JP4385393B2 - Connection structure between printed circuit board and heat sink - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a connection structure between a printed circuit board on which circuit components of a power supply device are mounted and a heat radiating plate connected to the ground pattern of the printed circuit board to dissipate heat generating components, and particularly to reduce EMI (electromagnetic interference). The present invention relates to a connection structure between a printed circuit board and a heat sink.
[0002]
[Problems to be solved by the invention]
FIG. 2 is a circuit diagram of a general power supply device mounted on this type of printed circuit board. In the figure, 1 is, for example, an AC power supply of 100 V AC, L and N are input terminals of a power supply device 2 to which the AC power supply 1 is connected. The AC input voltage applied to the input terminals + Vi and −Vi is supplied from the rectifier 4 and the smoothing. After being rectified and smoothed by the capacitor 5, power is converted by the inverter 8 including the switching element 6 and the transformer 7, and the voltage induced in the secondary winding of the transformer 7 is rectified and smoothed by the output side rectifying and smoothing circuit 9. A predetermined DC output voltage is supplied to the terminals + Vo and -Vo.
[0003]
Reference numerals 11 to 16 are bypass capacitors for short-circuiting a wiring circuit at an inconvenient location with a high-frequency potential to the ground line in a high-frequency manner. Here, the bypass capacitors are connected between the AC input voltage line and the ground line. Bypass capacitors 11 and 12, bypass capacitors 13 and 14 connected between the DC input voltage line and the ground line, and bypass capacitors 15 and 16 connected between the DC output voltage line and the ground line. The ground line is connected to the ground terminal FG on the primary side of the power supply device together with the input terminals L and N.
[0004]
By the way, such a power supply device 2 is used to radiate heat from the switching element 6 formed of a transistor, a FET (field effect transistor), or other heat-generating components, as pointed out in, for example, Japanese Patent Laid-Open No. 5-328710. In terms of structure, it is necessary to connect these heat generating components to the heat sink. And since such a heat sink becomes a conductor with a large area, it is usually grounded to a ground pattern formed on a printed circuit board and set to the same potential, thereby stabilizing the operation of the power supply device 2 and inducing interference. We are trying to remove it.
[0005]
Here, the conventional connection structure between the printed circuit board and the heat sink will be described with reference to FIG. 3. 21 is an insulating base material of the printed circuit board 20, 22 is a ground pattern formed on the insulating base material 21, and Although not shown, the primary part of the transformer 7 is mounted on one side of the printed board 20, that is, the right side here, and the secondary part of the transformer 7 is mounted on the other side, that is, the left side of the printed board 20. Reference numeral 23 denotes a secondary side capacitor corresponding to the bypass capacitors 15 and 16 in FIG. 2, and one end of the lead wire is soldered and connected to a plated through hole 25 formed at the secondary side end of the ground pattern 22. Another plated through hole 26 is formed at the primary side end of the ground pattern 22, and the ground terminal FG shown in FIG. 2 is connected thereto. Although not shown here, the other bypass capacitors 11 to 16 also have one end of their lead wires connected to the ground pattern 22 in the same manner as the secondary side capacitor 23.
[0006]
Reference numeral 27 denotes a metal heat radiating fin corresponding to a heat radiating plate, which is thermally connected to a heat generating component such as the switching element 6. The connecting piece 28 formed at the lower end of the heat radiating fin 27 is connected to the ground pattern 22 near the secondary capacitor 23. The ground terminal FG is connected to a metal casing (not shown) that accommodates the power supply device 2 so that the ground pattern 22 and thus the radiation fin 27 are kept at the same potential as the metal casing.
[0007]
However, in the conventional connection structure shown in FIG. 3, a part of the harmonic current flowing from the secondary side to the primary side of the ground pattern 22 is bypassed from the connection piece 28 near the secondary capacitor 23 to the radiation fin 27. As a result, there is a problem that the noise fin voltage increases as the radiating fin 27 becomes a noise radiation source.
[0008]
SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a connection structure between a printed board and a heat sink that can effectively reduce electromagnetic interference from the heat sink.
[0009]
[Means for Solving the Problems]
The connection structure between the printed circuit board and the heat sink in the present invention is the connection structure between the printed circuit board on which the components of the power supply device are mounted and the heat sink connected to the ground pattern of the printed circuit board. The heat sink is connected at one point to a connection portion of the ground pattern in the vicinity.
[0010]
In this way, the harmonic current that passes through the primary and secondary capacitors of the power supply device and enters the ground pattern flows from the secondary side of the ground pattern toward the primary side. The harmonic current does not flow into the heat sink because it is connected to only one point of the ground pattern in the vicinity of the input line, not on the output side. For this reason, the heat radiating plate does not become a noise radiation source, and electromagnetic interference from the heat radiating plate can be effectively reduced.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. 2 and 3 shown in the conventional example are denoted by the same reference numerals, and detailed description of common portions is omitted because it is redundant. In particular, since the circuit diagram shown in FIG. 2 is the same as that of the conventional example, description of the configuration and operation is omitted.
[0012]
FIG. 1 shows a connection structure between a printed circuit board 20 and a heat radiating fin 27 as a heat radiating plate according to an embodiment of the present invention. In this figure, in this embodiment, when the radiating fin 27 is set to the same potential as the ground terminal FG, the connection portion 31 of the ground pattern 22 connected to the connecting piece 28 of the radiating fin 27 is connected to the input line ( In this case, it is provided adjacent to the ground terminal FG near the line from the input terminals L, N to the rectifier 4 shown in FIG. This connection part 31 is actually formed by a plated through hole through which a screw 32 as a fixing member can be inserted, and there is no connection part connected to the heat radiation fin 27 in the ground pattern 22. Further, all the bypass capacitors 11 to 16 constituting the primary side capacitor (not shown) and the secondary side capacitor 23 are connected to the common ground pattern 22 at one end and not connected to the heat radiation fin 27. That is, the radiation fin 27 is connected to the connection portion 31 of the ground pattern 22 at one point. The connection portion 31 to the heat radiation fin 27 is provided on the input side of the ground pattern 22 from any plated through hole 25 that is a connection portion to the primary side capacitor or the secondary side capacitor. Then, the screw 32 is inserted from the solder surface of the printed circuit board 20 into the connecting portion 31 and screwed into a tapped hole formed in the connecting piece 28 of the heat radiating fin 27, thereby fixing the heat radiating fin 27 and the printed circuit board 20. It is like that.
[0013]
Thus, in this embodiment, when the power supply device 2 mounted on the printed circuit board 20 operates and heat-generating components such as the switching element 6 constituting the power supply device 2 generate heat, the heat has good thermal conductivity. The metal heat radiation fin 27 immediately conducts and absorbs and is discharged to the outside of a metal casing (not shown) that houses the power supply device 2.
[0014]
On the other hand, the harmonic current accompanying switching of the switching element 6 passes through the primary side capacitor and the secondary side capacitor 23 constituting the bypass capacitors 11 to 16 and enters the ground pattern 22. This high-frequency current flows from the secondary side of the ground pattern 22 to the metal casing through the ground terminal FG on the primary side. However, the connecting piece 28 of the radiation fin 27 is not on the secondary side of the ground pattern 22 but in the vicinity of the input line. Therefore, a part of the harmonic current bypasses from there and does not flow into the radiating fin 27. Therefore, the radiating fin 27 does not become a noise radiation source, and electromagnetic interference from the radiating fin 27 can be effectively reduced.
[0015]
As described above, in this embodiment, in the connection structure between the printed circuit board 20 on which the components of the power supply device 2 are mounted and the heat radiating fins 27 as the heat radiating plates connected to the ground pattern 22 of the printed circuit board 20, The radiating fin 27 is configured to be connected at one point to the connecting portion 31 of the ground pattern 22 in the vicinity of the two input lines.
[0016]
In this way, the harmonic current that passes through the primary side capacitor and the secondary side capacitor 23 and enters the ground pattern 22 flows from the secondary side of the ground pattern 22 toward the primary side. Harmonic current does not flow into the radiating fin 27 because it is connected not to the output side of the power supply device 2 but to only one point of the ground pattern 22 near the input line. For this reason, the radiation fin 27 does not become a noise radiation source, and electromagnetic interference from the radiation fin 27 can be effectively reduced.
[0017]
In particular, in the present embodiment, the connection portion 31 is provided on the input side of the power supply device 2 further than the connection portions with all the bypass capacitors 11 to 16 incorporated in the power supply device 2. Regardless of how the primary-side capacitor and the secondary-side capacitor are provided, the harmonic current does not flow into the radiating fin 27 by bypass, and the power supply device 2 having high reliability against noise can be constructed.
[0018]
In addition, this invention is not limited to the said Example, A various deformation | transformation implementation is possible. For example, FIG. 2 shows a circuit diagram of the power supply device 2 that converts an AC input voltage into a desired DC output voltage. However, the power supply device 2 that converts a DC input voltage into a DC output voltage may be used, and the circuit configuration thereof is particularly It is not limited. Further, the shape of the heat dissipating fins 27 may be appropriately modified within the scope of the present invention. Further, the connecting portion 31 may be structured to be directly soldered without using a fixing member such as a screw 32, for example.
[0019]
【The invention's effect】
The present invention provides a connection structure between a printed circuit board on which components of a power supply device are mounted and a heat sink connected to the ground pattern of the printed circuit board. The heat sink is connected at one point, and a connection structure between the printed board and the heat sink that can effectively reduce electromagnetic interference from the heat sink can be provided.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a connection structure between a printed board and a heat sink in an embodiment of the present invention.
FIG. 2 is a circuit diagram of a power supply apparatus common to an embodiment of the present invention and a conventional example.
FIG. 3 is a cross-sectional view showing a connection structure between a printed circuit board and a heat sink in a conventional example.
[Explanation of symbols]
20 Printed circuit board
22 Ground pattern
27 Heat dissipation fin (heat sink)
31 Connection

Claims (1)

In a connection structure between a printed board on which components of the power supply device are mounted and a heat sink connected to the ground pattern of the printed board, the heat sink is connected to the connection portion of the ground pattern in the vicinity of the input line of the power supply device. A connection structure between a printed circuit board and a heat sink, characterized by connecting the two at a single point.

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