Malfunction detecting apparatus for use in a CRT deflection circuit

Claim 2

Apparatus for preventing the generation of an excessively high voltage by the high voltage circuit of a television receiver, comprising: a horizontal output circuit responsive to horizontal scanning pulses and including a switching device, resonant capacitor and flyback transformer connected for producing periodic flyback pulses having a normal frequency component; power supply means coupled to said switching device for applying an operating voltage thereto; first detecting means comprising high pass filter means coupled to said flyback transformer to allow only high frequency components above said normal frequency to pass through, and rectifying means for detecting a high frequency component included in said flyback pulses in the event of a malfunction of said resonant capacitor, said high frequency component causing said high voltage circuit to generate an excessively high voltage; second detecting means coupled to said flyback transformer for detecting an excessive voltage level of said flyback pulses in the event that the operating voltage applied by said power supply means exceeds a predetermined level; switching means coupled to said first and second detecting means and actuated in response to said detected high frequency component and to said detected voltage level, respectively; and means for controlling said horizontal output circuit when said switching means is actuated thereby to reduce the level of said flyback pulses.

Claim 3

The apparatus of claim 1 wherein said second detecting means comprises a secondary winding included in said flyback transformer for producing pulses proportional to said flyback pulses, the amplitudes of said flyback pulses and said produced pulses increasing in the event that said operating voltage applied by said power supply means increases; and threshold detecting means coupled to said secondary winding for actuating said switching means when said produced pulse amplitude exceeds a threshold level.

Claim 4

The apparatus of claim 2 wherein said threshold detecting means comprises rectifier means for producing a rectified voltage corresponding to said produced pulse amplitude; reference voltage means; and comparator means for comparing said rectified voltage to said reference voltage, and to actuate said switching means when said rectified voltage exceeds said reference voltage.

Claim 5

The apparatus of claim 3 wherein said reference voltage means comprises a Zener diode.

Claim 6

The apparatus of claim 4 wherein said switching means is a transistor means, and said comparator means comprises the base-emitter junction of said transistor means, said Zener diode being connected to one of the base and emitter electrodes of said transistor means and supplied with a voltage derived from said rectified voltage, and said rectified voltage being applied to the other of said base and emitter electrodes of said transistor means, such that said transistor means is actuated when the Zener voltage produced by said Zener diode and said rectified voltage combine to forward bias said base-emitter junction.

Claim 7

The apparatus of claim 1 wherein said horizontal output circuit includes a voltage-controlled oscillator for driving said switching device, and oscillator control means for synchronizing said oscillator with said horizontal scanning pulses; and wherein said means for controlling said horizontal output circuit comprises means for supplying a predetermined voltage to said voltage-controlled oscillator through said actuated switching means, whereby said switching device is driven at a predetermined rate.

Claim 8

In a cathode ray tube having a high voltage circuit including a flyback transformer coupled to a horizontal deflection circuit for generating a normally high voltage in response to the flyback pulses produced by said flyback transformer during periodic retrace intervals, said horizontal deflection circuit including a switching device driven by horizontal scanning pulses and a resonant capacitor coupled to said flyback transformer for determining said flyback pulses, and a relatively low voltage power supply for providing an operating voltage to said switching device, apparatus for preventing said high voltage circuit from generating an excessively high voltage, comprising: a high-pass filter coupled to said flyback transformer for passing high frequency components included in said flyback pulses in the event of a malfunction in said horizontal deflection circuit, such as the disconnection of said resonant capacitor; first rectifying means coupled to said high-pass filter for producing an actuating signal in response to said passed high frequency components; second rectifying means coupled to said flyback transformer for producing a signal level proportional to the amplitude of said flyback pulses, and signal level increasing in the event that said low voltage power supply provides an increased operating voltage; comparator means coupled to said second rectifying means for comparing said signal level to a reference level; switch means coupled to said first rectifying means and to said comparator means, said switch means being actuated by said actuating signal and also when said signal level exceeds said reference level to supply a control signal; and means for varying the frequency of said horizontal scanning pulses in response to said control signal so as to decrease the amplitude of said flyback pulses.

Claim 9

In a cathode ray tube having a high voltage circuit including a flyback transformer coupled to a horizontal deflection circuit for generating a normally high voltage in response to the flyback pulses produced by said flyback transformer during periodic retrace intervals, said horizontal deflection circuit including a switching device driven by horizontal scanning pulses and a resonant capacitor coupled to said flyback transformer for determining said flyback pulses, and a relatively low voltage power supply for providing an operating voltage to said switching device, apparatus for preventing said high voltage circuit from generating an excessively high voltage, comprising: a high-pass filter coupled to said flyback transformer for passing high frequency components included in said flyback pulses in the event of a malfunction in said horizontal deflection circuit, such as the disconnection of said resonant capacitor; first rectifying means coupled to said high-pass filter for producing an actuating signal in response to said passed high frequency components; second rectifying means coupled to said flyback transformer for producing a signal level proportional to the amplitude of said flyback pulses, and signal level increasing in the event that said low voltage power supply provides an increased operating voltage; comparator means coupled to said second rectifying means for comparing said signal level to a reference level; switch means coupled to said first rectifying means and to said comparator means, said switch means being actuated by said actuating signal and also when said signal level exceeds said reference level to supply a control signal; and means for varying the frequency of said horizontal scanning pulses in response to said control signal so as to decrease the amplitude of said flyback pulses.

Claim 10

The apparatus of claim 7 wherein said switch means comprises transistor means having a base electrode coupled to said first rectifying means to receive said actuating signal; and wherein said comparator means comprises reference voltage means coupled to said base electrode, and means for applying said signal level to the emitter electrode of said transistor means.

Claim 11

The apparatus of claim 8 wherein said means for varying the frequency of said horizontal scanning pulses comprises a voltage-controlled oscillator for generating said horizontal scanning pulses, said voltage-controlled oscillator having a control input coupled to the collector electrode of said transistor means.

Claim 12

The apparatus of claim 7 wherein said comparator means includes a Zener diode for establishing said reference level.