Patent GB-1425829-A (GB)
Title: Vertical deflection circuit
IPC: H03F1/30
Filed: 1972-04-26
Abstract: 1425829 Sawtooth wave generators RCA CORPORATION 25 April 1973 [26 April 1972] 19388/72 Heading H3T A sawtooth generator comprises a pair of capacitors connected in series in the output circuit of a first active element and the input of a second active element so as to provide a charging current which maintains the second element and thus the first in a second conducting condition during the retrace and to restore the elements to a first condition when the current is insufficient to maintain the second element in the second conductive state, a third active element for providing a discharge path for the capacitors during the trace, a timing network connected to the control electrode of the first element for terminating the trace when a synchronizing pulse is not present and a further capacitor connected in parallel with one of the others for linearizing the discharge. During the trace the series capacitors 29, 30, connected in Miller fashion to transistor 19, discharge via resistor 31 and the collector-emitter path of 19 to produce a trace output at the junction of the capacitors. The discharge continues until either a synchronizing pulse is applied at 12 or until a timing capacitor 23 has charged through resistors 26 and 27 sufficiently to make transistor 25 commence to conduct. The current then flowing through this transistor charges the capacitors and also switches on a transistor 18 which by regenerative action causes both transistors 18, 25 to become fully conducting. Conduction of a diode 16 and the base-emitter path of 18 clamps the base of transistor 19 to prevent Miller action. When the charging current is no longer sufficient to maintain transistor 18 conducting, regenerative action switches off 18 and 25 and a new trace commences. A capacitor-resistor circuit 33, 34 connected across one of the series capacitors shapes the first part of the trace and resistors 36 and 37 provide S correction. The oscillator shown is followed by a driver amplifier for feeding deflection coils 48. The quiescent current in the series connected output transistors 43, 59 is controlled by a transistor 54 which compares the voltage across a sensing resistor 55 due to the quiescent current, with a voltage across diodes 44 and 53. During the first (relatively positive) part of the trace input wave from the oscillator the input to transistor 54 is clamped by diodes 44 and 45 so that the current in transistor 59 is maintained substantially at the quiescent level, the drive to the coils being provided by transistor 43. During the second (relatively negative) part of the trace the current through this transistor decreases only slightly from the quiescent level but diode 45 becomes non-conductive and sufficient drive is applied to the emitter of 54 to drive the output transistor 59. Resonant retrace takes place in the deflection coils, the circuit effectively damping the oscillation after half a cycle and a diode 36 isolating transistor 43 during the oscillation. Negative feedback is provided by resistors 67 and from 51 and a CR circuit 64, 65 effects linearization during the second part of the trace.