JPH10116550A - Protective element and its application method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly functional protective element having a simple structure as well as allowing easy manufacture, and a method for using the element, regarding a protective element for fusing a low-fusion point fusible alloy piece via the detection of the overvoltage of equipment, and the subsequent feed of power to a film resistor for heat generation as well as the isolation of the equipment and the film resistor from a power supply. SOLUTION: The first electrode 21, the second electrode 22, the third electrode 23 and the fourth electrode 24 are arranged on one side of an insulating board 1. In addition, a resistor R is provided across the second electrode 22 and the fourth electrode 24. Also, low-fusion point fusible alloy pieces A and B are respectively laid between the first electrode 21 and the second electrode 22, and between the second electrode 22 and the third electrode 23. Furthermore, flux 4 is applied to the low-fusion point fusible alloy pieces A and B, and one side of the insulating board 1 is covered with an insulation layer 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protection element used for protecting electric equipment from overvoltage and a method of using the same.

[0002]

2. Description of the Related Art When an equipment is cut off from a power supply when an overvoltage is applied to the equipment, a film resistor and a low melting point fusible alloy piece are arranged in parallel on one surface of an insulating substrate, and one surface of the insulating substrate is provided with an insulating layer. As shown in FIG. 4, the protective element E 'and the overvoltage detection energizing circuit F', for example, a Zener diode D 'is connected to the base side of the transistor Tr' as shown in FIG. Circuit F 'is inserted between the power supply S' and the protected device Z ', and when a reverse voltage equal to or higher than the breakdown voltage of the Zener diode D' acts on the device Z ', a base current flows. It is known that the device Z 'is cut off from the power supply S' by causing a collector current to flow in accordance with the source current to generate a film resistance R 'and blow the low melting point fusible alloy piece A'.

However, in the above protection element, even if the equipment Z 'is cut off from the power supply due to the fusing of the low melting point fusible alloy piece A', when the equipment Z 'has a capacitive load, for example, in the case of a storage battery, the residual voltage is low. For this reason, the base current may continue to flow and the heat generation of the film resistor R 'may be continued, which is dangerous.

Therefore, as shown in FIG. 5A, a composite electrode 20 'in which a central fuse electrode 21' and a heater one-sided T-shaped electrode 22 'are combined, and a heater-other side T-shaped electrode 22'. L-shaped electrode 2
3 'and both side electrodes 24' and 25 'are printed on the substrate 1', and as shown in FIG. 5 (b), a heater one-sided T-shaped electrode 22 'and a heater and others are formed. The film resistances R 'and R' extend between the two arms of the T-shape with the side T-shaped electrode 23 '.
And an insulating layer i ', i' is provided on each film resistor, and a low melting point is provided between the central fuse electrode 21 'of the composite electrode 20' and the fuse side electrodes 24 'and 25', respectively. The alloy pieces A ′ and A ′ were connected, and as shown in FIG.
It has been proposed to use a protection element comprising a flux layer 4 'and an external insulating layer 5' (Japanese Patent Laid-Open No. 7-15 / 1995).
No. 3367). In the protection circuit incorporating this protection element, as shown in FIG. 6, the film resistance R'-low melting point fusible alloy piece A '
Are provided, and the low melting point fusible alloy pieces A ′ of each pair are blown off by the heat generated by the current flowing through the film resistors R ′ of each pair. When a reverse voltage equal to or higher than the breakdown voltage of the Zener diode D 'acts on the device Z', a base current flows through the transistor Tr ', a collector current flows, and both film resistances R' and R 'are increased. Electric current is generated and the low melting point fusible alloy pieces A 'and A' are melted and cut off from the power supply S 'by the electric current generated by the film resistors R' and R ', and the film resistors R' and R 'are cut off. Is disconnected from the power supply S '.

[0005]

However, in the above-described protective element, since there are two pairs of the film resistance and the low melting point fusible alloy piece, it is necessary to adjust the resistance values of the two film resistances, and therefore, the production is difficult. Also, it is disadvantageous to reduce the size of the protection element because it is necessary to provide two sets of the film resistance and the low melting point fusible alloy piece in a plane. Furthermore, an insulating layer on the film resistance,
For example, a glass film is formed by screen printing, and it is difficult to avoid unevenness due to the mesh of the screen. Under such circumstances, the smooth spheroidization of the low-melting-point fusible alloy piece on the glass film is required. Difficult to guarantee.

An object of the present invention is to provide a protection element for detecting overvoltage of a device, energizing and generating heat in a film resistor to blow a low melting point fusible alloy piece, and cutting off the device and the film resistor from a power supply.
An object of the present invention is to provide a protective element having a simple structure, easy to manufacture, and excellent in operability, and a method for using the protective element.

[0007]

A protective element according to the present invention comprises a first electrode, a second electrode, a third electrode, and a fourth electrode provided on one surface of an insulating substrate, and extends over the second electrode and the fourth electrode. A resistor is provided, low melting point fusible alloy pieces A and B are connected between the first electrode and the second electrode and between the second electrode and the third electrode, respectively, and flux is applied to the low melting point fusible alloy piece. The insulating substrate is covered with an insulating layer so as to cover one surface of the insulating substrate. The protection element according to the present invention has the first electrode connected to the power supply side and the third electrode connected to the protected device side, and prevents the overvoltage of the protected device between the first electrode or the third electrode and the fourth electrode. An overvoltage detection energizing circuit for detecting and energizing the resistor to generate heat can be connected and used.

Further, in the protection element according to the present invention, the melting point of the low-melting-point fusible alloy piece A and the melting point of the low-melting-point fusible alloy piece B are different from each other, and each low-melting-point fusible alloy piece is used for a different circuit portion. Connect an overvoltage detection energizing circuit that detects different overvoltages and energizes and heats the resistance of the protection element at different temperatures, and heats up the resistor with a small overvoltage to melt one of the low melting point fusible alloy pieces. Then, one circuit portion can be cut off from the power supply, and then the resistor is heated and heated by a large overvoltage, and the other circuit portion is cut off from the power supply by fusing the other low melting point fusible alloy piece.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of a protection element according to the present invention. In FIG. 1, reference numeral 1 denotes a heat-resistant insulating substrate, for example, a ceramic plate. Reference numerals 21 to 24 denote first to fourth film-shaped electrodes formed on one surface of the insulating substrate by printing.
The second electrode 22 is provided between the tip of the first electrode 21 and the tip of the third electrode 23, and the fourth electrode 24 is further provided at a predetermined interval from the second electrode 22. . 31,
33 and 34 are lead wires (insulated wires) connected to the first, third and fourth electrodes, respectively. R is a film resistance provided by printing over the second electrode 22 and the fourth electrode 24. A is a low melting point fusible alloy piece connected between the tip of the first electrode 21 and the second electrode 22, and B is a low melting point fusible alloy connected between the second electrode 22 and the tip of the third electrode 23. It is a molten alloy piece, and the low melting point fusible alloy pieces A and B are the same material,
In the case of the same shape, a continuous line may be used as shown in the figure. 4 is a flux applied on the low melting point fusible alloy pieces A and B. Reference numeral 5 denotes an insulating layer provided so as to cover one surface of the insulating substrate 1, and an insulating material which can be coated at room temperature so as not to melt and flow the low melting point fusible alloy piece or flux.
For example, a cold-setting epoxy resin is used.

The protection element according to the present invention is used to shut off a device to be protected from an electric power supply when an overvoltage acts on the device. FIG. 2 is a circuit diagram for explaining the state of use of the device. F indicates a protection element according to the present invention, and F indicates an overvoltage detection energizing circuit. In FIG. 2, the protection element E and the overvoltage detection energizing circuit F according to the present invention are incorporated between the protected device Z and the power supply S, and the collector of the transistor Tr is connected to the fourth electrode 24 of the protection element E. The high-voltage side electrode of the gate D and the third electrode 2 of the protection element E
3 to the high voltage side terminal of the protected device Z, and
Is connected to the high voltage side terminal of the power supply S, and the emitter of the transistor Tr is grounded. In the circuit shown in FIG. 2, when an overvoltage equal to or higher than the breakdown voltage of the Zener diode D acts on the device Z, a base current flows through the transistor Tr, causing a large collector current to flow, causing the film resistor R to generate heat. The generated heat is transmitted to the low melting point fusible alloy pieces A and B via the second electrode 22 so that the low melting point fusible alloy pieces A and B are blown off while receiving the activation action of the already melted flux. Z is cut off from the power supply S, and the film resistor R is cut off from the power supply S. Therefore, after the low melting point fusible alloy piece B is blown, even if the overvoltage state of the device Z is maintained due to the residual charge and the transistor Tr is in the conductive state, the film due to the low melting point fusible alloy piece A being blown out. Since the resistance R is cut off from the power supply S, the continuation of heat generation of the film resistance R can be eliminated. In the above, the high voltage side electrode of the Zener diode D may be connected to the first electrode 21 side.

In the above, the fusing of the molten low-melting-point metal effectively contributes to the fact that the insulating substrate repels the molten metal and the electrodes are well wetted by the molten metal, and the surface smoothness of the insulating substrate is also an important condition. Yes (elements that make molten metal easier to flow). Thus, the ceramic plate is superior in surface smoothness as compared with a glass screen printing film and is advantageous. In the protection element according to the present invention, as shown in FIG. 3, the low melting point fusible alloy piece B is used as a fuse for the circuit portion Zb, and the low melting point fusible alloy piece A is used as a fuse for the circuit portion Za. In FIG. 3, the Zena diode Db is used.
Of the breakdown voltage Vb of the Zener diode Da
The melting point of the low melting point fusible alloy piece B is lower than the melting point of the low melting point fusible alloy piece A, the Zener diode Db is turned on by an overvoltage of Vb to Va, and a base current is passed. With the collector current corresponding to this base current, the resistor R of the protection element E is energized and heated to melt the low melting point fusible alloy piece B to cut off the circuit portion Zb from the power supply (ss' is a power supply terminal).
Thereafter, when an overvoltage of Va or more acts, the diode Da is made conductive and a base current flows, and the resistance R of the protection element E is heated by a collector current corresponding to this base current to generate a low melting point. The circuit portion Za can be cut off from the power supply (ss' is a power supply terminal) by fusing the alloy piece A.

In the protection element according to the present invention, a ceramic plate having a thickness of 100 to 1200 μm, for example, a 96% alumina ceramic plate can be used as the insulating substrate. In addition, it is also possible to use an insulated metal-based material. The plane dimensions of the insulating substrate are usually (3 mm to 20 m
m) × (3 mm to 20 mm) square or rectangular. In the protection element according to the present invention, the low melting point fusible alloy piece has a liquidus temperature of 75 ° C to 300 ° C and a diameter of 100 µm to 1 ° C.
A low-melting alloy round wire of 200 μm, a low-melting alloy square wire or a low-melting alloy foil having the same cross-sectional area as this can be used. In the protective element according to the present invention, the electrode is a conductor paste (a mixture of a conductor powder and a glaze, and the conductor powder includes a silver-platinum-based silver
(Palladium-based, copper-based) by screen printing and baking. Also, an insulating substrate with electrodes can be obtained by etching the copper foil of the copper foil laminated substrate. In the protection device according to the present invention, the film resistance is a resistance value.
For example, a mixture of ruthenium oxide powder or carbon powder and glaze is screen-printed on an insulating substrate and baked, and the film thickness is usually 1 to 30 μm.
m. As the film resistance, a Ti-Si based film resistance can be used. When the resistance value of the film resistor needs to be adjusted, the trimming is performed. it can. Furthermore,
When protection is required for long-term stability or the like, a protective film, for example, a glass film is formed on the film resistor. Either of the overlapping states of the film resistance end and the electrode end may be on the lower side. Instead of these film resistors, it is also possible to use chip resistors.

In the protective element according to the present invention, the flux prevents oxidation of the low melting point fusible alloy piece and dissolves some oxide film of the low melting point fusible alloy piece to facilitate cutting of the molten alloy. In general, rosin can be used as a main component, and if necessary, an activator (for example, hydrochloride of diethylamine) is added.

To manufacture the protection element according to the present invention, first to fourth electrodes are formed on one surface of an insulating substrate, a film resistor is printed, and a glass protective film is formed on the film resistor. The resistance value is adjusted by trimming, and if resistance protection is necessary, a glass film is formed on the film resistance, low melting point fusible alloy pieces A and B are connected, and a lead wire is connected to the electrode, A method can be used in which a flux is applied to a low melting point fusible alloy piece, then the substrate is immersed in an epoxy resin solution at room temperature, and the immersion coating layer is dried and cured.

[0015]

The protection element according to the present invention has one resistor and two low-melting-point fusible alloy pieces. When an overvoltage acts on the device to be protected, both resistors are energized and heated by the resistor. The low-melting-point fusible alloy piece can be blown to cut off the equipment to be protected from the power supply and to cut off the resistor from the power supply,
Conventional example, that is, a resistor is provided for each of both low-melting-point fusible alloy pieces, one low-melting-point fusible alloy piece is blown by the heat generation of one resistor, and the other is melted by the heat generation of the other resistor. It is structurally simpler than the configuration in which the low melting point fusible alloy piece is blown.

Further, unlike the conventional example in which an insulating glass film is provided on a film resistor and a low melting point fusible alloy piece is disposed on the insulating glass film, the film resistance and the low melting point fusible alloy piece are different from each other. And disposing the low melting point fusible alloy piece on a ceramic insulating substrate having a smoother surface than the surface of the insulating glass film (unevenness due to the screen mesh is inevitable on the screen printing). Because of the arrangement, the molten alloy can be smoothly flowed to be quickly divided, and excellent operability can be guaranteed. Further, when the resistance value adjustment is required, the resistance value adjustment by trimming may be performed for one film resistor, so that the number of manufacturing steps can be reduced, which is advantageous in manufacturing. Furthermore, different circuit parts can be disconnected from the power supply for different overvoltages.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an example of a protection element according to the present invention.

FIG. 2 is an explanatory diagram showing an example of a circuit using a protection element according to the present invention.

FIG. 3 is an explanatory diagram showing an example of a circuit using the protection element according to the present invention.

FIG. 4 is an explanatory diagram showing a conventional protection circuit.

FIG. 5 is an explanatory view showing a conventional protection element.

6 is an explanatory diagram showing a protection circuit using the protection element of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulating substrate 21 1st electrode 22 2nd electrode 23 3rd electrode 24 4th electrode A Low melting point fusible alloy piece B Low melting point fusible alloy piece R Resistance 4 Flux 5 Insulating layer E Protection element F Overvoltage detection energizing circuit Z Protective equipment S Power supply

Claims (3)

[Claims] A first electrode, a second electrode, and a first electrode on one surface of the insulating substrate;
A third electrode and a fourth electrode are provided, a resistor is provided between the second electrode and the fourth electrode, and a low melting point fusible alloy is provided between the first electrode and the second electrode and between the second electrode and the third electrode. A protective element comprising connecting the pieces A and B to each other, applying a flux to the low melting point fusible alloy piece, and covering one surface of the insulating substrate with an insulating layer. 2. The protection device according to claim 1, wherein the first electrode is connected to the power supply side, and the third electrode is connected to the device to be protected, and the first electrode or the third electrode and the fourth electrode are connected to each other. A method for using a protection element, comprising: connecting an overvoltage detection energizing circuit for detecting an overvoltage of a protected device and energizing and generating heat in the resistor. 3. The melting point of the low melting point fusible alloy piece A and the melting point of the low melting point fusible alloy piece B of the protection element according to claim 1, and each low melting point fusible alloy piece is used for a different circuit portion. Connect an overvoltage detection energizing circuit that detects different overvoltages and energizes and heats the resistance of the protection element at different temperatures, and heats up the resistor with a small overvoltage to melt one of the low melting point fusible alloy pieces. To disconnect one circuit from the power supply,
A method of using a protection element, characterized in that a resistor is energized and heated by a large overvoltage thereafter to cut off the other circuit portion from a power supply by fusing the other low melting point fusible alloy piece.