Rca Inc.

James E Hicks

Ronald E Fernsler

David W Luz

Chin Piao Huang

Nancy D Graves

Leslie N Thibodeau

John Chen

Ravadee Kliebphipat

A protection circuit for a video display apparatus causes shutdown to occur at substantially the same high voltage level for all fault conditions. The video display apparatus incorporates an SCR regulator and a high voltage transformer tuned to the third harmonic. To counter the effect of shutdown to occur at a higher voltage level for a shorted SCR fault than for other faults, the SCR anode control pulse is processed to provide a signal having different voltage levels for normal SCR operation and shorted SCR operation. The voltage level which occurs during a shorted SCR condition is selected to cause shutdown of the video display apparatus at substantially the same high voltage level as that for other fault conditions.

Regulator fault protection circuit

In a switching regulator power supply, the primary winding of a switching transformer is coupled to a source of input voltage and to a power switch. Secondary supply voltages for a load circuit such as a television receiver are obtained from a secondary winding of the transformer. A regulator control circuit develops a pulse width modulated signal that is used to control the duty-cycle of the power switch for regulating the supply voltages. A disabling circuit is coupled to the regulator control circuit and is responsive to a low bias voltage at a disabling control terminal to change the duty cycle of the power switch in a manner that disables the normal transfer of energy to the load circuit. A disabling input terminal is coupled to an input terminal of a comparator and to the disabling control terminal. The comparator output is coupled to a disabling switch having an output coupled to the disabling control terminal. A first signal generator is responsive to a first condition requiring the disabling of the power supply and develops at the disabling input terminal a first bias voltage that is low enough to, in turn, bias low the disabling control terminal to initiate the disabling of the power supply. A second signal generator is responsive to a second condition requiring the disabling of the power supply and develops a second bias voltage that is higher than the first bias voltage and is high enough to activate the comparator. When the comparator is activated, the disabling switch turns on to bias low the disabling control terminal to initiate the disabling of the power supply.

Shutdown circuit for a switching regulator in a remote controlled

In a television receiver having an SCR switching regulator power supply, excessive power supply loading or high line voltage may cause abnormal operation of the switching SCR resulting in a rapid variation of the regulated supply voltage above its regulated level. This voltage variation causes high peak current in the horizontal output transistor, causing it to fail. A detector circuit monitors both the average current and the peak current through the horizontal output transistor and causes the receiver to be disabled in the event either current level becomes excessive.

Horizontal output transistor protection circuit

A television receiver incorporates a common mechanism for disabling the receiver via the high voltage or fault protection circuit and via the remote control during normal operation. In one embodiment, the protection circuit is energized by the remote control in order to turn the receiver off. The remote control is used to reset the protection circuit in order to turn the receiver on.

Television receiver disabling circuit

A horizontal deflection circuit for a television receiver includes a switching output transistor which may experience high collector current under certain receiver conditions. A resistor is placed in the transistor emitter path to provide negative feedback to the base drive circuit in order to control transistor conduction. The horizontal deflection yoke is returned to the emitter of the output transistor so that yoke current will not flow through the resistor, which would otherwise degrade deflection linearity.

Horizontal deflection circuit

A high voltage generator of a television display is responsive to an alternating voltage, such as a retrace pulse voltage, for developing an ultor voltage at an ultor terminal. A protection circuit for the high voltage generator includes a comparator that develops a television display disabling signal when activated. A circuit that develops a sense voltage representative of the ultor voltage is coupled to an input terminal of the comparator so as to develop the disabling signal when the ultor voltage exceeds a predetermined level. To provide an overload disabling capability, an ultor beam current sensing circuit is coupled to the input terminal of an operational amplifier. The output terminal of the amplifier is coupled to a bias voltage source and to an input terminal of the comparator. When the ultor beam current exceeds a predetermined level indicative of high voltage generator overload operation, the operational amplifier applies the bias voltage to the comparator input to energize the comparator into developing the disabling signal. The magnitude of the bias voltage is such as to activate the comparator in substantial independence of the value of the ultor voltage sense voltage.

Television receiver high voltage generator protection circuit

A retrace pulse voltage is applied to a first flyback transformer winding of a horizontal deflection circuit to develop retrace pulse voltages across other flyback transformer windings. Second and third windings of the flyback transformer are coupled in a series arrangement with a controllable switch across a source of input voltage. A regulator control circuit turns on the SCR at a controllable instant within the trace interval of each deflection cycle to generate input current in the series arrangement. When the retrace pulse voltage is applied to the flyback transformer first winding, the input current begins to decrease in magnitude, commutating off the SCR within the retrace interval. The leakage inductance associated with the series arrangement of flyback transformer second and third windings and the total reflected retrace pulse voltage developed by the two windings determine the instant within retrace that the SCR is commutated off. The third winding is loosely coupled with the first winding, whereas the second winding is tightly coupled with the first winding. By varying the second to third winding turns ratio, the amount of leakage inductance in the series arrangement may be varied without significantly altering the magnitude of the total reflected retrace pulse voltage.

Commutated SCR regulator for a horizontal deflection circuit

A horizontal deflection circuit drives a deflection winding and an ultor voltage generator. The energizing voltage for the horizontal deflection generator is regulated by a switching regulator including an SCR, a filter inductor, a filter capacitor and an SCR turn-off winding. The turn-off winding couples a retrace pulse to the SCR during each horizontal retrace interval to turn the SCR off in preparation for the following regulation interval. A second winding is magnetically coupled to the deflection circuit and through a diode to the filter inductor for providing a path by which current can continue to flow in the filter inductor during SCR nonconduction and which effectively couples the filter inductance across the deflection winding. Variations in kinescope beam current cause corresponding variations in the current through the filter inductor at the end of the trace interval. The current variations in the filter inductor cause the diode to become nonconductive at times during the retrace interval which are related to the beam current, thereby changing the average time during which the filter inductor parallels the deflection winding and varying the retrace pulse duration in such a manner as to improve the ultor voltage generator regulation.

Growing community of inventors

New Palestine, IN, United States of America

James E Hicks