Abstract:
A PCT thermistor arrangement for use in a circuit for demagnetizing shadowmasks of color picture tubes, has at least two PTC thermistor elements which are designed as switching PTC thermistors, are or can be thermally coupled and are or can be electrically connected in parallel.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a PTC thermistor arrangement for use in a circuit for demagnetizing shadowmasks of colour picture tubes, having at least two PTC thermistors which are electrically connectable in parallel, that are thermally coupled and that are installed in a housing. 
     2. Description of the Prior Art 
     A PTC thermistor arrangement is disclosed in U.S Pat. No. 4,024,427, wherein the PTC thermistors are connected in series therein. 
     Japanese Application, JP-A 05 258905 discloses that the contact elements for a thermally coupled PTC thermistor arrangement be planarly supported at the housing wall. 
     PTC thermistor arrangements for the aforementioned purpose are disclosed in the applicant&#39;s 1996 Data Book “Kaltleiter”, pages 37 and 38. At least one PTC thermistor of this type is used in this context to reduce the current in a demagnetizing coil from an initial current value to a residual current value. According to one embodiment, a demagnetization circuit for the abovementioned purpose is formed by the series circuit of a PTC thermistor and a demagnetizing coil which is connected to an AC voltage source. 
     According to a further embodiment, a circuit arrangement of this type may also contain two thermally coupled PTC thermistors. The first is the switching PTC thermistor connected in series with the demagnetizing coil. The second is a heating PTC thermistor or power supply PTC thermistor which is thermally coupled to the switching PTC thermistor, and is connected in parallel with this series circuit. This circuit is also connected to an AC supply voltage. With this circuit, the residual current through the demagnetizing coil can be further reduced, compared with the abovementioned circuit, with just one switching PTC thermistor, because the switching PTC thermistor, in addition to its own heating, is externally heated by the power supply or heating PTC thermistor. 
     Depending on the picture tube properties, there is a need in some situations for low-impedance switches and/or those with a so-called “long decay” behaviour at high initial currents. Large-volume PTC thermistor wafers are provided in known solutions to address these requirements, via an electrical connection in parallel with two embodiment using a single PTC thermistor, or with two PTC thermistors of the embodiments explained used for extremely low-impedance concepts. 
     On the one hand, the parallel circuit enables the resistance to be halved for the purpose of the requisite property of low impedance, while, on the other hand, a turn-off delay is provided by the division of the initial current between two switches for the purpose of the requisite “long decay” behaviour. 
     Here, however wiring-up two housing designs to the demagnetizing coil, is expensive. 
     SUMMARY OF THE INVENTION 
     The present invention is based on the object of providing a simple and thus less expensive solution to the aforementioned problem. 
     This object is achieved according to the invention by means of a PTC thermistor arrangement that comprises a unit having two or more PTC thermistors connectable in parallel and thermally coupled. The unit is held into a housing by attachments on top, a recess on the bottom, and by spring contact elements within above line  27 , insert a centered heading. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The invention is explained in more detail below using exemplary embodiments in accordance with the figures of the following drawings. 
     FIG. 1 is a schematic circuit diagram of a demagnetization circuit arrangement with a PTC thermistor arrangement designed according to the invention; and 
     FIG. 2 is an illustrative vertical cross-section view showing an advantageous option for fitting a PTC thermistor arrangement according to the invention into a housing. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     According to FIG. 1, in a PTC thermistor arrangement, provision is made of two thermally coupled PTC thermistor wafers  10  and  11 , which serve as switches, are electrically connected in parallel or can be connected in parallel and are arranged in a circuit  17 ,  18  of an AC voltage source, which is not illustrated in the drawing, in series with a demagnetizing coil  19  of a television set. The thermal coupling of the PTC thermistor wafers  10  and  11  is indicated schematically by a dashed connection  12  in FIG.  1 . The thermally coupled PTC thermistor wafers  10  and  11  are arranged in a housing  2  which is indicated schematically by dot-dashed lines. 
     To allow a parallel connection one electrical terminal of the PTC thermistor wafers  10  and  11  is electrically connected to one another at a circuit node  13 . The respective other electrical terminals of each of, the PTC thermistor wafers  10  and  11  are routed to a circuit node  15  and  16 , respectively. These circuit nodes  15  and  16  may be routed out of the housing  2 , thereby enabling a user, depending on the application, to realize the parallel circuit of the PTC thermistor wafers  10  and  11  by way of an electrical connection of the circuit nodes  15  and  16 , indicated by a dashed line. 
     However, it is also possible for the terminals of the PTC thermistor wafers  10  and  11  leading to the circuit nodes  15  and  16  to be permanently electrically connected to one another inside the housing, with the result that the electrical connection in parallel of the two PTC thermistor wafers  10  and  11  is present inside the housing design in a manner predetermined by the manufacturer. 
     One possible advantageous embodiment of the fitting of a PTC thermistor arrangement according to FIG. 1 into a housing is illustrated in FIG.  2 . In this figure, the PTC thermistor arrangement formed by the PTC thermistor wafers  10  and  11  according to FIG. 1 is illustrated schematically by a unit  1 . In general terms, the entire arrangement is formed by the unit  1 , the housing  2  and spring contact elements  3  and  4 . For the following explanations, a housing top side is designated separately by  2 - 1  and a housing base by  2 - 2 . The unit  1  is held in its position at the housing top side  2 - 1  by way of attachments  2 - 3  and at the housing base  2 - 2  by way of a recess  2 - 4 . 
     The spring contact elements  3 ,  4  are each supported at two supporting points  3 - 1 ,  3 - 2  and  4 - 1 ,  4 - 2 ,  5  respectively, in the housing, the supporting points engaging on mutually remote sides of a respective contact point on the unit  1 . 
     The spring contact elements  3 ,  4  are preferably spring metal-sheet elements which are designed such that  10  they are preferably concave as seen in a direction from the supporting points  3 - 1 ,  3 - 2  and  4 - 1 ,  4 - 2 , respectively, on the housing  2  towards the contact point  3 - 5  and  4 - 5 , respectively, on the component body  1 . The supporting points  3 - 1 ,  3 - 2  and  4 - 1 ,  4 - 2  are situated, as illustrated, in the region of the housing top side  2 - 1  and housing base  2 - 2 . 
     In the region of the housing base  2 - 2 , the supporting points  3 - 1 ,  3 - 2  and, respectively,  4 - 1 ,  4 - 2  of the spring contact elements  3 ,  4  are preferably formed by an extension of the concave part of the spring contact elements being pierced through the housing base  2 - 2 . The piercing-through regions are in this case designated by  3 - 3  and  4 - 3 , respectively. 
     This design of the spring contact elements  3 ,  4  realizes, on the one hand, a high permanent clamping action which is of crucial importance for the service life performance of the PTC thermistor arrangement. Since, furthermore, the spring contact elements  3 ,  4  are pierced through the housing base  2 - 2  by means of their extensions  3 - 4  and  4 - 4 , respectively, the resulting housing opening remains restricted to the spring cross section. This results in a minimization of the housing opening with the significant advantage that external contaminants can largely be kept away from the housing interior, which in turn leads to an increase in the operational reliability. 
     The extensions  3 - 4  and  4 - 4  in this case correspond to the circuit nodes  15  and  16 , while the circuit node  13  is directly discernible from FIG.  2 .