JPH11252789A - Protector against overvoltage - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a protective circuit against overvoltage, which does not need replacement of protective circuit pats resulting from the action of protective circuit parts, by performing the protective action even in the case that the application of voltage is higher than the nominal voltage range of rating continues for a relatively long time. SOLUTION: This protector against overvoltage is installed on the power supply side of the power source receiving the power supply from the neutral line and high-potential line of a commercial power source, and this has a surge absorbing element 22 which is connected between a high potential line and a neutral line, a positive temperature coefficient thermistor 26 which is inserted in series to the high potential line on commercial power source side from a surge-absorbing element 22, and a heat-shrinkable tube 25 which properly conducts the heat generated in the surge-absorbing element 22 to the positive property thermistor 26 favorably. When an overvoltage is applied, the resistance value of the positive property temperature coefficient thermistor 26 rises through the heat generation of the surge absorbing element 22, and the current value drops from the rise in the resistance value of the positive temperature coefficient thermistor 26, and the heat generation of the surge absorbing element 22 is suppressed, and the heat generation (temperature rise) of the surge-absorbing element 22 means is limited to a point, where the heat generation of the surge-absorbing element 22 and the rise in the resistance value of the positive temperature coefficient thermistor 26 become balanced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overvoltage protection device for a power supply device, and more particularly, to an overvoltage protection device that uses a surge absorbing element to protect an overvoltage by a rise in temperature when a surge current flows.

[0002]

2. Description of the Related Art Generally, in a power supply device connected to a commercial power supply, an overvoltage protection device is provided to prevent damage to the power supply device due to an overvoltage or a surge voltage applied to a voltage supplied from the commercial power supply. Installed on the input side of the power supply. The above-mentioned overvoltage, for example, in consideration of the voltage drop due to the transmission line, in the case of transmitting power at a slightly higher voltage than the nominal voltage on the power transmission side, and at the end of the transmission line is a voltage close to the nominal voltage, When a voltage is supplied from a transmission line close to the transmission source, an overvoltage higher than the nominal voltage is supplied. The case where the above-described surge voltage occurs is, for example, a case where a momentary high-voltage surge component is superimposed on the transmission line due to electromagnetic induction due to lightning falling near the transmission line. Here, a conventional protection device against overvoltage and surge voltage will be described with reference to the drawings. FIG. 4 is a diagram showing an example of a conventional overvoltage protection device, in which a surge absorbing element 2 is inserted between a line on the input side of a commercial power supply in a power supply device 3 and the surge absorbing element 2 is further inserted.
The current fuse 1 is inserted in series with the high potential line on the upstream side of the commercial power supply. This surge absorbing element 2
For example, varistors and arresters are known. When a voltage higher than the rating of the surge absorbing element 2 is supplied between the lines, the surge absorbing element 2 enters a short-circuit mode, and a current (overcurrent) rapidly increases. It flows through the surge absorbing element 2. Then
The current exceeding the rated current also flows through the current fuse 1, and the current fuse 1 is blown, and the overvoltage (and overcurrent) is not supplied to the power supply on the downstream side of the commercial power supply. Will be protected. For example, a description will be given of a commonly used varistor as the surge absorbing element 2. The varistor hardly consumes current in a normal voltage range, but when a high voltage equal to or higher than the varistor voltage is applied, The varistor itself consumes current by clamping the voltage. Then
When the current consumed by the varistor flows to the circuit on the power supply side, the current fuse 1 is blown and the application of voltage (current) to the power supply device is eliminated, thereby protecting the power supply device.

FIG. 5 is a diagram showing another example of the conventional overvoltage protection device different from the example shown in FIG.
Is inserted between the lines on the input side of the commercial power supply in the power supply device 3, and the temperature fuse 14 and the current fuse 1 are further inserted in series with the high potential line on the upstream side of the commercial power supply with respect to the surge absorbing element 12. The surge absorbing element 12 and the thermal fuse 14 are, for example, disposed close to each other so as to be thermally coupled, or are fixed by a heat-shrinkable tube or the like while the two are kept in contact so that heat conduction is good. I have. In the case of FIG. 5, when a voltage equal to or higher than the rating of the surge absorbing element 12 is supplied between the lines, the surge absorbing element 12 enters a short-circuit mode until a current (overcurrent) suddenly flows through the surge absorbing element 12. Is the same as that of FIG. 4, but in the short-circuit mode of the surge absorbing element 12, the current fuse 1
Not only a high current when a high voltage several times the rated voltage, etc., at which the fuse is blown, but also several tens of percent of the rated voltage
The current flows even when a relatively low level high voltage such as a high voltage is applied. When the relatively low level high voltage is applied, the power consumption of the surge absorbing element 12 due to the short-circuit mode current and the power supply voltage is considerably large, so that the surge absorbing element 12 generates heat. Even if the thermal fuse 14 is blown and a relatively low level of high voltage continues, the overvoltage is not supplied to the power supply unit on the downstream side of the commercial power supply, so that the internal components of the power supply unit are protected from damage. Will be. The case of FIG. 5 will be described in the case of using a varistor similarly to the case of FIG. 4. If a high voltage higher than the varistor voltage is applied and current is consumed by the varistor, the current fuse 1 Since the current capacity is equal to or greater than the current value at that time, even when the current fuse 1 does not blow, the temperature fuse of the varistor (element) is blown by the temperature rise of the varistor (element) due to the current (power) consumed by the varistor. The device is protected from overheating and damage to components due to overvoltage. The overvoltage protection device of FIG.
The voltage at the power source should be relatively high when the power source is close to the power source of the transmission line as described above, or when the distance between the power source and the power transmission terminal is long, such as in a country with poor power supply conditions, where there are few substations. Therefore, there are relatively many opportunities to function. An advantage of the overvoltage protection device of FIG. 5 over the overvoltage protection device of FIG. 4 is that it is effective when a high voltage having a relatively lower level than the nominal voltage is applied for a long time. . When such a relatively low level of high voltage (overvoltage) is applied, even if the application of an instantaneous (short-time) overvoltage such as a surge voltage does not cause a problem, such an overvoltage is applied for a long time. When an excessive overvoltage is applied, the temperature of the elements and the like inside the power supply may rise abnormally, or the internal elements and the like may be damaged by the rise in temperature. Therefore, it is necessary to install an overvoltage protection device as shown in FIG. 5 even for such a low-level high voltage.

[0004]

However, in the case of a conventional overvoltage protection circuit using a thermal fuse, if an overvoltage is applied, the thermal fuse blows or a surge absorbing element (such as a varistor) is damaged. Then, the internal circuit of the power supply is protected and the danger of smoking or ignition is avoided, but when the power supply is restored later, it is necessary to replace the thermal fuse and varistor, etc. Because of the relatively high cost, such replacements are dangerous.
In many cases, replacement cannot be performed unless the inside of the housing is exposed, so that it is not preferable that the replacement be performed frequently for safety. In particular, in countries where power supply conditions are not favorable as described above, the transmission voltage is often higher than the rated voltage, so if an overvoltage protection circuit using a thermal fuse is installed in the power supply, the It has become necessary to replace thermal fuses, varistors, and the like of power supply devices. In view of the above problems, in the present invention, when application of a voltage higher than the rated nominal voltage range continues for a relatively long time, overvoltage protection that does not require replacement of the protection circuit component due to operation of the protection circuit component is performed. It is intended to provide a circuit.

[0005]

In order to achieve the above object, an overvoltage protection device according to the present invention comprises an overvoltage protection device provided on a power supply side of a power supply receiving power from a neutral line and a high potential line of a commercial power supply. A surge absorbing means connected between the high potential line and the neutral line; a positive temperature coefficient thermistor means inserted in series with a high potential line closer to the commercial power supply than the surge absorbing means; And a thermal coupling means that satisfactorily transmits the heat generated by the means to the positive temperature coefficient thermistor means.If an overvoltage is applied, the resistance value of the positive temperature coefficient thermistor increases due to heat generation of the surge absorbing means, As the resistance value of the positive temperature coefficient thermistor rises, the current value decreases, and the heat generation of the surge absorbing means is suppressed, and finally, the heat generation of the surge absorbing means and the rise of the resistance value of the positive temperature coefficient thermistor become flat. Heating (temperature rise) of the surge absorption means until it becomes will be limited.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of one embodiment of the present invention. 4 and 5 showing the prior art are denoted by the same reference numerals in FIGS. 1 and 3 as those in FIGS. 4 and 5, and description thereof is omitted. In FIG. 1, a current fuse 1 and a power supply 3 are the same as the current fuse and the power supply 3 in FIG. Further, the point where the surge absorbing element 22 is inserted between the lines on the input side of the commercial power supply in the power supply device 3 is the same as the point where the surge absorbing element 12 in FIG. However, it is not the thermal fuse but the positive temperature coefficient thermistor 26 and the current fuse 1 that are inserted in series with the high potential line on the upstream side of the commercial power supply with respect to the surge absorbing element 22. It is the positive temperature coefficient thermistor 26 that is arranged in close proximity so as to be connected to the above or fixed by a heat shrinkable tube or the like while being in contact with the heat conduction. In the operation in the case of FIG. 1, when a voltage higher than the rated voltage of the surge absorbing element 22 is supplied between the lines, the surge absorbing element 22 enters a short-circuit mode, and a current (overcurrent) rapidly drops the surge absorbing element 22. In the short-circuit mode of the surge absorbing element 22, not only a high current when a high voltage several times as high as the rated voltage at which the current fuse 1 is blown, but also a several Current flows even when a relatively low level high voltage such as a 10% higher voltage is applied. When the relatively low level high voltage is applied, the power consumption of the surge absorbing element 22 due to the short-circuit mode current and the power supply voltage is considerably large.
This is the same as the case of the prior art in FIG. When the temperature of the positive temperature coefficient thermistor 26 rises due to the temperature rise due to the heat generation of the surge absorbing element 22, the positive temperature coefficient thermistor 26 is an element whose resistance value increases as the temperature rises. For example, the current value flowing through the positive temperature coefficient thermistor 26 decreases due to the increase in the resistance value. Then
Since the value of the current flowing through the surge absorbing element 22 also decreases, the power consumption of the surge absorbing element 22 decreases, and accordingly, the calorific value of the surge absorbing element 22 also decreases. As a result, the temperature rise of the positive temperature coefficient thermistor 26 is also suppressed, so that the resistance value is also suppressed from increasing, and the surge absorbing element 2 whose current value is reduced is suppressed.
When the heat generation amount of No. 2 and the heat radiation amount of the surge absorbing element 22 and the positive temperature coefficient thermistor 26 are thermally balanced (saturation equilibrium), the temperature rise stops, and the internal components of the power supply device are protected from damage due to the temperature rise. .

Next, when the voltage applied to the power supply returns from the overvoltage state to the normal state (for example, the range of the rated voltage of the commercial power supply) as described above, the surge absorbing element 2
Since almost no current flows through 2, no heat is generated, and the temperature drops. Then, the temperature of the positive temperature coefficient thermistor 26 thermally coupled to the surge absorbing element 22 also decreases, so that the resistance value of the positive temperature coefficient thermistor 26 decreases, and a current flows, so that the power supply device automatically returns. As described above, in the case of the present embodiment, the protection is performed even if the overvoltage state continues, and when the overvoltage state returns to the normal state, it is necessary to stop using the power supply and replace the internal parts. Therefore, it is not necessary to perform dangerous processing by replacing parts of the power supply unit.

FIG. 2 is a perspective view showing an embodiment in which the surge absorbing element and the positive temperature coefficient thermistor of FIG. 1 are fixed close to each other so that heat conduction is good. In FIG.
The surge absorbing element 22 and the positive temperature coefficient thermistor 26 are fixed adjacent to each other so that the heat conduction is good and the contact area is maximized. As the fixing means, the heat-shrinkable tube 25 is covered so that both the surge absorbing element 22 and the positive temperature coefficient thermistor 26 can be accommodated, and the heat-shrinkable tube 25 is shrunk by applying heat and fixed. Instead of the heat-shrinkable tube 25, for example, a binding band used to collect a plurality of wiring members or fix the wiring members is used to fix both the surge absorbing element 22 and the positive temperature coefficient thermistor 26 so as to bind them. A similar descent can be obtained. Instead of fixing with the heat shrinkable tube 25, for example, both the surge absorbing element 22 and the positive temperature coefficient thermistor 26 are connected and fixed with an adhesive or resin having good thermal conductivity, or the surge absorbing element 22 and the positive temperature coefficient thermistor 26 are connected. Thermistor 2
A similar drop can be obtained by using a member such as a clip or a binder so as not to contact the lead terminal 6 or the like, or by wrapping and fixing an aluminum foil or the like around both to secure insulation.

FIG. 3 is a block diagram showing an embodiment in which a plurality of power supplies are provided in FIG. In FIG. 3, the current fuse 1 is the same as the current fuse in FIG. 5 of the prior art, so the same number is assigned and the description is omitted. FIG.
, The surge absorbing element 32 and the positive temperature coefficient thermistor 36,
In addition, as for the heat-shrinkable tube 35 that is fixed while keeping both of them in good contact with each other, the surge absorbing element 22 and the positive temperature coefficient thermistor 26 of the embodiment of FIG.
It is the same as the heat-shrinkable tube 25. The difference between FIG. 3 and FIG. 1 is that in FIG. 3, a plurality of power supplies 33 and 43 are provided, and the plurality of power supplies are installed in parallel on the downstream side of the overvoltage protection device when viewed from the commercial power supply side. . By installing the power supply device as shown in FIG. 3, a plurality of power supply devices can be protected by one overvoltage protection circuit due to different secondary voltage outputs or the like. By configuring and operating as described above, when an overvoltage is applied to the power supply device, the resistance value of the positive temperature coefficient thermistor increases due to the heat generated by the surge absorbing element, and the current increases due to the increase in the resistance value of the positive temperature coefficient thermistor. As the value decreases, the heat generation of the surge absorbing element is suppressed, and the heat generation (temperature rise) of the surge absorbing element is limited until the heat generation of the surge absorbing element and the increase in the resistance value of the positive temperature coefficient thermistor are finally balanced. Therefore, even when a voltage higher than the rated nominal voltage range continues for a relatively long time, the protection circuit components operate and it is necessary to replace the protection circuit components when the voltage returns to the normal voltage. It is possible to provide a zero overvoltage protection circuit.

[0010]

As described above, according to the present invention, when an overvoltage is applied, the resistance value of the positive temperature coefficient thermistor increases due to the heat generated by the surge absorbing element, and the current value increases due to the increase in the resistance value of the positive temperature coefficient thermistor. The heat generation of the surge absorbing element is suppressed, and the heat generation (temperature rise) of the surge absorbing element is limited until the heat generation of the surge absorbing element and the increase of the resistance value of the positive temperature coefficient thermistor are finally balanced. ,
Even if the application of a voltage higher than the rated nominal voltage range continues for a relatively long time, etc., it is possible to provide an overvoltage protection circuit that does not require replacement of the protection circuit component due to the operation of the protection circuit component. it can. In addition, there is no need to stop using the power supply and bring it to a service center or the like, or to order parts, and a power supply that does not have a danger when replacing protection circuit parts can be realized with a simple and low-cost circuit. .

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an embodiment of an overvoltage protection device according to the present invention.

FIG. 2 is a perspective view showing an embodiment in which the surge absorbing element and the positive temperature coefficient thermistor of FIG. 1 are fixed close to each other so that heat conduction is good.

FIG. 3 is a block diagram showing an embodiment in which a plurality of power supplies of FIG. 1 are used.

FIG. 4 is a block diagram showing a configuration of an example of a conventional overvoltage protection device.

FIG. 5 is a block diagram showing a configuration of an example of a conventional overvoltage protection device different from the example of FIG. 4;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Current fuse, 2, 12, 22, 32 ... Surge absorption element, 3, 33, 43 ... Power supply, 14 ...
Thermal fuse, 15, 25, 35 ... heat shrinkable tube, 26, 36 ... positive temperature coefficient thermistor

Claims (3)

[Claims] An overvoltage protection device provided on a power supply side of a power supply that receives power supply from a neutral line and a high potential line of a commercial power supply, wherein a surge absorbing device is connected between the high potential line and the neutral line. Means, a positive temperature coefficient thermistor means inserted in series from the surge absorbing means to the high potential line on the commercial power supply side, and a thermal coupling means for well transmitting heat generated by the surge absorbing means to the positive temperature coefficient thermistor means, An overvoltage protection device comprising: 2. The thermal coupling means according to claim 1, wherein said thermal coupling means is a fixing means for fixing said surge absorbing means and said positive temperature coefficient thermistor means close to each other so that heat conduction is good. Overvoltage protection device. 3. The power supply is a set of a plurality of independent power supplies, and one overvoltage protection device is connected between the commercial power supply and the plurality of independent power supplies so as to be shared by the plurality of power supplies. The overvoltage protection device according to claim 1, wherein: