Transformer and resonant circuit having same

Abstract

Provided is a transformer (1), which includes: a core (10) which forms a magnetic circuit and has a middle leg (10a) and a plurality of side legs (10b, 10c) branched from the middle leg (10a); primary windings (11) respectively wound around a first winding leg (10a) and a second winding leg (10b), which are selected from the middle leg (10a) and the side legs (10b, 10c); and a secondary winding (12) wound around either of the first winding leg (10a) or the second winding leg (10b), wherein a first magnetic flux generated by the primary windings (11) from the first winding leg (10a) and a second magnetic flux generated by the primary windings (11) from the second winding leg (10b) differ from each other by a predetermined value or more at a position at which the fluxes do not intersect with the secondary winding (12).

Claims

1. A transformer, characterized in comprising: a core configured to form a magnetic circuit and have a middle leg and a plurality of side legs branching off from the middle leg; primary windings respectively wound around the middle leg and one of the side legs, wherein winding direction of the primary winding wound around the middle leg and winding direction of the primary winding wound around the one of the side legs are opposite to each other; and a secondary winding wound around the one of the side legs, wherein a first magnetic flux generated by the primary windings from the middle leg and a second magnetic flux generated by the primary windings from the one of the side legs differ from each other by a predetermined value or more at a position at which the fluxes do not intersect with the secondary winding, wherein a cross-sectional area of the primary winding differs at the middle leg and the one of the side legs.

2. The transformer according to claim 1, characterized in that the core has a path of the magnetic flux, which does not intersect with the secondary winding, of the first magnetic flux and the second magnetic flux which are generated by the primary windings.

3. The transformer according to claim 2, characterized in that a gap is provided in the path.

4. The transformer according to claim 1, characterized in that the number of turns of the primary winding differs at the middle leg and the one of the side legs.

5. The transformer according to claim 1, characterized in that a gap is provided in either the middle leg or the one of the side legs, or gaps having different lengths are respectively provided in the middle leg and the one of the side legs.

6. A resonant circuit, characterized in comprising: the transformer according to claim 1; a resonant inductance; and a resonant capacitor, wherein the resonant circuit uses resonance of the resonant inductance and the resonant capacitor connected to an excitation inductance of the transformer.

7. The resonant circuit according to claim 6, characterized in that the resonant inductance and the resonant capacitor are connected in series to the excitation inductance.

8. The resonant circuit according to claim 7, characterized in that: the resonant circuit is an LLC type resonant circuit; and the excitation inductance/the resonant inductance ≤3.

9. The transformer according to claim 2, characterized in that the number of turns of the primary winding differs at the middle leg and the one of the side legs.

10. The transformer according to claim 3, characterized in that the number of turns of the primary winding differs at the middle leg and the one of the side legs.

11. The transformer according to claim 2, characterized in that a gap is provided in either the middle leg or the one of the side legs, or gaps having different lengths are respectively provided in the middle leg and the one of the side legs.

12. The transformer according to claim 3, characterized in that a gap is provided in either the middle leg or the one of the side legs, or gaps having different lengths are respectively provided in the middle leg and the one of the side legs.

13. The transformer according to claim 4, characterized in that a gap is provided in either the middle leg or the one of the side legs, or gaps having different lengths are respectively provided in the middle leg and the one of the side legs.

14. A resonant circuit, characterized in comprising: the transformer according to claim 2; a resonant inductance; and a resonant capacitor, wherein the resonant circuit uses resonance of the resonant inductance and the resonant capacitor connected to an excitation inductance of the transformer.

15. The resonant circuit according to claim 14, characterized in that the resonant inductance and the resonant capacitor are connected in series to the excitation inductance.

16. The resonant circuit according to claim 15, characterized in that: the resonant circuit is an LLC type resonant circuit; and a ratio between the excitation inductance and the resonant inductance is less than or equal to 3.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is an overview configuration diagram of a transformer 1 according to a first embodiment of the present invention.

(2) FIG. 2(a) is a schematic explanatory diagram of an excitation inductance Lm and a leakage inductance Llk in the transformer 1, and FIG. 2(b) is a schematic explanatory diagram of an example in which a gap is provided in a left leg 10c of a core 10 of the transformer 1.

(3) FIG. 3 is an explanatory diagram of parameters relevant to permeance P used in a magnetic circuit calculation.

(4) FIG. 4 is a schematic explanatory diagram of a method for giving a difference to a magnetomotive force F in the transformer 1.

(5) FIG. 5(a) to FIG. 5(c) are schematic explanatory diagrams of a method for giving a difference to magnetic resistance R in the transformer 1.

(6) FIG. 6(a) and FIG. 6(b) are schematic diagrams illustrating other winding methods of primary windings 11 and a secondary winding 12 (12a and 12b).

(7) FIG. 7(a) to FIG. 7(c) are schematic diagrams illustrating still other winding methods of the primary windings 11 and the secondary winding 12 (12a and 12b).

(8) FIG. 8 is an overview configuration diagram of a series resonant converter circuit 20 according to a second embodiment of the present invention.

(9) FIG. 9 is an overview configuration diagram of a core 10 of a first example of the first embodiment of the present invention.

(10) FIG. 10 is an overview configuration diagram of a core 10 of a second example of the first embodiment of the present invention.

(11) FIG. 11 is an overview configuration diagram of a core 10 of a third example of the first embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

(12) Hereinafter, several embodiments of the present invention will be described on the basis of the drawings.

First Embodiment

(13) FIG. 1 is an overview configuration diagram of a transformer 1 according to a first embodiment of the present invention. FIG. 2(a) is a schematic explanatory diagram of an excitation inductance Lm and a leakage inductance Llk in the transformer 1. FIG. 2(b) is a schematic explanatory diagram of an example in which a gap is provided in a left leg 10c of a core 10 of the transformer 1.

(14) As illustrated in FIG. 1, the transformer 1 includes a core 10 that forms a magnetic circuit, primary windings 11 that are input sides, and a secondary first winding 12a and a secondary second winding 12b (referred to collectively as a secondary winding 12) that are output sides. Here, a case in which a center tap is removed from the secondary winding 12 is shown, but if the center tap is not removed, only one of the secondary first winding 12a and the secondary second winding 12b may be used.

(15) The core 10 has one middle leg 10a and side legs 10b and 10c branching off into two from the middle leg 10a (distinguished by being called a right leg 10b and a left leg 10c as needed), and is made up of, for instance, an E type core and an I type core, or E type cores, or the like. A material of the core 10 may be a typical material.

(16) The primary windings 11 are wound around two legs that are arbitrarily selected from the middle leg 10a and the side legs 10b and 10c (which are a “first winding leg” and a “second winding leg” in this application, and the middle leg 10a and the right leg 10b herein) with winding directions (indicated by arrows superimposed on the primary windings 11 in the figure) opposite to each other. Hereinafter, the case in which the middle leg 10a and the right leg 10b are selected will be described by way of example. However, a combination of the two legs may be the left leg 10c and the middle leg 10a, or the left leg 10c and the right leg 10b.

(17) The secondary winding 12 is wound around any one of the selected two legs, that is, the middle leg 10a and the right leg 10b (here, the right leg 10b).

(18) For the primary windings 11 and the secondary winding 12, for instance a PCB board on which a pattern is formed (a pattern coil), an edgewise coil, or a copper foil may be used as a wire, in addition to a litz wire obtained by twisting fine wires and a single wire, but the present invention is not limited thereto. When the wire is used, the bobbin may be used together.

(19) In the configuration of this transformer 1, as illustrated in FIG. 2(a), if magnetic fluxes Φa and Φb are generated at the two legs (here, the middle leg 10a and the right leg 10b) around which the primary windings 11 are wound, and a sufficient difference (a difference that is greater than or equal to a predetermined given value) in the magnitudes of the magnetic fluxes Φa and Φb is present at positions at which the magnetic fluxes do not intersect with the secondary winding 12, the secondary winding 12 is wound around only one of the middle leg 10a and the right leg 10b, and the core 10 has a path (the left leg 10c) flowing the leakage inductance Llk. Thus, a high leakage inductance Llk can be obtained.

(20) As illustrated in FIG. 2(b), when a gap is provided in the path flowing the leakage inductance Llk in the core 10 of the transformer 1, the leakage inductance Llk can be arbitrarily adjusted by a length Gc of this gap.

(21) FIG. 3 is an explanatory diagram of parameters relevant to permeance P used in magnetic circuit calculation.

(22) Next, an example of a method for giving a difference to the magnitudes of the generated magnetic fluxes will be described, but a basis of the magnetic circuit calculation is checked first. Total magnetic flux Φ, a magnetomotive force F, and magnetic resistance R has a relation of the following formula.
Total magnetic flux Φ=Magnetomotive force F/Magnetic resistance R  (1)

(23) However, in the magnetic circuit calculation, since the magnetic resistance R is seldom used, and the permeance P that is a reciprocal of the magnetic resistance R is generally used, the following formula can be substituted for formula (1).
Total magnetic flux Φ=Magnetomotive force F.Math.Permeance P  (2)

(24) As illustrated in FIG. 3, this permeance P is expressed by the following formula when a magnetic path length is defined as L, a magnetic path cross-sectional area is defined as A, and permeability is defined as μ.
Penneance P=Permeability μ.Math.Magnetic path cross-sectional area A/Magnetic path length L  (3)

(25) FIG. 4 is a schematic explanatory diagram of a method for giving a difference to a magnetomotive force F in the transformer 1. FIG. 5(a) to FIG. 5(c) are schematic explanatory diagrams of a method for giving a difference to magnetic resistance R in the transformer 1.

(26) As an example of the method for giving the difference to the magnitudes of the generated magnetic fluxes, a difference may be given to magnetomotive forces F of the middle leg 10a and the right leg 10b of the transformer 1.

(27) Since the magnetomotive force F is expressed by the following formula, it is considered, for instance, to make the middle leg 10a and the right leg 10b different in the number of turns N from each other as illustrated in FIG. 4.

(28) Magnetomotive force F∝NI (where I is constant, and N is the number of turns of the coil)

(29) As another example of the method for giving the difference to the magnitudes of the generated magnetic fluxes, a difference may be given to the magnetic resistance R of each of the portions around which the primary windings 11 are wound in the core 10 of the transformer 1, particularly the middle leg 10a and the right leg 10b here.

(30) As can be seen from formula (3) above, since the permeability μ, the magnetic path cross-sectional area A, and the magnetic path length L are relevant to the permeance P (the reciprocal of the magnetic resistance R), at least one of these parameters needs only to be changed.

(31) For example, as illustrated in FIG. 5(a), a gap may be provided for at least one of the middle leg 10a and the right leg 10b, or illustrated in FIG. 5(b), when the gap is provided for both of them, a length of each gap may be changed. Since the gap portion and the core 10 are different in permeability μ from each other, the permeability μ at large is changed depending on the length of the gap. The gap is not necessarily provided at an upper side of the core 10 as illustrated in FIG. 5(a) and FIG. 5(b), and it may be provided for each of the middle leg 10a and the right leg 10b.

(32) As illustrated in FIG. 5(c), magnetic path cross-sectional areas Aa and Ab of the middle leg 10a and the right leg 10b may be made different from each other. However, the present invention is not limited to these methods.

(33) According to the first embodiment described above, the small transformer in which an additional member such as a magnet is not required, a loss caused when a leakage magnetic field intersects with its surrounding windings is not also increased, a reduction in efficiency caused by a proximity effect generated when the number of layers of the primary winding is increased is not also incurred, and a high leakage inductance is obtained can be realized.

Modification of the First Embodiment

(34) FIG. 6(a) and FIG. 6(b) are schematic diagrams illustrating other winding methods of the primary windings 11 and the secondary winding 12 (12a and 12b). FIG. 7(a) to FIG. 7(c) are schematic diagrams illustrating still other winding methods of the primary windings 11 and the secondary winding 12 (12a and 12b).

(35) In the aforementioned first embodiment, the primary windings 11 are wound around the middle leg 10a and the right leg 10b with the winding directions opposite to each other. The secondary winding 12 (the secondary first winding 12a and the secondary second winding 12b) is wound around the right leg 10b below the primary windings 11. However, the winding methods of the primary windings 11 and the secondary winding 12 are not limited thereto.

(36) For example, as illustrated in FIG. 6(a), the primary windings 11 and the secondary winding 12 may be alternately wound. Alternatively, as illustrated in FIG. 6(b), the primary winding 11, the secondary winding 12 (the secondary first winding 12a), the secondary winding 12 (the secondary second winding 12b), and the primary winding 11 may be wound from above in this order.

(37) The winding methods of the primary windings 11 and the secondary winding 12 in the first embodiment may be turned upside down as illustrated in FIG. 7(a). The winding methods illustrated in FIG. 6(a) may also be turned upside down as illustrated in FIG. 7(b). Likewise, the winding methods illustrated in FIG. 6(b) may also be turned upside down as illustrated in FIG. 7(c).

Second Embodiment

(38) FIG. 8 is an overview configuration diagram of a half bridge type series resonant converter circuit 20 according to a second embodiment of the present invention.

(39) The transformer 1 of the aforementioned first embodiment is suitable for, for instance, series resonant converter circuits of a half bridge and a full bridge, a phase shift full bridge circuit, a dual active bridge (DAB) circuit, or the like.

(40) It can be used in a resonant circuit that uses the resonance of a resonant inductance Lr and a resonant capacitor Cr which are connected in series to an excitation inductance of the transformer 1. An example of the resonant circuit is the half bridge type series resonant converter circuit 20 illustrated in FIG. 8. The half bridge type series resonant converter circuit 20 includes a capacitor C.sub.in, a capacitor C.sub.Q1, a capacitor C.sub.r1 capacitor C.sub.Q2, a capacitor C.sub.r2, a capacitor C.sub.d, a transistor Q.sub.1, a transistor Q.sub.2, a diode D.sub.Q1 a diode D.sub.Q2, a diode D.sub.1, a diode D.sub.2, a primary winding n.sub.1, a secondary winding n.sub.2 and a secondary winding n.sub.3.

(41) According to this second embodiment, the transformer 1 of the first embodiment which has a high leakage inductance is used, and thereby a series resonant converter in which a ratio (I=Lm/Lr) between the excitation inductance Lm and the resonant inductance Lr is small can be configured. Since a frequency characteristic is sharp, a wide range of output voltage can be obtained by changing a switching frequency or, when the output voltage is constantly controlled, an input range can be widened by changing a switching frequency.

(42) In the case of an LLC circuit, it is preferably configured such that the ratio (I=Lm/Lr) between the excitation inductance Lm and the resonant inductance Lr is less than or equal to 3.

First Example

(43) FIG. 9 is an overview configuration diagram of a core 10 of a first example of the first embodiment of the present invention. In the first example, as illustrated in FIG. 9, a core 10 was used in which a cross-sectional area Ac of the left leg 10c for a leakage inductance path was set to 1, a cross-sectional area Aa of the middle leg 10a was set to 2, and a cross-sectional area Ab of the right leg 10b was set to 2.

(44) The primary winding 11 was alternately wound around the middle leg 10a and the right leg 10b of the core 10 in the number 8 by two turns for the middle leg and one turn for the right leg for a total of 15 turns (ten turns of the middle leg and five turns for the right leg), and finally one turn for the right leg.

(45) Further, the secondary winding 12 was wound around the right leg 10b of the core 10 in the same direction as the primary winding 11 by two turns, and aside from this, the secondary winding 12 was wound around the right leg 10b in the direction opposite to the direction of the primary winding 11 by two turns.

(46) Measurement was performed using an LCR meter. A measurement condition was a frequency of 100 kHz. First, the secondary winding 12 was opened, and an inductance value Lp of the primary winding 11 was measured. Next, the secondary winding 12 was shorted, and the inductance Llk of the primary winding 11 was measured.

(47) This inductance Llk was a leakage inductance, and the excitation inductance Lm was given by Lm=Lp−Llk. When m=Lm/Llk, measured results were as follows.

(48) Lm=157.2 μH

(49) Llk=104.1 μH

(50) m≈1.5

(51) A high leakage inductance was obtained.

Second Example

(52) FIG. 10 is an overview configuration diagram of a core 10 of a second example of the first embodiment of the present invention. In the second example, as illustrated in FIG. 10, a core 10 was used in which a cross-sectional area Ac of the left leg 10c for a leakage inductance path was set to 1, a cross-sectional area Aa of the middle leg 10a was set to 3, and a cross-sectional area Ab of the right leg 10b was set to 2.

(53) The primary winding 11 was alternately wound around the middle leg 10a and the right leg 10b of the core 10 in the number 8 by one turn after another for a total of 16 turns (eight turns of the middle leg and eight turns for the right leg).

(54) Further, the secondary winding 12 was wound around the right leg 10b of the core 10 in the same direction as the primary winding 11 by two turns, and aside from this, the secondary winding 12 was wound around the right leg 10b in the direction opposite to the direction of the primary winding 11 by two turns.

(55) A measurement device, a measurement condition, and a measuring method were the same as in the first example. Measured results were as follows.

(56) Lm=227 μH

(57) Llk=89.8 μH

(58) m≈3.1

(59) A high leakage inductance was also obtained.

Third Example

(60) FIG. 11 is an overview configuration diagram of a core 10 of a third example of the first embodiment of the present invention. In the third example, as illustrated in FIG. 11, a core 10 was used in which a cross-sectional area Ac of the left leg 10c for a leakage inductance path was set to 1, a cross-sectional area Aa of the middle leg 10a was set to 2, and a cross-sectional area Ab of the right leg 10b was set to 2, and in which a length Ga of the gap of the middle leg 10a was set to 1, and a length Gb of the gap of the right leg 10b was set to 2.

(61) The primary winding 11 was alternately wound around the middle leg 10a and the right leg 10b of the core 10 in the number 8 by one turn after another for a total of 16 turns (eight turns of the middle leg and eight turns for the right leg).

(62) Further, the secondary winding 12 was wound around the right leg 10b of the core 10 in the same direction as the primary winding 11 by two turns, and aside from this, the secondary winding 12 was wound around the right leg 10b in the direction opposite to the direction of the primary winding 11 by two turns.

(63) A measurement device, a measurement condition, and a measuring method were the same as in the first example. Measured results were as follows.

(64) Lm=27.2 μH

(65) Llk=80.4 μH

(66) m≈0.89

(67) A high leakage inductance was also obtained.

(68) The configurations of the first embodiment, its modification, the second embodiment, and the first to third examples which are described above may be combined with one another as long as obstructive factors or the like are not especially present.

(69) The present invention can be carried out in various other modes without departing from the gist or the principal features thereof. For this reason, the aforementioned embodiments and examples are merely simple examples in every respect, and are not to be restrictively interpreted. The scope of the present invention is defined by the claims, and is not restricted at all by the text of the specification. Further, all alterations or modifications belonging to the equivalent scope of the claims are within the scope of the present invention.