Abstract An input switching thyristor of a deflection circuit is selectively excited at a sweep rate by a transistorized driver stage. A separate protective thyristor is disposed in a DC power source that supplies operating bias to the driver stage and to the switching thyristor via a supply capacitor. Initially, the supply capacitor is partially charged through a high-ohmic shunt resistor that budges the protective thyristor, whose control electrode is coupled to the output of the switching thyristor. A portion of the resulting voltage across the partially charged supply capacitor is applied via a voltage divider and a Zener diode to the base of a threshold-operated transistor that normally blocks the driver stage. When the supply capacitor has charged to a predetermined minimum value necessary to assume turn-on of the protective thyristor, the threshold-operated transistor is triggered to permit the driver stage to operate the switching thyristor at the sweep rate. The resulting turn-on of the protective thyristor permits the rapid completion of charge of the supply capacitor to its normal operating voltage, and thereafter provides full overload protection for the deflection circuit.
In a communications receiver wherein (a) a first input switching thyristor of a deflection circuit in the receiver is pulsed at a sweep rate by a driver stage when the latter is excited, (b) a supply capacitor is chargeable through a second protective thyristor by-passed by a high-impedance shunt to provide operating bias to both the driver stage and the switching thyristor, and, (c) the output of the switching thyristor is coupled to the control electrode of the protective thyristor, the improvement which comprises: normally disabled, thresholdoperated gating means connected to the driver stage for preventing the excitation of the driver stage by the supply capacitor while the gating means remains disabled; and means for coupling a selected portion of the voltage across the supply capacitor to the gating means for enabling the gating means when the voltage across the supply capacitor exceeds a predetermined mininmum value.
Claim 2
Dependent Claim
147 words
In a communications receiver wherein (a) a first input switching thyristor of a deflection circuit in the receiver is pulsed at a sweep rate by a driver stage when the latter is excited, (b) a supply capacitor is chargeable through a second protective thyristor by-passed by a high-impedance shunt to provide operating bias to both the driver stage and the switching thyristor, and, (c) the output of the switching thyristor is coupled to the control electrode of the protective thyristor, the improvement which comprises: normally disabled, thresholdoperated gating means connected to the driver stage for preventing the excitation of the driver stage by the supply capacitor while the gating means remains disabled; and means for coupling a selected portion of the voltage across the supply capacitor to the gating means for enabling the gating means when the voltage across the supply capacitor exceeds a predetermined mininmum value.
Claim 3
Dependent Claim
66 words
The improvement as defined in claim 1, in which the gating means comprises a first transistor having its collector emitter path connected in series with the driver stage, and in which the coupling means comprises, in combination, a voltage divider having its input terminals connected across the supply capacitor, and means for applying the output of the voltage divider to the base of the first transistor.
Claim 4
Dependent Claim
16 words
The improvement as defined in claim 2, in which the applying means comprises a Zener diode.
Claim 5
Dependent Claim
28 words
The improvement as defined in claim 2, in which the driver comprises a second transistor, and in which the first and second transistors are of opposite conductivity type.