SYSTEM FOR ISOLATION OF SOURCE REFERENCE POTENTIAL FROMNETWORK ALTERNATING CURRENT SOURCE IN A TELEVISION SET

摘要

1481518 D.C.-D.C. converting RCA CORPORATION 18 Oct 1974 [23 Oct 1973] 49217/73 Heading H2F [Also in Division H3] In or for a TV receiver, a mains-isolated power supply and line deflection circuit comprises a rectifier 203 coupled to the A.C. mains terminal without a transformer and feeding a smoothing circuit 204 ... 206 which supplies D.C. to a line deflection circuit of the type comprising a bidirectional trace switching device 221, 223 coupled via isolating windings of deflection transformer 230 to a bi-directional retrace switching device 209, 210 coupled to the output of rectifier 203. At least one secondary winding on the line deflection transformer 230 may provide D.C. supply for the rest of the receiver with respect to a reference potential (e.g. ground) isolated from the A.C. mains. As described, a small mains transformer 265 with rectifier 268 provides D.C. for the horizontal oscillator 275 the output of which is coupled via a further isolating transformer 280 to the retrace SCR 209 and directly to the trace SCR 221. At the beginning of each line, trace damper diode 223 is forward biased by the energy stored in line deflection windings 252 at the end of the previous retrace interval. Capacitor 225 and S-shaping capacitor 251 are charged via diode 223. At approximately midway through the line interval, diode 223 becomes reverse biased and SCR 221, previously gated by the horizontal oscillator 275, becomes conductive, reversing the current in windings 230 and in the deflection coils 252. Shortly before the beginning of the retrace interval, SCR 209 is turned on so that capacitor 214 discharges through windings 212 and 230a, the voltage across 230c reverse biasing SCR 221 and causing current to flow in diode 223. Diode 223 then becomes reverse biased and after a further oscillation, the fly-back is terminated by further conduction of diode 223, initiating the next line interval. Inductor 212 may be replaced by the leakage inductance of transformer 230. The fly-back pulses across winding 230b are rectified by a multiplier 260 to provide EHT for the anode of the cathode-ray tube. Trace waveforms across capacitor 246 and across winding 230d are available for supplying other parts of the receiver. In Fig. 1 (not shown) SCR 221 and diode 223 are connected on the primary side of the deflection transformer 230, SCR 221 being triggered by a winding coupled to inductor 208.