Electric lamp and discharge devices: systems – Cathode ray tube circuits – Power supply from deflection circuit source
Patent
1996-11-12
2000-10-17
Issing, Gregory C.
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Power supply from deflection circuit source
336182, 336192, H01J 2970, H01F 2728, H01F 2729
Patent
active
06133698&
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention concerns a stepped rectification high-voltage (HV) transformer, usable in particular to power cathode ray tubes (CRT) in televisions.
FIELD OF THE INVENTION
The stepped rectification of the high-voltage of the transformer means that the secondary coil of the transformer, known as the step-up coil, includes several HV outputs each of which is rectified by diodes. In the case of the power supply of a CRT of a TV, for example, the HV transformer must supply a high output voltage of about 25 to 35 KV to the anode of the CRT that emits and accelerates the beam of electrons required for operation of the tube, and a high voltage known as the focusing voltage, of the order of 10 to 12 KV, used to regulate the concentration of the beam of electrons in the CRT.
Generally, the secondary coil of the transformer is in the form of a winding on a support of tubular form. This winding is divided axially into at least three stages by at least two diodes that are positioned at the same axial level, that is to say in the same radial plane perpendicular to the axis of the windings, close to front face of the insulating casing of the transformer, this face being generally constituted by a potentiometer block connected to the focusing voltage output. The fact that the rectifying diodes are confined in a small space facing the potentiometer block leads to poor heat dissipation from the diodes which can result in a rapid rise in their temperature during operation, which is likely to reduce their operating life.
Furthermore, the HV outputs at the diodes of the transformer are located at different levels. For reasons of electrical safety of the transformer, a certain separation distance must be assured between the components located near the transformer and the points of connection of external HV cables to the HV outputs of the step-up coil. This distance is typically 2 to 4 cm. Consequently, the fact that the HV power supply output is generally located in the upper part of the step-up winding means that the corresponding chimney of the insulating casing surrounding the external cable must be made longer.
In order to reduce this supplementary insulating length of the cables, it is possible to move the electrical connection point further inside the insulating casing of the transformer, but this would require an additional connector (a conducting bar, for example), between the very high-voltage (VHV) output of the diode and the corresponding HV cable. This would cause additional fabrication problems of the transformer and reliability problems due to the high voltage.
In addition, in view of the high operating voltages within the transformer, the voltage strength limits of the components oblige a sufficient distance to be left between the coplanar diodes and the potentiometer block, which does not favor compactness of the transformer.
SUMMARY OF THE INVENTION
The object of the present invention, which provides a simple and effective solution to the problems described above, is a compact HV transformer with improved electrical connection characteristics and thermal dissipation.
Another object of the invention is to improve the reliability of the transformer by reducing its operating temperature, in particular near the diodes enclosed in the insulating casing.
The invention is therefore a stepped rectification high-voltage transformer including an insulating casing enclosing a primary winding and a secondary step-up winding that is mounted coaxially about the primary winding, the step-up winding having several stages each being connected to a diode, and at least two chimneys incorporated in the insulating casing and whose lower ends are each plugged by a conducting pellet that provides the electrical connection between said stages of the secondary winding and external high-voltage cables, wherein the lower ends of the chimneys are positioned substantially at the same axial level as two of said stage diodes and these two stage diodes each have one conducting end directly penetrating the lower f
REFERENCES:
patent: 4293903 (1981-10-01), Nochida et al.
patent: 4408176 (1983-10-01), Nakamura
*Patent Abstracts of Japan, vol. 007, No. 115, May 19, 1983 and Japanese Patent 58-035910 (*see above).
Millot Bernard
Rouhier Bruno
Issing Gregory C.
Sragow Daniel E.
Thomson Multimedia S.A.
Tripoli Joseph S.
Wein Frederick A.
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