Electricity: electrical systems and devices – Safety and protection of systems and devices – With specific voltage responsive fault sensor
Patent
1991-10-11
1994-10-04
DeBoer, Todd
Electricity: electrical systems and devices
Safety and protection of systems and devices
With specific voltage responsive fault sensor
361 86, 361 87, 361 94, 315388, 315411, 348377, H02H 320, H01J 2956
Patent
active
053531876
DESCRIPTION:
BRIEF SUMMARY
The invention relates to the field of protection circuits for television receivers, and in particular, to protection circuits for controlling power supply and deflection systems during overvoltage and overcurrent conditions.
Circuits for the generating operating voltages according to the principles of switched mode power supplies and resonant retrace circuits for generating line deflection currents and high voltage are subject to various overcurrent and overvoltage conditions. These conditions can be most troublesome when the power supply and line deflection circuits are combined in a Wessel configuration, wherein a single switching output stage controls both the switched mode power supply and the line deflection current generation.
A power supply and deflection system in a Wessel is configuration can comprise a switching transistor, power supply and flyback transformers and a horizontal deflection yoke. The switching transistor is coupled to both the power supply transformer, the flyback transformer and the horizontal deflection yoke. The flyback transformer has a number of windings coupled to rectifying circuits for supplying various operating voltages to various loads in the television, for example dynamic loads. The ultor voltage, for example, can represent a very significant dynamic load. The power supply transformer has a primary winding coupled between the switching transistor and a DC voltage source. The power supply transformer also has a secondary winding, coupled to a winding of the flyback transformer by an energy transfer diode. An on/off control signal is generated by a regulator responsive to variations in one or more of the operating voltages, due to the varying loads and resulting energy losses. The switching transistor is responsive to the on/off control signal to replenish the dynamic load losses in the flyback transformer and to control horizontal deflection.
In a Wessel configuration, such a circuit is particularly endangered by overloading. Overloading can result from a number of sources, for example, through a defective component, due to a sudden scene change from dark to light with accompanying high beam current or from other overload causes. In such cases, it is easy to reach saturation of the transformer. High voltage peaks can occur in or across the switching transistor, which can destroy the transistor.
It is an aspect of the invention to provide safety protection s from a plurality of current and voltage overload conditions, by monitoring feedback signals indicative of different voltage and current levels in various parts of a switched mode power supply and line deflection system.
A power supply and deflection system for a television receiver according to this aspect of the invention comprises a first transformer coupled to a deflection yoke and coupled to a derived secondary voltage source for driving a load, for example, for generating an ultor voltage. An on/off switch is responsive to an on/off signal, for example a pulse width modulated signal. A second transformer has a primary winding coupled to the switch and coupled to a DC voltage source and has a secondary winding coupled to the first transformer. The source of DC voltage may be from a bridge rectifier coupled to an AC mains supply.
A first sampling circuit generates a first feedback signal indicative of current flowing from the secondary winding to the first transformer. The first sampling circuit may comprise a sampling resistance coupled between the secondary winding of the first transformer and a source of ground potential, and a circuit for rectifying the voltage developed across the resistance. A first safety circuit responsive to the first feedback signal controls the effect of the on/off signal on the switch when the current flowing from the secondary winding to the first transformer exceeds a threshold, by limiting the on time of the switch to limit the peak value of the current. The on time may be limited by effectively lowering the DC level of the on/off control signal.
A second sampling circuit generates
REFERENCES:
patent: 3898523 (1975-08-01), Wessel
patent: 3979640 (1976-09-01), Fischman et al.
patent: 4042858 (1977-08-01), Collette et al.
patent: 4343028 (1982-08-01), Hicks
patent: 4965496 (1990-10-01), Haferl
"A New Horizontal Output Deflection Circuit" by P. L. Wessel, IEEE Transactions on Broadcast and Television Receivers, Aug. 1972, vol. BTR-18, No. 3, pp. 177-182.
"Low Power Consumption Drive for Wessel Horizontal Deflection System", by M. Fischman et al., IEEE Transactions on Consumer Electronics, vol. CE-21, No. 4, Nov. 1975, pp. 396-403.
"Selbstregelnde Transistor-Horizontalablenkschaltung fur Farbportables" by U. Hartmann et al., Funkschau, 1977, vol. 18, pp. 97-104.
Favreau Jean C.
Meinertz Friedrich
Oh Chon S.
DeBoer Todd
Fried Harvey D.
Laks Joseph J.
Thomson Consumer Electronics S.A.
Tripoli Joseph S.
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