JP2008166624A - Transformer and resonance type switching power supply using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transformer and a resonance type switching power supply, which can prevent an increase in size of the transformer due to a desired leakage inductance and allow miniaturization by eliminating the necessity of a large air gap. <P>SOLUTION: The transformer 1 is provided with an intermediate leg 2a; a core 2 consisting of side legs 2b, 2c branched from the intermediate leg; a primary winding 3 provided on the intermediate leg 2a of the core 2; and secondary windings 5, 6 provided at least any one of the side legs 2b, 2c. With this configuration, by adjusting the number of windings for the side legs 2b, 2c of the secondary windings 5, 6, necessary leakage inductance can be easily ensured without providing an air gap. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a transformer used in a switching power supply device, and more particularly to a tonula having a leakage inductance used in a resonant switching power supply.

  In general, a resonant switching power supply circuit has a configuration as shown in FIG. The DC input power supply 101 is, for example, a power supply obtained by rectifying and smoothing a commercial power supply using a rectifier diode and a capacitor. A current is supplied from the DC input power supply 101 to a series resonance circuit including the inductance element 102, the primary side winding of the insulating converter transformer 103, and the resonance capacitor 104. This current is switching-controlled by the driving circuit 7 in the switching transistors 105 and 106 having a half bridge configuration.

  The voltage obtained in the secondary winding of the insulating converter transformer 103 is supplied to the load 111 as a DC voltage output rectified and smoothed by the diodes 108 and 109 and the capacitor 110 by the center tap method. The drive circuit 107 is controlled, for example, by monitoring the output voltage, and obtains a constant output voltage even if the load varies.

  In the resonant switching power supply, the primary side winding of the insulating converter transformer 103 is equivalently short-circuited during the period when the output is obtained on the secondary side, and the resonance with the inductance element 102 during this period. The series resonance operation is performed by the capacitor 104 for use. In this example, an external coil is used for the inductance element 102, but the same operation is possible even if leakage inductance existing in the insulating converter transformer 103 is used.

Therefore, in order to ensure this leakage inductance, as shown in FIG. 7, a transformer using a divided bobbin is used, and an external inductance element is omitted (for example, see Patent Document 1). An equivalent circuit of such a split winding transformer is shown in FIG. In FIG. 7, 113 is a core, 114 is a divided bobbin, 114a is a bobbin divided portion, 115 is a primary side winding, and 116 is a secondary side winding.
JP 2001-237126 A

  As described above, in the case of a transformer using a divided bobbin, the leakage inductance value is secured by the distance between the primary side winding and the secondary side winding and the air gap. It was necessary to increase the distance between windings or to increase the air gap. As a result, the transformer shape becomes large. In addition, there is a problem such as loss due to an increase in leakage magnetic flux caused by increasing the air gap.

  The present invention solves the above problem, and in order to obtain a desired leakage inductance, the transformer shape does not become large, and it is not necessary to make a large air gap. An object of the present invention is to provide a resonant switching power supply using the same.

In order to achieve the above object, the invention of claim 1 is characterized in that a core comprising one middle leg forming a magnetic path, a side leg branched from the middle leg into at least two parts, and a core leg of the core. The transformer includes a primary winding provided and a secondary winding provided on at least one of the side legs.
According to a second aspect of the present invention, in the transformer, the secondary winding is provided on one of the side legs and a middle leg.
According to a third aspect of the present invention, the secondary winding is provided on both the side legs and the middle leg.
According to a fourth aspect of the present invention, a gap is provided in the middle leg.
According to a fifth aspect of the present invention, the winding is formed by printed wiring on a substrate.
According to a sixth aspect of the present invention, the secondary winding is mainly provided on the side leg, and the leakage inductance is controlled by the number of turns.
The invention according to claim 7 is a resonant switching power supply using any one of the above transformers.

According to the first to fourth aspects of the present invention, the necessary leakage inductance can be easily ensured without introducing an air gap by adjusting the number of turns wound on the side leg of the secondary side winding. This makes it possible to reduce the size of the transformer. In addition, the excitation inductance can be adjusted without reducing the leakage inductance.
According to the invention of claim 5, since the winding is constituted by pattern wiring, a bobbin or the like is not required, and the coil can be easily wound around the middle leg and the side leg.
According to the sixth aspect of the invention, a desired leakage inductance can be ensured without reducing the leakage inductance.
According to the invention of claim 7, external components can be reduced in the resonance type switching power supply.

<First Embodiment>
A transformer according to a first embodiment of the present invention will be described with reference to the drawings. 1 and 2 show the transformer of this embodiment. The transformer 1 includes a core 2 that forms a closed magnetic path, a primary side winding 3 that is an input side, and secondary side windings 4, 5, and 6 that are output sides. The core 2 includes one middle leg 2a and side legs 2b and 2c branched into two from the middle leg 2a. For example, the core 2 includes an E-type core and an I-type core or E-type cores.

  The primary winding 3 is provided on the middle leg 2a of the core. The secondary side windings 4, 5 and 6 are provided not only on the middle leg 2a but also on the side legs 2b and 2c. Here, the secondary winding 4 is wound around the middle leg 2a, and the secondary windings 5 and 6 are wound around the side legs 2b and 2c, respectively. One coil is continuous with a part of the secondary winding 4 and the secondary winding 5, and another coil is continuous with the remainder of the secondary winding 4 and the secondary winding 6. .

  The primary winding 3 is supplied with a switching operation current from a switching power supply, and the magnetic flux (indicated by an arrow) generated by the primary winding 3 passes through the middle leg 2a and is transmitted by the side legs 2b and 2c. Each becomes 1/2. Of the secondary side windings 4, 5, 6, the secondary side winding 4 wound around the middle leg 2 a is interlinked with the same amount of magnetic flux as that generated in the primary side winding 3. On the other hand, a half of the magnetic flux generated in the primary winding 3 is linked to the secondary windings 5 and 6 wound around the side legs 2b and 2c. Therefore, the magnetic flux not interlinked (magnetic flux passing through the side legs not winding the winding) becomes the primary side leakage inductance. When the number of turns of the secondary side winding 4 to the middle leg 2a is reduced and the number of turns of the secondary side windings 5 and 6 to the side legs 2b and 2c is increased, the leakage inductance increases.

  Therefore, by adjusting the number of turns wound around the middle leg 2a and the side legs 2b, 2c of the secondary windings 4, 5, 6, it is possible to easily secure the necessary leakage inductance without introducing an air gap. Is possible. The secondary windings 4, 5, and 6 may be provided mainly on the side legs 2b and 2c, and the leakage inductance may be controlled by the number of turns. FIG. 3 shows the relationship between the turn ratio of the secondary windings 5 and 6 of the side legs 2b and 2c and the leakage inductance with respect to the secondary winding 4 of the middle leg 2a. The horizontal axis of the figure is the turns ratio (= number of side leg turns / number of middle leg turns). As the number of side leg turns with respect to the number of middle leg turns increases, the leakage inductance decreases.

  In the above description, the secondary side winding is provided on both the middle leg 2a and the side legs 2b and 2c. However, the secondary side winding may be provided on one of the side legs 2b and 2c and the middle leg 2a. Details thereof will be described in a third embodiment described later.

<Second Embodiment>
A substrate transformer according to a second embodiment of the present invention will be described with reference to FIGS. In the present embodiment, a winding is formed by printed wiring. 4A, 4B, 4C, and 4D show the first to fourth layers of the printed coil board, which is a component of the board transformer, FIG. 4E shows the equivalent circuit of the coil, and FIG. Indicates cross sections of the substrate transformer.

  The printed coil substrate includes a first substrate 10 and a second substrate 20. The first substrate 10 has a primary side winding 3 composed of printed windings 31 and 32 formed in two layers on the front and back sides, that is, the first layer and the second layer. Secondary side winding 4 consisting of the middle leg side printed windings 41 and 42 formed on the front and back two layers, ie, the third and fourth layers, and the secondary side winding consisting of one side leg side printed winding. It has a secondary winding 6 comprising a wire 5 and a printed winding on the other side leg. Thus, the illustrated substrate transformer includes the primary side winding 3 and the secondary side windings 4, 5, 6 in two layers.

  The primary winding 3 is formed by connecting two printed windings 31, 32 on the front and back sides through through holes 14 penetrating the first substrate 10. The secondary winding 4 has a plurality of through-holes 24 formed through the second substrate 20 so that the printed windings 41 provided on the front and the back and the printed windings 42 are connected to each other to be continuous. It is formed in the coil. Moreover, it arrange | positions so that the center part of each printed winding may overlap with the perpendicular direction of a board | substrate. The center portion coincides with the center of the circular through holes 15 and 25 (openings) provided in the substrates 10 and 20.

  Specifically, with respect to the primary side winding 3, the printed winding 31 is spirally wired from the outermost circumference to the innermost circumference on the first layer, and the printed winding 32 is arranged on the innermost circumference on the second layer. Is wired spirally from the outermost side toward the outermost periphery. Since the printed windings 31 and 32 are configured in this way, the direction of magnetic flux is constant from the start of winding to the end of winding. 4A and 4B are input terminals on the primary side, and in this example, the printed windings 31 and 32 each have 8 turns, for a total of 16 turns.

  Regarding the secondary winding 4, the printed winding 41 and the printed winding 42 are alternately formed concentrically and spirally. The printed winding 41 is continuously connected to the secondary winding 5 formed of a printed winding through a through-hole and a connecting wire 41a on the back surface (fourth layer) side, and the printed winding 42 is formed of 2 formed of a printed winding. The secondary winding 6 is continuously connected through the through hole and the connecting wire 42a on the surface (third layer) side. EF and GH in FIGS. 4C and 4D serve as terminals of the secondary winding of the second winding. In this example, the middle-leg printed windings 41 and 42 each have three turns, and the side-leg secondary windings 5 and 6 each have one turn.

  Further, circular through holes 15 and 25 (openings) for inserting cores are provided in the center of the substrates 10 and 20, and rectangular through holes 16 in a plan view are provided on the left and right sides of the substrates 10 and 20. , 17 and 26, 27 (openings). As shown in FIG. 5, the substrates 10 and 20 are stacked and bonded with an insulating plate 30 interposed therebetween to form a substrate assembly 35. The insulating plate 30 is also provided with an equivalent opening at a position corresponding to the through hole of the substrate. Then, a core 2 made of ferrite or the like (consisting of an E-type core and an I-type core) is inserted into each opening and assembled to the board assembly 35 to constitute a board transformer 50.

  In the substrate transformer 50 of the present embodiment, the windings 3, 4, 5, 6 are formed by pattern wiring using the front and back layers of the printed wiring board. That is, since the primary side winding is formed using the first and second layers of the substrate and the secondary side winding is formed using the third and fourth layers, When the pattern width is the same, twice the number of turns can be realized, and when the number of turns is the same, a double pattern width can be secured. Also, if you want to increase the number of turns, you can increase the number of turns with the required pattern width by wiring the windings using even layers (for example, 4 layers) more than two layers. it can. Thereby, a low-profile transformer can be configured easily.

  Further, in the first embodiment described above, a bobbin for winding the side leg winding is required in addition to the bobbin for the middle leg, but in this embodiment, the winding is configured by pattern wiring. A bobbin or the like is not necessary, and the coil can be wound around the middle leg and the side leg very easily.

  Furthermore, the number of turns is not limited to integer turns such as 1 turn and 2 turns, but it can be adjusted to 0.5 turns or 0.8 turns depending on the winding position of the winding, and the necessary leakage inductance can be realized with high accuracy. It becomes possible.

<Third Embodiment>
In a transformer using a ferrite core, when a large current flows, a phenomenon occurs in which the magnetic flux density exceeds the saturation magnetic flux density of the ferrite and the inductance value rapidly decreases. In general, this characteristic is called a DC superposition characteristic. By providing a gap between the two cores combined as a countermeasure, the allowable current value for saturation is increased. Such a relationship between the gap and the current saturation is shown in FIG.

  In addition, when the core iron loss is taken into consideration, the primary winding number is determined from the magnetic flux density used, and a large inductance value may be obtained with respect to the inductance value necessary for the circuit. Even in such a case, an inductance value is adjusted by providing a gap.

  However, when the secondary side winding is wound around the side leg of the above-mentioned core to ensure the leakage inductance, the transformer 1 using the E-type core 61 and the I-type core 62 as shown in FIG. When the gap 63 is provided on both the legs and the side legs, as shown in FIGS. 11A and 11B, the excitation inductance decreases as the gap increases, but the leakage inductance value also decreases.

  Therefore, in the present embodiment, as shown in FIGS. 12A and 12B, the transformer 1 is provided with the gap 63 provided only in the middle leg 61a. Thereby, only the excitation inductance is reduced, and a desired leakage inductance value can be ensured without reducing the leakage inductance.

  Details of the present embodiment will be described below with reference to FIGS. 13 (a) and 13 (b). FIG. 13A shows a general transformer 100, and FIG. 13B shows the transformer 1 of this embodiment. The transformer 100 has a gap 63 in the middle leg / side leg, and the transformer 1 of the present embodiment has the gap 63 only in the middle leg.

  In these transformers, the main magnetic flux M1 generated in the primary coil 3 wound around the middle leg 61a causes a current to flow through the secondary winding 4 wound around the same middle leg 61a, thereby canceling the main magnetic flux M2. Will occur. A current generated in the secondary winding 4 wound around the middle leg 61a flows through the secondary winding 5 wound around the side leg 61c with the primary main magnetic flux M1 being canceled. The secondary windings 4 and 5 are continuously connected in the same manner as in the above embodiment. A magnetic flux M3 corresponding to this current is generated in the side leg 61c. As a result, since the magnetic flux is canceled by the primary winding 3 and the secondary winding 4 in the middle leg 61a, the magnetic flux is weakened. As a result, a magnetic flux loop that passes only through the side legs 61b and 61c leaks. It becomes inductance.

Here, in the case of the transformer 100 shown in FIG. 13 (a) in which the gap 63 is provided in both the middle leg and the side leg, there is a gap in the magnetic flux loop passing through the side legs 61b and 61c (part A). Inductance is reduced.
On the other hand, in the case of the transformer 1 provided with the gap 63 only in the middle leg 61a shown in FIG. 13B, there is no gap in the magnetic flux loop passing through the side legs 61b and 61c (part A). The leakage inductance does not decrease. This is shown in FIGS. 14 (a) and 14 (b).

  The present invention is not limited to the configuration of the embodiment described above, and various modifications can be made without departing from the spirit of the invention. In addition, in the resonant switching power supply using any of the above transformers, an effect such as reduction of external parts can be obtained.

1 is a cross-sectional view of a transformer according to a first embodiment of the present invention. The cross-sectional view of the transformer. The relationship figure of the turns ratio of the secondary side winding of the side leg with respect to the secondary side winding of the middle leg of the transformer, and the leakage inductance. (A) (b) (c) (d) is a figure which shows the 1st layer thru | or 4th layer of the printed coil board | substrate which is a component of the board | substrate transformer which concerns on 2nd Embodiment of this invention, (e) is a coil. Equivalent circuit diagram. Sectional drawing of the substrate transformer. FIG. 2 is a general resonant switching power supply circuit diagram. Sectional drawing of a general split winding transformer. The equivalent circuit diagram of a general split winding transformer. The relationship figure of the gap of a general transformer, and current saturation. Sectional drawing of the trans | transformer which winds a secondary side coil | winding to the side leg of a core, and provides a gap in a middle leg and a side leg used as the premise of 3rd Embodiment of this invention. (A) is the relationship figure of the gap and exciting inductance in the above-mentioned transformer, (b) is the relation figure of the gap and leakage inductance. (A) and (b) are sectional drawings of the transformer concerning a 3rd embodiment of the present invention. (A) is operation | movement explanatory drawing of a general transformer, (b) is operation | movement explanatory drawing of the trans | transformer of 3rd Embodiment. (A) is a relationship diagram of the gap and exciting inductance of the transformer concerning a 3rd embodiment, and (b) is a relationship diagram of a gap and leakage inductance.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transformer 2 Core 2a Middle leg 2b, 2c Side leg 3 Primary side winding 31, 32 Printed winding 4 Secondary side winding 41, 42 Printed winding 5,6 Secondary side winding 10 First board 20 Second substrate 35 Substrate assembly 50 Substrate transformer 61 E-type core 61a Middle leg 61b, 61c Side leg 62 I-type core 63 Gap

Claims (7)

A core composed of one middle leg forming a magnetic path and a side leg branched from the middle leg into at least two parts;
A primary winding provided on the middle leg of the core;
And a secondary winding provided on at least one of the side legs.   The transformer according to claim 1, wherein the secondary winding is provided on one of the side legs and a middle leg.   The transformer according to claim 1, wherein the secondary winding is provided on both of the side legs and the middle leg.   4. The transformer according to claim 2, wherein a gap is provided in the middle leg.   The transformer according to claim 1, wherein the winding is formed by printed wiring of a substrate.   3. The transformer according to claim 1, wherein the secondary winding is mainly provided on the side leg, and leakage inductance is controlled by the number of turns.   A resonant switching power supply using the transformer according to any one of claims 1 to 3.

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