JPH04190532A - Electronic parts protecting fuse - Google Patents

Abstract

PURPOSE:To prevent ignition of electronic parts such as a varistor and the like due to an eddy current in succession by providing a heat-contracted insulation tube with at least one or more apertures which is contracted by heat generated from a resistive element to fuse a metallic element of low melting point. CONSTITUTION:When a successive eddy current flows which is smaller than the maximum unfusible current of a metallic element of low melting point, a resistive element generates Joule heat. And the metallic element 7 of low melting point is fused by the Joule heat and at the same time a heat-contracted insulation tube 10 is contracted to fuse the metallic element 7 of low melting point, and an eddy current is completely cut off with the heat-contracted insulation tube breaking into the metallic element 7 of low melting point as an insulator. Namely, the maximum unfusible current value can be reduced without changing a fusible current due to a surge. Thereby, for instance, when the heat-contracted insulation tube 10 is used for protection of a varistor, the ignition of the varistor may be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a fuse for protecting electronic components that protects varistors and other equipment mainly from surge voltages caused by lightning. This relates to a fuse that cuts off overcurrent to prevent the varistor from catching fire or being destroyed due to overvoltage or leakage current when the varistor deteriorates.

Prior Art Conventionally, the protective fuse for this type of varistor was
It had the characteristics shown in the figure. FIG. 7 is a diagram showing the relationship between the applied current and the blowing time of a fuse for protecting a varistor (hereinafter referred to as "characteristics"), where Ic is the steady current of the circuit to be protected, and 1o is the relationship of the fuse This is the maximum unfused current.Inx is the surge of wave length Tt when n
This is the fusing current value when applied twice. In other words, this fuse has a voltage of To when a surge of wave length Tt is applied to the varistor to be protected n times, and if the standard value of the surge withstand capacity of the varistor is I n s and the limit value is I n I), >Ic, and lnp>Inx>Ins.

The operation of the varistor protection fuse having the following characteristics will be explained below.

This varistor protection fuse is used as shown in FIG. In FIG. 8, 1 is a varistor, 2 is a fuse for protecting the varistor, and 3 is a protected circuit. Varistor protection fuses 2 are connected to the power lines 4a and 4b, respectively.
, varistors 1 are connected in series, and a protected circuit 3 is connected between the series connection point and the power supply line 4b. Here, when a steady state or a surge within the standard value of the varistor 1 is applied to the power lines 4a and 4b, the varistor 1 absorbs the surge and the varistor protection fuse 2 does not blow due to its characteristics. , the protected circuit 3 continues to operate normally. If a surge that significantly exceeds the standard value of the varistor 1 enters the power lines 4a and 4b, the varistor protection fuse 2 will instantly melt due to its characteristics.
Ignition or destruction of the varistor 1 can be prevented.

Problems to be Solved by the Invention In such conventional varistor protection fuses, the maximum unfused current value of the fuse is considerably larger than the steady current value of the protected circuit, and the fuse may be continuously damaged due to power lines coming into contact with communication lines, etc. When an excessive voltage is applied or when the varistor deteriorates, the value of the current flowing through the fuse is often smaller than the maximum unfused current value of the fuse. Therefore, there is a problem in that the fuse having such an I-T characteristic does not blow, and current continues to flow through the varistor, causing the varistor to catch fire due to Joule heat.

The present invention has been made to solve these problems, and it is an object of the present invention to provide a fuse for protecting electronic components, which prevents electronic components such as the varistor from igniting due to continuous overcurrent.

Means for Solving the Problem In order to solve this problem, the fuse for protecting electronic components of the present invention includes a resistance element having an insulator on its surface, and a low melting point metal element electrically connected in series with the resistance element. and at least one opening that covers the surface of the resistance element and the low melting point metal element so that they are in close contact with each other, and that shrinks due to heat generation of the resistance element and melts the low melting point metal element. It consists of a heat-shrinkable insulating tube located approximately in the center.

Effect With this configuration, when a continuous overcurrent smaller than the maximum unfused current of the low melting point metal element flows through the fuse for protecting electronic components of the present invention, the resistance element generates heat due to Joule heat, and the heat causes the low melting point metal element to generate heat. The melting point metal element melts and the heat shrinkable insulating tube contracts at the same time, causing the low melting point metal element to melt and the heat shrinkable insulating tube serving as an insulator intervenes in the low melting point metal element, thereby completely eliminating the overcurrent. Can be blocked. That is, the value of the maximum non-fusing current can be reduced without changing the value of the fusing current due to surges, and when the fuse of the present invention is used to protect a varistor, for example, it is possible to prevent the varistor from catching fire. .

EXAMPLES Hereinafter, examples of the present invention will be described with reference to the drawings.

FIG. 1 is a front view of a fuse for protecting a varistor according to a first embodiment of the present invention, and FIG. 2 is a side view of the fuse for protecting a varistor according to the same embodiment as viewed from the direction of arrow A in FIG. . In FIG. 1-5 and FIG. 2, 5 is a resistance element such as a metal oxide, and is provided with connection lead wires 5a and 5b. 6
The surface of the resistor element 5 is coated with an insulator made of glass, for example. 7 is a low melting point metal element such as a eutectic solder wire of tin or lead, and one end of this low melting point metal element 7 and the connecting lead wire 5b are connected by a caulking 8a, and the other end of the low melting point metal element 7 is connected to the connecting lead wire 5b. Connection lead wire 9 is connected by caulking 8b. Reference numeral 10 denotes a heat-shrinkable insulating tube having an opening 10a at one location so that its diameter shrinks to be smaller than the diameter of the resistor element 5 due to heat, and an insulator 6 coating the surface of the resistor element 5.
The opening 1 is made such that the surface of the low melting point metal element 7 is in close contact with the surface of the hole 1.
Portions 10b and 10c, which are divided into two by 0a, cover and fix the low melting point metal element 7 so as to be in contact with them.

The operation of the varistor protection fuse configured as described above will be described below. This varistor protection fuse is used as shown in Figure 3. 11 is a barista,
The resistance value changes depending on the voltage and absorbs surges. 1
Reference numerals 2a and 12b are, for example, power supply lines, which are connected to one end of the connection lead wire 9 and the varistor 11, respectively, and the other end of the varistor 11 is connected to the connection lead wire 5a. Furthermore, a connection lead wire 5b and a power supply line 12b are connected to the protected circuit 13. Normally, there is a short circuit between the connection lead wire 9 and the connection lead wire 5b, and a short circuit between the connection lead wire 5b and the power supply line 12b due to the characteristics of the varistor 1, which has high resistance and is close to an open circuit. The protection circuit 13 has a steady current M
c is flowing.

Now, the maximum unfused current I'o of the low melting point metal element 7 and the standard value of the surge withstand capacity of this varistor 11 when a surge of wave tail length Tt is applied to the varistor 11 n times are set as bins, and the limit value is set as I′np, the fusing current value binnx of the low melting point metal element 7 when a surge of wave tail length Tt is applied n times
is I'o>I'c, and l'np>I'nx>T'n
The material and wire diameter of the low melting point metal element 7 are set so as to have an IT characteristic of s. Therefore, when a surge within the steady state or standard value is applied to the power lines 12a, 12b, the varistor 11 absorbs the surge, the low melting point metal element 7 does not melt, and the protected circuit 3 operates normally. When the varistor 11 continues to operate and a surge that greatly exceeds the standard value of the varistor 11 enters the power supply lines 12a, 12b, the low melting point metal element 7 instantly melts due to self-heating, and the varistor 1
1 can be prevented from catching fire or being destroyed.

In this circuit, power line 12a due to high voltage line contact
, 12b, or due to deterioration of the varistor 11, a continuous overcurrent may be applied to the varistor 1.
1, the resistance element 5 whose thermal resistance is larger than that of the varistor 11 generates heat, which causes the low melting point metal element 7 to melt, and at the same time, any of the divided portions 10b, 10c of the heat-shrinkable insulating duplex 10 or both of them contract in the radial direction, and the molten low melting point metal element 7 is pushed out by the radial contraction force of either or both of the divided portions 10b and 10c of the heat-shrinkable insulating duplex 10, The low melting point metal element 7 is separated into two parts by sandwiching either or both of the divided parts 10b and 10c of the heat-shrinkable insulating duplex 10 between them. That is, the overcurrent flowing through the varistor 11 can be removed by intervening in the low melting point metal element 7 of either or both of 10b and 10c of the heat-shrinkable insulating tube 10, which is an insulator, to separate the low melting point metal element 7. After that, it is completely cut off without any ground discharge. Therefore, the varistor 11 stops generating heat, and ignition can be prevented.

As described above, the varistor protection arm of this embodiment.

- As shown in Fig. 4, the fusing current Mn is caused by a surge.
The value of the maximum unfused current I'o of this fuse can be reduced without changing the value of x, which has the effect of preventing the varistor 11 from igniting. The I-T characteristic of element 7, curve B, is the I-T characteristic of this fuse.
It is a T characteristic.

Next, a second embodiment of the present invention will be described with reference to FIGS. 5 and 6. 5 is a front view of a fuse for protecting a varistor according to a second embodiment of the present invention, and FIG. 6 is a side view of a fuse for protecting a varistor image according to the same embodiment as viewed from the direction of arrow B in FIG. be. The difference from the first embodiment is that the heat-shrinkable insulating tube has two openings instead of one. The resistive element 14 is equipped with connection lead wires 14a and 14.b. 15 is an insulator made of, for example, glass, and the surface of the resistive element 14 is coated. 16 is made of, for example, tin or lead. is a low melting point metal element such as a eutectic solder wire, and one end of this low melting point metal element 16 and the connecting wire 14b are caulked 17.
a, and the other end of the low melting point metal element 16 and the connecting reet wire 18 are caulked 17F) by hj b'M
has been done. 19 has openings 19a at two locations whose diameter shrinks to be smaller than the diameter of the resistance element 14 due to heat;
19b with a heat-shrinkable insulating duplex, resistive element 1/I
opening 193 and] such that the low melting point metal element 7 contacts the surface of the insulator 15 coating the surface of
, 9b divided into three parts 19c.

19d and 19e do not contact the low melting point metal element 7-1
,0-- They are covered and fixed so that they are fixed.

The function of the varistor protection fuse constructed in this way is similar to that of the first embodiment, but compared to the first embodiment, the heat-shrinkable insulating tube has two openings, so that
The number of fusing points of the low melting point metal element is now three, the insulation distance is longer, and continuous overcurrent can be interrupted more reliably.

Further, it is possible to reduce the variation in the time required for melting.

In addition, in the examples of the present invention, glass was used as an insulator, but the insulator is not limited to this.
In addition, although tin and lead eutectic solder wires were used as the low melting point metal elements, the low melting point metal elements are not limited to these, and are further added at one or two locations on the heat-shrinkable insulating tube.
Although openings are provided at certain locations, the number of openings is of course not limited, and furthermore, although it is used as a fuse to protect the varistor, its use is not particularly limited to one varistor. Of course.

Effects of the Invention As described above, according to the present invention, a resistance element having an insulator on its surface, a low melting point metal element electrically connected in series with the resistance element, and a surface of the resistance element and the low melting point metal element electrically connected in series with the resistance element. The metal element is tightly covered with the metal element, and is contracted by the heat generated by the resistance element, and the low melting point metal element is melted, and an opening is formed in a part or several places of the contact surface with the low melting point metal element. By installing a heat-shrinkable insulating tube with a
The value of the maximum unfused current can be reduced, and when the fuse of the present invention is used, for example, to protect a varistor, it is possible to prevent the varistor from igniting.

[Brief explanation of drawings]

FIG. 1 is a front view showing the structure according to the first embodiment of the present invention, FIG. 2 is a side view as seen from the direction of arrow A in FIG. 1, and FIG.
The figure is a circuit diagram showing an example of use of the present invention, Fig. 4 is a characteristic diagram showing the relationship between applied current and blowout time in the same use example, and Fig. 5 is a structure according to a second embodiment of the present invention. 6 is a side view as seen from the direction of arrow B in FIG. 5, FIG. 7 is a characteristic diagram showing the relationship between applied current and blowing time of a conventional varistor protection fuse, and FIG. 8 is a characteristic diagram of the same varistor. FIG. 3 is a circuit diagram showing an example of how a protective fuse is used. 5.14...Resistance element, 6,15...
Insulator, 7.16...Low melting point metal element, 10.
19... Heat shrinkable insulating tube, 10a, 19a
, 19b...opening part. Name of agent: Patent attorney Haruaki Koba and two other people
Fear \, 卜, \ ()) Sound phrase c>c>sa force Ω \\N \\ren

Claims (1)

[Claims] a resistance element having an insulator on its surface; a low melting point metal element electrically connected in series with the resistance element; An electronic component configured with a heat-shrinkable insulating tube that shrinks due to heat generated by a resistance element, melts the low-melting point metal element, and has openings in a portion or several places of the contact surface with the low-melting point metal element. Protective fuse.