JP2024023816A - isolation transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small, low-profile isolation transformer that can suppress core magnetic saturation even in high-temperature environments while ensuring sufficient creepage distance.

SOLUTION: An isolation transformer includes a pair of E-shaped cores, a bobbin including a cylindrical body through which a central leg of the E-shaped core is passed, a coil member including a first winding and a second winding formed of a conductive wire wound around the outer periphery of the cylindrical body, a rectangular case that houses the coil member and includes a first terminal connected to the first winding and a second terminal connected to the second winding, the case includes an inner space surrounded by a base, a wall, and a top plate to accommodate the coil member, the pair of E-shaped cores and the coil member are arranged in the inner space, and the top plate is made of Mn-based ferrite and has a groove extending to the wall with a width for leading out the first winding.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to an isolation transformer used, for example, in an inverter for a drive motor of an electric vehicle (EV, HEV).

In recent years, in large-capacity switching power supplies used in automobiles and industrial equipment, efforts have been made to improve switching speeds in order to miniaturize power supply circuits. The adoption of silicon carbide (SiC), which can increase the Flyback type power supply circuits are the mainstream for SiC gate drive power supply circuits, and flyback type inverters have a switching frequency set in the range of 300kHz to 500kHz, excluding radio frequency bands (LW band, AM band), for noise countermeasures. is widespread. The isolation transformer used in such a flyback type inverter can be designed to be more compact as the switching frequency is higher, which greatly contributes to the miniaturization of the entire circuit.

On the other hand, with the increasing functionality of various applications, the voltage of power supply systems is increasing, and the demand for high withstand voltage products is also increasing for components used in switching power supplies. There is a demand for reinforcement.

As such an insulating transformer, for example, Patent Document 1 discloses a transformer that is compatible with high-density mounting and has a structure that ensures insulation between the transformer body and surrounding electronic components on the board on which the transformer is mounted. 9(A) and 9(B) are perspective views of the transformer 100 disclosed in Patent Document 1, viewed from the front side and the back side. Figure 9(A) is a perspective view of the transformer as seen from the front with the pin terminal side on the primary side facing you, and Figure 9(B) is a perspective view of the transformer as seen from the back side with the pin terminal side of the secondary side in front of you. FIG. The transformer 100 includes a transformer main body 110 including a pair of E-shaped cores 108, a bobbin 102, a primary winding 104 and a secondary winding 106, and an insulating cover 114 that accommodates the transformer main body 110.

With the primary winding 104 and the secondary winding 106 wound around the bobbin 102, central legs of a pair of E-shaped cores are inserted and attached to through holes formed in the bobbin 102. The central leg of the E-shaped core is close to each other within the through hole of the bobbin, and the side legs are close to the outside of the primary winding 104 and the secondary winding 106 to form a magnetic path. Further, a plurality of primary side pin terminals 112 connected to the primary winding 104 are attached to the flange portion 102e of the bobbin 102 in a state of protruding downward from the transformer.

The hollow, rectangular parallelepiped-shaped insulating cover 114 that accommodates the transformer body 110 is large enough to accommodate most of the transformer body 110 in its inner accommodation space, and has one side surface on the primary pin terminal 112 side of the transformer body 110. The transformer body 110 is surrounded by a top plate 114a and a bottom plate (not shown) that face each other vertically, and side plates 114c and 114d connected to the top plate 114a and the bottom plate. In the illustrated example, a sub-opening 114f (notch) is formed in the top plate 114a of the insulating cover 114, from which the E-shaped core 108 and the like of the transformer body 110 are partially exposed. On the side plate side facing the opening of the insulating cover 114, a plurality of secondary pin terminals 116 connected to the secondary winding 106 are attached to the bottom plate in a state of protruding downward from the transformer.

Lead wires 104a are drawn out from the beginning and end of the primary winding 104, and these lead wires 104a are each soldered and fixed to a pin terminal 112 on the primary side. In addition, the lead wires 106a are drawn out from the winding start and winding end of the secondary winding 106, respectively, and are drawn out through the sub-opening 114f of the insulating cover 114, and then downward from the top plate 114a along the side plate 114d. The terminals extend toward each other and are fixed to the pin terminals 116 on the secondary side by soldering.

JP2009-16581A

The generally defined insulation distance is the shortest distance between the exposed conductor of the primary winding and the secondary winding, and the creepage distance is the distance along the creeping surface of the insulator. In the transformer 100 of Patent Document 1, the distance is the distance between the upright pin terminal 104 on the primary side and the pin terminal 106 on the secondary side, and the E-shaped core 108 is regarded as a conductor, and the distance between the primary winding 104 If it is assumed that the E-shaped core 108 is the same potential body as the insulating cover 114, it is defined by the distance between the E-shaped core 108 exposed from the insulating cover 114 and the pin terminal 116 on the secondary side.

In the transformer of Patent Document 1, a transformer main body 110 is surrounded by an insulating cover 114, a lead wire 106a of the secondary winding 106 is drawn out through an opening provided in the insulating cover 114, and the lead wire 106a is passed from a top plate 114a to a side plate 114d. By extending it along the E-shaped core 108 and the secondary side pin terminal 116, a creepage distance is secured.

On the other hand, the transformer main body 110 is arranged so that the flange portion 102e on which the primary side pin terminal 104 is formed largely protrudes outward from the opening of the insulating cover 114. According to such a structure, while it is easy to ensure a creepage distance between the vertically arranged terminals, there is a restriction in reducing the mounting area of the transformer. In addition, since the primary side pin terminal 104 and the secondary side pin terminal 106 are provided on different members, when the insulating cover 114 and the transformer body 110 are combined, it is easy to cause misalignment or variation in the position of the terminals. In some cases, mounting on a circuit board was difficult.

Furthermore, since it has a vertical structure in which the E-shaped cores are stacked in a direction perpendicular to the circuit board on which it is mounted, it is not suitable for reducing the height of the transformer. Furthermore, the transformer is required to not be magnetically saturated even under a load condition in which the current flowing through the winding reaches its maximum value, and there are limits to the miniaturization of the E-shaped core so as to reduce its height. Further, in general, the saturation magnetic flux density Bs of the magnetic material constituting the core fluctuates with temperature, and tends to decrease as the environmental temperature rises. In automotive applications where the environmental temperature exceeds 100°C, it is also required to withstand magnetic saturation even when the switching power supply continues to operate under maximum load conditions.

Therefore, in order to solve the above-mentioned problems, the present invention aims to provide a small, low-profile insulation transformer that can suppress magnetic saturation of the core even in high-temperature environments while ensuring sufficient creepage distance. purpose.

The present invention provides a bobbin comprising a pair of E-shaped cores, a cylindrical body through which the center leg of the E-shaped core passes, and a bobbin formed of a conductive wire wound around the outer periphery of the cylindrical body. a coil member including a first winding and a second winding; a first terminal that accommodates the coil member and connects to the first winding; and a second terminal that connects to the second winding. and a rectangular case, the case having an inner space for accommodating the coil member, and the coil member is placed in the inner space so that the pair of E-shaped cores are placed horizontally. The pair of E-shaped cores have an effective cross-sectional area Ae of 15.5 mm ² or more and 21.0 mm ² or less, an effective magnetic path length le of 21.8 mm or more and 24.2 mm or less, and saturation at 130°C. This is an isolation transformer made of Mn-based ferrite with a magnetic flux density Bs of 0.35T or more.

In the present invention, the Mn-based ferrite preferably has a core loss of 7000 kW/m ³ or less at a frequency of 400 kHz, an excitation magnetic flux density of 240 mT, and a temperature of 23° C. to 130° C.
Further, a reinforced insulated wire is used for at least one of the windings, and the winding portion of the conducting wire constituting the first winding and the winding portion of the conducting wire constituting the second winding are different from each other. The winding portions of the conducting wire constituting the second winding are arranged to overlap in the radial direction of the cylindrical body so as to sandwich the winding portion of the conducting wire constituting the second winding. It is preferable that the coupling coefficient of the second winding is 0.990 or more.

According to the present invention, it is possible to suppress the magnetic saturation of the core even in a high temperature environment while ensuring a sufficient creepage distance, and it is possible to provide a small and low profile insulation transformer.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing an insulation transformer according to an embodiment of the present invention exploded into constituent members. FIG. 1 is a perspective view of an insulation transformer according to an embodiment of the present invention, seen from the front side. FIG. 1 is a perspective view of an insulation transformer according to an embodiment of the present invention, viewed from the back side. FIG. 1 is a sectional view of an isolation transformer according to an embodiment of the present invention. 1 is an equivalent circuit of a flyback converter using an isolation transformer according to an embodiment of the present invention. FIG. 2 is a schematic diagram for explaining a winding structure of an isolation transformer according to an embodiment of the present invention. It is a graph showing direct current superimposition characteristics at 130° C. calculated with the configuration of an isolation transformer including an embodiment of the present invention. It is a graph which shows the temperature characteristic of the magnetic core loss calculated with the structure of the isolation transformer of one Embodiment of this invention. It is a graph showing the direct current superposition characteristic at 130° C. of the isolation transformer of one embodiment of the present invention. FIG. 2 is a perspective view of a conventional isolation transformer seen from the front side. FIG. 2 is a perspective view of a conventional isolation transformer seen from the front side.

Although embodiments of the isolation transformer of the present invention will be described, the present invention is not limited to the forms described below. FIG. 1 is a perspective view of an isolation transformer according to an embodiment of the present invention, disassembled into component parts, and FIG. FIG. 2(B) is a perspective view of an insulation transformer according to an embodiment of the present invention viewed from the back side, and FIG. 3 is a sectional view of the insulation transformer according to an embodiment of the present invention. Further, FIG. 4 shows an example of an equivalent circuit of a flyback converter using an isolation transformer. An isolation transformer according to an embodiment of the present invention will be described with reference to these figures as appropriate.

For example, as shown in the equivalent circuit of FIG. 4, the flyback converter includes a first winding 80 on the primary side of an isolation transformer 1 connected to a DC voltage supply source, and a switch circuit connected to the first winding 80. A control IC that controls ON/OFF of the switch circuit, a Vcc winding 87 of the isolation transformer 1 that supplies power to the control IC, a second winding 85 on the secondary side of the isolation transformer 1, and the second winding 87 of the isolation transformer 1 that supplies power to the control IC. A rectifier circuit including a diode connected to line 85 and a capacitor is provided.

The isolation transformer 1 shown in FIGS. 1 to 3 is used in a flyback converter with a switching frequency of 300 kHz or more and 500 kHz or less, and can be arranged within a plane measuring 15.5 mm long and 13.0 mm wide, and has a height of 15.5 mm. This is a suitable configuration example as an insulation transformer of 0 mm or less.

The insulating transformer 1 includes a bobbin 30 including a cylindrical body, and a first winding 80 and a second winding 85 (hereinafter collectively referred to as A pair of E-shaped cores 10a and 10b are mounted on the bobbin 30 in a horizontal arrangement, and a case 50 is provided with a metal terminal 40. A coil member 60 is constituted by a bobbin 30 provided with E-shaped cores 10a and 10b, a first winding 80, a second winding 85, and a Vcc winding 87, and is housed in the case 50.

As shown in FIG. 1, each of the E-shaped cores 10a and 10b used in the isolation transformer 1 of this embodiment includes a pair of side legs 12, a center leg 11 disposed between them, and a side leg 12 and a rectangular connecting portion 13 that connects one end side of the central leg portion 11 to form a substantially E-shape. The central leg portion 11 is located at a position shifted toward one long side of the connecting portion 13, so that the cross-sectional area of the central leg portion 11 is approximately equal to the entirety of the left and right side legs 12 and 13.

The central legs 11 of the pair of cores 10a and 10b are inserted into the through hole 35 inside the cylindrical body of the bobbin 30, and the side legs 12 of the cores 10a and 10b are butted against each other to form the combined core 10a. , 10b are wrapped with insulating tape 90 and integrated to form the coil member 60. In many cases, a gap is provided between the central leg portions 11 of the pair of cores 10a and 10b in order to adjust the inductance. Cores 10a and 10b appear above and on the sides of coil member 60, and winding portions of windings 80, 85, and 87 and leg portions 32 of bobbin 30 appear below. As shown in FIGS. 1 and 3, on the lower side of the coil member 60, there is an open space on the lower side of the cores 10a, 10b where the windings 80, 85, 87 are not formed (below the connecting portion 13 of the core). However, a leg portion 32 connected to the collar portion 31 of the bobbin 30 is formed therein so as to protrude slightly from the outer periphery of the winding portion. In the illustrated example, the leg portion 32 is provided with a plurality of recesses through which the lead wires of the windings 80, 85, and 87 are passed. According to such a configuration, it is easy to attach the coil member 60 to the case 50, and by eliminating unnecessary space, it is possible to increase the volume ratio occupied by the cores 10a and 10b in the coil member 60. I can do it. Thereby, it is possible to downsize the coil member 60 and to create a redundant design that takes into account the magnetic saturation of the cores 10a and 10b even in a limited space.

It is preferable that the effective cross-sectional area Ae of the core is 15.5 mm ² or more and 21.0 mm ² or less, and the effective magnetic path length le is 21.8 mm or more and 24.2 mm or less. If the effective cross-sectional area Ae is outside the above range and is small, magnetic saturation is likely to occur, and if it is large, the core becomes large and it may be difficult to miniaturize the isolation transformer. Furthermore, if the effective magnetic path length le is outside the above range and is short, the initial inductance may increase and magnetic saturation may occur. Furthermore, since the area for winding the coil becomes narrower, it becomes difficult to wind the coil in an aligned manner, and if the wire diameter of the winding is made thinner, the heat generated by the coil increases, which may induce thermal runaway in the insulation transformer. If it is long, the core becomes large and it may be difficult to downsize the isolation transformer.

Moreover, as a magnetic material used for the core, Mn-based ferrite having a saturation magnetic flux density Bs at 130° C. of 0.35 T or more is preferable. The larger the saturation magnetic flux density Bs, the more compact the core can be, and it is preferable that the saturation magnetic flux density Bs is at least 0.35T or more. Further, it is preferable that the Mn-based ferrite has a core loss of 7000 kW/m ³ or less at a frequency of 400 kHz, an excitation magnetic flux density of 240 mT, and a temperature of 23° C. to 130° C. By keeping the magnetic core loss at temperatures between 23°C and 130°C to 7000kW/ ^m3 or less, the isolation transformer used can be used even when the switching power supply continues to be driven under maximum load conditions at environmental temperatures exceeding 100°C. It is possible to suppress thermal runaway.

FIG. 5 shows a schematic diagram for explaining the winding structure of the isolation transformer. A first winding 80, a second winding 85, and a Vcc winding 87 are provided in the cylindrical body of the bobbin 30, and the first winding 80 connects the second winding 85 and the Vcc winding 87. It has a sandwich roll structure. Such a winding structure allows the coupling coefficient between the first winding 80 and the second winding 85 to be 0.990 or more. The larger the coupling coefficient, the higher the power conversion efficiency, which is preferable.

Each winding uses a coated wire that has an insulating coating on a conductor made of a conductive material such as copper, aluminum, or an alloy thereof. Generally, enamelled copper wire coated with polyamide-imide insulation is used, but if you consider the insulation on the primary and secondary sides, reinforced insulated wire with multiple layers of insulation coating to improve insulation properties is used. It is preferable to use a double-layer insulated wire or a triple-layer insulated wire for at least one winding. Particularly when switching at high frequencies, it is preferable to use a litz wire, stranded wire or parallel wire for the winding, and to make it a reinforced insulated wire.

The case 50 includes a rectangular base 51 made of insulating resin, metal terminals 40 (T1 to T8) provided on the base 51, and further includes wall portions 52 standing from three edges of the base 51, 53, 54, and a top plate portion 55 that faces the base portion 51 and covers the upper end side of the wall portions 52, 53, 54. As shown in FIGS. 1 and 2, the case 50 has a box-like shape with an open side surface on the side where the metal terminals 40 (T1 to T4) are formed. Further, as shown in FIG. 3, the end portion of the metal terminal 40 is formed to be substantially the same as the lower surface of the base portion 51, or to slightly protrude from the lower surface.

At least the height of the wall parts 52, 53, 54 is formed higher than the above-mentioned coil member 60, and the above-mentioned coil member 60 is placed in the inner space surrounded by the base 51, the walls 52, 53, 54, and the top plate part 55. can be accommodated. In the illustrated example, the top plate portion 55 is provided with a groove portion extending to the wall portion 53 side and having a width that allows the lead wire of the first winding 80 to be drawn out.

The first terminal of the metal terminal 40 (T5 to T8) connected to the first winding 80 and the second terminal of the metal terminal 40 (T1 to T4) connected to the second winding 85 and the Vcc winding 87 are connected to the case 50. The terminals are integrally formed. When the case 50 is viewed from below, the entire lower surface of the base 51 is flat, but a stepped portion 52 extending from the wall 52 side of the case 50 to the wall 54 side is formed between the metal terminals 40. The creepage distance between the terminal and the second terminal can be increased. Furthermore, since the first terminal and the second terminal are integrally formed in the case 50, positional deviation between the terminals is suppressed compared to the conventional case, and problems such as poor connection when mounted on a circuit board are less likely to occur.

For the metal terminal 40, it is preferable to use SPCC, Kovar, which is an alloy of nickel, cobalt, phosphor bronze, and iron, 42 alloy, or CP wire.

The case 50 and the above-mentioned bobbin 30 are made of an insulating resin, and any resin that has insulation, mechanical strength, chemical resistance, heat resistance, moisture resistance, and moldability may be used, such as phenol resin, diallyl phthalate resin, PPS (Poly Phenylene Sulfide resin, liquid crystal polymer, PET (Polyethylene Terephthalate) resin, PBT (Poly Butylene Terephthalate) resin, ABS (Acrylic lonitrile butadiene styrene (acrylonitrile butadiene styrene) resins are preferred; Those molded by a known method such as injection molding can be used.

As shown in FIGS. 1 and 2, the coil member 60 is housed in a space within the case 50 and fixed with an adhesive (not shown) so that the E-shaped cores 10a and 10b are placed horizontally. For example, a silicone-based adhesive can be used for adhesion, and it is preferable to use an adhesive that has low hardness and can be used over a wide temperature range. Although the upper surface of the base 51 of the case 50 on which the coil member 60 is placed is flat, a depression may be provided to serve as an adhesive reservoir for positioning and fixing the coil member 60.

The lead wire 75 is drawn out from the beginning and end of the winding of the second winding 85 and the Vcc winding 87 provided on the coil member 60 through the groove formed in the leg portion 32 of the bobbin 30, and is drawn out from the side surface of the case 50. is tied around the second terminal of the metal terminal 40 (T1 to T4) on the open side and fixed by solder. In the example of the flyback converter shown in FIG. 4, the winding start side of the second winding 85 (○5 in FIG. 4) is connected to T1 of the metal terminal 40 of the isolation transformer 1, and the second winding 85 is connected to T2. The end of the roll (〇6) is connected. Further, the winding start side (07) of the Vcc winding 87 is connected to T3, and the winding end side (08) of the Vcc winding 87 is connected to T4.

The lead wire 70 is pulled out from the opening side of the case 50 from the beginning and end of the first winding 80, passes through the groove of the top plate 55 of the case 50, and runs along the plane of the wall 53 to connect the metal terminal 40. They are led out toward the first terminals (T5 to T8), tied together, and fixed with solder. In the illustrated example, two first windings 80 are used to enable parallel connection, and the winding start side (〇1) of one first winding 80 is connected to T8 of the metal terminal 40, and the other is connected to T7. The winding start side (02) of the first winding 80 is connected. Further, T6 is connected to the winding end side (〇3) of one first winding 80, and T5 is connected to the winding end side (〇4) of the other first winding 80, thereby completing an isolation transformer.

According to such a configuration, it is possible to increase the distance between the first terminal of the metal terminal 40 (T5 to T8) and the core 13 of the coil member 60, thereby ensuring creepage distance and improving insulation performance. can be improved.

As explained above, according to the present invention, it is possible to suppress the magnetic saturation of the core even in a high temperature environment while ensuring a sufficient creepage distance, and it is possible to provide a low-profile and small-sized isolation transformer. .

The isolation transformer shown in FIGS. 1 to 3 was manufactured with the following configuration. This isolation transformer can be placed within a plane measuring 15.5 mm long and 13.0 mm wide, has a height of 15.0 mm or less, has a creepage distance of 12.5 mm or more, and has an input inductance due to the first winding. It is used in a flyback type inverter with a switching frequency of 400 kHz and an input voltage of 17 to 25 V.

The case for determining the external dimensions of the isolation transformer is that the mounting surface is 12.5 mm in the X direction (B dimension), 15.2 mm in the Y direction (A dimension including metal terminals), and 14.5 mm in the Z direction (C dimension). The dimensions of the inside of the case that accommodates the coil member are 11.2 mm in the X direction, 10.7 mm in the Y direction, and 10.0 mm in the Z direction. As the core of the coil member that can be accommodated in the inner space of the case, an E-shaped core with a diameter of 10.4 mm in the X direction, 5.15 mm in the Y direction, and 7.5 mm in the Z direction was used. The combined E-shaped core has an effective cross-sectional area Ae of 15.9 mm ² and an effective magnetic path length le of 22.74 mm. Further, the gap length is 0.06 mm, and the volume Ve of the pair of E-shaped cores is 444 mm ² . The number of turns N1 of the first winding was set to 7 turns, and the number of turns N2 of the second winding was set to 16 turns in consideration of the voltage on the second winding side and the voltage drop due to the diode of the rectifier circuit. Considering the operating conditions of the flyback inverter, the peak current flowing through the first winding was set to 1.79A.

Two materials, Mn-based ferrite manufactured by Hitachi Metals, Ltd., were selected as the ferrite used for the E-type core, and the direct current superimposition characteristics and core loss were calculated from the magnetic characteristics of each material. Table 1 shows typical values listed in catalogs of the magnetic properties of each material. Note that each characteristic was evaluated using an annular core with an outer diameter of 25 mm, an inner diameter of 15 mm, and a height of 5 mm. Moreover, the saturation magnetic flux density at 130° C. for each is 350 mT or more.

(DC superposition characteristics)
Prepare an annular core with an outer diameter of 25 mm, an inner diameter of 15 mm, and a height of 5 mm created using ML25 and ML29D, and calculate the initial magnetization curve (Bm-Hm characteristic) of the DC B-H curve at 130°C and the DC superposition characteristic ( μΔ-Hm characteristics) were measured.
From the magnetic flux density Bm of the obtained initial magnetization curve and the magnetic field strength Hm, the magnetic field strength H' of a magnetic circuit composed of a pair of E-shaped cores with a magnetic path length Le and a gap length Lg can be calculated using equation (1). By further investigation, we obtained the BH' characteristics of a magnetic circuit constructed by combining E-type cores.
H'=(Hm×(Le-Lg)+Bm×Lg/μ ₀ )/Le (1)
Bm: magnetic flux density (T)
Hm: Magnetic field strength (A/m)
Le: magnetic path length of a pair of E-shaped cores (m)
Lg: Gap length between a pair of E-shaped cores (m)
μ ₀ : Vacuum permeability (4π×10 ⁻⁷ ) (H/m)
μΔ: Incremental permeability

From the incremental magnetic permeability μΔ of the DC superposition characteristic obtained from the annular core, the effective incremental magnetic permeability μΔe of a magnetic circuit composed of a pair of E-shaped cores with a magnetic path length Le and a gap length Lg was determined. Furthermore, using the magnetic field strength Hm of the DC superposition characteristic and the above-mentioned B-H' characteristic, the μΔe-H' characteristic is obtained in a magnetic circuit configured by combining an E-type core with a magnetic path length Le and a gap length Lg. I got it.
Furthermore, the primary inductance L due to the first winding was calculated from the number of turns of the first winding, the magnetic path length Le of the pair of E-shaped cores, and the effective cross-sectional area Ae. FIG. 6 shows the superimposition characteristic of the inductance L, which is obtained by converting the magnetic field strength H' into a superimposed current. It can be seen that among the two types of Mn-based ferrites, ML29D has better superimposition characteristics than ML25D.

(Magnetic core loss)
The operating magnetic flux density was calculated from the peak current flowing through the first winding and was set to 240 mT. FIG. 7 shows the relationship between core loss and temperature calculated at 23° C., 100° C., 130° C., and 150° C. based on the Stein-Metz experimental formula. It can be seen that ML29D has a smaller change in magnetic core loss with respect to temperature than ML25D, and has a smaller magnetic core loss at temperatures from 23° C. to 130° C., and has excellent temperature characteristics.

Based on the obtained results, an isolation transformer was created using Mn-based ferrite: ML29D for an E-type core. The external dimensions of the transformer are 12.5 mm in the X direction, 15.2 mm in the Y direction, and 14.5 mm in the Z direction. The case is made of diallyl phthalate resin, and the bobbin is made of phenolic resin. Two three-layer insulated wires made by bundling four wires with a wire diameter of φ0.14 are used as the first winding, and a polyurethane-coated copper wire (UEW wire) with a wire diameter of φ0.23 is used as the second winding. A polyurethane coated copper wire (UEW wire) with a wire diameter of φ0.23 was used for the winding, and as shown in Figure 4, the first winding sandwiched the second winding and the Vcc winding, and the first winding was made with 7 turns. A coil member was produced with 16 turns of the second winding and 3 turns of the Vcc winding. The outer dimensions of the coil member are 10.2 mm in the X direction, 10.2 mm in the Y direction, and 8.7 mm in the Z direction. The coil member is accommodated in the inner space of the case, and the lead wire of the first winding is pulled out from the top side of the insulation transformer, passed through the groove in the top plate of the case, and then passed along the plane of the wall to the metal terminal 40 (T5 to T8). ) was led out to the first terminal of the terminal, tied together and fixed with solder. In addition, the lead wires of the second winding 85 and the Vcc winding 87 are pulled out from the open side of the case, wrapped around the second terminals of the metal terminals 40 (T1 to T4), and fixed with solder to complete the insulation transformer. Created. The coupling coefficient between the first winding and the second winding at a frequency of 400 kHz was 0.994.

Using the obtained isolation transformer, the DC superposition characteristics of the input side inductance were evaluated under conditions of a frequency of 400 KHz and a temperature of 130°C. The results are shown in FIG. The change in inductance of the isolation transformer is small with respect to the superimposed current, and even when the peak current flowing through the first winding is 1.79 A, the change with respect to the initial inductance is about 0.5 μH. Even under the condition of 2.5 A, the change was as small as about 1.0 μH, and an isolation transformer was obtained that suppressed the magnetic saturation of the core even in a high-temperature environment and ensured a small size and sufficient creepage distance.

1 Insulation transformer 10a, 10b E-type core 30 Bobbin 40 Metal terminal 50 Case 60 Coil parts

Claims (4)

a bobbin including a pair of E-shaped cores, a cylindrical body through which the central leg of the E-shaped core is passed, a first winding formed of a conductive wire wound around the outer periphery of the cylindrical body; a coil member comprising a second winding;
a rectangular case that houses the coil member and includes a first terminal that connects to the first winding and a second terminal that connects to the second winding;
The case includes an inner space surrounded by a base, a wall, and a top plate to accommodate the coil member, and the pair of E-shaped cores and the coil member are arranged in the inner space,
The top plate portion includes a groove portion extending to the wall portion side with a width for leading out the first winding,
The pair of E-shaped cores have an effective cross-sectional area Ae of 15.5 mm ² or more and 21.0 mm ² or less, an effective magnetic path length le of 21.8 mm or more and 24.2 mm or less, and a saturation magnetic flux density Bs at 130°C. An insulating transformer made of Mn-based ferrite with a value of 0.35T or more. The isolation transformer according to claim 1,
Two of the first windings are provided in the groove,
An insulating transformer, wherein the two first windings are separated into a V-shape and led out from the groove, and each is connected to a corresponding first terminal. The isolation transformer according to claim 1 or 2,
The Mn-based ferrite is an insulation transformer having a frequency of 400 kHz, an excitation magnetic flux density of 240 mT, and a core loss of 7000 kW/m ³ or less at a temperature of 23° C. to 130° C. The isolation transformer according to claim 1 or 2,
A reinforced insulated wire is used for at least one of the windings, and the winding portion of the conducting wire constituting the first winding and the winding portion of the conducting wire constituting the second winding constitute the first winding. The winding portions of the conductive wire constituting the second winding are arranged to overlap in the radial direction of the cylindrical body portion so as to sandwich the winding portion of the conductive wire constituting the second winding,
An isolation transformer, wherein a coupling coefficient between the first winding and the second winding at a frequency of 400 kHz is 0.990 or more.

Images