Switching transformer, switching power supply device with the same, automotive electric compressor with the same and method for manufacturing switching transformer

Abstract

To provide a switching transformer capable of reducing only parasitic capacitance and lowering noise while maintaining magnetic coupling between the windings of the switching transformer.SOLUTION: A switching transformer 15 includes a primary winding 13 on low voltage side, a secondary winding 14 on the high voltage side, a central winding shaft section 61 on which the primary and secondary windings are wound and a core 46 having a bobbin 43 with a brim 62 and a middle leg 67 inserted into a through hole of the winding shaft section 61, and insulates the low voltage side from the high voltage side. An air gap layer G is configured between the winding shaft section 61 and the middle leg 67.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a switching transformer that insulates a low voltage side from a high voltage side, a switching power supply device including the same, an on-vehicle electric compressor including the same, and a method for manufacturing the switching transformer. [Background technology]

[0002] In recent years, as global environmental problems have become more apparent, hybrid and electric vehicles have been developed, and in the air conditioning systems for conditioning the interiors of these vehicles, an electric compressor equipped with a motor is used instead of an engine-driven compressor. In this case, the vehicle is equipped with a high-voltage power supply consisting of a high-voltage battery of, for example, about 300V direct current (DC300V), and a low-voltage power supply consisting of a normal battery of 12V direct current (DC12V), and the motor of the electric compressor is supplied with a voltage that is the DC voltage of the high-voltage power supply converted to AC by an inverter circuit.

[0003] On the other hand, the control circuit that controls the inverter circuit receives power by converting the DC voltage of the low-voltage power supply to a predetermined voltage (e.g., DC 15 V) using a switching power supply device. For this reason, this switching power supply device is provided with a switching transformer made of an insulating transformer, and the primary side of this switching transformer, i.e., the low-voltage side connected to the low-voltage power supply, is insulated from the secondary side, i.e., the high-voltage side connected to the high-voltage power supply.

[0004] In addition, in terms of noise reduction measures, the primary side (low voltage side) and secondary side (high voltage side) of the switching transformer were each grounded to the electric compressor chassis (chassis GND: earth) via a Y capacitor (line bypass capacitor), and an EMI filter circuit was also installed between the low voltage power supply and the switching power supply unit.

[0005] Here, some countermeasures against EMI noise caused by switching power supplies have been adopted in which a return capacitor is used to connect the primary ground and secondary ground, which are insulated by a switching transformer. This configuration is expected to return noise transmitted between the primary winding and secondary winding via the parasitic capacitance (coupling capacitance) between the windings of the switching transformer, suppress the common mode noise current flowing to the ground (chassis of the electric compressor), and reduce the noise voltage (see, for example, Patent Document 1).

[0006] In addition, switching transformers often adopt a sandwich winding structure in which the secondary winding is sandwiched between the primary windings in order to improve the degree of coupling between the primary winding and the secondary winding. However, improving the magnetic coupling using this structure is synonymous with increasing the opposing area of ​​the primary winding and secondary winding, which results in an increase in parasitic capacitance generated between the primary winding and secondary winding, increasing common mode noise.

[0007] Therefore, some have separated the primary winding and secondary winding of the switching transformer and reduced the opposing area between the primary winding and secondary winding to lower the magnetic coupling between the primary winding and secondary winding and reduce the parasitic capacitance between the windings. This configuration has the effect of reducing the amount of noise converted into common mode (for example, see Patent Document 2). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 7009325 [Patent Document 2] Patent Publication No. 2021-2913 Summary of the Invention [Problem to be solved by the invention]

[0009] Generally, in switching transformers, there is a trade-off between the magnetic coupling between the primary and secondary windings and the parasitic capacitance between them, and it has been difficult to reduce the parasitic capacitance while strengthening the magnetic coupling.However, the parasitic capacitance between the primary and secondary windings is a cause of common mode current (common mode noise), so it needs to be reduced.

[0010] In Patent Document 2, in order to reduce common mode noise, the degree of coupling between the primary winding and secondary winding is reduced, thereby reducing the parasitic capacitance between each winding and reducing the common mode current. However, with such a structure, the magnetic coupling between each winding is weak, making it difficult to ensure the voltage regulation that is essentially required for a power supply device, and therefore it has the disadvantage of being unsuitable for a feedbackless power supply (a power supply that does not control the switching on the primary side with the voltage on the secondary side).

[0011] Here, with regard to reducing EMI noise caused by switching power supply noise, it has been confirmed that not only the parasitic capacitance between the primary and secondary windings but also the parasitic capacitance between the windings via the switching transformer core has an effect in the high frequency band, causing noise deterioration.

[0012] The present invention has been made to solve the above-mentioned conventional technical problems, and has an object to provide a switching transformer that can reduce only the parasitic capacitance while maintaining the magnetic coupling between the windings of the switching transformer, thereby achieving reduced noise, a switching power supply device including the same, an on-board electric compressor including the same, and a method for manufacturing the switching transformer. [Means for solving the problem]

[0013] The switching transformer of the present invention has a primary winding and a secondary winding to insulate a low voltage side from a high voltage side, and is characterized in that it has a central winding shaft portion around which the primary winding and the secondary winding are wound, a bobbin having flange portions formed on both axial sides of the winding shaft portion, and a core having a center leg portion to be inserted into a through hole in the winding shaft portion, and an air gap layer or a shield layer is formed between the winding shaft portion and the center leg.

[0014] The switching transformer of the present invention according to claim 2 is characterized in that in the above-mentioned invention, a recess is formed on the inner surface of the winding shaft portion or on the outer surface of the center leg portion to form an air gap layer.

[0015] The switching transformer of the invention of claim 3 is characterized in that, in the invention of claim 1, the core has an outer leg portion that covers the outside of the bobbin, and this outer leg portion has a protruding portion that protrudes in a direction away from the center leg portion.

[0016] The switching transformer of the invention of claim 4 is characterized in that in the above invention, the dimension between the inner surface of the protruding portion and the primary winding or the secondary winding of the outermost layer is the same or approximately the same as the dimension in a direction perpendicular to the air gap layer or the center leg of the shield layer.

[0017] The switching power supply device of the invention of claim 5 is characterized in that the low-voltage side is connected to a low-voltage power supply and the high-voltage side is connected to a high-voltage power supply, and the primary winding of the switching transformer of each of the inventions above is the low-voltage side and the secondary winding is the high-voltage side, and the low-voltage power supply is switched to supply power to a control circuit located on the high-voltage side.

[0018] The in-vehicle electric compressor of the invention of claim 6 is characterized by comprising: the switching power supply device of the above invention which switches a low-voltage power supply mounted on a vehicle; a control circuit; an inverter circuit which is supplied with power from a high-voltage power supply mounted on the vehicle and controlled by the control circuit; and a motor which is driven by the inverter circuit.

[0019] The manufacturing method of a switching transformer of the invention of claim 7 is characterized in that, in the inventions of claims 1 to 4, when insulated wires are used as the primary winding and secondary winding, no barrier tape is used between the primary winding and secondary winding and the flange of the bobbin, and the width dimension of the flange is expanded within the range of the width dimension of this barrier tape.

[0020] The manufacturing method of a switching transformer of the invention of claim 8 is characterized in that in the above invention, the expanded width of the width dimension of the flange portion is the same as or approximately the same as the dimension of the air gap layer or the shield layer in a direction perpendicular to the center leg portion. Effect of the Invention

[0021] The parasitic capacitance between the primary winding and secondary winding of a switching transformer is caused by the physical distance between the windings, and is also caused by the parasitic capacitance via the core (made of ferrite: Mn-Zn or the like).

[0022] Therefore, in the present invention, a switching transformer having a primary winding and a secondary winding and insulating a low voltage side from a high voltage side includes a central winding shaft portion around which the primary winding and secondary winding are wound, a bobbin having flanges formed on both axial sides of the winding shaft portion, and a core having a center leg portion to be inserted into a through hole in the winding shaft portion, and an air gap layer or a shield layer is configured between the winding shaft portion and the center leg portion. Therefore, the distance between the innermost primary winding or secondary winding, where the primary winding or secondary winding is closest to the core, and the center leg portion of the core is secured by the air gap layer or shield layer, and it is possible to improve the coupling between the primary winding and secondary winding via the core.

[0023] In other words, it is possible to reduce the parasitic capacitance between the primary winding and secondary winding via the core, while maintaining the magnetic coupling between the windings, and as a result, reduce the amount of noise converted into common mode.

[0024] At this time, there is a concern that the provision of an air gap layer or the like may increase leakage flux, but the relative permeability of the core is sufficiently large and due to the structure of the switching transformer, the impact of increased leakage flux is limited.

[0025] In practice, the air gap layer is formed by forming a recess on the inner surface of the winding shaft portion or the outer surface of the center leg portion as in the invention of claim 2. The air gap layer formed with a recess can also be used when forming a shield layer.

[0026] In addition, if a protruding portion that protrudes in a direction away from the center leg is provided on the outer leg of the core that covers the outside of the bobbin as in the invention of claim 3, it becomes possible to avoid the inconvenience of the distance between the first winding or the secondary winding of the outermost layer and the outer leg of the core becoming close by providing an air gap layer or the like between the winding shaft part and the center leg, thereby making it possible to eliminate the increase in parasitic capacitance between the primary winding and the secondary winding via the outer leg of the core.

[0027] In this case, as in the invention of claim 4, by making the dimension between the inner surface of the protrusion and the primary winding or secondary winding of the outermost layer the same or approximately the same as the dimension in the direction perpendicular to the air gap layer or the center leg of the shield layer, it is possible to prevent unnecessary expansion of the external dimensions of the switching transformer.

[0028] The switching transformers of the above inventions are suitable for use in a switching power supply device in which the low-voltage side is connected to a low-voltage power supply and the high-voltage side is connected to a high-voltage power supply, as in the invention of claim 5, with the primary winding being on the low-voltage side and the secondary winding being on the high-voltage side, and which switches the low-voltage power supply to supply power to a control circuit located on the high-voltage side.

[0029] Furthermore, the switching power supply device of the above invention is extremely suitable for switching the low-voltage power supply mounted on a vehicle in an on-vehicle electric compressor that includes a control circuit, an inverter circuit that is supplied with power from a high-voltage power supply mounted on a vehicle and controlled by the control circuit, and a motor that is driven by the inverter circuit, as in claim 6.

[0030] Here, when insulated wires are used for the primary and secondary windings, if no barrier tape is used between the primary and secondary windings and the flange of the bobbin as in the invention of claim 7, and the width of the flange is increased within the range of the width of the barrier tape, it is possible to further reduce the parasitic capacitance between the primary and secondary windings via the core.

[0031] In this case as well, by making the expanded width of the flange portion the same as or approximately the same as the dimension of the air gap layer or the shield layer in the direction perpendicular to the center leg portion, as in the invention of claim 8, it is possible to obtain a sufficient effect of reducing the parasitic capacitance. [Brief description of the drawings]

[0032] [Figure 1] 1 is a block diagram of an electric circuit of an on-vehicle electric compressor according to an embodiment of the present invention to which a switching power supply device is applied; [Diagram 2] 1 is a diagram illustrating a structure of a switching transformer according to the present invention. [Diagram 3] 3 is a cross-sectional view of a core of the switching transformer of FIG. 2. [Figure 4] 3 is a diagram for explaining impedance between a primary winding and a secondary winding of the switching transformer of FIG. 2. [Diagram 5] 2 is a diagram for explaining the structure of a switching transformer of the switching power supply device of FIG. 1 when insulated electric wires are used as a primary winding and a secondary winding. [Figure 6] 2 is a diagram illustrating a grounding structure of a switching transformer of the switching power supply device of FIG. 1. [Figure 7] FIG. 7 is a cross-sectional view of a core of the switching transformer of FIG. [Figure 8] 7A to 7C are diagrams for explaining the effect of reducing common-mode noise by the ground structure of FIG. 6. [Figure 9] FIG. 7 is a diagram for explaining the effect of reducing common mode noise by the ground structure of FIG. 6. [Figure 10]7 is a diagram for explaining common mode noise when the grounding point is changed in the switching transformer of FIG. 6. FIG. [Figure 11] FIG. 7 is a diagram for explaining common mode noise when the grounding point is changed in the switching transformer of FIG. 6. [Figure 12] 7 is a diagram for explaining the grounding structure of the switching transformer in FIG. 6 having different winding specifications. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. (1) Vehicle-mounted electric compressor 1 In Fig. 1, reference numeral 1 denotes an on-vehicle electric compressor that constitutes a refrigerant circuit of a vehicle air conditioner that is installed in a vehicle such as an electric vehicle or a hybrid vehicle and that conditions the interior of the vehicle, and reference numeral 2 denotes its chassis (housing). Inside this chassis 2 are housed a compression mechanism (not shown), a motor 3 that drives this compression mechanism, an inverter circuit 4 for operating this motor 3, a control circuit 6 that controls this inverter circuit 4, EMI filter circuits 7 and 8, and a switching power supply device 9 of the present invention.

[0034] The vehicle is equipped with a high voltage power supply (HV power supply) 11 consisting of a high voltage battery of, for example, about 300V direct current (DC300V) for supplying power to and driving the motor 3 of the vehicle-mounted electric compressor 1 and a driving motor (not shown), and a low voltage power supply (LV power supply) 12 consisting of a normal battery (DC12V direct current 12V power supply), and the high voltage side of the vehicle-mounted electric compressor 1 is connected to the high voltage power supply 11, and the low voltage side is connected to the low voltage power supply 12. Also, the chassis 2 of the vehicle-mounted electric compressor 1 is conductive to the vehicle body and serves as an earth.

[0035] The inverter circuit 4 is composed of six switching elements (not shown) made of IGBTs or the like connected in a three-phase bridge, and each switching element is controlled by a gate drive signal generated by a gate driver of the control circuit 6. The control circuit 6 is composed of a microprocessor, and by switching each switching element of the inverter circuit 4 with the gate driver and performing PWM modulation, the DC voltage of the high-voltage power supply 11 is converted to a predetermined AC voltage and supplied to the motor 3.

[0036] The EMI filter circuit 7 is connected between the high-voltage power supply 11 and the inverter circuit 4, and serves to reduce EMI noise generated by switching of the inverter circuit 4. In addition, the EMI filter circuit 8 is connected between the low-voltage power supply 12 and the switching power supply 9, and serves to reduce EMI noise generated by switching in the switching power supply 9, as will be described later.

[0037] (2) Switching power supply unit 9 This switching power supply device 9 is a DC-DC converter that switches a low-voltage power supply 12 (DC 12V) to generate a predetermined DC voltage (HV15V, HV5V) and supplies power to the control circuit 6, and is configured by mounting each of the electric elements described below on a substrate 10. Note that HV15V is a voltage supplied to a gate driver (included in the control circuit 6) that generates a gate drive signal for the inverter circuit 4, and HV5V is a voltage that serves as the power source for the control circuit 6.

[0038] In this embodiment, the switching power supply device 9 has a switching transformer 15 configured as an insulating transformer including a primary winding 13 which is the low voltage side (connected to the low voltage power supply 12) and a secondary winding 14 which is the high voltage side (connected to the high voltage power supply 11) insulated from the primary winding 13. In this embodiment, a magnet wire is used for the primary winding 13, and the primary winding 13 has a first winding portion 51 (Np-1) having a winding start end 51A and a winding end 51B, and a second winding portion 52 (Np-2) which also has a winding start end 52A and a winding end 52B.

[0039] Then, winding end 52B of second winding portion 52 is connected to EMI filter circuit 8 via primary power supply line (LV+) 16, and is further connected to low-voltage power supply 12. Also, winding start end 52A of second winding portion 52 is connected to winding end end 51B of first winding portion 51, and winding start end 51A of first winding portion 51 is connected to the drain terminal of switching element 17, which is made of a MOSFET in this embodiment.

[0040] The source terminal of this switching element 17 is connected to LVGND18, which is the ground (primary side ground) on the low voltage side (connected to the low voltage power supply 12), and the winding starting end 51A of the first winding portion 51 of the switching transformer 15 is not directly connected to LVGND18.

[0041] In the figure, 19 is a switching power supply controller (controller), and this switching power supply controller 19 is supplied with power from low voltage power supply 12 via primary side power supply line 16. The output of switching power supply controller 19 is connected to the gate of switching element 17, and the switching of switching element 17 is controlled by this switching power supply controller 19.

[0042] As a result, the primary winding 13 of the switching transformer 15 is located on the low voltage side (connected to the low voltage power supply 12). Reference numeral 21 denotes a smoothing capacitor connected between the primary power supply line 16 and the primary ground 18. In this embodiment, the LVGND 18 insulated from the secondary side (HVGND 26 described later) by the switching transformer 15 is connected to the chassis 2 (earth) via a Y capacitor (line bypass capacitor) 22 that attenuates common mode noise. One end of the low voltage power supply 12 is also connected to the chassis 2.

[0043] Meanwhile, in this embodiment, a magnet wire is also used for the secondary winding 14 of the switching transformer 15, and the secondary winding 14 has a first winding portion 23 (Ns-1) having a winding start end 23A and a winding end 23B, and a second winding portion 24 (Ns-2) similarly having a winding start end 24A and a winding end end 24B. The winding end 24B of the second winding portion 24 is connected to HVGND 26, which is the ground (secondary side ground) on the high voltage side (connected to the high voltage power supply 11).

[0044] Then, winding start end 23A of first winding portion 23 is connected via diode 31 to HV15V line (first high-voltage power supply line) 32, and the gate driver of control circuit 6 described above is connected to this HV15V line 32. Winding start end 24A of second winding portion 24 is connected via diode 33 and regulator (LDO: low dropout regulator) 34 to HV5V line (second high-voltage power supply line) 36, and this HV5V line 36 serves as the power supply for control circuit 6.

[0045] Also, the winding start end 24A of the second winding portion 24 is connected to the winding end 23B of the first winding portion 23, and the winding end 24B of the second winding portion 24 is connected to the HVGND 26 as described above.

[0046] Note that 37 to 39 are smoothing capacitors connected between the HV15V line 32 and HVGND 26, and between the HV5V line 36 after the regulator 34 and HVGND 26, respectively. In the embodiment, HVGND 26 (secondary side ground) insulated from the primary side (LVGND 18) by the switching transformer 15 is connected to the chassis 2 (earth) via a Y capacitor (line bypass capacitor) 41 that attenuates common mode noise.

[0047] Then, the switching power supply controller 19 controls the switching of the switching element 17 so that DC15V (HV15V) is output to the HV15V line 32 in accordance with the turns ratio of the switching transformer 15. As a result, DC15V (HV15V) is supplied to the gate driver of the control circuit 6, and DC5V (HV5V) is supplied to the control circuit 6 itself from the intermediate output in accordance with the turns ratio of the first winding portion 23 and the second winding portion 24 via the regulator 34.

[0048] The switching power supply 9 switches on and off the low-voltage power supply 12 to supply power to the control circuit 6, and also uses the switching transformer 15 to insulate the low-voltage side on which the primary winding 13 is located (connected to the low-voltage power supply 12 as described above) from the high-voltage side on which the secondary winding 14 is located (connected to the high-voltage power supply 11 as described above) (indicated by the dashed line "insulation" in the figure). As a countermeasure against EMI noise caused by the switching of the switching element 17 of the switching power supply 9, the winding end 52B of the second winding portion 52 of the switching transformer 15 and the winding end 24B of the second winding portion 24 are coupled via a coupling capacitor 42.

[0049] In this way, by coupling the winding end 52B of the second winding portion 52 of the switching transformer 15 to the winding end 24B of the second winding portion 24 with the coupling capacitor 42, noise transmitted between the primary winding 13 and the secondary winding 14 via the parasitic capacitance (coupling capacitance) between the windings (between the primary winding 13 and the secondary winding 14) of the switching transformer 15 when the switching element 17 is switched is returned, and the common mode noise current flowing to the chassis 2 side (earth: ultimately the vehicle body side) of the electric compressor 1 is suppressed. This reduces the noise voltage.

[0050] (3) Structure of switching transformer 15 Next, the structure of the switching transformer 15 in this embodiment will be described with reference to Figures 2 and 3. In the figures, 43 denotes a bobbin around which the first winding portion 51 (Np-1) and the second winding portion 52 (Np-2) of the primary winding 13 and the first winding portion 23 (Ns-1) and the second winding portion 24 (Ns-2) of the secondary winding 14 are wound, 46 denotes a core, and 47 denotes a barrier tape.

[0051] The bobbin 43 is made of hard synthetic resin and has a central winding shaft portion 61 and flange portions 62 formed on both sides of the winding shaft portion 61 in the axial direction, and a through hole 60 is formed in the winding shaft portion 61. The first winding portion 51 (Np-1) and the second winding portion 52 (Np-2) of the primary winding 13 and the first winding portion 23 (Ns-1) and the second winding portion 24 (Ns-2) of the secondary winding 14 are wound on the outer surface of the winding shaft portion 61 of the bobbin 43, but in this embodiment, the first winding portion 51 (Np-1) is wound in the innermost layer, the second winding portion 24 (Ns-2) is wound outside of that, the first winding portion 23 (Ns-1) is wound outside of that, and the second winding portion 52 (Np-2) is wound in the outermost layer.

[0052] That is, the first winding portion 23 (Ns-1) and the second winding portion 24 (Ns-2) of the secondary winding 14 are sandwiched between the first winding portion 51 (Np-1) and the second winding portion 52 (Np-2) of the primary winding 13, thereby maintaining magnetic coupling between the primary winding 13 and the secondary winding 14. In this embodiment, a recess 63 is formed on the inner surface of the through hole 60 of the winding shaft portion 61 of the bobbin 43.

[0053] The barrier tape 47 is wound around the winding shaft portion 61 between the first and second windings 13, 14 and the flange portion 62 of the bobbin 43. In this case, the barrier tape 47 is necessary because the first and second windings 13, 14 are magnet wires as described above, and is wound around the winding shaft portion 61 with a width that satisfies the safety standard requirements.

[0054] Meanwhile, the core 46 is composed of a pair of core materials 46A, 46B made of ferrite (Mn-Zn). Each of the core materials 46A, 46B has an axisymmetric shape, and they are arranged facing each other as shown in Fig. 3 to form the core 46. Each of the core materials 46A, 46B has a base 66, a middle leg 67 protruding from the center of the base 66, and an outer leg 68 protruding from the outer end of the base 66.

[0055] Then, the center leg portions 67 of the core materials 46A, 46B are inserted from both sides into the through hole 60 of the winding shaft portion 61 of the bobbin 43 around which the primary and secondary windings 13, 14 and the barrier tape 47 are wound. In this state, the base portions 66 of the core materials 46A, 46B correspond to the outside of the flange portion 62 of the bobbin 43. Moreover, the outer leg portion 68 covers the outside of the second winding portion 52, which is the outermost layer in this embodiment. Furthermore, the outer leg portion 68 is formed with a protruding portion 68A that protrudes in a direction away from the center leg portion 67 (outward).

[0056] 3 shows a cross section of core 46 cut in the horizontal direction in FIG. 2. In addition, the black circles in FIG. 2 indicate the winding start ends of the aforementioned windings, and the white circles indicate the winding end ends. Also, the hatched circles indicate hot ends that vibrate at high frequency. Furthermore, the lower side (substrate 10 side) from center leg 67 in FIG. 2 is symmetrical to the upper side, so no reference numerals are attached.

[0057] In this embodiment, as described above, the recess 63 is formed on the inner surface of the through hole 60 of the winding shaft portion 61 of the bobbin 43, so that when the center leg portion 67 of the core 46 is inserted, an air gap layer (indicated by G in FIG. 2) is formed in the through hole 60 between the winding shaft portion 67 and the center leg portion 67. Also, as described above, the outer leg portion 68 is formed with the protruding portion 68A. This protruding portion 68A is formed corresponding to the second winding portion 52 of the outermost layer, and a predetermined distance is formed between the second winding portion 52 and the inner surface of the protruding portion 68A.

[0058] In this embodiment, the dimension of the gap between the second winding portion 52 and the inner surface of the protruding portion 68A is set to be the same as or approximately the same as the dimension of the air gap layer G in a direction perpendicular to the center leg portion 67.

[0059] In this manner, the air gap layer G is formed between the winding shaft portion 61 of the bobbin 43 of the switching transformer 15 and the center leg portion 67 of the core 46. This ensures a distance between the first winding portion 51 of the innermost layer, which is closest to the core 46, and the center leg portion 67 of the core 46 by the air gap layer G, thereby improving the coupling between the primary winding 13 and the secondary winding 14 via the core 46.

[0060] That is, the parasitic capacitance between the primary winding 13 and the secondary winding 14 via the core 46 is reduced, and as a result, the amount of noise converted to common mode can be reduced while maintaining the magnetic coupling between the windings 13 and 14. At this time, there is a concern that the provision of the air gap layer G may increase leakage flux, but the relative permeability of the core 46 is sufficiently large and the structure of the switching transformer 15 limits the impact of the increase in leakage flux.

[0061] In the embodiment, the outer leg 68 of the core 46 covering the outside of the bobbin 43 is provided with the overhanging portion 68A overhanging in a direction away from the center leg 67, so that the provision of the air gap layer G between the winding shaft portion 61 and the center leg 67 can avoid the inconvenience of the second winding portion 52 of the outermost layer becoming closer to the outer leg 68 of the core 46. This makes it possible to eliminate an increase in parasitic capacitance between the primary winding 13 and the secondary winding 14 via the outer leg 68 of the core 46.

[0062] Fig. 4 shows the frequency characteristics of the impedance between the primary winding and the secondary winding of the switching transformer. In this figure, L1 indicates the switching transformer 15 of the embodiment in Fig. 2, L2 indicates the case where the dimension in the direction perpendicular to the center leg 67 of the air gap layer G is double that in Fig. 2, L3 indicates the case where the air gap layer G is not provided, and L4 indicates the case where the primary winding and the secondary winding are separated as in the above-mentioned Patent Document 2.

[0063] In the case of L4, the magnetic coupling between the primary and secondary windings is reduced, so the impedance is high across the entire frequency range. In the case of L3, the impedance drops sharply in the FM band. In the case of L2, the distance between the outermost winding and the outer leg of the core is short, so the impedance is low in the FM band.

[0064] In contrast to these, L1 in the case of switching transformer 15 in Figures 2 and 3 has a low impedance like L3 in frequency bands lower than the FM band, and can be made higher in the FM band compared to L2 and L3, which shows that it is possible to reduce the amount of noise converted to common mode.

[0065] In the embodiment, the air gap layer G is formed by forming the recess 63 on the inner surface of the winding shaft portion 61 of the bobbin 43, and the air gap layer G can be easily formed. In this case, the recess 63 may be formed on the center leg portion 67 side of the core 46. Also, a shield layer may be formed on the air gap layer G formed by the recess 63. This shield layer is made of a low dielectric constant material.

[0066] In addition, in the embodiment, the dimension between the inner surface of the protruding portion 68A and the second winding portion 52 of the outermost layer is set to be the same as or approximately the same as the dimension in the direction perpendicular to the center leg portion 67 of the air gap layer G, so that unnecessary expansion of the outer dimensions of the switching transformer 15 can be prevented.

[0067] The switching power supply device 15 is extremely suitable for switching the low-voltage power supply 12 mounted on a vehicle in an on-vehicle electric compressor 1 that includes a control circuit 6, an inverter circuit 4 that is supplied with power from a high-voltage power supply 11 and controlled by the control circuit 6, and a motor 3 that is driven by the inverter circuit 4, as in the embodiment.

[0068] (4) Other structures of the switching transformer 15 Next, Fig. 5 shows the structure of a switching transformer 15 when insulated wires are used for the primary winding 13 and the secondary winding 14. In this figure, the same reference numerals as in Fig. 2 denote the same or similar functions.

[0069] In this embodiment, reinforced insulated wires having multiple layers of insulating coating are used for the primary winding 13 and secondary winding 14. Reinforced insulated wires differ from ordinary magnet wires (enameled wires) in that they have high insulation performance and do not require barrier tape due to safety standards.

[0070] Therefore, in this embodiment, the barrier tape 47 used in the previous embodiment is not used. Instead, the width of the flange 62 of the bobbin 43 is increased within the range of the width of the barrier tape 47. This makes it possible to further reduce the parasitic capacitance between the primary winding 13 and the secondary winding 14 via the core 62.

[0071] The width of the flange 62 of the bobbin 43 may be increased to the same or approximately the same as the dimension of the air gap layer G in a direction perpendicular to the center leg 67. This makes it possible to obtain a sufficient effect of reducing parasitic capacitance.

[0072] (5) Grounding of switching transformer 15 Next, the grounding structure and method of the switching transformer 15 in Fig. 1 will be described with reference to Fig. 6 to Fig. 12. Note that in each figure, the same reference numerals as in Fig. 1 to Fig. 5 denote the same or similar functions, and the switching transformer 15 in this case is also wired and connected in the same manner as in Fig. 1, so the description of Fig. 1 will be omitted.

[0073] 6, the switching transformer 15 is an insulating transformer made up of a primary winding 13 which is the low-voltage side connected to the low-voltage power supply 12 in this embodiment, and a secondary winding 14 which is the high-voltage side (connected to the high-voltage power supply 11 as described above) insulated from the primary winding 13. In this embodiment, a magnet wire is used for the primary winding 13, and the primary winding 13 has a first winding portion 51 (Np-1) having a winding start end 51A and a winding end 51B, and a second winding portion 52 (Np-2) which also has a winding start end 52A and a winding end 52B.

[0074] In FIG. 6, 43 denotes a bobbin around which the first winding portion 51 (Np-1) and the second winding portion 52 (Np-2) of the primary winding 13 and the first winding portion 23 (Ns-1) and the second winding portion 24 (Ns-2) of the secondary winding 14 are wound, 46 denotes a core, and 47 denotes a barrier tape.

[0075] The bobbin 43 is made of hard synthetic resin and has a hollow winding shaft portion 61 in the center and flange portions 62 formed on both axial sides of the winding shaft portion 61. The first winding portion 51 (Np-1) and the second winding portion 52 (Np-2) of the primary winding 13 and the first winding portion 23 (Ns-1) and the second winding portion 24 (Ns-2) of the secondary winding 14 are wound on the outer surface of the winding shaft portion 61 of the bobbin 43, and in the case of Fig. 6, the first winding portion 51 (Np-1) is wound in the innermost layer, the second winding portion 24 (Ns-2) is wound on the outer side thereof, the first winding portion 23 (Ns-1) is wound on the outer side thereof, and the second winding portion 52 (Np-2) is wound in the outermost layer.

[0076] That is, the winding specifications in FIG. 6 are configured such that the first winding portion 23 (Ns-1) and the second winding portion 24 (Ns-2) of the secondary winding 14 are sandwiched between the first winding portion 51 (Np-1) and the second winding portion 52 (Np-2) of the primary winding 13, thereby maintaining magnetic coupling between the primary winding 13 and the secondary winding 14.

[0077] The barrier tape 47 is wound around the winding shaft portion 61 between the first and second windings 13, 14 and the flange portion 62 of the bobbin 43. In this case, the barrier tape 47 is necessary because the first and second windings 13, 14 are magnet wires as described above, and is wound around the winding shaft portion 61 with a width that satisfies the safety standard requirements.

[0078] Meanwhile, the core 46 is composed of a pair of core materials 46A, 46B made of ferrite (Mn-Zn). Each of the core materials 46A, 46B has an axisymmetric shape, and they are arranged facing each other to form the core 46. Each of the core materials 46A, 46B has a base 66, a middle leg 67 protruding from the center of the base 66, and an outer leg 68 protruding from the outer end of the base 66.

[0079] Then, the center leg portions 67 of the core materials 46A, 46B are inserted from both sides into the winding shaft portion 61 of the bobbin 43 around which the primary and secondary windings 13, 14 and the barrier tape 47 are wound. In this state, the base portions 66 of the core materials 46A, 46B correspond to the outside of the flange portion 62 of the bobbin 43. The outer leg portions 68 described above cover the outside of the second winding portion 52, which is the outermost layer. Furthermore, the first winding portion 51 (Np-1) is adjacent to the center leg portion 67 of the core 46, and the second winding portion 52 (Np-2) is adjacent to the outer leg portions 68.

[0080] In addition, the black circles in Fig. 6 indicate the winding start ends of the aforementioned windings, and the white circles indicate the winding end ends. Also, the hatched circles indicate the hot ends that vibrate at high frequency. Furthermore, the lower side (substrate 10 side) from the center leg 67 in Fig. 6 is symmetrical to the upper side, so no reference numerals are attached.

[0081] An LVGND connection portion (land) 71, an HVGND connection portion (land) 72, and an earth connection portion (land) 73 are separately formed on the surface of the substrate 10 on which the switching transformer 15 is provided, and the LVGND connection portion 71 is conductive to the LVGND 18 mentioned above in FIG. 1, the HVGND connection portion 72 is conductive to HVGND 26, and the earth connection portion 73 is conductive to the earth (chassis 2).

[0082] On the other hand, the switching transformer 15 is provided with a ground terminal 74, and one end of this ground terminal 74 is electrically connected to the core 46. The other end of this ground terminal 74 of the switching transformer 15 is configured to be selectively connectable to any one of the LVGND connection portion 71, the HVGND connection portion 72, and the ground connection portion 73 described above.

[0083] (5-1) Grounding structure 1 of switching transformer 15 It is known that EMI noise can be improved by grounding the core 46, but in the case of a switching transformer 15 having the winding specifications of Fig. 6, that is, in the case where the first winding portion 51 of the primary winding 13 on the low-voltage side is located on the innermost layer and the second winding portion 52 is located on the outermost layer, the other end of the earth terminal 74 is connected to the LVGND connection portion 71 as shown in Fig. 6. As a result, the core 46 of the switching transformer 15 is grounded to the LVGND 18.

[0084] Fig. 8 shows the measurement results of common mode noise, where L6 is the case when the core 46 of the switching transformer 15 with the winding specifications in Fig. 6 is not grounded, and L5 is the case when the earth terminal 74 is connected to the LVGND connection part 71 and the core 46 is grounded to LVGND 18 as in Fig. 6. Also, Fig. 9 shows the difference between L5 and L6 in Fig. 8, where L7 is L5 and L8 represents the difference based on L7.

[0085] As shown by L6 in Fig. 8, the switching power supply device 9 of the embodiment contains a lot of high-frequency common mode noise on the low-voltage side (connected to the low-voltage power supply 12), but by grounding the core 46 of the switching transformer 15 to the LVGND 18 as shown in Fig. 6, the low-voltage side (connected to the low-voltage power supply 12) and the core 46 have the same potential, so that unnecessary reflux is suppressed, and the high-frequency noise (VHF band) on the low-voltage side is significantly improved by suppressing unnecessary coupling as shown by L5 in Fig. 8. This is also clear from a comparison between L7 and L8 in Fig. 9. The low-frequency noise on the high-voltage side is also improved by suppressing unnecessary coupling.

[0086] Here, the measurement results of common mode noise when the earth terminal 74 of the switching transformer 15 with the winding specifications in Fig. 6 is connected to the HVGND connection part 72 and the core 46 is grounded to HVGND 26 are shown in Fig. 10 and Fig. 11. L10 in Fig. 10 is the case when the core 46 of the switching transformer 15 is not grounded, and L9 is the case when the earth terminal 74 is connected to the HVGND connection part 72 and the core 46 is grounded to HVGND 26. Fig. 11 also shows the difference between L10 and L9 in Fig. 10, where L12 is L10 and L11 represents the difference based on L12.

[0087] When the core 46 of the switching transformer 15 with the winding specifications in Fig. 6 is grounded to HVGND 26, unnecessary coupling between the low-voltage side and the high-voltage side increases, so high-frequency noise on the low-voltage side leaks through the high-voltage side and increases. It can also be seen that low-frequency noise on the high-voltage side leaks through the low-voltage side and increases.

[0088] That is, in the case where the first winding portion 51 (Np-1) is wound in the innermost layer as shown in FIG. 6, the second winding portion 24 (Ns-2) is wound outside that, the first winding portion 23 (Ns-1) is wound outside that, and the second winding portion 52 (Np-2) is wound in the outermost layer, it can be seen that the core 46 should be grounded to the LVGND 18 with priority.

[0089] (5-2) Grounding structure of switching transformer 15 2 12, in the case of a winding specification in which the first winding portion 23 (Ns-1) of the secondary winding 14 on the high voltage side is wound in the innermost layer, the second winding portion 52 (Np-2) is wound outside that, the first winding portion 51 (Np-1) is wound outside that, and the second winding portion 24 (Ns-2) is wound in the outermost layer, the first winding portion 23 (Ns-1) is adjacent to the center leg portion 67 of the core 46, and the second winding portion 24 (Ns-2) is adjacent to the outer leg portion 68. In that case, it is preferable to connect the earth terminal 74 to the HVGND connection portion 72 and ground the core 46 to the HVGND 26.

[0090] 12 is grounded to HVGND 26, the high-voltage side (connected to high-voltage power supply 11) and core 46 will have the same potential, suppressing unnecessary reflux and significantly improving high-frequency noise on the high-voltage side by suppressing unnecessary coupling. Also, low-frequency noise on the low-voltage side will be improved by suppressing unnecessary coupling.

[0091] Depending on the winding specifications of the switching transformer 15 and the frequency band requiring noise reduction, it may be possible to connect the earth terminal 74 to the earth connection part 73 and ground the core 46 to the earth (chassis 2). That is, it is advisable to determine a priority grounding destination in advance according to the winding specifications and noise components of the primary winding 13 and secondary winding 14 of the switching transformer 15, and connect the earth terminal 74 to any one of the LVGND connection part 71, the HVGND connection part 72, and the earth connection part 73 during assembly.

[0092] In this way, the LVGND connection part 71, the HVGND connection part 72, and the earth connection part 73, which are respectively conductive to the LVGND 18 on the low voltage side, the HVGND 26 on the high voltage side, and the earth (chassis 2), are formed on the substrate 10, and the earth terminal 74 of the core 46 can be selectively connected to any of the LVGND connection part 71, the HVGND connection part 72, and the earth connection part 73. Therefore, it is possible to conductively connect the core 46 to any of the LVGND 18, the HVGND 26, and the earth (chassis 2) depending on the winding specifications of the primary winding 13 and the secondary winding 14 and the frequency band in which noise reduction is required.

[0093] This makes it possible to reduce common mode noise more effectively and simply.

[0094] In this case, in the case where the primary winding 13 and the secondary winding 14 wound around the bobbin 43 are wound in the innermost layer as shown in FIG. 6, by connecting the earth terminal 74 to the LVGND connection portion 71, unnecessary return current can be suppressed and a significant noise improvement effect can be obtained on the low voltage side.

[0095] On the other hand, in the case of a winding specification in which the secondary winding 14 is located in the innermost layer as shown in FIG. 12 among the primary winding 13 and secondary winding 14 wound around the bobbin 43, by connecting the earth terminal 74 to the HVGND connection portion 72, it is possible to suppress unnecessary return current and obtain a significant noise improvement effect on the high voltage side.

[0096] Furthermore, in the case of a winding specification in which the first winding portion 51 is located in the innermost layer and the second winding portion 52 is located in the outermost layer as shown in FIG. 6, with the primary winding 13 being close to the center leg portion 67 and the outer leg portion 68 of the core 46, by connecting the earth terminal 74 to the LVGND connection portion 71, unnecessary return current can be suppressed and a significant noise improvement effect can be obtained on the low voltage side.

[0097] On the other hand, in the case of a winding specification in which the first winding portion 23 is located in the innermost layer and the second winding portion 24 is located in the outermost layer as shown in FIG. 12, with the secondary winding 14 being close to the center leg portion 67 and the outer leg portion 68 of the core 46, by connecting the earth terminal 74 to the HVGND connection portion 72, unnecessary return current can be suppressed and a significant noise improvement effect can be obtained on the high voltage side.

[0098] The winding specifications of switching transformer 15 are not limited to those described above, and the present invention is also effective for different winding specifications. In the embodiment, the high voltage power supply 11 and the low voltage power supply 12 are mounted on the vehicle, and the primary winding 13 (first winding portion 51, second winding portion 52) of switching transformer 15 is on the low voltage side, and the secondary winding 14 (first winding portion 23, second winding portion 24) is on the high voltage side. However, the present invention is also effective for a vehicle in which only high voltage power supply 11 is mounted and switching transformer 15 generates a low voltage to be supplied from high voltage power supply 11 to control circuit 6.

[0099] In this case, contrary to the above embodiment, the primary winding 13 having the first winding portion 51 and the second winding portion 52 becomes the high voltage side, and the secondary winding 14 having the first winding portion 23 and the second winding portion 24 becomes the low voltage side. Therefore, for example, in the case of a winding specification in which the first winding portion 51 is the innermost layer and the second winding portion 52 is the outermost layer, the earth terminal 74 is connected to the HVGND connection portion 72, and in the case of a winding specification in which the first winding portion 23 is the innermost layer and the second winding portion 24 is the outermost layer, the earth terminal 74 is connected to the LVGND connection portion 71.

[0100] Furthermore, in the embodiment, the switching power supply device 9 for the vehicle-mounted electric compressor 1 has been taken as an example for explanation, but the present invention is effective for various switching power supply devices having a switching transformer. [Explanation of symbols]

[0101] 1. Vehicle-mounted electric compressor 2 Chassis (earth) 3 Motor 4. Inverter Circuit 6 Control Circuit 7, 8 EMI filter circuits 9. Switching Power Supply Unit 10 Substrate 11 High voltage power supply 12 Low voltage power supply 13 Primary Winding 14 Secondary Winding 15 Switching transformer 17 Switching elements 18 LVGND 19 Switching power supply controller (controller) 23 First winding section (secondary winding) 24 Second winding section (secondary winding) 26 HVGND 43 Bobbin 46 cores 51 First winding section (primary winding) 52 Second winding section (primary winding) 60 Through Hole 61 Winding shaft section 62 Flange 63 Recess 67 Middle leg 68 External legs 68A Overhang 71 LVGND connection 72 HVGND connection 73 Earth connection G Air gap layer

Claims

1. In a switching transformer having a primary winding and a secondary winding and isolating a low voltage side from a high voltage side, a bobbin having a central winding shaft portion around which the primary winding and the secondary winding are wound, and flange portions formed on both sides of the winding shaft portion in an axial direction; a core having a center leg portion that is inserted into the through hole of the winding shaft portion, A switching transformer, characterized in that an air gap layer or a shield layer is formed between the winding shaft portion and the center leg portion.

2. 2. The switching transformer according to claim 1, wherein a recess is formed on an inner surface of the winding shaft portion or an outer surface of the center leg portion to form the air gap layer.

3. 2. The switching transformer according to claim 1, wherein the core has an outer leg portion covering an outside of the bobbin, and the outer leg portion has a protruding portion protruding in a direction away from the center leg portion.

4. 4. The switching transformer according to claim 3, wherein a dimension between an inner surface of the protruding portion and the primary winding or the secondary winding of the outermost layer is the same as or approximately the same as a dimension of the air gap layer or the shield layer in a direction perpendicular to the center leg portion.

5. The low voltage side is connected to a low voltage power supply, and the high voltage side is connected to a high voltage power supply, 5. A switching power supply device including a switching transformer according to claim 1, wherein the primary winding of the switching transformer is on the low voltage side and the secondary winding is on the high voltage side, and the low voltage power supply is switched to supply power to a control circuit located on the high voltage side.

6. 6. An on-vehicle electric compressor comprising: the switching power supply device according to claim 5 which switches the low-voltage power supply mounted on a vehicle; the control circuit; an inverter circuit which receives power from the high-voltage power supply mounted on the vehicle and is controlled by the control circuit; and a motor which is driven by the inverter circuit.

7. 5. The method for manufacturing a switching transformer according to claim 1, wherein, when insulated wires are used as the primary winding and the secondary winding, no barrier tape is used between the primary winding and the secondary winding and a flange of the bobbin, and a width dimension of the flange is expanded within the range of a width dimension of the barrier tape.

8. 8. The method for manufacturing a switching transformer according to claim 7, wherein an expanded width of the flange portion is the same as or approximately the same as a dimension of the air gap layer or the shield layer in a direction perpendicular to the center leg portion.

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