JPH10106803A - Positive thermistor for overcurrent protection - Google Patents

Abstract

An object of the present invention is to provide an overcurrent protection positive temperature coefficient thermistor capable of easily adjusting a response time in which a current attenuates due to a temperature rise of a positive temperature coefficient thermistor element. SOLUTION: A positive temperature coefficient thermistor (10) for overcurrent protection according to the present invention electrically connects a positive temperature coefficient thermistor element (1) having a pair of electrodes (5) and an electrode (5) of the positive temperature coefficient thermistor element (1). Externally connected lead (2), and an insulating envelope (3) surrounding the positive temperature coefficient thermistor element (1), and attenuates due to temperature rise of the positive temperature coefficient thermistor element (1) A conductive regenerator (4) having a heat capacity corresponding to the current response time is fixed to the electrode (5).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a positive temperature coefficient thermistor,
In particular, the present invention relates to a positive temperature coefficient thermistor for overcurrent protection, which can easily adjust a response time in which a current attenuates due to a temperature rise of the temperature coefficient element.

[0002]

2. Description of the Related Art A thermistor having a positive temperature coefficient, whose resistance value increases with an increase in temperature, is called a "positive temperature coefficient thermistor".
Various positive temperature coefficient thermistors are known as described in JP-A-136201, JP-A-60-254701 and JP-A-63-244702. In the conventional overcurrent protection PTC thermistor 20 shown in FIG. 8, an electrode 5 made of a metal such as silver or nickel is formed on a PTC thermistor element (PTC element) 1, and an external lead 2 is soldered to the electrode 5. After that, it is manufactured by applying an electrically insulating paint 3 as an insulating envelope.

[0003]

For example, in a device that operates a load using a motor as a power source, if the motor is locked and the power is continuously supplied, the motor may overheat and cause burn-in. For this reason, a method is generally used in which a positive temperature coefficient thermistor is connected to a motor and the current is attenuated by operating the positive temperature coefficient thermistor when abnormal heat generation continues for a certain period of time. However, the time during which the current decays due to the temperature rise of the PTC thermistor element,
That is, if the "response time" is made uniform, the following problem occurs, and it is necessary to set various response times. For example, it takes a certain amount of time from the start of energization to a stopped motor to the actual start of the motor, but the time required for starting is short when the load connected to the motor is small, and the load is large. The case tends to be longer. Therefore, if the response time of the PTC thermistor is long when the load is small, there is a danger that the motor will burn.If the response time is short when the load is large, the PTC thermistor will operate before the motor starts and the current will be reduced. , The motor cannot be started. Therefore, it is desirable to set the response time of the PTC thermistor to be short when the load is small and long when the load is large. As described above, the overcurrent protection positive temperature coefficient thermistor is used for various devices having an electric circuit, but the response time to be set differs depending on the configuration of the device. The response time of the PTC thermistor has been changed by changing the shape. However, when changing the size and shape of the PTC thermistor element itself, various types of molding dies are required, which has been a factor of high cost. Further, in order to extend the response time by using a positive temperature coefficient thermistor element having the same specific resistance, it is necessary to increase the size of the positive temperature coefficient thermistor element. At the time, a problem occurred. Therefore, the present invention provides a positive temperature coefficient thermistor for overcurrent protection that can easily adjust a response time at which a current attenuates due to a temperature rise of the positive temperature coefficient thermistor element without changing the size and shape of the positive temperature coefficient thermistor element. The purpose is to do.

[0004]

A positive temperature coefficient thermistor (10) for overcurrent protection according to the present invention comprises a positive temperature coefficient thermistor element (1) having a pair of electrodes (5) and an electrode of the positive temperature coefficient thermistor element (1). An external lead (2) electrically connected to (5) and an insulating outer enclosure (3) surrounding the thermistor element (1) are provided. In the present invention, a conductive heat storage element (4) having a heat capacity corresponding to a response time of a current attenuated due to a temperature rise of the positive temperature coefficient thermistor element (1) is fixed to the electrode (5). The heat storage body (4) is made of, for example, stainless steel, copper, silver, iron, phosphor bronze, brass, lead, tin or aluminum. A pair of heat accumulators (4) may be fixed to each of a pair of electrodes (5) of the positive temperature coefficient thermistor element (1), and one heat accumulator (4) may be fixed to one electrode of the positive temperature coefficient thermistor element (1). (5) may be fixed. In the embodiment of the present invention, an annular projection (13) projecting from one main surface (11) is provided on the periphery of the heat storage element (4), and the annular projection (13) of the heat storage element (4) projects from the side. Is fixed to the electrode (5) of the positive temperature coefficient thermistor element (1) by solder (9). The heat storage body (4) and the external lead (2) may be formed integrally.

According to the present invention, a positive temperature coefficient thermistor element (1)
By changing the heat capacity of the heat storage element (4) fixed to the electrode (5), the response time during which the current attenuates due to the temperature rise of the PTC thermistor element (1) can be easily adjusted. For example, when the heat storage element (4) having a large heat capacity is fixed, more heat generated from the positive temperature coefficient thermistor element (1) can be stored, so that the temperature rise of the positive temperature coefficient thermistor element (1) is limited to some extent, Time can be lengthened. In addition, when the heat storage element (4) having a small heat capacity is fixed, the amount of heat generated from the positive temperature coefficient thermistor element (1) is reduced, so that the temperature rise of the positive temperature coefficient thermistor element (1) is restricted. And the response time can be shortened. A method of selectively fixing heat storage elements (4) having different heat capacities, a method of fixing a plurality of heat storage elements (4) in combination, and a method of connecting the heat storage elements (4) to both or one of the positive characteristic thermistor elements (1). The response time can be adjusted by fixing to the electrode (5). Therefore, without changing the size and shape of the positive temperature coefficient thermistor element (1) itself, the heat storage element (4) having a heat capacity corresponding to a desired response time can be used as the electrode (5) of the positive temperature coefficient thermistor element (1).
And the response time can be easily adjusted.
In the case where an annular projection (13) projecting from one main surface (11) is provided on the periphery of the heat storage element (4), the side on which the annular projection (13) of the heat storage element (4) projects has a positive characteristic. When the solder (9) is fixed to the electrode (5) of the thermistor element (1) with solder (9), the solder (9) is securely held between the heat storage body (4) and the electrode (5) of the positive temperature coefficient thermistor element (1). , The adhesion strength can be increased.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a positive temperature coefficient thermistor for overcurrent protection according to the present invention will be described below with reference to FIGS. Overcurrent protection positive temperature coefficient thermistor 10 shown in FIG.
Is a PTC thermistor element 1 having a pair of electrodes 5 formed thereon.
And an external lead 2 electrically connected to the electrode 5 of the positive temperature coefficient thermistor element 1 by soldering, and an insulating envelope 3 surrounding the positive temperature coefficient thermistor element 1. further,
The electrode 5 of the positive temperature coefficient thermistor element 1 has a conductive heat storage 4
Are fixed by soldering. The PTC thermistor element 1 mainly includes barium titanate (BaTiO ₃ ), zinc oxide (ZnO—NiO—TiO ₂ ), and lead oxide (Pb).
Ceramic materials such as (Fe _1/2 Nb _1/2 ) O ₃ ) and plastic materials are used. As shown in FIG. 2, an annular protruding portion 13 protruding from one main surface 11 is provided on the periphery of the heat storage body 4, and the side of the heat storage body 4 from which the annular protruding portion 13 protrudes is soldered with a positive temperature coefficient thermistor element. The first electrode 5 is fixed. Thereby, the solder 9 is securely held between the heat storage element 4 and the electrode 5 of the positive temperature coefficient thermistor element 1, and the adhesion strength can be increased. As shown in FIG. 1, when the heat storage element 4 is sandwiched between the positive-characteristic thermistor element 1 and the external lead 2, if the specific resistance of the heat storage element 4 is large, a large voltage drop occurs in the heat storage element 4. When the voltage at the element 1 decreases, heat generation may be insufficient and the current may not be attenuated. Therefore, it is desirable that the heat storage body 4 has a small specific resistance, and a metal such as stainless steel, copper, silver, iron, phosphor bronze, brass, lead, tin or aluminum can be preferably used. The specific resistances of stainless steel and copper are 55 to 75 × 10 ⁻⁶ Ωcm and 2 × 10 ⁻⁶ Ωcm, respectively. Generally, if the specific resistance of the heat storage unit 4 is 1 × 10 ⁻³ Ωcm or less, the heat storage unit 4 has almost no effect of the voltage drop. In the embodiment shown in FIG. 1, when the heat storage element 4 is interposed between the positive-characteristic thermistor element 1 and the external lead 2, the heat flux of the external lead 2 decreases, and the electric circuit on which the positive-characteristic thermistor 10 is mounted This has the advantage that the thermal effect on the surface can be reduced. On the other hand, as shown in FIGS. 3 and 4, a structure in which the heat storage body 4 is not sandwiched between the positive characteristic thermistor element 1 and the external lead 2 is also possible. In this case, the external lead 2 is connected to the positive characteristic thermistor element. Since it is directly connected to the first electrode 5, there is no problem even if the specific resistance of the heat storage unit 4 is slightly large. Further, in the embodiment shown in FIGS. 3 and 4, the thickness of the connection portion of the external lead 2 can be reduced as compared with FIG.
There is an advantage that the PTC thermistor 10 is compact.

In the present invention, the response time during which the current is attenuated due to the temperature rise of the positive temperature coefficient thermistor element 1 is easily adjusted by changing the heat capacity of the heat storage element 4 fixed to the electrode 5 of the positive temperature coefficient thermistor element 1. it can. For example, when the heat storage element 4 having a large heat capacity is fixed, more heat generated from the positive temperature coefficient thermistor element 1 can be stored.
The temperature rise of the PTC thermistor element 1 is restricted to some extent, and the response time can be extended. When the heat storage element 4 having a small heat capacity is fixed, the amount of heat generated from the positive temperature coefficient thermistor element 1 is reduced, so that the function of limiting the temperature rise of the positive temperature coefficient thermistor element 1 is reduced and the response time is reduced. Can be shorter. In addition to selectively fixing heat storage elements 4 having different heat capacities, a plurality of heat storage elements 4
In addition, depending on whether the heat storage element 4 is fixed to both or one of the electrodes 5 of the positive temperature coefficient thermistor element 1, the response time at which the current is attenuated due to the temperature rise of the positive temperature coefficient thermistor element 1 is reduced. Can be adjusted. Therefore, the heat storage element 4 having a heat capacity corresponding to a desired response time is fixed to the electrode 5 of the PTC thermistor element 1 without changing the size and shape of the PTC thermistor element 1 itself, so that the response time can be easily reduced. Can be adjusted.

[0008] The present invention is not limited to the above embodiment, but can be modified. For example, in order to reduce the number of parts and simplify the work process, the heat storage body 4 and the external leads 2 may be formed integrally as shown in FIG. In the embodiment of FIG. 1, the pair of heat storage elements 4 are fixed to each of the pair of electrodes 5 of the PTC thermistor element 1. However, as shown in FIG. May be fixed only to the electrode 5. Further, the shape of the positive temperature coefficient thermistor is not limited to a disk shape, and the present invention is applicable to a washer type, a pipe type, a rod type, a pellet type, and a flake type. Since the temperature of the positive temperature coefficient thermistor element 1 may rise to about 130 ° C. due to heat generation, a metal plate is generally suitable for the heat storage body 4, but a conductive resin having heat resistance,
Other conductive materials such as conductive ceramics are also applicable. In addition, since the positive temperature coefficient thermistor element 1 attenuates the current due to a sharp increase in electric resistance caused by a temperature rise due to heat generation, if a member having high thermal conductivity is arranged around the element,
The amount of heat radiation per unit time from the PTC thermistor element 1 increases, and the response time can be delayed.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Resistance 7 at diameter 7 mm, thickness 0.5 mm, 25 ° C.
Cream solder is applied to a pair of electrodes 5 of the Ω positive characteristic thermistor element 1 and a 0.3 mm thick disk-shaped SUS304 (a kind of Cr-Ni stainless steel) plated with solder to have heat capacity is stored. Two pieces of the body 4 were adhered, and the external leads 2 were attached to each heat storage body 4 and cream solder was applied, followed by reflow soldering. Subsequently, a silicone-based insulating paint was applied to form an insulating envelope 3. Thus, a positive temperature coefficient thermistor 10 having the structure shown in FIG. 1 was obtained. FIG. 7 shows the change over time of the current when the current of 0.1 Ω is connected to the positive temperature coefficient thermistor according to the present embodiment and a current is supplied from a 2 V DC power supply. While the response time of the conventional positive temperature coefficient thermistor 20 having no heat storage shown in FIG. 8 is 3.3 seconds (D in the figure), the response time of the present embodiment having the heat storage 4 with a diameter of 6 mm is Was 6.4 seconds (A in the figure). In this embodiment, the “response time” means a time required for a current passing through the positive temperature coefficient thermistor to attenuate to 電流 of the current at the start of energization. Further, when the diameter of the heat storage element 4 of this embodiment is 5 mm and 4 mm, the response times are 5.6 seconds (B in the figure) and 4.5 seconds (C in the figure), respectively. By changing the heat capacity, the response time of the positive temperature coefficient thermistor could be freely changed.
When a sufficient time has elapsed from the start of energization, the heat storage body 4
Regardless of the presence or absence of the heat sink, a substantially constant current value was obtained in each case, and the heat balance of the positive temperature coefficient thermistor element 1 was obtained. It turned out to be almost constant.

[0010]

According to the present invention, there is provided an overcurrent protection device capable of easily adjusting a response time at which a current is attenuated due to a temperature rise of a PTC thermistor element without changing the size and shape of the PTC thermistor element. Since a positive temperature coefficient thermistor can be obtained, it is not necessary to prepare various types of molding dies for the positive temperature coefficient thermistor element, and the manufacturing cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a front sectional view of a positive temperature coefficient thermistor according to the present invention.

FIG. 2 is a partially enlarged view of FIG. 1;

FIG. 3 is a front sectional view showing another embodiment of the present invention.

FIG. 4 is a sectional view taken along line AA of FIG. 3;

FIG. 5 is a cross-sectional plan view showing another embodiment of the present invention.

FIG. 6 is a front sectional view showing still another embodiment of the present invention.

FIG. 7 is a graph showing a temporal change of a current passing through a thermistor having a positive characteristic;

FIG. 8 is a sectional view of a conventional PTC thermistor;

[Explanation of symbols]

1. Positive thermistor element, 2. External lead,
3. Insulating paint (insulating enclosure), 4. Thermal storage,
5 ··· electrode, 9 ··· solder, 10 ··· positive temperature coefficient thermistor, 11 ··· one main surface, 13 ··· annular protrusion,

Claims (5)

[Claims] 1. A capacitor comprising: a PTC thermistor element having a pair of electrodes; an external lead electrically connected to an electrode of the PTC thermistor element; and an insulating envelope surrounding the PTC thermistor element. A current protection positive temperature coefficient thermistor, wherein a conductive heat storage element having a heat capacity corresponding to a response time of a current attenuated due to a temperature rise of a positive temperature coefficient thermistor element is fixed to an electrode. Positive thermistor. 2. The heat storage body is made of stainless steel, copper, silver, iron, phosphor bronze, brass, lead, tin or aluminum.
4. A positive temperature coefficient thermistor for overcurrent protection according to item 1. 3. The overcurrent protection positive temperature coefficient thermistor according to claim 1, wherein a pair of heat accumulators is fixed to each of a pair of electrodes of the positive temperature coefficient thermistor element. 4. The thermal storage element according to claim 1, further comprising an annular projecting portion projecting from one of the main surfaces on a peripheral edge of the thermal storage element, and a side on which the annular projecting section of the thermal storage element projects is fixed to an electrode of the positive temperature coefficient thermistor element by soldering. Positive thermistor for overcurrent protection. 5. The overcurrent protection positive temperature coefficient thermistor according to claim 1, wherein the heat storage body and the external lead are formed integrally.