JPH0845748A - Mounting structure of printed coil transformer - Google Patents

Abstract

PURPOSE:To enhance cooling efficiency of a power-supply transformer by a method wherein a heat dissipation resistance from winding heating parts to pin terminals is reduced using a printed coil transformer. CONSTITUTION:A transformer, which is constituted in a structure where a DC voltage Vin, to a primary winding n1 is turned off by a switching element Tr and a switching signal, induced in a secondary winding n2 is rectified, smoothed, and is fed to a load RL, and is used as a switching power supply, is one of a structure, wherein internal layer patterns 52 are laminated using an insulative resin, the internal layer patterns are allotted to the primary winding and the secondary winding and at the same time, a printed coil transformer 50 having pin terminals 53 which are connected with both ends of the primary and secondary windings and consist of an iron material, a heat sink 30 which is grounded to an AC ground of the switching power supply and at the same time, is mounted on the element Tr and a secondary side rectifying circuit, and a wiring pattern 12 for transferring heat between each terminal of this printed coil transformer and the heat sink 30 are provided on a mounting substrate 10.

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 improvement of a structure for facilitating heat dissipation.

[0002]

2. Description of the Related Art A structure for radiating heat generated by an electronic component, as disclosed in Japanese Utility Model Laid-Open No. 4-8390 proposed by the present applicant, uses a heat conductive plate to dissipate a radiator or a housing. The structure that transfers heat to is known. However, in the use of a switching power supply with an output of about 100 W, what is recognized as an electronic component that generates heat is a switching transistor or diode, and a transformer has a large shape, so that it depends on natural heat radiation.

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

FIG. 9 is a circuit diagram of the device shown in FIG. 8. As in FIG. 8, the heat radiation path is indicated by an arrow ↑. In the figure, a DC voltage from an input power source Vin is applied to the primary winding n1 of the transformer T via an input capacitor Cin. Then, the switching transistor Tr connected to the primary winding n1 turns on / off the current flowing through the primary winding n1. Then, since the switching signal is induced in the secondary winding n2 of the transformer T, the output voltage Vout is supplied to the load R _L by 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 the heating element, the switching transistor Q
_{There is a Tr} , a transformer Q _{T and a} diode Q _D , which are substantially independent. That is, in the transformer T, the heat generated from the winding 43 becomes a problem, but there are two main heat dissipation paths, namely, convective heat dissipation from the surface of the transformer and conductive heat transfer via the terminal 44. Among them, conduction heat transfer has a large thermal resistance, and is negligible as compared with convection heat dissipation. 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 the thermal resistance is relatively high. For example, the core 43 is JIS
The thermal resistance is 70 ° C when using EER25.5 specified in
/ W.

[0006]

By the way, the transformer T
When cooling only with convection heat dissipation, it is necessary to increase the volume by 2.8 times when the heat loss is doubled ("Design of heat countermeasures for electronic devices" p.280). Therefore, there is a problem that the transformer shape becomes large as the power consumption increases.

When convective heat dissipation is used, the heat resistance changes depending on the arrangement of parts around the transformer, and the thermal resistance decreases at a position where cooling air is blown well, for example. Become. Therefore, there has been a problem that if the arrangement of components is changed during power supply circuit design, the cooling capacity of the transformer changes significantly, and the power supply circuit design and thermal design cannot be separated, which complicates the design work. The present invention solves such a problem, and an object of the present invention is to provide a mounting structure of a printed coil transformer in which the cooling efficiency of the power transformer is high and the thermal design can be performed regardless of the 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 for a switching power supply that is rectified and smoothed and supplied to a load _RL , in which 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 pin terminals 53 made of a copper-based material connected to both ends of the primary winding and the secondary winding, grounded to the AC ground of the switching power supply, and connected to the switching element and the secondary. A heat sink 30 mounted on the side rectification circuit, and a wiring pattern 12 for transferring heat between each pin terminal of the print coil and the heat sink are provided. It is characterized in that it is provided on the mounting substrate 10 on which the switching power supply is mounted.

[0009]

According to the structure of the present invention, since the transformer is the printed coil type transformer, the insulating resin is used for the insulation of the primary winding and the secondary winding. Then the transformer shape becomes smaller. Further, the printed coil type transformer and the heat sink are thermally connected by using the pin terminal and the wiring pattern, and the heat radiation resistance is reduced. Therefore, the conduction heat dissipation becomes dominant in the heat dissipation of the transformer, and the thermal design is less affected by the arrangement of other components like convective heat transfer.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG.
FIG. 3 is a side view illustrating a mounting state of a switching power supply showing an embodiment of the present invention. In FIG. 1, components having the same functions as those in FIG. 8 are designated by the same reference numerals and the description thereof will be omitted. The print coil type transformer 50 is a conventional bobbin and a conductor integrated with each other, and a specific detailed structure is disclosed in, for example, Japanese Patent Application No. 6-128531 proposed by the present applicant. Here, the core 51 is mounted in the central portion, and the inner layer pattern 52 is laminated using an insulating resin. Insulation between the primary winding and the secondary winding in the radial direction and the axial direction centering on the core 51 is ensured by the thickness of the solid insulator. The withstand voltage of the insulating resin is 10 kV / mm, which is about 10 times that of 1 kV / mm of air. 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 winding and the secondary winding of the transformer, and are made of a copper material in order to reduce thermal resistance. Since the winding is not wound around the pin terminal 53, the bending rigidity of the pin terminal 53 can be small. Therefore, compared with the conventional soot-plated iron wire, the heat conductivity of the copper-based material is 10 times or more, so that the heat generated in the winding of the transformer is smoothly transferred to the wiring pattern 12 via the pin terminals 53. The wiring pattern 12 is formed on the mounting substrate 10, and a copper-based material is used to reduce electric resistance. The mounting substrate 10 fixing terminal 32 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. The elements having the same functions as those in FIG.
Here, the primary winding n1 and the secondary winding n2 of the transformer 40 are
● is attached to the AC ground side of. Heat sink 30
Is connected to the AC ground side. This can reduce noise propagation due to stray capacitance between the heat sink 30 and surrounding components.

FIG. 3 is an equivalent circuit diagram of the heat radiation path of the device of FIG. In the printed coil transformer, the transformer shape is remarkably downsized as compared with the conventional one, so that the cooling capacity by convective heat dissipation is reduced due to the smaller surface area. On the other hand, for conduction heat transfer, the winding heat generating portion to the pin terminal 53
Heat resistance R52 up to and from pin terminal 53 to wiring pattern 1
There is a thermal resistance R53 up to 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 /
It is about W and the thermal resistance R53 is about 10 ° C / W per one with a terminal diameter φ of 1.0 mm and a terminal length of 5 mm, so if the five pin terminals 53 are configured, it will be about 2 ° C / W. It can be set to a sufficiently low value. Therefore, the total thermal resistance R52 + 53 from the winding heating portion to the wiring pattern 12 can be set to about 6 ° C / W, which is 1/10 of that of the conventional example.
It has some thermal resistance. By the way, thermal resistance R12 and thermal resistance R
Since 30 can have a sufficiently small thermal resistance by design, a sufficient cooling capacity can be obtained by conduction heat transfer.

FIG. 4 is a constitutional perspective view showing a second embodiment of the present invention, and FIG. 5 is a circuit diagram of the device of FIG. Here, the heat sinks 30 on the primary side and the secondary side of the switching power supply are shared. With this configuration, the heat dissipation efficiency is better than in the case where the heat sinks 30 on the primary side and the secondary side of the switching power supply are separated.

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

[0016]

As described above, according to the present invention,
In radiating the heat generated in the primary winding and the secondary winding of the transformer, the heat radiation resistance from the winding heating portion to the pin terminal 53 is reduced by using the printed coil type transformer. Cooling by conduction heat dissipation becomes easy,
In particular, when the transformer is downsized and the convective heat dissipation capacity is small, it is easy to cool the transformer. Further, since the heat generated by the transformer is substantially cooled by conduction and heat dissipation using the heat sink 30, there is an effect that the thermal design is not affected by the arrangement of electronic components.

[Brief description of drawings]

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

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

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

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

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.

7 is a circuit diagram of the device of FIG.

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

9 is a circuit diagram of the device of FIG.

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

[Explanation 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

Claims (1)

[Claims] A direct current voltage (Vin) applied to a primary winding (Np) is turned on and off by a switching element (Tr), a switching signal induced in a secondary winding (Ns) is rectified and smoothed, and a load ( A transformer used for a switching power supply supplied to R _L ), wherein inner layer patterns (52) are 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 pin terminals (53) made of a copper-based material, which are connected to both ends of a winding and a secondary winding, and grounded to the AC ground of the switching power supply, and the switching element and A heat sink (30) attached to the secondary side rectifying circuit and a wiring pattern (12) for transferring heat between each pin terminal of the print coil and the heat sink are provided. Mounting structure of a printed-coil transformer, characterized in that provided in the mounted by a mounting board of the switching power supply (10).