Electric motor and air conditioner having the same

Abstract

The motor of the present application has a mechanism for detecting overcurrent of an inverter circuit. The motor has a rotor, a stator, and a substrate, the substrate having: a power transistor constituting an inverter circuit that switches the direction of current flowing to the winding of the stator; a first resistor provided between the power transistor and a ground terminal for detecting overcurrent of the inverter circuit; a second resistor provided between the power transistor and the first resistor for detecting current flowing to the winding of the stator; and a zener diode connected in parallel with the first resistor.

Description

Technical Field

[0001] This disclosure relates to an electric motor having an inverter circuit and an air conditioner having an electric motor. Background Technology

[0002] For example, Patent Document 1 proposes a method for controlling an inverter circuit based on the current value detected by a phase current detection unit, as a control method for an electric motor. Furthermore, it proposes a method that uses an overcurrent protection unit to detect overcurrent in the inverter circuit and protect the power switching semiconductors constituting the inverter circuit from the effects of overcurrent. Based on the structure of Patent Document 1, it is possible to miniaturize the electric motor and prevent damage to the inverter circuit caused by overcurrent flowing in the power switching semiconductors.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2005-304176

[0004] In the structure of Patent Document 1, if the motor malfunctions due to a short circuit in the inverter circuit (either a single arm or a single phase), and a large current flows through the overcurrent detection resistor (which serves as an overcurrent protection unit), the overcurrent detection resistor will be severely burned. Furthermore, if a fire starts from the overcurrent detection resistor, its smoke will be emitted to the outside of the motor. Summary of the Invention

[0005] This disclosure was made to solve the above-mentioned problems, and the purpose is to provide an electric motor capable of suppressing the burnout of a resistor used for detecting overcurrent, and an air conditioner equipped with the electric motor.

[0006] The electric motor disclosed herein includes a rotor, a stator, and a substrate. The substrate includes: a power transistor constituting an inverter circuit that switches the direction of current flowing to the windings of the stator; a first resistor disposed between the power transistor and a ground terminal for detecting overcurrent in the inverter circuit; a second resistor disposed between the power transistor and the first resistor for detecting current flowing to the windings of the stator; and a Zener diode connected in parallel with the first resistor.

[0007] According to the electric motor disclosed herein, since the Zener diode is connected in parallel with the first resistor used for detecting overcurrent, the burn-out of the first resistor can be suppressed. Attached Figure Description

[0008] Figure 1 This is a schematic diagram of the electric motor involved in Embodiment 1.

[0009] Figure 2 This is a block diagram illustrating the circuit structure of the built-in substrate involved in Embodiment 1.

[0010] Figure 3 This is a block diagram showing the circuit structure of the amplifier circuit involved in Embodiment 1.

[0011] Figure 4 This is a schematic diagram illustrating an example of the configuration of the Zener diode involved in Embodiment 1.

[0012] Figure 5 This is a schematic diagram showing an example of the configuration of the first resistor involved in Embodiment 1.

[0013] Figure 6 This is a schematic diagram of the air conditioner involved in Embodiment 2. Detailed Implementation

[0014] The electric motor according to this embodiment will now be described. Furthermore, the size relationships of the constituent components in the following drawings may sometimes differ from the actual situation. Also, in the following drawings, parts marked with the same reference numerals are the same or equivalent parts, which is consistent throughout the specification. Furthermore, the forms of the constituent elements expressed throughout the specification are merely illustrative and are not limited to these descriptions.

[0015] Implementation Method 1

[0016] <The Structure of an Electric Motor>

[0017] Figure 1 This is a schematic diagram of the electric motor 1 according to Embodiment 1. The electric motor 1 according to this embodiment is, for example, a brushless DC motor. Figure 1 In order to illustrate the structure of motor 1, a portion of it is represented by a cross-sectional structure.

[0018] like Figure 1 As shown, the electric motor 1 includes: a rotor 30 to which a rotating shaft 31 is inserted; a stator 20 disposed on the outer periphery of the rotor 30; and an internal substrate 11 on which circuitry for controlling the drive of the rotor 30 is mounted. The internal substrate 11 and the stator 20 are integrally formed by molding resin 12. The internal substrate 11 and the stator 20 constitute a molded stator 10. A recess is formed in the molded stator 10, and the rotor 30 is housed in the recess of the molded stator 10. A rotor insulation portion 32 is sandwiched between the rotor 30 and the rotating shaft 31, thereby insulating the rotor 30 from the rotating shaft 31.

[0019] An output-side bearing 33 supporting the rotating shaft 31 is provided at one end of the rotating shaft 31. A reverse output-side bearing 34 supporting the rotating shaft 31 at the other end is provided at the other end of the rotating shaft 31. The reverse output-side bearing 34 is covered by a conductive bracket 60. The outer ring of the reverse output-side bearing 34 is embedded in the inner side of the bracket 60. The bracket 60 is embedded in the inner periphery of the molding die 10 in such a way that it blocks the opening of the recess of the molding die 10.

[0020] The stator 20 has a cylindrical shape. The stator 20 includes: a plurality of stator cores 21 arranged radially around a rotation axis 31; an insulator 23 integrally formed with the plurality of stator cores 21; and windings 22 wound around the plurality of stator cores 21. The stator cores 21 are constructed by stacking electromagnetic steel plates. The windings 22 are made of conductive wires such as copper or aluminum. For example, as described later... Figure 2 As shown, winding 22 consists of U-phase winding 22U, V-phase winding 22V, and W-phase winding 22W. In the following description, the three-phase windings are sometimes collectively referred to as winding 22. The stator core 21 and winding 22 are insulated by insulator 23.

[0021] The outer peripheral surface of the rotor 30, housed in the recess of the stator 10, faces the stator core 21. The outer peripheral surface of the rotor 30 is composed of a magnet 40. The magnet 40 is manufactured, for example, by injection molding a permanent magnet such as a ferrite magnet, or a bonded magnet made of a mixture of rare-earth magnets and thermoplastic resin. The magnet is inserted into a metal mold for injection molding, and the molding is performed while applying orientation.

[0022] An internal substrate 11 is disposed axially between the output-side bearing 33 and the stator 20 along the rotation shaft 31. The internal substrate 11 has a circular plate shape with a hole formed in the center. The rotation shaft 31 is inserted into the hole of the internal substrate 11. One side of the internal substrate 11 faces the end face of the stator 20 along the rotation shaft 31. The mounting surface of the internal substrate 11 is arranged perpendicularly to the axial direction of the rotation shaft 31. The internal substrate 11 and the stator 20 are fixed together by molding resin 12.

[0023] A magnetic sensor 50 can also be mounted on the built-in substrate 11. In this case, if the magnetic sensor 50 is positioned closer to the rotation axis 31 than the winding 22 of the stator 20, the influence of the magnetic flux generated from the winding 22 of the stator 20 on the magnetic sensor 50 is suppressed. The magnetic sensor 50 can be a digital sensor such as a Hall IC, or an analog sensor such as a Hall element. Hall ICs include: non-silicon Hall ICs where the sensor section and amplification section are composed of different semiconductor chips, where the sensor section is composed of a semiconductor other than silicon and the amplification section is composed of silicon; and Hall ICs where the sensor section and amplification section are composed of a single silicon semiconductor chip. Since the non-silicon Hall IC has two chips built-in, the sensor center is positioned at a different location than the center of the IC body. The sensor section of the non-silicon Hall IC uses semiconductors such as indium antimonide (InSb). Compared to silicon semiconductors, these non-silicon semiconductors have advantages such as increased sensitivity and the ability to suppress offsets caused by stress deformation.

[0024] When a magnetic sensor 50 is mounted on the built-in substrate 11, the magnet 40 of the rotor 30 can, for example, be composed of a sensor magnet portion and a main magnet portion with an outer diameter larger than that of the sensor magnet portion. The sensor magnet portion serves to enable the magnetic sensor 50 to detect the position of the rotor 30. The main magnet portion serves to generate a rotational force in the rotor 30 based on the magnetic flux generated by the winding 22. If the magnet 40 is considered as a cylinder with the rotation axis 31 as its central axis, the diameter of the sensor magnet portion is smaller than the diameter of the main magnet portion. According to this structure, magnetic flux easily flows from the magnetic poles of the sensor magnet portion into the magnetic sensor 50. Figure 1 In the structural example shown, the sensor magnet section and the main magnet section can be distinguished by a step difference provided on the magnet 40. Furthermore, although in Figure 1 In the structural example shown, the main magnet section and the sensor magnet section of the magnet 40 are composed of a single magnet, but the main magnet section and the sensor magnet section can also be composed of separate magnets.

[0025] The built-in substrate 11 is provided with a wire lead-out portion 14 for introducing the wire 13 into the motor 1. The wire 13 is a wire that connects the host system of the motor 1 to the motor 1. The host system of the motor 1 refers to the control board of the device that houses the motor 1. For example, in the case where the motor 1 is built into an air conditioner, the control board of the air conditioner is equivalent to the host system of the motor 1.

[0026] <Circuit Structure>

[0027] Figure 2 This is a block diagram illustrating the circuit structure of the built-in substrate 11 according to Embodiment 1. For example... Figure 2As shown, the built-in substrate 11 includes a power transistor 81, a controller 70, a gate driver circuit 82, and an amplifier circuit 72 constituting an inverter circuit. A first resistor 71 is provided between the power transistor 81 and the ground terminal G. A second resistor 74 is provided between the power transistor 81 and the first resistor 71. A Zener diode 73 is connected in parallel with the first resistor 71 across its terminals. The controller 70 and the amplifier circuit 72 are connected between a control power supply 78 and the ground terminal G.

[0028] In the built-in substrate 11, the power transistor 81, controller 70, and gate driver circuit 82 are, for example, constituted by a single integrated circuit (IC). The power transistor 81 and gate driver circuit 82 can also be constituted by a single IC as an intelligent power module (IPM).

[0029] The inverter circuit converts the DC voltage input from the bus power supply 77 into a three-phase AC voltage through the operation of power transistors 81. Power transistors 81 are positioned between the bus power supply 77 and the ground terminal G. For example, power transistors 81 consist of six power transistors, two for each phase, and are connected to the three-phase windings 22U, 22V, and 22W via winding terminals not shown.

[0030] Specifically, the power transistor 81 is composed of the upper arm power transistor 81A of the U phase, the upper arm power transistor 81B of the V phase, and the upper arm power transistor 81C of the W phase. The power transistor 81 is composed of the lower arm power transistor 81D of the U phase, the lower arm power transistor 81E of the V phase, and the lower arm power transistor 81F of the W phase.

[0031] The upper arm power transistor 81A and the lower arm power transistor 81D of phase U are connected to the phase U winding 22U. The upper arm power transistor 81B and the lower arm power transistor 81E of phase V are connected to the phase V winding 22V. The upper arm power transistor 81C and the lower arm power transistor 81F of phase W are connected to the phase W winding 22W. In the following description, the power transistors of each phase are sometimes collectively referred to as power transistor 81. Power transistor 81 is, for example, a superjunction MOSFET, a planar MOSFET, or an IGBT.

[0032] The second resistor 74 is provided for detecting the phase current flowing to the winding 22 of each phase. The second resistor 74 only needs to be connected to the lower arm power transistors of at least two of the U, V, and W phases. Figure 2In the example shown, the second resistor 74 includes a second resistor 74U disposed between the lower arm power transistor 81D of phase U and the ground terminal G, and a second resistor 74V disposed between the lower arm power transistor 81E of phase V and the ground terminal G. The resistance value of the second resistor 74 is, for example, 1Ω.

[0033] The voltage across the second resistor 74 is input to the amplifier circuit 72. For example, the voltage across the second resistor 74U is input to the U-phase amplifier circuit 72U, and the voltage across the second resistor 74V is input to the V-phase amplifier circuit 72V. The voltage across the second resistor 74 is amplified in the amplifier circuit 72 and output to the phase current detection unit 70B of the controller 70.

[0034] The controller 70 generates a switching signal based on the current detected by the phase current detection unit 70B and outputs it to the gate driver circuit 82. The phase current detection unit 70B is, for example, an A / D converter. The controller 70 can also be a special-purpose IC such as an ASIC (Application Specific Integrated Circuit). The controller 70 can also be a structure with a memory for storing programs and a CPU (Central Processing Unit) for executing processes according to the programs.

[0035] The gate driver circuit 82 controls the power transistor 81 to be in an on state and an off state according to the switching signal. The gate driver circuit 82 turns the power transistor 81 on by applying a voltage higher than the threshold voltage to the gate electrode. Conversely, the gate driver circuit 82 turns the power transistor 81 off by applying a voltage lower than the threshold voltage to the gate electrode.

[0036] A first resistor 71 is connected between the power transistor 81 and the ground terminal G, and a second resistor 74 is connected between the second resistor 74 and the ground terminal G. The first resistor 71 is provided to detect overcurrent in the power transistor 81. The resistance value of the first resistor 71 is, for example, 1Ω. The voltage across the first resistor 71 is input to the overcurrent detection unit 70A of the controller 70. If the voltage across the first resistor 71 is above a certain value, the power transistor 81 is turned off under the control of the controller 70.

[0037] The Zener diode 73 connected in parallel with the first resistor 71 is, for example, a Zener diode. The Zener diode 73 has the following characteristics: no current flows until the applied voltage reaches the breakdown voltage, and when the applied voltage becomes greater than the breakdown voltage, a current flows in which the voltage applied to the Zener diode 73 becomes equal to the breakdown voltage.

[0038] If the Zener diode 73 is not connected in parallel with the first resistor 71, and a short circuit occurs in either the arm or phase of the power transistor 81, an overcurrent will flow in both the power transistor 81 and the first resistor 71. In this case, although the power transistor 81 is protected by the first resistor 71, the first resistor 71 itself is not protected, and therefore, it may burn out, catch fire, or smoke due to the overcurrent. In particular, the effects of overcurrent become significant when a metal film resistor is used as the first resistor 71.

[0039] When the Zener diode 73 and the first resistor 71 are connected in parallel, if the voltage applied to the Zener diode 73 reaches its breakdown voltage, current flows through the Zener diode 73. If the breakdown voltage of the Zener diode 73 is reached due to an overcurrent generated in the power transistor 81, current flows through the Zener diode 73, thus maintaining the current in the first resistor 71 at a constant value. This prevents the current flowing to the first resistor 71 from becoming an overcurrent, suppressing burnout, fire, or smoke in the first resistor 71.

[0040] <Structure of Amplifier Circuit>

[0041] Figure 3 This is a block diagram showing the circuit structure of the amplifier circuit 72 according to Embodiment 1. For example... Figure 3 As shown, the amplifier circuit 72 includes an operational amplifier 75 and multiple resistors, including an input resistor 76. To remove noise, the amplifier circuit 72 also uses a capacitor (not shown). The input resistor 76 includes a third resistor 76P on the positive side of the amplifier circuit 72 and a fourth resistor 76N on the negative side of the amplifier circuit 72.

[0042] As the operational amplifier 75, for example, a rail-to-rail type operational amplifier can be used. In the rail-to-rail type operational amplifier 75, the output can be distributed across a range from the power supply voltage to ground voltage, thus maximizing the amplification achieved by the amplifier circuit 72. Furthermore, by using the rail-to-rail type operational amplifier 75, noise immunity is improved, enabling more stable and efficient control.

[0043] Operational amplifier 75 may, for example, be an operational amplifier whose output is not rail-to-rail. In this case, the output of operational amplifier 75 is smaller than that of rail-to-rail operational amplifier 75, so a bias circuit (not shown) can be included in the input of operational amplifier 75. Furthermore, in this case, to increase the output voltage from operational amplifier 75, the power supply voltage of operational amplifier 75 can be increased, for example, to 15V, and a diode (not shown) can be included between the signal between operational amplifier 75 and controller 70, and between the control power supply 78.

[0044] <Operation of Motor 1>

[0045] Next, the operation of the motor 1 will be explained. The motor 1 is driven to rotate, for example, by sensorless control. In sensorless control, the magnetic flux position of the magnet 40 of the rotor 30 is inferred from the current value of the winding 22 of the stator 20. According to the magnetic pole position, the six power transistors 81 are switched on or off at appropriate times, thereby obtaining rotational power.

[0046] The controller 70 calculates the phase currents of winding 22U and winding 22V based on the voltage value across the second resistor 74 input to the phase current detection unit 70B after being amplified by the amplifier circuit 72, and infers the magnetic pole position of the magnet 40.

[0047] The controller 70 generates switching commands based on the estimated magnetic pole position of the magnet 40 and the speed command signal from the host system, and outputs them to the gate driver circuit 82. Based on the switching commands output by the controller 70, the gate driver circuit 82 controls the six power transistors 81 to be in an on or off state. This generates current in the windings 22U, 22V, and 22W of each phase at appropriate times, causing the rotor 30 to rotate. Furthermore, the controller 70 detects the phase current and performs control to minimize the current, thereby achieving more efficient control.

[0048] When the voltage across the first resistor 71 input to the overcurrent detection unit 70A exceeds a certain value, the controller 70 determines that an overcurrent has occurred in the power transistor 81 and generates a switching signal to set the power transistor 81 to the off state. The switching signal is output to the gate driver circuit 82, which forcibly turns the power transistor 81 off. Thus, the power transistor 81 is protected from damage by the current.

[0049] In the event that both the power transistor 81 and the first resistor 71 have overcurrent flowing through them, the overcurrent in the first resistor 71 is suppressed by the Zener diode 73, thus preventing the first resistor 71 from burning out, catching fire, or smoking due to overcurrent. By connecting the Zener diode 73 in parallel with the first resistor 71, the first resistor 71 can detect the overcurrent in the power transistor 81 while avoiding burnout caused by the overcurrent.

[0050] In addition, the Zener diode 73 also has the effect of suppressing surge voltage applied to the input side of the operational amplifier 75. To more effectively suppress surge voltage, a third resistor 76P can be provided in the operational amplifier 75. The third resistor 76P is located between the positive input terminal of the amplifier circuit 72, which is connected to the electrode of the power transistor 81 side of the second resistor 74, and the first resistor 71. The third resistor 76P functions as a noise removal and bias circuit. The resistance value of the third resistor 76P can be, for example, several hundred Ω to several kΩ. In particular, if the ratio of the current sensing resistor to the amplifier circuit input resistor 76 is greater than the ratio of the control power supply voltage, i.e., the voltage of the operational amplifier 75 power supply, to the voltage of the bus power supply 77, the effect of suppressing surge voltage is greater.

[0051] A three-phase current flows in the first resistor 71, which is also flowing in the windings 22U, 22V, and 22W. Therefore, if the resistance of the second resistor 74 is greater than one-third of the resistance of the first resistor 71, the first resistor 71 is highly likely to burn out. In such a case, the burning out of the first resistor 71 can be suppressed by using a Zener diode 73.

[0052] The above description uses a control method that infers the phase current and switches the power transistor 81 using sensorless control as an example. However, the control method can also be a structure that infers the magnetic pole position of the rotor 30 using the phase current and the magnetic sensor 50. In this case, it is also possible to achieve more efficient control by detecting the phase current and minimizing the current.

[0053] Furthermore, the structure described above describes the controller 70 generating a switching signal that forcibly turns the power transistor 81 off based on the voltage across the first resistor 71. However, the switching signal that forcibly turns the power transistor 81 off can also be generated by the gate driver circuit 82.

[0054] Furthermore, while the structure of the overcurrent detection unit 70A being built into the controller 70 has been described above, the overcurrent detection unit 70A may also be built into the gate driver circuit 82.

[0055] In addition to the structure described above, a temperature sensing element for detecting the temperature of the power transistor 81 can also be mounted on the built-in substrate 11. The power transistor 81 is forcibly turned off by a signal from the temperature sensing element, thus protecting the power transistor 81 from overheating.

[0056] <Example of Zener Diode 73 Configuration>

[0057] Figure 4 This is a schematic diagram illustrating an example of the configuration of the Zener diode 73 according to Embodiment 1. For example... Figure 4 As shown, the Zener diode 73 can be mounted on the side of the built-in substrate 11 opposite to the side facing the stator 20. This improves the heat dissipation of the Zener diode 73 and further delays its failure.

[0058] <Example of the configuration of the first resistor 71>

[0059] Figure 5 This is a schematic diagram illustrating an example of the configuration of the first resistor 71 according to Embodiment 1. For example... Figure 5 As shown, the first resistor 71 can be disposed on the side of the built-in substrate 11 opposite to the side where the lead wire 14 is mounted. If the first resistor 71 burns out, the flame or smoke will be discharged to the outside through the space between the molding resin 12 of the stator 20 and the lead wire 14, but through... Figure 5 That configuration can reduce the amount of flames or smoke emitted to the outside.

[0060] According to the motor 1 described above in Embodiment 1, if a voltage of a certain value or higher is applied to the Zener diode 73 connected in parallel with the first resistor 71, current flows in the Zener diode 73, and the current in the first resistor 71 does not increase. Therefore, even if the current flowing in the power transistor 81 increases due to a short circuit in one arm of the power transistor 81, overcurrent flow in the first resistor 71 is suppressed. Thus, even if an overcurrent occurs in the power transistor 81, the power transistor 81 can be protected, and burnout of the first resistor 71 can be avoided.

[0061] In addition, since the voltage in the amplifier circuit 72 is suppressed by setting the Zener diode 73, surge voltage is not easily generated in the amplifier circuit 72.

[0062] Furthermore, since surge voltage is suppressed by Zener diode 73, a rail-to-rail type operational amplifier that can output the voltage value of second resistor 74 in the range from power supply voltage to ground can be used as the operational amplifier constituting amplifier circuit 72.

[0063] Furthermore, a third resistor 76P is provided between the input terminal of amplifier circuit 72 and operational amplifier 75. The ratio of the resistance value of the second resistor 74 to the resistance value of the third resistor 76P is greater than the ratio of the control power supply voltage to the bus power supply voltage. Therefore, surge voltage generated in amplifier circuit 72 is suppressed.

[0064] Furthermore, in the motor 1 according to Embodiment 1, even if the resistance value of the first resistor 71 is greater than one-third of the resistance value of the second resistor 74, the Zener diode 73 can be used to suppress the first resistor 71 from catching fire or emitting smoke.

[0065] In addition, the motor 1 according to this embodiment 1 can avoid the burnout of the first resistor 71 and can reduce the resistance value of the second resistor 74 to easily detect the current flowing to the winding 22.

[0066] Furthermore, in this embodiment 1, the heat dissipation performance of the Zener diode 73 is improved by placing the Zener diode 73 on the side opposite to the stator 20 in the surface of the built-in substrate 11. This prevents the Zener diode 73 from being thermally damaged before the power transistor 81.

[0067] In addition, even if the output of motor 1 is 100W or more, the first resistor 71 can be prevented from burning out because of the Zener diode 73.

[0068] In addition, the first resistor 71 is disposed on the side opposite to the side where the wire 13 is disposed in the surface of the built-in substrate 11, so that even if a flame or smoke is generated, the flame or smoke is suppressed from being discharged through the wire 13.

[0069] Implementation Method 2

[0070] <Examples of Air Conditioner Applications>

[0071] Figure 6 This is a schematic diagram of the air conditioner 200 according to Embodiment 2. Figure 6 As shown, the air conditioner 200 includes an indoor unit 210 and an outdoor unit 220 connected to the indoor unit 210. The indoor unit 210 is equipped with an indoor unit fan 213, and the outdoor unit 220 is equipped with an outdoor unit fan 223. Both the outdoor unit fan 223 and the indoor unit fan 213 are equipped with an electric motor 1 as described in Embodiment 1 as a drive source.

[0072] If the air conditioner 200 becomes larger, the motor output will exceed 100W. Even in this case, since a Zener diode 73 is connected in parallel with the first resistor 71 on the built-in board 11 of the motor 1, the possibility of the first resistor 71 burning out or catching fire and emitting smoke due to the increase in motor output can be reduced. In particular, by using the motor 1 according to Embodiment 1 in a fan motor used in a commercial air conditioner or a package air conditioner, the effect of significantly reducing the burning out or catching fire and emitting smoke of the first resistor 71 can be obtained.

[0073] Furthermore, the increased output also leads to an increase in noise applied to the input of operational amplifier 75. In this case, the noise of operational amplifier 75 can also be reduced by Zener diode 73.

[0074] In addition to air conditioners 200, electric motor 1 can also be used in devices such as ventilation fans, household appliances, and machine tools.

[0075] Explanation of reference numerals in the attached figures

[0076] 1...Motor; 10...Molded stator; 11...Built-in substrate; 12...Molded resin; 13...Wire; 14...Wire lead-out section; 20...Stator; 21...Stator core; 22...Winding; 22U...U-phase winding; 22V...V-phase winding; 22W...W-phase winding; 23...Insulator; 30...Rotor; 31...Rotating shaft; 32...Rotor insulation; 33...Output side bearing; 34...Reverse output side bearing; 40...Magnet; 50...Magnetic sensor; 60...Bracket; 70...Controller; 71...First resistor; 72...Amplifier circuit; 73...Zenyl stabilizing diode; 74...Second resistor; 7 5...Operational amplifier; 76...Amplifier circuit input resistor; 76N...Fourth resistor; 76P...Third resistor; 77...Bus power supply; 78...Control power supply; 81...Power transistor; 81A...U-phase upper arm power transistor; 81B...V-phase upper arm power transistor; 81C...W-phase upper arm power transistor; 81D...U-phase lower arm power transistor; 81E...V-phase lower arm power transistor; 81F...W-phase lower arm power transistor; 82...Gate driver circuit; 200...Air conditioner; 210...Indoor unit; 213...Indoor unit fan; 220...Outdoor unit; 223...Outdoor unit fan; G...Grounding terminal.

Claims

1. An electric motor, wherein, The electric motor has the following features: Rotor; Stator; and substrate, The substrate comprises: Power transistors constitute an inverter circuit that switches the direction of the current flowing toward the windings of the stator. A first resistor is disposed between the power transistor and the ground terminal to detect overcurrent in the inverter circuit. A second resistor is disposed between the power transistor and the first resistor for detecting the current flowing to the winding of the stator; as well as A Zener diode is connected in parallel with the first resistor. The motor also includes an amplifier circuit that amplifies the voltage value of the second resistor. The amplifier circuit has an operational amplifier. The amplifier circuit includes a third resistor between its input terminal and the operational amplifier. The ratio of the resistance value of the second resistor to the resistance value of the third resistor is greater than the ratio of the voltage of the power supply of the amplifier circuit to the voltage of the bus power supply.

2. The electric motor according to claim 1, wherein, The operational amplifier is a rail-to-rail type operational amplifier.

3. The electric motor according to claim 1 or 2, wherein, The electric motor also includes a controller for controlling the inverter circuit. Power is supplied from a power source to the controller and the amplifier circuit.

4. The electric motor according to claim 1 or 2, wherein, The resistance value of the first resistor is greater than one-third of the resistance value of the second resistor.

5. The electric motor according to claim 1 or 2, wherein, The resistance value of the second resistor is less than 1Ω.

6. The electric motor according to claim 1 or 2, wherein, One side of the substrate faces the axial end faces of the stator and the rotor. The Zener diode is disposed on the other side of the substrate.

7. The electric motor according to claim 1 or 2, wherein, The output is over 100W.

8. The electric motor according to claim 1 or 2, wherein, The substrate is provided with a wire lead-out portion for connection to a wire. The first resistor is provided on the side of the substrate opposite to the side where the lead wire is provided.

9. An air conditioner, wherein, The electric motor having any one of claims 1 to 8.

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