JPS6242485Y2 - - Google Patents

Description

[Detailed description of the invention] This invention takes measures against short circuits and burnouts of ceramic varistors used for surge absorption caused by continuous overvoltage, and prevents the varistors from shorting even when continuous overvoltage is applied. The purpose of the present invention is to provide a surge absorber that can sufficiently exhibit the surge absorption function.

Varistors, which are made of ceramic mainly made of zinc oxide, are connected between power lines or the ground to protect electronic equipment from surge voltages such as lightning.
It has become widely used in recent years.

Currently, the mainstream of this type of varistor is a varistor mainly made of zinc oxide, but this varistor has an extremely large voltage nonlinearity index (usually 30
(above), below a certain voltage (hereinafter referred to as varistor voltage), it acts as an insulator, and exhibits an extremely low resistance value for voltages above that, resulting in the current associated with that voltage flowing through the varistor. It has the characteristic of limiting the voltage to a low level. Therefore, when this type of varistor is used as a surge absorber, the varistor voltage is set to be somewhat higher than the peak value of the normal circuit voltage in order to operate it as an insulator under normal conditions. For example, when using between AC100V lines, the varistor voltage is set to about 220V.

FIG. 1 shows an example of the circuit. 1 is the power wire, which in this case is AC100V. 2 is a varistor connected between the lines. If the varistor voltage of varistor 2 is 220V, the power supply voltage is AC100V
There is no problem even if the voltage rises from 140V to AC140V.
This does not affect the ballista 2 in any way. However, an overvoltage of 140 VAC or more may be applied to the varistor 2 due to a large change in load, an open phase in the neutral wire of a single-phase three-wire distribution line, or other ground faults. In this case, the peak value of the overvoltage greatly exceeds the varistor voltage of the varistor 2, and the current from the power supply continuously flows into the varistor 2. Therefore, the varistor 2 generates excessive heat, resulting in short-circuit damage.

A possible solution to this problem is to set the varistor voltage even higher, but this raises the problem of increasing the limit voltage during surge absorption and making it difficult to coordinate with electronic equipment.

The present invention provides a surge absorber that does not significantly increase the limiting voltage during surge absorption, which is the problem mentioned above, and does not cause short-circuit breakdown even in the case of continuous overvoltage.

FIG. 2 shows the circuit of the surge absorber of the present invention. Reference numeral 3 denotes a first varistor which has the same varistor voltage as the conventional varistor 2. 4 is a positive temperature coefficient thermistor electrically connected in series with the first varistor 3, and the first varistor 3 and the positive coefficient thermistor 4 are also thermally coupled.
The resistance value of this positive temperature coefficient thermistor 4 increases rapidly when the temperature exceeds a certain level, and in the case of the circuit of the present invention, the resistance value at room temperature is set to about 5 ohms. Reference numeral 5 denotes a second varistor electrically connected in parallel to the positive temperature coefficient thermistor 4, and the varistor voltage can be arbitrarily selected depending on the degree of estimated overvoltage, but in this example, it was set to 220V.

Now, assume that an AC overvoltage of 200V is continuously applied to this circuit. When the temperature of the PTC thermistor 4 does not rise in response to AC overvoltage, the resistance of the PTC thermistor 4 is lower than the resistance of the second varistor 5, and the power supply current flows through the first varistor 3 and the PTC thermistor 4. It flows through the thermistor 4. At this time, both the first varistor 3 and the positive temperature coefficient thermistor 4 generate heat due to the continuous inflow current. At this time, since the first varistor 3 is thermally coupled to the PTC thermistor 4, the temperature rise of the PTC thermistor 4 is larger than the temperature rise due to the PTC thermistor 4 alone. Due to this temperature rise, the resistance value of the positive temperature coefficient thermistor 4 increases rapidly, and the inflow current is limited to an extent that does not cause the first varistor 3 to be destroyed by short circuit. Furthermore, after the continuous overvoltage is removed, the temperature of the PTC thermistor 4 decreases again, returning to the state before the overvoltage was applied. on the other hand,
When a surge voltage is applied to this circuit, the surge current first flows through the first varistor 3 and the positive temperature coefficient thermistor 4 as described above, and if the second varistor 5 is not present at this time, the limiting voltage will be It will look like A in Figure 4. The reason why the limit voltage increases rapidly with the increase in current is that the voltage drop across the positive temperature coefficient thermistor 4 increases linearly.
In order to prevent this limit voltage from increasing, the second varistor 5 is used. That is,
When the voltage drop across the positive characteristic thermistor 4 exceeds the varistor voltage of 220V of the second varistor 5, the second varistor 5 starts operating and suppresses the increase in the limit voltage, and the limit voltage of the circuit of the present invention is reduced to 220V. As shown in Figure 4 (b), it has a sufficiently low rise characteristic.

Now, FIG. 3 shows the structure of a specific example of the surge absorber of the present invention.

6 is the second varistor, 7 is the positive temperature coefficient thermistor, 8 is the first varistor, 9 is a wafer for connecting the second varistor 6 and the positive coefficient thermistor 7 in parallel, and 10 and 11 are both It is an electrical terminal.

Here, the positive temperature coefficient thermistor 7, the first varistor 8, and the second varistor 6 are connected to the waving 9 and the electric terminals 10, 11 so as to have the circuit configuration shown in FIG.
connected by. Further, the positive temperature coefficient thermistor 7 is coupled so that the heat of the first varistor 8 is easily transferred.

By configuring the circuit configuration of the surge absorber of the present invention as described above, the following effects can be obtained.

(1) A positive temperature coefficient thermistor is connected in series to the first varistor, and the first varistor and the positive coefficient thermistor are thermally coupled, so surge absorption does not cause short-circuit damage even in the case of continuous overvoltage. A vessel is obtained.

(2) Since the second varistor is connected in parallel to the positive temperature coefficient thermistor, it can withstand surge voltages.
A sufficiently low limiting voltage can be obtained.

Further, by thermally coupling the first varistor and the positive temperature coefficient thermistor, the response to resistance changes of the positive coefficient thermistor becomes faster, and the effect of protecting the first varistor from destruction becomes higher.

[Brief explanation of drawings]

Figure 1 is an electrical circuit diagram of a conventional surge absorber.
Fig. 2 is an electrical circuit diagram showing an embodiment of the surge absorber of the present invention, Fig. 3 is a sectional view showing an example of the specific configuration of the surge absorber, and Fig. 4 is the limiting voltage of the surge absorber. It is a characteristic diagram. 3, 8...First varistor, 4, 7...Positive characteristic thermistor, 5, 6... Second varistor.

Claims (1)

[Scope of utility model registration request] The first varistor and the positive thermistor are electrically connected in series and thermally coupled, and the second varistor is connected to the positive thermistor. A surge absorber characterized by being electrically connected in parallel to.