Deflection system with positive feedback

In an electron beam deflection circuit which is coupled to a source of operating energy and which is responsive to a source of periodic drive signal to provide a periodic sawtooth current in a deflection coil, each period of the signal having a retrace interval and a scanning interval, the sawtooth current having a substantially linear ramp during the scanning intervals thereby storing energy in the deflection coil, the deflection circuit including a switching transistor having its base lead coupled to respond to the periodic drive signal and having its collector lead connected in circuit with a tank network, the tank network including the deflection coil and a damping diode;

• the circuit operation being such that during the retrace intervals the transistor is cut off and the damping diode becomes forward biased after the stored energy completes about one-half cycle of an oscillation in the tank network and continues to be forward biased to damp such oscillation and to complete a current path for the sawtooth current until approximately the midpoint of the ensuing scanning interval when the forward bias of the diode is removed and the collector to emitter path of the switching transistor thereafter completes the current path for the sawtooth current for the remainder of the scanning interval;
• the deflection circuit being further characterized by;
• a transformer having a first primary winding coupled to receive the periodic drive signal, a second primary winding coupled to the emitter lead and a secondary winding coupled to the base lead of the switching transistor;
• the first primary winding conducting a current pulse during each retrace interval to cut off the switching transistor, the stored energy decaying and providing base current to the switching transistor during the first half of each scanning interval, the second primary winding providing base current during the second half of each scanning interval;
• and by
• the transformer coupling between the switching transistor base and emitter leads providing positive feedback so as to control the base current for the switching transistor throughout the time that the switching transistor is conducting.