| 摘要 |
1509182 Converting circuits for television receivers COMMUNICATIONS PATENTS Ltd 14 April 1975 [17 April 1974] 16887/74 Heading H2F In a TV receiver, having a line scanning circuit including a commutating capacitor arrangement C4 supplied from a D.C. source C5B which includes a controlled rectifier THY1, means THY2 are provided for recovering energy from the commutating capacitor C4 of the line deflection circuit and returning it to the source C5B of D.C. voltage and further means, TR1 responsive to the failure of the energy recovery means for switching off the controlled rectifier THY1. In the TV receiver described the mains voltage LN is rectified by diode D and thyristor THY1 and feeds a smoothing circuit C5A, C5B, the output of which is passed via diodes D10, D11 and terminal X to the line deflection circuit comprising thyristor THY22 and commutating capacitor C4. An auxiliary winding W1 on the line output transformer LT5 provides positive and negative square waves at Y and Z. These are compared and used to control transistors TR3, TR2 which determine the conduction angle of the energy recovering thyristor THY2 so as to tend to maintain a constant voltage on C4 and hence constant scan amplitude. Under fault conditions, the pulse amplitude across R17 will increase, breaking down Zener diode D9, turning on THY2 so as to minimize the voltage at terminal X. If a fault occurs in THY2, an A.C. waveform will appear across R17 which turns on TR1 so as to block the gate signals on the rectifying thyristor THY1 and so inhibit its operation. Alternatively, a resistor may be included in the cathode lead of THY2 which normally provides a hold off bias for TR1. |
