Power supply circuit and motor unit

Abstract

To provide a power supply circuit that improves protection performance for protecting a circuit element from a lightning surge voltage, and a motor unit equipped with the power supply circuit.SOLUTION: In a motor unit that includes a power supply circuit, a drive circuit, a control circuit, and a DC motor, and uses a single-phase AC voltage supplied via a two-core power cable as a power supply voltage, the power supply circuit 2 for converting an AC input into a DC output has magnetically coupled first coil 11 and second coil 12, and includes a common mode choke coil 10 to be electrically connected to the AC input, a first surge absorbing element 51 to be electrically connected in parallel with the first coil, a second surge absorbing element 52 to be electrically connected in parallel with the second coil, a rectifier circuit 60 for rectifying the AC voltage input from the AC input through the common mode choke coil into a DC output, and a smoothing circuit 70 for smoothing the DC voltage output from the rectifier circuit.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a power supply circuit and a motor unit. [Background technology]

[0002] In a power supply circuit that converts a single-phase AC voltage supplied from a commercial AC power source into a DC voltage, it is necessary to protect the circuit elements from a lightning surge voltage that enters the power supply circuit from the commercial AC power source. For example, Patent Document 1 discloses a power supply circuit equipped with a surge absorbing component connected between the same poles or between opposite poles before and after a line filter transformer in an AC line as a measure against a common-mode lightning surge voltage. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 3116565 Summary of the Invention [Problem to be solved by the invention]

[0004] In the power supply circuit of Patent Document 1, surge absorbing components are connected only between the same poles or between the opposite poles before and after the line filter transformer, so only one of the two coils in the line filter transformer can be protected from lightning surge voltages.

[0005] The present invention has been proposed in consideration of the above circumstances, and has an object to provide a power supply circuit that can improve the protection performance for protecting circuit elements from lightning surge voltages, and a motor unit equipped with the power supply circuit. [Means for solving the problem]

[0006] One aspect of the power supply circuit of the present invention is a power supply circuit that converts an AC input into a DC output, the power supply circuit having a first coil and a second coil that are magnetically coupled, a common mode choke coil that is electrically connected to the AC input, a rectifier circuit that rectifies an AC voltage input from the AC input via the common mode choke coil to the DC output, and a smoothing circuit that smoothes a DC voltage output from the rectifier circuit, and further comprising a first surge absorbing element that is electrically connected in parallel with the first coil, and a second surge absorbing element that is electrically connected in parallel with the second coil.

[0007] One aspect of the motor unit of the present invention comprises a DC motor, a power supply circuit of the above aspect, a drive circuit that generates a drive voltage for driving the DC motor using a DC voltage output from the power supply circuit and outputs the drive voltage to the DC motor, and a control circuit that outputs a control signal from which the drive voltage is generated to the drive circuit. Effect of the Invention

[0008] According to the above aspects of the present invention, there are provided a power supply circuit capable of improving the protection performance for protecting circuit elements from a lightning surge voltage, and a motor unit including the power supply circuit. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a block diagram showing the configuration of a motor unit in this embodiment. [Diagram 2] FIG. 2 is a circuit diagram showing the configuration of the power supply circuit in this embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Fig. 1 is a block diagram showing the configuration of a motor unit 1 in this embodiment. As shown in Fig. 1, the motor unit 1 includes a power supply circuit 2, a drive circuit 3, a control circuit 4, and a DC motor 5. The motor unit 1 uses, as a power supply voltage, a single-phase AC voltage supplied from a commercial AC power source (not shown) via a two-core power cable 6. The two-core power cable 6 has a power line 7 electrically connected to the L terminal of the commercial AC power source, and a neutral line 8 electrically connected to the N terminal of the commercial AC power source.

[0011] The power supply circuit 2 converts an AC input from a commercial AC power source into a DC output. More specifically, the power supply circuit 2 converts a single-phase AC voltage supplied from the commercial AC power source via a two-core power cable 6 into a DC voltage, and outputs the DC voltage to the drive circuit 3. The power supply circuit 2 includes a first AC input terminal P1, a second AC input terminal P2, a first DC output terminal P3, a second DC output terminal P4, and a body earth terminal P5.

[0012] The first AC input terminal P1 is electrically connected to the power line 7. The second AC input terminal P2 is electrically connected to the neutral line 8. That is, a single-phase AC voltage is input to the power supply circuit 2 from a commercial AC power supply via the first AC input terminal P1 and the second AC input terminal P2.

[0013] The first DC output terminal P3 and the second DC output terminal P4 are each electrically connected to the drive circuit 3. The power supply circuit 2 outputs a DC voltage to the drive circuit 3 via the first DC output terminal P3 and the second DC output terminal P4.

[0014] The body earth terminal P5 is electrically connected to an external metal member (not shown). For example, the metal member electrically connected to the body earth terminal P5 is a metal case that houses the power supply circuit 2. The metal case that houses the power supply circuit 2 may be the housing of the motor unit 1. The power supply circuit 2 is electrically connected to a metal member such as a metal case via the body earth terminal P5.

[0015] The drive circuit 3 generates a drive voltage for driving the DC motor 5 using the DC voltage output from the power supply circuit 2, and outputs the drive voltage to the DC motor 5. For example, the drive circuit 3 is a three-phase full-bridge circuit composed of six power semiconductor switching elements. The drive circuit 3 converts the DC voltage supplied from the power supply circuit 2 into a three-phase AC voltage, and outputs the three-phase AC voltage to the DC motor 5 as a drive voltage.

[0016] The control circuit 4 outputs a control signal from which a drive voltage is generated to the drive circuit 3. The control circuit 4 outputs a control signal to each of the six power semiconductor switching elements, thereby controlling the on and off operations of each power semiconductor switching element.

[0017] For example, the control circuit 4 receives a rotation speed command signal from a higher-level control device (not shown) and outputs a control signal to the drive circuit 3 to rotate the DC motor 5 at a target rotation speed instructed by the rotation speed command signal. For example, the control circuit 4 is a processor with a built-in memory (not shown). As an example, the control circuit 4 is an MCU (Microcontroller Unit). The control circuit 4 controls the drive circuit 3 according to a program previously stored in the memory.

[0018] The DC motor 5 rotates in response to a drive voltage supplied from the drive circuit 3. For example, the DC motor 5 is a three-phase brushless DC motor that rotates in response to a three-phase AC voltage supplied from the drive circuit 3.

[0019] Hereinafter, the configuration of the power supply circuit 2 in this embodiment will be described in detail with reference to Fig. 2. Fig. 2 is a circuit diagram showing the configuration of the power supply circuit 2. As shown in Fig. 2, the power supply circuit 2 includes a common mode choke coil 10, a fuse 20, a first capacitor 30, a varistor 40, a first surge absorbing element 51, a second surge absorbing element 52, a rectifier circuit 60, a smoothing circuit 70, a bypass circuit 80, a second capacitor 90, a first AC line L1, a second AC line L2, a first DC line L3, and a second DC line L4.

[0020] The common mode choke coil 10 has a first coil 11 and a second coil 12 that are magnetically coupled. One end of the first coil 11 is electrically connected to one end of a first AC line L1. The other end of the first AC line L1 is electrically connected to a first AC input terminal P1 via a fuse 20. That is, one end of the first coil 11 is electrically connected to the first AC input terminal P1 via the first AC line L1 and the fuse 20.

[0021] One end of the second coil 12 is electrically connected to one end of the second AC line L2. The other end of the second AC line L2 is electrically connected to the second AC input terminal P2. That is, one end of the second coil 12 is electrically connected to the second AC input terminal P2 via the second AC line L2. In this manner, the first AC line L1 and the second AC line L2 are a pair of wirings that transmit the single-phase AC voltage input to the power supply circuit 2 via the two-core power cable 6 to the common mode choke coil 10.

[0022] The other end of each of the first coil 11 and the second coil 12 is electrically connected to a rectifier circuit 60. Specifically, the other end of the first coil 11 is electrically connected to an anode terminal of a first diode 61 included in the rectifier circuit 60. The other end of the second coil 12 is electrically connected to an anode terminal of a third diode 63 included in the rectifier circuit 60.

[0023] The first capacitor 30 is electrically connected between one end of the first coil 11 and one end of the second coil 12. Specifically, one end of the first capacitor 30 is electrically connected to one end of the first coil 11 via a first AC line L1, and the other end of the first capacitor 30 is electrically connected to one end of the second coil 12 via a second AC line L2. For example, the first capacitor 30 is a film capacitor.

[0024] The varistor 40 is electrically connected in parallel with the first capacitor 30. Specifically, one end of the varistor 40 is electrically connected to one end of the first coil 11 via the first AC line L1, and the other end of the varistor 40 is electrically connected to one end of the second coil 12 via the second AC line L2. The varistor 40 is disposed in a stage preceding the first capacitor 30.

[0025] The first surge absorbing element 51 and the second surge absorbing element 52 are elements that absorb surge voltages. In detail, the surge absorbing element in this embodiment is an element that has the property of functioning as an insulator when a voltage equal to or lower than a predetermined value is applied, and functioning as a conductor when a voltage exceeding the predetermined value is applied.

[0026] The first surge absorbing element 51 is electrically connected in parallel with the first coil 11. Specifically, one end of the first surge absorbing element 51 is electrically connected to one end of the first coil 11, and the other end of the first surge absorbing element 51 is electrically connected to the other end of the first coil 11.

[0027] The second surge absorbing element 52 is electrically connected in parallel with the second coil 12. Specifically, one end of the second surge absorbing element 52 is electrically connected to one end of the second coil 12, and the other end of the second surge absorbing element 52 is electrically connected to the other end of the second coil 12.

[0028] As an example, the first surge absorbing element 51 and the second surge absorbing element 52 are arresters. As another example, the first surge absorbing element 51 and the second surge absorbing element 52 may be varistors.

[0029] The rectifier circuit 60 rectifies the single-phase AC voltage input from the first AC input terminal P1 and the second AC input terminal P2 via the common mode choke coil 10 into a DC voltage. The rectifier circuit 60 has a first diode 61, a second diode 62, a third diode 63, and a fourth diode 64.

[0030] The anode terminal of the first diode 61 is electrically connected to the other end of the first coil 11, the other end of the first surge absorbing element 51, and the cathode terminal of the second diode 62. The anode terminal of the third diode 63 is electrically connected to the other end of the second coil 12, the other end of the second surge absorbing element 52, and the cathode terminal of the fourth diode 64.

[0031] The cathode terminal of the first diode 61 is electrically connected to the cathode terminal of the third diode 63 and one end of the first DC line L3. The anode terminal of the second diode 62 is electrically connected to the anode terminal of the fourth diode 64 and one end of the second DC line L4.

[0032] The other end of the first DC line L3 is electrically connected to the first DC output terminal P3. The other end of the second DC line L4 is electrically connected to the second DC output terminal P4. In this manner, the first DC line L3 and the second DC line L4 are a pair of wirings that transmit a DC voltage from the rectifier circuit 60 to the smoothing circuit 70.

[0033] The smoothing circuit 70 smoothes the DC voltage output from the rectifier circuit 60. The smoothing circuit 70 has a third capacitor 71 and a fourth capacitor 72. The third capacitor 71 is electrically connected between the first DC line L3 and the second DC line L4. For example, the third capacitor 71 is an electrolytic capacitor. The fourth capacitor 72 is electrically connected between the first DC line L3 and the second DC line L4, and is disposed in a subsequent stage of the third capacitor 71.

[0034] The bypass circuit 80 has a varistor 81 and an arrester 82 electrically connected in series between the first DC line L3 and the second DC line L4. One end of the varistor 81 is electrically connected to the first DC line L3. One end of the arrester 82 is electrically connected to the other end of the varistor 81, and the other end of the arrester 82 is electrically connected to the second DC line L4. The bypass circuit 80 is disposed between the rectifier circuit 60 and the smoothing circuit 70.

[0035] The second capacitor 90 is electrically connected between a second DC line L4, which has a lower potential than the first DC line L3, and a body earth terminal P5. That is, the second DC line L4 is electrically connected to a metal member, such as a metal case that houses the power supply circuit 2, via the second capacitor 90 and the body earth terminal P5. For example, the second capacitor 90 is a ceramic capacitor.

[0036] In the power supply circuit 2 configured as described above, when a common mode lightning surge voltage enters the inside of the power supply circuit 2 from the first AC input terminal P1 via the power line 7 of the two-core power cable 6, the lightning surge voltage is transmitted to the first coil 11 of the common mode choke coil 10 via the first AC line L1.

[0037] In this case, since the first surge absorbing element 51 is electrically connected in parallel with the first coil 11, the lightning surge voltage is transmitted to the rectifier circuit 60 via the first surge absorbing element 51 without passing through the first coil 11. The lightning surge voltage transmitted to the rectifier circuit 60 via the first surge absorbing element 51 is transmitted to the first DC line L3 via the first diode 61.

[0038] On the other hand, when a common mode lightning surge voltage enters the inside of the power supply circuit 2 from the second AC input terminal P2 via the neutral wire 8 of the two-core power cable 6, the lightning surge voltage is transmitted to the second coil 12 of the common mode choke coil 10 via the second AC line L2.

[0039] In this case, since the second surge absorbing element 52 is electrically connected in parallel with the second coil 12, the lightning surge voltage is transmitted to the rectifier circuit 60 via the second surge absorbing element 52 without passing through the second coil 12. The lightning surge voltage transmitted to the rectifier circuit 60 via the second surge absorbing element 52 is transmitted to the first DC line L3 via the third diode 63.

[0040] The lightning surge voltage transmitted to the first DC line L3 is transmitted to the second DC line L4 via a bypass circuit 80 having a varistor 81 and an arrester 82. The lightning surge voltage transmitted to the second DC line L4 is transmitted to a metal member, such as a metal case that contains the power supply circuit 2, via a second capacitor 90 and a body earth terminal P5.

[0041] As described above, when a common mode lightning surge voltage enters the power supply circuit 2 from a commercial AC power source via the two-core power cable 6, the lightning surge voltage is transmitted through the path described above, thereby protecting not only the first coil 11 and the second coil 12 of the common mode choke coil 10, but also the circuit elements arranged after the smoothing circuit 70 from the common mode lightning surge voltage.

[0042] When a normal mode lightning surge voltage enters the power supply circuit 2 from the commercial AC power source via the two-core power cable 6, the varistor 40 electrically connected between the first AC line L1 and the second AC line L2 absorbs the lightning surge voltage, thereby protecting each circuit element from the normal mode lightning surge voltage.

[0043] As described above, the power supply circuit 2 of this embodiment is a power supply circuit 2 that converts an AC input into a DC output, and has a first coil 11 and a second coil 12 that are magnetically coupled, a common mode choke coil 10 that is electrically connected to the AC input, a rectifier circuit 60 that rectifies the AC voltage input from the AC input via the common mode choke coil 10 into a DC output, and a smoothing circuit 70 that smoothes the DC voltage output from the rectifier circuit 60. The power supply circuit 2 is also equipped with a first surge absorption element 51 that is electrically connected in parallel with the first coil 11, and a second surge absorption element 52 that is electrically connected in parallel with the second coil 12.

[0044] As described above, the power supply circuit 2 of the present embodiment includes the first surge absorption element 51 electrically connected in parallel with the first coil 11 of the common mode choke coil 10, and the second surge absorption element 52 electrically connected in parallel with the second coil 12 of the common mode choke coil 10. In the power supply circuit of Patent Document 1, only one of the two coils of the common mode choke coil can be protected from a surge voltage, but the power supply circuit 2 of the present embodiment can protect both the first coil 11 and the second coil 12 of the common mode choke coil 10 from a lightning surge voltage. Thus, according to the present embodiment, a power supply circuit 2 is provided that can improve the protection performance for protecting circuit elements from a lightning surge voltage.

[0045] In the power supply circuit 2 of the present embodiment, the first surge absorbing element 51 and the second surge absorbing element 52 are arresters.

[0046] According to the power supply circuit 2 of the present embodiment as described above, both the first coil 11 and the second coil 12 of the common mode choke coil 10 can be effectively protected, in particular, from a relatively high lightning surge voltage of about several kV that occurs due to a lightning strike.

[0047] In the power supply circuit 2 of the present embodiment, the first surge absorbing element 51 and the second surge absorbing element 52 may be varistors.

[0048] According to the power supply circuit 2 of the present embodiment as described above, both the first coil 11 and the second coil 12 of the common mode choke coil 10 can be effectively protected, particularly from a relatively low lightning surge voltage of about several hundred volts that occurs due to a lightning strike.

[0049] The power supply circuit 2 of this embodiment further includes a first DC line L3 and a second DC line L4 that transmit a DC voltage from the rectifier circuit 60 to the smoothing circuit 70, and a bypass circuit 80 having a varistor 81 and an arrester 82 electrically connected in series between the first DC line L3 and the second DC line L4.

[0050] According to the power supply circuit 2 of the present embodiment as described above, the lightning surge voltage sent to the output side (particularly the first DC line L3) of the rectifier circuit 60 via at least one of the first surge absorbing element 51 and the second surge absorbing element 52 can be bypassed to the second DC line L4 at the upstream stage of the smoothing circuit 70. The arrester 82 has a characteristic of continuing to allow a current to flow once it has started to flow, but the constant voltage set by the varistor 81 can prevent the current from continuing to flow.

[0051] The power supply circuit 2 of this embodiment further includes a body earth terminal P5 electrically connected to a metal member such as a metal case that contains the power supply circuit 2, and a second capacitor 90 electrically connected between a second DC line L4, which has a lower potential than the first DC line L3, and the body earth terminal P5.

[0052] According to the power supply circuit 2 of the present embodiment as described above, the lightning surge voltage bypassed to the second DC line L4 by the bypass circuit 80 upstream of the smoothing circuit 70 can be dissipated via the second capacitor 90 and the body earth terminal P5 to a metal member such as a metal case that contains the power supply circuit 2, thereby protecting the circuit elements subsequent to the smoothing circuit 70 from the lightning surge voltage.

[0053] The motor unit 1 of this embodiment comprises a DC motor 5, a power supply circuit 2, a drive circuit 3 that generates a drive voltage for driving the DC motor 5 using a DC voltage output from the power supply circuit 2 and outputs the drive voltage to the DC motor 5, and a control circuit 4 that outputs a control signal to the drive circuit 3 from which the drive voltage is generated.

[0054] As described above, the motor unit 1 of the present embodiment includes the power supply circuit 2 capable of improving the protection performance for protecting the circuit elements from the lightning surge voltage. Therefore, according to the present embodiment, the motor unit 1 capable of improving the protection performance for protecting the circuit elements from the lightning surge voltage is provided.

[0055] [Variations] The present invention is not limited to the above-described embodiment, and the configurations described in this specification can be appropriately combined within a range that does not contradict each other. For example, the following modifications can be made.

[0056] In the above embodiment, a three-phase brushless DC motor is exemplified as the DC motor 5, but the DC motor of the present invention may be a DC motor other than a three-phase brushless DC motor. Furthermore, an inrush current suppressing element (power thermistor) may be provided in any one of the first AC line L1, the second AC line L2, the first DC line L3, and the second DC line L4. In the above embodiment, the power supply circuit 2 of the motor unit 1 has been illustrated as an example of the power supply circuit of the present invention, but the power supply circuit of the present invention can be widely used as a power supply circuit for electronic devices that use, as their power supply voltage, a single-phase AC voltage supplied from a commercial AC power source via a two-core power cable 6.

[0057] The present technology can be configured as follows. (1) A power supply circuit that converts an AC input into a DC output, the power supply circuit having a first coil and a second coil that are magnetically coupled, a common mode choke coil that is electrically connected to the AC input, a rectifier circuit that rectifies an AC voltage input from the AC input through the common mode choke coil to the DC output, and a smoothing circuit that smoothes a DC voltage output from the rectifier circuit, the power supply circuit further comprising: a first surge absorbing element that is electrically connected in parallel with the first coil, and a second surge absorbing element that is electrically connected in parallel with the second coil. (2) The power supply circuit according to (1), wherein the first surge absorbing element and the second surge absorbing element are arresters. (3) The power supply circuit according to (1), wherein the first surge absorbing element and the second surge absorbing element are varistors. (4) The power supply circuit according to any one of (1) to (3), further comprising: a pair of wirings that transmit the DC voltage from the rectifier circuit to the smoothing circuit; and a bypass circuit having a varistor and an arrester electrically connected in series between the pair of wirings. (5) The power supply circuit described in (4), further comprising: a body earth terminal electrically connected to an external metal member; and a capacitor electrically connected between the body earth terminal and one of the pair of wirings, the other of the pair of wirings having a lower potential than the other of the pair of wirings. (6) A power supply circuit for converting an AC input into a DC output, the power supply circuit comprising: a common mode choke coil having a first coil and a second coil magnetically coupled to the AC input, a rectifier circuit for rectifying an AC voltage input from the AC input through the common mode choke coil into the DC output, and a smoothing circuit for smoothing a DC voltage output from the rectifier circuit, the power supply circuit further comprising: a pair of wiring for transmitting the DC voltage from the rectifier circuit to the smoothing circuit, and a bypass circuit having a varistor and an arrester electrically connected in series between the pair of wiring. (7) The power supply circuit described in (6), further comprising: a body earth terminal electrically connected to an external metal component; and a capacitor electrically connected between the body earth terminal and one of the pair of wirings, the other of the pair of wirings having a lower potential than the other of the pair of wirings. (8) The power supply circuit according to (6) or (7), further comprising a first surge absorption element electrically connected in parallel to the first coil, and a second surge absorption element electrically connected in parallel to the second coil. (9) The power supply circuit according to (8), wherein the first surge absorbing element and the second surge absorbing element are arresters. (10) The power supply circuit according to (8), wherein the first surge absorbing element and the second surge absorbing element are varistors. (11) A motor unit comprising: a DC motor; a power supply circuit according to any one of (1) to (10); a drive circuit that generates a drive voltage for driving the DC motor using a DC voltage output from the power supply circuit and outputs the drive voltage to the DC motor; and a control circuit that outputs a control signal for generating the drive voltage to the drive circuit. [Explanation of symbols]

[0058] Reference Signs List 1...motor unit, 2...power supply circuit, 3...drive circuit, 4...control circuit, 5...DC motor, 10...common mode choke coil, 11...first coil, 12...second coil, 20...fuse, 30...first capacitor, 40...varistor, 51...first surge absorbing element, 52...second surge absorbing element, 60...rectifier circuit, 70...smoothing circuit, 80...bypass circuit, 81...varistor, 82...arrester, 90...second capacitor, L1...first AC line, L2...second AC line, L3...first DC line, L4...second DC line, P1...first AC input terminal, P2...second AC input terminal, P3...first DC output terminal, P4...second DC output terminal, P5...body earth terminal

Claims

1. 1. A power supply circuit that converts an AC input into a DC output, comprising: a common mode choke coil having a first coil and a second coil magnetically coupled to each other and electrically connected to the AC input; a rectifier circuit that rectifies an AC voltage input from the AC input through the common mode choke coil into the DC output; A smoothing circuit that smoothes the DC voltage output from the rectifier circuit, a first surge absorbing element electrically connected in parallel with the first coil; a second surge absorbing element electrically connected in parallel with the second coil; A power supply circuit comprising:

2. 2. The power supply circuit according to claim 1, wherein the first surge absorbing element and the second surge absorbing element are arresters.

3. 2. The power supply circuit according to claim 1, wherein the first surge absorbing element and the second surge absorbing element are varistors.

4. a pair of wires for transmitting the DC voltage from the rectifier circuit to the smoothing circuit; a bypass circuit having a varistor and an arrester electrically connected in series between the pair of wirings; The power supply circuit of claim 1 further comprising:

5. a body earth terminal electrically connected to an external metal member; a capacitor electrically connected between the one of the pair of wirings, the other of which has a lower potential than the other of the pair of wirings, and the body earth terminal; The power supply circuit of claim 4 further comprising:

6. 1. A power supply circuit that converts an AC input into a DC output, comprising: a common mode choke coil having a first coil and a second coil magnetically coupled to each other and electrically connected to the AC input; a rectifier circuit that rectifies an AC voltage input from the AC input through the common mode choke coil into the DC output; A smoothing circuit that smoothes the DC voltage output from the rectifier circuit, a pair of wires for transmitting the DC voltage from the rectifier circuit to the smoothing circuit; a bypass circuit having a varistor and an arrester electrically connected in series between the pair of wirings; A power supply circuit comprising:

7. a body earth terminal electrically connected to an external metal member; a capacitor electrically connected between the one of the pair of wirings, the other of which has a lower potential than the other of the pair of wirings, and the body earth terminal; The power supply circuit of claim 6 further comprising:

8. a first surge absorbing element electrically connected in parallel with the first coil; a second surge absorbing element electrically connected in parallel with the second coil; The power supply circuit of claim 7 further comprising:

9. 9. The power supply circuit according to claim 8, wherein the first surge absorbing element and the second surge absorbing element are arresters.

10. 9. The power supply circuit according to claim 8, wherein the first surge absorbing element and the second surge absorbing element are varistors.

11. A DC motor; A power supply circuit according to any one of claims 1 to 10; a drive circuit that generates a drive voltage for driving the DC motor using a DC voltage output from the power supply circuit and outputs the drive voltage to the DC motor; a control circuit that outputs a control signal to the drive circuit, the control signal causing the drive voltage to be generated; A motor unit comprising:

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