High-voltage switching for three-color line-sequential color television

Abstract

This specification discloses a color television system of the type in which a full color image is produced by superimposed red and white images corresponding to different color video signals representing different wavelength contents of the televised scene. The red and white images are produced by accelerating the electron beam to different velocities and the velocity of the electron beam is switched between these different velocities to produce the two superimposed images at the end of each line scan. The system incorporates a high voltage switching system to switch the voltage level applied to the screen of the picture tube in order to provide the necessary velocity switching of the electron beam. This switching comprises a transformer, the second winding of which is coupled with the relatively large capacitance provided by the screen of the picture tube. The primary side of the transformer is switched between open circuit and short circuit conditions. Energy is coupled into .[.and out of.]. the resonant circuit comprising the transformer inductance and the capacitance of the picture tube during a short circuit condition to cause the switching between high voltage levels on the picture tube.

What I claim as new and desire to secure by Letters Patent of the United States is: 
     
       1. Apparatus for producing stepped voltages, comprising inductive means in resonant-circuit combination with capacitance, means for .[.coupling.]. .Iadd.transferring .Iaddend.electrical energy in a direction into said resonant-circuit combination while simultaneously temporarily lowering the effective inductance of said inductive means in said combination, means for .[.coupling.]. .Iadd.transferring .Iaddend.electrical energy in a direction .[.out of.]. .Iadd.within .Iaddend.said resonant-circuit combination while simultaneously temporarily lowering the effective inductance of said inductive means in said combination, at least one of said .[.coupling.]. .Iadd.transferring .Iaddend.means including means for .[.coupling.]. .Iadd.transferring .Iaddend.the total of said energy in one of said directions in more than one discrete step at different times, one of said .[.coupling.]. .Iadd.transferring .Iaddend.means including means for supplying electrical energy to storage simultaneously with its lowering of said effective inductance, and the other of said .[.coupling.]. .Iadd.transferring .Iaddend.means including means for discharging the storage of said energy simultaneously with its lowering of said effective inductance. 
     
     
       2. Apparatus for producing stepped voltages as set forth in claim 1 wherein said means for .[.coupling.]. .Iadd.transferring .Iaddend.the total of said energy in one of said directions includes means for .[.coupling.]. .Iadd.transferring .Iaddend.portions of the total of said energy in said one of said directions in immediate succession to one another after a predetermined time delay. 
     
     
       3. Apparatus for producing stepped voltages as set forth in claim 2 wherein said means for .[.coupling.]. .Iadd.transferring .Iaddend.the total of said energy in one of said directions includes means for .[.coupling.]. transferring two portions which comprise the total of said energy in said one of said directions. 
     
     
       4. Apparatus for producing stepped voltages as set forth in claim 3 wherein said one of said directions comprises the direction into said resonant-circuit combination. 
     
     
       5. Apparatus for producing stepped voltages as set forth in claim 3 wherein said means for .[.coupling.]. .Iadd.transferring .Iaddend.energy into and .[.out of.]. .Iadd.within .Iaddend.said resonant-circuit combination includes means for successively and repeatedly coupling said two portions of said energy in one of said directions and then coupling the total of said energy in the other of said directions, each after a predetermined time delay. 
     
     
       6. Apparatus for producing stepped voltages, comprising inductive means having an inductance portion connected in resonant-circuit combination with capacitance, said inductive means including inductance-changing means coupled with said inductance portion and capable of being switched between different states in which it causes said inductance portion to exhibit different values of inductance, and control means for switching said inductance-changing means between said different stages, said control means including means for coupling a predetermined amount of electrical energy into the resonant-circuit combination synchronously with the occurrence of certain of said states, .[.and means for coupling said amount of electrical energy out of said combination synchronously with the occurrence of certain of said states, at least one of.]. said coupling means including means for coupling said predetermined amount of energy in more than one step at different times during occurrence of certain of said states. 
     
     
       7. Apparatus for producing stepped voltages as set forth in claim 6 wherein said inductive means comprises a transformer, wherein said inductance portion comprises a winding of said transformer, wherein said inductance-changing means includes primary winding means inductively coupled with said transformer winding, and wherein said different states include a substantially short-circuited state and a substantially open-circuited state of said primary winding means. 
     
     
       8. Apparatus for producing stepped voltages as set forth in claim 7 wherein said means for coupling said energy into said combination comprises low-impedance D-C source means and means for intermittently drawing current from said source means through said primary winding means in a sense to shock-excite said combination in one direction and to change the state thereof to said substantially short-circuited state. 
     
     
       9. Apparatus for producing stepped voltages as set forth in claim 8 wherein said certain of said states comprises said substantially short-circuited state, and .[.wherein said.]. .Iadd.further including .Iaddend.means for .[.coupling.]. .Iadd.transferring .Iaddend.energy .[.out of.]. .Iadd.within .Iaddend.said combination .[.comprises means for.]. .Iadd.by .Iaddend.intermittently drawing current through said primary winding means in a sense to excite said combination in the opposite direction. 
     
     
       10. Apparatus for producing stepped voltages as set forth in claim 9 wherein said means for coupling said energy into said combination includes means for storing energy intermittenly drawn from said source means, and wherein said means for .[.coupling.]. .Iadd.transferring .Iaddend.energy .[.out of said combination.]. includes means for intermittently drawing current through said primary winding means at least in part from said means for storing energy. 
     
     
       11. Apparatus for producing stepped voltages as set forth in claim 9 wherein said means for intermittently drawing current from said source means and from said means for storing energy includes a plurality of electronic valving means and means for electrically biasing different ones of said valving means into conductive states periodically in a predetermined sequence. 
     
     
       12. Apparatus for producing stepped voltages as set forth in claim 11 wherein said valving means comprise semiconductor current-controlling devices each adapted to conduct current flow therethrough separately responsive to electrical biasing thereof into a conductive state, and wherein said means for electrically biasing comprises means for applying to gating electrodes of said devices spaced pulses which bias said devices into a conductive state, said pulses being of durations not substantially in excess of one-half cycle of the natural frequency exhibited by said combination when the inductance exhibited by said transformer windings is relatively low as the result of a substantially short-circuited state of said primary winding means. 
     
     
       13. Apparatus for producing stepped voltages as set forth in claim 12 wherein said means for coupling said energy into said combination includes means for storing energy intermittently drawn from said source means, and wherein said valving means includes means connecting said primary winding means with said source means through at least one of said devices, and means connecting said primary winding means in discharging relation to said means for storing energy through at least another one of said devices. 
     
     
       14. Apparatus for producing stepped voltages as set forth in claim 13 wherein said source means includes sources of at least different D-C voltage levels, and wherein said means connecting said primary winding means with said source means includes means connecting said primary winding means with one of said sources through one of said devices, and means connecting said primary winding means with a different one of said sources through a different one of said devices. 
     
     
       15. Apparatus for producing stepped voltages as set forth in claim 14 wherein said means for storing energy comprises a storage capacitor, and wherein the capacitance of said capacitance is smaller than that of said storage capacitor and absorbs most of the energy which it shares with said storage capacitor. 
     
     
       16. Apparatus for producing stepped voltages comprising inductive means in resonant-circuit combination with capacitance, at least three control means each electrically energizable to conduct current and thereby change the effective inductance of said inductive means, means for coupling electrical energy into said resonant-circuit combination synchronously with the change in effective inductance of said inductive means by at least one of said control means, means for electrically .[.coupling.]. .Iadd.transferring .Iaddend.energy .[.out of.]. .Iadd.within .Iaddend.said resonant circuit synchronously with the change in effective inductance of said inductive means by at least one other of said control means, and means for energizing said control means to conduct currents in a predetermined repeated sequence, .[.said means for coupling energy coupling.]. substantially the same amount of energy .Iadd.being coupled .Iaddend.into and .[.out of.]. .Iadd.transferred within .Iaddend.said resonant-circuit combination during each said sequence. 
     
     
       17. Apparatus for producing stepped voltages comprising a transformer including primary and secondary winding means, a capacitive load in parallel circuit combination with said secondary winding means, a first electrical power source of relatively low D-C voltage level, a second electrical power source of relatively high D-C voltage level, storage capacitor means, first, second and third thyristors, means connecting said primary winding means and said storage capacitor means with said first source through said first thyristor and with said second source through said second thyristor, means connecting said primary winding means in discharging relation to said storage capacitor means through said third thyristor, and means for periodically gating said thyristors into conduction a different spaced times in a predetermined sequence. 
     
     
       18. Apparatus for producing stepped voltages as set forth in claim 17 wherein said gating means includes means gating said thyristors in a sequence wherein gating of said second thyristor follows gating of said first thyristor in said sequence. 
     
     
       19. Apparatus for producing stepped voltages as set forth in claim 17 wherein said gating means includes means sequentially gating said thyristors into conduction for periods each not substantially in excess of about one-half cycle of the natural resonant frequency of said combination which is exhibited when said thyristors are gated into conduction. 
     
     
       20. Apparatus for producing stepped voltages as set forth in claim 19 wherein said means sequentially gating said thyristors into conduction gates said thyristors for said periods with predetermined spacings therebetween which are in excess of said periods. 
     
     
       21. Apparatus for producing stepped voltages as set forth in claim 19 wherein said primary winding means comprises a single winding, and wherein said third thyristor is connected to conduct current in a direction different from the currents conducted by said first and second thyristors. 
     
     
       22. Apparatus for producing stepped voltages as set forth in claim 19 wherein said primary winding means comprises two windings, and wherein said connecting means includes means connecting one of said primary windings with said sources through said first and second thyristors, and means connecting the other of said primary windings in discharging relation to said storage capacitor means through said third thyristor. 
     
     
       23. Apparatus for producing stepped voltages as set forth in claim 19 wherein said primary winding means comprises three windings, and wherein said connecting means includes means separately connecting two of said primary windings with said sources through different ones of said first and second thyristors, and means separately connecting the third of said primary windings in discharging relation to said storage capacitor means through said third thyristor. 
     
     
       24. Apparatus for producing stepped voltages as set forth in claim 17 wherein said first electrical power source comprises a further storage capacitor. 
     
     
       25. Apparatus for producing stepped voltages as set forth in claim 17 further comprising a further D-C source of high voltage, and means superimposing the voltage across said combination upon the voltage from said last-mentioned D-C source. 
     
     
       26. Television apparatus wherein scanning electrons in a picture tube are modulated by different accelerating potentials, comprising inductive means in resonant-circuit combination with capacitance, at least three control means each electrically energizable to conduct current and thereby change the effective inductance of said inductance means, means for coupling electrical energy into said resonant-circuit combination synchronously with the change in effective inductance of said inductance means by at least one of said control means, means for electrically .[.coupling.]. .Iadd.transferring .Iaddend.energy .[.out of.]. .Iadd.within .Iaddend.said resonant-circuit combination synchronously with the change in effective inductance of said inductance means by at least one other of said control means, means energizing said control means to conduct currents in a predetermined repeated sequence in synchronism with the line-scanning frequency for the picture tube, and means applying electrical signals from said resonant-circuit combination to the picture tube in control of the modulation of the scanning electrons thereof, .[.said means for coupling energy coupling.]. substantially the same amount of energy .Iadd.being coupled .Iaddend.into and .[.out of.]. .Iadd.transferred within .Iaddend.said resonant-circuit combination during each said sequence. 
     
     
       27. Television apparatus as set forth in claim 26 wherein said inductive means comprises a transformer including secondary winding means in said combination and primary winding means, wherein each of said control means includes first, second and third thyristors, wherein said means for coupling energy into said combination includes first and second electrical power sources of relatively low and high D-C voltage levels, respectively, and means connecting said primary winding means with said first and second sources through said first and second thyristors, respectively, wherein said means for .[.coupling.]. .Iadd.transferring .Iaddend.energy .[.out of said combination.]. includes a storage capacitor and means connecting said capacitor for charging through said first and second thyristors and for discharging through said primary winding means and said third thyristor, and wherein said means energizing said control means comprises means applying gating pulses to gating leads of said thyristors in said predetermined repeated sequence. 
     
     
       28. Television apparatus as set forth in claim 27 wherein said means applying gating pulses applies brief gating pulses to said first and then to said second thyristor in said sequence, said gating pulses being spaced by substantially the duration of one line scan in said picture tube. 
     
     
       29. Television apparatus as set forth in claim 27 wherein the capacitance of said capacitance is of the order of 10.sup. -6  times that of said storage capacitor, and wherein said means applying electrical signals from said combination to said picture tube includes a further D-C source of high voltage and means applying electrical signals from said combination to an accelerating anode of said picture tube in superimposed relation to the high voltage from said last-mentioned D-C source. 
     
     
       30. The method of producing stepped voltages across a highly capacitive load in tuned circuit combination with inductive means which comprises intermittently coupling electrical energy into the combination in a plurality of successive steps while simultaneously temporarily lowering the effective inductance of the inductive means in the combination, intermittently .[.coupling.]. .Iadd.transferring .Iaddend.energy .[.out of.]. .Iadd.within .Iaddend.the combination at times following said successive steps while simultaneously temporarily lowering the effective inductance of the inductive means in the combination, and lowering the effective inductance of said inductive means in the combination at the times of the different intermittent couplings .Iadd.and transfers .Iaddend.by storing electrical energy and discharging the stored energy. 
     
     
       31. The method of producing stepped voltages as set forth in claim 30 wherein the storing of electrical energy is performed while coupling energy into said combination and the discharging of the stored energy is performed while .[.coupling.]. .Iadd.transferring .Iaddend.energy .[.out of.]. .Iadd.within .Iaddend.said combination. 
     
     
       32. The method of producing stepped voltages as set forth in claim 31 wherein said coupling of energy into said combination is performed in two successive steps, and wherein the storing and discharging includes cyclically storing and discharging substantially the same amount of energy. .Iadd. 33. Apparatus for generating a three-level stepped voltage waveform across a capacitive load comprising: an inductive reactor having an output circuit for connection to said capacitive load and an input circuit;   first controlled rectifier means for selectively producing a pulse of current through said input circuit in one direction thereby changing the charge on said capacitive load to obtain a first voltage on said load with respect to the initial voltage on said load;   second controlled rectifier means for selectively shorting said input circuit to produce a pulse of current through said input circuit in the opposite direction thereby changing the charge on said load to obtain a second voltage on said load which is of opposite polarity to said first voltage with respect to said initial voltage;   third controlled rectifier means for selectively producing a second pulse of current through said input circuit in said one direction, the sum of the two said pulses in said one direction being substantially equal in magnitude to the one pulse in said opposite direction thereby to return said load substantially to said initial voltage; and   means for sequentially energizing said first, second and third rectifier means at timed intervals, each of said rectifiers being reverse biased and turned off by resonance of said inductive reactor with said capacitive load after each respective current pulse is completed, whereby a three-level stepped voltage waveform is generated across said load. .Iaddend..Iadd. 34. Apparatus for generating a three-level stepped voltage wave form across a capacitive load comprising:   an inductive reactor having an output circuit for connection to said capacitive load and an input circuit;   first controlled rectifier means for selectively connecting said input circuit across a voltage source to produce a pulse of current through said input circuit in one direction thereby changing the charge on said capacitive load to obtain a first voltage on said load with respect to the initial voltage on said load;   second controlled rectifier means for selectively shorting said input circuit to produce a pulse of current through said input circuit in the opposite direction thereby changing the charge on said load to obtain a second voltage on said load which is of opposite polarity to said first voltage with respect to said initial voltage;   third controlled rectifier means for selectively connecting said input circuit across a voltage source thereby to produce a second pulse of current in said one direction, the sum of the two said pulses in said one direction being substantially equal in magnitude to the one pulse in said opposite direction thereby to return said load substantially to said initial voltage; and   means for sequentially energizing said first, second and third rectifier means at timed intervals, each of said recitifiers being reverse biased and turned off by resonance of said inductive reactor with said capacitive load after each respective current pulse is completed whereby a three-level stepped voltage waveform is generated across said load.   
     
     
        .Iaddend..Iadd. 35.  Apparatus as set forth in claim 34 wherein said inductive reactor comprises a transformer having a primary winding and a secondary winding which comprises said input circuit and said output circuit respectively. .Iaddend..Iadd. 36. Apparatus as set forth in claim 34 wherein said first, second and third rectifier means comprises SCR's. .Iaddend..Iadd. 37. In a color display system including a kinescope having a phosphor screen which, in response to impinging electrons, emits light of different colors when different electron accelerating voltages are applied thereto, said screen comprising a capacitive electrical load; apparatus for applying three different accelerating voltages in sequence to said screen comprising: a step-up transformer having a high voltage secondary winding one end of which is connected to said screen and the other end of which is connected to a high voltage D.C. bias source, said transformer having also a primary winding which is inductively coupled to said secondary winding;   first controlled rectifier means for selectively connecting said primary winding across a first voltage source to produce a pulse of current through said primary winding in one direction thereby to obtain a first voltage on said screen with respect to the voltage provided by said bias source;   second controlled rectifier means for selectively shorting said primary winding to produce a pulse of current through said primary winding in the opposite direction thereby to obtain a second voltage on said screen which is of opposite polarity to said first voltage with respect to the voltage provided by said bias source;   third controlled rectifier means for selectively connecting said primary winding across a second voltage source thereby to produce a second pulse of current in said one direction, the sum of the two said pulses in said one direction being substantially equal in magnitude to the one pulse in said opposite direction thereby to return said screen substantially to the voltage provided by said bias source; and   means for sequentially energizing said first, second and third rectifier means at timed intervals, each of said rectifiers being reverse biased and turned off by resonance of said transformer with said capacitve screen after each respective current pulse is completed whereby three different accelerating voltages are applied in sequence to said screen. .Iaddend.