JPS638083Y2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to a surge absorption device that has a ceramic varistor mainly made of metal oxide such as zinc oxide. The present invention provides a surge absorption device having an electrode structure for reducing the voltage drop caused and obtaining a low limiting voltage.

Conventional examples are shown in FIGS. 1 to 4. 1 in Fig. 1 is the voltage-current characteristic of the ceramic varistor mentioned earlier, and 2 is generally called the varistor voltage.
This is the voltage at which current suddenly begins to flow. As can be understood from FIG. 1, at voltages below the varistor voltage, the ceramic varistor almost acts as an insulator and has almost no leakage current. Normally, the circuit voltage used by this varistor is set to be lower than this varistor voltage.

However, when a high pulse-like voltage such as a lightning surge is applied to the circuit voltage, the ceramic varistor exhibits an extremely low resistance value, allows a surge current to flow due to the surge voltage, and suppresses the surge voltage.

The general structure of this ceramic varistor is explained in the second section.
As shown in the figure. In FIG. 2, 3 is a sintered body of a ceramic varistor, 4 is an electrode baked with Ag or the like on the sintered body 3, and 5 is a lead wire soldered to the electrode 4. In order to protect semiconductor equipment and the like from surge voltages, the lead wires 5 of the ceramic varistor shown in FIG. 2 are attached between power supply lines or signal lines to absorb surges. In some cases, it may also be inserted between the line and the ground.

FIG. 3 shows an equivalent circuit for the surge current of the ceramic varistor shown in FIG. 2. however,
It is assumed that the ceramic varistor is already connected to the power supply line or signal line. In the figure, 6 is a power supply line or a signal line, which is on the surge voltage inlet side. 7
8 is the inductance of the lead wire 5, 9 is the resistance of the lead wire 5, and 10 is the varistor that has the characteristics of the sintered body 3, which eliminates the influence of the lead wire 5. This is the terminal connected to the protective equipment.

Now, if a surge current flows as shown by the arrow in Figure 3, a voltage drop will occur in the inductance 8 and the resistor 9, and the limiting voltage will be added to the original limiting voltage of the varistor 7, resulting in poor protection characteristics. . This tendency shows that the larger the current flowing into the varistor 7, and the higher the frequency component of the current, the larger the voltage drop across the inductance 8 and resistor 9, and the number of limiting voltages of the varistor 7.
It is not uncommon for it to reach 10%.

FIG. 4 shows this situation. The horizontal axis is the surge current expressed logarithmically, and the vertical axis is the limit voltage expressed logarithmically. In the figure, 11 is the original limiting voltage characteristic of the varistor 7, 12 is the inductance 8, and the resistance 9.
13 is the limited voltage seen from terminal 10 in Figure 3, that is, the protected equipment side, which is the sum of the voltage-current characteristics of 11 and 12 in terms of voltage. It is. In this way, even though the varistor 7 originally has the characteristic 11, in the structure shown in Fig. 2, its limiting voltage becomes 13, which is extremely harmful from the point of view of protection. It is a characteristic.

The present invention removes these harmful characteristics using an electrode structure, brings out the inherent characteristics of ceramic varistors, protects the protected equipment from surge voltages, and at the same time facilitates connection to printed circuit boards and improves mechanical efficiency. This provides stable installation.

FIG. 5 shows an equivalent circuit of the present invention for FIG. 3. As is clear from the figure, the 10 power supply lines or signal line terminals are connected to both ends of the varistor 7, that is, terminal 1.
4, and the structure is such that no voltage drop across the inductance 8 and resistance 9 is applied to the terminal 10, that is, to the protected device side.

FIG. 6 shows an embodiment of the surge absorbing device according to the present invention. In Fig. 6, 15 is a ceramic varistor, and 16 is a U that produces the equivalent circuit of Fig. 5.
The letter-shaped electrode 17 is two terminals provided at the tip of the electrode 16 for electrical connection. In this case, the electrodes 16 are attached to the front and back of the varistor 15 with the electrodes 16 facing in opposite directions, the U-shaped legs are bent in a direction substantially perpendicular to the plane of the varistor 15, and the length of the legs is set on a horizontal printed circuit board, etc. Varistor 1 when installed
Place the barista 15 in advance so that 5 is horizontal.
The legs of one U-shaped electrode are shortened by the thickness of the electrode. Note that the varistor 15 and the electrode 16 are electrically connected by, for example, solder.

The operating principle of a ceramic varistor having a U-shaped electrode 16 as shown in FIG. 6 will be explained. In FIG. 6, A is a point at the center of the U-shaped electrode 16, and B and C are respective terminal portions. For example, assume that a surge voltage is now applied between both electrodes 16 of the varistor 15 through C and the terminal facing C. At this time, the surge current flows from the front to the back of the diagram, heading from point C to point A. At this time, a certain voltage drop occurs between A and C. This is the voltage drop due to the inductance 8 and resistance 9 shown above. However, since no surge current is flowing between A and B, no voltage drop occurs between them. Therefore, the potential at point B is equal to that at point A. Since the potential at point A indicates the limited voltage of the ceramic varistor 15, point B indicates the inherent limited voltage of the varistor, which satisfies the equivalent circuit shown in FIG. In addition, in Fig. 5, A of Fig. 7,
Points corresponding to B and C are indicated by the same symbols A, B, and C.

A surge absorbing device having such a U-shaped electrode structure can be mounted in an extremely mechanically stable manner by providing four holes on a printed circuit board, as in the conventional device shown in FIG.

Fig. 7 shows a U-shaped electrode 16 formed into a U-shape by providing a slit 18, which is structurally strong and allows for larger load current paths C, A, and B in Fig. 5. becomes possible.

In Fig. 8, instead of punching or slitting the constriction of the U-shape, grooves or depressions shown as 19 are provided on the front and back of the electrode 16, or on either side, making the electrode thinner in that part than in other parts, thereby reducing the resistance. By increasing the component, the surge current can be
7, the flow is made to flow in a U-shaped part. Although there is only one groove or recess 19 in FIG. 8, the effect will be greater if a plurality of grooves or recesses 19 are provided. Furthermore, pleats may be provided instead of grooves or depressions to increase the conductive distance.

All of the above-mentioned structures do not have electrical insulation such as exterior packaging, but may be coated or cased with resin or the like to ensure insulation from other parts.

As explained above, according to the present invention, by using the U-shaped electrode structure, the surge absorber can
By forming a terminal structure, it is possible to obtain the original limited voltage of a ceramic varistor with almost no effect of voltage drop due to surge current flowing through the lead wire, and it has excellent protection characteristics.

Also, by using two U-shaped electrodes,
Obtaining 4 terminals in the same direction while having the above effects,
When attached to a printed circuit board, etc., mechanically strong and compact attachment is possible.

Furthermore, by using two U-shaped electrodes in opposite directions, it is possible to reduce the height above the printed circuit board.

Furthermore, by obtaining the configuration of the U-shaped electrode by providing a central slit, it is possible to increase the current carrying capacity of the U-shaped part.

In addition, by housing it in an insulating coating or an insulating material, it is possible to have electrical insulation properties and to avoid environmental influences such as humidity.

[Brief explanation of the drawing]

Figure 1 is a voltage-current characteristic diagram of a ceramic varistor, Figure 2 is a diagram showing the configuration of a conventional varistor, Figure 3 is an equivalent circuit diagram for the surge current of the varistor in Figure 2, and Figure 4 is the diagram shown in Figure 2. 5 is a basic equivalent circuit diagram of the present invention, FIG. 6 is a perspective view of a surge absorbing device in an embodiment of the present invention, and FIG. 7 is a diagram of other electrodes in the same device. FIGS. 8a and 8b are a front view and an X-Y cross-sectional view showing still another example of the electrode in the same device. 15...varistor, 16...U-shaped electrode, 17
... terminal, 18 ... slit, 19 ... groove or recess.

Claims (1)

[Claims for Utility Model Registration] (1) A ceramic varistor made of a metal oxide such as zinc oxide and having an excellent voltage non-linearity index, and a substantially U-shaped ceramic varistor made of a highly conductive metal, with two ends having electrical terminals. and electrically connect the electrode plates to the ceramic varistor by positioning them on both the front and back electrodes of the ceramic varistor in opposite directions, and connecting the electrical terminals at the tips of the respective electrode plates to the ceramic varistor. The ceramic varistor is bent in the same direction approximately perpendicular to the plane of the ceramic varistor,
A surge absorption device with four electrical terminals protruding in the same direction. (2) By making a slit in the electrode plate,
The surge absorbing device according to claim 1, which is characterized in that it is configured in a letter shape. (3) The surge absorber according to claim 1 of the utility model registration claim, characterized in that the electrode plate is formed by providing a groove or a depression in a portion corresponding to the constriction so that the thickness of the electrode plate is thinner than in other parts. Device. (4) The surge absorbing device according to claim 1 of the utility model registration, characterized in that the electrode plate is obtained by providing pleats in the portion corresponding to the constriction to increase the conductive distance.