GB1429998A - Instant-on circuit for a television receiver - Google Patents

Abstract

1429998 Converting RCA CORPORATION 8 May 1973 [10 May 1972 3 July 1972] 21749/73 Heading H2F In an "instant on" circuit for a TV receiver of the type in which the line deflection circuit comprises trace and retrace switching devices 46, 42, power for the cathode-ray tube filament is derived from a transformer 26 the current in which is periodically changed by the retrace 42 and in which the "instant-on-off" switch 90 in its OFF position is arranged to disable the action of the trace switch 46 and inhibit at least one of the signal processing stages (e.g. the video 110). As described, the A.C. supply 10 is rectified at 16 and smoothed at 18 and feeds current via two windings of transformer 26 to the line deflection circuit comprising trace thyristor 46 and retrace thyristor 42. The current in transformer 26 is periodically changed at the frequency of the line oscillator 30 so that the resulting voltage in winding 26d supplies the filament of the cathode-ray tube 94. The voltage induced in winding 26c is rectified at 80 and supplies the video 110 when the "instant-on-off" switch 90 is in its ON position. In the OFF position of switch 90, the trace switch 46 is short-circuited, the circuit being so arranged that under such conditions the cathode-ray tube filament is operated at 5 v., the tuning of the line deflection circuit being changed when the switch 90 is set to ON so that the filament voltage is then increased to its operating value of 6 v. Further adjustment of the standby and ON filament voltages is achieved by diode 302, resistor 300 and possibly another resistor (Figs. 2 and 3, not shown). A winding 68c supplies flyback pulses to EHT rectifier and flywheel sync. circuits. The voltage across windings 68b is rectified at 130 and supplies power to the chroma amplifier 124. The field deflection circuit 98 is switched by contacts 4 and 5 of switch 90. A thermistor 14 limits the peak current in rectifier 16.