Resonant scan deflection circuit with flyback voltage limiting

A protective circuit for use with a resonant type deflection circuit, including a voltage source for providing a controllable voltage, a deflection coil connected to the voltage source, a deflection transistor connected to one end of the deflection coil, and a deflection transistor driving circuit connected to the deflection transistor and having an input terminal for connection to a sync pulse generator for driving the transistor into a switched condition in response to a sync pulse received from the sync pulse generator, said protective circuit comprising:

• current sensing means for connection in series with the deflection coil for sensing the magnitude of the current in the deflection coil and for developing a voltage representative of the sensed current;
• compensating means for connection to the voltage source for compensating for variations in the turn-off delay time of the deflection transistor at different scanning rates of the sync pulses from the sync pulse generator and for developing a voltage in accordance therewith in response thereto;
• and
• comparator means connected to said current sensing means and to said compensating means for comparing the voltage developed by said current sensing means and the voltage developed by said compensating means and for developing an output signal in accordance with the comparison and, in use, for applying said output signal to the deflection transistor driving circuit for driving the deflection transistor into its switched condition when the output signal from said comparator means is received by the deflection transistor driving circuit before the sync pulse is received thereby;
• whereby the deflection transistor is protected from an excessively large flyback voltage.