FORM 2 THE PATENTS ACT, 1970 (39 of 1970) & THE PATENTS RULES, 2003 COMPLETE SPECIFICATION [See section 10, Rule 13] ELECTRIC MOTOR, AIR CONDITIONER, AND CONTROL BOARD; MITSUBISHI ELECTRIC CORPORATION, A CORPORATION ORGANISED AND EXISTING UNDER THE LAWS OF JAPAN, WHOSE ADDRESS IS 7-3, MARUNOUCHI 2-CHOME, CHIYODA-KU, TOKYO 1008310, JAPAN THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED 2 DESCRIPTION Field [0001] The present disclosure relates to an electric motor including an inverter, an air conditioner, and a 5 control board. Background [0002] Control of a conventional brushless directcurrent (DC) motor is a control that can be achieved by a 10 simple circuit configuration (including only a combinational circuit), such as 120-degree conduction control. Therefore, noise is hardly generated by a power supply circuit. In brushless DC motor control of recent years, complicated control such as 150-degree conduction 15 control, sine-wave conduction control, phase control, or sensorless control is performed. As a result, the complexity of a circuit configuration of a control unit increases, and clock frequency also increases. This leads to generation of a large amount of noise. 20 [0003] In the electric motor described in Patent Literature 1, noise is removed by an inductor connected to a power-supply line between a power-supply receiving unit of a microcomputer and a reference-voltage power-supply circuit that outputs a high voltage. 25 Citation List Patent Literature [0004] Patent Literature 1: Japanese Patent Application Laid-open No. 2005-219625 30 Summary of Invention Problem to be solved by the Invention 3 [0005] However, the technique of Patent Literature 1 described above has a problem in that noise reduction measures are taken only for the reference-voltage powersupply circuit that outputs a high voltage, resulting in 5 insufficient noise reduction. [0006] The present disclosure has been made in view of the above, and an object of the present disclosure is to obtain an electric motor capable of sufficiently reducing noise. 10 Means to Solve the Problem [0007] In order to solve the above-described problem and achieve the object, an electric motor of the present disclosure includes: a stator; a rotor; and a control board 15 that supplies current to the stator. The control board includes: a high-voltage circuit connected to a highvoltage power supply; and a low-voltage circuit connected to a low-voltage power supply. The high-voltage circuit includes an inverter that converts an input direct-current 20 voltage into an alternating-current voltage and supplies the alternating-current voltage to the stator, the lowvoltage circuit includes a control unit that controls the inverter, and a first inductor is disposed on a low-voltage power-supply line that is a line connecting the low-voltage 25 power supply and the low-voltage circuit. Effects of the Invention [0008] The electric motor according to the present disclosure has an effect of enabling noise to be 30 sufficiently reduced. Brief Description of Drawings [0009] FIG. 1 is a diagram showing a configuration 4 example of an electric motor according to a first embodiment. FIG. 2 is a diagram illustrating a circuit configuration of a built-in board included in the electric 5 motor according to the first embodiment. FIG. 3 is a diagram showing a first example of disposing an inductor on the built-in board according to the first embodiment. FIG. 4 is a diagram showing a second example of 10 disposing inductors on the built-in board according to the first embodiment. FIG. 5 is a diagram showing a third example of disposing inductors on the built-in board according to the first embodiment. 15 FIG. 6 is a diagram showing a fourth example of disposing inductors on the built-in board according to the first embodiment. FIG. 7 is a diagram illustrating a circuit configuration of a built-in board of a comparative example. 20 FIG. 8 is a diagram showing a first example of a configuration of an upper surface of the built-in board according to the first embodiment. FIG. 9 is a diagram for describing a relationship between temperature and inductance values. 25 FIG. 10 is a diagram showing a second example of the configuration of the upper surface of the built-in board according to the first embodiment. FIG. 11 is a diagram schematically illustrating the inside of the electric motor according to the first 30 embodiment. FIG. 12 is a diagram illustrating inductance frequency characteristics of inductors included in the electric motor according to the first embodiment. 5 FIG. 13 is a diagram showing a configuration example of an air conditioner according to a second embodiment. FIG. 14 is a diagram for describing a low-voltage power-supply generation circuit included in an electric 5 motor of the air conditioner according to the second embodiment. FIG. 15 is a diagram showing a configuration example of processing circuitry to be used in a case where a control unit included in the electric motor according to 10 each of the first and second embodiments is implemented by a processor and a memory. FIG. 16 is a diagram showing an example of processing circuitry to be used in a case where the control unit included in the electric motor according to each of the 15 first and second embodiments is implemented by dedicated hardware. Description of Embodiments [0010] Hereinafter, an electric motor, an air 20 conditioner, and a control board according to embodiments of the present disclosure will be described in detail with reference to the drawings. [0011] First Embodiment. FIG. 1 is a diagram showing a configuration example of 25 an electric motor according to a first embodiment. An electric motor 1 is a brushless DC motor. In FIG. 1, the electric motor 1 is partially illustrated in cross section for describing the configuration of the electric motor 1. Note that although FIG. 1 illustrates a radial-gap 30 brushless DC motor, the electric motor 1 of the first embodiment is not limited to the radial-gap brushless DC motor. [0012] The electric motor 1 includes a rotor 30, a 6 stator 20, a built-in board 11, and a molding resin 12. The built-in board 11 is a control board. A rotating shaft 31 is inserted in the rotor 30. The stator 20 is provided on an outer periphery of the rotor 30. The built-in board 5 11 includes a plated circuit that is a circuit that controls the driving of the rotor 30. [0013] The stator 20, the built-in board 11, and the molding resin 12 are fixed by a molded stator 10. The stator 20 and the built-in board 11 are integrally molded 10 by the molded stator 10. That is, the stator 20 and the built-in board 11 are fixed by the molded stator 10 so that the stator 20 and the built-in board 11 are integrated with each other. A recess is provided in the molded stator 10. The recess is formed such that the rotor 30 can be 15 accommodated in the recess. [0014] The built-in board 11 is integrated with the stator 20 by the molding resin 12 (resin having a relative permittivity of, for example, 3 to 4) having a permittivity higher than the permittivity of air. Therefore, capacitive 20 coupling (parasitic capacitance) between board patterns formed on the built-in board 11 increases, so that noise easily propagates between the board patterns. In the first embodiment, even when noise easily propagates as described above, noise is reduced by an inductor to be described 25 below. [0015] The stator 20 includes a plurality of stator cores 21, an insulator 23, and a winding 22. The insulator 23 is integrally molded with the stator cores 21. The stator cores 21 each include magnetic steel sheets 30 laminated together. The insulator 23 insulates the stator cores 21 from the winding 22. [0016] In the electric motor 1, the winding 22 is wound around the stator cores 21, which is integrally molded with 7 the insulator 23, through each slot of the stator cores 21 to form the stator 20. The winding 22 is made of copper, aluminum, or the like. [0017] An output-side bearing 33 that rotatably supports 5 the rotating shaft 31 is provided on one end of the rotating shaft 31. A counter-output-side bearing 34 that rotatably supports the rotating shaft 31 is provided on another end of the rotating shaft 31. [0018] The counter-output-side bearing 34 is covered 10 with a bracket 60 that is electrically conductive. The bracket 60 is configured such that a press-fitted portion 61 of the bracket 60 is fitted into an inner peripheral portion of the molded stator 10 in such a way as to cover an opening of the recess provided in the molded stator 10. 15 In addition, an outer ring of the counter-output-side bearing 34 is fitted into the bracket 60. [0019] The built-in board 11 includes a circuit including a power integrated circuit (IC) (power IC 80 to be described below), a control unit 70 to be described 20 below, and a magnetic sensor 50. The power IC 80 supplies power to the winding 22. The magnetic sensor 50 detects the position of the rotor 30. [0020] The built-in board 11 is disposed perpendicular to a direction of an axis of the rotating shaft 31, between 25 the output-side bearing 33 and the stator 20, and is fixed to the insulator 23. Furthermore, the plated circuit of the built-in board 11 and the winding 22 are connected via a winding terminal. A lead exit portion 14 is disposed on the built-in board 11. A lead wire 13 connecting to a host 30 system is drawn from the lead exit portion 14. The host system is a system including the electric motor 1. For example, the lead wire 13 is connected to a board (such as an indoor-unit board 211 to be described below) on a unit 8 side of an air conditioner. In addition, passive elements such as an operational amplifier, a comparator, a regulator, a diode, a resistor, a capacitor, and a fuse are disposed on the built-in board 11. 5 [0021] The built-in board 11 has a disk shape, and has a through hole formed in the center. The rotating shaft 31 is passed through the through hole provided in the built-in board 11. The built-in board 11 is disposed inside the electric motor 1 such that an upper surface and a bottom 10 surface are perpendicular to the direction of the axis of the rotating shaft 31. [0022] A rotor insulating portion 32 which is an annular member is disposed on an outer peripheral portion of the rotating shaft 31. The rotor 30 includes a magnet 40 15 disposed inside the molded stator 10. The magnet 40 is located in such a way as to face the stator cores 21, on an outer peripheral side of the rotating shaft 31 and the rotor insulating portion 32. The magnet 40 includes a cylindrical permanent magnet. The magnet 40 is fixed to 20 the rotating shaft 31. [0023] The magnet 40 is produced by injection molding of a ferrite magnet or a bonded magnet formed by a mixture of a rare-earth magnet (a samarium-iron-nitrogen, a neodymium, or the like) with a thermoplastic resin material. A magnet 25 is built into a metal mold for injection molding of the magnet 40, and the magnet 40 is molded while being oriented. [0024] The magnet 40 includes a sensor-magnet portion and a main-magnet portion in the direction of the axis of the rotating shaft 31. The sensor-magnet portion is part 30 of the magnet 40 closer to the magnetic sensor 50. The rest of the magnet 40 serves as the main-magnet portion. The sensor-magnet portion causes the magnetic sensor 50 to detect the position of the rotor 30. The main-magnet 9 portion causes the rotor 30 to generate a turning force according to magnetic flux generated by the winding 22. [0025] The magnet 40 is smaller in outer diameter on a side closer to the magnetic sensor 50 of the built-in board 5 11. That is, in the magnet 40, the outer diameter of the sensor-magnet portion is smaller than the outer shape of the main-magnet portion. This shape of the magnet 40 allows magnetic flux to easily flow into the magnetic sensor 50 mounted on the built-in board 11. In order to 10 minimize the effect of the magnetic flux generated by the winding 22 of the stator 20, the magnetic sensor 50 is located away from the winding 22, that is, located closer to the rotating shaft 31. [0026] Note that although FIG. 1 illustrates a case 15 where the main-magnet portion and the sensor-magnet portion are included in the single magnet 40, the main-magnet portion and the sensor-magnet portion may be provided as separate magnets. [0027] A Hall IC that outputs digital signals may be 20 used as the magnetic sensor 50. Alternatively, a Hall element that outputs analog signals may be used as the magnetic sensor 50. That is, the magnetic sensor 50 may detect the position of the rotor 30 by using a Hall IC, or may detect the position of the rotor 30 by using a Hall 25 element. [0028] In addition, the Hall IC may be a Hall IC (Hall IC of a first method) that detects the position of the rotor 30 by the first method, or may be a Hall IC (Hall IC of a second method) that detects the position of the rotor 30 30 by the second method. [0029] In the Hall IC of the first method, a sensor portion and an amplification portion are formed of separate semiconductor chips. In the Hall IC of the first method, 10 the sensor portion is made of a semiconductor other than silicon, and the amplification portion is made of silicon. Hereinafter, the Hall IC of the first method is referred to as a non-silicon Hall IC. In the Hall IC of the second 5 method, a sensor portion and an amplification portion are included in a single silicon semiconductor chip. [0030] Two chips are built into the non-silicon Hall IC. Therefore, the sensor portion is disposed such that the center of the sensor portion does not coincide with the 10 center of an IC body. A non-silicon semiconductor such as indium antimonide (InSb) is used for the sensor portion of the non-silicon Hall IC. Non-silicon semiconductors are advantageous in that non-silicon semiconductors have better sensitivity than silicon semiconductors, and that offset 15 due to stress strain in non-silicon semiconductors is smaller than in silicon semiconductors. [0031] Next, a circuit configuration of the built-in board 11 illustrated in FIG. 1 will be described. FIG. 2 is a diagram illustrating a circuit configuration of the 20 built-in board included in the electric motor according to the first embodiment. FIG. 2 illustrates the built-in board 11, the winding 22, and the magnetic sensors 50. [0032] The built-in board 11 includes an inductor 73A disposed on a low-voltage power-supply line as a 25 countermeasure against noise. Details of the inductor 73A provided as a countermeasure against noise will be described below. [0033] The built-in board 11 includes an inverter IC and an overcurrent detection resistor 75. The inverter IC 30 controls the driving of the electric motor 1 including the winding 22. Specifically, the built-in board 11 includes the power IC 80, the control unit 70, and the overcurrent detection resistor 75. The power IC 80 includes an 11 inverter 81, a gate drive circuit 82, and a protection circuit 83. [0034] The control unit 70 is connected to the host system, the gate drive circuit 82, a ground 79A, and the 5 magnetic sensors 50. Furthermore, the control unit 70 is connected to a low-voltage power supply 78 via a connection point 48. The inductor 73A is disposed between the connection point 48 and the low-voltage power supply 78. That is, the control unit 70 is connected to the low10 voltage power supply 78 via the connection point 48 and the inductor 73A. In addition, the control unit 70 is connected to a ground 79C via a connection point 41, a connection point 42, and the overcurrent detection resistor 75. 15 [0035] The gate drive circuit 82 is connected to the low-voltage power supply 78 via the connection point 48 and the inductor 73A, and is connected to a high-voltage power supply 77 via a connection point 47. The low-voltage power supply 78 outputs a voltage lower than a voltage of the 20 high-voltage power supply 77. The high-voltage power supply 77 is a bus power supply. [0036] Furthermore, the gate drive circuit 82 is connected to the inverter 81. In addition, the gate drive circuit 82 is connected to the protection circuit 83 and a 25 ground 79B via a connection point 43. [0037] The protection circuit 83 is connected to the connection point 41 and the connection point 43. That is, the protection circuit 83 is connected to the ground 79C via the connection point 41, the connection point 42, and 30 the overcurrent detection resistor 75. In addition, the protection circuit 83 is connected to the ground 79B via the connection point 43. [0038] The inverter 81 is connected to the electric 12 motor 1 including the winding 22. In addition, the inverter 81 is connected to the ground 79C via the connection point 42 and the overcurrent detection resistor 75. The grounds 79A to 79C are common grounds having the 5 same potential. In the following description, the grounds 79A to 79C are collectively referred to as a ground 79. [0039] The power IC 80 is also referred to as an intelligent power module (IPM). The inverter 81 includes six power transistors 81A to 81F. 10 [0040] In the power IC 80, the six power transistors 81A to 81F may be separately provided, or may be provided as a single IC. In a case where the six power transistors 81A to 81F are separately provided, the gate drive circuit 82 may be provided as a single IC, or may include three ICs 15 provided separately for three phases. In addition, the gate drive circuit 82 and the control unit 70 may be provided as a single IC. Furthermore, the control unit 70 may include a single dedicated IC (control IC), or may include a microcomputer (hereinafter, referred to as a 20 microcomputer) or the like. [0041] The power transistors 81A to 81F each include a super-junction metal oxide semiconductor field effect transistor (MOSFET), a planar MOSFET, an insulated gate bipolar transistor (IGBT), or the like. 25 [0042] In the first embodiment, a description will be given of a case where the magnetic sensor 50 detects positions of magnetic poles of the rotor 30 corresponding to a position of magnetic flux, and the built-in board 11 controls the electric motor 1 based on the positions of the 30 magnetic poles. Note that the built-in board 11 may perform sensorless control of the electric motor 1 while estimating the positions of the magnetic poles from a current flowing through the winding 22 and voltages applied 13 to and generated by the winding 22. Furthermore, in order to detect a current, the built-in board 11 may amplify a current signal obtained by use of a shunt resistor and a current sensor, with an operational amplifier or the like. 5 In addition, the built-in board 11 may use a comparator to generate, from the current signal, a signal for overcurrent protection to be provided to the control unit 70. [0043] On the built-in board 11, a voltage (for example, 15 V) for driving the gates of the power transistors 81A to 10 81F may be different from a microcomputer power-supply voltage (for example, 5 V) that is a voltage for driving the control unit 70 such as a microcomputer. In this case, the electric motor 1 uses a regulator to generate another power supply from one power supply provided from the 15 outside. For example, a power supply of 15 V is provided to the built-in board 11 from the outside, and the regulator generates a power supply of 5 V and provides the power supply to the built-in board 11. The regulator may be built into the gate drive circuit 82 or the power IC 80. 20 [0044] The inverter 81 converts an input direct-current voltage into an alternating-current voltage for three phases including a U phase, a V phase, and a W phase, and supplies the alternating-current voltage to the winding 22 of the stator 20. The power transistor 81A is a U-phase 25 upper-arm power transistor. The power transistor 81B is a V-phase upper-arm power transistor. The power transistor 81C is a W-phase upper-arm power transistor. The power transistor 81D is a U-phase lower-arm power transistor. The power transistor 81E is a V-phase lower-arm power 30 transistor. The power transistor 81F is a W-phase lowerarm power transistor. [0045] The electric motor 1 includes, as the winding 22, a U-phase winding 22U, a V-phase winding 22V, and a W-phase 14 winding 22W. The U-phase winding 22U is connected to the power transistors 81A and 81D. The V-phase winding 22V is connected to the power transistors 81B and 81E. The Wphase winding 22W is connected to the power transistors 81C 5 and 81F. [0046] The gate drive circuit 82 controls the turning-on and turning-off of the power transistors 81A to 81F according to switching signals received from the control unit 70. 10 [0047] Three magnetic sensors 50 are disposed around the winding 22. Each of the three magnetic sensors 50 outputs, to the control unit 70, a magnetic-pole position signal corresponding to the position of the rotor 30. [0048] The protection circuit 83 protects the inverter 15 81 and the gate drive circuit 82. For example, the protection circuit 83 prevents a high current from flowing back to the gate drive circuit 82 from the ground 79. In addition, when at least one of the inverter 81 and the gate drive circuit 82 has a high temperature, the protection 20 circuit 83 turns off all the power transistors 81A to 81F of the inverter 81 to prevent element destruction due to high temperature. [0049] The overcurrent detection resistor 75 is connected to lower-arm switches included in the power 25 transistors 81D to 81F. In addition, the built-in board 11 includes an overcurrent detection unit (not illustrated) that detects an overcurrent. The overcurrent detection unit prevents an overcurrent from flowing through the winding 22 and achieves overcurrent protection by 30 monitoring the voltage of the overcurrent detection resistor 75 so as to turn off the power transistors 81A to 81F when the voltage of the overcurrent detection resistor 75 reaches or exceeds a specific voltage value. The fact 15 that a voltage across the overcurrent detection resistor 75 reaches or exceeds the specific voltage value corresponds to an overcurrent detection signal to be input from the overcurrent detection resistor 75 to the control unit 70. 5 The overcurrent detection unit achieves overcurrent protection based on the overcurrent detection signal. Note that the overcurrent detection unit may be built into the control unit 70, or may be built into the gate drive circuit 82. 10 [0050] Note that a temperature-sensitive element (not illustrated) may be provided on the built-in board 11 or the like. In this case, when receiving a signal indicating an anomalous temperature from the temperature-sensitive element, the control unit 70 forcibly turns off the power 15 transistors 81A to 81F. [0051] The control unit 70 generates switching signals for controlling the turning-on and turning-off of the power transistors 81A to 81F at a specific frequency (hereinafter, referred to as a carrier frequency) according to a speed 20 command signal received from the host system. [0052] The control unit 70 performs pulse width modulation (PWM) control on the power transistors 81A to 81F by outputting the switching signals to the gate drive circuit 82. The control unit 70 estimates positions of the 25 magnetic poles of the rotor 30 based on the magnetic-pole position signal input from the magnetic sensor 50, and calculates a rotational speed of the rotor 30 from the estimated positions of the magnetic poles. The control unit 70 outputs a rotational speed signal indicating the 30 calculated rotational speed to the host system. [0053] Note that the control unit 70 may be a dedicated IC such as an application specific integrated circuit (ASIC). Furthermore, the control unit 70 may include a 16 memory that stores a program and a central processing unit (CPU) that executes processing according to the program. A hardware configuration of the control unit 70 will be described below. 5 [0054] In the case of three phases, the electric motor 1, which is a brushless DC motor, obtains rotational power by switching the six power transistors 81A to 81F at appropriate timings according to the positions of the magnetic poles of the magnet 40 of the rotor 30. Switching 10 signals to be used for the switching are generated by the control unit 70. The operation principle of the electric motor 1 will be described. [0055] In the electric motor 1, the control unit 70 estimates the positions of the magnetic poles of the rotor 15 30 based on the magnetic-pole position signal from the magnetic sensor 50 or a value of current flowing through the winding 22. The control unit 70 generates switching signals for switching the power transistors 81A to 81F according to the positions of the magnetic poles of the 20 rotor 30 and the speed command signal output from the host system. The gate drive circuit 82 performs switching between the turning-on and turning-off of the power transistors 81A to 81F according to the switching signals generated by the control unit 70. 25 [0056] For example, in the 120-degree conduction control, timings for the switching between the turning-on and turning-off of the six power transistors 81A to 81F coincide with the rising edge and falling edge of each of detection signals regarding detection by three Hall ICs. 30 Therefore, in the 120-degree conduction control, the control unit 70 can be implemented by a combinational circuit requiring no clock. [0057] Meanwhile, in the case of control requiring 17 estimation of positions of magnetic poles, such as 150- degree conduction control, sine-wave conduction control, phase control, or sensorless control, the control unit 70 includes a complicated digital circuit including a clock. 5 For example, timing between the rising edge and falling edge of each of the detection signals regarding detection by the three Hall ICs is finely estimated in estimation of positions of magnetic poles. [0058] Sensorless control is control that does not use 10 the magnetic sensor 50. In the sensorless control, positions of magnetic poles are estimated from a value of current detected by a current detection resistor, a current detection transformer, or the like, to perform control. That is, in the case of the sensorless control, the control 15 unit 70 estimates positions of magnetic poles based on a current flowing through the winding 22 and a voltage applied to the winding 22, and thus, complicated processing and calculation are required. Therefore, in the case of the sensorless control, the complexity of the circuit of 20 the control unit 70 further increases, and it is necessary to increase clock frequency in the control unit 70. [0059] For example, in order to achieve noise reduction, higher efficiency, and stable control, the clock frequency of the control unit 70 is 100 times or more a carrier 25 frequency that is a frequency at which the power transistors 81A to 81F are switched. [0060] Next, the inductor 73A disposed on the built-in board 11 as a countermeasure against noise will be described. In the first embodiment, the inductor 73A is 30 disposed on the low-voltage power-supply line of the builtin board 11 as a countermeasure against noise. Noise in the first embodiment refers to noise (electromagnetic interference (EMI)) generated by the electric motor 1 and a 18 product equipped with the electric motor 1. This noise includes noise of a noise terminal voltage, noise of noise power, radiation noise, and the like. [0061] The low-voltage power-supply line is a line 5 connecting the low-voltage power supply 78 and a circuit (low-voltage circuit) that operates at a low voltage on the built-in board 11. In addition, an inductor may be disposed on a high-voltage power-supply line of the builtin board 11. The high-voltage power-supply line is a line 10 connecting the high-voltage power supply 77 and a circuit (high-voltage circuit) that operates at a high voltage on the built-in board 11. [0062] Furthermore, an inductor may be disposed on a ground (GND) line of the built-in board 11. The ground 15 line is a line connecting the ground 79 and a circuit on the built-in board 11. Note that a ground line for a lowvoltage circuit and a ground line for a high-voltage circuit may be separately disposed as ground lines on the built-in board 11. 20 [0063] FIG. 3 is a diagram showing a first example of disposing an inductor on the built-in board according to the first embodiment. On the built-in board 11, a lowvoltage circuit 72 is connected to the low-voltage power supply 78, and a high-voltage circuit 71 is connected to 25 the high-voltage power supply 77. In addition, the lowvoltage circuit 72 and the high-voltage circuit 71 are connected to a connection point 45, and the connection point 45 is connected to the ground 79. The low-voltage circuit 72 includes, for example, a digital circuit 30 including a sequential circuit. [0064] The low-voltage circuit 72 includes a first circuit, the control unit 70, and the protection circuit 83. The first circuit is part of the gate drive circuit 82. 19 The high-voltage circuit 71 includes a second circuit and the inverter 81. The second circuit is part of the gate drive circuit 82. In the gate drive circuit 82, the first circuit included in the low-voltage circuit 72 and the 5 second circuit included in the high-voltage circuit 71 are different circuits. [0065] In the first example of disposing an inductor on the built-in board 11, a single inductor, that is, the inductor 73A is disposed. The inductor 73A, which is a 10 first inductor, is disposed on a low-voltage power-supply line connecting the low-voltage circuit 72 and the lowvoltage power supply 78. With this configuration, the built-in board 11 can reduce noise generated on the builtin board 11 by means of the inductor 73A. 15 [0066] FIG. 4 is a diagram showing a second example of disposing inductors on the built-in board according to the first embodiment. In the second example of disposing inductors on the built-in board 11, two inductors 73A and 73B are disposed. The inductor 73B, which is a second 20 inductor, is disposed on a high-voltage power-supply line connecting the high-voltage circuit 71 and the high-voltage power supply 77. With this configuration, the built-in board 11 can reduce noise generated on the built-in board 11 by means of the inductors 73A and 73B. 25 [0067] FIG. 5 is a diagram showing a third example of disposing inductors on the built-in board according to the first embodiment. In the third example of disposing inductors on the built-in board 11, three inductors 73A to 73C are disposed. The inductor 73C is disposed on a ground 30 line connecting the connection point 45 and the ground 79. With this configuration, the built-in board 11 can reduce noise generated on the built-in board 11 by means of the inductors 73A to 73C. 20 [0068] FIG. 6 is a diagram showing a fourth example of disposing inductors on the built-in board according to the first embodiment. In the fourth example of disposing inductors on the built-in board 11, four inductors 73A, 73B, 5 73D, and 73E are disposed. The inductor 73D is disposed on a ground line connecting the low-voltage circuit 72 and the connection point 45. The inductor 73E is disposed on a ground line connecting the high-voltage circuit 71 and the connection point 45. With this configuration, the built-in 10 board 11 can reduce noise generated on the built-in board 11 by means of the inductors 73A, 73B, 73D, and 73E. [0069] FIG. 7 is a diagram illustrating a circuit configuration of a built-in board of a comparative example. The built-in board of the comparative example includes a 15 low-voltage circuit 72X and a high-voltage circuit 71X. The low-voltage circuit 72X is a circuit similar to the low-voltage circuit 72, and the high-voltage circuit 71X is a circuit similar to the high-voltage circuit 71. [0070] The low-voltage circuit 72X is connected to a 20 low-voltage power supply 78X that is a power supply similar to the low-voltage power supply 78. The high-voltage circuit 71X is connected to a high-voltage power supply 77X that is a power supply similar to the high-voltage power supply 77. Furthermore, the low-voltage circuit 72X and 25 the high-voltage circuit 71X are connected to a connection point 45X that is a connection point similar to the connection point 45, and the connection point 45X is connected to a ground 79X. [0071] On the built-in board of the comparative example, 30 no inductor is disposed on a low-voltage power-supply line connecting the low-voltage circuit 72X and the low-voltage power supply 78X. In addition, no inductor is disposed on a high-voltage power-supply line connecting the high- 21 voltage circuit 71X and the high-voltage power supply 77X. Furthermore, no inductor is disposed on a ground line from the low-voltage circuit 72X to the ground 79X, and no inductor is disposed on a ground line from the high-voltage 5 circuit 71X to the ground 79X. Therefore, the built-in board of the comparative example cannot reduce noise generated on the built-in board of the comparative example. [0072] FIG. 8 is a diagram showing a first example of a configuration of an upper surface of the built-in board 10 according to the first embodiment. The configuration of the upper surface of the built-in board 11 illustrated in FIG. 5 will be described with reference to FIG. 8. As illustrated in FIG. 8, the built-in board 11 has a disk shape, and has a through hole 35 formed in the center. The 15 rotating shaft 31 is passed through the through hole 35. [0073] The power IC 80, which supplies power to the winding 22, the inductors 73A to 73C, and the control unit 70 are disposed on the upper surface of the built-in board 11. Note that although not illustrated, the overcurrent 20 detection resistor 75 and the like are disposed on the upper surface or bottom surface of the built-in board 11. [0074] The inductors 73A to 73C are disposed closer to the lead exit portion 14 than to the power IC 80 including the power transistors 81A to 81F. That is, the inductors 25 73A to 73C are located such that distances to the lead exit portion 14 are shorter than distances to the power IC 80. [0075] As a result, the inductors 73A to 73C are less likely to be affected by heat radiated by the power transistors 81A to 81F, so that temperature-induced changes 30 in inductance values of the inductors 73A to 73C decrease. When an inductance value fluctuates, noise reduction effect decreases due to unmatched impedance or the like. Meanwhile, noise reduction effect increases in the first 22 embodiment because a change in the inductance value is small. That is, the inductors 73A to 73C are less likely to be affected by heat radiated by the power transistors 81A to 81F. Therefore, the built-in board 11 can prevent 5 noise removal performance from being changed by a change in an inductance value due to temperature characteristics of the inductors 73A to 73C. [0076] In addition, since the inductors 73A to 73C are disposed closer to the lead exit portion 14 than to the 10 power IC 80, wiring on the built-in board 11 is facilitated. As a result, the built-in board 11 can be reduced in size, and the manufacturing cost of the electric motor 1 can be reduced by the reduction in the size of the built-in board 11. In addition, since the length of wiring of the built15 in board 11 is shortened by the reduction in the size of the built-in board 11, noise can be reduced. [0077] Furthermore, in the case of an inductor having inductance negatively correlated with temperature, impedance generally decreases due to an increase in 20 temperature, and thus noise reduction effect may be greatly deteriorated. Note that the case where inductance is negatively correlated with temperature is not limited to a case where inductance is negatively correlated with an entire temperature range, but also includes a case where 25 inductance is negatively correlated with a temperature that falls within part of the temperature range (negatively correlated with a temperature of, for example, 60°C or higher). [0078] FIG. 9 is a diagram for describing a relationship 30 between temperature and inductance values. In a graph illustrated in FIG. 9, the horizontal axis represents temperature, and the vertical axis represents the value of inductance. FIG. 9 illustrates an inductance temperature 23 characteristic for each current magnitude. [0079] An inductance temperature characteristic 74A is an inductance temperature characteristic to be obtained when a current having a first current value flows through 5 an inductor. An inductance temperature characteristic 74B is an inductance temperature characteristic to be obtained when a current having a second current value flows through the inductor. An inductance temperature characteristic 74C is an inductance temperature characteristic to be obtained 10 when a current having a third current value flows through the inductor. The following holds: first current value