GB1031973A - Electron beam convergence apparatus - Google Patents

Abstract

1,031,973. Cathode-ray tube circuits. RADIO CORPORATION OF AMERICA. July 14, 1964 [Aug. 5, 1963], No. 29013/64. Heading H4T. Relates to dynamic convergence circuits for a multiple-beam colour image reproducing cathode-ray tube reproducer. Fig. 1 (not shown). According to the invention at least one dynamic convergence electromagnet is provided and a transistor couples a source of sawtooth waves to the winding of the electromagnet only during the latter half of the line periods. The arrangement described, Fig. 2 (not shown), comprises dynamic convergence electromagnets 31, 32, 33 associated with transistors 47, 59, 70 and line 42 and field 67 output stages, the line output transformer 36 having additional secondary windings 38, 39 and the field output transformer having additional secondary windings 52, 84. Considering firstly the circuit operation at line frequency, wiper 46 controls the peak amplitude of the substantially parabolic current wave in windings 34G, 34R; valve 42 conducts only during the second half of each line period, Fig. 3, there being developed in the collector circuit of transistor 47 a substantially parabolic wave produced by integration of the sawtooth wave. During the non-conducting periods of transistor 47, which occur in the first half of each line period, the energy stored in windings 34G, 34R is dissipated in circuits which include a waveshaping network 54 and substantially no current flows through the windings at the centre of each line period. Shaping of the parabolic wave is effected by potentiometer 57. The relative currents through the windings is effected by adjustment of inductor 49. A sawtooth wave component at line frequency is supplied to windings 34G, 34R by secondaries 38, 39, the relative proportions being adjustable by potentiometer 41. For the winding 34B, wiper 58 determines the peak-to-peak amplitude of the parabolic current wave at line frequency, and wave-shaping circuit 62 incorporates a diode 64 to prevent current flow therein during the periods when transistor 59 conducts. Fieldfrequency operation is isolated from linefrequency operation by chokes 82, 86, and the energization of transistor 70 is controlled by potentiometer 72; diode 76 augments the energization during the latter part of the field period.