Thomson Tubes & Displays, S.a.

Jean M Perreaut

Bruno F Roussel

Didier Thibaudin

A focusing device for a cathode ray tube comprises a plurality of substantially cylindrical permanent magnets, each having a longitudinal axis. A holder positions the magnets in an annular array at substantially equally spaced intervals in which the axes are substantially parallel to one another. Annular flanges of high magnetic permeability are disposed over longitudinally opposite ends of the magnets. First and second annular windings are symmetrically disposed substantially adjacent to and inwardly from the array of magnets. The magnetic mass of the focusing device can be varied by changing the number of magnets and/or the length of the magnets in the array. The magnets are magnetized in situ in the array by energizing a winding common to each of the magnets, after which the common winding is removed.

Magnetic focusing device

A focusing unit for a cathode ray tube comprises a plurality of permanent magnets, each having a longitudinal axis, and a plurality of coils. A form holds the magnets in a first annular array at substantially equally spaced intervals in which the magnet axes are substantially parallel to a longitudinal axis defined by the first annular array and holds the coils in a second annular array at positions spaced angularly between the magnets. Annular flanges of high magnetic permeability are disposed over longitudinally opposite ends of the magnets. At least one annular winding is disposed substantially adjacent to and inwardly from the first array of the magnets. In one embodiment, the coils are helical coils disposed in substantial circumferential alignment with the first annular array of the magnets. The helical coils each having a substantially is radially aligned longitudinal axis. In another embodiment, the plurality of coils are spaced radially between the first array of the magnets and the at least one annular winding. Each of these coils defines a substantially radially aligned longitudinal axis. In each embodiment, the plurality of coils of the second array are coupled in two interleaved sets for generating two quadripole focusing fields for correcting astigmatic aberrations of an electron beam in the cathode ray tube.

Permanent magnet focus unit with integral astigmatism corrector

A magnetic focusing device is disposed around the neck of a cathode ray tube. The device comprises a magnetic frame formed by constituent pieces having different magnetic permeabilities and having a gap in a portion thereof radially closest to the neck. A static focusing coil is enclosed in the frame and energized by a direct current. A dynamic focusing coil is energized by a periodically variable current and disposed between the static coil and the neck of the tube. The dynamic focusing coil is disposed near the gap and uses as a magnetic circuit the portion of the frame consisting of the material whose imaginary component of magnetic permeability is the lowest.

Magnetic focusing device for cathode ray tubes

An electron beam focusing device is provided for apparatus such as cathode ray tubes wherein an electron beam is scanned on a flat surface normal to the beam and converged at a point on the flat surface using magnetic fields. The focusing device includes a static field generator for converging the beam, and a dynamic focus device. The dynamic focus device is comprises a first winding coupled to a power supply, for example a current supply, for providing a magnetic field substantially defining a parabola during a trace interval of the beam to account for the variation in beam path length which occurs with scanning, and a second winding magnetically coupled to the first winding. An energy storing circuit coupled to the first and second windings stores energy during the trace interval and releases energy during the retrace interval such that the second winding induces a reverse current in the first winding, thereby returning current to the power supply during retrace. A thyristor switch references energy induced in the first winding by the second winding to ground during the retrace intervals.

Focusing device with two dynamic windings for energy recovery

A focus coil for a television is disposed between scanning electron beam generator and a planar screen and has a winding coupled between a power supply and a current sink for providing a magnetic focusing field due to current in the coil. A focusing circuit comprises a resonant circuit coupled to the focus coil for generating a parabolic current in the focus coil to account for variations in the distance between the focusing device and the screen during scanning. The resonant circuit stores a portion of the energy developed during trace intervals and returns this energy to the power supply during retrace intervals. The resonant circuit includes a capacitor and an additional coil, in series with one another, and together in parallel with the focus coil. The additional coil is magnetically coupled to the focus coil and induces a reverse current in the focus coil during the retrace interval for returning energy to the power supply.

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Dijon, France

Jean M Perreaut