This is a full modular chassis type.
Even it's large and modular construction it's not a simple circuitry.
SABA ULTRACOLOR CHASSIS CM Controlled power supply for a television receiver equipped with remote control:BLAUPUNKT SWITCH MODE POWER SUPPLY.Blaupunkt-Werke GmbH (Hildesheim, DT)
A single isolation transformer supplies both the remote control receiver and the television receiver. A pulse generator such as a blocking oscillator which energizes the primary winding of the isolation transformer has its pulse width controlled in response to the loading of the circuit of the secondary winding of the isolation transformer, as measured by the voltage across a resistor in the circuit of a primary winding. This measuring resistor is interposed between the emitter of the switching transistor of the blocking oscillator and the receiver chassis. A transistor switching circuit for cutting off the low voltage supply to the scanning circuit oscillators of the television receiver is responsive to the output of the remote control receiver, to a signal from an operating control of the television receiver, and to an indication of overcurrent in the picture tube, independently.
an on-off switch for connecting and disconnecting the television receiver and its power supply circuit respectively to and from the electricity supply mains;
pulse generating means arranged for energization through said on-off switch;
an isolation transformer having its primary winding supplied with the output of said pulse generating means;
a power conversion circuit connected to the secondary winding of said isolation transformer for energization thereby, for supplying an operating voltage for the scanning circuits of the television receiver and for supplying a plurality of other voltages to said receiver, at least one of which other voltages is also supplied to said scanning circuits;
means for reducing energy transfer through said pulse generating means to said isolation transformer when said television receiver is in the stand-by condition.
2. A power supply circuit as defined in claim 1, in which said pulse generating means includes rectifying means energized through said on-off switch for supplying direct current for energization of said pulse generating means. 3. A power supply circuit as defined in claim 2, in which said energy transfer reducing means includes means for varying the width (duration) of pulses generated by said pulse generating means in response to the extent of loading of the secondary circuit of said isolating transformer as measured in the primary circuit of said transformer. 4. A power supply circuit as defined in claim 2, in which said pulse generating means includes a blocking oscillator and said energy transfer reducing means includes means for reducing the width (duration) of the pulses generated by said blocking oscillator. 5. A power supply circuit as defined in claim 4, in which said blocking oscillator includes a switching transistor (5) and a load measuring resistor (7) interposed in a connection between the emitter of said switching transistor and the receiver chassis, and in which said pulse width reducing means is responsive to the voltage drop across said load measuring resistor. 6. A power supply circuit as defined in claim 5, in which said pulse width reducing means includes a controllable resistance (10) in the circuit of said blocking oscillator controlled in response to the voltage drop across said load measuring resistor. 7. A power supply circuit as defined in claim 1, in which said operating voltage connected and disconnected to said scanning circuits by said controlled switching means is the low voltage supply voltage (U 3') of the line scan and picture scan oscillators of the television receiver and in which said controlled switching means is controlled so as to switch off said low voltage supply voltage to put the television receiver in the stand-by condition. 8. A power supply circuit as defined in claim 7, in which said controlled switching means includes a first switching transistor (15) at the collector of which there is applied a direct current supply voltage (U 3) energized through said isolating transformer and a second switching transistor (24) for controllably short-circuiting the base bias of said first switching transistor, whereby a stabilized low voltage (U 3') exists at the emitter of said first switching transistor (15) when a positive signal is supplied from an operating control of the television receiver or from said remote control receiver to the base of said second switching transistor (24). 9. A power supply circuit as defined in claim 7, in which said controlled switching means is responsive independently to an overcurrent condition in the picture tube for switching off said low voltage supply voltage (U 3') in response to said overcurrent condition.
In recent times television receivers have frequently been provided with ultrasonic remote control devices for the purpose of offering easier control. As more and more television receivers are utilized in combination with additional equipment, it becomes increasingly necessary to connect the receivers only indirectly to the electric power mains (house wiring). In a known advantageous solution of this problem, a power supply unit includes an isolating transformer which is wired up with a blocking oscillator in the primary circuit. The blocking oscillator is supplied with a d-c voltage which is obtained by rectification of the supply voltage. Compared to the isolating transformers which are directly mains-operated, these so-called switch-mode power supply units have the advantage that they can be made in considerably smaller size, as they are operated at a significantly higher frequency, and the further advantage that they require less expensive means for rectification.
It is necessary to supply television receivers equipped with ultrasonic remote control with the possibility for a stand-by operation in which only the ultransonic receiver is supplied with power and, in some cases, also the heating current for the picture tube. Usually a separate power supply unit is provided for the ultrasonic receiver and the heating of the picture tube, a unit that includes an isolating transformer of its own, the primary winding of which is directly mains-fed. Upon transition from normal operation to stand-by operation, the power supply unit of the blocking osciallator is switched off, so that the television receiver receives only the relatively small quantity of energy required for the ultrasonic receiver and, in some cases, also for the heating of the picture tube.
Because of the required second isolating transformer, this known circuit has the disadvantages that it requires both greater space and greater expenditure.
It is the object of the present invention to develop a simplified power supply unit which does not have the above-mentioned disadvantages.
SUMMARY OF THE INVENTION
Briefly, the television receiver and the ultrasonic receiver are connected to the same isolating transformer; means for the switching from normal operation to stand-by operation and vice versa are placed in the secondary circuit of the isolating transformer, and means are arranged in the primary circuits of the isolating transformer for reducing the amount of energy made available for stand-by operation purposes.
The main advantages of the present invention are that no separate isolating transformer is required for supplying the current during the stand-by operation, and that, during the stand-by operation, it is nevertheless only the power required for this operation which is consumed.
An advantageous embodiment of the present invention obtains reduction of the energy quantum transmitted through the power supply during stand-by by reduction of the pulse width of the pulses generated by the blocking oscillator.
Another advantageous embodiment of the present invention utilizes measurement in the primary circuit of the isolating transformer of variation in load occurring in the secondary circuit as a control variable for determining the pulse width.
A further advantageous embodiment of the present invention obtains the control variable for the pulse width across a measuring resistor interposed in the connection of the emitter of the switching transistor of the blocking oscillator to the chassis.
Still another advantageous embodiment of the present invention provides that the voltage drop across the measuring resistor controls a controllable resistor.
The advantageous embodiments described above offer highly simple and advantageous possibilities for measuring the variation in load upon switching between normal and stand-by operation, as well as for the consequent control of the energy transmitted via the isolating transformer.
The possibility of a simple and inexpensive switching between normal and stand-by operation is achieved by effecting the switching between normal and stand-by operation by means of switching on or switching off, respectively, the low voltage supply of the line scan oscillator, and, especially, by a first switching transistor which short-circuits the base bias of a second switching transistor at the collector of which a direct current supply voltage is present and at the emitter of which a stabilized low voltage exists, when a positive signal is supplied from the operating control of the television receiver or from the remote control receiver to the base of the first switching transistor.
The circuit arrangements just mentioned offer the advantage that they may simultaneously be utilized as a protective circuit. This is achieved by a switching-off device for the low voltage which can also be triggered at any time by a signal built up by overcurrent in the picture tube.
The invention is further described by way of illustrative example by reference to the annexed drawings in which:
FIG. 1 is a circuit diagram, partly in block form, of an embodiment of the invention;
FIG. 2 is a circuit diagram of one form of means for interrupting the power to the picture circuits in the stand-by condition in connection with the circuit of FIG. 1, and
FIG. 3 is a circuit diagram of one way of controlling the pulse width of the blocking oscillator 4 in response to the switching circuit 8 in the circuit of FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
An on-off power switch 2 of the television receiver is connected to the supply terminals 1, providing a primary operating control for the receiver. Consquently, the supply voltage is also present at the output of the operating control 2 when the television receiver is turned on thereby, and arrives at a rectifying stage 3 comprising means for rectifying and smoothing the supply current as well as for suppressing interference. A d-c voltage, feeding a blocking oscillator stage 4, is present at the output of the recifying stage 3. The main part of the blocking oscillator 4, symbolically represented in FIG. 1 by a fragmentary circuit diagram, is a switching transistor 5, in the load circuit of which the primary winding of an isolating tranformer 6 is placed. A measuring resistor 7 is connected between the emitter of the switching transistor 5 and the chassis, across which measuring resistor a voltage is taken and applied to a load-dependent control circuit 8. The voltage taken at the measuring resistor 7 is fed via a resistor 9 to the base of a transistor 10 which serves as a controllable load for the blocking oscillator 4. A resistor 11 and a capacitor 12, each of which is connected to chassis with its other terminal, are also connected to the base of the transistor 10. The emitter of transistor 10 is connected to chassis, while the collector of the transistor 10 is connected back to the blocking oscillator stage 4.
In the secondary circuit of the isolating transformer 6, a d-c voltage supply stage or power conversion circuit 13 is placed, substantially consisting of a rectifying circuit 14, which, in the example shown, is provided with six outputs at which the voltages U 1 to U 5 can be taken off with respect to the sixth output connected to the chassis. At the terminal U 3, there is, in addition, a branch feeding both the collector-to-emitter path of the transistor 15 and also, through a resistor 16, the collector-to-emitter path of the transistor 15a. The emitter of the transistor 15a is directly connected to the base of transistor 15. The emitter of the transistor 15 is connected to chassis via a series connection of a resistor 17, a potentiometer 18, and a further resistor 19. The tap of the potentiometer 18 is connected to the base of a further transistor 20. The transistor 20 is connected to chassis by means of its emitter via a Zener diode 21, the collector of the transistor 20 controlling the base of the transistor 15a. The emitter of the transistor 20 is connected to the emitter of the transistor 15 via a resistor 22. A terminal for tapping off the voltage U 3' is connected to the emitter of the transistor 15.
The base of the transistor 15a is connected to a switching stage 23 responsive to a remote control ultrasonic receiver by a conductor leading to the collector of a switching transistor 24 which is connected to chassis via its emitter. The base of the switching transistor 24 is connected to an input terminal 28 leading into the television receiver via two resistors 25, 26 and a capacitor 27 connected in series, that input terminal 28 passing on switching signals from the receiver to the switching transistor 24, as will be explained in more detail below.
The cathode of a diode 29, which is connected to chassis via its anode, is connected to the junction point of the resistor 26 and the capacitor 27. The junction point of the two resistors 25, 26 is connected to chassis via a capacitor 30. The base of the switching transistor 24 is connected to chassis via a resistor 31. Furthermore, that base electrode is also connected to a terminal 32 to which an electrical switching signal is applied which is either built up in response to an ultrasonic signal received by the remote control receiver 32' or is supplied from an operating control of the television receiver. At the terminal 32, the switching transistor 24 receives the signal containing the information whether the television receiver is to work in the normal operating condition, i.e. to receive and process the sound and video signals, or in the stand-by condition in which it is substantially only the ultrasonic receiver that is supplied with current.
When a positive signal arrives at the base of the switching transistor 24, the latter becomes conductive, and causes chassis potential to be present at the base of transistor 15a. The transistor 15 is thereby blocked, and there is no longer any voltage at the terminal U 3'. Since the voltage U 3' serves as an operating voltage for the line and picture scan oscillator, the deflecting stages of the receiver cannot work and no high voltage and other related supply voltages are generated at the line circuit transformer. In consequence, by means illustrated diagrammatically in FIG. 2, the electric circuits connected to the terminals U 1 to U 3 are interrupted. The voltages U 4 and U 5 serve for supplying the ultrasonic receiver, i.e. they are required for the stand-by operation.
In case no counteracting means should be provided for, the variation in load would cause a voltage rise in the secondary circuit of the isolating transformer 6, which effect is, of course, not desired. Therefore, a measuring resistor is connected in the primary circuit in the emitter line of the switching transistor 5 of the blocking oscillator 6, the variation in load in the secondary circuit appearing at the measuring resistor 7 as a current variation. The current change thus produced, causes a variation in the base bias of the transistor 10, the capacitor 12 having an integrating effect to avoid undesired effects due to interference pulses and abrupt load fluctuations.
The change of the working point of the transistor 10 causes a change in the pulse width in the blocking oscillator stage 4, as more fully shown in FIG. 3, so that the energy quantum transmitted via the isolating transformer 6 is such that the required voltages are present in the secondary circuit. It should also be mentioned that the load-dependent switch 8 and the circuit of FIG. 3 are represented only by way of illustration and that many circuit arrangements may be devised by straight-forward application of known principles for controlling the pulse width.
Using the circuit diagram according to FIG. 3 it is possible in a simple manner to control the pulse width of the blocking oscillator 4 in response to the switching circuit 8.
According to the circuit diagram of FIG. 2 the terminal U1 is connected to a line scan oscillator circuit 40, the terminal U2 to a picture scan oscillator circuit 41 and the terminal U3 to a circuit 42 for a sound output stage. The circuits 40, 41, 42 get their operating voltage from the terminal U3'. If the operating voltage U3' is zero, the circuits 40, 41, 42 are interrupted. In this case the voltages at the terminals U1, U2, U3 remain.
The blocking oscillator stage 4 shown in detail in FIG. 3 incorporates an externally triggered blocking oscillator arranged to be triggered through an oscillator operating preferably at the line scanning frequency, which is to say its wave form is not particularly critical and it should be provided with means to keep it in step with the line scanning frequency, as is known to be desirable. The transistors 51 and 52 of the triggered output stage of the blocking oscillator circuit could be regarded as constituting a differential amplifier the inputs of which are defined by the base connections of the respective transistors 51 and 52. The input voltage applied to the base connection of transistor 52 is the Zener voltage of the Zener diode 53, thus a constant reference voltage. The operating voltage for the transistors 51 and 52 and for the Zener diode 53 is obtained from the supply voltage UB, which is to say from the rectifier 3. The diode 67 protects the transistor 52, for example at the time of the apparatus being switched on, against damage from an excessively high emitter-base blocking voltage. The capacitor 65 prevents undesired oscillation of the circuit of transistors 51 and 52, which could give rise to undesired disturbances.
At the base of the transistor 51, there is present as input voltage for the circuit a composite voltage that is the sum of three voltages. These are, first, the line scan frequency trigger voltage coupled through the capacitor 63; second, a bias voltage dependent upon the loading of the blocking oscillator stage resulting from the load on the secondary of the transformer 6, but detected by the voltage across the resistor 7 and actually controlled by the load-sensitive control circuit 8, and, third, a regulating voltage applied at the terminal 71 of the resistor 70, which regulating voltage is proportional to the voltage of the secondary winding of the transformer 6 and can accordingly be provided by one or another of the output circuits of the rectifier 14 of FIG. 1 or by a separate winding of the transformer 6 and a separate rectifier element connected in circuit therewith. This regulating voltage and the control voltage provided by the control circuit 8 are applied to the resistor 61 which completes the circuit for both of these bias voltages and their combined effect constitutes the bias voltage for the transistor 51 which determines its working point.
The circuit of the transistors 51 and 52 operates as an overdriven differential amplifier. When the trigger voltage exceeds the threshold determined by the base voltage of the transistor 51, the circuit produces an approximately rectangular output voltage pulse of constant amplitude. Since the trigger voltage is recurrent, the result is a periodic succession of rectangular output voltage pulses, but the duration or pulse width of these pulses depends upon the loading and the output voltage of the stage. The output voltage of the circuit constituted by the transistors 51 and 52 comes from the emitter connection of the transistor 52 and is furnished to the switching transistor 5, preferably through a driver stage 54, such as a transformer or another transistor stage for better matching of the circuit impedances. Of course, the collector circuit of the transistor 5 includes the primary winding of the transformer 6 of FIG. 1.
SABA ULTRACOLOR T6787 Telecommander CM CHASSIS 75 206 000 30 UniLine Assymetric top-bottom pincushion correction circuit
In a top-bottom pincushion correction circuit having a saturable reactor with a control winding coupled to a source of deflection current at a horizontal scan frequency and an output winding coupled to a source of deflection current at a vertical scan frequency, a means coupled to the control winding unbalances the waveform applied thereto from the source of deflection current at a vertical scan frequency to provide asymmetric top-bottom pincushion correction.
1. In a cathode ray tube scanning system having a cathode ray tube with an associated deflection yoke which includes horizontal and vertical deflection windings coupled to a source of deflection current at horizontal and vertical scan frequencies and a top and bottom pincushion correction circuit having a saturable reactor with a control winding coupled to the source of deflection current at a horizontal scan frequency and an output winding coupled to a source of deflection current at a vertical scan frequency and to a shunt connected capacitor and impedance, the improvement comprising:
means coupled to said output winding for unbalancing the waveform applied thereto from said source of deflection current at a vertical scan frequency to provide asymmetric top-bottom pincushion correction, said means of a form to provide a substantially constant crossover point of said waveform.2. The improvement of claim 1 wherein said means for unbalancing the waveform applied to said control winding is in the form of a series connected unidirectional conduction device and impedance shunting said control winding. 3. The improvement of claim 2 wherein said series connected unidirectional conduction device and impedance are in the form of a series connected diode and alterable impedance. 4. The improvement of claim 2 wherein said impedance shunting said control winding is alterable to effect control of the amount of unbalance or asymmetry between top and bottom pincushion correction waveform. 5. In a top and bottom pincushion correction circuit for a cathode ray tube scanning system wherein the correction circuit includes a saturable reactor with a control winding coupled to a source of deflection current at a horizontal scan frequency and an output winding shunted by a parallel coupled capacitor and impedance and coupled to a source of deflection current at a vertical scan frequency, the improvement comprising:
a series connected unidirectional conduction device and impedance coupled to said output winding for controlling the asymmetry of a top and bottom pincushion correction waveform.6. The improvement of claim 5 wherein said means for controlling the assymetry of a top and bottom pincushion correction waveform is in the form of a series connected diode and alterable resistor shunting said control winding. 7. The improvement of claim 6 wherein said alterable resistor provides control of the amount of asymmetry of the top to bottom pincushion correction waveform. 8. The improvement of claim 6 wherein said series connected diode and alterable resistor effect unbalance of said pincushion correction waveform with respect to a substantially constant crossover point.
CROSS-REFERENCE TO OTHER APPLICATIONS
A co-pending application entitled "Top-Bottom Pincushion Correction Circuit" bearing U.S. Ser. No. 622,134, now U.S. Pat. No. 3,982,156, filed Oct. 14, 1975 in the name of Tex K. Monroe and assigned to the Assignee of the present application provides a pincushion correction circuit of improved efficiency wherein ringing current of a control winding are transferred to an output winding.
BACKGROUND OF THE INVENTION
This invention relates to top-bottom pincushion correction circuits and more particularly to apparatus for providing an unbalanced top-bottom pincushion correction signal.
As is well known in the cathode ray tube scanning art, the displayed raster of a cathode ray tube is composed of successively spaced horizontal scan lines forming a substantially rectangular-shaped raster. Although the raster is desirably rectangular under normal operation conditions, it is well known that such a desirable condition fails to exist in almost all instances and the raster is distorted in a manner which has become known as top-bottom pincushion distortion.
As is well-known, top-bottom pincushion distortion is indicated by the departure of the horizontal scan lines from a straight-line configuration. Specifically, the horizontal scan lines at the top half of the raster tend to bow downwardly toward the center while the horizontal scan lines at the bottom half of the raster tend to bow upwardly toward the center of the raster.
Also, it is well-known, many modern television receivers have picture tubes mounted near the floor or at least below the normal level of viewer observation. Thus, the average viewer looks down at the raster on the picture tube which has the effect of making normally straight lines near the top of the raster appear bowed inwardly at the center. At the bottom of the raster, the normally straight lines appear to be bowed outward or barrelled at the center of the raster.
One known prior art technique for overcoming the above-described distortion problems was to utilize a movable bias magnet whereby a magnetic field was employed to set up a field in the pincushion transformer to compensate for the distortions. In another method, a DC current was added to the ramp-like waveform of the pincushion correction voltage applied to the vertical windings of the deflection yoke in an effort to provide a desired upbalance in the resultant raster of the cathode ray tube.
Although the above-mentioned methods provided some relief and were reasonably successful, they did leave much to be desired. For example, altering the magnetic flux with a magnet or adding a DC current to effect unbalance of the pincushion correction waveform tends to undesirably alter the crossover point or the point whereat the waveform shifts from one polarity to the other. As a result, the total raster is affected rather than only the positive or negative portion of the waveform which requires correction.
OBJECTS AND SUMMARY OF THE INVENTION
An object of the present invention is to provide an improved cathode ray tube scanning system. Another object of the invention is to enhance the top-bottom pincushion correction of a cathode ray tube scanning system. Still another object of the invention is to provide improved apparatus for unbalancing the amount of top-bottom pincushion correction in a cathode ray tube scanning system. A further object of the invention is to provide circuitry for controlling the unbalance of a top-bottom pincushion control circuit.
These and other advantages and capabilities are achieved in one aspect of the invention by a top-bottom pincushion correction circuit having a saturable reactor with a control winding coupled to a source of deflection current at a horizontal scan frequency and an output winding coupled to a source of deflection current at a vertical scan frequency and a means coupled to the output winding for unbalancing the waveform applied thereto from the source of deflection current at a vertical scan frequency.
BRIEF DESCRIPTION OF THE DRAWINGS
The sole FIGURE is a block and schematic diagram of a television receiver utilizing a preferred form of asymmetric top-bottom pincushion correction circuitry.
PREFERRED EMBODIMENT OF THE INVENTION
For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims in conjunction with the accompanying drawing.
Referring to the drawing, a color television receiver includes an antenna 3 for intercepting and applying transmitted color television signals to a signal receiver 5. The signal receiver 5 includes the usual radio frequency (RF), intermediate frequency (IF), and video amplifier and detector stages to provide a composite color video signal.
The composite color video signal from the signal receiver 5 is applied to a video amplifier stage 7. The video amplifier stage 7 provides an output signal which is applied to a chrominance signal channel 9 wherefrom are derived signals representative of color information in the transmitted signal. These color information signals from the chrominance signal channel 9 are applied to a color cathode ray tube 11 to effect the desired display of color information.
Another output from the video amplifier stage 7 is applied to a luminance signal channel 13 wherein signals representative of image information are derived and applied to the color cathode ray tube 11. Still another output from the video amplifier stage 7 is applied to a sync pulse separator stage 15 wherein sync pulse signals at the vertical scan rate are separated from the video signal and applied to a vertical drive circuit 17. Also, sync pulse signals at the horizontal scan rate are separated from the video signal and applied to a horizontal drive circuit 19.
The horizontal drive circuit 19 is coupled to a horizontal output circuit 21 which includes a transistor 23 having an emitter connected to circuit ground and a collector coupled by a winding 25 of a horizontal flyback transformer 27 to a potential source B+. A parallel connected capacitor 29 and damper diode 31 couple the collector of the transistor 23 to circuit ground while a series connected "S" curve correction capacitor 33 and a horizontal deflection yoke winding 35 shunt the parallel connected capacitor 29 and damper diode 31. The horizontal deflection yoke winding 35 is a part of a deflection yoke 37 associated with the cathode ray tube 11 as indicated by the arrows labeled "H".
A winding 39 on the horizontal flyback transformer 27 has one end grounded and the opposite end coupled to a pair of series connected control windings 41 and 43 disposed on an outer pair of leg members of a saturable reactor 45. The saturable reactor 45 is of the well-known "E" type construction and the control windings 41 and 43 are connected in a magnetically opposing manner to circuit ground.
An output from the vertical drive circuit 17 is AC coupled by a capacitor 47 to a vertical deflection yoke winding 49 which is a part of the deflection yoke 37 as indicated by the arrows labeled "V". The vertical deflection yoke winding 49 is coupled to an output winding 51 affixed to the center leg member of the saturable reactor 45. The output winding 51 is shunted by a capacitor 53 to provide a resonant circuit and an adjustable resistor 55 shunts the output winding 51 and capacitor 55 to provide for varying the Q of the resonant circuit.
Also, a series connected alterable impedance, depicted as an adjustable resistor, 57 and a unidirectional conduction device, illustrated as a diode 59, are shunted across the parallel connected output winding 51, capacitor 53, and alterable impedance 57. This series connected adjustable resistor 57 and diode 59 serve to effect unbalance of the waveform applied thereto whereby asymmetric top-bottom pincushion correction is effected without undesired alteration of the crossover point of the waveform.
As to operation, the winding 39 coupled to the flyback transformer 27 provides horizontal flyback pulse signals 61 which are applied to the series connected control windings 41 and 43 affixed to the saturable reactor 45. Since the control windings 41 and 43 are oppositely poled, they tend to drive horizontal flux through the center leg of the saturable reactor 45 in opposite directions. Thus, equal flux contributions from the control windings 41 and 43 cause cancellation of horizontal frequency flux variations whereupon no energy is transferred into the center leg whereon the output winding 51 is disposed. However, a difference in flux contribution by the control windings 41 and 43 produces horizontal frequency variations to the output winding 51.
As to dynamic control of the relative horizontal flux contributions, the vertical drive circuit 17 provides a vertical scanning current, waveform 63, having a crossover point 65 with a ramp-like portion 67 of one polarity and a ramp-like portion 69 of the opposite polarity. During a first portion of vertical scanning, the vertical scanning current, portion 67, induces a flux into the center leg of the saturable reactor 45 which opposes the flux linkages of the center leg to one outside leg and adds to the flux linkages of the center leg to the other outside leg. The opposite flux conditions exist when the second portion, portion 69, of the vertical scanning current is applied to the winding 51. Thus, a maximum amplitude of horizontal frequency signals is transferred to the output winding 51 when the vertical scanning current is maximum and a polarity crossover occurs intermediate the maximum horizontal signal amplitude transfer.
Additionally, an unbalance of the vertical scanning current, waveform 63, modulated by the horizontal frequency variations is obtainable by adding the series connected adjustable resistor 57 and diode 59. In accordance with the connections of the diode 59, the diode 59 is reverse biased and does not affect the resultant pincushion correction waveform when the correction waveform is of one polarity. However, when the polarity of the correction waveform reverses, the diode 59 conducts which causes the adjustable resistor 57 to load down the circuit and reduce the magnitude of the pincushion correction waveform.
Obviously, reversing the connections of the diode 59 will result in a reversal of the unbalance of the resultant pincushion correction waveform. The magnitude of the unbalance or correction is selectively chosen by altering the adjustable resistor 57. Moreover, it can readily be seen that the unbalance circuitry has no effect upon the crossover point 65 since loading of the circuitry is dependent upon current flow through the series connected resistor 57 and diode 59 whereas current flow is not present or at a minimum at the crossover point.
Thus, there has been provided a unique asymmetric top-bottom pincushion control circuit. The circuit is inexpensive of components and construction while enhancing the capabilities of a cathode ray tube scanning system. Also, the circuit provides a technique to effect unbalance of the top-bottom pincushion correction signals without undesired alterations in the crossover point of the correction signals. Moreover, the circuit provides apparatus for easily controlling the degree of unbalance desired.
While there has been shown and described what is at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention as defined by the appended claims.