JP2008085004A - Loosely-coupled transformer and switching power supply - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain miniaturization and reduce external magnetic flux leakage by setting a coupling coefficient between winding coils at a suitable value. <P>SOLUTION: This loosely-coupled transformer comprises an E-shaped ferrite core 10 having a central leg 11, side legs 12 and a plate-like member 13; an E-shaped ferrite core 20 having a central leg, side legs 22 and a plate-like member 23 linking the central leg and the side legs 22; a nearly square-shaped ferrite core 30 disposed between the side legs 12 and the side legs 22; a primary winding 40 provided inside the side legs 12 and around the central leg 11; and a secondary winding 50 provided inside the side legs 22 and around the central leg. A first magnetic gap is defined between the central legs, and a second magnetic gap is formed between the side surfaces of the central legs and the inner surface of the nearly square-shaped ferrite core 30. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a loosely coupled transformer mainly used for a main transformer of a resonance type DC-DC converter and a switching power supply including the same.

  Conventionally, in this type of loosely coupled transformer, the coupling between the primary coil (primary winding) and the secondary coil (secondary winding) is lowered by providing a leakage leg in the horizontal-shaped magnetic core, or 1 A structure is adopted in which the distance between the secondary coil and the secondary coil is increased to reduce the degree of coupling between the coils. For example, there are Patent Document 1 and Patent Document 2 below.

Japanese Utility Model Publication No. 61-179696 Japanese Utility Model Publication No. 5-73926

  However, as the switching frequency increases, miniaturization of the transformer is required. However, the conventional structure is difficult to cope with in terms of securing the floor area and the distance between the coils.

  Conventionally, as means for reducing the coupling coefficient of the transformer, means for increasing the distance between the coils of the primary and secondary coils or providing a leakage foot or the like have been taken. However, increasing the distance between the coils increases the floor area. In addition, if the coupling coefficient is lowered with a leakage foot or the like, a large leakage magnetic flux is generated from the transformer due to the lowering of the coupling coefficient, and there is a high possibility that eddy current loss and noise will be adversely affected on the printed circuit board wiring pattern and peripheral components. (In particular, it becomes a problem when using high frequency.) As a result, heat may be generated in the primary and secondary coils, the copper foil of the printed board, and the like, which may be a source of radiation noise. In order to prevent the generation of radiation noise, it is necessary to cover the entire transformer with a metal case or the like. However, there is a problem that the metal case itself generates heat, leading to an increase in cost.

  An object of the present invention is to provide a loosely coupled transformer in which the coupling coefficient between coils can be set to an appropriate value and the size of the coil is reduced and leakage of magnetic flux to the outside is reduced.

  Other objects and novel features of the present invention will be clarified in embodiments described later.

To achieve the above object, a loosely coupled transformer according to a first aspect of the present invention includes a first central leg, a first side leg surrounding at least both sides thereof, the first central leg, and the first central leg. A first magnetic core having a first plate-like portion connecting the side legs of the first magnetic core;
A second central leg; a second side leg surrounding at least both sides of the second central leg; and a second plate-like portion connecting the second central leg and the second side leg. A second magnetic core;
A ring-shaped magnetic core sandwiched between the first side leg and the second side leg;
A first coil provided around the first central leg inside the first side leg;
A second coil provided around the second central leg inside the second side leg,
A first magnetic gap is provided between the first and second central legs, and a second magnetic gap is provided between a side surface of the first and second central legs and an inner surface of the ring-shaped magnetic core. It is a feature.

  In the loosely coupled transformer of the first aspect, the first and second magnetic cores may be E-shaped cores, and the ring-shaped magnetic core may be a rectangular core.

  In the loosely coupled transformer according to the first aspect, the first magnetic gap may be surrounded by the ring-shaped magnetic core.

The loosely coupled transformer according to the second aspect of the present invention includes a first central leg, a first side leg surrounding at least both sides thereof, a first central leg and the first side leg connected to each other. A first magnetic core having one plate-like portion;
A second magnetic core having a second plate-like portion and second side legs provided on at least both sides of the second plate-like portion;
A ring-shaped magnetic core sandwiched between the first side leg and the second side leg;
A first coil provided around the first central leg inside the first side leg;
A second coil provided around the first central leg inside the second side leg,
A first magnetic gap is provided between the first central leg and the second plate-like portion, and a second magnetic gap is provided between the side surface of the first central leg and the inner surface of the ring-shaped magnetic core. It is characterized by that.

  In the loosely coupled transformer of the second aspect, the first magnetic core is an E-type core, the second magnetic core is a U-type core, and the ring-shaped magnetic core is a R-shaped core. It is characterized by.

  In the loosely coupled transformer of the first or second aspect, the coil may be formed of a multilayer substrate on which a conductor pattern is formed.

  A switching power supply according to a third aspect of the present invention includes the loosely coupled transformer according to the first or second aspect.

  The loosely coupled transformer according to the present invention can provide the following effects.

(1) Between the first central leg of the first magnetic core and the second central leg of the second magnetic core, or the first central leg of the first magnetic core and the second magnetic core The self-inductance of each of the first and second coils can be mainly adjusted by the size of the first magnetic gap provided between the second plate-like portion and the second plate-like portion.

(2) The degree of coupling between the first and second coils is mainly determined by the size of the second magnetic gap between the inner surface of the ring-shaped magnetic core provided between the first and second magnetic cores and the central leg. Can be adjusted.

(3) Therefore, even if the self-inductance of each coil requires a relatively large value and the degree of coupling needs to be low, such as the main transformer of a resonant DC-DC converter, for example, Since the degree of coupling can be appropriately set with the magnetic gap, it is not necessary to increase the first magnetic gap, and the self-inductance can be maintained large. Further, since it is not necessary to increase the interval between the coils in order to reduce the degree of coupling, the size can be reduced.

(4) The magnetic flux leakage can be shielded by the ring-shaped magnetic core, and magnetic flux leakage to the outside can be reduced to prevent adverse effects on other components.

  In the following, embodiments of a loosely coupled transformer and a switching power supply will be described with reference to the drawings as the best mode for carrying out the present invention.

  In the embodiment of the loosely coupled transformer of FIGS. 1 to 4, the loosely coupled transformer 1 mainly used for the main transformer of the resonant DC-DC converter is an E as a first and second vertical magnetic core. Type ferrite cores 10 and 20 (including shapes modified from other basic E-types), and a R-shaped ferrite core (rectangular ring type ferrite core) 30 as an intermediate ring-shaped magnetic core, A primary coil 40 and a secondary coil 50 are provided.

  As can be seen from the cross-sectional view of FIG. 3 and the core structure of FIG. 4, the E-type ferrite core 10 includes a central leg 11, side legs 12 surrounding both sides thereof, and a plate connecting the central leg 11 and the left and right side legs 12. Similarly, the E-type ferrite core 20 includes a central leg 21, side legs 22 surrounding both sides thereof, and a plate-like part 23 that connects the central leg 21 and the left and right side legs 22. Have. A square-shaped ferrite core 30 is sandwiched (intervened) between the side legs 12 of the E-type ferrite core 10 and the side legs 22 of the E-type ferrite core 20. In other words, the side legs 12 are in contact with the upper surface of the R-shaped ferrite core 30 and the side legs 22 are in contact with the lower surface.

  The center legs 11 and 21 are longer than the side legs 12 and 22, respectively, and a first magnetic gap G1 is provided between the front end surfaces of the center legs 11 and 21, as shown in FIG. A second magnetic gap G <b> 2 is provided between the side surfaces of the center legs 11, 21 and the inner surface of the square-shaped ferrite core 30.

  The primary coil 40 and the secondary coil 50 may be a winding wound with an insulation-coated conductive wire, but may be formed of a multilayer substrate on which a conductor pattern is wound around a required number of times. The primary coil 40 is disposed around the center leg 11 inside the left and right side legs 12 of the E-type ferrite core 10, and the secondary coil 50 is located inside the left and right side legs 22 of the E-type ferrite core 20. Arranged around the center leg 21. Therefore, the square ferrite core 30 is located between the primary coil 40 and the secondary coil 50.

  In the case of a main transformer of a resonance type DC-DC converter, it is necessary to satisfy conditions such as a self-inductance, a leakage inductance, and a coupling coefficient between the primary and secondary coils. In the conventional transformer structure, if the distance between the primary and secondary coils is increased in order to reduce the coupling degree, that is, the coupling coefficient, the size cannot be reduced, and if the magnetic gap between the central legs is increased, the self-inductance decreases. In addition, if a leakage leg is further provided, there is a problem that magnetic flux leakage to the outside cannot be prevented.

  In the embodiment of the present invention, the above-mentioned problem is caused by interposing the R-shaped ferrite core 30 between the E-type ferrite core 10 provided with the primary coil 40 and the E-type ferrite core 20 provided with the secondary coil 50. The point is solved.

  3 is a cross-sectional view of the magnetic circuit including the first and second magnetic cores 10 and 20 and the square ferrite core 30 in FIG. 3, and the magnetic path of the magnetic flux generated when the primary coil 40 and the secondary coil 50 are energized. It can be considered that there is a main magnetic path Φ1 and auxiliary magnetic paths Φ2, Φ3, and by reducing the first magnetic gap G1 of the main magnetic path Φ1, the self-inductance of the primary and secondary coils 40, 50 Can be set large (there is a relationship of G1 decrease → self inductance increase).

  On the other hand, the secondary magnetic path Φ2 circulates only around the primary coil 40, and the secondary magnetic path Φ3 circulates only around the secondary coil 50. The ratio of the magnetic flux passing through the secondary magnetic paths Φ2 and Φ3 is increased or decreased. By doing so, the degree of coupling (coupling coefficient) between the primary and secondary coils 40 and 50 can be greatly changed.

  That is, if the second magnetic gap G2 in the secondary magnetic paths Φ2 and Φ3 is large, the magnetic resistance of the secondary magnetic paths Φ2 and Φ3 is large, and the ratio of the magnetic flux flowing through the main magnetic path Φ1 is large, and the secondary magnetic paths Φ2, Φ3 The proportion of magnetic flux flowing through is small. Since the main magnetic path Φ1 is a magnetic path contributing to the coupling between the primary and secondary coils 40 and 50, the degree of coupling is high.

  Conversely, when the second magnetic gap G2 in the secondary magnetic paths Φ2 and Φ3 is reduced, the magnetic resistance of the secondary magnetic paths Φ2 and Φ3 is reduced, and the ratio of the magnetic flux flowing through the main magnetic path Φ1 is reduced, and the secondary magnetic path Φ2 , Φ3 increases the proportion of magnetic flux. Since the secondary magnetic paths Φ2 and Φ3 are magnetic paths that do not contribute to the coupling between the primary and secondary coils 40 and 50, the degree of coupling is low.

  According to this embodiment, the following effects can be obtained.

(1) In the case of a main transformer of a resonance type DC-DC converter, it is necessary to satisfy conditions such as self-inductance, leakage inductance, and coupling coefficient between primary and secondary coils (for example, coupling coefficient k≈0.7). However, in this embodiment, the self-inductance of the primary and secondary coils 40 and 50 can be changed greatly in the second magnetic gap G2 without much change, and the first magnetic The self-inductance and the leakage inductance of the primary and secondary coils 40 and 50 can be set to appropriate values with the gap G1. That is, the self-inductance and the coupling coefficient can be designed independently by adjusting the two magnetic gaps G1 and G2. Further, since it is not necessary to increase the interval between the coils in order to reduce the degree of coupling, the size can be reduced.

(2) Both the first magnetic gap G1 and the second magnetic gap G2 are in a positional relationship surrounded by a square-shaped ferrite core 30 having a rectangular ring shape. The leakage magnetic flux can be shielded, and adverse effects on other components can be prevented. In other words, it is possible to reduce the influence of the leakage magnetic flux on the wiring pattern of the printed circuit board and the electronic components arranged around the printed circuit board.

(3) The primary coil 40 and the secondary coil 50 are located away from the first magnetic gap G1, and the eddy currents of the primary coil 40 and the secondary coil 50 due to the leakage magnetic flux from the first magnetic gap G1. Loss and associated heat generation can be prevented. The leakage magnetic flux from the second magnetic gap G2 is generated substantially in parallel with the winding surfaces of the primary coil 40 and the secondary coil 50, and the influence is small because the amount of magnetic flux is small. Therefore, for example, when the planar transformer is formed by reducing the size and thickness of the coils 40 and 50 using a multilayer substrate, the heat generation of the coils can be reduced.

  FIG. 5 shows another embodiment of the loosely coupled transformer according to the present invention, which is an example in which the shape of the magnetic core is partially changed. In FIG. 5, a loosely coupled transformer 1A includes an E-type ferrite core 60 (which includes other basic E-shaped shapes) as a first and second vertical magnetic core, and a U-type. A ferrite core 70, a square-shaped ferrite core (square ring ferrite core) 30 as an intermediate ring-shaped magnetic core, a primary coil 40, and a secondary coil 50 are provided.

  The E-type ferrite core 60 has a center leg 61, side legs 62 surrounding both sides thereof, and a plate-like portion 63 that connects the center leg 61 and the left and right side legs 62. The U-type ferrite core 70 has left and right sides. It has the side leg 72 and the plate-shaped part 73 which connects them. The square-shaped ferrite core 30 is sandwiched (intervened) between the side legs 62 of the E-type ferrite core 60 and the side legs 72 of the U-type ferrite core 70. In other words, the side legs 62 are in contact with the upper surface of the R-shaped ferrite core 30 and the side legs 72 are in contact with the lower surface.

  The central leg 61 is longer than the side legs 62, and a first magnetic gap G 1 is provided between the tip surface of the central leg 61 and the plate-like portion 73. A second magnetic gap G <b> 2 is provided between the side surface of the central leg 61 and the inner surface of the square-shaped ferrite core 30.

  The primary coil 40 is disposed around the central leg 61 inside the left and right side legs 62 of the E-type ferrite core 60, and the secondary coil 50 is located inside the left and right side legs 22 of the U-type ferrite core 70. Arranged around the center leg 61. Therefore, the square ferrite core 30 is located between the primary coil 40 and the secondary coil 50.

  In this case, the position of the first magnetic gap G1 is different from that in the embodiment shown in FIGS. 1 to 4, but the self-magnetism is adjusted in the same manner as in the embodiment shown in FIGS. 1 to 4 by adjusting the two magnetic gaps G1 and G2. The inductance and the coupling coefficient can be designed independently and set to appropriate values, and the same effect can be obtained.

  In the present invention, it is also possible to employ a pot-type core having side legs that substantially surround the entire circumference of the center leg as the first and second magnetic cores, and between the first and second magnetic cores. The shape of the ring-shaped magnetic core interposed between the first and second magnetic cores may be a circular ring other than the square shape in accordance with the shapes of the first and second magnetic cores.

  FIG. 6 shows an example of a circuit configuration of a switching power supply including the above-described loosely coupled transformers 1 and 1A, and shows a half-bridge type. In FIG. 6, two equal-capacitance capacitors C1 and C2 are connected in series to the DC power supply 80, and two switching elements S1 and S2 are connected. One end of the primary coil 40 of the loosely coupled transformer 1, 1A is connected to the connection point of the capacitors C1, C2, and the other end is connected to the connection point of the switching elements S1, S2. When the switching elements S1 and S2 are alternately turned on and off, a current whose direction is periodically reversed can be passed through the primary coil 40. The switching frequency can be set to, for example, 1 MHz or more.

  The secondary coil 50 of the loosely coupled transformer 1, 1A is connected to a rectifying / smoothing circuit composed of diodes D1, D2 and a capacitor C3 for rectifying and smoothing the induced voltage. The output of the rectifying / smoothing circuit is the load RL. To be supplied.

  Since the switching power supply having such a loosely coupled transformer 1, 1 A can reduce the size of the loosely coupled transformer part and can arrange components near the loosely coupled transformer due to the effect of shielding the leakage magnetic flux from the magnetic gap. The configuration can also be reduced in size.

  In addition, as a circuit configuration of the switching power supply of the present invention, a circuit configuration other than the half-bridge method is possible, and if necessary, the loosely coupled transformer of the present invention is added to the primary coil or the secondary coil and another coil. Can be provided in the first or second magnetic core. Moreover, a midpoint tap can also be provided in a primary coil or a secondary coil.

  Although the embodiments of the present invention have been described above, it will be obvious to those skilled in the art that the present invention is not limited to these embodiments, and various modifications and changes can be made within the scope of the claims.

1 is a perspective view showing an embodiment of a loosely coupled transformer according to the present invention. It is the same exploded perspective view. It is the longitudinal cross-sectional view. It is a perspective view which shows the magnetic core structure in embodiment. It is a perspective view which shows other embodiment of the loose coupling transformer which concerns on this invention. It is a circuit diagram of a switching power supply provided with a loosely coupled transformer according to the present invention.

Explanation of symbols

1,1A Loosely coupled transformer
10, 20, 60 E-type ferrite core 11, 21, 61 Central leg 12, 22, 62, 72 Side leg 13, 23, 63, 73 Plate-shaped part 30 Ro-shaped ferrite core 40 Primary coil 50 Secondary coil 70 U type ferrite core
C1, C2, C3 Capacitor D1, D2 Diode G1, G2 Magnetic gap S1, S2 Switching element

Claims (7)

A first magnetic core having a first central leg, a first side leg surrounding at least both sides thereof, and a first plate-like portion connecting the first central leg and the first side leg. When,
A second central leg; a second side leg surrounding at least both sides of the second central leg; and a second plate-like portion connecting the second central leg and the second side leg. A second magnetic core;
A ring-shaped magnetic core sandwiched between the first side leg and the second side leg;
A first coil provided around the first central leg inside the first side leg;
A second coil provided around the second central leg inside the second side leg,
A first magnetic gap is provided between the first and second central legs, and a second magnetic gap is provided between a side surface of the first and second central legs and an inner surface of the ring-shaped magnetic core. A loosely coupled transformer.   2. The loosely coupled transformer according to claim 1, wherein the first and second magnetic cores are E-type cores, and the ring-shaped magnetic core is a square-shaped core.   The loosely coupled transformer according to claim 1, wherein the first magnetic gap is surrounded by the ring-shaped magnetic core. A first magnetic core having a first central leg, a first side leg surrounding at least both sides thereof, and a first plate-like portion connecting the first central leg and the first side leg. When,
A second magnetic core having a second plate-like portion and second side legs provided on at least both sides of the second plate-like portion;
A ring-shaped magnetic core sandwiched between the first side leg and the second side leg;
A first coil provided around the first central leg inside the first side leg;
A second coil provided around the first central leg inside the second side leg,
A first magnetic gap is provided between the first central leg and the second plate-like portion, and a second magnetic gap is provided between the side surface of the first central leg and the inner surface of the ring-shaped magnetic core. A loosely coupled transformer characterized by that.   5. The loosely coupled transformer according to claim 4, wherein the first magnetic core is an E-type core, the second magnetic core is a U-type core, and the ring-shaped magnetic core is a rectangular core.   6. The loosely coupled transformer according to claim 1, wherein the coil is made of a multilayer substrate on which a conductor pattern is formed.   A switching power supply comprising the loosely coupled transformer according to claim 1, 2, 3, 4, 5 or 6.

Images