JP6409668B2 - Trance - Google Patents

Description

  The present invention relates to a transformer used in a DC-DC converter.

  Conventionally, a transformer used for a DC-DC converter is known (see Patent Document 1 below). The transformer includes a core made of a soft magnetic material, and a primary coil and a secondary coil wound around the core.

  There are various circuit systems for DC-DC converters, and push-pull type DC-DC converters are known as one type. A primary coil of a transformer for a push-pull type DC-DC converter includes two primary side small coils connected in series with each other, and a center tap (primary side center tap) is provided between the two primary side small coils. Is provided. The secondary coil has the same structure. That is, the secondary coil of the transformer for the push-pull type DC-DC converter includes two secondary side small coils connected in series with each other, and a center tap (secondary coil) is provided between the two secondary side small coils. A secondary center tap) is provided.

JP 2001-237128 A

  However, the transformer may generate a relatively large common mode noise current. That is, as will be described later, when a push-pull type DC-DC converter is operated, a noise current is generated due to stray capacitances parasitic on the two primary small coils. A noise current generated due to one of the two stray capacitances and a noise current generated due to the other stray capacitance flow in opposite directions with respect to GND. Therefore, if the difference between the capacitance values of the two stray capacitances is small, the magnitude of the noise current becomes substantially equal, and the magnitude of the noise current flowing into GND and the magnitude of the noise current flowing out of GND become substantially equal. Therefore, it becomes difficult to generate a common mode noise current. However, if there is a large difference in the capacitance values of the stray capacitances parasitic on the two primary side small coils, the magnitude of the noise current generated due to each stray capacitance becomes non-uniform, and the common mode noise current It tends to occur.

Similarly, if there is a large difference in the capacitance values of the stray capacitances parasitic on the two secondary side small coils, the magnitude of the noise current generated due to each stray capacitance becomes non-uniform, and the common mode Noise current is likely to occur.
Therefore, a transformer that can further reduce the common mode noise current is desired.

  The present invention has been made in view of such a background, and an object of the present invention is to provide a transformer capable of further reducing common mode noise current.

One aspect of the present invention is a transformer used in a push-pull type DC-DC converter,
A core made of soft magnetic material;
A primary coil and a secondary coil wound around the core;
The primary coil includes two primary side small coils of a primary side first small coil and a primary side second small coil connected in series with each other, and a primary provided between the two primary side small coils. Side center tap,
The secondary coil is connected in series between two secondary small coils of a secondary side first small coil and a secondary side second small coil, and the two secondary side small coils. A secondary side center tap provided,
A first small coil pair in which the primary side first small coil is disposed on the inner side of the primary side second small coil, and the primary side second small coil is disposed on the inner side of the primary side first small coil. The primary coil is wound around the core so that two small coil pairs with the second small coil pair are both formed.
A third small coil pair in which the secondary side first small coil is arranged on the inner side of the secondary side second small coil, and the secondary side second small coil is more than the secondary side first small coil. The transformer is characterized in that the secondary coil is wound around the core so that two small coil pairs are formed together with a fourth small coil pair arranged inside.

In the transformer, the primary coil is wound around the core so that two small coil pairs of the first small coil pair and the second small coil pair are formed.
Therefore, the difference in capacitance value between the stray capacitance parasitic on the primary first small coil and the stray capacitance parasitic on the primary second small coil can be reduced. That is, in the first small coil pair, the primary side first small coil is arranged on the inner side of the primary side second small coil. Therefore, in the first small coil pair, the stray capacitance between the primary side first small coil and the core is larger than the stray capacitance between the primary side second small coil and the core. In the second small coil pair, the primary side second small coil is arranged on the inner side of the primary side first small coil. Therefore, in the second small coil pair, the stray capacitance between the primary second small coil and the core is larger than the stray capacitance between the primary first small coil and the core. Therefore, by forming both the first small coil pair and the second small coil pair, stray capacitance between the primary side first small coil and the core, and between the primary side second small coil and the core, The difference in capacitance value from the stray capacitance can be reduced.

  Moreover, the transformer is often housed in a metal case or the like. By accommodating the transformer in the case so that the distance between the first small coil pair and the case wall portion and the distance between the second small coil pair and the case wall portion are constant, The difference in capacitance value between the stray capacitance between the case wall portion and the stray capacitance between the primary second small coil and the case wall portion can be reduced.

  Thus, the transformer can reduce the difference in capacitance value between the stray capacitance parasitic on the primary first small coil and the stray capacitance parasitic on the primary second small coil. Therefore, it is possible to reduce the difference in magnitude between the noise currents generated due to these stray capacitances. Therefore, the difference in magnitude between the noise current flowing into GND via one of the two stray capacitances and the noise current flowing out of GND via the other stray capacitance can be reduced. Therefore, the generation of common mode noise current can be suppressed.

In the transformer, the secondary coil is wound around the core so that two small coil pairs of the third small coil pair and the fourth small coil pair are formed.
Therefore, the difference in capacitance value between the stray capacitance parasitic on the secondary side first small coil and the stray capacitance parasitic on the secondary side second small coil can be reduced. Therefore, the difference in magnitude between the noise currents generated by the two stray capacitances can be reduced, and the generation of the common mode noise current can be suppressed.

  As described above, according to the present invention, a transformer capable of further reducing the common mode noise current can be provided.

FIG. 3 is a cross-sectional view of a transformer in the first embodiment. The schematic diagram of FIG. The circuit diagram of the DC-DC converter in the 2nd electricity supply mode in Example 1. FIG. The circuit diagram of the DC-DC converter in the 1st electricity supply mode in Example 1. FIG. FIG. 3 is a timing diagram of the first switch and the second switch in the first embodiment. The graph showing the state of the 1st switch and the 2nd switch in Example 1, and each parameter. Sectional drawing which represented the trans | transformer typically in Example 2. FIG. FIG. 10 is a cross-sectional view schematically showing a transformer in Example 3, which is a cross-sectional view taken along the line XIII-XIII in FIG. 9. IX-IX sectional drawing of FIG. FIG. 12 is a cross-sectional view schematically showing a transformer in Example 4 and is an XX cross-sectional view of FIG. 11. XI-XI sectional drawing of FIG. The expanded sectional view of one core leg periphery of a transformer in Example 5. FIG. 10 is an enlarged cross-sectional view around the other core leg of the transformer in the fifth embodiment. The circuit diagram of the DC-DC converter in the comparative example 1. FIG. The circuit diagram of the DC-DC converter in the comparative example 2. FIG. The graph showing the state of the 1st switch and the 2nd switch in comparative example 2, and each parameter.

  The transformer can be used for an in-vehicle DC-DC converter to be mounted on a vehicle such as a hybrid vehicle or an electric vehicle.

Example 1
Examples of the transformer will be described with reference to FIGS. As shown in FIG. 3, the transformer 1 of this example is used in a push-pull type DC-DC converter 10. The transformer 1 includes a core 2 made of a soft magnetic material, a primary coil 3, and a secondary coil 4. The primary coil 3 and the secondary coil 4 are wound around the core 2.

The primary coil 3 is provided between two primary side small coils P of a primary side first small coil P1 and a primary side second small coil P2 connected in series with each other, and the two primary side small coils P. Primary side center tap 35 formed.
The secondary coil 4 includes two secondary side small coils S, a secondary side first small coil S1 and a secondary side second small coil S2, which are connected in series with each other, and the two secondary sides. A secondary center tap 45 provided between the small coils S;

As shown in FIG. 1, the primary coil 3 includes a first small coil pair 11 in which the primary first small coil P <b> 1 is arranged on the inner side of the primary second small coil P <b> 2, and the primary second small coil P <b> 2 is primary. The two small coil pairs 11 and 12 are wound around the core 2 so as to form both the second small coil pair 12 disposed on the inner side of the side first small coil P1.
Further, the secondary coil 4 includes a third small coil pair 13 in which the secondary side first small coil S1 is disposed on the inner side of the secondary side second small coil S2, and a secondary side second small coil S2 having two. It is wound around the core 2 so that two small coil pairs 13 and 14 are formed together with the fourth small coil pair 14 disposed on the inner side of the secondary first small coil S1.

  The transformer 1 of this example is used for an in-vehicle DC-DC converter to be mounted on a vehicle such as a hybrid vehicle or an electric vehicle.

  FIG. 2 is a sectional view schematically showing FIG. As shown in the figure, the transformer 1 of this example includes a metal case 17. The core 2 is insulated, and the case 17 is connected to GND. The core 2 includes two core legs 28 including a first core leg 28a and a second core leg 28b, and a connecting portion 29 that connects the two core legs 28a and 28b. The transformer 1 in this example is an inner iron type. In this example, the primary winding 3 and the secondary winding 4 are wound around the two core legs 28a and 28b, respectively.

  The first core leg 28a includes a secondary side first small coil S1, a primary side first small coil P1, a primary side second small coil P2, and a secondary side second small coil S2, in this order from the inside to the outside. It is wound. A first small coil pair 11 is formed by the primary coil 3 wound around the first core leg 28a. That is, in the 1st core leg 28a, the primary side 1st small coil P1 is distribute | arranged inside the primary side 2nd small coil P2. The third small coil pair 13 is formed by the secondary coil 4 wound around the first core leg 28a. That is, in the 1st core leg 28a, the secondary side 1st small coil S1 is distribute | arranged inside the secondary side 2nd small coil S2.

  Further, the second core leg 28b is provided with the secondary side second small coil S2, the primary side second small coil P2, the primary side first small coil P1, and the secondary side first small coil S1, from the inside to the outside, They are wound in this order. A second small coil pair 12 is formed by the primary coil 3 wound around the second core leg 28b. That is, in the 2nd core leg 28b, the primary side 2nd small coil P2 is distribute | arranged inside the primary side 1st small coil P1. The fourth small coil pair 14 is formed by the secondary coil 4 wound around the second core leg 28b. That is, in the second core leg 28b, the secondary side second small coil S2 is arranged on the inner side of the secondary side first small coil S1.

  Next, the structure and operation of the DC-DC converter 10 will be described. As shown in FIGS. 3 and 4, the DCDC-converter 10 of this example includes the transformer 1, the two switches SW1 and SW2, the two diodes 85 and 86, the choke coil 84, and the smoothing capacitor. 82, 83. The first switch SW1 is connected to the primary side first small coil P1, and the second switch SW2 is connected to the primary side second small coil P2. The primary center tap 35 is connected to the positive electrode 801 of the DC power supply 8. The secondary side center tap 45 is connected to the positive side terminal 811 of the load 81. The first diode 85 is connected to the secondary side first small coil S1, and the second diode 86 is connected to the secondary side second small coil S2.

Stray capacitances C _p1 and C _p2 are parasitic between the primary first small coil P1 and GND and between the primary second small coil P2 and GND, respectively. Further, stray capacitances C _s1 and C _s2 are also parasitic between the secondary first small coil S1 and GND and between the secondary second small coil S2 and GND, respectively.
The stray capacitance _Cp1 collectively represents a plurality of stray capacitances existing between the primary side small coil P1 and GND. That is, as shown in FIG. 1, stray capacitance is parasitic between the primary first small coil P <b> 1 and the core 2. Further, stray capacitance is also parasitic between the case 17 connected to the GND and the core 2. Furthermore, stray capacitance is also parasitic between the primary first small coil P1 and the case 17. The plurality of stray capacitances are collectively represented as stray capacitance C _p1 . The same applies to C _p2 , C _s1 , and C _s2 .

As shown in FIG. 5, the first switch SW1 and the second switch S2 are alternately turned on after a predetermined time. The period T of the switches SW1 and SW2, the time D1 when the first switch SW1 is turned on, the time D2 when the second switch SW2 is turned on, the input voltage Vi, and the output voltage Vo have the following relationship: is there.
Vo = (D1 + D2) / T × Vi
The DC-DC converter 10 is configured to obtain a desired output voltage Vo by PWM control of the switches SW1 and S2.

  As shown in FIG. 6, the DC-DC converter 10 turns on only the first switch SW1, turns on only the first switch SW1, turns off both the switches SW1 and SW2, and turns on only the second switch SW2. The second energization mode and the second off mode in which both switches are turned off are sequentially performed. In the first energization mode, since the first switch SW1 is on, the voltage Vd1 (see FIG. 4) at the drain terminal of the first switch SW1 is 0V. In the first energization mode, the voltage V1 is applied to the primary first small coil P1. The same voltage as this voltage is also generated in the primary side second small coil P2. Accordingly, the voltage Vd2 at the drain terminal of the second switch SW2 is 2Vi, which is the sum of the voltage Vi of the primary center tap 35 and the voltage Vi generated in the primary second small coil P2.

  As shown in FIG. 6, after the first energization mode, the first off mode is entered. In the first off mode, since the two switches SW1 and SW2 are both turned off, the voltages Vd1 and Vd2 are equal to the voltage Vi of the primary center tap 35.

  After the first off mode, the second energization mode is entered. In the second energization mode, the relationship between the voltages Vd1 and Vd2 is opposite to that in the first energization mode. That is, Vd2 becomes 0V and Vd1 becomes 2Vi.

  After the second energization mode, the second off mode is set. In the second off mode, as in the first off mode, the two voltages Vd1 and Vd2 are Vi.

For example, at the moment of switching from the first off mode to the second energization mode, the voltage Vd2 falls from Vi to 0. That is, the voltage applied to the stray capacitance C _p2 (see FIG. 3) decreases from Vi to 0. Therefore, in the direction the charge stored in the floating capacitance C _p2 escapes, noise current i _p2 flows. At this time, the voltage Vd1 rises from Vi to 2Vi. That is, the voltage applied to the stray capacitance C _p2 (see FIG. 3) increases from Vi to 2Vi. Therefore, the noise current i _p1 flows in the direction in which charges are stored in the stray capacitance C _p2 . The noise current i _p1 returns to the stray capacitance C _p2 through the case 17 and the like.

As described above, in this example, the primary winding is formed so that the two small coil pairs 11 and 12 of the first small coil pair 11 (see FIGS. 1 and 2) and the second small coil pair 12 are formed. 3 is wound around the core 2. The axial direction of the primary coil 3 of the two primary side small coils P1, P2 included in the first small coil pair 11 and the two primary side small coils P1, P2 included in the second small coil pair 12 ( The lengths in the Z direction are equal. Thus, the stray capacitance C _p1 parasitic on the primary side first small coil P1 and the stray capacitance C _p2 parasitic on the primary side second small coil P2 are made uniform. In this way, as shown in FIG. 3, the magnitudes of the noise currents i _p1 and i _p2 generated due to the two stray capacitances C _p1 and C _p2 are equal to each other. Accordingly, noise current flows from the GND via the magnitude of the noise current _{i p1} that has flowed into the GND via the stray capacitance _{C p1} of one of the two stray capacitances _{C p1, C p2,} the other stray capacitance _{C p2} i The magnitude of _p2 becomes equal. Therefore, the common mode noise current is reduced.

Also, as shown in FIG. 6, for example, at the moment of switching from the second energization mode to the second off mode, the voltage Vd2 increases from 0 to Vi. At this moment, the voltage Vd1 decreases from 2Vi to Vi. Therefore, as shown in FIG. 4, noise currents i _p1 and i _p2 flow in the opposite direction to the moment when the first off mode is switched to the second energization mode (see FIG. 3). In this example, since the two stray capacitances C _p1 and C _p2 are equalized, it is possible to suppress the occurrence of a large common mode noise current in this case as well.

Thus, in the DC-DC converter 10 of this example, every time the switches SW1 and SW2 are switched, the voltages applied to the two stray capacitances C _p1 and C _p2 change in the opposite directions by Vi. Therefore, each time the switches SW1 and SW2 are switched, noise currents i _p1 and i _p2 flowing in opposite directions are generated. However, since the two stray capacitances C _p1 and C _p2 are equalized in this example, the magnitudes of these noise currents i _p1 and i _p2 can be equalized. Therefore, it is possible to suppress the generation of a large common mode noise current.

Further, as described above, the stray capacitances C _s1 and C _s2 are parasitic in the secondary side first small coil S1 and the secondary side second small coil S2 (see FIG. 3), respectively. When the switches S1 and S2 are switched, the voltages Vk1 and Vk2 applied to the stray capacitances C _s1 and C _s2 change in the opposite directions by Vi. Accordingly, the noise currents i _s1 and i _s2 flow in opposite directions.

In this example, the secondary winding 4 is connected to the core 2 so that two small coil pairs 13, 14, that is, a third small coil pair 13 (see FIGS. 1 and 2) and a fourth small coil pair 14 are formed. It is wound around. The lengths in the Z direction between the two secondary small coils S1 and S2 included in the third small coil pair 13 and the two secondary small coils S1 and S2 included in the fourth small coil pair 14 Are equal to each other. Thus, the stray capacitance C _s1 parasitic on the secondary side first small coil S1 and the stray capacitance C _s2 parasitic on the secondary side second small coil S2 are made uniform. In this way, as shown in FIG. 3 and FIG. 4, the magnitudes of the noise currents i _s1 and i _s2 generated due to the two stray capacitances C _s1 and C _s2 are equal to each other. Thus, through the magnitude of the noise current _{i s1, i s2,} which has flowed into the GND via one of the stray capacitance _{C s} of the two stray capacitance _{C s (C s1, C s2} ), and the other stray capacitance _{C s} The magnitudes of the noise currents i _s1 and i _s2 flowing out from the GND become equal. Therefore, the common mode noise current can be reduced.

  As shown in FIGS. 1 and 2, in this example, the primary first small coil P <b> 1 and the secondary first small coil S <b> 1 are adjacent to each other in the radial direction (X direction) of the primary coil 3. Further, the primary side second small coil P2 and the secondary side second small coil S2 are adjacent to each other in the radial direction. A current flows through the primary first small coil P1 and the secondary first small coil S1 simultaneously in the first energization mode (see FIG. 6). In the first energization mode, no current flows through the primary side second small coil P2 and the secondary side second small coil S2. The primary side second small coil P2 and the secondary side second small coil S2 simultaneously flow in the second energization mode. In the second energization mode, no current flows through the primary side first small coil P1 and the secondary side first small coil S1.

The effect of this example will be described. As shown in FIGS. 1 and 2, in this example, the primary coil 3 is arranged so that the two small coil pairs 11 and 12, that is, the first small coil pair 11 and the second small coil pair 12 are both formed. It is wound around the core 2.
Therefore, a difference in capacitance value between the stray capacitance C _p1 parasitic on the primary first small coil P1 and the stray capacitance C _p2 parasitic on the primary second small coil P2 can be reduced. That is, as shown in FIGS. 1 and 2, in the first small coil pair 11, the primary side first small coil P <b> 1 is disposed on the inner side than the primary side second small coil P <b> 2. Therefore, in the first small coil pair 11, the stray capacitance between the primary side first small coil P1 and the core 2 is larger than the stray capacitance between the primary side second small coil P2 and the core 2. In the second small coil pair 12, the primary side second small coil P <b> 2 is arranged on the inner side of the primary side first small coil P <b> 1. Therefore, in the second small coil pair 12, the stray capacitance between the primary side second small coil P <b> 2 and the core 2 is larger than the stray capacitance between the primary side first small coil P <b> 1 and the core 2. Therefore, by forming both the first small coil pair 11 and the second small coil pair 12, the stray capacitance between the primary side first small coil P1 and the core 2 and the primary side second small coil P2 The difference in capacitance value from the stray capacitance with the core 2 can be reduced.

  The transformer 2 is housed in a metal case 17. The distance from the first small coil pair 11 to the first case wall 171 and the distance from the second small coil pair 12 to the second case wall 172 are equal to each other. Therefore, the difference in capacitance value between the stray capacitance between the primary first small coil P1 and the case 17 and the stray capacitance between the primary second small coil P2 and the case 17 is small.

As described above, when both the first small coil pair 11 and the second small coil pair 12 are formed, the difference in stray capacitance between the primary side small coils P1, P2 and the core can be reduced, and the primary side small coil can be reduced. The difference in stray capacitance between P1 and P2 and the case 17 can be reduced. Accordingly, the difference in capacitance value between the stray capacitance C _p1 parasitic on the primary first small coil P1 (see FIGS. 3 and 4) and the stray capacitance C _p2 parasitic on the primary second small coil P2 is reduced. be able to. Therefore, the difference between the noise currents i _p1 and i _p2 generated by the two stray capacitances C _p1 and C _p2 can be reduced. Therefore, a noise current _{i p1, i p2} flowing into GND via stray capacitance _{C p} of one of the two floating capacitance _{C p (C p1, C p2} ), from the GND via the other stray capacitance _{C p} The difference in magnitude with the flowing out noise currents i _p1 and i _p2 can be reduced. Therefore, the generation of common mode noise current can be suppressed.

In this example, as shown in FIGS. 1 and 2, the second small coil pair 13 and 14, the third small coil pair 13 and the fourth small coil pair 14, are formed so that both are formed. A coil 4 is wound around the core 2.
Therefore, for the same reason as the primary coil 3, the stray capacitance C _s1 (see FIGS. 3 and 4) parasitic to the secondary first small coil S1 and the stray capacitance C parasitic to the secondary second small coil S2 are used. The difference in capacitance value from _s2 can be reduced. Therefore, the difference between the noise currents i _s1 and i _s2 generated due to the two stray capacitances C _s1 and C _s2 can be reduced, and the generation of the common mode noise current can be suppressed.

Here, if the capacitance value difference between the stray capacitance C _p1 parasitic on the primary side first small coil P1 and the stray capacitance C _p2 parasitic on the primary side second small coil P2 is large, it is shown in FIG. Thus, the magnitudes of the noise currents i _p1 and i _p2 generated due to these stray capacitances C _p1 and C _p2 become uneven. Therefore, the difference current flows as the primary side common mode noise current i _Np . On the other hand, as shown in FIG. 1, if the primary coil 3 is wound so that both the first small coil pair 11 and the second small coil pair 12 are formed as in this example, The difference in capacitance value between the stray capacitances C _p1 and C _p2 parasitic on the primary side small coils P1 and P2 can be reduced. Therefore, as shown in FIGS. 3 and 4, the difference between the noise currents i _p1 and i _p2 generated due to the stray capacitances C _p1 and C _p2 can be reduced, and the primary common mode noise current i _Np is generated. Can be suppressed.

Further, if the capacitance value difference between the stray capacitance C _s1 parasitic on the secondary first small coil S1 and the stray capacitance C _s2 parasitic on the secondary second small coil S2 is large, FIG. As shown, the magnitudes of the noise currents i _s1 and i _s2 generated due to these two stray capacitances C _s1 and C _s2 become uneven. Therefore, the difference current flows as the secondary-side common mode noise current _iNs . On the other hand, if the secondary coil 4 is wound so that both the third small coil pair 13 and the fourth small coil pair 14 are formed as shown in FIG. It is possible to reduce the difference in capacitance value between the stray capacitances C _s1 and C _s2 parasitic in the two secondary side small coils S1 and S2. Therefore, as shown in FIGS. 3 and 4, the difference between the noise currents i _s1 and i _s2 caused by these stray capacitances C _s1 and C _s2 can be reduced, and the secondary-side common mode noise current i _Ns can be reduced. Generation can be suppressed.

Further, in this example, as shown in FIG. 1, two primary side small coils P1, P2 included in the first small coil pair 11, and two primary side small coils P1, P2 included in the second small coil pair 12, Are equal in length in the Z direction.
Therefore, the stray capacitances C _p1 and C _p2 that are parasitic on the two primary side small coils P1 and P2 can be equalized.

Similarly, in this example, as shown in FIG. 1, two secondary small coils S1 and S2 included in the third small coil pair 13 and two secondary small coils S1 included in the fourth small coil pair 14. , S2 have the same length in the Z direction.
Therefore, the stray capacitances C _s1 and C _s2 that are parasitic on the two secondary small coils S1 and S2 can be made uniform. Therefore, generation of common mode noise current can be further suppressed.

As shown in FIGS. 1 and 2, the transformer 1 of this example includes two core legs 28a and 28b. Of the two core legs 28a, 28b, only one first small coil pair 11 is formed on one core leg 28a. Further, only the second small coil pair 12 is formed on the other core leg 28b. That is, in this example, only one of the first small coil pair 11 and the second small coil pair 12 is formed on each core leg 28a, 28b. Similarly, in this example, only one of the third small coil pair 13 and the fourth small coil pair 14 is formed on each core leg 28a, 28b.
As shown in FIG. 10, both the first small coil pair 11 and the second small coil pair 12 can be formed on each of the core legs 28a and 28b. However, in this case, since the winding method is complicated, it may be difficult to manufacture the transformer 1. On the other hand, if it is like this example, the winding method of the primary coil 3 and the secondary coil 4 can be simplified. Therefore, the transformer 1 can be easily manufactured.

Moreover, as shown in FIG. 1, in this example, the primary side first small coil P1 and the secondary side first small coil S1 are adjacent to each other in the radial direction (X direction). Further, the primary side second small coil P2 and the secondary side second small coil S2 are adjacent to each other in the radial direction.
In this way, the generation of common mode noise current can be further suppressed. That is, if the primary first small coil P1 and the secondary first small coil S1 are adjacent to each other, the small coils P1 and S1 can be brought close to each other. Therefore, the leakage inductance parasitic on these small coils P1 and S1 can be reduced. If the primary second small coil P2 and the secondary second small coil S2 are adjacent to each other, the small coils P2 and S2 can be brought close to each other. Therefore, the leakage inductance parasitic on these small coils P2 and S2 can be reduced. Therefore, generation of common mode noise current due to these leakage inductances can be suppressed.

As shown in FIG. 15, if a large leakage inductance L is parasitic on each of the small coils P1, P2, S1, and S2, the large common mode noise currents i _Np and i _Ns are caused by these inductances L. Is likely to occur. For example as shown in FIG. 16, while the second conduction mode, current I ₂ flows through the primary side second small coil P2 and leakage inductance L _p2. Due to the connected choke coil 84 to the secondary side of the transformer 1, by receiving this influence, the current I ₂ does not change abruptly, gradually changes. When the value of the current i ₂ changes with time, the voltage drops by a value L _p2 dI ₂ / dt obtained by multiplying the time change amount dI ₂ / dt by the leakage inductance L _p2 . That is, the voltage applied to the primary side second small coil P2 is Vi−L _p2 dI ₂ / dt. The same voltage as this voltage is generated in the primary side first small coil P1. Therefore, the change amount ΔVd1 of the voltage Vd1 when the first off mode is switched to the second energization mode is expressed by the following equation (1).
ΔVd1 = Vi−L _p2 dI ₂ / dt (1)

In the second energization mode, since the second switch SW2 is turned on, the voltage Vd2 becomes 0V. That is, when switching from the first off mode to the second energization mode, the voltage Vd2 decreases from Vi to 0. Therefore, the change amount ΔVd2 of Vd2 becomes Vi as shown in the following equation (2).
ΔVd2 = Vi (2)

On the other hand, the noise current i _p1 generated due to the stray capacitance C _p1 of the primary first small coil P1 is expressed by the following equation.
i _p1 = C _p1 · ΔVd1 / Δt
Substituting the above equation (1) here,
i _p1 = C _p1 · (Vi−L _p2 dI ₂ / dt) / Δt (3)
It becomes.

Further, the noise current i _p2 generated due to the stray capacitance C _p2 of the primary second small coil P2 is expressed by the following equation.
i _p1 = C _p2 · ΔVd2 / Δt
Substituting the above equation (2) here,
i _p2 = C _p2 · Vi / Δt (4)

From the above formulas (3) and (4), even if C _p1 = C _p2
i _Np = i _p1 −i _p2 = C _p1 · (−L _p2 dI ₂ / dt) / Δt
It can be seen that a common mode noise current i _Np represented by

Similarly, the common mode noise current i _Ns is also generated on the secondary side due to the leakage inductance L _s2 . Further, during the first energization mode, common mode currents i _Np and i _Ns are generated due to the leakage inductances L _p1 and L _s1 for the same reason as in the second energization mode.

On the other hand, as shown in FIG. 1, if the primary side first small coil P1 and the secondary side first small coil S1 are adjacent to each other in the radial direction (X direction) as shown in this example, these small values are obtained. The coils P1 and S1 can be brought close to each other. Therefore, the leakage inductances L _p1 and L _s1 parasitic on the small coils P1 and S1 can be reduced. In this example, since the primary second small coil P2 and the secondary second small coil S2 are adjacent to each other in the radial direction, the small coils P2 and S2 can be brought close to each other. Therefore, the leakage inductances L _p1 and L _s1 parasitic on the small coils P2 and S2 can be reduced. Therefore, generation of large common mode noise currents i _Np and i _Ns due to the leakage inductance L can be suppressed.

  As described above, according to this example, it is possible to provide a transformer that can further reduce the common mode noise current.

  In this example, only the core 2, the primary coil 3, and the secondary coil 4 are accommodated in the case 17, but the present invention is not limited to this. That is, the case 17 may house electronic components such as the switches SW 1 and SW 2 and the diodes 85 and 86 that constitute the DC-DC converter 10. That is, the case 17 for the transformer 1 may be used, or the case 17 for the DC-DC converter 10 may be used.

(Example 2)
In the following embodiments, the same reference numerals used in the drawings among the reference numerals used in the drawings represent the same components as in the first embodiment unless otherwise specified.

  In this example, the order of winding the primary coil 3 and the secondary coil 4 is changed. As shown in FIG. 7, the core 2 of the present example includes two core legs 28 a and 28 b as in the first embodiment. The first core leg 28a includes a primary side first small coil P1, a secondary side first small coil S1, a primary side second small coil P2, and a secondary side second small coil S2 from the inside to the outside. It is wound in this order. A first small coil pair 11 is formed by the primary coil 3 wound around the first core leg 28a. The third small coil pair 13 is formed by the secondary coil 4 wound around the first core leg 28a.

The second core leg 28b has a primary side second small coil P2, a secondary side second small coil S2, a primary side first small coil P1, and a secondary side first small coil S1, on the inner side. It is wound in this order from the outside to the outside. A second small coil pair 12 is formed by the primary coil 3 wound around the second core leg 28b. The fourth small coil pair 14 is formed by the secondary coil 4 wound around the second core leg 28b.
In addition, the configuration and operational effects similar to those of the first embodiment are provided.

(Example 3)
In this example, the winding method of the primary coil 3 and the secondary coil 4 is changed. As shown in FIGS. 8 and 9, the transformer 1 of this example is a so-called outer iron type. The core 2 includes one core leg 28. The primary coil 3 is wound around the single core leg 28 so that both the first small coil pair 11 and the second small coil pair 12 are formed. The secondary coil 4 is wound around the core leg 28 so that both the third small coil pair 13 and the fourth small coil pair 14 are formed.

  The first core portion 281 of the core leg 28 includes a secondary side second small coil S2, a primary side second small coil P2, a primary side first small coil P1, and a secondary side first small coil S1. It is wound in this order from the inside to the outside. A second small coil pair 12 is formed by the primary coil 3 wound around the first core portion 281. Further, the fourth small coil pair 14 is formed by the secondary coil 4 wound around the first core portion 281.

The second core portion 281 of the core leg 28 includes a secondary side first small coil S1, a primary side first small coil P1, a primary side second small coil P2, and a secondary side second small coil S2. It is wound in this order from the inside to the outside. The first small coil pair 11 is formed by the primary coil 3 wound around the second core portion 282. The third small coil pair 13 is formed by the secondary coil 4 wound around the second core portion 282.
In addition, the configuration and operational effects similar to those of the first embodiment are provided.

Example 4
In this example, the winding method of the primary coil 3 and the secondary coil 4 is changed. As shown in FIGS. 10 and 11, the core 2 of this example includes two core legs 28a and 28b and a connecting portion 29 that connects these core legs 28a and 28b, as in the first embodiment. The transformer 1 of this example is an inner iron type. In this example, the primary coil 3 is wound so that both the first small coil pair 11 and the second small coil pair 12 are formed on each core leg 28a, 28b. Further, the secondary coil 4 is wound around the core legs 28a and 28b so that both the third small coil pair 13 and the fourth small coil pair 14 are formed.

  The first core portion 281 of the first core leg 28a includes a secondary side second small coil S2, a primary side second small coil P2, a primary side first small coil P1, and a secondary side first small coil S2. Are wound in this order from the inside to the outside. A second small coil pair 12 is formed by the primary coil 3 wound around the first core portion 281. The fourth small coil pair 14 is formed by the secondary coil 4 wound around the first core portion 281.

  The second core portion 282 of the second core leg 28a includes a secondary side first small coil S1, a primary side first small coil P1, a primary side second small coil P2, and a secondary side second small coil S2. Are wound in this order from the inside to the outside. The first small coil pair 11 is formed by the primary coil 3 wound around the second core portion 282. Further, the third small coil pair 13 is formed by the secondary coil 4 wound around the second core portion 282.

  The second core leg 28b is also wound with the primary coil 3 and the secondary coil 4 in the same manner as the first core leg 28a.

  The effect of this example will be described. In this example, the first small coil pair 11 to the fourth small coil pair 14 are formed on each of the core legs 28a and 28b. Therefore, as shown in FIG. 10, even if the position of the transformer 1 in the case 17 is shifted, the stray capacitance can be equalized. That is, as shown in FIG. 10, the position of the transformer 1 is shifted, the first core leg 28 a approaches the first case wall 171, and the second core leg 28 b is separated from the second case wall 172. is there. Even in this case, in this example, since both the first small coil pair 11 and the second small coil pair 12 are formed on the first core leg 28a, the primary side first small coil P1 and the first case wall portion 171 are formed. And the stray capacitance between the primary side second small coil P2 and the first case wall portion 171 can be equalized. In addition, since both the third small coil pair 13 and the fourth small coil pair 14 are formed on the first core leg 28a, it is between the secondary first small coil S1 and the first case wall 171. The stray capacitance and the stray capacitance between the secondary side second small coil S2 and the first case wall portion 171 can be equalized.

Although not shown, the position of the transformer 1 may be shifted, the second core leg 28b may approach the second case wall 172, and the first core leg 28a may be separated from the first case wall 171. Even in this case, in this example, since the first small coil pair 11 to the fourth small coil pair 14 are all formed on the second core leg 28b, the stray capacitance parasitic on the primary side small coils P1 and P2 is equalized. In addition, the stray capacitance parasitic on the secondary side small coils S1, S2 can be equalized. Therefore, the generation of common mode noise current can be suppressed.
In addition, the configuration and operational effects similar to those of the first embodiment are provided.

(Example 5)
In this example, the winding method of the primary coil 3 and the secondary coil 4 is changed. As shown in FIGS. 12 and 13, in this example, the primary side first small coil P <b> 1 and the secondary side first small coil S <b> 1 are bifilar wound around the core 2. That is, the primary side first small coil P1 and the secondary side first small coil S1 are gathered together and wound around the core 2 while being twisted. Similarly, the primary side second small coil P <b> 2 and the secondary side second small coil S <b> 2 are bifilar wound around the core 2. That is, the primary side second small coil P2 and the secondary side second small coil S2 are gathered together and wound around the core 2 while being twisted.

When bifilar winding is used, generation of leakage inductance can be further suppressed. Therefore, the leakage inductance of the primary coil 3 and the secondary coil 4 is less likely to be generated, and the generation of the common mode noise current due to the leakage inductance can be more effectively suppressed.
In addition, the configuration and operational effects similar to those of the first embodiment are provided.

DESCRIPTION OF SYMBOLS 1 Transformer 10 DC-DC converter 11 1st small coil pair 12 2nd small coil pair 13 3rd small coil pair 14 4th small coil pair 2 Core 3 Primary coil 35 Primary side center tap 4 Secondary coil 45 Secondary side center Tap P Primary side small coil P1 Primary side first small coil P2 Primary side second small coil S Secondary side small coil S1 Secondary side first small coil S2 Secondary side second small coil

Claims (6)

A transformer (1) used in a push-pull type DC-DC converter (10),
A core (2) made of soft magnetic material;
A primary coil (3) and a secondary coil (4) wound around the core (2);
The primary coil (3) includes two primary side small coils (P) of a primary side first small coil (P1) and a primary side second small coil (P2) connected in series to each other, and the two A primary side center tap (35) provided between the primary side small coils (P),
The secondary coil (4) includes two secondary small coils (S), a secondary first small coil (S1) and a secondary second small coil (S2) connected in series to each other. A secondary center tap (45) provided between the two secondary small coils (S),
The first small coil pair (11) in which the primary side first small coil (P1) is arranged on the inner side of the primary side second small coil (P2), and the primary side second small coil (P2) are The primary coil (11, 12) is formed so that both of the two small coil pairs (11, 12) are formed together with the second small coil pair (12) arranged on the inner side of the primary first small coil (P1). 3) is wound around the core (2),
A third small coil pair (13) in which the secondary side first small coil (S1) is arranged on the inner side of the secondary side second small coil (S2), and the secondary side second small coil (S2). ) Is formed so that both of the two small coil pairs (13, 14) are formed together with the fourth small coil pair (14) arranged on the inner side of the secondary first small coil (S1). A transformer (1), wherein the secondary coil (4) is wound around the core (2).   The two primary small coils (P1, P2) included in the first small coil pair (11) and the two primary small coils (P1, P2) included in the second small coil pair (12). Means that the lengths of the primary coils (3) in the axial direction are equal to each other, the two secondary small coils (S1, S2) included in the third small coil pair (13), and the fourth small coil The transformer (1) according to claim 1, characterized in that the two secondary side small coils (S1, S2) included in the coil pair (14) are equal in length in the axial direction.   The core (2) includes two core legs (28) and a connecting portion (29) for connecting the two core legs (28), and each of the core legs (28) includes the first core legs (28). The primary coil (3) is wound so that both the small coil pair (11) and the second small coil pair (12) are formed, and each of the core legs (28) has the first coil The said secondary coil (4) is wound so that both the 3 small coil pair (13) and the said 4th small coil pair (14) may be formed, The Claim 1 or Claim characterized by the above-mentioned. The transformer (1) according to 2.   The core (2) includes two core legs (28) and a connecting portion (29) for connecting the two core legs (28), and each of the core legs (28) includes the first core legs (28). The primary coil (3) is wound so that only one of the small coil pair (11) and the second small coil pair (12) is formed, and the individual core legs (28) The secondary coil (4) is wound so that only one of the third small coil pair (13) and the fourth small coil pair (14) is formed. The transformer (1) according to claim 1 or 2.   In the DC-DC converter (10), a current flows through the primary side first small coil (P1) and the secondary side first small coil (S1), and the primary side second small coil (P2) and the above A current flows in the first energization mode in which no current flows through the secondary side second small coil (S2), the primary side second small coil (P2) and the secondary side second small coil (S2); The primary side first small coil (P1) and the secondary side first small coil (S1) are configured to alternately perform two energization modes: a second energization mode in which no current flows, and the primary side The first small coil (P1) and the secondary side first small coil (S1) are adjacent to each other in the radial direction of the primary coil (3), and the primary side second small coil (P2) and the secondary side Two small coils (S2) are adjacent to each other in the radial direction. Transformer according to any one of claims 1 to 4, wherein (1).   The primary side first small coil (P1) and the secondary side first small coil (S1) are bifilar wound, and the primary side second small coil (P2) and the secondary side second small coil are wound. The transformer (1) according to claim 5, wherein (S2) is bifilar wound.

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