JPH0715090Y2 - Small fuse for printed wiring board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a structure of a small fuse for a printed wiring board which is required to have high breaking performance.

(Prior Art) FIG. 3 shows an external perspective view (A) and a sectional view (B) of an example of a conventional small fuse for a printed wiring board. This type of fuse has a height of 9.5 mm and a width of 10 mm. Often, the external dimensions are about 6 mm in depth. In FIGS. 3A and 3B, 1 is a fuse element, 2 is a cover, 3 is a body, 4 is an insulating material, and 5 is a terminal (metal plate or wire). The cover 2 is made of a transparent resin, and is widely put into practical use as a small fuse for a printed board in which the fusing of the fuse element 1 can be visually confirmed.

FIG. 4 is a sectional view showing another structural example of a small fuse (Japanese Utility Model Laid-Open No. 56-107654). In this example, a metal cover 6 and a metal base 7 are used in place of the insulating cover and the base, and terminals are used. Glass 8 is used for insulation from 5.

(Problems to be solved by the invention) The fuse shown in FIG. 3 can be interrupted without a problem when a relatively small overcurrent flows, but when an overcurrent due to a load short circuit or the like flows, the fuse occurs at the time of interruption. There is a risk that the insulating cover 2 will be destroyed due to the increase in the air pressure inside the fuse, and at the same time the high temperature metallic gas will be ejected, causing the destruction and burning of peripheral parts.

When the fuse of FIG. 4 is interrupted by an excessive current such as when a circuit is short-circuited, the fuse element 1 instantly becomes hot gas and fills the sealed internal space. This metal gas increases the air pressure inside the fuse.
However, in this example, the material of the cover 6 has a large heat capacity,
Since the metal has good heat conductivity, the cover 6 absorbs the heat energy of the metal gas to cool the gas. This effect suppresses an increase in the internal air pressure of the fuse and blocks the arc current flowing through the metal gas, so that the breaking performance can be improved. However, in such a structure, since the entire cover 6 is made of metal, it is not possible to visually confirm the blowout of the fuse. Further, since the metal cover 6 is exposed, when the cover 6 is mounted on a high-density printed wiring board. There is also a risk of short-circuiting between other parts and electric shock to the human body. Further, the material of the cover 6 is limited to several kinds of highly malleable materials such as aluminum from the viewpoint of workability, and since glass is used to insulate the terminals 5, it is extremely difficult to perform automated assembly. ,
It has not been put to practical use until now because of the high cost.

The object of the present invention is to eliminate such drawbacks of the prior art, and to provide a structure capable of easily confirming the fusing state visually and a structure capable of improving the breaking performance without causing damage or burning of peripheral parts. An object of the present invention is to provide a small fuse for a printed wiring board that also has the dual function.

(Means for Solving the Problems) In order to achieve this object, a small fuse for a printed wiring board according to the present invention has a hermetically sealed housing formed by a body made of heat-resistant resin and a transparent cover made of heat-resistant resin. A pair of printed wiring board connecting metal terminals fixedly penetrating through the body is connected to one end of each of the fuse elements projecting into a space inside the housing, and a fuse element is bridge-connected to the fuse element and the metal terminal. A small fuse for a printed wiring board, the connection portion of which is covered with a heat-resistant insulating material, in order to prevent destruction of the housing when the fuse is short-circuited and interrupted, the space is provided with a predetermined distance from the fuse element. It is fixed so as to cover the fuse element and absorbs the high heat generated when the short circuit of the fuse element is interrupted. It has a configuration wherein the cooling body brass plate or copper net wire heat capacity is provided.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view (A) and a perspective view (B) of a cooling body of an embodiment of the present invention. The outer shape and dimensions are the same as those in Fig. 3, but a cooling body 9 made of a brass plate having a thickness of 0.4 mm is inserted inside the transparent insulating cover 2 made of heat-resistant polycarbonate resin. Since both end portions 9a of the cooling body 9 have a structural size that fits in the gap between the cover 2 and the body 3 as shown in the figure, there is no risk that the cooling body 9 rattles or comes into contact with the fuse element 1.

In order to confirm the insertion effect of the cooling body 9, short circuit interruption is performed,
The difference in the breaking performance with and without the brass plate cooling body was investigated. First
The table shows the results, and the numbers in the table show the number of "failures" for 20 tests.

Here, "failure" is the following phenomenon.

That is, when a large current flows through the fuse element, the element is instantly vaporized and becomes a high temperature metallic gas, and the heat causes an increase in atmospheric pressure inside the fuse. This is because the larger the metal content of the fuse element, that is, the larger the rated current of the fuse, the higher the internal atmospheric pressure.
Due to this increase in atmospheric pressure, the cover is cracked or the cover is detached from the body. The destruction state of this component is "failure". When such a "failure" occurs, not only is the fuse destroyed, but also the metallic gas inside the fuse is released, causing damage or burnout of nearby electronic components.
Also, there is a risk of causing a secondary failure such as a short circuit of wiring material.

As is clear from Table 1, it can be said that the insertion performance of the brass-copper plate cooling body 9 clearly improved the breaking performance.

Further, in the case of using a cooling body using a metal net made of 0.02 mmφ copper wire instead of the cooling body made of the brass plate,
It was confirmed that it has more stable blocking characteristics than the brass plate cooling body due to the effect of increasing the surface area effective for cooling and the effect of improving the absorbability of high temperature metallic gas.

As described above, inserting the metal cooling body in the vicinity of the fuse and expanding the effective surface area of the cooling body cools the high temperature metallic gas vaporized by the fuse element generated when the fuse element is cut off, increasing the air pressure inside the fuse. It has been confirmed that it has an effect of suppressing the fuse, and it has become clear that this is a very effective means for improving the breaking performance of the fuse.

FIG. 2 is a cross-sectional view of a cylindrical structure which is another embodiment of the present invention, (A) is a vertical sectional view and (B) is a horizontal sectional view. In this case, the cylindrical cooling body 9 is inserted and fitted along the inner wall of the transparent cylindrical insulating cover 2.
The fuse of this structure is also similar to that of FIG. 1 in that the position of the cooling body is slightly different from that of the fuse of the first type, so that the short-circuit breaking performance is the same as that of FIG.

(Effect of the Invention) As is clear from the above description, in the small fuse according to the present invention, a metal cooling body is inserted inside the transparent resin cover 2 so that the inside can be seen at least from one direction of the cover. This has significantly improved short-circuit breaking performance and safety, which are one of the most important conditions expected of a fuse, without impairing the advantage that the blowout of the fuse can be visually confirmed.

In addition, since the metal part of the cooling body is not exposed to the outside of the fuse, it can be used for a printed circuit board mounted with high density. In addition, the structure is higher than that of the conventional fuse, for example, in the example of FIG. 1 (B), only a cooling body having a height of 4 mm width (up to both ends of the bent leg) of 8 mm and a depth of 2 mm is added. As a result, it has become possible to realize a compact fuse for printed wiring boards, which has high reliability, is inexpensive, and has much improved breaking performance as in the past.

[Brief description of drawings]

FIG. 1 is a sectional view (A) of a structure example of a small fuse according to the present invention and a perspective view (B) of a cooling body, FIG. 2 is a sectional view of a structure example of another small fuse according to the present invention, and FIG. An external perspective view (A) and a sectional view (B) of an example of a small fuse for a printed wiring board, and FIG. 4 are sectional views showing the structure of another conventional small fuse. 1 ... Fuse element, 2 ... Cover, 3 ... Body, 4 ... Insulation material, 5 ... Terminal, 6 ... Metal cover, 7
…… Metal base, 8 …… Glass, 9 …… Cooling body, 9a ……
Cooling body legs.

Continuation of the front page (56) References Shown 60-87455 (JP, U) Shown 57-183654 (JP, U) Shown 40-20505 (JP, Y1)

Claims (1)

[Scope of utility model registration request] 1. A hermetically sealed housing is formed by a body made of heat-resistant resin and a transparent cover made of heat-resistant resin, and a pair of metal terminals for connecting a printed wiring board fixed through the body are provided inside the housing. A fuse element is bridge-connected between each one end protruding into the space of
A small fuse for a printed wiring board, wherein a connecting portion between the fuse element and the metal terminal is covered with a heat-resistant insulating material, in order to prevent the housing from being broken when the fuse is short-circuited and interrupted, the fuse is provided in the space. A brass plate or a copper mesh wire cooling body having a heat capacity that is fixed to cover the fuse element at a predetermined distance from the element and absorbs high heat generated when the fuse element is short-circuited and cut off is provided. Small fuse for printed wiring boards.