PTC Heater with Reduced Switch-On Current

Abstract

A positive temperature coefficient (PTC) heater is disclosed. In an embodiment the PTC heater includes a main body having a length L, a width B, and a height H made of a PTC material and a first electrode and a second electrode made of an electrically conductive material, wherein the following is true for L, B, and H: LBH, and wherein the electrodes are connected to the main body so that the following is true for a spacing d thereof from one another: d>H.

Claims

1-12. (canceled)

13. A positive temperature coefficient (PTC) heater comprising: a main body having a length L, a width B, and a height H made of a PTC material; and a first electrode and a second electrode made of an electrically conductive material, wherein the following is true for L, B, and H: LBH, and wherein the electrodes are connected to the main body so that the following is true for a spacing d thereof from one another: d>H.

14. The PTC heater according to claim 13, wherein the following is true: LB>H.

15. The PTC heater according to claim 13, wherein the main body has a shape of a cuboid, a cylinder, a film, or an ellipsoid.

16. The PTC heater according to claim 13, wherein the main body comprises doped BaTiO.sub.3.

17. The PTC heater according to claim 13, wherein the main body comprises Sr, Pb, and/or Ca.

18. The PTC heater according to claim 13, wherein the main body comprises a rare earth element, Mn, Fe, and/or Al.

19. The PTC heater according to claim 13, wherein the following is true: 2.5 cmL5 cm, 1 cmB4 cm, and 100 mH.

20. The PTC heater according to claim 13, further comprising a carrier, wherein the main body is arranged on the carrier.

21. The PTC heater according to claim 13, wherein the electrodes comprise Cr, Ni, Ti, Al, Ag, Cu, and/or Au.

22. The PTC heater according to claim 13, further comprising a dielectric layer on a lateral surface of the main body.

23. The PTC heater according to claim 22, wherein the dielectric layer comprises an oxidic ceramic.

24. The PTC heater according to claim 13, further comprising a cooling element connected to the main body, wherein the cooling element is configured to emit heat dissipated in the main body to surroundings.

25. A PTC heater comprising: a main body having a length L, a width B, and a height H made of a PTC material; a first electrode and a second electrode made of an electrically conductive material; and a dielectric layer on a lateral surface of the main body, wherein the following is true for L, B, and H: LBH, and wherein the electrodes are connected to the main body so that the following is true for a spacing d thereof from one another: d>H.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Central features of the present PTC heater, functional principles, and details of several nonrestrictive exemplary embodiments are explained in greater detail in the schematic figures.

[0031] In the figures:

[0032] FIG. 1 shows a perspective view of a heater;

[0033] FIG. 2 shows the meaning of the terms length, width, height;

[0034] FIG. 3 shows an alternative option for arranging the electrodes;

[0035] FIG. 4 shows a known heater having short current path;

[0036] FIG. 5 shows a cross section through a heater;

[0037] FIG. 6 shows a cross section through a heater having an alternative electrode shape;

[0038] FIG. 7 shows a cross section through a heater having one insulation layer;

[0039] FIG. 8 shows a cross section through a heater having two insulation layers;

[0040] FIG. 9 shows the possibility of arranging electrodes on the same surface of the main body;

[0041] FIG. 10 shows the possibility of providing a cooling element for improved heat dissipation; and

[0042] FIG. 11 shows the possibility of arranging the main body on a carrier.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0043] FIG. 1 shows a fundamental design, in which the heater HZ has a main body GK, which is arranged between a first electrode EL1 and a second electrode EL2. The arrow indicates a possible direction of the electrical current in this case. The main body GK has the shape of a cuboid by way of example in FIG. 1. The electrodes are arranged in this case on ends of the main body which do not have the shortest spacing. The path of the electrical current is therefore relatively long. The electrical field strength is thus reduced in the main body and the number of the grain boundaries which the electrical current has to overcome is increased.

[0044] FIG. 2 shows the meaning of the terms length, width, and height with respect to a main body. In this case, the length is essentially the greatest-possible spacing of opposing ends, sections, or surfaces of the main body GK. The height is a measure of the shortest-possible spacing of opposing surfaces, sides, ends, or sections of the main body.

[0045] The shape of the main body is not restricted to cuboids or cuboid-like shapes. All possible shapes to which a length, a width, and a height may be assigned in accordance with the relationship LBH are possible.

[0046] FIG. 3 shows the possibility of arranging the two electrodes so that the main body is arranged in between, without the electrodes having the longest-possible spacing from one another. However, it is to be noted that the electrodes in particular do not have the shortest-possible spacing from one another, to avoid the above-mentioned disadvantages of known PTC heaters.

[0047] FIG. 4 shows in particular the typical geometry of a routine PTC heater. The electrodes EL1, EL2 are arranged in relation to the interposed main body so that the path which the electrical current has to take (arrow) is as short as possible. This is because in this case the electrodes themselves may be designed as large-area as possible and simultaneously may be used as a heat bridge for a well-functioning heat discharge to the surroundings.

[0048] FIG. 5 shows a possible shape of the electrodes EL1, EL2. The material of the electrodes covers the lateral surfaces facing away from one another of opposing ends of the main body GK in this case.

[0049] FIG. 6 shows an alternative embodiment of the shape of the electrodes. They are not restricted to the opposing end faces. Rather, the electrodes also still extend a certain amount beyond the edges to the adjoining lateral surfaces of the respective electrode. If the electrodes are embodied as clamp electrodes, they may thus be connected relatively easily on the material of the main body GK and have a relatively stable mechanical contact at the same time. The electrical resistance is accordingly also low at the transition from the material of the electrodes to the material of the main body.

[0050] FIG. 7 shows the possibility of arranging a dielectric layer as insulation IS on at least one side of the main body.

[0051] FIG. 8 shows that both opposing surfaces having the shortest possible spacing from one another can be covered by a separate insulation layer IS. The path from a point in the main body GK to the surroundings of the main body frequently leads in this case via the lateral surface on which the insulation layers are arranged, since these sides are in particular the sides which are formed large-area because of the low thickness. Accordingly, these surfaces may be used well to discharge dissipated heat.

[0052] In order that the electrical current from one electrode to the other electrode also actually takes the path through the main body GK and does not take a path of a lower electrical resistance via surroundings of the main body GK, the main body GK is insulated by the dielectric layer at least on the critical regions.

[0053] It can depend on the external surroundings of the main body and/or the PTC heater in this case as to whether an insulation layer is arranged now only on one side of the main body (as shown in FIG. 7) or on two sides of the main body (as shown in FIG. 8).

[0054] FIG. 9 shows, by way of example and in a perspective view, that the shape of the main body is not restricted to cuboids. Cylinders having a low height, i.e., round plates, but also other shapes such as plates having oval outlines, can be used.

[0055] Moreover, FIG. 9 additionally shows that the electrodes are to be arranged at the remote ends of the main body. Since the distance of electrodes is important, but not the side of the main body, both electrodes can also be arranged on the same side of the main body to arrive at the above-mentioned advantages of the presented PTC heater.

[0056] FIG. 10 shows the possibility of bringing a cooling element KK into thermal contact with the main body GK. In order that electrical current between the electrodes does not flow via the cooling element KK, it is preferably galvanically separated from the electrical system by a dielectric insulation layer IS. Cooling element and insulation layer can be arranged in this case on one, or also on both large-area sides of the PTC heater. The cooling element preferably has a large surface, for example, by means of cooling ribs, to keep the resistance of the heat flow low.

[0057] FIG. 11 shows the possibility of arranging the main body on a carrier TR.

[0058] The described configuration of the main body enables the main body to be designed as a thin film. In order that sufficient mechanical stability is also maintained in thin films, the film can be arranged on the carrier TR and can be connected thereto. Heat can be emitted to the surroundings via the carrier TR, on the one hand, but also via a cooling element, on the other hand.

[0059] Additional cavities can be arranged in the carrier TR or in a cooling element KK, in which a liquid having high specific heat capacity, for example, cooling water, can flow to improve the heat emission and attain a higher thermal power range.

[0060] The thermal power range can be in this case between a few watts, for example, 2 W, and several hundred watts, for example, 300 W.

[0061] A typical electric power in this case is approximately 50 W, 100 W, 150 W, or 200 W.

[0062] Corresponding PTC heaters have an efficiency of nearly 100%.

[0063] The PTC heater is not restricted to the features mentioned or the exemplary embodiments shown. A heater can have additional circuit elements, feelers, thermal coupling elements, or the like.