showing a configuration of a motor drive device. [Diagram 2] FIG. 2A is a graph showing an example of the charge current and each voltage value at room temperature, FIG. 2B is a graph showing an example of the charge current and each voltage value at high temperature, and FIG. 2C is a graph showing an example of the charge current and each voltage value at room temperature. [Diagram 3] FIG. 3A is a graph showing an example of the discharge current and each voltage value at room temperature, FIG. 3B is a graph showing an example of the discharge current and each voltage value at high temperature, and FIG. 3C is a graph showing an example of the discharge current and each voltage value at low temperature. [Figure 4]13 is a flowchart of a slew rate setting process. [Diagram 5] 1 is a graph showing an example of a relationship between a detected temperature and a charge current. [Figure 6] 1 is a graph showing an example of a relationship between a detected temperature and a discharge current. [Figure 7] FIG. 7A is a graph showing an example of the charge current and each voltage value at room temperature in a conventional configuration, FIG. 7B is a graph showing an example of the charge current and each voltage value at high temperature in a conventional configuration, and FIG. 7C is a graph showing an example of the charge current and each voltage value at low temperature in a conventional configuration. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. [1. Embodiment] [1-1. Configuration] As shown in Fig. 1, a motor driving device 20 of this embodiment drives a motor 10. The motor 10 is a three-phase brushless motor.

[0011] Motor drive device 20 includes an inverter circuit 22, a drive unit 24, a power supply unit 26, a control unit 30, and a temperature detection unit 34. Motor drive device 20 is configured to drive a blower motor 10 that blows air in response to a command from an air conditioner ECU (not shown), for example.

[0012] The power supply unit 26 generates a power supply voltage Vcc for operating the internal circuits such as the control unit 30. The inverter circuit 22 is a circuit that receives power from a battery 40 and applies the battery voltage between terminals T1, T2, and T3 of each phase U, V, and W of the motor 10 (i.e., between UV, VW, and WU) to energize the stator coil and rotate the motor 10.

[0013] The stator coils of the motor 10 for each phase U, V, and W are Y-connected. An inverter circuit 22 is connected to three terminals T1, T2, and T3 on the opposite side to the Y-connected terminals. The inverter circuit 22 includes a three-phase full-bridge circuit having six switching elements Q1, Q2, Q3, Q4, Q5, and Q6 (hereinafter, Q1 to Q6).

[0014] Switching elements Q1, Q2, and Q3 (hereinafter, Q1 to Q3) serve as so-called high-side switches and are arranged between the positive electrode side of the battery 40 and terminals T1, T2, and T3 of the respective phases U, V, and W of the motor 10. Switching elements Q4, Q5, and Q6 (hereinafter, Q4 to Q6) serve as so-called low-side switches and are arranged between the negative electrode side of the battery 40 and terminals T1, T2, and T3 of the respective phases U, V, and W of the motor 10.

[0015] Therefore, in the inverter circuit 22, a battery voltage is applied between any of the terminals T1, T2, and T3 of the motor 10 by turning on one high-side switch and one low-side switch that are in different phases.

[0016] By switching the switching elements Q1 to Q6 to be turned on, the terminal to which the battery voltage is applied and the application direction of the battery voltage can be switched. Alternatively, the current can be controlled by PWM-controlling the on-time of one of the switching elements of the high-side switch and the low-side switch. In this embodiment, the control unit 30 controls the rotation of the motor 10 using a duty control in which the on-time of the high-side switch is controlled with a duty of 100% and the on-time of the low-side switch is controlled with a duty of 100% or less. Note that although the switching elements Q1 to Q6 are MOSFETs in this embodiment, they may be other semiconductor elements such as bipolar transistors or relay switches. In addition, the control unit 30 may control the rotation of the motor 10 using a duty control in which the on-time of the low-side switch is controlled with a duty of 100% and the on-time of the high-side switch is controlled with a duty of 100% or less.

[0017] The operation of turning on any of the switching elements Q1 to Q3, which are high-side switches, and increasing the potential of the corresponding terminal T1, T2, T3 (hereinafter also referred to as the motor applied voltage) is called charging. Also, the current (i.e., gate current) flowing through the gates of the switching elements Q1 to Q3 during charging is called the charging current.

[0018] Moreover, the operation of turning on any of the switching elements Q4 to Q6, which are low-side switches, and lowering the potential of the corresponding terminal T1, T2, T3 to ground is called discharge. Moreover, the gate current of the switching elements Q4 to Q6 during discharge is called discharge current.

[0019] The drive unit 24 turns on or off the switching elements Q1 to Q6 in the inverter circuit 22 in accordance with the control signal output from the control unit 30, thereby passing current through the stator coils of the respective phases U, V, and W of the motor 10, thereby rotating the motor 10. The drive unit 24 is also configured to perform constant current control so that the magnitudes of the charge current and the discharge current are constant at target values.

[0020] The temperature detection unit 34 is configured, for example, as a circuit that detects the temperature around the switching elements Q1 to Q6. The temperature detection unit 34 is disposed near the switching elements Q1 to Q6, for example, on the same substrate as the switching elements Q1 to Q6. The temperature detection unit 34 may be configured as a known temperature sensor.

[0021] The control unit 30 is an electronic control device mainly composed of a microcomputer including a CPU 30a, a ROM 30b, and a RAM 30c. Various functions of the microcomputer are realized by the CPU 30a executing a program stored in a non-transient real recording medium. In this example, the ROM 30b corresponds to the non-transient real recording medium storing the program. Furthermore, the execution of this program executes a method corresponding to the program. Note that some or all of the functions executed by the CPU 30a may be configured as hardware using one or more ICs, etc. Also, the number of microcomputers constituting the control unit 30 may be one or more. Note that the ROM 30b stores temperature maps 34a and 34b, which will be described later.

[0022] The control unit 30 performs PWM control of the current flowing through the stator coils of each phase U, V, W so that the operating state (e.g., rotation speed, temperature, etc.) of the controlled object becomes a target value. For example, if the controlled object is a blower for an air conditioner, the control unit 30 performs PWM control so that the air volume of the blower becomes a predetermined air volume. Also, if the controlled object is a urea solution pressure delivery pump, the control unit 30 performs PWM control so that the urea pressure of the urea solution pressure delivery pump becomes a predetermined urea pressure.

[0023] [1-2. Processing Overview] It is known that the switching elements Q1 to Q6 have so-called temperature characteristics, that is, characteristics that change with temperature. In particular, the slew rate of the switching elements Q1 to Q6 changes with temperature. The slew rate is a value that specifies the response speed of the output change with respect to the input change, and is expressed in units of V / μs.

[0024] The slew rate has a large effect on the threshold arrival time. The threshold arrival time is the time it takes for the switching elements Q1 to Q6, to which the drive current is supplied, to transition from off to on. In other words, it is the time from when the input of the gate current, which is the drive current for the switching elements Q1 to Q6, begins until conduction begins between the source and drain of the switching elements Q1 to Q6 and the motor applied voltage begins to change.

[0025] In switching elements Q1 to Q3, which are high-side switches with a conventional configuration to which the configuration of the present disclosure is not applied, the threshold arrival time is, for example, based on the normal temperature (e.g., 25°C) shown in Fig. 7A, and at higher temperatures becomes shorter than the reference, as shown in Fig. 7B. This is because the threshold voltage Vth, which is the gate-source voltage at which the motor applied voltage begins to change, becomes lower due to temperature changes. In this case, when the gate current is constant, the gate-source voltage VGS reaches the threshold voltage Vth in a shorter time, so the threshold arrival time is shorter and the motor applied voltage rises in a shorter time.

[0026] Also, the time to reach the threshold at a lower temperature is longer than the reference, as shown in Fig. 7C. This is because the threshold voltage Vth increases with temperature change. In this case, it takes a longer time for the gate-source voltage VGS to reach the threshold voltage Vth, so the time to reach the threshold is longer and the motor applied voltage takes a longer time to rise.

[0027] Incidentally, in a configuration in which the motor 10 is controlled using the switching elements Q1 to Q6, it is necessary to provide a dead time so as not to short-circuit the battery 40. The dead time is the time during which the switching elements Q1 to Q3, which are high-side switches, and the switching elements Q4 to Q6, which are corresponding low-side switches, are simultaneously turned off. The dead time must be set taking into consideration the worst-case conditions at high temperatures, when the time to reach the threshold is the shortest. However, if the dead time is set in this way, the dead time becomes considerably long, particularly at low temperatures, and the operating efficiency of the motor 10 decreases.

[0028] Therefore, in this embodiment, in order to make the slew rate, particularly the time to reach the threshold, as constant as possible regardless of the temperature, the control unit 30 controls the amount of gate current using the drive unit 24. Specifically, as shown in Figures 2A, 2B, and 2C, the control unit 30 controls the charge current of the switching elements Q1 to Q3, which are high-side switches.

[0029] At room temperature, as shown in Fig. 2A, the charge current is controlled to be a reference current amount, which is a current amount that is a predetermined current amount, at the time to reach the threshold value. After the time to reach the threshold value has elapsed, the charge current is controlled to be a normal current amount, which is a current amount slightly smaller than the reference current amount.

[0030] At high temperatures, the charge current is controlled to be smaller than the reference current amount and the normal current amount, as shown in Fig. 2B, so that the threshold arrival time is approximately the same as the threshold arrival time at normal temperatures. After the threshold arrival time has elapsed, the charge current is controlled to be the normal current amount.

[0031] At low temperatures, the charge current is controlled to be greater than the reference current amount, as shown in Fig. 2C, so that the time to reach the threshold value is roughly the same as the time to reach the threshold value at room temperature. After the threshold value arrival time has elapsed, the charge current is controlled to be the normal current amount.

[0032] As shown in Figures 3A, 3B, and 3C, the discharge currents of the switching elements Q4 to Q6, which are low-side switches, are also controlled. Note that in Figures 3A, 3B, and 3C, only the discharge currents are shown as gate currents, and the charge currents are not shown. During discharge, PWM control is performed after the threshold time has elapsed.

[0033] At room temperature, as shown in FIG. 3A, after switching elements Q1 to Q3, which are high-side switches, are turned off, switching elements Q4 to Q6, which are low-side switches, are turned on to start the threshold arrival time. During this threshold arrival time, the discharge current is controlled to become a reference current amount, which is a predetermined current amount. Note that the reference current amount of the discharge current can be set to a value different from the reference current amount of the charge current. After the threshold arrival time has elapsed, the discharge current is controlled to become a normal current amount, which is a current amount slightly smaller than the reference current amount.

[0034] At high temperatures, the discharge current is controlled to be greater than the reference current amount, as shown in Fig. 3B, so that the threshold arrival time is roughly the same as the threshold arrival time at normal temperatures. In this way, the threshold arrival time, which tends to be longer at high temperatures, is set to the same as at normal temperatures. After the threshold arrival time has elapsed, the discharge current is controlled to be the normal current amount.

[0035] At low temperatures, the discharge current is controlled to be smaller than the reference current amount and larger than the normal current amount, as shown in Fig. 3C, so that the threshold arrival time is approximately the same as the threshold arrival time at normal temperatures. In this way, the threshold arrival time, which tends to be shorter at low temperatures, is set to approximately the same as at normal temperatures. After the threshold arrival time has elapsed, the discharge current is controlled to be the normal current amount.

[0036] [1-2. Processing] Next, the slew rate setting process executed by the control unit 30 will be described with reference to the flowchart of Fig. 4. The slew rate setting process is a process that starts when the power of a controlled object such as an air conditioner is turned on.

[0037] In the slew rate setting process, the control unit 30 performs an initial setting of the slew rate in S110 as shown in Fig. 4. Here, the aforementioned reference current amount is set as the initial value of the charge current and the discharge current.

[0038] Next, in S120, the control unit 30 acquires the detection result by the temperature detection unit 34. Next, in S130, the control unit 30 acquires the temperature maps 34a, 34b, and sets the slew rate based on the temperature maps 34a, 34b. Note that the temperature maps 34a, 34b may be determined in advance, or may be determined by learning on the shipping line, for example.

[0039] Here, the amount of the charge current is set to decrease approximately linearly as the temperature increases, for example, as shown in Fig. 5. By setting the amount of the charge current in this manner, the rate of change of the gate-to-source voltage VGS of the switching elements Q1 to Q3 can be set, as described in Figs. 2A, 2B, and 2C. Therefore, the time to reach the threshold during charging can be controlled to be approximately constant.

[0040] On the other hand, the amount of discharge current is set to increase approximately linearly as the temperature increases, for example, as shown in Fig. 6. By setting the amount of discharge current in this manner, the rate of change of the gate-to-source voltage VGS of the switching elements Q4 to Q6 can be set, as described in Figs. 3A, 3B, and 3C. Therefore, the time to reach the threshold during discharge can be controlled to be approximately constant.

[0041] The vertical axis of the graphs shown in FIGS. 5 and 6 may indicate the amount of charge current and discharge current themselves, or may indicate the magnification of the charge current or discharge current with respect to a reference current amount.

[0042] Returning to FIG. 4, the control unit 30 then updates the slew rate setting in S140, and then returns to the process of S120.

[0043] [1-3. Effects] According to the embodiment described above in detail, the following effects are achieved. (1a) One aspect of the present disclosure is a motor drive device 20 configured to drive a motor 10. The motor drive device 20 includes a drive unit 24, a control unit 30, and a temperature detection unit .

[0044] The drive unit 24 has a plurality of switching elements Q1-Q6, and is configured to supply power to the motor 10 using the plurality of switching elements Q1-Q6. The control unit 30 is configured to control the magnitude of a drive current (e.g., gate current Ig) for driving the plurality of switching elements Q1-Q6. The temperature detection unit 34 is configured to detect the temperatures of the plurality of switching elements Q1-Q6. The control unit 30 is configured to control the magnitude of the drive current in accordance with the temperature detected by the temperature detection unit 34, so that the slew rates of the plurality of switching elements Q1-Q6 are constant regardless of temperature.

[0045] With this configuration, the control unit 30 controls the slew rate to be constant regardless of temperature, so that the timing at which voltage is applied to the motor 10 can be made generally constant. This makes it possible to set a shorter dead time in the motor drive device 20 that drives the motor 10, thereby improving the operating efficiency of the motor 10.

[0046] Furthermore, the above configuration can improve current distortion of the voltage applied to the motor caused by temperature fluctuations, thereby suppressing torque ripple in the motor 10 and fluctuations in the motor drive sound.

[0047] Furthermore, with the above configuration, the variation in the time to reach the threshold caused by temperature fluctuations is reduced, so the dead time to be set can be made shorter, thereby reducing losses caused by providing extra dead time.

[0048] Furthermore, with the above configuration, it is not necessary to take into account the temperature characteristics of the FETs during FET switching design, EMC (electromagnetic compatibility), and thermal design, so that the number of development steps for the motor drive device 20 can be reduced.

[0049] Furthermore, with the above configuration, the variation in switching caused by temperature fluctuations can be reduced, and therefore the variation in the motor applied voltage and the actual dead time can also be reduced. In other words, the difference between the set dead time and the actual dead time, and the difference between the set motor applied voltage and the actual motor applied voltage can be reduced.

[0050] (1b) In one aspect of the present disclosure, the control unit 30 is configured to control the magnitude of the drive current in accordance with temperature maps 34a and 34b prepared in advance. According to this configuration, since the slew rate is adjusted using the temperature maps 34a and 34b, feedback control and complicated calculations for obtaining the slew rate are not required, and the function of adjusting the slew rate can be realized with a simple configuration. Also, the slew rate can be set in real time according to temperature changes.

[0051] (1c) In one aspect of the present disclosure, the multiple switching elements Q1 to Q6 are FETs, and the control unit 30 is configured to control the magnitude of the gate current. With this configuration, even if a configuration using FETs whose characteristics are easily changed by temperature is used, the operating efficiency of the motor 10 can be improved satisfactorily.

[0052] (1d) In one aspect of the present disclosure, the control unit 30 is configured to set a threshold arrival time, which is the time it takes for the switching elements Q1 to Q6 to which the drive current is supplied to transition from OFF to ON after the supply of the drive current is started.

[0053] According to this configuration, the switching elements Q1 to Q6 are controlled so that the time until they start to function is constant, so that the dead time of the switching elements Q1 to Q6 can be shortened.

[0054] (1e) In one aspect of the present disclosure, the control unit 30 may control the magnitude of the drive current regardless of the temperature while the switching elements Q1 to Q6 to which the gate current is supplied are maintained on. According to such a configuration, after the switching elements Q1 to Q6 transition to ON (that is, after the threshold reaching time has elapsed), control is performed regardless of the temperature, so that the control can be simplified.

[0055] 2. Other embodiments Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments and can be implemented in various modified forms.

[0056] (2a) In the above embodiment, the temperature detection unit 34 is used to set the slew rate, but the present invention is not limited to this. For example, the temperature detection unit 34 may be used for other purposes. Specifically, the temperature detection unit 34 may be used as a protection circuit, for example, to stop the operation of an object depending on the temperature, to limit the operation so as to suppress heat generation, etc.

[0057] (2b) In the above embodiment, only one temperature detector 34 is provided, but a temperature detector 34 may be provided for each of the switching elements Q1 to Q6. In this case, the control unit 30 may set a different slew rate according to the temperature for each of the switching elements Q1 to Q6.

[0058] (2c) In the above embodiment, the slew rate is set based on the temperature maps 34a and 34b, but this is not limiting. For example, if the temperature maps 34a and 34b are not provided, a function may be set so that the threshold arrival time does not change with temperature, and the slew rate may be set by a calculation using the function.

[0059] (2d) In the above embodiment, the control unit 30 controls the magnitude of the drive current regardless of the temperature after the threshold arrival time has elapsed, but this is not limited to the above. For example, the control unit 30 may control the magnitude of the gate current according to the temperature even after the threshold arrival time has elapsed. In this case, for example, the control unit 30 may determine the magnitude of the gate current after the threshold arrival time has elapsed by setting a magnification of the normal current amount based on the temperature maps 34a and 34b.

[0060] (2e) The control unit 30 and the method by the control unit 30 described in the present disclosure may be realized by a dedicated computer provided by configuring a processor and a memory programmed to execute one or more functions embodied in a computer program. Alternatively, the control unit 30 and the method by the control unit 30 described in the present disclosure may be realized by a dedicated computer provided by configuring a processor with one or more dedicated hardware logic circuits. Alternatively, the control unit 30 and the method by the control unit 30 described in the present disclosure may be realized by one or more dedicated computers configured by a combination of a processor and a memory programmed to execute one or more functions and a processor configured with one or more hardware logic circuits. In addition, the computer program may be stored in a computer-readable non-transitory tangible recording medium as instructions executed by a computer. The method for realizing the functions of each unit included in the control unit 30 does not necessarily need to include software, and all of the functions may be realized using one or more hardware.

[0061] (2f) Multiple functions possessed by one component in the above embodiments may be realized by multiple components, or one function possessed by one component may be realized by multiple components. Also, multiple functions possessed by multiple components may be realized by one component, or one function realized by multiple components may be realized by one component. Also, part of the configuration of the above embodiments may be omitted. Also, at least part of the configuration of the above embodiments may be added to or substituted for the configuration of another of the above embodiments.

[0062] (2g) In addition to the motor drive device 20 described above, the present disclosure can be realized in various forms, such as a system including the motor drive device 20 as a component, a program for causing a computer to function as the motor drive device 20, a non-transient physical recording medium such as a semiconductor memory on which the program is recorded, and a motor drive method.

[0063] [Technical idea disclosed in this specification] [Item 1] A motor drive device (20) configured to drive a brushless motor (10), a drive unit (24) having a plurality of switching elements (Q1, Q2, Q3, Q4, Q5, Q6) and configured to supply power to the brushless motor using the plurality of switching elements; a control unit (30) configured to control a magnitude of a drive current for driving the plurality of switching elements; a temperature detector (34) configured to detect a temperature of the plurality of switching elements; Equipped with The control unit controls the magnitude of the drive current in accordance with the temperature detected by the temperature detection unit so that a slew rate of the plurality of switching elements becomes constant regardless of temperature. The motor drive device is configured as described above. [Item 2] Item 1 is a motor driving device according to the present invention; The control unit controls the magnitude of the drive current according to a temperature map (34a, 34b) that is prepared in advance and in which temperature and the magnitude of the drive current are associated with each other. The motor drive device is configured as described above. [Item 3] The motor drive device according to item 1 or 2, The plurality of switching elements are FETs, and the control unit controls the magnitude of a gate current. The motor drive device is configured as described above. [Item 4] A motor drive device according to any one of items 1 to 3, The control unit sets, as the slew rate in accordance with the temperature, a threshold arrival time that is a time from when the supply of the drive current is started until when a switching element to which the drive current is supplied transitions from off to on. The motor drive device is configured as described above. [Item 5] Item 4. The motor drive device according to item 4, The control unit controls the magnitude of the drive current regardless of temperature while the switching element to which the drive current is supplied is maintained in an on state. The motor drive device is configured as described above. [Explanation of symbols]

[0064] 10...motor, 20...motor drive device, 22...inverter circuit, 24...drive section, 26...power supply section, 30...control section, 30a...CPU, 30b...ROM, 30c...RAM, 34...temperature detection section, 34a, 34b...temperature map, 40...battery, Q1 to Q6...switching elements, T1 to T3...terminals.

Claims

1. A motor drive device (20) configured to drive a brushless motor (10), comprising: a drive unit (24) having a plurality of switching elements (Q1, Q2, Q3, Q4, Q5, Q6) and configured to supply power to the brushless motor using the plurality of switching elements; A control unit (30) configured to control a magnitude of a drive current for driving the plurality of switching elements; a temperature detection unit (34) configured to detect a temperature of the plurality of switching elements; Equipped with The control unit controls the magnitude of the drive current in accordance with the temperature detected by the temperature detection unit so that a slew rate of the plurality of switching elements becomes constant regardless of temperature. The motor drive device is configured as described above.

2. 2. The motor drive device according to claim 1, The control unit controls the magnitude of the drive current according to a temperature map (34a, 34b) that is prepared in advance and in which temperature and the magnitude of the drive current are associated with each other. The motor drive device is configured as described above.

3. 3. The motor drive device according to claim 1, The plurality of switching elements are FETs, and the control unit controls the magnitude of a gate current. The motor drive device is configured as described above.

4. 3. The motor drive device according to claim 1, The control unit sets, as the slew rate in accordance with the temperature, a threshold arrival time that is a time from when the supply of the drive current is started until when a switching element to which the drive current is supplied transitions from off to on. The motor drive device is configured as described above.

5. 5. The motor drive device according to claim 4, The control unit controls the magnitude of the drive current regardless of temperature while the switching element to which the drive current is supplied is maintained in an on state. The motor drive device is configured as described above.

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