DE2109760A1 - Electrical safety fuse - Google Patents

Description

M 1101

PATENT LAWYERS Dr.-lng. HAHS RUSCHKE Dipl.-Ing.HONZ AGULAR

BERLiM 33 AufiU * ia-Viktoria-Sir * e OB

Telefonaktiebolaget LM Ericsson ,, Stockholm J2, Sweden

Electrical safety fuse

The currently commonly used fuses have a metal part which melts when the current reaches a certain level Value, causing a power interruption will. In systems such as telephone exchanges where a large number of fuses are required and where the space of the Component boards or foil cards are small, such fuses but too expensive and too big.

The invention relates to a fuse which is cheap to manufacture and which takes up only a small amount of space. It is particularly suitable for use in component boards or foil cards where the invention is incorporated as a component in certain cases and can replace an ordinary component. It consists of a film resistor that is placed on a thin surface "of fragile, insulating material, e.g. ceramics, applied with such a shape i; jt, das;:, they withstand the stresses up to

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withstands a certain continuous maximum operating current and breaks at an even higher current, whereby a break in the resistance film occurs. This puncture will achieved through the combination of a locally concentrated heat emission and a thin base. The invention is through the lying claims determined.

The invention will now be described with reference to the accompanying Drawings described, which show the security elements greatly enlarged.

1 shows a safety fuse in plan view; Fig. 2 shows the same fuse from the side;

3, 4, 5 and 6 show different shapes in plan view and positions of the metal film;

7 and 8 show different designs of the plate from FIG

9 and 10 show two layout forms from the side, where an elastic element is attached between the terminals of the fuse. To clarify the drawing the metal film was drawn dark.

An embodiment of the resistor with an optimized safety function is shown in its simplest form in FIGS. 1 and 2, a thin ceramic plate 1 carries a film 2 made of a resistance layer with low-resistance end metallizations J and 4; for connecting external conductors, which for example consist of metal contacts, as they are known per se for soldering a foil card. The resistance layer is relatively thin and is produced by screen printing and firing a platinum-palladium-metal powder paste or by thick vapor deposition of tantalum. This is advantageous because the amount of withholdings is geometric

10984Π / 1109

Shape left out of consideration, primarily on the elastic properties and the thickness of the ceramic plate and depends less on the resistance film. To be precise, a is based Thick film resistor on a ceramic mineral base according to Fig. on known methods and designs. The present invention uses this as a means of realizing a special function and a component, with further specific ones constructive changes a safety fuse with a large range of parameters both in terms of cut-off current as well as breaking power, breaking time and a suitable relationship between breaking current and maximum continuous current is achieved. "

The Sicnerungselement according to Figures 1 and 2, as a thick film resistor is carried out on a uniformly thick ceramic plate of 13 x 13 ^: Ο, υΟ mm, e.g. a very small switch-off power of I3 V «and a maximum power in continuous Have operation of 4 W. At the absc ± acJ.ten the Plate roughly parallel to the Endmetallisievungen 3 and 4, like it durcii indicated by the dashed line 5, and it results an immediate break in the resistance. Investigations have however shown that? with unchanged plate size A considerably more sensitive fuse can be achieved, i.e. the one that cuts out at a lower power, by using the Resistance film arranges asymmetrically. Dor mechanism of the Prediction function is that performance in the Layer creates an uneven temperature across the plate, which, in the case of a film shape according to FIG. 1, has the highest temperature approximately along the center line parallel to the electrodes 3 and 4 and reaches the lowest temperature under the electrodes themselves. When changing the shape and position of the resistor film, the even greater difference between the highest and ■ the lowest temperature of the plate, greater sensitivity can be achieved. So a form gives de ^ Film 2 according to FIG. 3 a, considerably more sensitive fuse. It was also found that given external ladders 3

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and 4 and contact metallizations, but with maximum asymmetry., i.e. a layer in the form of a strip at the end of the edge of the mineral pad, a worse result is obtained than with a layer. that "shifted a little towards the center of the plate is.

Another embodiment shown in FIG. 6 has one Incision 6 in the resistance layer 2, which is produced by sandblasting or with a laser beam. This execution is also advantageous because it can be combined with adjusting the resistance, which is often done by cutting out happens. The designs of the film resistors, which offer advantages for the function as a fuse, contradict in most cases directly to the generally applied rules of good design practice for thick film resistors, the among other things recommend the smallest difference in the operating temperature on the supporting surface.

Zv / ei modifications of the shape of the film 2 are shown in FIGS 5, one incisions ό with a remaining narrow resistance strip and the other has a gradual transition from a wide to a narrow cross-section.

If the crack occurs in plate 1, then it has to be that way become wide so that no metal breaks remain between the connections 3 and 4. The width of a jump in a resistance fuse e.g. according to Fig. 3 * in a foil card soldered in is to some extent a function of the applied Power. A much higher performance results in a more pronounced jump. The quality of the plate in terms of the crack in the event of an overload due to the resistance, it can also be improved in another way. After that, the emergence of a is marked Jump facilitated by making a notch 7 on the edge of the plate, as inclined in Fig. Υ wi ^ -d, or by the The middle part of the plate is made thinner than the outer edges

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7 and 8. In particular, the embodiment according to Fig. 8 with the longitudinal groove 8 is advantageous because it is compatible with the normal "method of screen printing the resistor and the connections of the plate, since the groove 8 does not form the plate significantly weakens the pressure forces that occur in silk screen printing.

This enables an even better determination of the estimation function can be achieved that between the terminals 3 and 4 preferably an elastic element, e.g. an insulated spiral spring, is attached firmly under pressure over the hottest point of the layer or a stopper made of silicone catalyst, as shown in FIG. 9 and 10, respectively, in which, the plate 1 with the film 2 of the side is seen. In both cases, the elastic element 11 is directly between those attached to the end metallizations Conductors (possibly for soldering into a foil card) intended. These conductors have a large one in certain cases Area so that effective cooling of the end metallizations is achieved, creating an additional concentration of heating on the film itself is achieved. The elastic element can also have the function of an indicator that shows that the Switching off has taken place, for example, in that the element then shows a previously hidden colored surface or even just falls off.

- patent claims -

10984Π / 1109

Claims (4)

τ hoi Claims Electrical fuse, consisting of a film of an electrically conductive material, which is provided with electrical input and output connections, the Materia.1 being applied to a thin plate of insulating material, and characterized in that the insulating material of the thin plate (l ) is of such a nature that it becomes fragile when heated, and that the insulating material and the resistance of the film (2) between the terminals (J ₃ H-) are chosen so that the plate is heated by the The current flowing through the film (2) creates a crack in the plate, through which the film (2) is broken and collapsed permanent break between the connections is achieved within predetermined current and time limits. 2. Electrical fuse according to claim 1, characterized in that the width of the film (2), counting from one connection (j5) to the other ( ² J-), is considerably smaller at a point at which a notch is provided . 10984Π / 1109 - γ - T 1101 3. Electrical fuse according to Anspi'uch 1, characterized in that metallic conductors (9, 10) , which are anchored to the input?:; - and output connections of the film (2), have such a size and shape that a substantial Part of the heat is removed from the film. 4. Electrical fuse according to claim 1, characterized in that that the plate (2) is provided with a mechanical weakening by reducing the cross section along a line that is at an angle to the line between the terminals. 5. Electrical fuse according to claim 1, characterized in that an elastic element (11) is arranged between the connections (3, K) under pressure. Heipa / Br. 109840/1109 Blank page