EP1921636B1 - Electrical assembly comprising PTC-resistor elements - Google Patents

Description

An electrical subassembly which comprises a protective device provided for suppressing signal lines on the basis of PTC resistor elements is known, for example, from the publication DE 10243113 A1 known.

From the EP 0443618 is an electrical assembly with two electrically interconnected PTC resistor elements known.

An object to be solved is to provide an electrical assembly which is a safe against sparking protection device against high current load and high transient current pulses to protect signal lines.

It is an electrical assembly with a housing and at least two PTC resistor elements, which are arranged in the housing specified. The housing is closed. The resistance elements each have a base body in a flat design and arranged on its main surfaces electrodes, wherein at each electrode of the respective resistive element at a solder joint, a lead wire is soldered. Each resistance element has an electrically insulating sheath which covers the solder joints. The resistive elements are electrically isolated from each other.

The resistive elements preferably have PTC properties. PTC stands for Positive Temperature Coefficient.

In principle, it is possible to arrange only one resistive element or more than two resistive elements in a closed housing instead of a plurality of resistive elements.

The envelope is particularly advantageous for ensuring the function of the assembly, which consists in a current limit in the occurrence of overvoltages in the form of transient pulses. The resistance of the resistance elements grows through the heating of the body, which is caused by the current pulse. The current is limited by the triggering of the resistance element above an intended protection level.

The cover protects against flashovers between the resistive elements and therefore ensures a high dielectric strength of the assembly. This is particularly advantageous if, for reasons of space savings on a separating device between the resistive elements must be waived.

The assembly complies with prescribed requirements for a permanent high voltage AC load which can occur in the signal line to be protected. In case of failure, the body can be thermally destroyed. If the resistive elements are destroyed, sparks or even a flame may occur which can be trapped by the housing. The closed housing made of a fire-resistant, d. H. non-flammable, material protects the environment from fire danger.

The housing material preferably has a high heat capacity. Thus, in particular in case of failure, the heat transfer is prevented on a circuit board on which the module is mounted.

1. a) Impuls 2500 V, 500 A, Pulsdauer 2/10 µs;
2. b) Wechselspannung 600 V, 3A, Zeitdauer 1,1 sec.

The module can, for example, under the following test conditions their function, in particular the current limit above a predetermined level of protection, ensure:

1. a) pulse 2500 V, 500 A, pulse duration 2/10 μs;
2. b) alternating voltage 600 V, 3A, duration 1.1 sec.

1. a) Impuls 5000 V, 500 A, die Pulsdauer 2/10 µs;
2. b) Wechselspannung 600 V, 60A, Zeitdauer 5,0 sec.

Die Pulsdauer 2/10 µs bedeutet, dass die Anstiegszeit 2 µs und die Abfallszeit 10 µs beträgt.Despite the intended destruction of the resistive element, a fire resistance of the assembly is ensured in the following test conditions:

1. a) pulse 5000 V, 500 A, the pulse duration 2/10 μs;
2. b) alternating voltage 600 V, 60 A, duration 5.0 sec.

The pulse duration 2/10 μs means that the rise time is 2 μs and the fall time is 10 μs.

Hereinafter, advantageous embodiments of the assembly are given, which can be combined with each other.

The PTC resistor elements, in principle, replace fuses and have the economic advantage of being tripped and limiting the current in the event of a momentary overshoot of a protection level, but still remain functional. Only when a maximum current is exceeded does it destroy the resistor element.

In a preferred variant, in each case one resistance element of the module is provided per signal line of a telephone connection. Since a telephone connection comprises a forward and return line, that is to say two signal lines, two of the resistance elements are provided. The resistance elements form protection devices to avoid the risk of defects caused by faults on the telephone line, in particular a line failure. The disturbances can z. B. caused by a lightning strike. A mains voltage-carrying line can also induce surges in the telephone line by a touch.

Each resistive element is preferably arranged in a series branch of the signal line. When crossing one maximum current, there is an interruption by the destruction of the resistive element.

The resistance elements preferably have the same resistance values within the permitted tolerance. Narrow tolerance limits are advantageous in this regard.

The main body preferably contains a material with PTC properties. The base body preferably contains a sintered ceramic material, for example based on barium titanate. In one variant, the main body contains a proportion of lead. By an advantageously selected composition of ceramic components, it is possible to dispense with lead. The lead-free assemblies are particularly environmentally friendly.

The resistance element or its basic body is characterized by a characteristic resistance to temperature. Up to a switching point, the resistance depends essentially linearly on the temperature. At a temperature above the switching point, the resistance value increases non-linearly with the temperature, very quickly. The switching point depends on the material of the main body.

The main body has a flat design, z. B. that of a round disc. The basic body can also have a rectangular or another basic shape. The base body preferably has flattened or rounded edges. The main body preferably has a resistance of 5 to 100 ohms at room temperature. The breakdown voltage of the main body is preferably at least 600 V.

The area of the respective electrode is preferably smaller than 0.5 cm ² . The area of the respective electrode is preferably larger than 0.18 cm ² . The diameter of the electrode is preferably at least 5 mm.

The electrodes are preferably made solderable. This can be accomplished by a solderable outer layer of the respective electrode. The solderable outer layer preferably contains silver.

Highly current-carrying, long-term stable electrodes of the resistor elements can be created for example by a suitable Schichenfolge. Each electrode is the lowest, d. H. facing the base body, electrode layer, a Cr layer. Another electrode layer may contain nickel. The uppermost electrode layer, which is preferably arranged on the nickel layer, preferably contains silver and / or tin.

At each electrode of the respective resistor element, a lead wire is soldered to a solder joint. The lead wire preferably has a round cross section, but this does not preclude a different shape for the lead wires.

By soldering the lead wire, a low-resistance contacting of the resistance element is ensured. A solder joint remains virtually corrosion-free even under unfavorable operating conditions and is therefore characterized by a stable resistance over the life of the assembly.

The solder joints as well as the body are preferably covered by the sheath, which increases the corrosion resistance of the solder joints.

The wrapper preferably has elastic properties and can stretch or shrink depending on the temperature. Thus, thermally induced mechanical stresses between the sheath and the resistive element can be prevented. Alternatively, the coefficient of thermal expansion of the envelope can be adapted to that of the basic body.

To apply the cladding to the surface of the resistive element, the deposition of material in an electric field applied between the material and the surface to be coated is provided.

The envelope may be formed, for example, by a paint layer applied in a spraying process. In the deposition of the paint layer, a spray is generated. The paint drops are preferably charged electrostatically. The surface of the resistive element is also preferably electrostatically charged, but with the charge polarity reversed. Thus, the paint drops are attracted by the surface of the resistive element. The electrostatic spraying of a coating makes it possible to achieve highly homogeneous, thin layers. A thin envelope has the advantage that it does not substantially increase the preferably small heat capacity of the resistive element. Thus, a homogeneous heating of the body of the resistive element and consequently a rapid and reliable triggering of this resistive element is achieved as soon as the current to be limited reaches the protection level.

The wrapper may contain a silicone compound. The cladding may contain a glass content or SiO ₂ . Epoxy powder is also suitable.

The thickness of the sheath is preferably chosen smaller than 200 μm. Even a thickness of less than 100 microns while ensuring sufficient edge coverage is adjustable in principle. This is especially true for the main body with flattened or rounded edges. The thickness of the casing is preferably homogeneous both on main surfaces and in the region of the edges of the basic body.

The housing has a carrier plate on which the resistance elements are arranged. The resistance elements are preferably oriented upright.

The housing has a lid which can be fastened on the carrier plate. The lid closes on all sides with the carrier plate.

In an advantageous variant, the housing has a partition which is provided between the resistance elements at least in the area of their solder joints.

The partition may be formed by an inner wall of the lid. The partition can also be formed by a part of the support plate. In the support plate, a recess or an opening for receiving a portion of the partition wall is preferably formed.

The downwardly facing region of the dividing wall is preferably tapered in cross section. This facilitates the insertion of the partition into the recess or opening provided for this purpose the carrier plate.

In the support plate openings are formed through which the leads of the resistive elements are performed.

The facing to the support plate portion of the respective resistance element is recessed in a recess of the support plate. The depressions of the carrier plate provided for receiving resistance elements have a stable position with minimal potential energy with respect to a rolling movement of the resistance element. For example, these recesses may have a depth that increases in cross-section perpendicular to the thickness direction of the respective resistive element from inside to outside in both opposite directions. During the rolling movement of the resistance element creates a restoring force, which brings it back to the stable position. Thus, the rolling of a disc-shaped base body is prevented.

The bottom of the recess may for example be formed as a part of a cylinder jacket surface. Two obliquely extending to the center of the depression surfaces, such as levels, are also suitable.

The parts of the housing, d. H. the lid and the carrier plate are preferably each made as a molded part. You can z. B. in an injection molding process.

The housing contains a material that is dimensionally stable and fireproof to at least 250 °. As material for the housing thermoplastic materials are particularly well suited. Thermosets are also considered.

As housing material is in principle also ceramic into consideration. Also suitable as housing material are plastics, in particular polymer plastics, for example liquid-crystalline polymers.

The housing material can be glass-reinforced, which is particularly advantageous in terms of good fire resistance. The glass content may for example be between 10 and 70%.

Each resistance element is dimensioned with respect to its resistance value, the switching point of the main body material and geometric dimensions so that it has a protection level of less than 500 mA. The protection level is the minimum value of the current at which the current limit is triggered by the resistance element.

A low level of protection is advantageous because in this case the circuit to be protected by the resistive element, e.g. B. on the side of the consumer, can be designed for smaller currents. A low level of protection can be set by a particularly small heat capacity of the resistance element.

A particularly low protection level of less than 200 mA can also be set. A large resistance value of a resistive element, e.g. B. at least 30 ohms, preferably at least 50 ohms, is advantageous for setting a particularly low level of protection. The switching point of the PTC material is preferably set at 120 ° or below 120 ° by a suitable composition of this material. The switching point may also be selected at 100 ° or below, but preferably at least 20 ° above the temperature range specified for the assembly or application.

As an alternative to a cover, the housing can have a potting compound, by means of which the resistance elements fixed on the carrier plate are potted. The resistive elements are preferably overmolded using a mold.

• Figur 1 einen Teillängsschnitt der Baugruppe mit zwei scheibenförmigen Widerstandselementen, die im geschlossenen Gehäuse angeordnet sind;
• Figur 2 in einem Teilquerschnitt die Baugruppe gemäß der Figur 1;
• Figur 3 im Querschnitt ein Widerstandselement mit einer Isolierumhüllung;
• Figur 4 eine Seitenansicht der Baugruppe gemäß der Figur 1;
• Figur 5 eine Draufsicht auf die Unterseite der Baugruppe gemäß der Figur 1;
• Figur 6 im Querschnitt die Baugruppe gemäß der Figur 1;
• Figur 7 im Längsschnitt die Baugruppe gemäß der Figur 1;
• Figur 8 eine Seitenansicht des Gehäuses der Baugruppe gemäß der Figur 1;
• Figur 9 eine Draufsicht auf die Unterseite der Trägerplatte des Gehäuses gemäß der Figur 8;
• Figur 10 im Teilquerschnitt die Trägerplatte des Gehäuses gemäß der Figur 8;
• Figur 11 im Querschnitt die Trägerplatte des Gehäuses gemäß der Figur 8;
• Figur 12 die Trägerplatte des Gehäuses gemäß der Figur 8 in einer perspektivischen Ansicht von unten;
• Figur 13 die Trägerplatte des Gehäuses gemäß der Figur 8 in einer perspektivischen Ansicht von oben;
• Figur 14 eine Draufsicht auf die Unterseite des Deckels des Gehäuses gemäß der Figur 8;
• Figur 15 im Längsschnitt den Deckel des Gehäuses gemäß der Figur 8;
• Figur 16 im Teilquerschnitt den Deckel des Gehäuses gemäß der Figur 8.

In the following, the specified assembly and its advantageous embodiments will be explained with reference to schematic and not to scale figures. Show it:

• FIG. 1 a partial longitudinal section of the assembly with two disc-shaped resistance elements, which are arranged in a closed housing;
• FIG. 2 in a partial cross section, the assembly of Figure 1;
• FIG. 3 in cross-section, a resistance element with an insulating sheath;
• FIG. 4 a side view of the assembly according to the FIG. 1 ;
• FIG. 5 a plan view of the underside of the assembly according to the FIG. 1 ;
• FIG. 6 in cross-section, the assembly according to the FIG. 1 ;
• FIG. 7 in longitudinal section, the assembly according to FIG. 1 ;
• FIG. 8 a side view of the housing of the assembly according to the FIG. 1 ;
• FIG. 9 a plan view of the underside of the support plate of the housing according to the FIG. 8 ;
• FIG. 10 in the partial cross section, the support plate of the housing according to the FIG. 8 ;
• FIG. 11 in cross-section, the support plate of the housing according to the FIG. 8 ;
• FIG. 12 the support plate of the housing according to the FIG. 8 in a perspective view from below;
• FIG. 13 the support plate of the housing according to the FIG. 8 in a perspective view from above;
• FIG. 14 a plan view of the underside of the lid of the housing according to the FIG. 8 ;
• FIG. 15 in longitudinal section the cover of the housing according to the FIG. 8 ;
• FIG. 16 in the partial cross section of the cover of the housing according to the FIG. 8 ,

From a number of in the FIGS. 1 ff., Components of the assembly shown similarly, only one component is described for the sake of clarity. However, the description applies to all components of the respective type. This applies in particular to resistance elements 11, 12, solder joints 5, connecting wires 41, 42, base body 15, centering devices 33, recesses 27, 29, 38, recesses 26 and openings 20, 28.

The assembly with resistance elements 12, 13 and a housing, which has a support plate 2 and a cover 3, is in the FIGS. 1, 2 . 6 and 7 presented. The resistance element is in the FIG. 3 shown. The housing with the lid and the support plate attached to it is shown in Figures 4, 5, 8 and 9. Different views of the carrier plate are in the FIGS. 10 to 13 shown. Different views of the lid are in the FIGS. 14 to 16 shown.

The housing comprises a support plate 2, on which two upright aligned resistance elements 11, 12 are arranged at a distance from each other. The major surfaces of the resistive elements are aligned parallel to each other.

Between the resistance elements 11, 12, a partition wall 31 is provided, which is formed by an inner housing wall, for example, the inner wall of the lid 3. This wall extends at least to a point which is just below solder joints 5 at which the leads 41, 42 are attached to the electrodes of the resistive elements. It is particularly advantageous if the partition extends at least to the top of the support plate 2. It is advantageous if the lower region of this wall protrudes into a depression or opening 20 provided in the carrier plate 2, see FIG. 7 ,

The partition wall 31 may alternatively be formed by a protruding from the support plate wall which is formed in the support plate or fixed to the support plate. The height of this wall extends at least to a point which is just above solder joints 5 at which the connecting wires 41, 42 are attached to the electrodes of the resistive elements.

The structure of the preferably identically formed resistance elements 11, 12 is in the FIG. 3 explained. The resistance element comprises a base body 15 and two layer electrodes 16, 17, between which the base body 15 is arranged.

At the first electrode 16 of the resistive element, a first lead wire 41 and the second electrode 17, a second lead wire 42 is attached. The preferred method of attachment is soldering. At the connection points of the electrodes 16, 17 and the connecting wires 41, 42 solder joints 5 are formed, which increase the total thickness of the resistive element.

The solder joint 5 is preferably located approximately in the middle of the major surface of the resistive element or the electrode 16, 17. Deviations from this are possible. However, a certain minimum distance between the solder joint and the lowest point of the resistive element is advantageous, if - as in FIG. 6 explained - the lower portion of the resistive element in a recess 29 of the support plate 2 is to be sunk.

The resistive element is covered except for the connecting wires 41, 42 in an advantageous variant by an electrically insulating sheath 6. This enclosure also covers the solder joints 5. Therefore, two resistance elements to be electrically insulated from one another in a variant without the partition wall 31 arranged therebetween can be arranged at a particularly small distance from one another.

The sheath 6 has a preferably homogeneous thickness, which is preferably 200 micrometers or less. An example applied in a spray process insulating varnish is particularly suitable as material for the wrapping. For sufficient edge coverage, it is advantageous if the body has no sharp edges. Its edges can be flattened, for example, by being grasped. Rounded edges are also beneficial.

The connecting wires 41, 42 are guided so that they have a sloping region. This area extends along the main surface of the resistive element. Preferably, the second lead wire 42 forms an angle to the first lead wire 41. This angle may be, for example, between 60 ° and 120 °. The connecting wire 41, 42 is bent or bent in the further course such that its lower region is oriented substantially vertically.

The connecting wire 41, 42 is performed through an opening 28 of the support plate 2. The diameter of the opening 28 is preferably larger than that of the connecting wire 41, 42 chosen. A fixation of the resistance elements on the support plate is possible in that the openings 28 are adapted to the diameter of the leads rather closely in the lower region.

The end of the wire 41, 42, which projects out of the carrier plate for electrical contacting of the resistor element, is preferably bent in such a way that it is aligned parallel to the base surface of the carrier plate. This exposed wire end has a contact region 43, which forms an external contact of the resistance element and the assembly.

The support plate 2 has a base portion 21 which is lowered from an upper portion of the support plate, see FIG. 6 , As a result, the arranged at the end of the connecting wires 41, 42 contact area 43 for contacting z. B. made accessible by a measuring tip of a test device.

The support plate 2 has recesses 27 which are arranged on the underside. The purpose of these wells is among other things material savings in the production of the carrier plate. These recesses have an uneven floor, so that a minimum thickness of the support plate 2 is ensured despite the recesses 29.

Each of the recesses 29 is provided for receiving a lower portion of the resistive element 11, 12.

In principle, the disc-shaped resistance element can be laterally displaced after installation in the carrier plate by rolling with respect to its initial position. This can be disadvantageous since the length of the protruding wire ends can be changed. In particular, an external contact may be longer than the other, which may affect mechanical properties of the assembly.

To prevent the unwinding of the disk-shaped resistance element, the bottom of the recess 29 is formed so uneven, and raised to the outside, that in the lateral displacement of the resistance element restoring forces arise that bring this resistance element back to its original position. The bottom of the recess 29 follows in cross section preferably a circular arc with a larger radius than that of the resistive element.

The support plate 2 has in the FIG. 13 shown recesses 26, in which a part of the outwardly facing connecting wire of the respective resistive element 11, 12 is housed. The support plate 2 also has recesses 25, in which a part of the inwardly oriented connecting wire of the respective resistance element 11, 12 is arranged. With these recesses, it is possible to reduce the length of the housing.

The support plate 2 has two mutually opposite side walls 23. In principle, further side walls can be provided. The support plate may be formed, for example in the form of a trough. The housing has a lid 3 having two open sides and two opposing side walls 35, which are preferably aligned substantially perpendicular to the longitudinal direction of the assembly. But it is also possible that all side walls of the housing are formed by the side walls of the lid 3. The lid is then formed in the form of a cap, which preferably has a rectangular bottom.

It is also conceivable that at least one wall of the housing is formed by a side wall of the lid and a side wall of the carrier plate which is adapted to this shape.

The lid 3 is fixed by means of latching devices 32 on end sides of the carrier plate 2. The latching devices are designed for example as snap hooks. The latching devices can in principle be replaced by other fastening elements. The lid and the support plate may, for. B. by riveting, screwing or gluing firmly together.

The lid 3 has a recess 38 which extends in the longitudinal direction of the assembly. This depression has the shape of a shallow and relatively wide groove. In this depression upper portions of the resistive elements 11, 12 protrude. It serves as a positioning element, which acts similar to the recess 29 of the support plate 2 against the rolling of the resistance elements. The bottom of the recess 38 is slightly flattened so that a predetermined minimum thickness of the lid 3 is ensured in the region of this depression.

The depressions 29 of the support plate 2 and the recess 38 of the lid 3 are advantageous because they u. a. serve to reduce the overall height of the assembly.

The cover 3 has centering devices 33, which are arranged between the resistance elements 11, 12 and prevent their tilting from the vertical orientation. They can be in pimples or as in the FIGS. 14, 15 be indicated flat elements formed. Between the centering devices 33 and the resistance elements, there is preferably a narrow gap for the consideration of tolerances of the thickness during the production of the main body 15.

The design possibilities of the presented component, in particular as far as the shape of components of the carrier plate and the lid are concerned, are not exhausted by the variant explained in the figures. The depressions and recesses can be arbitrarily shaped. There may also be provided further depressions or openings. The number of resistance elements can be greater than two.

The partition wall 31 may be formed wide so that it extends to the side walls 23, 35 of the housing. Thus, a separate closed cell is formed for each of the resistive elements 11, 12.

LIST OF REFERENCE NUMBERS

11, 12

resistive elements

15

Basic body of the resistance element

16

first electrode of the resistive element

17

second electrode of the resistive element

2

support plate

20

Opening for receiving the partition wall 31

21

plinth

23

Side wall of the carrier plate 2

25

recess

26

Recess, in which the outwardly facing connecting wire is arranged

27

bottom-side recess of the support plate

28

Opening for the passage of connecting wires 41, 42

29

Deepening for receiving a resistance element

3

cover

31

partition wall

32

latching

33

centering

35

Sidewall of the lid

38

Deepening of the lid

41

first connection wire

42

second connecting wire

43

Contact area of the connection wire

5

soldered point

6

insulating cladding

Claims (16)

1. Electrical assembly

   - comprising a housing (2, 3) and at least two PTC resistor elements (11, 12) which are arranged in the housing (2, 3),

   - wherein the resistor elements (11, 12) each have a base body (15) of flat design and electrodes (16, 17) arranged on its main surfaces,

   - wherein a connecting wire (41, 42) is soldered to each electrode (16, 17) of the respective resistor element (11, 12) at a soldering point (5),

   - wherein each resistor element (11, 12) has an electrically insulating sheath (6) which covers the soldering points (5),

   - wherein the resistor elements (11, 12) are arranged to be electrically insulated from one another,

   - wherein the housing (2, 3) is closed.
2. Assembly according to Claim 1,

   - wherein the housing has a carrier plate (2), on which the resistor elements (11, 12) are arranged.
3. Assembly according to Claim 1 or 2,

   - wherein the resistor elements (11, 12) are aligned upright.
4. Assembly according to one of Claims 1 to 3,

   - wherein the thickness of the sheath (6) does not exceed 200 µm.
5. Assembly according to one of Claims 1 to 4,

   - wherein the thickness of the sheath (6) on main surfaces and in the area of the edges of the base body (15) is largely homogenous.
6. Assembly according to one of Claims 1 to 5,

   - wherein the base body (15) has flattened edges.
7. Assembly according to Claim 2,

   - wherein the housing has a cover (3) which is fixed to the carrier plate (2).
8. Assembly according to one of Claims 1 to 7,

   - wherein the housing has a dividing wall (31) which is provided between the resistor elements (11, 12), at least in the area of the soldering points (5).
9. Assembly according to Claim 8,

   - wherein the dividing wall (31) is formed by an inner wall of the cover,

   - wherein an area of the dividing wall (31) is arranged in an opening (20) in the carrier plate (2).
10. Assembly according to one of Claims 1 to 9,

    - wherein openings (28), through which the connecting wires (41, 42) are led, are formed in the carrier plate (2).
11. Assembly according to one of Claims 2 to 10,

    - wherein a section of the resistor elements (11, 12) is countersunk in depressions (29) in the carrier plate (2).
12. Assembly according to one of Claims 1 to 11,

    - wherein the housing contains a thermoplastic.
13. Assembly according to one of Claims 1 to 12,

    - wherein the housing contains a glass fibre-reinforced material.
14. Assembly according to one of Claims 1 to 13,

    - wherein the housing contains a polymer-based material.
15. Assembly according to one of Claims 1 to 14,

    - wherein the housing is dimensionally stable to at least 250°.
16. Assembly according to one of Claims 1 to 15,

    - wherein each resistor element (11, 12) is dimensioned with respect to its resistance value, the switching point of the base body material and geometric dimensions, such that it exhibits a protection level of less than 500 mA.

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