Electric circuit

Abstract

To prevent a main circuit unit, which is powered by a power source, from being destroyed by a lightning surge.SOLUTION: A power source unit (10) is provided with: a bias route (40, 40a-40c) through which some of the current including the lightning surge current, which overlaps the current from a power source (2), flows; and an impedance increase circuit (11) for increasing the equivalent impedance between the power source (2) and a main circuit unit (50), on the basis of the current which flows through the bias route (40, 40a-40c).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to an electric circuit including a power supply unit and a main circuit unit to which power is supplied from a power source via the power supply unit. [Background technology]

[0002] Patent Document 1 discloses an electric circuit including a power supply unit and a main circuit unit to which power is supplied from an AC power supply via the power supply unit. In this electric circuit, the power supply unit includes a reactor and a converter circuit, and the main circuit unit includes a capacitor and an inverter circuit. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-124104 A Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, in an electric circuit such as that disclosed in Patent Document 1, there is a risk that the main circuit portion may be destroyed by a lightning surge when lightning strikes.

[0005] The present disclosure has been made in consideration of the above points, and aims to make a main circuit section to which power is supplied from a power source less susceptible to destruction by a lightning surge. [Means for solving the problem]

[0006] A first aspect is an electric circuit including a power supply unit (10) and a main circuit unit (50) to which power is supplied from a power source (2) via the power supply unit (10), wherein the power supply unit (10) includes a bypass path (40, 40a to 40c) for passing a part of a current including a lightning surge current superimposed on a current from the power source (2), and is characterized in that the power supply unit (10) includes an impedance increasing circuit (11) for increasing an equivalent impedance between the power source (2) and the main circuit unit (50) based on the current flowing through the bypass path (40, 40a to 40c).

[0007] Here, the lightning surge current is a current superimposed on the current that flows due to the voltage normally supplied from the power source (2). The lightning surge current flows when the voltage of the power source (2) rises due to the occurrence of a lightning surge. In the first aspect, when the lightning surge current is superimposed on the current from the power source (2), a part of the current including the lightning surge current flows through the bypass path (40, 40a to 40c) and the equivalent impedance between the power source (2) and the main circuit section (50) is increased, thereby reducing the current flowing from the power source (2) to the main circuit section (50). Therefore, the main circuit section (50) is less likely to be destroyed by a lightning surge.

[0008] The second aspect is the first aspect, wherein the impedance increasing circuit (11) increases the impedance by electric energy sent to the bypass path (40, 40a to 40c) when a part of a current including the lightning surge current flows through the bypass path (40, 40a to 40c).

[0009] In the second aspect, the electrical energy of the lightning surge current is used to prevent the lightning surge current from entering the main circuit portion (50), thereby making effective use of energy.

[0010] The third aspect is the first or second aspect, wherein the impedance increasing circuit (11) generates, based on the current flowing through the bypass path (40, 40a to 40c), a voltage between the power source (2) and the main circuit unit (50) in a direction for suppressing a current including the lightning surge current from flowing through the main circuit unit (50).

[0011] A fourth aspect is any one of the first to third aspects, characterized in that the impedance increasing circuit (11) has a main winding (30) provided on a path for supplying power from the power source (2) to the main circuit unit (50), and an auxiliary winding (41) provided on the bypass path (40) and magnetically coupled to the main winding (30), and by flowing a part of a current including the lightning surge current through the auxiliary winding (41), a magnetic flux passing through the main winding (30) is changed to generate the voltage.

[0012] In the fourth aspect, when a lightning surge is applied between any two lines from the power source (2), the equivalent impedance between the power source (2) and the main circuit section (50) can be increased, thereby suppressing a voltage increase in the main circuit section (50).

[0013] A fifth aspect is the fourth aspect, characterized in that the bypass path (40, 40a to 40c) is provided with a surge absorber (42) connected in series with the auxiliary winding (41).

[0014] In the fifth aspect, when no lightning surge is occurring, the surge absorber (42) regulates current from flowing through the bypass paths (40, 40a to 40c). On the other hand, when a lightning surge is occurring, a current flows through the bypass paths (40, 40a to 40c) due to a short circuit in the surge absorber (42). Therefore, it is not necessary to have a computer control whether or not to allow a current to flow through the bypass paths (40, 40a to 40c), and therefore it is possible to reduce the delay time from the occurrence of a lightning surge until a current flows through the bypass paths (40, 40a to 40c).

[0015] A sixth aspect is the fourth or fifth aspect, characterized in that the main winding (30) and the auxiliary winding (41) have the same polarity.

[0016] In the sixth aspect, when a current flows through the bypass path (40, 40a to 40c), a voltage can be generated in the main winding (30) in a direction that prevents a current, including a lightning surge current, from flowing through the main circuit portion (50).

[0017] A seventh aspect is any one of the first to sixth aspects, characterized in that the power source (2) is an AC power source, the power source unit (10) includes a rectifier circuit (20) that rectifies the AC output from the power source (2), and the main circuit unit (50) includes an inverter circuit (60) that converts the DC output by the rectifier circuit (20) into AC by switching operation, and a capacitor (70) connected between input nodes (60a, 60b) of the inverter circuit (60) and that tolerates pulsation of the output voltage of the rectifier circuit (20).

[0018] In the seventh aspect, when a lightning surge current is superimposed on the current from the power source (2), the current flowing from the power source (2) to the capacitor (70) can be reduced, thereby suppressing a voltage rise in the capacitor (70), thereby enabling the capacitor (70) to be made smaller. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a circuit diagram showing a configuration of a power conversion device as an electric circuit according to a first embodiment of the present disclosure. [Diagram 2] FIG. 2 is a view equivalent to FIG. 1 of a comparative example. [Diagram 3] FIG. 3 shows the voltage across the bypass path, the input voltage of the main circuit section, the voltage of the main winding, and the input current of the main circuit section in the comparative example. [Figure 4]FIG. 4 is a timing chart in which the solid lines indicate the voltages at both ends of the bypass path, the input voltage of the main circuit unit, the voltage of the main winding, the input current of the main circuit unit, and the voltage of the auxiliary winding in the first embodiment, and the dashed lines indicate the voltages at both ends of the bypass path, the input voltage of the main circuit unit, the voltage of the main winding, and the input current of the main circuit unit in the comparative example. [Diagram 5] FIG. 5 is a view of a modification of the first embodiment, which corresponds to FIG. [Figure 6] FIG. 6 is a view corresponding to FIG. 1 of the second embodiment. [Figure 7] FIG. 7 is a view corresponding to FIG. 1 of the third embodiment. [Figure 8] FIG. 8 is a view of a modified example of the third embodiment, which corresponds to FIG. [Figure 9] FIG. 9 is a view corresponding to FIG. 1 of the fourth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the following embodiments are essentially preferred examples and are not intended to limit the scope of the present invention, its applications, or its uses.

[0021] First Embodiment 1 shows a power conversion device (1) as an electric circuit according to a first embodiment of the present disclosure. This power conversion device (1) converts input AC supplied from a power source (2) into AC having a desired frequency and a desired voltage and supplies the AC to a load (3). The power source (2) is a three-phase AC power source. The load (3) is a motor.

[0022] The power conversion device (1) includes a power supply section (10), a main circuit section (50) to which power is supplied from a power source (2) via the power supply section (10), and a control device (not shown).

[0023] The power supply unit (10) includes a rectifier circuit (20), a main winding (30), and a bypass path (40).

[0024] The rectifier circuit (20) rectifies the three-phase AC output from the power source (2) to the first to third power lines (L1 to L3) into DC. The rectifier circuit (20) has first to third input terminals (20a to 20c) connected to the first to third power lines (L1 to L3) and first and second output terminals (20d, 20e) that output DC. More specifically, the rectifier circuit (20) is a full-wave rectifier circuit. The rectifier circuit (20) has six diodes (21 to 26) connected in a bridge configuration as rectifier elements. The diodes (21 to 26) have their cathodes facing the first output terminal (20d) and their anodes facing the second output terminal (20e).

[0025] The main winding (30) is provided on a path for supplying electric power from the power source (2) to the main circuit section (50). Specifically, one end of the main winding (30) is connected to a first output terminal (20d) of the rectifier circuit (20), and the other end of the main winding (30) is connected to the main circuit section (50), which will be described later in detail. In other words, the main winding (30) is connected in series with the rectifier circuit (20) and the main circuit section (50).

[0026] Both ends of the bypass path (40) are connected to the first and second output terminals (20d, 20e) of the rectifier circuit (20). The bypass path (40) is provided with an auxiliary winding (41) magnetically coupled to the main winding (30) and a varistor (42) connected in series with the auxiliary winding (41) as a surge absorber, in this order from the first output terminal (20d). The main winding (30) and the auxiliary winding (41) have the same polarity.

[0027] The main winding (30) and the auxiliary winding (41) constitute an impedance increasing circuit (11) that increases the equivalent impedance between the power source (2) and the main circuit section (50) based on the current flowing through the bypass path (40). Here, the equivalent impedance means |Vb| / |Im|, where Vb is the voltage across the bypass path (40) and Im is the current flowing from the power source section (10) to the main circuit section (50).

[0028] The main circuit section (50) includes an inverter circuit (60) and a capacitor (70).

[0029] The inverter circuit (60) converts the direct current output by the rectifier circuit (20) into a three-phase alternating current by a switching operation and supplies the three-phase alternating current to the load (3). The inverter circuit (60) is controlled by a control device (not shown) using a pulse width modulation (PWM) control method. More specifically, the inverter circuit (60) has six switching elements (61a-66a) and six free wheel diodes (61b-66b). The six switching elements (61a-66a) are bridge-connected. More specifically, the inverter circuit (60) has three switching legs connected between first and second input nodes (60a, 60b). Each switching leg is formed by connecting two switching elements (61a-66a) in series with each other. The first input node (60a) is connected to the other end of the main winding (30), and the second input node (60b) is connected to the second output terminal (20e) of the rectifier circuit (20).

[0030] In each of the three switching legs, the midpoint between the upper arm switching elements (61a to 63a) and the lower arm switching elements (64a to 66a) is connected to the coil of each phase (u-phase, v-phase, and w-phase coil) of the load (3). Freewheeling diodes (61b to 66b) are connected in anti-parallel to each of the switching elements (61a to 66a). Each of the switching elements (61a to 66a) is configured with an IGBT (Insulated Gate Bipolar Transistor). However, each of the switching elements (61a to 66a) may be configured with a power MOSFET (Metal Oxide Semiconductor Field Effect Transistor) including a wide band gap semiconductor such as silicon carbide (SiC) or gallium nitride (GaN).

[0031] The capacitor (70) is connected between the first and second input nodes (60a, 60b) of the inverter circuit (60). The capacitor (70) is a film capacitor or a ceramic capacitor. Since film capacitors and ceramic capacitors generally have a smaller capacitance than electrolytic capacitors, the capacitor (70) does not sufficiently smooth the output voltage of the rectifier circuit (20). In other words, the capacitor (70) allows pulsation of the output voltage of the rectifier circuit (20). Thus, the voltage between the first and second input nodes (60a, 60b) of the inverter circuit (60) has a pulsating component. Since the rectifier circuit (20) performs full-wave rectification, the frequency of this pulsating component is 2N times the frequency of the AC voltage output by the power source (2), where N is the number of phases of the power source (2).

[0032] Here, when the inductance of the main winding (30) is L (H), the carrier frequency of the PWM control of the inverter circuit (60) is fc (Hz), the capacitance of the capacitor (70) is C (F), and the value of the constant K is ¼, the inductance of the main winding (30) and the capacitance of the capacitor (70) are set so that the following equation 1 holds:

[0033]

number

[0034] This allows the main winding (30) and the capacitor (70) to absorb switching noise generated in the inverter circuit (60). By using power MOSFETs made of silicon carbide or gallium nitride, which are capable of high-speed switching, for each of the switching elements (61a-66a), it is possible to increase the carrier frequency fc and reduce the inductance of the main winding (30) and the capacitance of the capacitor (70).

[0035] In addition, when the power supply voltage of the power supply (2) is Vac (V) and the maximum power consumption of the load (3) is Pmax (W), the capacitance of the capacitor (70) is set so that the following formula 2 holds true.

[0036]

number

[0037] By setting the capacitance of the capacitor (70) in this manner, the fifth and seventh harmonics from the rectifier circuit (20) can be reduced.

[0038] 2 shows a power converter (1) according to a comparative example. In this comparative example, an auxiliary winding (41) is not provided in a bypass path (40) of the power converter (1). The other configurations are the same as those of the first embodiment.

[0039] FIG. 3 shows the voltage Vb across the bypass path (40) and the input voltage V of the main circuit unit (50) in the comparative example. DC , the voltage V of the main winding (30) L 4 shows the voltage Vb across the bypass path (40), the input voltage V of the main circuit unit (50), and the current Im of the main winding (30) in the order from top to bottom. DC , the voltage V of the main winding (30) L 4, the voltage Vb across the bypass path (40) and the input voltage V of the main circuit unit (50) in the comparative example are shown in solid lines from top to bottom. DC , the voltage V of the main winding (30) L , and the current Im of the main winding (30) are also indicated by dashed lines. The voltages and currents shown in Fig. 3 and Fig. 4 are those when the switching of the switching elements (61a-66a) of the inverter circuit (60) is stopped by control of a control device (not shown). In Fig. 3 and Fig. 4, Vmax indicates the peak value of the power supply voltage supplied by the power supply (2) when no lightning surge is occurring.

[0040] In the first embodiment, when a lightning surge occurs, the voltage Vb across the bypass path (40) rises, as shown by the arrow in Fig. 4. In response to this, a current Im including the lightning surge current flows through the main winding (30), and the capacitor (70) is gradually charged, thereby causing the input voltage V DCThe lightning surge current is a current that is superimposed on the current that flows due to the voltage normally supplied from the power source (2). The lightning surge current flows when the voltage of the power source (2) rises due to the occurrence of a lightning surge. A part of the current including the lightning surge current that is superimposed on the current from the power source (2) flows as a current Is through the bypass path (40) including the auxiliary winding (41), thereby reducing the current that flows from the power source (2) and the power supply unit (10) to the main circuit unit (50). When the current Is flows through the bypass path (40), the auxiliary winding (41) changes the magnetic flux passing through the main winding (30) due to the electrical energy sent to the bypass path (40), and generates a voltage in the main winding (30), i.e., between the power source (2) and the main circuit unit (50), in a direction that suppresses the flow of the current including the lightning surge current to the main circuit unit (50). This increases the equivalent impedance between the power source (2) and the main circuit unit (50). Therefore, as shown in the area surrounded by the two-dot chain line in FIG. 4, in the first embodiment, when a lightning surge occurs and a current Is flows through the bypass path (40), the voltage V L 4, the current Im of the main winding (30) is smaller than that of the comparative example. As a result, the input voltage V DC Therefore, the main circuit portion (50) is less likely to be damaged by a lightning surge than in the comparative example.

[0041] Moreover, in the first embodiment, when a lightning surge current is superimposed on the current from the power source (2), the current flowing from the power source (2) to the main winding (30) and the capacitor (70) can be reduced compared to the comparative example. Therefore, the main winding (30) and the capacitor (70) can be made smaller than in the comparative example.

[0042] Furthermore, in the first embodiment, the electrical energy of the lightning surge current can be used to prevent the lightning surge current from entering the main circuit portion (50), thereby making effective use of energy.

[0043] In the first embodiment, the varistor (42) is provided in the bypass path (40), so that it is possible to prevent a current from flowing through the bypass path (40) when no lightning surge is occurring. On the other hand, when a lightning surge occurs, a current can be caused to flow through the bypass path (40) by short-circuiting the surge absorber (42). This eliminates the need for a computer to control whether or not to allow a current to flow through the bypass path (40), and therefore it is possible to reduce the delay time from the occurrence of a lightning surge until a current flows through the bypass path (40).

[0044] 3 and 4 show examples of voltages and currents when the switching of the switching elements (61a to 66a) is stopped. When the switching of the switching elements (61a to 66a) is stopped, the charge of the capacitor (70) does not flow to the load (3), so that the input voltage V DC However, even when the switching elements (61a-66a) are performing a switching operation to supply a current to the load (3), the effect of reducing the current flowing from the power source (2) to the main winding (30) and the capacitor (70) during the occurrence of a lightning surge can be obtained.

[0045] Variation of the First Embodiment 5 shows a power converter (1) according to a modification of the first embodiment of the present disclosure. In this modification, one end of the main winding (30) is connected to the second output end (20e) of the rectifier circuit (20), and the other end of the main winding (30) is connected to the second input node (60b) of the inverter circuit (60). A first input node (60a) of the inverter circuit (60) is connected to the first output end (20d) of the rectifier circuit (20). In the bypass path (40), an auxiliary winding (41) and a varistor (42) are provided in this order from the second output end (20e) side.

[0046] The other configurations are the same as those in the first embodiment, so the same components are given the same reference numerals and detailed descriptions thereof are omitted.

[0047] Second Embodiment 6 shows a power conversion device (1) according to a second embodiment of the present disclosure. In the second embodiment, first to third main windings (30a to 30c) and first to third bypass paths (40a to 40c) are provided between a power source (2) and a rectifier circuit (20).

[0048] Specifically, the first main winding (30a) is provided between the power source (2) and the first input terminal (20a) of the rectifier circuit (20), that is, on the first power line (L1).

[0049] The second main winding (30b) is provided between the power source (2) and the second input terminal (20a) of the rectifier circuit (20), that is, on the second power line (L2).

[0050] The third main winding (30c) is provided between the power source (2) and the third input terminal (20c) of the rectifier circuit (20), that is, on the third power line (L3).

[0051] In addition, first to third bypass paths (40a to 40c) are provided as the bypass path (40).

[0052] One end of the first bypass path (40a) is connected to the first power line (L1) at a position closer to the power source (2) than the first main winding (30a). Meanwhile, the other end of the first bypass path (40a) is connected to the second power line (L2) at a position closer to the rectifier circuit (20) than the second main winding (30b). The auxiliary winding (41) and the varistor (42) of the first bypass path (40a) are connected in this order from the first power line (L1) side.

[0053] One end of the second bypass path (40b) is connected to the second power line (L2) at a position closer to the power source (2) than the second main winding (30b). Meanwhile, the other end of the second bypass path (40b) is connected to the third power line (L3) at a position closer to the rectifier circuit (20) than the third main winding (30c). The auxiliary winding (41) and the varistor (42) of the second bypass path (40b) are connected in this order from the second power line (L2) side.

[0054] One end of the third bypass path (40c) is connected to the third power line (L3) at a position closer to the power source (2) than the third main winding (30c). Meanwhile, the other end of the third bypass path (40c) is connected to the first power line (L1) at a position closer to the rectifier circuit (20) than the first main winding (30a). The auxiliary winding (41) and the varistor (42) of the third bypass path (40c) are connected in this order from the third power line (L3) side.

[0055] The other configurations are the same as those in the first embodiment, so the same components are given the same reference numerals and detailed descriptions thereof are omitted.

[0056] Third Embodiment FIG. 7 illustrates a power conversion device (1) according to a third embodiment of the present disclosure. In the third embodiment, the power source (2) is a single-phase AC power source. Therefore, the rectifier circuit (20) has only first and second input terminals (20a, 20b) connected to the first and second power lines (L1, L2) as input terminals. The number of diodes (21-24) provided in the rectifier circuit (20) is four. A main winding (30) is provided between the power source (2) and the rectifier circuit (20). That is, the rectifier circuit (20) is connected to the power source (2) via the main winding (30).

[0057] In particular, the main winding (30) is provided on the first power line (L1), that is, between the power source (2) and the first input terminal (20a) of the rectifier circuit (20).

[0058] One end of the bypass path (40) is connected to the first power line (L1) on the power source (2) side relative to the main winding (30). Meanwhile, the other end of the bypass path (40) is connected to the second power line (L2). The auxiliary winding (41) and the varistor (42) are connected in this order from the first power line (L1) side.

[0059] The capacitance of the capacitor (70) is set so as to allow pulsation of the output voltage of the rectifier circuit (20) whose maximum value is at least twice as large as its minimum value.

[0060] The other configurations are the same as those in the first embodiment, so the same components are given the same reference numerals and detailed descriptions thereof are omitted.

[0061] Variation of the Third Embodiment FIG. 8 shows a power converter (1) according to a modification of the third embodiment of the present disclosure. In this modification, the main winding (30) is provided on the second power line (L2), i.e., between the power source (2) and the second input terminal (20b) of the rectifier circuit (20). One end of the bypass path (40) is connected to the second power line (L2) on the power source (2) side of the main winding (30). Meanwhile, the other end of the bypass path (40) is connected to the first power line (L1). The auxiliary winding (41) and the varistor (42) are connected in this order from the second power line (L2) side.

[0062] The other configurations are the same as those in the third embodiment, so the same components are given the same reference numerals and detailed descriptions thereof are omitted.

[0063] Fourth Embodiment 9 shows a power converter (1) according to a fourth embodiment of the present disclosure. In the fourth embodiment, the power source (2) is a DC power source. Also, the power source section (10) does not include a rectifier circuit (20).

[0064] The other configurations are the same as those in the first embodiment, so the same components are given the same reference numerals and detailed descriptions thereof are omitted.

[0065] In the first embodiment, the power supply (2) may be a single-phase AC power supply, and the rectifier circuit (20) may be the rectifier circuit (20) of the third embodiment, that is, the rectifier circuit (20) having four diodes (21-24).

[0066] In the above-described first to fourth embodiments and the modified examples of the first and third embodiments, another power conversion circuit, such as a DC-DC converter having a function of performing power conversion, such as stepping up or stepping down a DC voltage, by switching operation, may be provided instead of the inverter circuit (60). The power conversion circuit may then constitute the main circuit section (50).

[0067] In addition, in the above-described first to fourth embodiments and the modified examples of the first and third embodiments, the main circuit section (50) has a power conversion function using the inverter circuit (60). However, the main circuit section (50) does not necessarily have to have this power conversion function.

[0068] In addition, in the above-described first to fourth embodiments and the modified examples of the first and third embodiments, a part or all of the rectifier circuit (20) may be configured with power MOSFETs including wide band gap semiconductors such as IGBTs and silicon carbide and gallium nitride, instead of the diodes (21 to 26).

[0069] Although the embodiments and modifications have been described above, it will be understood that various modifications of form and details are possible without departing from the spirit and scope of the claims. Furthermore, the above embodiments and modifications may be appropriately combined or substituted as long as the functions of the subject of the present disclosure are not impaired. [Industrial Applicability]

[0070] INDUSTRIAL APPLICABILITY As described above, the present disclosure is useful as an electric circuit including a power supply unit and a main circuit unit to which power is supplied from a power source via the power supply unit. [Explanation of symbols]

[0071] 1 Power conversion device 2 power supply 10 Power supply section 11 Impedance increasing circuit 20 Rectifier circuit 30 Main Winding 40 Bypass Route 41 Auxiliary Winding 42 Varistor (surge absorber) 50 Main circuit section 60 Inverter circuit 60a First input node 60b Second input node 70 Capacitor

Claims

1. a rectifier circuit (20) that rectifies AC to DC and outputs the DC from first and second output terminals (20d, 20e); a main circuit section (50) to which the power output by the rectifier circuit (20) is supplied; a main winding (30) having one end connected to one of the first and second output ends (20d, 20e) of the rectifier circuit (20) and the other end connected to the main circuit section (50); a bypass path (40) having one end connected to the first output end (20d) of the rectifier circuit (20) and the other end connected to the second output end (20e) of the rectifier circuit (20); The bypass path (40) is provided with an auxiliary winding (41) magnetically coupled to the main winding (30) and a surge absorber (42) connected in series with the auxiliary winding (41) in this order from the one output end side, and the main winding (30) and the auxiliary winding (41) have the same polarity as each other in an electric circuit.

2. a main circuit section (50); a main winding (30) having one end connected to one of first and second output ends of a DC power source (2) and the other end connected to the main circuit section (50); a bypass path (40) having one end connected to a first output end of the DC power supply (2) and the other end connected to a second output end of the DC power supply (2); The bypass path (40) is provided with an auxiliary winding (41) magnetically coupled to the main winding (30) and a surge absorber (42) connected in series with the auxiliary winding (41) in this order from the one output end side, and the main winding (30) and the auxiliary winding (41) have the same polarity as each other in an electric circuit.

3. a rectifier circuit (20) that rectifies AC input from a power source (2) to first and second input terminals (20a-20c) into DC and outputs the DC; a main circuit section (50) to which the power output by the rectifier circuit (20) is supplied; main windings (30, 30a to 30c) provided on first power lines (L1 to L3) between the power source (2) and first input terminals (20a to 20c) of the rectifier circuit (20); a bypass path (40, 40a to 40c) having one end connected to the first power line (L1 to L3) at a position closer to the power source (2) than the main windings (30, 30a to 30c) and the other end connected to a second power line (L1 to L3) between the power source (2) and a second input terminal (20a to 20c) of the rectifier circuit (20); an auxiliary winding (41) magnetically coupled to the main winding (30, 30a to 30c) and a surge absorber (42) connected in series with the auxiliary winding (41) are provided in the bypass path (40, 40a to 40c) in this order from the first power lines (L1 to L3) side; The main winding (30, 30a to 30c), the rectifier circuit (20), and the main circuit section (50) are connected in series in an electric circuit.

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