JP3022180B2 - Mounting structure of printed coil type transformer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed coil type transformer suitable for use in a switching power supply, and more particularly to an improved structure for facilitating heat radiation.

[0002]

2. Description of the Related Art As disclosed in Japanese Utility Model Laid-Open No. 4-8390 proposed by the present applicant, a structure for releasing heat generated from an electronic component uses a heat conducting plate to dissipate a radiator or a housing. There is a known structure for transferring heat. However, in an application of a switching power supply having an output of about 100 W, electronic components that generate heat are switching transistors and diodes, and transformers rely on natural heat radiation because of their large size.

FIG. 8 is a side view showing a mounted state of a conventional switching power supply, and a heat radiation path is indicated by an arrow ↑. In the drawing, a mounting substrate 10 is formed in a flat plate shape using an insulating material such as an epoxy resin, and a wiring pattern 12 formed of a conductive material such as copper is provided on one surface or both surfaces. The electronic component 20 generates heat such as a power diode or a power transistor.
0. The heat sink 30 is mounted on the mounting substrate 10.
And thermally radiates heat by contacting the electronic component 20. The transformer 40 uses a conventional winding,
It is mounted on the mounting board 10. Its internal structure is such that a core 41 is mounted in a middle hole of the bobbin 42 and a winding 43 is wound around the bobbin 42 in order to improve electromagnetic coupling. The winding 43 is connected to a terminal 44, and this terminal 4
4 is soldered to a through hole provided in the mounting board 10.

FIG. 9 is a circuit diagram of the device shown in FIG. 8, and a heat radiation path is indicated by an arrow に, as in FIG. In the figure, a DC voltage is applied from an input power source Vin to a primary winding n1 of a transformer T via an input capacitor Cin. Then, the current flowing through the primary winding n1 is turned on / off by the switching transistor Tr connected to the primary winding n1. Then, since a switching signal is induced in the secondary winding n2 of the transformer T, the output voltage Vout is supplied to the load _RL after being rectified by the diode D and rectified by the capacitor Cout.

FIG. 10 is an equivalent circuit diagram of a heat radiation path of a conventional device. As a heating element, a switching transistor Q
_Tr, there are trans Q _T and diode Q _D, each substantially independent. That is, in the transformer T, the heat generated from the winding 43 becomes a problem, and there are two main routes of the heat radiation, that is, convection heat radiation from the surface of the transformer and conduction and heat conduction through the terminal 44. Among them, conduction heat transfer is negligible compared to convection heat dissipation due to its large thermal resistance. The thermal resistance is particularly large because an insulator or air is interposed between the winding heat generating portion and the terminal 44, and the terminal 44 itself is a tin-plated iron wire, so that the thermal resistance is relatively high. For example, JIS as core 43
Using EER25.5 specified in the above, the thermal resistance is 70 ° C
/ W.

[0006]

The transformer T
If the heat is cooled only by convection heat dissipation, the volume must be increased by 2.8 times if the heat loss is doubled ("Designing thermal measures for electronic equipment" p.280). For this reason, there is a problem that the transformer shape becomes large as the power consumption increases.

[0007] When convection heat radiation is used, the thermal resistance changes depending on the arrangement of components around the transformer. For example, the thermal resistance decreases in a position where cooling air is applied well, but conversely if it is behind a tall electronic component. Become. Therefore, if the component arrangement is changed at the time of designing the power supply circuit, the cooling capacity of the transformer greatly changes, and there is a problem that the power supply circuit design and the thermal design cannot be separated and the design work becomes complicated. SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a mounting structure of a printed coil type transformer which has a high cooling efficiency of a power transformer and can be thermally designed irrespective of component arrangement.

[0008]

According to the present invention for achieving the above object, a DC voltage Vin applied to a primary winding Np is turned on / off by a switching element Tr, and a switching signal induced in a secondary winding Ns is generated. A transformer used as a switching power supply for supplying a load _RL after rectifying and smoothing, wherein inner layer patterns 52 are laminated using an insulating resin, and each inner layer pattern is assigned to the primary winding and the secondary winding. A printed coil transformer 50 having a pin terminal 53 made of a copper-based material connected to both ends of the primary winding and the secondary winding, the switching coil and the secondary element being grounded to the AC ground of the switching power supply; A heat sink 30 mounted on the side rectifier circuit, and a wiring pattern 12 for conducting heat between each pin terminal of the printed coil and the heat sink. The switching power supply is provided on a mounting substrate 10 on which the switching power supply is mounted.

[0009]

According to the structure of the present invention, since a printed coil type transformer is used for the transformer, an insulating resin is used to insulate the primary winding and the secondary winding, which is compared with the conventional air insulation. As a result, the transformer shape becomes smaller. Further, the printed coil type transformer and the heat sink are thermally connected by using the pin terminals and the wiring pattern, so that the heat radiation resistance is reduced. Therefore, conduction heat dissipation becomes dominant in heat dissipation of the transformer, and the thermal design is less affected by the arrangement of other components, such as convection heat transfer.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG.
FIG. 1 is a side view illustrating a mounted state of a switching power supply according to an embodiment of the present invention. In FIG. 1, components having the same functions as those in FIG. 8 are denoted by the same reference numerals, and description thereof will be omitted. The printed coil type transformer 50 is an integrated type of a conventional bobbin and a conductive wire, and a specific detailed structure is disclosed in, for example, Japanese Patent Application No. 6-128531 proposed by the present applicant. Here, a core 51 is mounted at the center, and an inner layer pattern 52 is laminated using an insulating resin. The insulation between the primary winding and the secondary winding in the radial and axial directions around the core 51 is ensured by the thickness of the solid insulator. Its withstand voltage is about 10 times that of 1 kV / mm of air and 10 kV / mm for insulating resin. Therefore, the thickness of the insulating layer can be reduced to 1/10 as compared with the conventional air insulation. Then, each inner layer pattern 52 is assigned to the primary winding and the secondary winding.

The pin terminals 53 are connected to both ends of the primary and secondary windings of the transformer, and are made of a copper-based material to reduce the thermal resistance. Since the structure is not such that a winding is wound around the pin terminal 53, the bending rigidity of the pin terminal 53 is small. Therefore, when compared with the conventional soot-plated iron wire, the thermal conductivity of the copper-based material is 10 times or more, so that the heat generated in the winding of the transformer is smoothly conducted to the wiring pattern 12 via the pin terminal 53. The wiring pattern 12 is formed on the mounting substrate 10, and is made of a copper-based material to reduce electric resistance. The terminal 32 for fixing the mounting board 10 of the heat sink 30 is connected to the wiring pattern 12.

FIG. 2 is a circuit diagram of the apparatus shown in FIG. 1. Components having the same functions as those shown in FIG.
Here, the primary winding n1 and the secondary winding n2 of the transformer 40
Is marked on the AC ground side. Heat sink 30
Are connected to the AC ground side. Thus, noise propagation due to stray capacitance between the heat sink 30 and the surrounding components can be reduced.

FIG. 3 is an equivalent circuit diagram of a heat radiation path of the device of FIG. In the printed coil type transformer, the shape of the transformer is much smaller than that of the conventional type, so that the cooling capacity by convective heat radiation is reduced by the reduced surface area. On the other hand, as for the conduction heat transfer, the pin terminal 53
The thermal resistance R52 up to the pin terminal 53 and the wiring pattern 1
2, a thermal resistance R12 from the wiring pattern 12 to the fixing terminal 32, and a thermal resistance R30 of the heat sink 30. Here, the thermal resistance R52 is 10 ° C /
W and the thermal resistance R53 is about 10 ° C./W per one for a terminal diameter φ of 1.0 mm and a terminal length of 5 mm. It can be set to a sufficiently low value. Accordingly, the thermal resistance R52 + 53 from the winding heat-generating portion to the wiring pattern 12 can be reduced to approximately 6 ° C./W, which is 1/10 of the conventional example.
About the same thermal resistance. By the way, thermal resistance R12 and thermal resistance R
In the case of 30, the heat resistance can be made sufficiently small by design, so that a sufficient cooling capacity can be obtained by conduction heat transfer.

FIG. 4 is a perspective view showing the configuration of a second embodiment of the present invention, and FIG. 5 is a circuit diagram of the apparatus shown in FIG. Here, the heat sink 30 on the primary side and the secondary side of the switching power supply is shared. With this configuration, the heat radiation efficiency becomes better than when the primary side and the secondary side heat sinks 30 of the switching power supply are separated.

FIG. 6 is a perspective view showing the configuration of a third embodiment of the present invention, and FIG. 7 is a circuit diagram of the apparatus shown in FIG. Here, an additional heat sink 34 is provided because the cooling capacity is insufficient only with the heat sink 30 for the electronic component 20. The additional heat sink 34 is also thermally connected to the wiring pattern 12 to help the transformer 40 radiate heat. This wiring pattern 12 is used as an AC ground.

[0016]

As described above, according to the present invention,
In radiating the heat generated by the primary and secondary windings of the transformer, the printed coil type transformer is used to reduce the heat radiation resistance from the winding heating part to the pin terminals 53, so that compared to the conventional method Cooling by conduction heat dissipation becomes easy,
In particular, there is an effect that cooling becomes easy when the size of the transformer is reduced and the convection heat radiation ability is small. Further, since the heat generated by the transformer is substantially cooled by conduction heat radiation using the heat sink 30, there is also an effect that the thermal design is not affected by the arrangement of the electronic components.

[Brief description of the drawings]

FIG. 1 is a side view illustrating a mounted state of a switching power supply according to an embodiment of the present invention.

FIG. 2 is a plan view of a flat coil portion 23 for an auxiliary winding.

FIG. 3 is an equivalent circuit diagram of a heat radiation path of the device of FIG.

FIG. 4 is a configuration perspective view showing a second embodiment of the present invention.

FIG. 5 is a circuit diagram of the device of FIG.

FIG. 6 is a configuration perspective view showing a third embodiment of the present invention.

FIG. 7 is a circuit diagram of the device of FIG. 6;

FIG. 8 is a side view illustrating a mounting state of a conventional switching power supply.

FIG. 9 is a circuit diagram of the device of FIG.

FIG. 10 is an equivalent circuit diagram of a heat radiation path of a conventional device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Mounting board 12 Wiring pattern 20 Electronic component 30 Heat sink 50 Print coil type transformer 52 Inner layer pattern 53 Pin terminal

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01F 27/08 H01F 30/00

Claims (1)

(57) [Claims] A switching element (Tr) turns on and off a DC voltage (Vin) applied to a primary winding (Np), rectifies and smoothes a switching signal induced in a secondary winding (Ns), and loads the load ( R _L ), wherein the inner layer pattern (52) is laminated using an insulating resin, each inner layer pattern is assigned to the primary winding and the secondary winding, and A printed coil type transformer (50) having a pin terminal (53) made of a copper-based material connected to both ends of the winding and the secondary winding, and grounded to the AC ground of the switching power supply; A heat sink (30) mounted on the secondary side rectifier circuit and a wiring pattern (12) for conducting heat between each pin terminal of the printed coil and the heat sink are applied. Mounting structure of a printed-coil transformer, characterized in that provided in the mounted by a mounting board of the switching power supply (10).