Vertical retrace circuit with zoom and centered fast retrace

摘要

A television receiver is controlled as to the degree of vertical zoom via a deflection current ramp that varies in slope and which may be delayed to achieve panning. Due to the increased slope when zoomed, the deflection current and the electron beam complete a trace in less time than the normal vertical interval. The deflection current is maintained at one extreme or the other outside the trace interval, and the beam is blanked. A retrace signal generator (10a, C17, U07) coupled in a feedback (IERROR) loop with the power supply for the deflection circuit determines the midpoint of the blanking period and generates a fast retrace (VRESET) at or near the midpoint. The feedback loop is arranged to minimize the DC average current in the deflection winding by having a current source responsive to the DC average current for charging a timing ramp (C17) that triggers retrace upon reaching a threshold. The slope of the timing ramp varies with DC loading, thus advancing or retarding retrace to center retrace in the blanking interval.