Vertical deflection circuit with retrace switch protection

Claim 1

A vertical deflection circuit comprising: a deflection winding; a deflection amplifier with an input terminal and having an output terminal coupled to said deflection winding for generating a trace current in said deflection winding during a trace interval in each deflection cycle in response to drive signals coupled to said input terminal; a first voltage source coupled to said amplifier for providing an operating voltage to said amplifier; a second voltage source; bidirectional switching means coupled between said output terminal and said second voltage source for providing a voltage of greater magnitude than said first voltage source for generating a retrace current in said deflection winding during a retrace interval in each deflection cycle, said bidirectional switching means including a controlled semiconductor comprising a control terminal coupled to a first terminal at which there is developed a deflection rate signal and a main conductive path coupled to said second voltage souce and one of said output terminal and said deflection winding, said control terminal responsive to said drive signals for biasing said main conductive path from one conduction state to another for providing said voltage of greater magnitude during at least a portion of said retrace interval; and variable resistance means coupled in series with said main conductive path, said variable resistance means providing a relatively large resistance to the current in said main conductive path when said drive signals bias said main conductive path into conduction during a substantial portion of said trace interval for limiting the current in said main conductive path, and said variable resistance means otherwise providing a relatively small resistance during said retrace interval.