GB1503518A - Generating a sawtooth deflection current - Google Patents

Abstract

1503518 Sawtooth deflection circuits PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 7 March 1975 [11 March 1974] 9577/75 Heading H3T [Also in Division H2] In a deflection circuit, a first switch S1 is arranged to couple the deflection coil L1 to a capacitance Ct during the trace interval, a second switch S2 is coupled to the first switch S I via at least a capacitor C and arranged to control the replenishment of energy to capacitor Ct from current provided by a third switch T3 without the interposition of a charging or energy storing inductor. At the beginning of each trace, thyristor T1<SP>11</SP> is conductive so that a decreasing current is driven by Ct through deflection coils L1 (which may be transformer coupled). At the mid trace point, thyristor T1<SP>1</SP> is turned on so as to accommodate the reversed current in L1. Thyristor T2 is triggered near the end of the trace, so that a half cycle flyback pulse is developed by resonating C, L I, Ct. Thyristor T1<SP>11</SP> and T3 are turned on at the end of the flyback, T3 passing only a short pulse of current to replenish losses. A pulse position modulator 3 controls the gating time of thyristor T3 so as to maintain constant the voltage across capacitor Ct and hence the scan amplitude. In Fig. 1 (not shown) thyristor T1<SP>11</SP> is replaced by a diode and an inductor is included in series with C. Further low value inductors may be included for suppressing high frequency transients. Auxiliary supply voltages and the required high voltage can be generated by means of windings coupled to L 1 and/or by means of a transformer in series with a capacitor across C. The thyristors may be replaced by transistors.