JP3185962B2 - Protection circuit and protection element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protection circuit which uses a PTC element and a low melting point metal body in combination to prevent both overcurrent and overvoltage.

[0002]

2. Description of the Related Art Conventionally, as one of protective elements for preventing overcurrent, a current fuse made of a low-melting metal such as lead, tin, and antimony and cut off by overcurrent to cut off current has been widely used. ing.

A PTC element (PTC thermistor) is known as a protection element for preventing an overcurrent.
The PTC element is a resistor element in which conductive particles are dispersed in a crystalline polymer (for example, a polyolefin resin).
When an overcurrent state occurs, heat is generated, and the crystalline polymer expands, thereby increasing the resistance value, thereby suppressing the current flowing through the circuit.

[0004]

However, with the recent development of the industry, there has been a demand for a protection element which operates by an overvoltage, in addition to the conventional current fuse and PTC element.

[0005] For example, in a lithium ion battery, which has attracted attention as a secondary battery having a high energy density, dendrite is generated on the electrode surface due to overcharging, and the battery performance is greatly impaired. It is necessary to prevent that. However,
A protective element useful for preventing such an overvoltage has not been developed so far. Actually, as a protection mechanism for a lithium ion battery, a protection mechanism is provided to prevent the fuse from blowing when a current exceeding a specified value flows to the battery due to a short circuit or the like, but such a protection mechanism is overcharged. Can not be used to prevent For this reason,
There is a need for a new protective element to prevent overcharging, and in particular, a protective element used when charging such a battery, which has no danger of ignition or the like, and has high safety in use. It has been demanded.

In addition, the resistance value of the PTC element increases when an overcurrent occurs, and the PTC element can be used as it is when the current returns to normal after suppressing the overcurrent. However, the current must be completely cut off during the overcurrent. However, there is a problem that a small amount of current continues to flow. On the other hand, the fuse is blown by an overcurrent to completely cut off the current, but there is a problem that once the fuse is blown by the overcurrent, it cannot be used again.

The present invention is intended to solve the above-mentioned problems of the prior art relating to the protection element, and operates as a protection element not only at the time of overcurrent but also at the time of overvoltage, and at the time of overcurrent or overvoltage. It is an object of the present invention to enable element reuse as much as possible after operation.

[0008]

SUMMARY OF THE INVENTION The present inventors connect a PTC element and a low-melting metal body such as a fuse in series so that the PTC element operates first in the event of an overcurrent, and then the PTC element operates. In addition to the fact that the PTC element and the low-melting metal body connected in series as described above, in addition to the PTC element and the low-melting metal body connected in series, a circuit combining It has been found that the above object can be achieved as a protection circuit against the above, and the present invention has been completed.

That is, according to the present invention, P
TC element and low melting point metal, protection circuit connected to protected device
A voltage detecting means that operates when the terminal voltage of the path becomes equal to or higher than a predetermined voltage; and a heating element that generates heat when energized by the operation of the voltage detecting means, and the heating element is disposed in proximity to the low melting point metal body. A protection circuit, wherein current is normally supplied to the device to be protected through the series-connected PTC element and a low-melting metal body.

Further, the present invention provides a useful element for forming a protection circuit, in which a PTC element and a low melting point metal body are arranged in series on a substrate, and heat is generated in proximity to the PTC element or the low melting point metal body. A protection element provided with a body ,
Normal energization of the protected device was connected in series with the
Provided is a protection element characterized by being made through a PTC element and a low melting point metal body .

Hereinafter, the present invention will be described in detail with reference to the drawings. In each of the drawings, the same reference numerals represent the same or equivalent components.

FIG. 1A is a protection circuit diagram of a basic mode of the present invention. As shown in FIG.
TC element 1 and low melting point metal body 2 are connected in series,
One terminal of the heating element 3 is further connected to the connection point. Here, the heat generating element 3 is provided so that when the heat generating element 3 generates heat, the heat is sufficiently transmitted to the low melting point metal body 2 and the low melting point metal body 2 can be blown. It is assumed that they are arranged close to 2. Thus, the heating element 3
In order to dispose the low-melting metal member 2 and the low-melting metal member 2 close to each other, for example, an insulating layer 5 may be formed on the heating element 3 and the low-melting metal member 2 may be laminated thereon. This circuit is provided with a voltage detecting means 20 composed of a zener diode and a transistor.

The terminals A1 and A2 of such a circuit are connected to electrode terminals of a device to be protected, such as a lithium ion battery, and the terminals B1 and B2 are connected to a charger used in connection with the device to be protected. Are connected. According to this circuit configuration, when the charging of the lithium ion battery progresses and a reverse voltage equal to or higher than a predetermined breakdown voltage is applied to the zener diode of the voltage detecting means 20, the base current ib flows abruptly. Large collector current ic
Is supplied to the heating element 3, and the heating element 3 generates heat. Therefore, the low-melting metal member 2 located in the position close to the heating element 3 is blown, and the progress of overcharge in a protected device such as a lithium ion battery connected to the terminals A1 and A2 is prevented.

On the other hand, terminals A1-B of this circuit
If an overcurrent exceeding the specified value flows during 1,
The TC element 1 functions as an original protection element against overcurrent. That is, the resistance value of the PTC element 1 increases due to the overcurrent, and the current is suppressed. If the current returns to normal after the action of the PTC element, the protection circuit can be used as before. However, the current suppressing action of the PTC element 1 is not sufficient. If an overcurrent still flows between the terminals A1 and B1, the low-melting metal body 2 acts as a protection element against the overcurrent, and is blown. To shut off the current.

Therefore, according to this circuit, the suppression of the overcurrent is first achieved by the PTC element 1 which can be reused.
When the overcurrent cannot be prevented even after that, the operation of the low-melting-point metal body 2 is used, so that it is possible to ensure the reuse of the circuit as much as possible and to surely prevent the overcurrent.

It should be noted that there is no special requirement for differentiating the action of the PTC element 1 and the low melting point metal body 2 at the time of overcurrent as described above. Such an effect can be obtained by connecting an arbitrary PTC element 1 and a low melting point metal body 2 in series. Therefore, the PTC element 1 and the low-melting-point metal body 2 can be appropriately selected according to the current value to be suppressed.

For example, as the PTC element 1, a crystalline polymer such as high-density polyethylene, ethylene acrylate copolymer, polycaprolactone, etc.
A material in which carbon black, metal powder, metal-coated particles and the like are dispersed can be used. Further, those formed from an inorganic composition containing barium titanate as a main component can also be used.

The low-melting-point metal body 2 can be made of various low-melting-point metals conventionally used for fuse materials, and can be made of, for example, the alloys shown in Table 1.

[0019]

[Table 1] Alloy composition liquidus point (° C.) Bi: Sn: Pb = 52.5: 32.0: 15.595 Bi: Pb: Sn = 55.5: 44.0: 1.0 120 Pb: Bi: Sn = 43.0: 28.5: 28.5 137 Bi: Pb = 55.5: 44.5 124 Bi: Sn = 58.0: 42.0 138 Sn: Pb = 63.0: 37.0 183 Sn: Ag = 97.5: 2.5 226 Sn: Ag = 96.5: 3.5221 Pb: In = 81.0: 19.0 280 Zn: Al = 95.0: 5.0 282 In: Sn = 52.0: 48.0 118 Pb: Ag: Sn = 97.5: 1.5: 1.0309 The heating element 3 may be made of an organic material or an inorganic material, but it is preferable to use an inorganic material from the viewpoint of safety. That is, by forming the heating element 3 from an inorganic material, the influence of heat on the resistance value of the heating element itself can be greatly suppressed. Therefore, even when the heating element 3 is energized for a long time and the heating element 3 continues to generate heat, the heating state can be stabilized and runaway can be prevented. Examples of such an inorganic material include a material composed of a conductive material such as ruthenium oxide and carbon black and an inorganic binder such as water glass.

The protection circuit of the present invention can take various forms other than the circuit shown in FIG. For example, as shown in FIG. 1B, not only the heating element is provided close to the low melting point metal body 2 (heating element 3a), but also the PTC
It may be provided close to the element 1 (heating element 3b). As a result, the PTC element 1 is heated at the time of overvoltage, so that at the time of overvoltage, the PTC element 1 can be actuated first, and then the low melting point metal body 2 can be actuated. It is possible to reliably prevent the overvoltage while securing.

As shown in FIG. 1 (c), two PTC elements 1a, 1b and low melting point metal bodies 2a, 2b may be provided, and heating elements 3a, 3b may be provided close to them. . In the case of the embodiment shown in FIGS. 1A and 1B, it is conceivable that the heating elements 3, 3a, and 3b continue to be energized even after the low-melting-point metal body 2 is blown at the time of overvoltage. According to the embodiment of FIG. 1 (c), the low-melting metal members 2a, 2a
After b is blown, the power supply to the heating elements 3a and 3b is cut off, so that the safety of the circuit can be further improved.

In addition, the circuit shown in FIG.
It can be deformed as shown in FIG. Among these, the embodiment of FIG. 1C is preferable.

Further, as shown in FIG. 3 (a), two PTC elements 1a and 1b arranged in series and a voltage detecting means 20b which operates when one end a of the PTC elements 1a and 1b have a predetermined voltage or more, The heating elements 3b-i, 3b-ii, which are energized by the operation of the voltage detection means 20b and generate heat, the two low-melting metal bodies 2a, 2b arranged in series, and one end d thereof have a predetermined voltage or more. , And the heating elements 3a-i and 3a-ii, which are energized and generate heat by the operation of the voltage detecting means 20a, may be separately provided. Thereby, the two voltage detecting means 20
a, 20b, the PTC elements 1a, 1b,
The voltage detection means 20b on the b side can be set to operate at a lower voltage than the voltage detection means 20a on the low melting point metal 2a, 2b side.
b, and when the overvoltage cannot be suppressed by the action of the PTC elements 1a and 1b,
It is possible to reliably obtain a time lag in the action of acting b.

The embodiment shown in FIG. 3A can be simplified as required, for example, as shown in FIG. 3B.

In the protection circuit of the present invention as described above,
In the embodiment shown in FIGS. 1A to 2G, P
A TC element and a low melting point metal body are arranged in series, and the PT
It can be easily formed by using a C element or a protection element provided with a heating element in the vicinity of a low melting point metal body.

FIG. 4 is an example of such a protection element, and is a plan view (FIG. 4A) and a cross section of a protection element 30 which can be suitably used in the circuit shown in FIG. It is a figure (the same figure (b)). As shown in the figure, the protection element 30 includes a PTC element 1 laminated on a substrate 4 via a PTC electrode 6a, a heating element 3, and an insulating layer 5.
And a low melting point metal body electrode 6c. The PTC element 1, the intermediate electrode 6b
The low-melting-point metal body electrode 6c is connected to the low-melting-point metal foil 2 as a low-melting-point metal body. Also,
The heating element 3 is connected to the heating element terminal electrodes 6d and 6e, and the heating element terminal electrode 6d and the intermediate electrode 6b are connected.
These are covered with a protective cap 7.

Here, the substrate 4 is made of a plastic film, a glass epoxy substrate, a ceramic substrate, a metal substrate,
Although it can be composed of various base materials such as a polyester substrate and a phenol substrate, it is particularly preferable to use an inorganic substrate such as a ceramic substrate or a metal. By using an inorganic substrate as the substrate 4, when the heating element 3 made of an inorganic material is formed on the substrate 4, an inorganic resistance paste is applied to the substrate and fired easily as described later. A heating element can be formed. Furthermore, since the substrate itself can be made nonflammable, it is possible to enhance the safety in use of the protection element.

The thickness of the substrate 4 is not particularly limited, but is usually 0.1 to 1.0 m from the viewpoint of miniaturization of the protection element.
m is preferable.

The heating element 3 is preferably formed from an inorganic material as described above. In this case, a commercially available inorganic resistance paste can be used. The heating element 3 made of an inorganic material can be easily formed by applying an inorganic resistance paste on a substrate and baking it. However, even if an organic component is contained in the resistance paste, the organic component can be used. Is decomposed and removed in the baking process, so that the resistive paste applied to the substrate may contain an organic component.

The insulating layer 5 is a layer that insulates the heating element 3 from the low melting point metal foil 2. The material for forming the insulating layer 5 is not particularly limited. For example, various organic resins such as epoxy, acrylic, and polyester or inorganic materials containing SiO ₂ as a main component can be used. When an organic resin is used for the insulating layer 5, an inorganic powder having high thermal conductivity may be dispersed. Thereby, the heating element 3
Can be efficiently conducted to the low melting point metal foil 2. As such an inorganic powder, for example, boron nitride (thermal conductivity 0.18 cal /
cm · sec · ° C), alumina (thermal conductivity 0.08ca)
1 / cm · sec · ° C.) or the like.

The electrodes 6a, 6b, 6c, 6d, 6e can be formed in the same manner as electrode terminals generally formed on a substrate. For example, a copper foil patterned, a copper pattern sequentially plated with nickel and gold, or a copper pattern plated with solder,
Alternatively, it can be formed from printed conductive paste or the like.

As described above, the PTC element 1 may be formed by forming a coating material in which conductive fine particles are dispersed in a polymer into a film. In addition, an inorganic PTC element containing barium titanate as a main component can also be used.

As the low melting point metal foil 2, a metal foil of a low melting point metal body as described above can be used. In this case, the thickness of the metal foil is usually 10 to 5 in view of characteristics and production.
It is preferable that the thickness be about 00 μm.

The protective cap 7 protects the PTC element 1 and the low melting point metal foil 2 on the substrate 4 from the outside, and also prevents leakage of the molten material when the low melting point metal foil 2 of the protection element is melted. Provided. As the protective cap 7, for example, a cap made of a heat-resistant and flame-retardant material such as 4,6-nylon or a liquid crystal polymer can be used. Further, instead of the protective cap 7, an external case made of a heat-resistant polymer such as an epoxy-based or phenol-based polymer or a resin seal can be provided.

As a method for manufacturing such a protection element 30, for example, the electrodes 6a, 6
c, 6d and 6e are formed, and then an inorganic paste is applied by screen printing or the like, and then fired to form a heating element 3
Is formed, and an insulating resin is applied to the surface of the heating element 3 by printing or the like and cured to form an insulating layer 5,
Further, an electrode 6b is formed thereon by an ordinary method. Also,
The PTC element 1 is crimped on the electrode 6a,
It can be obtained by placing the low melting point metal foil 2 over the insulating layer 5 and the electrode 6c and connecting them with a solder paste or the like.

The protection element 30 is an element which can be suitably used for forming the protection circuit shown in FIG.
Also in the protection circuits of FIGS. 2B to 2G, suitable protection elements 31 to 36 are respectively provided with a PTC element, a low-melting-point metal body, and a heating element on a substrate according to the above-described protection element 30. It can be configured by the following.

Similarly, for the formation of the protection circuit shown in FIG. 3, the PTC elements 1a and 1b, the low-melting metal bodies 2a and 2b, and the heating elements 3a-i, 3a-ii, and 3b
, 3b-ii may be formed, but in this case, the low melting point metal body 2 is formed on one substrate.
a, 2b and the heating elements 3a-i, 3a-ii are formed, and the PTC is separately formed on a separate substrate.
A protection element 60 incorporating the elements 1a and 1b and the heating elements 3b-i and 3b-ii may be formed and connected in series.

FIG. 5 is a plan view (FIG. 5A) and a cross-sectional view (FIG. 6B) of the protection element 50 incorporating the low melting point metal body in this case, and FIG. 6 incorporates the PTC element. It is the top view (the same figure (a)) and sectional drawing (the same figure (b)) of the protection element 60. These can also be formed according to the protection element 30 described above.

For example, the protection element 50 shown in FIG. 5 has electrodes 6p, 6q, 6r and heating elements 3a-i, 3a-ii on a substrate 4.
Are formed in a predetermined pattern, and the two heating elements 3a-i, 3
a-ii, an insulating layer 5 is formed on each of the insulating layers 5.
And the low melting point metal foil 2 is thermocompressed on the electrodes 6p and 6r,
It can be formed by sealing the upper portion with an inner sealing portion 8 and an outer sealing portion 9.

The inner sealing portion 8 prevents the surface of the low melting point metal foil 2 from being oxidized and removes the metal oxide film formed on the surface of the low melting point metal foil 2 so that the low melting point metal foil 2 has a predetermined temperature. It is provided to ensure that the fusing when heated to a certain temperature occurs. Further, the inner sealing portion 8 is preferably formed of a material having a lower melting point or lower softening point than the low melting point metal foil 2 so as not to hinder the melting of the low melting point metal foil 2. Therefore, the inner sealing portion 8 can be formed from a sealing material having an action of removing a metal oxide film such as an organic acid and an inorganic acid. Among them, a non-corrosive solid flux containing abietic acid as a main component is preferred. This is because abietic acid is solid and inactive at room temperature, but melts when heated to about 120 ° C. or higher, becomes active and exerts the action of removing metal oxides. This is because not only can the fusing when heated to a predetermined temperature be ensured, but also the storage stability of the protection element can be improved. As a method of forming the inner sealing portion 8 using a solid flux, the solid flux is heated and melted without using a solvent, and the melt is applied to the low melting point metal foil 2 in order to prevent craters. Is preferred. Although the thickness of the inner sealing portion 8 depends on the kind of the sealing material, it is usually about 10 to prevent the surface oxidation of the low melting point metal foil 2 or to remove the surface oxide film. ~
It is preferably 100 μm.

The outer sealing portion 9 is provided to protect the inside of the protection element from the outside and to prevent the melt from flowing out from the protection element to the outside, similarly to the above-described protection cap 7. I have. Therefore, the outer sealing portion 9
Can be formed from a material having a higher melting point or a higher softening point than the low-melting metal foil 2, for example, an epoxy-based sealing material, a phenol-based sealing material, or the like.

FIG. 6 shows a protection element 60 incorporating a PTC element which can be suitably used in the circuit of FIG.
3A and 3B are a plan view (FIG. 3A) and a cross-sectional view (FIG. 3B). This protection element 60 also has electrodes 6x, 6y,
6z and the heating elements 3b-i, 3b-ii are formed in a predetermined pattern, and the insulating layer 5 is formed on the two heating elements 3b-i, 3b-ii.
To form Then, the PTC element 1 is placed on the electrodes 6x and 6z.
b, 1a are placed, and the two PTC elements 1b, 1a are connected by a metal foil 10 and covered with a protective cap 7.

[0043]

According to the protection circuit of the present invention, since the PTC element and the low-melting-point metal body are connected in series, the PTC element is first activated at the time of an overcurrent, and then the operation of the PTC element is insufficient. Can be caused to act on the low melting point metal body.
Therefore, it is possible to reliably prevent the overcurrent while allowing the protection element to be reused as much as possible.

According to the protection circuit of the present invention, the PTC
In addition to the element and the low-melting metal element, the voltage detecting means and the heating element are used, so that the heating element generates heat at the time of overvoltage, thereby causing the PTC element to exhibit a current suppressing function, and Can exhibit a current interruption function. Therefore, safety can be ensured while allowing the protection element to be reused as much as possible even at the time of overvoltage.

The protection element of the present invention has a PTC element and a low-melting-point metal body connected in series on a substrate, and a heating element disposed close to the PTC element or the low-melting-point metal body. Therefore, the protection circuit of the present invention can be easily formed by this protection element.

[0046]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments.

Example 1 A protection element 30 having the structure shown in FIG. 4A was manufactured as follows.

First, an alumina-based ceramic plate (0.5 mm thick) is prepared as the substrate 4, and a PTC electrode 6 a and a low-melting metal body electrode are formed thereon using a silver paste (QS174, manufactured by DuPont). 6c, heating element terminal electrode 6
d and 6e were formed in a predetermined pattern. Then, a heating element 3 was formed by applying a ruthenium oxide-based resistance paste (DP1900, manufactured by DuPont) in a predetermined pattern and baking it at 870 ° C. for 30 minutes. Next, the heating element 3
The insulating layer 5 was formed by applying a silica-based insulating paste (AP5364, manufactured by DuPont) and baking it at 500 ° C. for 30 minutes. Further, an intermediate electrode 6b was formed thereon similarly to the electrodes 6a and 6c. Next, the PTC element 1 (2 mm × 2 mm × thickness 200 mm) is placed on the PTC electrode 6 a.
.mu.m) and a low melting point metal foil (Sn: Sb = 95: 5, liquidus point 240.degree. C., 1 mm.times.6) so as to cover the PTC element 1, the intermediate electrode 6b, and the low melting point metal body electrode 6c.
mm × 100 μm thick) 2 were connected by a solder paste.

Here, as the PTC element 1, the following components were kneaded at 190 ° C. using a pressure kneader.
The film was formed into a film having a thickness of 300 μm by hot pressing (190 ° C., 5 kgf / cm ² , 10 seconds), and further sandwiched between Ni foils.
kgf / cm ² for 20 seconds) to obtain a thickness of 200
What was formed into a μm film shape was used.

[Blending of PTC element] High-density polyethylene 44 parts by weight (Hi-Zex5000H, manufactured by Mitsui Petrochemical Co., Ltd.) Ethylene-ethyl acrylate copolymer 22 parts by weight (NUC6170, manufactured by Nippon Unicar Co., Ltd.) Conductive particles: 34 parts by weight (MSB-10A, manufactured by Nippon Carbon Co., Ltd.) after mounting PTC element 1 and low melting point metal foil 2 on substrate 4, liquid crystal to protect these A polymer (manufactured by Nippon Petrochemical Co., Ltd.) was cut into a cap and fitted on the substrate 4 to obtain a protection element 30.

Comparative Example 1 Example 1 was repeated except that the PTC element 1 was not provided and the low melting point metal foil 2 was directly connected to the PTC electrode 6a.
A protection element of a comparative example without the C element was produced.

Evaluation Regarding the protective elements of Example 1 and Comparative Example 1 obtained above,
The following tests (a) to (f) were performed. Table 2 shows the results.

(A) PTC element-low melting point metal foil resistance: FIG.
Was measured using a digital multimeter (R6871E, manufactured by ADVANTEST CORPORATION).

(B) Heating element resistance: terminal electrode 6d for the heating element
The resistance between 6e was measured in the same manner as in (a) above.

(C) Fusing of the low melting point metal body and trip heat of the PTC element: Lead wires are drawn out from the PTC electrode 6a and the low melting point metal body electrode 6c in FIG. 4 and are connected to the heating element 3 and a DC power source (6033A, (Made by YHP Co., Ltd.), and the calorific value when the low melting point metal foil 2 was blown and when the PTC element 1 tripped was calculated by I ² R.

(D) Trip time: For the protection element of the first embodiment, a lead wire is drawn out from the PTC electrode 6a and the intermediate electrode 6b in FIG. 4, and this is connected to a DC power supply (6033A, Y
HP Co., Ltd.) and a current of 20 A is supplied.
(KERD). Then, the time during which the current value sharply decreased was determined.

(E) Trip current: For the protection element of the first embodiment, a lead wire is drawn out from the PTC electrode 6a and the intermediate electrode 6b in FIG.
HP Co., Ltd.), the current was increased at a rate of 0.1 A / sec, and the value when the current value was drastically reduced was read.

(F) Low-melting metal fusing time: time from application of a voltage of 5 V between the electrodes 6d and 6e to heat the heating element 3 until the low-melting metal foil 2 is melted and the current stops. Was measured using a stopwatch.

[0059]

[Table 2] Example 1 Comparative Example 1 (a) PTC element—low melting point metal foil resistance: 50 mΩ 20 mΩ (b) Heating element resistance: 11Ω 11Ω (c) Low melting point metal body fusing and trip heat of PTC element: 2W 2.2W (e ) Trip time: 2 msec-(f) Trip current: 6 A-(g) Low melting point metal fusing time: 5 sec 5 sec From the results in Table 2, the protection element of Example 1 is PTC element 1
When a current of 6 A or more flows through the PTC element 1, the PTC element 1 trips before the low-melting-point metal foil 2 blows, and the current is suppressed.

Further, since it was confirmed that the low melting point metal foil 2 was blown by energizing the heating element 3, as shown in FIG. 1, the protection element 10 and the voltage detection means 20 of this embodiment were connected to each other. It can be seen that the protection element 10 is also useful as a protection element for preventing overvoltage by being assembled in a circuit.

Example 2 A protection element 60 having the structure shown in FIG. 6 was manufactured as follows.

First, an alumina-based ceramic plate (0.5 mm thick) is prepared as the substrate 4, and the terminal electrodes 6 d and 6 e for the heating element and the PTC electrode 6 x are formed thereon using a silver paste (QS174, manufactured by DuPont). , 6z and the intermediate electrode 6y in a predetermined pattern. Next, a ruthenium oxide-based resistance paste (DP1900, manufactured by DuPont) was applied in a predetermined pattern, and baked at 870 ° C. for 30 minutes to form heating elements 3b-ii and 3b-i. Next, a silica-based insulating paste (AP53) is formed on the heating elements 3b-ii and 3b-i.
46, manufactured by DuPont) and baked at 500 ° C. for 30 minutes to form an insulating layer 5. On the other hand, on the PTC electrodes 6x, 6z, a PTC element (2 m
m × 2 mm × thickness 200 μm) 1a, 1b are placed, and a low melting point metal foil (Sn: Sb = 95: 5, liquidus point 240) is applied to these PTC elements 1a, 1b and the intermediate electrode 6y.
2 ° C., 1 mm × 6 mm × thickness 100 μm) 2 were connected by a solder paste.

A protection device 50 having the structure shown in FIG. 5 was manufactured as follows.

First, an alumina-based ceramic plate (thickness: 0.5 mm) was prepared as the substrate 4, and a silver paste (QS174, manufactured by DuPont) was used thereon, and the low-melting metal electrodes 6p, 6r, Electrode 6q, heating element terminal electrode 6
d and 6e were formed in a predetermined pattern. Next, a ruthenium oxide-based resistance paste (DP1900, manufactured by DuPont) was applied in a predetermined pattern, and baked at 870 ° C. for 30 minutes to form heating elements 3a-ii and 3a-i.
Next, a silica-based insulating paste (AP5364, manufactured by DuPont) is applied on the heating elements 3a-ii and 3a-i,
For 30 minutes to form the insulating layer 5. A low-melting metal foil 2 (1 mm × 5 mm × 100 μm thick) similar to that of Example 1 was hot-pressed (145 ° C., 5 kgf / c) on the low-melting-point metal body electrodes 6 p and 6 r and the intermediate electrode 6 q.
m ² for 5 seconds). During the hot pressing, a thickness of 25 mm is applied between the low melting point metal foil 2 and the press head.
A μm polyimide film was interposed. Further, the inner sealing portion 8 was formed of an organic acid, and the outer sealing portion 9 was formed of a liquid crystal polymer to obtain a protection element 50.

By connecting the low-melting-point metal body electrode 6r of the obtained protection element 50 and the PTC electrode 6x of the protection element 60 with a lead wire, the two protection elements 50 and 60 were connected in series and energized. In this case, the current value was changed as shown in Table 3, and the presence or absence of trip of the PTC element of the protection element 60 and the presence or absence of fusing of the low melting point metal foil 2 of the protection element 50 were observed. Table 3 shows the results.

[0066]

[Table 3] Current value PTC element trip Fusing of low melting point metal foil 2A No No 4A No No 6A Yes No 8A Yes No From the results in Table 3, it can be seen that when these protection elements are energized in series and a current of 6 A or more is energized, the PTC element operates before the low-melting-point metal foil is blown, and the amount of energization is drastically reduced. Therefore, it can be seen that even in the case where a short circuit occurs in a circuit in which these protection elements are mounted, the PTC element operates before the low-melting-point metal foil is blown, and the current during the short circuit can be suppressed.

[0067]

According to the circuit of the present invention, not only overcurrent but also overvoltage can be prevented. Further, at the time of overcurrent or overvoltage, the current can be suppressed first by the operation of the reusable PTC element, and when the operation of the PTC element is insufficient, the circuit can be cut off by fusing the low melting point metal body. Therefore, it is possible to secure high safety while ensuring reuse of the element as much as possible.

[Brief description of the drawings]

FIG. 1 shows a protection circuit of the present invention.

FIG. 2 is a protection circuit according to the present invention.

FIG. 3 is a protection circuit according to the present invention.

FIG. 4 is a plan view (FIG. 4A) and a cross-sectional view (FIG. 4B) of the protection element of the present invention.

FIGS. 5A and 5B are a plan view (FIG. 5A) and a cross-sectional view (FIG. 5B) of a protection element using a low-melting-point metal body, which is useful for the protection circuit of the present invention.

6A and 6B are a plan view (FIG. 6A) and a cross-sectional view (FIG. 6B) of a protection element using a PTC element, which is useful for the protection circuit of the present invention.

[Explanation of symbols]

 1, 1a, 1b PTC element 2, 2a, 2b Low melting point metal body (low melting point metal foil) 3 Heating element 4 Substrate 5 Insulating layer 6a, 6x, 6z PTC electrode 6b, 6q, 6y Intermediate electrode 6c, 6p, 6r Low melting metal electrode 6d, 6e Heating element terminal electrode 7 Protective cap 8 Inner sealing portion 9 Outer sealing portion 10 Metal foil 20 Voltage detecting means 30 Protective element 40 Protective element 50 Protective element 60 Protective element

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yuji Furuuchi 12-3 Satsuki-cho, Kanuma City, Tochigi Prefecture Inside Sony Chemical Co., Ltd. (56) References JP-A-7-114661 (JP, A) JP-A-5- 299206 (JP, A) JP-A-57-116537 (JP, A) JP-A-4-46502 (JP, A) JP-A-62-1198646 (JP, U)

Claims (3)

(57) [Claims] 1. A voltage detecting means which operates when a terminal voltage of a protection circuit connected to a device to be protected becomes higher than a predetermined voltage, and a PTC element and a low melting point metal body connected in series, and A protection circuit having a heating element that generates heat when energized, and wherein the heating element is disposed in proximity to the low-melting metal body, the normal energization of the device to be protected is connected in series. A protection circuit which is formed through a PTC element and a low melting point metal body. 2. The protection circuit according to claim 1, wherein the heating element is disposed close to both the low-melting-point metal body and the PTC element. 3. A voltage detecting means which operates when a terminal voltage of a PTC element becomes equal to or higher than a predetermined voltage, a heating element which is energized by the operation of the voltage detecting means and generates heat, and a terminal voltage of the low melting point metal body is a predetermined voltage. 2. The protection circuit according to claim 1, wherein the voltage detection means which operates by the above operation and the heating element which is energized and generates heat by the operation of the voltage detection means are provided separately.