Electrical resistors – Resistance value responsive to a condition – Current and/or voltage
Utility Patent
1999-07-16
2001-01-02
Easthom, Karl D. (Department: 2832)
Electrical resistors
Resistance value responsive to a condition
Current and/or voltage
C338S0220SD, C338S237000, C338S236000, C338S235000
Utility Patent
active
06169472
ABSTRACT:
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'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
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Siemens 1996 Data Book “Kaltleiter” pp. 37-38.
Easthom Karl D.
Schiff & Hardin & Waite
Siemens Matsushita Components GmbH & Co. KG
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