JP2011134744A - Switching transformer and switching power source - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a switching transformer capable of suppressing a surge voltage generated at an output rectifying diode more effectively. <P>SOLUTION: The switching transformer includes a primary coil 1 provided on an input side, a first secondary coil 21 electrically insulated from the primary coil 1 and provided on an output side, and a first auxiliary coil 41 electrically insulated from the first secondary coil 21 and provided on the input side. The first secondary coil 21 and first auxiliary coil 41 are each formed in a plate-like and annular shape, and a coil formation region of the first secondary coil 21 and a coil formation region of the first auxiliary coil 41 are disposed so as to superpose each other. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a switching transformer and a switching power supply using the same.

  Switching power supplies such as an insulating AC (Alternating Current) / DC (Direct Current) converter and a DC / DC converter using a switching transformer are used in various applications. Such a switching power supply is provided with a relatively large heat sink for removing heat generated by internal loss. Therefore, in order to reduce the size of the switching power supply, it is effective to reduce the size of the relatively large heat sink. For this purpose, it is necessary to reduce internal loss and suppress heat generation by increasing efficiency.

  Generally, a diode (output rectifier diode) is used for rectification of the secondary (output) side coil of the transformer. Since the ratio of the loss of the output rectifier diode is the largest among the internal losses, it is important to reduce the loss of the output rectifier diode.

  Here, there are two types of output rectifier diodes, a Schottky diode and a fast recovery diode. The fast recovery diode has a high withstand voltage but a large forward voltage drop. On the other hand, the Schottky diode has a low withstand voltage but a small forward voltage drop. Therefore, if a Schottky diode with a low withstand voltage can be used, loss due to a forward voltage drop can be reduced.

  However, in a switching power supply using a switching transformer, a surge voltage is generated, so that a fast recovery diode having a high withstand voltage is usually used as an output rectifier diode. In addition, it is conceivable to use a Schottky diode with a low withstand voltage as the output rectifier diode after suppressing the surge voltage with a snubber circuit, etc., but since the loss due to the snubber circuit increases, the loss should be reduced as a whole. I can't.

  On the other hand, in order to reduce the surge voltage, a method is known in which an auxiliary coil having a smaller number of turns than the primary coil is provided on the primary coil side of the switching transformer. Thereby, the surge voltage of the output rectifier diode can be clamped.

  Patent Document 1 discloses a primary coil patterned on a printed circuit board.

JP 2004-303857 A

  As described above, the smaller the forward voltage drop of the output rectifier diode, that is, the lower the withstand voltage, the smaller can be achieved by higher efficiency. For this purpose, it is necessary to increase the magnetic coupling between the secondary coil and the auxiliary coil of the switching transformer and more effectively suppress the surge voltage of the output rectifier diode.

  The present invention has been made in view of the above technical background, and an object thereof is to provide a switching transformer that can more effectively suppress a surge voltage generated in an output rectifier diode.

The switching transformer according to the first aspect of the present invention includes:
A primary coil provided on the input side;
A first secondary coil electrically insulated from the primary coil and provided on the output side;
A switching transformer comprising: a first auxiliary coil electrically insulated from the first secondary coil and provided on the input side;
Both the first secondary coil and the first auxiliary coil are formed in a flat plate shape and an annular shape,
The coil formation region of the first secondary coil and the coil formation region of the first auxiliary coil are arranged so as to overlap each other.
Thereby, the magnetic coupling between the auxiliary coil and the secondary coil can be increased, and the surge voltage can be effectively suppressed.

A switching transformer according to a second aspect of the present invention is the first aspect,
The first auxiliary coil is
A printed circuit board;
A wiring patterned in a spiral shape is provided on the printed circuit board.
Thereby, productivity can be improved.

A switching transformer according to a third aspect of the present invention is the second aspect,
The wiring is patterned on both sides of the printed board and integrated by through holes penetrating the printed board.
As a result, the number of turns of the coil can be increased without increasing the space, and the drawing of the wiring can be facilitated.

The switching transformer according to a fourth aspect of the present invention is characterized in that, in the first to third aspects, the first secondary coil is a one-turn coil made of a plate-like bus bar.
As a result, the magnetic coupling between the auxiliary coil and the secondary coil can be reliably increased.

A switching transformer according to a fifth aspect of the present invention is the first to fourth aspects, wherein the switching transformer is electrically insulated from the primary coil and faces the first secondary coil via the primary coil on the output side. A second secondary coil disposed;
A second auxiliary coil electrically insulated from the second secondary coil and provided on the input side;
Both the second secondary coil and the second auxiliary coil are formed in a flat plate shape and an annular shape,
The coil forming region of the second secondary coil and the coil forming region of the second auxiliary coil are arranged so as to overlap each other.

  A switching power supply according to a sixth aspect of the present invention includes the switching transformer according to any one of the first to fifth aspects, and includes an output rectifier diode connected to the first secondary coil.

A switching power supply according to a seventh aspect of the present invention is the sixth aspect,
The output rectifier diode is a Schottky diode.
Thereby, the loss by an output rectifier diode can be reduced.

  ADVANTAGE OF THE INVENTION According to this invention, the switching transformer which can suppress the surge voltage of an output rectifier diode more effectively can be provided.

2 is an exploded perspective view of the switching transformer according to Embodiment 1. FIG. FIG. 3 is an assembled perspective view of the switching transformer according to the first embodiment. 2 is a top view and a bottom view of an auxiliary coil according to Embodiment 1. FIG. 2 is a top perspective view of an auxiliary coil according to Embodiment 1. FIG. 1 is a circuit diagram of an isolated DC / DC converter according to Embodiment 1. FIG.

  Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings. However, the present invention is not limited to the following embodiment. In addition, for clarity of explanation, the following description and drawings are simplified as appropriate.

(Embodiment 1)
FIG. 1 is an exploded perspective view of the switching transformer according to the first embodiment of the present invention. The switching transformer includes a primary coil 1, a pair of secondary coils 21, 22, two pairs of insulating sheets 31, 32, 51, 52, a pair of auxiliary coils 41, 42, and a pair of cores 61, 62. I have.

  The primary coil 1 is, for example, a winding coil in which a copper wire having a diameter of about 2 to 3 mm is spirally wound in the longitudinal direction of the primary coil 1 eight times (8 turns), and formed into a cylindrical shape as a whole. is there. In FIG. 1, the primary coil 1 is schematically drawn in a cylindrical shape. The material of the primary coil 1 is not limited to a copper wire, and may be other metal wires. Further, the number of turns is also determined as appropriate.

  As shown in FIG. 1, a secondary coil 21 is disposed on the upper side of the cylindrical primary coil 1, and a secondary coil 22 is disposed on the lower side. The secondary coils 21 and 22 are both electrically insulated from the primary coil 1 by an insulator (not shown). On the other hand, the secondary coils 21 and 22 are both magnetically coupled to the primary coil 1. Here, each of the secondary coils 21 and 22 is a one-turn coil, and is a bus bar made of, for example, a copper plate having a thickness of about 1 mm. In the present embodiment, the secondary coils 21 and 22 are each formed of a one-turn coil bus bar, but may be formed in a flat plate shape and an annular shape, for example, a pattern formed on a printed board. . Here, the reason why the secondary coils 21 and 22 are formed in a flat plate shape and an annular shape is to improve magnetic coupling with auxiliary coils 41 and 42 described later.

  As shown in FIG. 1, the secondary coil 21 includes a coil portion 21a and a terminal portion 21b. The coil portion 21a is formed in an annular shape (ring shape, donut shape), and a part of the ring is divided. Then, a pair of terminal portions 21b are formed so as to protrude from both ends of the divided coil portion 21a. A through hole for electrical connection is formed at the tip of each terminal portion 21b.

  Similarly, the secondary coil 22 includes a coil portion 22a and a terminal portion 22b. The coil portion 22a is formed in an annular shape (ring shape, donut shape), and a part of the ring is divided. And it forms so that a pair of terminal part 22b may protrude from the both ends of the divided coil part 22a. A through hole for electrical connection is formed at the tip of each terminal portion 22b.

  As shown in FIG. 1, the terminal portions 21b and 22b are appropriately bent according to the position of the wiring. Similar to the primary coil 1, the material of the secondary coils 21 and 22 is not limited to the copper plate, and may be, for example, an aluminum plate or another metal plate.

  As shown in FIG. 1, an insulating sheet 31 is disposed above the secondary coil 21, and an insulating sheet 32 is disposed below the secondary coil 22. The insulating sheets 31 and 32 have the same shape, and both are formed in an annular shape (ring shape or donut shape), and are made of, for example, nomex paper having a thickness of about 0.1 mm. However, the present invention is not limited to this, and other insulating materials can be used.

  As shown in FIG. 1, the auxiliary coil 41 is disposed above the insulating sheet 31, and the auxiliary coil 42 is disposed below the insulating sheet 32. The auxiliary coils 41 and 42 are coils provided on the primary (input) side in order to reduce a surge voltage due to switching, and have fewer turns than the primary coil 1. Further, the auxiliary coils 41 and 42 are electrically insulated by the secondary coils 21 and 22 and the insulating sheets 31 and 32, respectively. On the other hand, the auxiliary coils 41 and 42 are both magnetically coupled to the secondary coils 21 and 22. Details of the structure of the auxiliary coils 41 and 42 will be described later.

  As shown in FIG. 1, an insulating sheet 51 is disposed above the auxiliary coil 41, and an insulating sheet 52 is disposed below the auxiliary coil 42. Since the insulating sheets 51 and 52 are the same as the insulating sheets 31 and 32, description thereof is omitted.

  As shown in FIG. 1, the core 61 is disposed above the insulating sheet 51, and the core 62 is disposed below the insulating sheet 52. The cores 61 and 62 have the same shape, and include convex portions 61a and 62a and storage portions 61b and 62b, respectively. That is, the cores 61 and 62 have a so-called PQ type shape, and are made of ferrite, for example.

  Here, FIG. 2 is an assembly perspective view of the switching transformer of FIG. As shown in FIGS. 1 and 2, the convex portions 61 a and 62 a of the cores 61 and 62 are arranged to face each other. Then, the cores 61 and 62 having the same shape are disposed so as to abut against each other and to be mirror-symmetric with respect to the abutting surface in the assembled state.

  In the assembled state, the convex portions 61 a and 62 a of the cores 61 and 62 are formed of the primary coil 1, the pair of secondary coils 21 and 22, the two pairs of insulating sheets 31, 32, 51 and 52, and the pair of auxiliary coils 41. , 42 is inserted into a hole formed in the central portion. On the other hand, the coil portions 21a and 22a of the primary coil 1, the pair of secondary coils 21 and 22, the two pairs of insulating sheets 31, 32, 51 and 52, and the coil portions of the pair of auxiliary coils 41 and 42 are cores. 61 and 62 are accommodated in the accommodating portions 61b and 62b. Further, the terminal portions 21b and 22b of the secondary coils 21 and 22 protrude from one open portion of the storage portions 61b and 62b, and the terminal portions of the auxiliary coils 41 and 42 protrude from the open portion on the opposite side.

  Next, details of the structure of the auxiliary coils 41 and 42 will be described with reference to FIGS. FIG. 3 is a top view (a) and a bottom view (b) of the auxiliary coils 41, 42. Since the auxiliary coils 41 and 42 have the same structure, FIG. 3 shows the auxiliary coil 41. As shown in FIGS. 3A and 3B, the auxiliary coil 41 includes a printed circuit board 4a, a wiring 4b, a through hole 4c, and terminal holes 4d and 4e.

  Here, as shown in FIG. 3A, wiring 4b made of copper extending from the terminal hole 4d to the through hole 4c is spirally patterned on the upper surface of the printed board 4a. On the other hand, as shown in FIG. 3B, a wiring 4b made of copper from the terminal hole 4e to the through hole 4c is spirally patterned on the lower surface of the printed board 4a. For example, the copper wiring has a thickness of 35 μm and a width of 1 mm.

  Here, FIG. 4 is a top perspective view of the auxiliary coil 41. The solid line shows the wiring 4b formed on the upper surface, and the dotted line shows the wiring 4b formed on the lower surface. As shown in FIG. 4, the wiring 4b formed on the upper and lower surfaces of the printed board 4a is integrally formed through the through hole 4c, and constitutes the auxiliary coil 41 as a whole. 3 and 4 show an example of the auxiliary coil 41 having 7 turns (7 turns), the number of turns is not limited to this.

  As described above, in the switching transformer according to the present embodiment, the secondary coils 21 and 22 are one-turn coils configured by plate-like bus bars. The auxiliary coils 41 and 42 are composed of wiring 4b patterned on the printed circuit board 4a. That is, the secondary coils 21 and 22 and the auxiliary coils 41 and 42 are not wound coils wound in the vertical direction like the primary coil 1, and are both formed in a flat plate shape and an annular shape. And the coil formation area of the secondary coil 21 and the auxiliary coil 41 is arrange | positioned so that the coil formation area of the secondary coil 22 and the auxiliary coil 41 may overlap, respectively.

  With such a configuration, the magnetic coupling between the auxiliary coil 41 and the secondary coil 21, and the auxiliary coil 42 and the secondary coil 22 can be increased. As a result, a surge voltage due to switching can be reduced, and an output rectifier diode, which will be described later, can be used that has low internal loss and low withstand voltage. Specifically, the withstand voltage of a fast recovery diode that has been conventionally used can be lowered. Further, the withstand voltage can be further reduced by replacing the fast recovery diode with a Schottky diode.

  Further, in the auxiliary coils 41 and 42, the wiring 4b is formed in a spiral shape on both the upper and lower surfaces of one printed circuit board 4a, so that the number of turns of the coil can be increased without increasing the space. At the same time, the wiring 4b can be easily drawn out to the terminal holes 4d and 4e. Further, as described above, the wirings 4b formed on both the upper and lower surfaces have the same shape, and the upper and lower surfaces of the printed circuit board 4a are not distinguished from each other. Further, since there is no distinction between the auxiliary coil 41 and the auxiliary coil 42, they can be made the same part, and handling becomes easy and productivity is improved.

  Next, an insulated DC / DC converter that is an aspect of a switching power supply using the switching transformer according to the present embodiment will be described with reference to FIG. FIG. 5 is a circuit diagram of the isolated DC / DC converter according to the first embodiment. As shown in FIG. 5, the circuit of this insulation type DC / DC converter is a full-bridge two-phase full-wave rectification circuit, and converts a DC voltage of 334V into a DC voltage of 14V. For example, it is used to generate an auxiliary machine voltage in an electric vehicle or a hybrid car. The configuration according to the present embodiment is suitable for voltage conversion from about 100V to V400V to about 8V to 15V, for example.

  The isolated DC / DC converter according to the first embodiment includes a switching transformer T, switching transistors TR1 to TR4, surge clamping diodes D1 to D4, a resonance coil L1, output rectifier diodes OD1 and OD2, and snubber circuits SC1 and SC2. A smoothing coil L2 and a smoothing capacitor C1 are provided. Here, the switching transformer T is the switching transformer shown in FIG. 1 and includes a primary coil, secondary coils 21 and 22, and auxiliary coils 41 and.

  The switching transistors TR1 to TR4 are all n-type field effect transistors, and are repeatedly turned on and off at a frequency of, for example, several tens of kHz to several hundreds of kHz based on a control signal input to each gate of the switching transistors TR1 to TR4. ing. Here, the switching transistors TR1 and TR4 are turned on or off at the same timing, and the switching transistors TR2 and TR3 are turned on or off at the same timing. On the other hand, the switching transistors TR1 and TR4 and the switching transistors TR2 and TR3 are turned on or off in a complementary manner.

  Here, the drains of the switching transistors TR1 and TR3 are both connected to the input side high potential terminal P, and the sources are connected to the drains of the switching transistors TR2 and TR4, respectively. The sources of the switching transistors TR2 and TR4 are both connected to the input-side low potential terminal N.

  One end of the resonance coil L1 is connected to a node between the source of the switching transistor TR1 and the drain of the switching transistor TR2. The other end of the resonance coil L1 is connected to one end of the primary coil 1. The other end of the primary coil 1 is connected to a node between the source of the switching transistor TR3 and the drain of the switching transistor TR4.

  The cathode of the surge clamping diode D1 is connected to the input side high potential terminal P, and the anode is connected to the cathode of the surge clamping diode D2. The anode of the surge clamp diode D2 is connected to the input side low potential terminal N. That is, the surge clamping diodes D1 and D2 are connected in series. Similarly, the cathode of the surge clamp diode D3 is connected to the input side high potential terminal P, and the anode is connected to the cathode of the surge clamp diode D4. The anode of the surge clamp diode D4 is connected to the input side low potential terminal N. That is, the surge clamping diodes D3 and D4 are connected in series. The surge clamp diodes D1 and D2 connected in series and the surge clamp diodes D3 and D4 connected in series are connected in parallel.

  One end of the auxiliary coil 41 is connected to a node between the surge clamp diodes D1 and D2 connected in series, and the other end is connected to a node between the surge clamp diodes D3 and D4 connected in series. With such a configuration, a surge transmitted from the secondary coil 21 can be clamped.

  Similarly, one end of the auxiliary coil 42 is connected to a node between the surge clamp diodes D1 and D2 connected in series, and the other end is connected to a node between the surge clamp diodes D3 and D4 connected in series. Yes. With such a configuration, a surge transmitted from the secondary coil 22 can be clamped.

  As described above, the secondary coils 21 and 22 are electrically insulated from the primary coil 1 and the auxiliary coils 41 and 42 and are magnetically coupled. One ends of the secondary coils 21 and 22 are both grounded. That is, it is connected to the ground GND. The other ends of the secondary coils 21 and 22 are connected to the anodes of the output rectifier diodes OD1 and OD2, respectively. The cathodes of the output rectifier diodes OD1 and OD2 are both connected to one end of the smoothing coil L2. The other end of the smoothing coil L2 is connected to the output side high potential terminal B. One end of the smoothing capacitor C1 is connected to the output side high potential terminal B, and the other end is grounded. With such a configuration, the smoothing coil L2 and the smoothing capacitor C1 smooth the output voltage.

  Each of the snubber circuits SC1 and SC2 includes a capacitor and a resistor connected in series. The snubber circuit SC1 is connected in parallel with the output rectifier diode OD1, and protects the output rectifier diode OD1 from a surge. The snubber circuit SC2 is connected in parallel with the output rectifier diode OD2, and protects the output rectifier diode OD2 from a surge.

  Next, the operation of the insulated DC / DC converter using the switching transformer according to the present embodiment will be described with reference to FIG. When the switching transistors TR1 and TR4 are switched from OFF to ON and the switching transistors TR2 and TR3 are switched from ON to OFF, a downward current flows in the primary coil 1 in FIG. In this case, an upward current in FIG. 5 flows through the secondary coil 21, and an output voltage is generated via the output rectifier diode OD1. Further, the surge voltage generated on the output rectifier diode OD2 side due to this switching is clamped by the auxiliary coil 42 via the secondary coil 22.

  On the other hand, when the switching transistors TR2 and TR3 are switched from OFF to ON and the switching transistors TR1 and TR4 are switched from ON to OFF, an upward current flows in the primary coil 1 in FIG. In this case, a downward current in FIG. 5 flows through the secondary coil 22, and an output voltage is generated via the output rectifier diode OD2. Further, the surge voltage generated on the output rectifier diode OD1 side due to this switching is clamped by the auxiliary coil 41 via the secondary coil 21.

  As described above, in the switching transformer according to the embodiment of the present invention, the secondary coils 21 and 22 and the auxiliary coils 41 and 42 are both wound coils wound in the vertical direction like the primary coil 1. Instead, they are all formed in a flat plate shape and an annular shape. And the coil formation area of the secondary coil 21 and the auxiliary coil 41, and the coil formation area of the secondary coil 22 and the auxiliary coil 41 are respectively arranged via insulators (insulating sheets 31 and 32 in the present embodiment). They are arranged so as to overlap.

  With such a configuration, the magnetic coupling between the auxiliary coil 41 and the secondary coil 21, and the auxiliary coil 42 and the secondary coil 22 can be increased. As a result, the surge voltage due to switching can be reduced, and the output rectifier diodes OD1 and OD2 that have low internal loss and low withstand voltage can be used. Specifically, the withstand voltage of a fast recovery diode that has been conventionally used can be lowered. Further, the withstand voltage can be further reduced by replacing the fast recovery diode with a Schottky diode. Heat generation is suppressed by this high efficiency, and it is possible to contribute to the miniaturization of the heat sink and the entire AC / DC converter and DC / DC converter device.

1 Primary coil 21, 22 Secondary coil 21a, 22a Coil portion 21b, 22b Terminal portion 31, 32, 51, 52 Insulation sheet 41, 42 Auxiliary coil 4a Printed circuit board 4b Wiring 4c Through hole 4d, 4e Terminal holes 61, 62 Core 61a, 62a Convex part 61b, 62b Storage part B Output side high potential terminal C1 Smoothing capacitor D1-D4 Surge clamp diode L1 Resonance coil L2 Smoothing coil N Input side low potential terminal OD1, OD2 Output rectifier diode P Input side high Potential terminals SC1, SC2 Snubber circuit T Switching transformer
TR1-TR4 switching transistor

Claims (7)

A primary coil provided on the input side;
A first secondary coil electrically insulated from the primary coil and provided on the output side;
A switching transformer comprising: a first auxiliary coil electrically insulated from the first secondary coil and provided on the input side;
Both the first secondary coil and the first auxiliary coil are formed in a flat plate shape and an annular shape,
A switching transformer in which a coil formation region of the first secondary coil and a coil formation region of the first auxiliary coil overlap each other. The first auxiliary coil is
A printed circuit board;
The switching transformer according to claim 1, further comprising: a wiring patterned in a spiral shape on the printed circuit board.   3. The switching transformer according to claim 2, wherein the wiring is patterned on both surfaces of the printed circuit board and integrated by through holes penetrating the printed circuit board.   The switching transformer according to any one of claims 1 to 3, wherein the first secondary coil is a one-turn coil including a plate-like bus bar. A second secondary coil that is electrically insulated from the primary coil and disposed opposite to the first secondary coil via the primary coil on the output side;
A second auxiliary coil electrically insulated from the second secondary coil and provided on the input side;
The second secondary coil and the second auxiliary coil are both formed in a flat plate shape and an annular shape,
5. The coil forming region of the second secondary coil and the coil forming region of the second auxiliary coil are arranged so as to overlap each other. 6. Switching transformer. The switching transformer according to any one of claims 1 to 5 is provided,
A switching power supply comprising an output rectifier diode connected to the first secondary coil.   The switching power supply according to claim 6, wherein the output rectifier diode is a Schottky diode.

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