JP2015222758A - Step-down transformer and step-down converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow for reduction in the heating of a primary coil and enhancement of heat dissipation, in a step-down transformer.SOLUTION: Spacer conductors (101ab, 101ac, 101bb, 101bc) are arranged between first and third secondary coils (L2a, L2c) and heat dissipation patterns (111a, 111b) formed on a first outer layer. The spacer conductors (101ab, 101ac, 101bb, 101bc) form a space between the first and third secondary coils (L2a, L2c), and the heat dissipation patterns (111a, 111b) formed on the first outer layer, and electrically connects the first and third secondary coils (L2a, L2c), and the heat dissipation patterns (111a, 111b) formed on the first outer layer.

Description

  The present invention relates to a step-down transformer and a step-down converter using the step-down transformer.

  Conventionally, a low voltage side coil (secondary side coil) in which a conductive plate is punched is formed above and below a high voltage side coil (primary side coil) in which a sheet-like conductor having a coil pattern and an insulating layer are integrally provided. A transformer composed of stacked layers is known. For example, the primary coil is formed on a printed circuit board, and the secondary coil is formed of a copper plate, an aluminum plate, or the like (see, for example, Patent Document 1 and Patent Document 2).

JP 2004-303857 A JP 2011-77328 A

  Heat is generated when a current flows through the primary side coil and the secondary side coil. Therefore, it is necessary to radiate heat from the primary side coil and the secondary side coil. In the step-down transformer, since the current flowing through the secondary coil is larger than the current flowing through the primary coil, the heat generation of the secondary coil is particularly large. The primary side coil in which such secondary side coils are stacked one above the other (that is, sandwiched between the secondary side coils) is not easily radiated.

  The transformer which patent document 2 discloses has the structure by which the heat-transfer area | region was provided in the position which does not overlap with a secondary side coil among the printed circuit boards in which the coil pattern of the primary side coil was formed. The primary coil is dissipated by the heat transfer region. However, since the heat transfer region is provided at a position away from the coil pattern of the primary coil, for example, the central portion of the coil pattern (the central portion of the heat generating portion) is not easily radiated. Further, when the number of turns of the primary coil increases, the number of turns of the coil pattern also increases. Therefore, for example, the width of the coil pattern is narrowed and the resistance value is increased, and the heat generation of the primary side coil is further increased. Although the resistance value can be reduced by increasing the thickness of the coil pattern, it involves an increase in cost.

  The present invention has been made to solve the above-described problems, and is intended to enable reduction of heat generation and improvement of heat dissipation of a primary coil in a step-down transformer.

  A step-down transformer according to the present invention is a step-down transformer that steps down a voltage input to a primary side and outputs the voltage to a secondary side, and includes a multilayer substrate, first to fourth secondary coils, and a spacer conductor. With. The multilayer substrate includes a first outer layer, a second outer layer, an inner layer, a heat dissipation pattern, and first and second coil patterns. The first outer layer is the upper surface layer. The second outer layer is a lower surface layer. The heat dissipation pattern is formed on each of the first and second outer layers. The first primary coil pattern is provided on the inner layer. The second primary coil pattern is provided in the inner layer and is connected in series to the first primary coil pattern. The first secondary coil is located above the multilayer substrate. The first secondary coil is magnetically coupled to the first primary coil pattern. The second secondary coil is positioned below the multilayer substrate and is connected to the first secondary coil. The second secondary coil is magnetically coupled to the second primary coil pattern. The third secondary coil is located above the multilayer substrate. The third secondary coil is magnetically coupled to the first primary coil pattern. The fourth secondary coil is located below the multilayer substrate and is connected to the third secondary coil. The fourth secondary coil is magnetically coupled to the second primary coil pattern. The spacer conductor is disposed between the first and third secondary coils and the heat dissipation pattern formed in the first outer layer. The spacer conductor forms a space between the first and third secondary coils and the heat dissipation pattern formed in the first outer layer, and the first and third secondary coils, The heat dissipation pattern formed on the outer layer is electrically connected.

  With the configuration described above, the primary coil pattern provided in the inner layer of the multilayer substrate is radiated through the heat dissipation pattern formed in the outer layer of the multilayer substrate. In the primary coil pattern, since the first and second primary coil patterns are connected in series, the heat generated in the primary coil pattern is the heat generated in the first primary coil pattern, Dispersed in the heat generated in the second primary coil pattern. Therefore, the heat generation of the primary coil pattern is reduced.

  Moreover, according to the said structure, a space (space) is formed by the spacer conductor between the 1st and 3rd secondary coil and the thermal radiation pattern formed in the 1st outer layer. By forming the space, the heat generated in the secondary coil becomes difficult to be transmitted to the primary coil pattern. As a result, the primary coil pattern is easily radiated.

  The first and third secondary coils and the heat radiation pattern formed on the first outer layer are electrically connected by the spacer conductor. Therefore, the heat radiation pattern formed in the first outer layer has the same potential as the secondary coil. Therefore, the magnetic coupling between the primary side coil pattern and the secondary side coil is not hindered by the heat radiation pattern.

  A step-down converter according to the present invention includes the step-down transformer described above.

  According to the present invention, in the step-down transformer, it is possible to reduce the heat generation of the primary coil and improve the heat dissipation.

FIG. 3 is a diagram for explaining a circuit block of the converter according to the first embodiment. It is a figure for demonstrating typically the waveform of the primary side voltage of a transformer part, and the waveform of a secondary side voltage. It is a perspective view of a converter. It is the perspective view which expanded the transformer part in FIG. It is a disassembled perspective view of a transformer part. It is a figure for demonstrating a 1st outer layer. It is a figure for demonstrating a 1st inner layer. It is a figure for demonstrating a 2nd inner layer. It is a figure for demonstrating a 2nd outer layer. It is sectional drawing of a transformer part. It is a figure for demonstrating a thermal radiation path | route. 10 is a diagram for explaining an example of a shape of a spacer conductor used in Embodiment 2. FIG. It is a figure for demonstrating another shape of a spacer conductor. FIG. 6 is a diagram for explaining a circuit block of a converter according to a third embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated. In the description of the embodiment, when the number and amount are referred to, it is not necessarily limited to the number and amount unless otherwise specified.

[Embodiment 1]
FIG. 1 is a diagram for explaining a circuit block of converter 100 according to the first embodiment. Converter 100 is a step-down converter. In the example shown in FIG. 1, converter 100 is an insulating step-down converter.

  Referring to FIG. 1, converter 100 includes terminals T1P, T1N, T2P, and T2N, a primary side circuit 1, a transformer unit 2, a secondary side circuit 3, and a control circuit 4.

  The terminal T1P is a positive input terminal. The terminal T1N is a negative-side input terminal. The terminal T2P is a positive output terminal. The terminal T2N is an output terminal on the negative electrode side. The primary circuit 1 is a circuit provided on the high voltage side (primary side) of the transformer unit 2. The secondary side circuit 3 is a circuit provided on the low voltage side (secondary side) of the transformer unit 2.

  DC voltage Vpn is input to terminals T1P and T1N. The DC voltage Vpn is supplied from, for example, a DC voltage source (not shown).

  Primary circuit 1 includes an input capacitor C1, switching elements S1a to S1d, and nodes N1ab and N1cd.

  Primary circuit 1 converts DC voltage Vpn input to terminals T1P and T1N into an AC voltage and outputs the AC voltage to nodes N1ab and N1cd. The primary side circuit 1 is a general DC-AC (DC-AC) inverter circuit.

  The input capacitor C1 is provided at the input portion of the primary side circuit 1. One end of the input capacitor C1 is connected to the terminal T1P, and the other end is connected to the terminal T1N. For example, the ripple superimposed on the DC voltage Vpn is removed by the input capacitor C1. In particular, the ripple may increase when the wiring from the DC voltage source (not shown) to the terminals T1P and T1N is long.

  Switching elements S1a and S1b are connected in series and arranged between terminal T1P and terminal T1N. Similarly, switching elements S1c and S1d are connected in series and arranged between terminal T1P and terminal T1N.

  The switching elements S1a to S1d are, for example, field effect transistors (MOSFETs). However, the type of the switching element is not particularly limited. The drain of the switching element S1a is connected to the terminal T1P, and the source is connected to the node N1ab. The drain of the switching element S1b is connected to the node N1ab, and the source is connected to the terminal T1N. The drain of the switching element S1c is connected to the terminal T1P, and the source is connected to the node N1cd. The drain of the switching element S1d is connected to the node N1cd, and the source is connected to the terminal T1N.

  The gates and sources of the switching elements S1a to S1d are connected to the control circuit 4, respectively. Each gate voltage (gate-source voltage) of the switching elements S1a to S1d is controlled by a control signal from the control circuit 4. That is, the switching operation of the switching elements S1a to S1d is controlled by the control circuit 4.

  Transformer unit 2 includes primary coils L1a and L1b, secondary coils L2a to L2d, and nodes N2ab and N2cd. The transformer unit 2 is a step-down transformer that steps down the voltage input to the primary side and outputs it to the secondary side.

  Primary coils L1a and L1b are connected in series and arranged between nodes N1ab and N1cd. Specifically, one end of the primary coil L1a is connected to the node N1ab. The other end of the primary coil L1a is connected to one end of the primary coil L1b. The other end of primary side coil L1b is connected to node N1cd. By connecting the primary side coils L1a and L1b in series, a coil having a number of turns equal to the number of turns of the primary side coil L1a and the number of turns of the primary side coil L1b is realized.

  One end of secondary coil L2a and one end of secondary coil L2b are connected to each other at node N2ab. One end of secondary coil L2c and one end of secondary coil L2d are connected at node N2cd.

  When a current flows through the primary coil 1a, the primary coil 1a and the secondary coils L2a and L2b are magnetically coupled. When a current flows through the primary coil 1b, the primary coil 1b and the secondary coils L2c and L2d are magnetically coupled.

  Transformer secondary side circuit 3 includes rectifying elements D1a to D1d, smoothing coils L3a and L3b, and a smoothing capacitor C3.

  The rectifying elements D1a to D1d are, for example, diodes. However, the type of rectifying element is not particularly limited. All of the anodes of the rectifying elements D1a to D1d are connected to the terminal T2N. The cathode of the rectifying element D1a is connected to the other end of the secondary coil L2a. The cathode of the rectifying element D1b is connected to the other end of the secondary coil L2b. The cathode of the rectifying element D1c is connected to the other end of the secondary coil L2c. The cathode of the rectifying element D1d is connected to the other end of the secondary coil L2d.

  One end of smoothing coil L3a is connected to node N2ab, and the other end is connected to terminal T2P. One end of smoothing coil L3b is connected to node N2cd, and the other end is connected to terminal T2P.

  One end of the smoothing capacitor C3 is connected to the terminal T2P, and the other end is connected to the terminal T2N.

  The output of the transformer secondary side circuit 3 is fed back to the control circuit 4. Thereby, the control circuit 4 can control the switching elements S1a to S1d while monitoring the output of the transformer secondary side circuit 3.

  The control circuit 4 transmits (applies) a control signal (control voltage) having a complementary logic level to the gates of the switching elements S1a and S1b and the gates of the switching elements S1c and S1d. Thereby, an AC voltage having an amplitude value of DC voltage Vpn is generated between nodes N1ab and N1cd.

  The alternating voltage generated between the nodes N1ab and N1cd is applied to the primary side coils L1a and L1b of the transformer unit 2. Thereby, an alternating current flows through the primary side coils L1a and L1b.

  When an alternating current flows through the primary side coils L1a and L1b, an alternating current flows through the secondary side coils L2a to L2d by magnetic coupling. Thereby, an alternating voltage is generated in the secondary coils L2a to L2d.

  The voltage generated in the secondary side coils L2a to L2d is a voltage stepped down from the voltage applied to the primary side coils L1a and L1b. The ratio (step-down ratio) between the voltage applied to the primary side coils L1a and L1b and the voltage generated in the secondary side coils L2a to L2d is the number of turns of the primary side coils L1a and L1b and the secondary side coils L2a to L2a. It is determined by the ratio (turn ratio) with the number of turns of L2d.

  The AC voltage generated in the secondary coils L2a to L2d is rectified by the rectifying elements D1a to D1d. The rectified voltage is smoothed by the smoothing coils L3a and L3b and the smoothing capacitor C3. As a result, a DC voltage is output between the terminals T2P and T2N.

  The level of the DC voltage output between the terminals T2P and T2N can be adjusted by changing the turn ratio between the primary side coils L1a and L1b and the secondary side coils L2a to L2d. For example, if the number of turns of the primary side coils L1a and L1b is 4 turns and the number of turns of the secondary side coils L2a to L2d is 1 turn, the primary side coils L1a and L1b and the secondary side coils L2a to L2d The turns ratio is 8: 1.

  The control circuit 4 controls the switching elements S1a to S1d while monitoring the voltage of the smoothing capacitor C3 so that a desired DC voltage is output between the terminals T2P and T2N.

  FIG. 2 is a diagram for schematically explaining the waveform of the input side voltage (primary side voltage) and the waveform of the output side voltage (secondary side voltage) of the transformer unit 2. In FIG. 2, the horizontal axis indicates time, and the vertical axis indicates voltage.

  Referring to FIGS. 1 and 2, in converter 100, at time t0, switching elements S1a to S1d are all turned off (non-conducting state).

  At time t10, switching elements S1a and S1d are turned on (conductive state), and switching elements S1b and S1c are turned off. As a result, the voltage at the node N1ab rises to a voltage (+ Vpn) that is higher than the voltage at the node N1cd by the DC voltage Vpn. A voltage (+ Vpn) between N1ab and N1cd is applied to the primary coils L1a and L1b. Accordingly, a reduced voltage (+ Vpn / 8) is generated in secondary coils L2a and L2c. At the same time, the secondary side coils L2b and L2d generate a voltage (-Vpn / 8) having the same magnitude as that of the voltage generated in the secondary side coils L2a and L2c but having the opposite polarity.

  At time t20, all of switching elements S1a to S1d are turned off. Thereby, for example, it can be avoided that all the switching elements S1a to S1d are simultaneously turned ON and the terminals T1P and T1N are short-circuited.

  At time t30, switching elements S1b and S1c are turned on, and switching elements S1a and S1d are turned off. As a result, the voltage at the node N1ab drops to a voltage (−Vpn) that is lower than the voltage at the node N1cd by the DC voltage Vpn. A voltage (−Vpn) between N1ab and N1cd is applied to the primary side coils L1a and L1b. Accordingly, a reduced voltage (−Vpn / 8) is generated in secondary coils L2a and L2c. At the same time, the secondary side coils L2b and L2d generate a voltage (+ Vpn / 8) having the same magnitude as that of the voltage generated in the secondary side coils L2a and L2c but having the opposite polarity.

  At time t40, switching elements S1a to S1d are all turned off again. After time t40, the operations from time t0 to t40 are repeated.

  As described above with reference to FIGS. 1 and 2, converter 100 includes a step-down transformer (transformer unit 2) that steps down the voltage input to the primary side and outputs the voltage to the secondary side. Since the primary side coils L1a and L1b and the secondary side coils L2a to L2d generate heat due to current, it is necessary to dissipate heat. The transformer unit 2 is a step-down transformer, and the current flowing through the secondary coils L2a to L2d is larger than the current flowing through the primary coils L1a and L1b. Therefore, in converter 100, the heat generation of secondary coils L2a to L2d is relatively large. When the secondary side coils L2a to L2d generate heat, there is a possibility that the heat radiation of the primary side coils L1a and L1b may be hindered.

  Next, heat dissipation of converter 100 including primary side coils L1a and L1b and secondary side coils L2a to L2d will be described.

  FIG. 3 is a perspective view of converter 100. Referring to FIG. 3, converter 100 further includes a housing H. The housing H accommodates the primary side circuit 1, the transformer unit 2, the secondary side circuit 3, and the control circuit 4. The housing H is made of aluminum, for example. Note that some components of the converter 100 such as the components of the control circuit 4 and the cover of the housing H are not shown.

  As described above, the primary side circuit 1 includes four switching elements (switching elements S1a to S1d in FIG. 1). The transformer unit 2 includes core body portions 21ah and 21bh, which will be described later. Secondary circuit 3 includes smoothing coils L3a and L3b.

  The components of the converter 100 such as the primary side circuit 1, the transformer unit 2, the secondary side circuit 3, and the control circuit 4 are arranged on the bottom surface S of the housing H as parts. Each part can generate heat by operation. The heat generated in each component is, for example, transferred to the housing H (the bottom surface S) and then released to the outside of the converter 100. If the temperature of each component of converter 100 becomes too high, normal operation of converter 100 may be hindered.

  The housing H is cooled. The casing H may be cooled by air cooling or water cooling, for example. By cooling the housing H, each component is easily radiated through the housing H. That is, the housing | casing H has a function as a heat sink.

  4 and 5 are diagrams for explaining the transformer section 2. 4 is an enlarged perspective view of the transformer section 2 in FIG. Referring to FIG. 4, transformer section 2 includes primary side coils L1a and L1b (not shown in FIG. 4) described above with reference to FIG. 1, and secondary side coils L2a to L2d. Furthermore, the transformer unit 2 includes core body portions 21ah and 21bh, which will be described later, insulating resins 22ah and 22bh, and a printed circuit board 23.

  FIG. 5 is an exploded perspective view of the transformer unit 2. Referring to FIG. 5, transformer part 2 includes primary side coils L1a and L1b, secondary side coils L2a to L2d, core body parts 21ah and 21bh, insulating resins 22ah and 22bh, printed circuit board 23, Insulation sheets 24a and 24b, core bottom surface portions 25ah and 25bh, and spacer conductors 101aa to 101ad and 101ba to 101bd are further included.

  The core body 21ah has a core axis 21ac. The core main body 21bh has a core axis 21bc. The main component of the core main body portions 21ah and 21bh is a magnetic material. Core shaft centers 21ac and 21bc are inserted into openings H1a and H1b, respectively.

  The printed circuit board 23 has openings H1a and H1b and primary coils L1a and L1b. The primary coil L1a is provided around the opening H1a. The primary coil L1b is provided around the opening H1b.

  The printed board 23 is a multilayer board having four wiring layers. However, the number of wiring layers is not particularly limited. Of the four wiring layers, two wiring layers are outer layers (surface layers) of the printed circuit board 23, and the other two wiring layers are inner layers of the printed circuit board 23. The primary coils L1a and L1b are provided in the inner layer of the printed circuit board 23. Specifically, in the inner layer of the printed circuit board 23, the primary side coils L1a and L1b are formed as a wiring pattern. On the outer layer of the printed board 23, a wiring pattern for heat dissipation (not shown in FIG. 5) is formed. In the printed board 23, each wiring layer is insulated by, for example, resin. Therefore, the heat radiation wiring pattern formed in the outer layer and the primary side coils L1a and L1b provided in the inner layer are insulated from each other. On the other hand, in the printed circuit board 23, each wiring layer is thermally connected by resin. Therefore, the heat generated in the primary side coils L1a and L1b provided in the inner layer is transmitted to the heat radiation wiring pattern formed in the outer layer through the resin.

  Secondary coils L2a and L2b have an arc-shaped wiring pattern that overlaps with primary coil L1a. Secondary coils L2c and L2d have a wiring pattern on an arc that overlaps with primary coil L1b.

  The secondary side coil L2a is arranged so as to overlap the primary side coil L1a in the vertical direction ("UD direction" shown in FIG. 5). In the example illustrated in FIG. 5, the secondary coil L <b> 2 a is located above the printed circuit board 23 (U direction side). Secondary coil L2a is magnetically coupled to primary coil L1a.

  The secondary coil L2b is disposed so as to overlap the primary coil L1a in the vertical direction. The secondary side coil L2c is located below the printed circuit board 23 (D direction side). Secondary coil L2b is magnetically coupled to primary coil L1a.

  The secondary side coil L2c is disposed so as to overlap the primary side coil L1b in the vertical direction. The secondary coil L2c is positioned above the printed circuit board 23. Secondary coil L2c is magnetically coupled to primary coil L1b.

  The secondary coil L2d is disposed so as to overlap the primary coil L1b in the up-down direction. The secondary coil L2c is located below the printed circuit board 23. Secondary coil L2d is magnetically coupled to primary coil L1b.

  As shown in FIG. 5, the core axis 21ac is inserted into the secondary coils L2a and L2b, and the core axis 21bc is inserted into the secondary coils L2c and L2d. The primary side coils L1a and L1b and the secondary side coils L2a to L2d are arranged so as to share the core axes 21ac and 21bc, thereby improving the magnetic coupling between them. As a result, the function of the transformer unit 2 as a step-down transformer is enhanced.

  In FIG. 5, one end of the secondary coil L <b> 2 a and one end of the secondary coil L <b> 2 b are electrically connected at a location connected by a one-dot chain line. This connection location corresponds to the node N2ab in FIG. Similarly, one end of the secondary coil L2c and one end of the secondary coil L2d are electrically connected. This connection location corresponds to the node N2cd in FIG.

  The spacer conductors 101aa to 101ad and 101ba to 101bd are arranged between the secondary coils L2a and L2c and the heat radiation pattern formed on the outer layer above the printed circuit board 23. Specifically, one side of the spacer conductors 101aa to 101ad and 101ba to 101bd is connected to the heat radiation pattern. The connection is realized by soldering, for example. The other sides of the spacer conductors 101aa to 101ad and 101ba to 101bd are in contact with the secondary coils L2a and L2c.

  With the spacer conductors 101aa to 101ad and 101ba to 101bd, the printed circuit board 23 and the secondary coils L2a and L2c are arranged with a space therebetween. That is, the spacer conductors 101aa to 101ad and 101ba to 101bd form a space between the secondary coils L2a and L2c and the heat radiation pattern formed on the outer layer above the printed circuit board 23, and the secondary coil L2a. L2c and the heat radiation pattern formed on the outer layer above the printed circuit board 23 are electrically connected.

  The heat radiation pattern formed on the outer layer below the printed circuit board 23 is in close contact with the secondary coils L2b and L2d. Accordingly, the secondary coils L2b and L2d are electrically connected to the heat radiation pattern formed on the outer layer below the printed circuit board 23.

  For this reason, the heat radiation patterns formed on the upper and lower outer layers, respectively, and the secondary coils L2a to L2d are electrically connected. Therefore, the heat dissipation pattern has the same potential as the secondary side coils L2a to L2d.

  If the heat dissipation pattern and the secondary side coils L2a to L2d are not electrically connected, the heat dissipation pattern is not at the same potential as the secondary side coils L2a to L2d. For example, the primary side coils L1a and L1b It can be an intermediate potential between the potential and the potential of the secondary coils L2a to L2d. In that case, the heat dissipation pattern functions as a shield plate, and magnetic coupling between the primary side coils L1a and L1b and the secondary side coils L2a to L2d is prevented. Further, when the heat dissipation pattern functions as a shield plate, heat is also generated in the heat dissipation pattern.

  On the other hand, since the heat radiation pattern is set to the same potential as the secondary side coils L2a to L2d, magnetic coupling between the primary side coils L1a and L1b and the secondary side coils L2a to L2d is caused by the heat radiation pattern. There is no hindrance.

  Therefore, it is preferable that the heat radiation pattern and the secondary side coils L2a to L2d are electrically connected satisfactorily. Good electrical connection means, for example, connection through as little electrical resistance as possible. For this purpose, for example, the insulating resins 22ah and 22bh may be pressed downward by an elastic member such as a spring.

  The insulating resin 22ah is inserted between the core main body 21ah and the secondary coil L2a to insulate the core main body 21ah from the secondary coil L2a. Similarly, the insulating resin 22bh is inserted between the core main body 21bh and the secondary coil L2c to insulate the core main body 21bh from the secondary coil L2c.

  The bottom surface S of the housing H has a placement portion Sa. The placement portion Sa is a protrusion formed so as to extend upward from the bottom surface S.

  The insulating sheet 24a is disposed on the placement portion Sa. A part of the secondary coil L2b is disposed on the insulating sheet 24a. Since the mounting portion Sa has a predetermined height, a part of the secondary coil L2b is supported by the insulating sheet 24a and the mounting portion Sa so as to be positioned above the core bottom surface portion 25ah. Therefore, the secondary coil L2b (other part) and the core bottom surface part 25ah are arranged with a space therebetween. Thereby, the secondary side coil L2b and the core bottom face part 25ah are insulated from each other.

  Similarly, a part of the secondary coil L2d is disposed on the insulating sheet 24b. The insulating sheet 24b is disposed on a placement unit (not shown). Since the mounting portion has a predetermined height, a part of the secondary coil L2d is supported by the insulating sheet 24b and the mounting portion so as to be positioned above the core bottom surface portion 25bh. Therefore, the secondary coil L2d (other part) and the core bottom surface part 25bh are arranged with a space therebetween. Thereby, the secondary coil L2d and the core bottom surface portion 25bh are insulated from each other.

  As described above, the housing H functions as a heat sink. That is, the heat sink (housing H) is positioned below the secondary coils L2b and L2d. The insulating sheets 24a and 24b are disposed between the secondary coils L2b and L2d and the heat sink. The insulating sheets 24a and 24b thermally connect the secondary coils L2b and L2d and the heat sink.

  6 to 9 are diagrams for explaining the wiring patterns of the respective wiring layers of the printed circuit board 23 shown in FIG. 5 and the like. 6 to 9, printed circuit board 23 includes wiring layers L1 to L4 as the wiring layers. The wiring layers L1 to L4 are stacked in this order. The wiring layer L1 is a wiring layer on the surface layer (first outer layer) located on the uppermost side (the U direction side in FIG. 4) in the printed circuit board 23. The wiring layer L2 is an inner layer (first inner layer) wiring layer located below the wiring layer L1 (the D direction side in FIG. 4) on the printed circuit board 23. The wiring layer L3 is a wiring layer of an inner layer (second inner layer) located below the wiring layer L2 in the printed circuit board 23. The wiring layer L4 is a wiring layer of the surface layer (second outer layer) located on the lowermost side in the printed circuit board 23.

  FIG. 6 is a diagram for explaining the wiring layer L1 (first outer layer). Referring to FIG. 6, wiring layer L1 includes heat radiation patterns 111a and 111b, vias 112a and 112b, and thermal diffusion patterns 113aa to 113ah. Openings H1a and H1b are formed in the wiring layer L1.

  The heat dissipation pattern 111a is a heat dissipation pattern formed around the opening H1a. The heat dissipation pattern 111b is a heat dissipation pattern formed around the opening H1b.

  The via 112a is a via hole (through via) that penetrates each layer and electrically connects them. As will be described later, the via 112a is used to connect the wiring layer L2 and the wiring layer L3. Therefore, in the wiring layer L1, the via 112a is electrically isolated from other portions. Specifically, the heat dissipation patterns 111a and 111b and the vias 112a and 112b are arranged so as not to overlap. Thereby, heat dissipation patterns 111a and 111b and vias 112a and 112b are insulated. Note that vias that connect only the wiring layers L2 and L3 can be used, but using such vias increases costs, for example, compared to using through vias. That is, the cost can be reduced by using the via 112a as a through via.

  Spacer conductors 101aa to 101ad and 101bb to 101bd are provided on the heat radiation patterns 111a and 111b. Specifically, spacer conductors 101aa to 101ad are provided on the heat radiation pattern 111a. Spacer conductors 101bb to 101bd are provided on the heat dissipation pattern 111b. As described above, each spacer conductor is soldered to each heat radiation pattern. Soldering is performed by, for example, a reflow soldering process after removing the resist in a portion where each spacer conductor is provided from a solder resist formed on each heat radiation pattern.

  FIG. 7 is a diagram for explaining the wiring layer L2 (first inner layer). Referring to FIG. 7, wiring layer L2 includes vias 112a and 112b, thermal diffusion patterns 113ca to 113cf, coil wiring patterns 114a and 114b, connection patterns 115a and 115b, and transformer connection parts V1 and V2. . Similarly to the wiring layer L1, openings H1a and H1b are also formed in the wiring layer L2.

  The coil wiring pattern 114a is wound around the opening H1a. The number of turns of the coil wiring pattern 114a can be set to 2 turns, for example. The coil wiring pattern 114b is wound around the opening H1b. The number of turns of the coil wiring pattern 114b can also be set to 2 turns, for example.

  The connection pattern 115a connects the coil wiring pattern 114a and the transformer connection part V1. The transformer connection unit V1 corresponds to the node N1ab shown in FIG. The connection pattern 115b connects the coil wiring pattern 114b and the transformer connection part V2. The transformer connection unit V2 corresponds to the node N1cd shown in FIG.

  FIG. 8 is a diagram for explaining the wiring layer L3 (second inner layer). Referring to FIG. 8, wiring layer L3 includes vias 112a and 112b, thermal diffusion patterns 113da to 113df, coil wiring patterns 114c and 114d, and connection pattern 115c. Similarly to the wiring layers L1 and L2, openings H1a and H1b are also formed in the wiring layer L3.

  The coil wiring pattern 114c is wound around the opening H1a. For example, the number of turns of the coil wiring pattern 114c can be two turns. The coil wiring pattern 114d is wound around the opening H1b. The number of turns of the coil wiring pattern 114d can also be set to 2 turns, for example.

  The connection pattern 115c connects the coil wiring pattern 114c and the coil wiring pattern 114d.

  Here, referring to FIG. 7 and FIG. 8, the coil wiring pattern 114c is connected to the coil wiring pattern 114a through the via 112a. Coil wiring patterns 114a and 114c constitute a first primary coil pattern provided in the inner layer (wiring layers L2 and L3). The coil wiring pattern 114b is connected to the coil wiring pattern 114d through the via 112b. The coil wiring patterns 114b and 114d constitute a second primary coil pattern provided in the inner layer (wiring layers L2 and L3). Coil wiring patterns 114b and 114d (second primary coil pattern) are connected in series to coil wiring patterns 114a and 114c (first primary coil pattern) via connection pattern 115c.

  FIG. 9 is a diagram for explaining the wiring layer L4 (second outer layer). Referring to FIG. 9, wiring layer L4 includes vias 112a and 112b, heat radiation patterns 111c and 111d, and thermal diffusion patterns 113ba to 113bh. Similarly to the wiring layers L1 to L3, openings H1a and H1b are also formed in the wiring layer L4.

  The heat dissipation pattern 111c is formed around the opening H1a. The heat radiation pattern 111d is formed around the opening H1b.

  The heat dissipation patterns 111c and 111d and the vias 112a and 112b are arranged so as not to overlap. Thereby, the heat radiation patterns 111c and 111d and the vias 112a and 112b are insulated.

  Here, a path of current flowing through the inner layer, that is, a path of current flowing through the wiring layer L2 (FIG. 7) and the wiring layer L3 (FIG. 8) will be described. Referring to FIGS. 7 and 8, the current input to transformer connection portion V1 passes through connection pattern 115a, coil wiring pattern 114a, via 112a, and coil wiring pattern 114c (that is, the first primary coil pattern). . Furthermore, the current passes through the connection pattern 115c, passes through the coil wiring pattern 114d, the via 112b, and the coil wiring pattern 114b (that is, the second primary coil pattern) and is output to the transformer connection portion V2. Note that the current input to the transformer connection V2 is output to the transformer connection V1 through a path opposite to that described above.

  10 is a cross-sectional view of the transformer section 2 taken along the line XX of FIG. For convenience of explanation, only a part of the configuration of the transformer unit 2 is illustrated.

  Referring to FIG. 10, bottom surface S (hereinafter simply referred to as “housing H” including bottom surface S) of housing H shown in FIG. 4 and the like has a convex cross section upward (U direction). . On the other hand, the printed circuit board 23 and the secondary coils L2b and L2d as a whole have a concave cross section facing downward (D direction).

  The secondary coil L2b is thermally connected to the housing H via the insulating sheet 51c. The insulating sheet 51c corresponds to the insulating sheet 24a in FIG. The secondary coil L2d is thermally connected to the housing H via the insulating sheet 51b. The insulating sheet 51b corresponds to the insulating sheet 24b in FIG. A portion of the printed circuit board 23 that does not overlap with the secondary coils L2b and L2d (a central portion of the printed circuit board 23) is thermally connected to the housing H via the insulating sheet 51a. Therefore, the heat generated in the printed circuit board 23 and the secondary side coils L2a to L2d is transferred to the housing H and then released to the outside of the housing H. That is, the primary side coils (coil wiring patterns 114a to 114d) and the secondary side coils L2a to L2d provided in the inner layer of the printed circuit board 23 are dissipated.

  FIG. 11 is a diagram for explaining a heat dissipation path. In FIG. 11, the heat dissipation path passing through the insulating sheets 51c and 51a is indicated by arrows. The description of the heat dissipation path passing through the insulating sheet 51b shown in FIG. 10 is the same as the heat dissipation path passing through the insulating sheet 51c described below.

  Referring to FIG. 11, the heat generated in coil wiring patterns 114a to 114d of wiring layers L2 and L3, that is, the heat generated mainly in the primary coil is connected to the connection patterns in wiring layers L2 and L3 (the connections in FIG. 7). Patterns 115a and 115b, connection pattern 115c in FIG. 8) and thermal diffusion patterns (thermal diffusion patterns 113ca to 113cf in FIG. 7 and thermal diffusion patterns 113da to 113df in FIG. 8). Thereby, the heat generated in the primary coil is diffused in the plane direction of the wiring layers L2 and L3 (P1). The diffused heat is transferred to the heat radiation pattern 111a of the wiring layer L1 and the heat radiation pattern 111c of the wiring layer L4 through the insulating resin (P2).

  The heat transferred to the heat radiation pattern 111a and the like of the wiring layer L1 passes through the heat diffusion pattern (such as the heat diffusion patterns 113aa to 113ah in FIG. 6) and is transferred toward the insulating sheet 51a (P3), and the wiring layers L2 and L3 , L4 and the insulating sheet 51a and transmitted to the housing H (P4, P5). The heat transferred to the heat dissipation pattern 111a and the like of the wiring layer L1 can also be released to the space between the heat diffusion pattern and the secondary coil L2a (P9).

  The heat transferred to the heat dissipation pattern 111c and the like of the wiring layer L4 is transferred to the housing H mainly through the following two types of paths. The first path is the same as that of the wiring layer L1. That is, it is a path that passes through the heat diffusion pattern (heat diffusion patterns 113ba to 113bh in FIG. 9) and transmits toward the insulating sheet 51a side (P6), and passes through the insulating sheet 51a to the housing H (P5). . The second path is a path that transmits to the secondary coil L2b (P7), passes through the insulating sheet 51c, and transmits to the housing H (P8).

  Thus, thermal diffusion is performed in the plane direction by the thermal diffusion pattern formed in the wiring layers L2 and L3 which are inner layers. Furthermore, thermal diffusion is performed in the plane direction also by the thermal diffusion pattern formed in the wiring layers L1 and L4 which are outer layers. Therefore, for example, even at the center of the coil wiring pattern, heat is easily radiated. Further, the primary side coil is divided into left and right parts by primary side coils L1a and L1b connected in series, so that the heat generation of the primary side coil is dispersed. Therefore, the heat generation of the primary side coil is reduced.

  The heat generated in the secondary coil L2a passes through the connection point with the secondary coil L2b (the chain line in FIG. 5) and is transferred to the secondary coil L2b. The heat transmitted to L2b is transmitted to the housing H through the insulating sheet 51b together with the heat generated in the secondary coil L2b.

  In order to improve thermal conductivity, the secondary coil L2a can be formed of, for example, a copper plate or an aluminum plate. By making copper or aluminum into a plate shape (a shape having a thickness) instead of a sheet shape, for example, the thermal diffusion effect in the planar direction is enhanced. Thereby, the secondary side coil L2a is smoothly radiated of heat via the secondary side coil L2b.

  Here, if there is no spacer conductor 101 and the secondary coil L2a and the heat radiation pattern 111a of the wiring layer L1 etc. are in contact with each other with a large contact area, most of the heat generated in the secondary coil L2a is This is transmitted to the heat radiation pattern 111a of the wiring layer L1. Then, the heat passes through the heat diffusion pattern of the wiring layer L1 and is transmitted toward the insulating sheet 51a side. The heat transferred to the insulating sheet 51a side is transferred to the housing H through the wiring layers L1 to L4 and the insulating sheet 51a. That is, the heat dissipation path of the secondary coil L2a and the heat dissipation path of the primary coil (wiring patterns of the wiring layers L2 and L3) overlap. Therefore, heat dissipation of the primary coil is hindered.

  On the other hand, as shown in FIG. 11 and the like, the secondary coil L2a and the heat dissipation pattern 111a of the wiring layer L1 are connected via the spacer conductors 101ab and 101ac, so that the spacer conductors 101ab and 101ac are not passed. The contact area between the secondary coil L2a and the wiring layer L1 is reduced as compared with the case where the secondary coil L2a and the heat radiation pattern 111a of the wiring layer L1 are connected. Therefore, the heat generated in the secondary coil L2a is not easily transmitted to the heat radiation pattern 111a of the wiring layer L1. Therefore, the heat dissipation of the primary coil is not hindered and the heat dissipation of the primary coil is improved. In the example shown in FIG. 10, the spacer conductor (spacer conductor 101ab or the like) has a rectangular cross-sectional shape.

  In addition, the effect of improving the thermal diffusion in the planar direction of the printed circuit board 23 at the portion to which the spacer conductor of the wiring layer L1 is connected can be expected by the spacer conductor (such as the spacer conductor 101ab). As the spacer conductor, for example, a metal such as copper or aluminum can be used.

  As described above, according to the first embodiment, the heat of the primary coil formed in the inner layer of the printed circuit board 23 is diffused in the plane direction by the connection pattern and the heat dissipation pattern, so that the heat dissipation efficiency is improved. .

  Furthermore, since the primary side coil is divided into two (primary side coils L1a and L1b), heat generation is dispersed. Therefore, the heat generation of the primary side coil is reduced.

  Further, the secondary side coils L2a and L2c and the printed board 23 are arranged with a space (with a space) by the spacer conductor 101. Thereby, it can suppress that the heat which generate | occur | produced with the secondary side coils L2a and L2c is transmitted to the printed circuit board 23. FIG. Therefore, heat dissipation of the primary side coil included in the printed circuit board 23 is ensured.

  The secondary coils L2b and L2d and the printed circuit board 23 are thermally connected to the housing H via insulating sheets 51b, 51c and 51a. Therefore, the secondary coils L2b and L2d and the printed board 23 are efficiently radiated.

  In addition, the spacer conductor 101 fixes the heat radiation pattern of the outer layer (wiring layer L1) of the printed circuit board 23 to the potentials of the secondary coils L2a and L2b. Accordingly, it is possible to prevent the magnetic coupling between the primary side coil and the secondary side coil, which are generated when the heat radiation pattern functions as a shield plate, and the heat generation of the heat radiation pattern.

  As described above, according to the first embodiment, it is possible to reduce the heat generation of the primary coil and improve the heat dissipation.

[Embodiment 2]
In the first embodiment, the case of a spacer conductor having a rectangular cross-sectional shape (such as the spacer conductor 101ab in FIG. 10) has been described. However, by devising the shape of the spacer conductor, heat dissipation can be further improved. is there. In the second embodiment, an example of a spacer conductor with improved heat dissipation will be described.

  FIG. 12 is a diagram for explaining an example of the shape of the spacer conductor used in the second embodiment. Since the portions corresponding to the respective components shown in FIG. 7 are the same, description thereof will not be repeated here.

  Referring to FIG. 12, spacer conductor 101y includes a contact portion 101ya and a connection portion 101yb. The contact portion 101ya and the connection portion 101yb have a convex cross section as a whole.

  The contact portion 101ya is in contact with the secondary coil L2a. The connection portion 101yb is connected to a heat radiation pattern 111a formed on the outer layer (wiring layer L1) of the printed board 23. The area of the contact surface between the contact portion 101ya and the secondary coil L2a is smaller than the area of the connection surface between the connection portion 101yb and the heat radiation pattern 111a. As a result, the contact thermal resistance increases, and the heat generated in the secondary coil L <b> 2 a becomes difficult to be transmitted to the heat radiation pattern 111 a of the printed circuit board 23. Further, the cross-sectional area in the thickness direction (vertical direction) of the spacer conductor 101y is also reduced, and the thermal resistance is increased. This also makes it difficult for the heat of the secondary coil L2a to be transferred to the heat dissipation pattern 111a of the printed board 23.

  Here, since the area connecting the spacer conductor 101y and the heat radiation pattern 111a is maintained, for example, in the same size as in FIG. 11, the portion of the printed circuit board 23 of the wiring layer L1 to which the spacer conductor 101y is connected. The thermal diffusion effect in the planar direction is also maintained.

  Since the spacer conductor 101y is used to make the potential of the heat radiation pattern 111a and the potential of the secondary coil L2a the same, so much current does not flow through the spacer conductor 101y (many currents). Flows to the secondary coil L2a). Therefore, even if the sectional area in the thickness direction is small like the spacer conductor 101y, the potential of the heat radiation pattern 111a and the like and the potential of the secondary coil L2a are the same.

  FIG. 13 is a view for explaining still another shape of the spacer conductor. Since the portions corresponding to the respective components shown in FIG. 7 are the same, description thereof will not be repeated here.

  Referring to FIG. 13, spacer conductor 101z includes a contact portion 101za, a connection portion 101zb, and a side plate portion 101zc.

  The contact portion 101za is in contact with the secondary coil L2a. The connection portion 101zb is connected to a heat dissipation pattern 111a formed on the printed board 23. The side plate portion 101zc connects the contact portion 101za and the connection portion 101zb.

  The area of the contact surface between the contact portion 101za and the secondary coil L2a is smaller than the area of the connection surface between the connection portion 101zb and the heat radiation pattern 111a formed on the printed board 23. By enlarging the connection surface with the heat radiation pattern 111a, the portion of the printed board 23 that enhances the thermal diffusion effect can be enlarged. Furthermore, by reducing the side plate portion 101zc, the cross-sectional area in the thickness direction of the spacer conductor 101z is reduced. Thereby, the thermal resistance in the thickness direction can be increased. Heat generated by the secondary coil L2a is not easily transmitted to the heat radiation pattern 111a of the printed circuit board 23 or the like.

  According to the second embodiment, the spacer conductor (the spacer conductor 101y in FIG. 12 and the FIG. The shape of the spacer conductor 101z) is determined. As a result, the heat generated in the secondary coil L2a is not easily transmitted to the heat radiation pattern 111a of the printed circuit board 23 and the like. Further, the thermal diffusion effect in the planar direction of the printed circuit board 23 can be improved.

[Embodiment 3]
In the step-down transformer described above (transformer unit 2 shown in FIG. 1 and the like), the heat radiation of the primary side coil and the secondary side coil includes the heat radiation via the insulating sheets 51a to 51c. In the third embodiment, a method for further improving heat dissipation by improving the thermal conductivity of the insulating sheets 51a to 51c will be described.

  FIG. 14 is a diagram for explaining a circuit block of converter 100A according to the third embodiment. Referring to FIG. 14, converter 100 </ b> A differs from converter 100 (FIG. 1) in that it further includes a wire W and a housing H. Since the configuration of other parts of converter 100A is the same as the corresponding part of converter 100 shown in FIG. 1 and the like, description thereof will not be repeated here.

  The wire W electrically connects the terminal T2N and the housing H. Thereby, the housing | casing H is made into the same electric potential as terminal T2N. Note that the means used to electrically connect the terminal T2N and the housing H is not limited to the wire W.

  As for insulating sheets 51a-51c shown in Drawing 10 etc., thermal conductivity improves, so that a sheet is thin, for example. On the other hand, the thinner the sheet, the lower the insulation performance. Therefore, it is possible to improve the thermal conductivity by reducing the voltage applied to the insulating sheets 51a to 51c and adopting the thin insulating sheets 51a to 51c. The insulating sheets 51a to 51c are inserted between the secondary coil (secondary coils L2b and L2d in the example shown in FIG. 10) and the housing H. Therefore, the voltage applied to the insulating sheets 51a to 51c can be reduced by reducing the potential difference between the secondary coil and the housing H.

  As shown in FIG. 14, by making the potential of the housing H similar to the potential of the terminal T2N that is the reference potential of the secondary side (secondary side coils L2a to L2d) of the transformer unit 2 by the wire W, The voltage applied to the insulating sheets 51a to 51c (FIG. 10) can be made the same as the voltage on the secondary side. As a result, a secondary-side voltage is applied to the insulating sheets 51a to 51c inserted between the secondary-side coil and the housing H. Since the transformer unit 2 is a step-down transformer, the voltage on the secondary side is lower than the voltage on the primary side. That is, a secondary side voltage lower than the primary side voltage is applied to the insulating sheets 51a to 51c.

  Without the wire W, the potential of the housing H is not fixed. For this reason, the housing | casing H may have the electric potential of a primary side, for example. In this case, a voltage corresponding to the voltage difference between the primary side voltage and the secondary side voltage is applied to the insulating sheets 51a to 51c. Therefore, the voltage applied to the insulating sheets 51a to 51c may be larger than the secondary voltage.

  On the other hand, if the potential of the housing H is fixed to the potential of the terminal T2N, a large voltage such as the primary voltage is not applied to the insulating sheets 51a to 51c. Thin insulating sheets having a minimum thickness that can withstand the voltage on the secondary side can be used for the insulating sheets 51a to 51c. By adopting such thin insulating sheets 51a to 51c, the thermal conductivity can be improved.

  As mentioned above, although embodiment of this invention was described, combining the characteristic part of each embodiment mentioned above suitably is planned from the beginning. The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiment but by the scope of claims for patent, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims for patent.

  L1b, L1a Primary side coil, 2 transformer part, 3 secondary side circuit, 4 control circuit, 21ah, 21bh core body part, 21ac, 21bc core axis, 22ah, 22bh insulating resin, 23 printed circuit board, 24a, 24b, 51a-51c insulating sheet, 25ah, 25bh core bottom surface, 100, 100A converter, 101, 101aa-101ad, 101ba-101bd, 101y, 101z spacer conductor, 101ya, 101za contact part, 101yb, 101zb connection part, 101zc side plate part, 111a-111d Heat dissipation pattern, 112a, 112b Via, 113aa-113ah, 113ba-113bh, 113ca-113cf, 113da-113df Thermal diffusion pattern, 114a-114d Coil wiring pattern 115a-115c connection pattern, C1 input capacitor, C3 smoothing capacitor, D1a-D1d rectifier, H housing, H1a, H1b opening, L1-L4 wiring layer, L2a-L2d secondary coil, L3a, L3b smoothing coil, N1ab, N2ab node, S bottom surface, S1a to S1d switching element, Sa mounting part, T1P, T1N, T2N, T2P terminal, V1, V2 transformer connection part, Vpn DC voltage, W wire.

Claims (5)

A step-down transformer that steps down the voltage input to the primary side and outputs it to the secondary side,
A multilayer substrate including a first outer layer being an upper surface layer, a second outer layer being a lower surface layer, and an inner layer;
A heat dissipation pattern formed on each of the first and second outer layers;
A first primary coil pattern provided in the inner layer;
A second primary coil pattern provided in the inner layer and connected in series to the first primary coil pattern;
A first secondary coil positioned above the multilayer substrate and magnetically coupled to the first primary coil pattern;
A second secondary coil located below the multilayer substrate and connected to the first secondary coil and magnetically coupled to the first primary coil pattern;
A third secondary coil located above the multilayer substrate and magnetically coupled to the second primary coil pattern;
A fourth secondary coil located below the multilayer substrate and connected to the third secondary coil and magnetically coupled to the second primary coil pattern;
The first and third secondary coils and the first coil are disposed between the first and third secondary coils and the heat radiation pattern formed in the first outer layer. A space is formed between the heat radiation pattern formed on the outer layer and the first and third secondary coils are electrically connected to the heat radiation pattern formed on the first outer layer. A step-down transformer comprising a spacer conductor. A heat sink located below the second and fourth secondary coils;
An insulating member disposed between the second and fourth secondary coils and the heat sink, and thermally connecting the second and fourth secondary coils and the heat sink. The step-down transformer according to claim 1, further comprising: The spacer conductor is
A connection surface connected to the heat dissipation pattern formed in the first outer layer;
The step-down transformer according to claim 1, further comprising a contact surface that contacts the first and third secondary coils and has an area smaller than the connection surface.   The step-down transformer according to claim 2, wherein the heat sink has a reference potential common to the voltage output from the step-down transformer to the secondary side.   A step-down converter comprising the step-down transformer according to any one of claims 1 to 4.

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