Instant-on circuit for a television receiver offering independent filament voltage control

Claim 1

In a supply circuit for powering the filament of a cathoderay kinescope of a television receiver of the type including a horizontal oscillator and first and second switching means operable between conductive and non-conductive states for providing trace and retrace portions of developed horizontal deflection currents to said cathode-ray device and for generating such high voltages as are necessary for the reproduction of transmitted image signals applied to said device via included signal processing stages within said receiver, the combination comprising: a source of alternating voltage; first means coupling said voltage source to energize said horizontal oscillator to provide output signals to said second switching means for alternatively operating it and said first switching means in their conductive and non-conductive states; second means coupled to said second switching means for providing energizing potentials for said cathode-ray filament to power said kinescope, said potentials being of a magnitude dependent upon the relative conduction time of said second switching means as compared to that of said first switching means; third means coupled to said voltage source for providing energizing potentials for said signal processing stages for developing said image signals for reproduction; said third means including third switching means for energizing said signal processing stages when it is desired to enable image reproduction by said television receiver and for deenergizing said signal processing stages when it is desired to disable said image reproduction, with said third switching means being additionally coupled to inactivate said first switching means when image reproduction is disabled, to alter the relative conduction times of said first and second switching means in a direction to reduce the magnitude of energizing potential continuing to be applied to said cathoderay filament via said oscillator and said second switching means, even though said receiver is switched to its nonoperative condition; and said second means including impedance means serially coupled with said cathode-ray kinescope for selectively controlling the magnitude of energizing potential applied to its filament and the ratio of such potentials as are applied to said cathode-ray filament between the non-operative and operative conditions of said receiver.