Side pincushion modulator circuit with overstress protection
First Claim
1. A side pincushion correction circuit with overstress protection, comprising:
- a deflection winding;
a trace capacitance coupled to said deflection winding for developing a trace voltage;
first switching means for applying said trace voltage to said deflection winding to generate a deflection trace current in said deflection winding;
a first retrace capacitance coupled to said deflection winding for generating a deflection retrace current in said deflection winding;
a modulator inductance;
a modulator capacitance coupled to said modulator inductance for developing a modulator voltage;
second switching means for applying said modulator voltage to said modulator inductance to generate a sawtooth modulator current in said modulator inductance;
a second retrace capacitance coupled to said modulator inductance for generating a retrace current in said modulator inductance;
a source of operating voltage;
means including a flyback transformer winding coupled to said source of operating voltage for charging said trace and modulator capacitances;
controllable shunting means coupled to said modulator capacitance and responsive to bias voltages for developing a shunt current to control said trace and modulator voltages;
means for applying to said controllable shunting means a vertical rate bias voltage to vary said shunt current at a vertical rate to provide side pincushion correction;
a source of reference voltage; and
means for clamping said modulator capacitance to said source of reference voltage to bypass current from said modulator capacitance when the voltage thereacross exceeds a predetermined level.
1 Assignment
0 Petitions
Accused Products
Abstract
A side pincushion corrected deflection circuit for a television receiver includes a deflection winding, a trace capacitor and a first switch for generating scanning current in the deflection winding. A modulator circuit includes a modulator inductor and capacitor and a second switch for generating a sawtooth modulator current in the inductor. The trace and modulator capacitors are charged from a B+ operating voltage source through the primary winding of a flyback transformer. A transistor stage in the modulator circuit shunts current away from the modulator capacitor to control the modulator and trace capacitor voltages. A vertical rate bias voltage is applied to the transistor stage and varies the shunt current at a vertical rate in a parabolic manner to provide side pincushion correction. Under fault conditions, such as an open-circuited deflection winding or trace capacitor, the modulator capacitor voltage tends to undesirably increase above the peak voltage developed under normal operating conditions. To prevent overstressing the modulator transistor stage, a diode clamp is coupled between the modulator capacitor and a source of reference voltage, thereby preventing the modulator capacitor voltage from substantially exceeding the reference voltage level.
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Citations
5 Claims
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1. A side pincushion correction circuit with overstress protection, comprising:
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a deflection winding; a trace capacitance coupled to said deflection winding for developing a trace voltage; first switching means for applying said trace voltage to said deflection winding to generate a deflection trace current in said deflection winding; a first retrace capacitance coupled to said deflection winding for generating a deflection retrace current in said deflection winding; a modulator inductance; a modulator capacitance coupled to said modulator inductance for developing a modulator voltage; second switching means for applying said modulator voltage to said modulator inductance to generate a sawtooth modulator current in said modulator inductance; a second retrace capacitance coupled to said modulator inductance for generating a retrace current in said modulator inductance; a source of operating voltage; means including a flyback transformer winding coupled to said source of operating voltage for charging said trace and modulator capacitances; controllable shunting means coupled to said modulator capacitance and responsive to bias voltages for developing a shunt current to control said trace and modulator voltages; means for applying to said controllable shunting means a vertical rate bias voltage to vary said shunt current at a vertical rate to provide side pincushion correction; a source of reference voltage; and means for clamping said modulator capacitance to said source of reference voltage to bypass current from said modulator capacitance when the voltage thereacross exceeds a predetermined level. - View Dependent Claims (2, 3, 4, 5)
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Specification