KR100318397B1 - NTC Thermistor - Google Patents

Abstract

An object of the present invention is to provide an NTC thermistor capable of reliably and safely suppressing a large rush current. The NTC thermistor according to the present invention houses the thermistor element 3 in which electrodes 3b and 3c are formed on both surfaces in a case 2 made of a heat resistant resin. The thermistor element 3 is elastically sandwiched and supported between the pair of metal terminals 5 and 6 drawn out of the case 2 in the case 2.

Description

NTC Thermistor

The present invention relates to an NTC (Negative Temperature Coefficient) thermistor which can be used for suppressing rush current in an electronic device, for example. More specifically, the NTC thermistor element is housed in a resin case. An NTC thermistor having an improved structure in which metal terminals are drawn out of a resin case.

In various electronic devices and electric devices, a large inrush current is generated when the power switch is turned ON. Therefore, various types of NTC thermistors are used to protect the apparatus by suppressing the inrush current.

When the power switch of the target device is turned on, the NTC thermistor incorporated in the device suppresses the inrush current by the resistance of the NTC thermistor element. After the inrush current is suppressed, since the resistance thereof has negative resistance temperature characteristics, the resistance value thereof decreases due to self-heating, whereby a predetermined normal circuit operation becomes possible.

6 shows a conventional inrush current suppressing NTC thermistor 56. This NTC thermistor is comprised as an electronic component with lead terminals 54a and 54b. In order to manufacture this NTC thermistor 56, as shown in FIG. 5, silver paste is first apply | coated to both surfaces of the disk-shaped ceramic body 51 containing a plurality of types of oxides of transition elements, such as Mn and Ni, By baking, the electrode 52 is formed, thereby obtaining the thermistor element 53.

Next, the lead terminals 54a and 54b are bonded to the electrodes 52 of both main surfaces of the thermistor element 53 by solder X. As the lead terminals 54a and 54b, lead wires having a diameter of about 0.5 to 1.0 mm can be used. Thereafter, degreasing washing is performed, and as shown in FIG. 6, the NTC thermistor 56 is obtained by coating the thermistor element 53 with the exterior resin material 55, for example, by a powder coating method.

On the other hand, Japanese Patent Laid-Open No. 7-37706 discloses an NTC thermistor having NTC thermistor elements formed by forming electrodes on both main surfaces of a ceramic body containing an oxide of a rare earth transition element. This NTC thermistor element is housed in a resin case and is elastically sandwiched between metal terminals and supported by the metal terminals. By using NTC thermistor elements using so-called "LaCo-based" oxides, the power consumption in a steady state can be sufficiently reduced, the resistance is small, the B constant at room temperature is small, and the B constant at high temperature is large. Therefore, it is described that a large current can flow.

In recent years, the size of various electronic devices and electrical devices has increased, and inrush current suppression in a large current region is strongly demanded. In addition, the Product Liability Act is said to require the safety of electrical and electronic components more strongly than ever.

In the NTC thermistor 56 described above, however, since the thermistor element 51 contains Ni-based and / or Mn-based oxides, the B constant is less than 2000-3500K. Therefore, when the normal current value of the circuit is used in a large current region of more than 5A, the device temperature becomes 160 ° C or more, and the device heat generation becomes very large, thus soldering between the thermistor element 51 and the lead terminals 54a and 54b. There was a risk that the part was melted, the exterior resin material 55 was melted and deformed, or the circuit board on which the NTC thermistor 56 was mounted was damaged. For this reason, the NTC thermistor element 56 with a lead terminal has been mainly used for a circuit with a relatively small steady current.

In the NTC thermistor disclosed in Japanese Patent Application Laid-open No. Hei 7-37706, the thermistor element containing LaCo-based oxide is used as described above, and therefore it can be used in a high current circuit. In addition, since the thermistor element is stored in the resin case and the thermistor element is elastically supported by the metal terminal, the external resin material of the case does not melt, and problems such as dissolution of the soldered portion between the lead wire and the thermistor element are unlikely to occur.

However, in the situation where it is desired to suppress a larger inrush current, this kind of NTC thermistor cannot sufficiently cope with the recent demand.

Accordingly, it is an object of the present invention to provide an NTC thermistor capable of reliably and safely suppressing a larger inrush current than can be suppressed by conventional NTC thermistors.

1A and 1B are side cross-sectional and front views, respectively, illustrating an NTC thermistor implementing the present invention.

2 is an exploded perspective view illustrating a process of assembling the NTC thermistor of FIGS. 1A and 1B.

3 is a perspective view showing the appearance of the NTC thermistor of FIGS. 1A and 1B.

4 is a circuit diagram showing an example of a current limiting circuit incorporating the thermistor of the present invention.

5 is a front view for explaining a process of manufacturing a conventional NTC thermistor.

FIG. 6 is a front view showing the NTC thermistor of the prior art produced through the process shown in FIG.

<Description of Major Symbols in Drawing>

1: NTC thermistor

2: resin case

2a: resin case body

2b: opening

2c: lid

2e, 2f: leg

3: thermistor element

3a: thermistor block

3b, 3c: electrode

4: positioning holder

4a: opening

5, 6: metal terminals

7: current limiting circuit

In order to achieve the object of the present invention and other objects, the NTC thermistor according to the present invention, the thermistor element having an electrode formed on both sides and having a negative resistance temperature characteristics,

A resin case accommodating the thermistor element,

It is made of Cu, it characterized in that it comprises a pair of metal terminals to be elastically supported by sandwiching the thermistor element, and to be drawn out of the case.

Here, the inner ends of the metal terminals are bent toward each other to form an elastic contact portion.

According to a preferred embodiment, the thermistor element contains an oxide of a rare earth transition element or mainly a LaCo-based oxide, the metal terminal contains a Cu—Ti alloy, and the electrode contains an Ag—Pd alloy.

The portion drawn out of the resin case of each metal terminal may have an end portion shaped like a male tab. The resin case can have a leg portion projecting outward, and a holder for preventing misalignment of the thermistor element is housed in the case. Such a holder may include a plate-shaped member fixed to the resin case and having an opening having an inner diameter larger than the outer diameter of the thermistor element.

(Example)

Hereinafter, the present invention will be described in more detail with reference to the drawings.

1A and 1B are a side sectional view and a front view showing an NTC thermistor 1 embodying the present invention.

The NTC thermistor 1 has a structure in which the thermistor element 3 is housed in a case 2 made of PPS (polyphenylene sulfide) resin. In the resin case 2 according to the present invention, since the PPS resin is excellent in heat resistance, even if the thermistor element 3 is self-heated and brought to a high temperature state, the resin case 2 is hardly deformed or melted. Preferably, the type of PPS resin is selected in consideration of the type of thermistor element 3 so that its softening point is equal to or higher than the maximum temperature reached at the time of self-heating of the thermistor element 3. Deformation and melting by heat can be prevented even more reliably.

The present invention is not limited only to using PPS resin to form the resin case 2. Examples of materials that can be used to form the resin case 2 include liquid crystal polymers, polyether ether ketones, polyimides, polyamides, in addition to PPS resins, and are also advantageous for polystyrene, phenol, nylon, nylon 6 or nylon 66, and the like. The composite material which improved heat resistance by adding a filler is included.

The resin case 2 has a substantially rectangular parallelepiped shape. The thermistor element 3 has a structure in which electrodes 3b and 3c are formed on both main surfaces of a disc shaped thermistor block 3a containing an oxide of LaCo-based transition element (hereinafter referred to as LaCo-based oxide).

The electrodes 3b and 3c are made of an Ag-Pd alloy containing Ag and Pd in a ratio of 7: 3 by weight. The electrodes 3b and 3c are formed by applying and baking a conductive Ag-Pd paste. Further, in order to prevent migration between the electrodes 3b and 3c, the diameters of the electrodes 3b and 3c are formed smaller than the diameter of the thermistor block 3a.

In order to prevent the thermistor element 3 from displacing in the vertical direction in the resin case 2 in FIG. 1, in particular, to prevent the lower part of the thermistor element 3 from contacting the bottom surface of the resin case 2. In the resin case 2, a plate-shaped positioning holder 4 having a circular opening 4a is formed, and the thermistor element 3 is held in the opening 4a.

Although the material which comprises the positioning holder 4 is not specifically limited, For example, it can comprise with suitable insulating materials, such as a synthetic resin and a ceramic material. The opening 4a of the positioning holder 4 has a diameter slightly larger than that of the thermistor element 3 in order to achieve the holding and positioning action of the thermistor element 3 described above.

The thermistor element 3 is elastically sandwiched and supported between the pair of long metal terminals 5 and 6 in the resin case 2. The metal terminals 5 and 6 respectively have flat terminal bodies 5a and 6a drawn out from the inside of the resin case 2 to the outside of the resin case 2 downward. The inner end portions (inside of the resin case 2) of the terminals 5 and 6 are bent toward each other by about 180 degrees to form the elastic contact portions 5b and 6b. Therefore, the thermistor element 3 is elastically sandwiched and supported between the metal terminals 5 and 6 by spring-like elasticity of the elastic contact portions 5b and 6b of the pair of metal terminals 5 and 6.

Further, the outer end portions drawn out of the resin cases 2 of the metal terminals 5 and 6 are configured to have a male tab shape, respectively, as shown in Figs. 1B and 2. Therefore, not only can it be surface-mounted on a printer circuit board, but it is also easy to connect by wire. However, the shape of the outer edges of the metal terminals 5 and 6 does not limit the scope of the present invention, and can be formed into a suitable shape suitable for surface mounting on a normal printed circuit board.

In addition, the metal terminals 5 and 6 are preferably made of copper or an alloy thereof. Since these metal materials have relatively low specific resistance per unit volume, self-heating of the metal terminals 5 and 6 itself under a large current is reduced. That is, when a large inrush current flows through the thermistor, melting, deformation, etc. of the resin case 2 can be prevented effectively. As the material for the terminals 5 and 6, Cu-Ti alloy is preferably used, whereby deterioration of elasticity due to heat of the elastic contact portions 5b and 6b of the metal terminals 5 and 6 can be suppressed.

The NTC thermistor 1 can be assembled as shown in FIG. The thermistor element 3 disposed in the opening 4a of the positioning holder 4 is inserted into the resin case 2 through the lower opening 2b of the resin case body 2a. After inserting the metal terminals 5 and 6 from the upper opening, the lid 2c is positioned so as to be close to the upper opening of the main body 2a, and fixed with an adhesive (not shown). In addition, the adhesive does not necessarily need to be used, and as shown in FIG. 2, the protrusion 2d is formed on the side surface of the lid 2c, and the recessed portion into which the protrusion 2d is fitted is the main body of the resin case 2. It is formed in the inner surface of (2a), and can be fixed by fitting the protrusion 2d of the lid 2c to the recessed part of the resin case main body 2a.

Moreover, the leg parts 2e and 2f which protrude downward from the lower surface of the resin case 2 can be formed integrally with the lid 2c as shown in FIG. Alternatively, the leg portions 2e and 2f can be constituted by separate members fixed to the lower surface of the lid 2c by an adhesive.

3 shows the NTC thermistor 1 fully assembled in this way.

The leg portions 2e and 2f are shorter than the distance at which the metal terminals 5 and 6 protrude outward from the lower surface of the case 2. Therefore, when the NTC thermistor 1 is mounted on the printed circuit board, the NTC thermistor 1 can be stably arranged, and a small gap is formed between the resin case 2 and the printed circuit board to form the NTC thermistor ( The heat transfer from 1) to a printed circuit board can be suppressed.

NTC thermistor 1 according to the invention has many advantages. These advantages are as follows.

Since the thermistor element 3 is elastically supported by being sandwiched between the elastic contact portions 5b and 6b of the metal terminals 5 and 6, a bonding material such as solder necessary for supporting it can be omitted. Therefore, in the present invention, problems such as elution of solder due to heat generation of the thermistor element 3 do not occur. In addition, since the thermistor element 3 is supported so as not to contact the resin case 2, deformation or melting of the resin case 2 due to heat generation of the NTC thermistor 3 is unlikely to occur.

In addition, since the thermistor block 3a of the thermistor element 3 contains LaCo oxide according to a preferred embodiment of the present invention, the B constant of the thermistor block 3a is very large, 4000 to 5000K. In conventional NTC thermistors mainly composed of Mn oxides and Ni oxides, the B constant is about 2500-3500K. Therefore, in the thermistor element 3 of the present invention, when the same current is loaded, the heat generation of the thermistor element 3 can be made very small.

In addition, since the thermistor element 3 is disposed in the opening 4a of the positioning holder 4, even if the thermistor element 3 slightly shifts in the vertical direction, the thermistor element 3 and the resin case 2 The contact with the inner surface of the can be prevented.

In addition, since the electrodes 3b and 3c contain Ag-Pd alloys, the inter-electrode migration can be more reliably prevented than the electrodes made of Ag. As a result, it is possible to more reliably prevent the short circuit when a large current flows.

The above-described embodiments can be modified in various ways within the scope of the present invention. The positioning holder is not limited to one having a circular opening, and may have an opening of another shape such as a rectangular opening. In addition, the positioning holder does not have to have an opening. Instead, a plurality of projections extending from the inner surface of the main body 2a of the resin case 2 toward the outer circumferential surface of the thermistor element 3 can be formed.

As shown in Fig. 2, the metal terminals 5 and 6 have two elastic contact portions 5b and 6b, respectively, but the elastic contact portions 5b and 6b are disposed between the thermistor elements 3 stably. As long as it can be clamped, it may be comprised by a single part.

4 shows an example of a circuit incorporating the current limiting circuit using the NTC thermistor 1 described above. In FIG. 4, the NTC thermistor 1 is connected in series with the halogen lamp heater 11 in order to limit the inrush current to the halogen lamp heater 11. Here, when the thermistor element 3 in NTC thermistor 1 accommodates the thermistor block containing LaCoO ₃ , the element temperature at the time of self-heating is 160 degreeC, when used in the large current area | region exceeding 5 A, for example. It becomes abnormal. However, since the NTC thermistor 1 has the structure described above, even if the temperature of the thermistor element 3 is 160 ° C or higher, deformation or melting of the NTC thermistor 1 is unlikely to occur.

As described above, in the NTC thermistor according to the present invention, since the NTC thermistor element is housed in the resin case, even when the NTC thermistor element is brought to a high temperature state, compared with the conventional NTC thermistor covered with the outer resin, deformation due to heat is prevented. It is hard to occur. In addition, since the thermistor element is elastically sandwiched and supported by the metal terminal, it is not necessary to fix it using a bonding material such as solder, so that even if the thermistor element generates heat, a short accident due to melting of the bonding material occurs. I never do that.

In addition, since the metal terminal is made of a Cu-based metal material and has a low specific resistance per unit volume, the self-heating of the metal terminal itself is small, and heat generation to the resin case or the circuit board is small even when heat is generated. It is hard to occur.

Therefore, even when such an NTC thermistor is used for applications in which a large inrush current of 5 A or more is loaded, it is difficult to cause deformation or damage, and therefore, it is preferable to protect an electric device or an electronic device in which such a large inrush current occurs. It becomes possible to provide an NTC thermistor.

In addition, the NTC thermistor of the present invention can reliably and safely suppress inrush current larger than that which can be suppressed by a conventional NTC thermistor.

Claims (9)

A thermistor element having electrodes on both sides facing each other and having negative resistance temperature characteristics, A resin case accommodating the thermistor element, and A pair of metal terminals extending out of the resin case while elastically sandwiching the thermistor element, And the metal terminals contain Cu, and inner ends of the metal terminals are bent inward toward each other to form an elastic contact portion. The NTC thermistor of claim 1, wherein the thermistor element contains an oxide of a rare earth transition element. The NTC thermistor of claim 2, wherein the rare earth transition element is mainly LaCo. The NTC thermistor of claim 1, wherein the metal terminal comprises a Cu—Ti alloy. The NTC thermistor according to claim 1, wherein each of the pair of metal terminals has an end portion located outside the resin case and formed in a male tab shape. The NTC thermistor according to claim 1, wherein the resin case has a leg portion protruding outward. The NTC thermistor according to claim 1, wherein the resin case houses a holder for supporting the thermistor element and preventing displacement of the thermistor element. 8. The NTC thermistor according to claim 7, wherein the holder includes a plate-shaped member fixed to the resin case and having an opening larger than the diameter of the thermistor element. The NTC thermistor of claim 1, wherein the electrode contains an Ag-Pd alloy.