JP2002075750A - Transformer and power unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transformer, which can easily make leakage inductances variable and a power unit, which can effectively utilize the capacity of the transformer. SOLUTION: The transformer 10 is provided with bobbins 12 and a core 14. The center shaft of one 12A of the bobbins 12 passes through a bobbin 22 for primary winding, and the bobbin 22 is fixed to the bobbin 12a by tightening nuts 24 and 26 from both sides. Similarly, the center shaft of the other bobbin 12B passes through a bobbin 28 for secondary winding and the bobbin 28 is fixed to the bobbin 12B, by tightening nuts 30 and 32 from both sides. The position of the bobbin 28 for secondary winding can be adjusted, by adjusting the tightening positions of the nuts 24, 26, 30, and 32. Therefore, the distance ΔX between primary and second windings can be set arbitrarily.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a transformer and a power supply, and more particularly, to a transformer and a power supply used for a switching power supply.

[0002]

2. Description of the Related Art Conventionally, in a switching power supply device, when performing a soft switching operation in order to achieve high efficiency and low noise, an inductance or a capacitor is used to gradually increase or decrease a voltage or a current. Are known.

In particular, when using an inductance,
An example in which a leakage inductance is used without separately providing an inductance in order to reduce the cost is disclosed in January 1998.
It is described in the text of the monthly and February 1999 Switching Power Supply Technical Forum (Japan Management Association).

According to this, it has been found that the leakage inductance value of an inductance used for soft switching is very small, and greatly changes due to a subtle difference in the structure of a core and a winding constituting a transformer.
For this reason, it is difficult to obtain the target leakage inductance value.Conventionally, in order to set the leakage inductance to the target value, the leakage inductance is measured after manufacturing the transformer, and the transformer having the target leakage inductance is measured. Sorting, the product yield will be worse,
There was a problem.

On the other hand, a transformer for hard switching is designed so that the flux linkage between the primary winding and the secondary winding is increased as much as possible and the leakage inductance is reduced as much as possible.
FIG. 11 shows a cross-sectional view of a hard switching transformer. As shown in FIG. 11, the transformer 100 includes a bobbin 1
02 is wound around the secondary winding 104, and the primary winding 1 is
06 is wound, and the center axis of the core 108 is inserted through the axis of the bobbin 102. In this way, by winding the primary winding 106 outside the secondary winding 104, the linkage flux generated in the core 108 passing through the axis of the bobbin 102 is designed to be as large as possible.

FIG. 12 shows an example of a soft switching transformer. As shown in FIG. 12A, the transformer 100 has a primary winding 106 and a secondary winding 104 divided and wound around a bobbin 102. Therefore, FIG.
As shown in (B), the secondary winding 1 from the primary winding 106 side.
A leakage magnetic flux Δφ is generated toward the 04 side, and the magnetic flux φa becomes a magnetic flux φb. The leakage inductance forms a resonance inductance. In this case, the amount of interlinkage magnetic flux is determined by the relative positional relationship between the primary winding and the secondary winding.

[0007] The leakage inductance can be obtained, for example, as follows. First, the main magnetic flux generated by the current i ₁ flowing through the primary winding is φ ₁ , and the leakage magnetic flux is φ _1
Assuming that _S1 , the following equation holds.

W ₁ (φ ₁ + φ _S1 ) = L ₁ · i ₁ (1) where W ₁ is the number of turns of the primary winding, and L ₁ is the inductance of the primary winding. Further, if the main magnetic flux φ ₂ generated by the current i ₂ flowing through the secondary winding and the leakage magnetic flux φ _S2 are given, the following equation is established.

W ₂ (φ ₂ + φ _S2 ) = L ₂ · i ₂ (2) where W ₂ is the number of turns of the secondary winding, and L ₂ is the inductance of the secondary winding. The mutual induction between the primary winding and the secondary winding is M
Then, the following equation is established.

W ₂ · φ ₁ = M · I ₁ (3) W ₁ · φ ₂ = M · I ₂ (4) From the equations (1) and (3), the following equation is established.

[0011]

(Equation 1)

The following equation holds from the above equation (5).

[0013]

(Equation 2)

Here, R ₁ is the leakage magnetic resistance of the space. Further, F ₁ is a magnetomotive force and is represented by F ₁ = W ₁ · i ₁ , and therefore, the equation (6) is represented by the following equation.

[0015]

(Equation 3)

Here, 1 / R ₁ = A · L ₁ (A is a constant specific to the core), and the equation (7) is expressed by the following equation.

[0017]

(Equation 4)

From equation (8), the primary leakage inductance L _l1
Is represented by the following equation.

[0019]

(Equation 5)

[0020] The primary similarly leakage inductance L _l2 is given by the following equation.

[0021]

(Equation 6)

[0022]

However, since the above-described leakage inductance is determined by the positional relationship between the primary winding and the secondary winding, that is, the amount of interlinkage magnetic flux determined by the shape of the bobbin, the required leakage inductance is reduced. There is a problem that bobbins having different shapes must be manufactured according to the inductance.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and provides a transformer capable of easily changing the leakage inductance and a power supply device capable of effectively utilizing the transformer capacitance. The purpose is to:

[0024]

In order to achieve the above object, a structure having an adjusting mechanism capable of arbitrarily varying the leakage inductance may be provided.

FIG. 13A shows the results of measurement of the leakage inductance with respect to the distance between the windings by the present applicant. The measurement of the leakage inductance with respect to the distance between the windings was performed with a configuration as shown in FIG. That is, L is wound around the core 108 and used to measure the inductance.
The winding B connected to the CR meter 110 was moved in the direction of the arrow in the figure, and the leakage inductance L was measured by the LCR meter 110 while approaching the winding A wound around the core 108 and short-circuited.

As shown in FIG. 13A, the leakage inductance L increases as the inter-winding distance ΔX between the winding A and the winding B increases. This is because the equivalent magnetic resistance viewed from the magnetomotive force source (primary winding side) changes depending on the distance between the windings, and thus the leakage magnetic flux between the winding A and the winding B relatively changes.

Therefore, in order to make the leakage inductance arbitrarily variable, it is preferable to adopt a structure in which the relative positional relationship between the primary winding and the secondary winding can be made variable. That is, the fact that the amount of interlinkage magnetic flux changes by making the relative positional relationship between the primary winding and the secondary winding variable is used.

The measuring method of the leakage inductance is as follows.
As an example, it is generally known that it can be obtained by a simple equivalent circuit of a transformer as shown in FIG.
The equivalent circuit of the transformer illustrated in FIG.
(Resistance g0) and an inductance 114 (inductance b0) in a parallel circuit, a resistor 116 (resistance r
1), inductance 118 (inductance value x
1), a series circuit of a resistor 120 (resistance value a ₂ · r2: a is a constant determined by the turns ratio of the transformer) and an inductance 122 (inductance value a ² · x2).

For such an equivalent circuit, FIG.
As shown in (B), the secondary side is short-circuited and the LCR meter 1
When measuring the leakage inductance at 10, the resistance 112
May be regarded as open, and the resistors 116 and 120 may be regarded as short-circuited. Therefore, the leakage inductance Δx viewed from the primary side is expressed by the following equation.

[0030]

(Equation 7)

Here, b0≫Δx.

As described above, since the leakage inductance is uniquely determined based on the relative positional relationship between the windings, it is preferable that the distance between the windings can be set arbitrarily.

Therefore, the transformer according to the first aspect of the present invention provides a first bobbin for winding a primary winding, a second bobbin for winding a secondary winding, the first bobbin and the second bobbin. And an adjusting means for adjusting a distance between the first bobbin and the second bobbin in a longitudinal direction of the iron core.

According to the present invention, the iron core, that is, the core is inserted into the first bobbin for winding the primary winding and the second bobbin for winding the secondary winding. When a current flows through the primary winding on which the first bobbin is wound, a current flows through the secondary winding by electromagnetic induction in accordance with the turn ratio of the primary winding and the secondary winding. When a current flows through the primary winding and the secondary winding, a magnetic flux is generated in a direction intersecting the direction of the current, that is, in the longitudinal direction of the iron core.

The adjusting means adjusts the distance between the first bobbin and the second bobbin in the longitudinal direction of the iron core, that is, the direction in which the magnetic flux is generated. Thus, the distance between the first bobbin and the second bobbin in the longitudinal direction of the iron core can be adjusted, so that the target leakage inductance can be easily set.

The adjusting means may be a supporting means for movably supporting at least one of the first bobbin and the second bobbin.
This may be achieved, for example, by providing a thread on the iron core or a member covering the iron core, providing a thread groove on the first bobbin and the second bobbin, and supporting the first bobbin and the second bobbin as a screw structure. The bobbins may be supported by being tightened from both sides with nuts or the like.

Also, as described in claim 3, the adjusting means may be a spacer for regulating the distance between the first bobbin and the second bobbin in the longitudinal direction of the iron core.

According to a fourth aspect of the present invention, there is provided a bobbin for winding a primary winding and a secondary winding, and a shaft portion for inserting the bobbin, wherein the primary winding and the secondary winding are provided. A first iron core connected to a predetermined area around the bobbin around which is wound, and a first iron core connected to the shaft portion and rotatably supported by the first iron core in a predetermined area different from the predetermined area. 2
And an iron core.

According to the present invention, the first iron core has the shaft portion for inserting the bobbin for winding the primary winding and the secondary winding, and is connected to a predetermined area around the bobbin. Have been. For example, the first iron core may be shaped so that the magnetic flux generated in the iron core goes around.

The second core is connected to the shaft of the first core, and is rotatably supported in a predetermined area different from the predetermined area with respect to the first iron core. For example, the second iron core may be shaped so that the magnetic flux generated in the iron core goes around.

As described above, since the first iron core or the second iron core is fixed, the other iron core can be rotated when the first iron core or the second iron core is fixed. Thereby, the spatial magnetoresistance between the first iron core and the second iron core can be changed. When the space magnetic resistance changes, the leakage inductance also changes. Therefore, by rotating and fixing any of the iron cores, the leakage inductance can be easily set to the target value.

FIG. 15 shows an example of a conventional general soft-switching power supply. As shown in FIG. 15, the switching power supply 130
2A and a transformer 134 having a secondary winding 132B provided with a middle point. The transformer 134 has a built-in leakage inductance 136.

One end of the primary winding 132A is connected to one end of the resonance capacitor 138, the source terminal of the MOS-FET 140A and the drain terminal of the MOS-FET 140B. The drain terminal of the MOS-FET 140A is connected to the positive side of the DC power supply 142 and one end of the input voltage dividing capacitor 144A. The other end of the input voltage dividing capacitor 144A is connected to the other end of the resonance capacitor 138, the other end of the primary winding 132A, and one end of the capacitor 144B. The other end of the capacitor 144B is M
It is connected to the source terminal of the OS-FET 140B and to the negative side of the DC power supply 142.

A control circuit 146 is connected to the gate terminals of the MOS-FETs 140A and 140B. Control circuit 1
Reference numeral 46 denotes a control signal for turning on / off the MOS-FETs 140A and 140B alternately at a predetermined timing.
The signals are output to the gate terminals of the ETs 140A and 140B. As a result, voltages having different polarities are alternately applied to the primary winding 132A of the transformer 134. That is, the primary winding 13
The circuit on the 2A side is a so-called half-bridge type.

One end of the secondary winding 132B of the transformer 134 is connected to the anode of the rectifying diode 148, and the other end of the secondary winding 132B is connected to the rectifying diode 15B.
0 anode is connected. Rectifier diode 14
The cathodes of 8,150 are connected to one end of a smoothing choke coil 152. The other end of the smoothing choke coil 152 is connected to one end of an output capacitor 154 and a load 156. The middle point of the secondary winding 132B is connected to the other end of the output capacitor 154 and the load 156.

Although not shown, a detection circuit for detecting an output voltage to the load 156 is provided.
46 controls the MOS-FETs 140A and 140B so that the output voltage is stabilized based on the detection voltage.

FIG. 16 shows operation waveforms of various parts of the switching power supply 130. As shown in FIG. 16E, when the load is appropriate, the voltage V3 of the resonance capacitor 138 charges and discharges during the idle period of the MOS-FETs 140A and 140B (Toff period shown in FIG. 16C).
At light load, as shown in FIG. 16D, the energy stored in the leakage inductance 136 is absorbed by the resonance capacitor 138, and the MOS-FET 140A operates before the voltage V3 becomes the power supply voltage Vin. For this reason,
It becomes a hard switching operation.

As shown in FIG. 16 (F), when the load is heavy, the energy stored in the leakage inductance 136 is not absorbed by the resonance capacitor 138, and the voltage V3 exceeds the power supply voltage Vin. At this time, the voltage V generated in the primary winding 132A of the transformer 10
p ′ is the voltage generated by the leakage inductance 136 as Vr
Then, it is expressed by the following equation.

Vp '= Vp-Vr (12) As a result, the voltage V seen from the primary side is applied to the transformer 134.
p 'will decrease. On the other hand, the voltage Vs ′ generated on the secondary side is Np, the number of turns of the primary winding 132A,
If the number of turns of 32B is Ns, it is expressed by the following equation.

Vs ′ = (Ns / Np) · (Vp−Vr) (13) Normally, the control circuit 146 controls the output voltage so that the output voltage is stabilized by frequency control or duty control as the voltage decreases. If the control area is deviated, there is a problem that the output is reduced, and the capacity of the transformer may not be fully utilized. In such a case, for example, by switching the inductance between the light load side and the rated load side, the energy stored in the leakage inductance can be controlled.

Therefore, the invention according to claim 5 provides a transformer comprising: a bobbin on which a plurality of primary windings and secondary windings are wound; and an iron core for inserting the bobbin; Switching means for switching the power applied to the primary winding, and selecting means for selecting a corresponding primary winding according to the power induced on the secondary winding side, I do.

According to the present invention, a plurality of primary windings are provided. The plurality of primary windings are wound around the bobbin such that the leakage inductances have different values. The selection means switches the power applied to the primary winding by the switching means, and thereby selects a corresponding primary winding according to the power induced on the secondary winding side. For example,
If the power output to the secondary winding is large, select the primary winding with small leakage inductance.If the power output to the secondary winding is small, select the primary winding with large leakage inductance. I do.

As described above, since the leakage inductance can be selected according to the output power, soft switching can be optimally performed from a light load to a heavy load.

[0054]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] A first embodiment of the present invention will be described below with reference to the drawings.

FIG. 1A shows a transformer 1 according to the present invention.
0 is shown. 2B is a cross-sectional side view taken along line AA ′ of the transformer 10 shown in FIG. 1A, and FIG. 1C is a front view of the transformer 10 shown in FIG. (D) shows a side view of FIG. (C). FIG. 2 is an exploded view of the transformer 10.

As shown in FIG. 1A, the transformer 10 includes a bobbin 12 and a core 14. Bobbin 12
As shown in FIGS. 1 and 2, the two bobbins 12A and 12B
The core 14 has a substantially E-shaped core 14.
A, 14B. Also, FIG.
As shown in (D), the bobbins 12A and 12B are provided with a plurality of terminals 16 for attaching the transformer 10 to a substrate.

The center shaft 20 of the bobbins 12A and 12B is provided with a thread, and the center shaft 20 of the bobbins 12A and 12B is provided with a thread.
A mounting hole for mounting the cores 14A and 14B is provided therein. Thereby, the cores 14A, 14B
Can be attached to the bobbins 12A and 12B.

A thread is provided on the center shaft 20 of the bobbin 12A, and the center shaft 20 is inserted through a primary winding bobbin 22 for winding a primary winding (not shown).
4, 26, the primary winding bobbin 22 is tightened from both sides. The nuts 24 and 26 are made of a non-magnetic material or a magnetic material, and by adjusting the tightening position of the nuts 24 and 26, the primary winding bobbin 22
Can be adjusted. That is, the primary winding bobbin 22 is movable along the central axis direction of the core 14 and can be fixed at an arbitrary position.

Similarly, the center shaft 20 of the bobbin 12B is provided with a thread. The center shaft 20 passes through a bobbin 28 for secondary winding for winding a secondary winding (not shown), and nuts 30 and 32. Thereby, the secondary winding bobbin 28 is tightened from both sides. These nuts 30 and 32
The secondary winding bobbin 2 is made of a non-magnetic material or a magnetic material by adjusting the tightening position of the nuts 30 and 32.
8 can be adjusted. That is, the secondary winding bobbin 28 is movable along the central axis direction of the core 14 and can be fixed at an arbitrary position.

As described above, since the primary winding bobbin 22 and the secondary winding bobbin 28 can be set at arbitrary positions, the connection between the primary winding and the secondary winding shown in FIG. The distance ΔX between the windings can be set arbitrarily.

The bobbin 22 for the primary winding is the first bobbin of the present invention, the bobbin 28 for the secondary winding is the second bobbin of the present invention, the center shaft 18 is the iron core of the present invention, the nut 24, 2
6, 30, and 32 respectively correspond to the support means of the present invention.

The setting of the leakage inductance is performed as follows. First, the primary winding bobbin 22 is connected to the nuts 24, 2.
6, the nuts 30 and 32 for tightening the secondary winding bobbin 28 are loosened, and the secondary winding side is short-circuited as shown in FIG. Then, while gradually approaching the secondary winding bobbin 28 from a location farthest from the primary winding bobbin 22, for example, the leakage inductance viewed from the primary winding side is measured by the LCR meter 110. Then, when the measured leakage inductance matches the target value, the secondary winding bobbin 28 is tightened and fixed with nuts 30 and 32.

As described above, since the distance between the primary winding and the secondary winding can be arbitrarily set, the leakage inductance can be easily set to the target value.
Therefore, it is possible to improve the yield of products and easily configure a switching power supply capable of performing a soft switching operation using the leakage inductance.

[Second Embodiment] Next, a second embodiment of the present invention will be described. In the second embodiment, a modified example of the transformer 10 described in the first embodiment will be described. The same parts as those of the transformer 10 described in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

The transformer 10 shown in FIG.
4, 36 and 38 are provided. These spacers are fixed to the bobbin 12 by screws 40, 42, and 44, respectively. The primary winding bobbin 22 is fixed by being sandwiched by spacers 34 and 36 from both sides, and the secondary winding bobbin 28 is fixed by being sandwiched by spacers 36 and 38 from both sides.

As described above, the inter-winding distance between the primary winding and the secondary winding is determined by the thickness of the spacer. Therefore,
Plural types of spacers 34, 36, 38 having different thicknesses
Are prepared, and a combination of spacers 34, 36, and 38 that can obtain a target leakage inductance is selected and fixed.

If the magnetic flux distribution of the core 14 is disturbed by forming the screws 40, 42, 44 from a magnetic material, the screws 40, 42, 44 may be formed from a non-magnetic material. Further, the spacers 34, 36, 38 may be fixed to the bobbin 12 by an adhesive instead of the screws 40, 42, 44.

[Third Embodiment] Next, a third embodiment of the present invention will be described. In the third embodiment, a modified example of the transformer 10 in the above embodiment will be described. Note that the same parts as those of the transformer 10 described in the above embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

FIG. 4A is a plan view of the transformer 10 according to the present embodiment. FIG. 2B is a front view of the transformer 10 shown in FIG. 1A, and FIG. 2C is a cross-sectional side view of the transformer 10 shown in FIG. It is shown.

As shown in FIG.
Is provided with cores 14A and 14B, and a central shaft 18 of the core 14A.
Pass through the center axis of the bobbin 12. Bobbin 12
As shown in FIG. 4 (A), the central portion is divided by a partition plate 46 into a primary winding and a secondary winding.

As shown in FIG. 4C, the partition plate 46 has two slide holes 48. Core 14
A and 14B are supported by a core fixing member 50, and the core fixing member 50 is fixed to the partition plate 46 by tightening the nut 52 through the slide hole 48. Also,
By loosening the nut 52, the core 14A can be moved along the slide hole 48 in the direction of arrow A in FIG. The core 14B is fixed. That is, the relative positional relationship between the core 14A and the core 14B can be changed by moving the core 14A.

When the relative positional relationship between the cores 14A and 14B changes in this way, the spatial magnetic resistance between the two changes, and the leakage inductance changes. Therefore, the core 14
By changing the relative positional relationship between A and the core 14B, the leakage inductance can be set arbitrarily.

The core 14A corresponds to the first core of the present invention, and the core 14B corresponds to the second core of the present invention.

The setting of the leakage inductance is performed as follows. That is, the nut 52 for fixing the core fixing member 50 is loosened, and the secondary winding side is short-circuited. Then, while gradually moving the core 14B, for example, in the direction of arrow A shown in FIG. 4C, the leakage inductance as viewed from the primary winding side is measured by the LCR meter 110. Then, when the measured leakage inductance matches the target value, the core 14A is tightened and fixed with the nut 52.

As described above, since the relative positional relationship between the cores 14A and 14B can be adjusted, the target leakage inductance can be easily set.

Note that, as shown in FIG.
Instead, a plurality of mounting holes 54 may be provided in the partition plate 46, and the core fixing member 50 may be fixed to the partition plate 46 with the nuts 52 in the mounting holes 54. Also,
Instead of the nut 52, it may be fixed to the partition plate 54 with an adhesive.

[Fourth Embodiment] Next, a fourth embodiment of the present invention will be described. In the fourth embodiment, a description will be given of a switching power supply device capable of selecting a leakage inductance in a load condition.

As shown in FIG. 6, the switching power supply 60 includes a transformer 10 having primary windings 54A and 54B and a secondary winding 56 provided with a middle point. Further, the transformer 10 includes the leakage inductances 58A and 58A.
B is built in and shown in FIG. 6 as an equivalent circuit.

The transformer 10 has a bobbin 12 and a core 14 as shown in FIG. The center shaft 18 of the core 14 passes through the center shaft 20 of the bobbin 12. A secondary winding 56 is wound around the center shaft 20 of the bobbin 12, a primary winding 54B is provided outside the secondary winding 56, and a primary winding 54 is further provided outside the primary winding 54B.
A is wound each.

As shown in FIG. 7A, the secondary winding 56,
The winding widths of the primary windings 54A and 54B (the width in the direction of the generated magnetic flux, that is, the longitudinal direction of the center shaft 20) are different from each other. That is, the secondary winding 56, the primary windings 54B, 5
The winding width decreases in the order of 4A. For this reason, different magnitudes of leakage inductance are generated between the primary winding 54A and the secondary winding 56 or between the primary winding 54B and the secondary winding 56. The electrical structure of such a transformer is shown in an equivalent circuit in FIG. In this case, the inductance value Lr1 of the leakage inductance 58A> the inductance value Lr2 of the leakage inductance 58B.

By selectively switching the primary windings 54A and 54B according to the load conditions to switch the leakage inductances 58A and 58B, the energy W _Lr1 stored in the leakage inductances according to the magnitude of the output current. Can be controlled.

As shown in FIG. 6, the primary windings 54A, 54
One end of B is connected to the collectors of the transistors 62A and 62B, respectively. The emitters of the transistors 62A and 62B are connected to one end of a resonance capacitor 64 and one end of voltage dividing capacitors 66 and 68, respectively. The other end of the voltage dividing capacitor 66 is connected to the plus side of the DC power supply 70 and the drain of the MOS-FET 71, and the other end of the voltage dividing capacitor 68 is connected to the minus side of the DC power supply 70 and the source of the MOS-FET 72. I have.

The source of the MOS-FET 71 and the MOS-
The drain of the FET 72 is connected to the other ends of the primary windings 54A and 54B.

The gates of the MOS-FETs 71 and 72 are connected to a control circuit 76. The control circuit 76 includes a MOS-
A control signal for turning on and off the FETs 71 and 72 alternately at a predetermined timing is output to the gate terminals of the MOS-FETs 71 and 72. Thereby, the primary winding 5 of the transformer 10
Voltages having different polarities are alternately applied to 4A or 54B. That is, the circuit on the primary winding side is a so-called half-bridge type.

One end of the secondary winding 56 of the transformer 10 is connected to the anode of a rectifying diode 78, and the other end of the secondary winding 56 is connected to the anode of a rectifying diode 80. The cathodes of the rectifier diodes 78 and 80 are connected to one end of a smoothing choke coil 82. The other end of the smoothing choke coil 82 is connected to one end of an output capacitor 84 and a load 86. Also, 2
The middle point of the next winding 56 is connected to the other end of the output capacitor 84 and the current detecting means 88.

The current detecting means 88 is connected to the reference voltage power supply 90 and the comparator 92. The current detecting means 88 detects a current supplied to the load 86, converts the current into a voltage, and outputs the voltage to the comparator 92. The comparator 92 compares the detection voltage with the reference voltage Vref, and outputs the comparison result to the selection circuit 94. For example, a high level is output when the detection voltage is equal to or higher than the reference voltage Vref, and a low level is output when the detection voltage is equal to or lower than the reference voltage Vref. The selection circuit 94 includes the driving circuit 9
6, 98. The driving circuit 96A is connected to the transistor 62A, and the driving circuit 96B is connected to the transistor 62B.

As the selection circuit 94, for example, a non-contact switch circuit such as a contact switch circuit or a semiconductor switch can be used.
Select B. For example, when the comparator 92 outputs a low level, that is, when the detection voltage is lower than the reference voltage Vref (at a light load), the drive circuit 96A is selected to select the primary winding 54A having a large leakage inductance. I do. As a result, the driving circuit 96A outputs the transistor 62A
Is turned on, and a current flows through the primary winding 54A. At this time, since the driving circuit 96B is not selected, the transistor 62B remains off, and no current flows through the primary winding 54B.

At such a light load, the energy W _Lr1 is stored in the leakage inductance 58A by the current I _p1 flowing through the primary winding 54A of the transformer 10. This energy W _Lr1 is transmitted to the resonance capacitor 64 during a period in which the MOS-FETs 71 and 72 are both inactive (off), and raises the potential of V3 shown in FIG. That is, as shown in FIG. 16, if the transmission of the energy W _Lr1 is completed by the time when the pause period of both the MOS-FETs 71 and 72 is completed, the potential of V3 becomes equal to the input voltage Vin, and
The S-FET 71 turns on.

However, if the output current increases and the energy W _Lr1 stored in the leakage inductance 58A increases and cannot be absorbed by the resonance capacitor 64,
As shown in FIG. 16, the potential of V3 becomes equal to the input voltage Vin before the period in which both the MOS-FETs 71 and 72 are inactive.
Will be the same as

Therefore, when the comparator 92 outputs a high level, that is, when the detection voltage is equal to or higher than the reference voltage Vref, the primary winding 5 having a small leakage inductance is output.
The drive circuit 96B is selected to select 4B. As a result, the drive circuit 96B turns on the transistor 62B, and a current flows through the primary winding 54B. At this time, since the driving circuit 96A is not selected, the transistor 62A is not selected.
A remains off, and no current flows through primary winding 54A.

As described above, the detection voltage is equal to the reference voltage Vref.
In the above case, the primary winding 54B having a small leakage inductance is selected, so that the current I
Energy W _Lr2 smaller than energy W _Lr1 due to _p2
Is stored in the leakage inductance 58B. Therefore, the storage time of the energy charged in the resonance capacitor 64 is optimized, and the voltage waveform of V3 is optimized as shown in FIG. That is, an optimal soft switching operation is performed.

As described above, when the output current is large, by selecting the primary winding having the smaller leakage inductance, there is no surplus energy, and the voltage rise of V3 can be suppressed. This can prevent the generation of the reverse voltage V _Lr that reduces the primary voltage of the transformer.

As described above, since the rise and fall characteristics of the switching waveform can be improved by switching the leakage inductance, as shown in FIG. 8, the resonance condition is not satisfied unlike the related art, and the control is stabilized. Even in a region where the output voltage cannot be obtained, the output voltage can be stabilized as shown by the dotted line in FIG.

Further, as shown by the dotted line in FIG. 9, by switching the leakage inductance, the transformer capacity can be effectively used beyond the conventional transformer capacity.

[Fifth Embodiment] Next, a fifth embodiment of the present invention will be described. In the fifth embodiment, a modification of the switching power supply device described in the fourth embodiment will be described. The same parts as those of the switching power supply device described in the fourth embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

The switching power supply shown in FIG.
Are different from the switching power supply shown in FIG. 1 in that MOS-FETs 73 and 74 are added instead of the transistors 62A and 62B, and a resonance capacitor 65 is added.

In such a switching power supply device, when the load is light, the drive circuit 96A is selected by the selection circuit 94 so as to select the primary winding 54A having a large leakage inductance. As a result, the driving circuit 96A has the MOS-FE
By controlling T71 and T72, a current flows through the primary winding 54A. At this time, since the drive circuit 96B is not selected, the MOS-FETs 73 and 74 remain off, and no current flows through the primary winding 54B.

On the other hand, when the output current increases and the detection voltage becomes equal to or higher than the reference voltage Vref, the driving circuit 9 selects the primary winding 54B having a small leakage inductance.
6B is selected. As a result, the driving circuit 96B
By controlling the S-FETs 73 and 74, a current flows through the primary winding 54B. At this time, since the drive circuit 96A is not selected, the MOS-FETs 71 and 72 remain off, and no current flows through the primary winding 54A.

As described above, since the leakage inductance can be switched according to the detected voltage, an optimal soft switching operation can be performed. Further, since the resonance capacitors are separately provided for each of the leakage inductances, the circuit design can be facilitated.

[0100]

As described above, according to the first to fourth aspects of the present invention, there is an effect that the leakage inductance can be easily set to the target value.

According to the fifth aspect of the invention, there is an effect that the soft switching can be optimally performed from a light load to a heavy load.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a transformer according to a first embodiment.

FIG. 2 is an exploded view of a transformer according to the first embodiment.

FIG. 3 is an exploded view of a transformer according to a second embodiment.

FIG. 4 is a schematic configuration diagram of a transformer according to a third embodiment.

FIG. 5 is a schematic configuration diagram of a transformer according to a third embodiment.

FIG. 6 is a schematic configuration diagram of a switching power supply device according to a fourth embodiment.

FIG. 7 is a schematic configuration diagram of a transformer according to a fourth embodiment.

FIG. 8 is a diagram for describing output characteristics when the leakage inductance is switched.

FIG. 9 is a diagram for describing output characteristics when the leakage inductance is switched.

FIG. 10 is a schematic configuration diagram of a switching power supply device according to a fifth embodiment.

FIG. 11 is a schematic configuration diagram of a conventional hard switching transformer.

FIG. 12 is a schematic configuration diagram of a conventional transformer for soft switching.

FIG. 13 is a diagram for describing a relationship between a distance between windings and a leakage inductance.

FIG. 14 is a diagram illustrating a simplified equivalent circuit of a transformer and measurement of leakage inductance.

FIG. 15 is a schematic configuration diagram of a conventional switching power supply.

FIG. 16 is a waveform diagram showing waveforms of various parts of a conventional switching power supply.

[Explanation of symbols]

 Reference Signs List 10 transformer 12 bobbin 14 core 16 terminal 18 choke coil 22 bobbin for primary winding 24, 26, 30, 32 nut 28 bobbin for secondary winding

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01F 30/00 H01F 27/24 Z H02M 3/28 31/00 M

Claims (5)

[Claims] A first bobbin for winding a primary winding; a second bobbin for winding a secondary winding; an iron core passing through the first bobbin and the second bobbin; The first bobbin and the second bobbin in the longitudinal direction of the iron core;
A transformer for adjusting a distance from the bobbin; 2. The transformer according to claim 1, wherein the adjusting means is a supporting means for movably supporting at least one of the first bobbin and the second bobbin. 3. The transformer according to claim 1, wherein the adjusting means is a spacer that regulates a distance between the first bobbin and the second bobbin in the longitudinal direction. 4. A bobbin for winding a primary winding and a secondary winding, and a shaft portion for inserting the bobbin, and a bobbin around which the primary winding and the secondary winding are wound. A first core connected to a surrounding predetermined region; and a second core connected to the shaft portion and rotatably supported in a predetermined region different from the predetermined region with respect to the first core. Equipped transformer. 5. A transformer having a bobbin on which a plurality of primary windings and secondary windings are wound, and a core for inserting the bobbin, and a power applied to the plurality of primary windings. A power supply device comprising: switching means for switching; and selecting means for selecting a corresponding primary winding according to electric power induced on the secondary winding side.