| 摘要 |
1500664 Overload cut-out arrangements in television power supply circuits INTERNATIONAL STANDARD ELECTRIC CORP 6 July 1976 [8 July 1975] 27983/76 Heading H2F In a power supply circuit for a television receiver including a controlled semi-conductor switch or thyristor Th for interrupting the supply current iA in the event of overloads in the scanning circuits, a control pulse derived from the line scan pulses being for this purpose applied to the gate electrode of the switch, and in which the switch is by-passed by a resistor R9 for allowing sufficient current to flow to the scanning circuits for producing a control pulse sufficient to operate the switch during the starting phase, a signal, which is out of phase with respect to the wave form of the voltage VA at the input, e.g. from a rectifier G.R., to the thyristors, is applied to the gate electrode of the switch Th to modify the current iG flowing thereto, such as to avoid firing of the thyristor Th in the starting phase at a time when the voltage UA is at a maximum. The signal may be produced in various ways. In Fig. 2a, a resistor R31 connected between point 3 in a smoothing circuit C3, R4, C4 and point 4 in the circuit of the gate electrode replaces the biasing resistor (R3, Fig. 1a, not shown) in a known circuit where it would be connected between points 2 and 4. The phase change introduced by the smoothing circuit is thereby applied to the current iG. Resistor R31 may be replaced by a capacitor (C5, Fig. 3, not shown) in which case a biasing resistor (R3) is also used. Alternatively, various circuits may be used between points 1 and 4, such as a circuit for sharpening the waveform appearing at point 1 to change the phase of its peak, a phase inverter, Fig. 4b, or a transformer (Fig. 5, not shown), connected such as to act substantially as a phase inverter. |
