US3868538A

US3868538A - Ferro-resonant high voltage system

Info

Publication number: US3868538A
Application number: US359582A
Authority: US
Inventors: David L Blanchard
Original assignee: Zenith Radio Corp
Current assignee: Zenith Electronics LLC
Priority date: 1973-05-11
Filing date: 1973-05-11
Publication date: 1975-02-25
Anticipated expiration: 1992-02-25

Abstract

A cathode ray tube high-voltage supply system is of the type in which sawtooth-shaped pulses are developed in a first transformer winding in order to produce a scanning waveform in a deflection yoke on the tube. So-called fly-back energy, developed as a result of magnetic field collapse in the yoke during retrace, is utilized, in turn, to produce high-voltage output pulses in another winding to which a load is coupled that requires a broad, generally-square pulse shape. The first winding is wound upon a first ferromagnetic core that defines a non-saturating magnetic circuit. The other winding is wound upon a second ferromagnetic core which, together with a portion of the first core, defines a second magnetic circuit that saturates in operation. A capacitor included in the load is coupled across the other winding and controls the energy in said second magnetic circuit in such a manner as to supply the load with pulses that are broad and have a generally-square shape.

Description

United States Patent 91 Blanchard [4 1 Feb. 25, 1975 FERRO-RESONANT HIGH VOLTAGE [58] Field of Search 315/27 TD, 27 XY, 27 R, 315/28-29, 18, 25; 336/178 [56] References Cited UNITED STATES PATENTS 2,451,026 10/1948 Friend 315/27 XY 2,606,304 8/1952 3,205,401 9/1965 3,609,446 9/1971 3,717,789 2/1973 Wolber 315/27 XY Primary Examiner-Malcolm F. Hubler Assistant Examiner-J. M. Potenza Attorney, Agent, or Firm-Nicholas A. Camasto; John J. Pederson SAWTOOTH SHAPER DEFLECTION HORIZONTAL DRIVE [57] ABSTRACT A cathode ray tube high-voltage supply system is of the type in which sawtooth-shaped pulses are developed'in a first transformer winding in order to produce a scanning waveform in a deflection yoke on the tube. So-called fly-back energy, developed as a result of magnetic field collapse in the yoke during retrace,

is utilized, in turn, to produce high-voltage output pulses in another winding to which a load is coupled that requires a broad, generally-square pulse shape. The first winding is wound upon a first ferromagnetic core that defines a non-saturating magnetic circuit. The other winding is wound upon a second ferromagnetic core which, together with a portion of the first core, defines a second magnetic circuit that saturates in operation. A capacitor included in the load is coupled across the other winding and controls the energy in said second magnetic circuit in such a manner as to supply the load with pulses that are broad and have a generallysquare shape.

13 Claims, 3 Drawing Figures llllll mlll CIRCUIT FOCUS 1 FERRO-RESONANT HIGH VOLTAGE SYSTEM BACKGROUND OF THE INVENTION The present invention pertains to high voltage supplies for cathode ray tubes. More particularly, it relates to such systems which also supply scanning energy to a deflection yoke and utilize counter energy developed by the yoke during the retrace intervals to produce output pulses from which the high voltage is derived.

Cathode ray tubes such as those commonly employed in television receivers require a comparatively high final anode voltage in order adequately to develop the reproduced image. For example, color im age reproducers frequently require a final anode voltage of between and kilovolts. Even comparatively small-screen monochrome image reproducers still necessitate the development of high voltages measured in terms of kilovolts, a level many times that of any other voltage required for energizing the different stages in the associated receiver. Conveniently, it has been the practice for many years to derive the necessary energy for development of the high voltage from the collapse of the magnetic field in the deflection yoke during each retrace interval of the horizontal scanning function. Typically, generally square-shaped driving pulses, repeating at the horizontal scanning rate, are applied to a primary winding on what is called the horizontal-output or flyback transformer. That winding may serve as an autotransformer and may have a tap to which the deflection yoke is connected. During the retrace interval, a surge of energy is fed back from the yoke to the winding as a result of the collapse of the magnetic field in the yoke. This surge of energy produces an output in what is often referred to as a tertiary winding on the same transformer core and which is arranged so as to effect a substantial step-up in the output pulse voltage level. The tertiary winding may either be a continuation of the primary winding, thus functioning still further as an auto-transformer, or be a separate winding Wound upon the core of the transformer. In any event, the stepped-up output pulses are then rectified and stored in a filter capacitor from which the unidirectional high voltage is supplied to the final anode of the cathode ray tube. Also conventionally wound upon the core of the transformer is a secondary winding which is employed to develop waveforms employed elsewhere in the television receiver to perform variable correction, compensation and gating functions.

In many cases, the entire voltage step-up has been achieved in the transformer itself by means of appropriate selection of the ratio of tertiary to primary winding turns. With the peak level voltage in the transformer itself thus at a very high level, it has been necessary to attend careful to the insulation qualities within the transformer. Even the eventual dielectric breakdown has too often been encountered and resulted in a somewhat expensive replacement.

To the end of reducing the high voltage level necessary to be reached in the transformer itself, another approach has been to operate the transformer so that the peak tertiary voltage level is of a substantially lower value and then employ a separate voltage multiplier to develop the ultimately required high voltage level. In a typical example the level of the output pulses from the tertiary winding of the transformer is 9 kilovolts, and a voltage tripler circuit is then employed to increase that level to the 27 kilovolts required by an associated color image reproducer. conventionally, the voltage multiplier is a ladder arrangement of diodes and capacitors with the diodes serving to rectify the output pulse energy and the capacitors accumulating charges while individually operating in succession so as to step-up the voltage. In an effort to achieve a longer charging time for the multiplier capacitors, and thus obtain better regulation, it has been recognized that it is desirable to produce a significant fifth harmonic component in the output pulses. In consequence, they tend to be flatter and broader. In one approach reasonably successful for that purpose, the tertiary winding is link coupled to the primary winding with the link itself being tuned to the third harmonic of the scanning frequency.

While progress thus has been made in the attainment of improved high-voltage supplies of the kind discussed, a number of problems are still encountered. In at least some cases, ringing during the scanning interval causes the voltage multiplier to conduct during peak negative tips of the ringing cycle, so as to result in a non-linear behavior of the anode regulation curve. Another cause for undesired decrease in anode voltage, over that of which the system is capable, is that the flat portion of the peak positive output pulse still may have a duration of only a few microseconds. Such limited conduction time restricts the amount of charge that can be transferred into a voltage multiplier by reason of the finite time constant associated with the capacitors therein as well as the forward impedances of the diodes and the output impedance of the tertiary winding. A still further cause of degradation of anode voltage re gulation, related to the other two, is that the output impedance of the low-voltage power supply generally must be increased in order to minimize picture size variation stemming from the anode voltage variation.

In one specific approach utilizing a voltage multiplier and in which fifth harmonic content is included in the output pulses, the system includes a saturable reactor regulator which stores energy in the reactor magnetic field, during scanning time, that is returned to the transformer during retrace time so as to increase the load current. The result is the production of a higher peak-positive tertiary or output voltage for charging the voltage multiplier capacitors. However, it is found that detuning of the harmonics occurs and the problem of maintaining constant picture size often becomes severe. Such detuning is a result of a change in primary inductance with anode current change that produces an unbalance in the tuning of the transformer. This contributes to non-minimum ring conditions during scanning as well as a non-linear regulation curve at required anode currents. In addition, the regulating range is limited by the change in inductance of the reactor between the minimum and maximum energy demands of the load. Moreover, energy exchange occurs only during the peak-positive tertiary output pulse in the retrace interval. There is no increase in energy available during the scanning time interval.

OBJECTS OF THE INVENTION It is, therefore, a general object of the present invention to provide a new and improved cathode ray tube high-voltage supply system generally of the foregoing character but in which problems such as those just discussed are overcome or at least significantly minimized.

Another object of the present invention is to provide a new and improved system of the foregoing character which optimizes anode voltage regulation characteristics while yet maintaining simplicity in the design of the horizontal deflection system and without requiring extensive changes in design of the associated image reproducing system.

A further object of the present invention is to provide a new and improved cathode ray tube high-voltage supply system of a kind including a voltage multiplier which is fed with output pulses that exhibit minimum ringing during associated scanning intervals and a flat, wide positive peak in order to obtain a linear change in anode voltage with change in anode current as well as to obtain substantial charging of capacitors in the multiplier during the period of rectification.

A still further object of the present invention is to provide a new and improved cathode ray tube highvoltage supply system which exhibits a comparatively low output impedance and develops output pulses characterized by having a constant peak-to-peak voltage excursion that is independent of minor low-voltage supply variations.

One specific object of the present invention is to provide a supply system of the foregoing character which provides an output waveform of a symmetrical flattopped shape while yet preserving with minimum distortion an asymmetrical shape of developed input pulses.

A related object of the present invention is to provide a cathode ray tube high-voltage supply system which provides overload protection for the primary driving source.

SUMMARY OF THE INVENTION The invention thus pertains to a cathode ray tube high-voltage supply system in which sawtooth-shaped current pulses are developed in a first transformer winding in order to produce a scanning waveform in a deflection yoke on the cathode ray tube. Energy developed, as a result of collapse of the magnetic-field in the deflection yoke, is utilized, in turn, to produce highvoltage output pulses in a second winding. To the end of generating a broad generally-square pulse shape for application to the load coupled to the second winding, 21 first closed magnetic circuit is non-saturating in response to development of the sawtooth-shaped pulses and includes a first ferromagnetic core upon which the first winding is wound. A second closed magnetic circuit, on the other hand, saturates in response to the energy developed as a result of the field collapse in the deflection yoke and includes only a portion of the first core together with a second ferromagnetic core upon which the second winding is wound. Finally, a capacitor, included in the load, is coupled across the second winding. The capacitor has a value enabling the current cycles in the second winding to coincide with the current cycles in the first winding sufficiently that the yoke field collapse initiates saturation reversal in the second core.

BRIEF DESCRIPTION OF THE DRAWINGS The features of this invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood, however, by reference to'the following description taken in conjunction with the accompanying drawings, in the several figures of which like reference numerals identify like elements, and in which:

FIG. 1 is a block diagram of a color television receiver in which the present invention is embodied;

FIG. 2 is a more detailed block diagram of the horizontal system included in the diagram of FIG. 1; and

FIG. 3 is a schematic diagram of a portion of the system of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Except for modifications to be particularized in connection with the discussion of FIG. 3, FIGS. 1 and 2 illustrate, with certain simplifications non-essential to an understanding of the present invention, the various different stages or systems which together constitute a conventional color television receiver. Thus, a tuner 20 selects a composite television signal in a desired channel received by an antenna 21. Employing the usual superheterodyne technique, tuner 20 converts the signal frequencies in the range of whatever channel is selected to a constant frequency range, and those converted signals are fed to an intermediate-frequency amplifier 22. The amplified intermediate-frequency signals are then fed to a video detector 23 which develops and supplies a video amplifier 24 with a brightness of luminance signal. The latter, in turn, is supplied as one input to a color image reproducer 25.

A portion of the amplified intermediate-frequency signal from amplifier 22 also is fed to a sound-sync detector 26 from which an audio signal is derived and amplified by a sound system 27 and fed to a sound reproducer 28. Detector 26 serves still further by extracting synchronizing information from the intermediatefrequency signals and feeding such information to a vertical system 29 that, in turn, produces a scanning waveform which is fed to a yoke 31 mounted on the neck of reproducer or cathode ray tube 25. Similarly, synchronizing information from detector 26 is fed to a horizontal system 32 which develops a horizontal scanning waveform which is fed to deflection yoke 31. The horizontal and vertical scanning waveforms energize respective deflection coils within yoke 31 so as to cause the electron beams to scan an image raster on the faceplate of tube 25 in a pattern composed of a series of horizontal lines successively spaced apart in a vertical direction. Another function of horizontal system 32 is to develop a high-voltage HV which is applied to the final anode of cathode ray tube 25. To assure the proper landing of the different electron beam components upon their assigned phosphor areas of the faceplate, the receiver also includes respective vertical and horizontal convergence systems 34 and 35. In each case, a sample of the corresponding vertical and horizontal waveforms is converted to a different, conven tionally parabolic, shape and then applied to a convergence yoke 36 also mounted on tube 25.

Specifically for the reproduction of color, the receiver circuitry is responsive to color-representative information fed from video detector 23 to a chroma amplifier 38. That information defines both the hue and the saturation in the image to be reproduced and also includes a color reference signal. As standardized in the United States and Canada, the latter takes the form of a burst at 3.58 megahertz which is transmitted along with the information for synchronizing the horizontal scanning function. The frequency and phase of the burst is the same as that of a suppressed carrier in the composite television signal upon which the hue and saturation information are modulated.

One function of chroma amplifier 38 is to segregate out and supply the color reference information or burst signal to a chroma demodulator 39 so that the hue information in the chroma signal, also fed from amplifier 38 to demodulator 39, is properly demodulated in a manner to produce faithful color-control signals which are fed as another input to cathode ray tube 25 in order to modulate the action of its corresponding plurality of three different electron beams that respectively activate the conventional red, green and blue phosphor areas.

As so far described, the receiver in FIG. 1 is entirely conventional. Of course, it will be understood to include the usual additional features that have been found to be desirable. For example, manuallyadjustable controls are provided for the viewer in a typical receiver so that he may selectively adjust such functions as volume, brightness, contrast, tone of the sound and hue of the color. Similarly, the receiver conventionally will include a number of automatic systems for governing such functions as intermediate-frequency carrier amplitude and frequency, amplitude of the burst signal, phase and frequency of the reference signal actually used in operation of chroma demodulator 39 and contrast in the reproduced image. However, the control of such functions is well known and forms no part of the subject matter to which the present description is directed.

FIG. 2 illustrates in more detail the different stages within horizontal system 32 of FIG. 1. It thus includes a horizontal oscillator 42 the frequency and phase of which is compared in an automatic-frequency control 45 with the incoming synchronizing pulses from detector 26. Any departure in the operation of oscillator 42 as compared with the synchronizing pulses results in the feeding back from automatic-frequency control 45 of a correcting signal which, thereby, serves to maintain synchronization of oscillator 42 with the received synchronizing information. The signals developed by oscillator 42 are then fed through a driver 43 to a horizontal output stage 44 which develops horizontal output pulses that are fed to a horizontal sweep transformer 46.

ln a manner which, as such, is conventional, sweep transformer 46 develops a number of different output signals. As was also mentioned in connection with FIG. 1, it produces a horizontal scanning waveform which is applied to the deflection yoke as well as providing a sample of that waveform to the convergence system. In addition, its output signals include gating pulses that are fed to other portions of the overall receiver so as to time operation of different functions, such as automatic-gain control and automatic-chroma control, to occur at desired intervals in the received composite television receiver signal. Furthermore, sweep transformer 46 develops different voltages that are applied to various stages and components in the television receiver. As indicated, these include certain low voltages and, in particular, output pulses which are supplied to a highvoltage tripler 48. The latter serves to rectify the output pulses as well as to substantially step-up their voltage level so as to produce the very high voltage HV which is applied to the final anode of tube 25. Tripler 48 also develops a similarly high-level focus voltage that also is applied to cathode ray tube 25. Additionally included in the system is a sawtooth shaper 49 which receives a sample of the waveform developedl in horizontal sweep transformer 46 and feeds it back to automaticfrequency control 45 for the purpose of governing operation of the latter in order to maintain production of the appropriately desired waves of sawtooth shape in transformer 46.

As illustrated in FIG. 2 and as so far described, the arrangement and functioning of the horizontal system could be entirely in a known manner such as in accordance with that discussed in the introduction. As embodied herein, however, horizontal system 32 is specifically improved in the manner particularized in FIG. 3. That is, horizontal drive pulses from driver 43 are applied across the primary winding of an isolation transformer 50 from one end of the secondary of which those pulses are fed through a grounded feed-through capacitor 51 and a choke 52 to the base of an NPN transistor 53. The other end of the secondary winding of transformer 50 is returned to ground through a resistor 54 by-passed by a capacitor 55. The emitter of transistor 53 is returned to ground, while its collector is shunted to ground by a capacitor 56 and through a damping diode 57 by-passed by a capacitor 58. The collector of transistor 53 is also connected through a high-frequency choke 60 and a grounded feed-through capacitor 61 to a tap 62 on a primary winding 63 wound upon one leg of a first ferromagnetic core 64 which forms part of horizontal sweep transformer 46. Tap 62 is by-passed to ground by

capacitors

66 and 67 and is also connected through a diode 68 and a resistor 69 to a terminal 70 at which, in operation, a comparatively high, but yet low-voltage, appears. Resistor 69 also is by-passed to ground by a capacitor 71. Connected between the lower end of winding 63 and ground is the series combination of another diode 74, a resistor and a capacitor 76, with diode 74 bypassed by a capacitor 77. Another direct-current potential, of a value somewhat higher than the normal B+ supply, is developed at a terminal. 78 connected to the junction between resistor 75 and capacitor 76.

For supplying operating DC power, the conventional low-voltage source 8+ is connected through a resistor 80 to a tap 81 on winding 63 intermediate tap 62 and the lower end of that winding. The junction between resistor 80 and tap 81 is filtered to ground by a capacitor 83 and also is connected through a diode 84 and a resistor 85 to a point of supply of a comparatively lowvoltage waveform utilized in a conventional manner by certain correction circuits in the television receiver. The upper or high-potential end of winding 63 is connected directly to one side of the horizontal deflection windings in yoke 31, the other end of those windings being returned to ground.

In operation, a negative-going rectangular pulse is applied to the base of transistor 53. When the latter conducts, the inductance in winding 63 causes the current to rise slowly so as to result in a sawtooth waveform. When transistor 53 is cut off by action of the applied pulse, magnetic energy stored in winding 63 causes its current to reverse direction and flow through damping diode 57, also generating a voltage pulse across winding 63. The current in diode 57 slowly de- 7 creases to zero, at which time transistor 53 again conducts and the cycle is repeated. Thus, the scanning waveform actually applied to the horizontalcoils in deflection yoke 31 is a sawtooth current repeating at the standard horizontal deflection frequency of 15,750 hertz. By inductive coupling through core 64, similar but lesser-amplitude sawtooth current waveforms are induced in a secondary winding 87 also wound on a leg of core 64. Winding 87 is tapped intermediate its length to ground so as to produce both negative-and positivegoing pulses at respective different taps along the 1 length of winding 87. As indicated, these different taps serve to provid'e'the waveformsat different amplitudes and polarities as required for use in the different correction circuits as well as to return the abovementioned compensation waveform to sawtooth shaper 49.

Also included as a part of the overall structure of transformer 46 is a tertiary winding 89 which feeds output pulses to a voltage multiplier 90 which in this case specifically is a tripler that also functions as a-full-wave rectifier. In itself, tripler 90 is of known form. Thus, multiplier 90 includes a plurality of charging capacitors 91 cross-coupled in a ladder array of diodes 92 so as to triple the voltage level of the output pulses while at the same time rectifying the output pulse energy so as to produce a unidirectional high voltage l-IV at the output of the tripler. The side of the first diode presented with the output pulses is coupled to ground through one of capacitors 91, while the others of those capacitors are connected individually between the different respective junctions between the various diodes. In operation, the application of an exemplary 9-kilovolt output pulse to the input side of multiplier 90 results in the appearance of approximately 9 kilovolts at the junction between the first commonly connected pair of diodes, approximately 18 kilovolts at the common junction between the third and fourth diodes and approximately 27 kilovolts at the multiplier output terminal HV. That output terminal also is returned to ground through the series combination of a potentiometer 94, another potentiometer 95 and a resistor 96. From the tap on potentiometer 94, the requisite focus potential for application to cathode-ray tube 25 is derived. In practice, potentiometer 94 serves as a bleeder resistor, while potentiometer 95 is accessible for manual adjustment of the focus potential.

Ignoring structure and components shown in FIG. 3 but not yet specifically described, the operation of the system depicted in FIG. 3 is known, as such. Such an arrangement has been commercially employed, for example, in the 25DC56 chassis manufactured by Zenith Radio Corporation of Chicago, III. in 1973. The overall function of the horizontal system is primarily to provide the scanning waveforms necessary to energize the horizontal coils in the deflection yoke while at the same time recovering energy produced inherently within the deflection coils, upon collapse of the magnetic field developed thereby at the beginning of each retrace interval, and thus during the time interval between the horizontal scanning pulses. That recovered energy produces the output pulses delivered by tertiary winding 89. As already noted, transformer 46 also serves to develop various different correcting, gating and compensating waveforms as well as permitting the production of different lower voltages for use elsewhere in the television receiver circuitry.

Notwithstanding the similarity of operation to that of known circuitry already alluded to, the illustrated embodiment of transformer 46 includes additional features enabling the attainment of the objectives mentioned in the introduction. To that end, it will be observed that core 64 is shaped to define a closed magnetic circuit. Moreover, the magnetic characteristics of its material together with its dimensions are selected to insure against saturation of core 64 in response either to development of the sawtooth-shaped current waveforms or in the presence of the energy developed and fed back to core 64 as a result of magnetic field collapse in the yoke. Furthermore, tertiary Winding 89 is wound upon a second ferromagnetic core 98 which bridges only a portion 99 of core 64. Thus, it will be observed that core 98 together with portion 99 define a second closed magnetic circuit. In this case, however, the magnetic characteristics and dimensions of core 98 are selected so as to saturate in response to energy induced in core 98 as a result of the magnetic field collapse in the yoke. In common parlance, transformer 46 thus may be viewed as including a primary leg 100 upon which winding 63 is wound, a tertiary leg 101 upon which winding 89 is wound and portion 99 of core 64 which functions as a shunt leg between the other two legs. In a manner known, as such, dielectric-filled

gaps

102 and 103 may be included respectively in each of

legs

100 and 99 to assist in achieving the desired operating reluctances in those two legs.

A storage capacitor 105 is coupled across tertiary winding 89. Its capacitance is selected to have a value that enables the current cycles in tertiary winding 89 to coincide with the current cycles in primary winding 63 sufficiently that collapse of the magnetic field in yoke 31 initiates or triggers a reversal of saturation in core 98. At the same time, the core structure is designed to allow capacitor 105 to store sufficient extra energy to supply losses in the core and load.

Completing the circuitry, one end of winding 89 is connected to an input of multiplier 90, while the other end of that winding is connected to ground. As specifically illustrated, capacitor 105 is a discrete component separate both from winding 89 and from the capacitance presented by multiplier 90. In practice, however, the capacitance necessary may be obtained from either one or both of the stray capacitance in winding 89 and the input capacitance of multiplier 90.

In operation, the action of the system including winding 89 and capacitor 105 is such as to feed output pulses to multiplier 90 which feature a wide, flattopped shape that, in turn, enables charging of the capacitors in multiplier 90 during a significantly large portion of each retrace interval. A typical pulse, of width W, is depicted in FIG. 3. Capacitor 105 is in itself a storage device which stores energy during each retrace interval and then delivers that energy back into the total network so as to make broad pulses available for supplying energy to the voltage multiplier. One primary result is the attainment of good quality highvoltage regulation. At the same time, the operation of saturable core 98 is such as to have essentially no effect upon the shape of the horizontal scanning pulse present in primary winding 63. Viewed another way, the illustrated arrangement permits the employment of saturation in the operating characteristics of the tertiary winding so as to obtain desired nonlinear effect while at the same time operation in primary winding 63 is always of a linear characteristic.

Considering the mode of operation in more detail, it may be noted first that the flux waveform in winding 89 is of generally triangular shape, while that in winding 63 is of sawtooth shape. After retrace, and the attendant collapse of the magnetic field in the yoke, the flux level in winding 63 is a maximum; the core under winding 89 would then be saturated except that the charge on capacitor 105 cannot change by reason of the high value of inductance in its discharge path. Consequently, the flux winding 89 increases in a generally sawtooth manner, while the balance of the flux goes into shunt leg 99. The rate of increase of flux in winding 89 is determined essentially only by core 98 and capacitor 105 as a result of which the voltage induced across winding 89, and hence the charge on capacitor 105, is constant and does not depend on the primary circuit including winding 63. At approximately the middle of the cycle of current waveform, core 98 saturates and the inductance in winding 89 drops, affording capacitor 105 a discharge path. Because of saturation, the flux in core 98 can no longer increase, so that the induced voltage, produced by change in flux, falls to zero. In discharging through the now-low inductance of winding 89, there is an overshoot and capacitor 105 is charged in the reverse direction. Core 98 then comes out of saturation and the inductance presented by winding 89 again becomes of a high value so that once more charge is locked into capacitor 105. The flux level now drops slowly, holding the voltage across winding 89 until core 98 becomes saturated in the opposite direction at which time the cycle repeats.

Several further features preferably are included in the design of the system in order to optimize operation. In still more detail, then, transformer 46 is designed so that its primary magnetic circuit in core 64 is operating on the normal or linear B-H characteristic while the tertiary magnetic circuit including core 98 is allowed to operate into the saturated regions of its B-H characteristic. Shunt leg 99 both enables saturation of the tertiary magnetic circuit and prevents saturation of the primary circuit. That is, the shunt path provided by leg portion 99 completes the magnetic circuit for the primary winding while the tertiary is in saturation. That shunt path also serves to reduce the amount of tertiary flux that otherwise would link the primary magnetic circuit.

As already indicated, the magnetic reluctance of primary leg 100 and shunt leg 99 is determined in each case by the inclusion of

air gaps

102 and 103. On the other hand, the reluctance of tertiary leg 101 is determined by its length and cross-sectional area alone. In practice, the cross-sectional areas of all three legs are chosen so that only tertiary leg 101 is forced into saturation and caused to exhibit a large reluctance. Consequently, the flux coupling from the primary leg to the tertiary leg may become small without effecting flux coupling in the reverse direction. That is, when the tertiary leg reaches saturation, any additional increase in the primary flux must go through the shunt leg and this, in turn, increases the magnetomotive force that appears across the tertiary leg.

In addition to saturation of tertiary leg 101, capacitor 105 serves to control the voltage-current phase relationship in the tertiary winding in order to obtain the desired waveform transformation. That is, use of the capacitor causes the voltage to lag the current so that energy is stored in the capacitor. While the rate of charge accumulated in capacitor will be low at small flux magnitudes, because the tertiary winding will then appear as a large inductance, when saturation is reached the tertiary inductance decreases substantially so that capacitor 105 accumulates charge rapidly. When that stored energy subsequently is released through tertiary winding 89, this likewise decreases the flux in tertiary leg 101 and forces the latter out of saturation. As the inductance of winding 89 thus again becomes larger, it controls the rate at which the stored energy is returned to core 98. AS already noted, the energy stored in capacitor 105 at core saturation is sufficient to force tertiary leg 101 again to enter saturation at the opposite flux extreme during the return of energy from the capacitor. Thus, the tertiary core is forced to traverse the hysteresis loop of its B-H characteristic curve.

In traversing the unsaturated region of that B-H curve, the change in voltage across tertiary winding 89 is small, since capacitor 105 discharges and charges through a comparatively large inductance as determined by the minimum value of tertiary reluctance. On the other hand, the change in voltage across winding 89 during the saturation interval is comparatively large, since at that time the capacitor is completing its discharge or charge through a small inductance as determined by the maximum value of the tertiary reluctance. Preferably, the parameters are selected so that there is one complete traversal of the hysteresis loop for each cycle of applied primary waveform in order to achieve maximum efficiency. Sufficient energy is exchanged between capacitor 105 and tertiary core 98 so as to maintain essentially equal levels of positive and negative core saturation. Consequently, symmetry of the output pulse waveform is obtained. In turn, the peakto-peak voltage of the output pulses is substantially independent of the input voltage, since the flux-time relationship when the core is substantially saturated is dependent instead only on the B-H characteristic, the value of capacitor 105, the core dimensions and the number of turns of winding 89.

By design of the system as specified, the action of the storage capacitor together with the non-linear reluctance behavior in the tertiary path results in the development of output pulses having a waveform which is approximately square in shape and nearly independent of B+ low-voltage supply variations. In addition, it is desired to minimize distortion of the waveform in primary winding 63. To that end, shunt leg 99 is designed, by means of the selection of its cross section and the size of gap 103, to exhibit a reluctance much smaller than that of primary leg 100. Consequently, the tertiary magnetic circuit flux path is primarily only through the shunt leg portion of core 64 since, as already indicated, the cross-sectional area of the shunt leg portion is sufficiently large to prevent its own saturation.

In accordance with conventional practice, the required core dimension can be determined from the reluctance requirements, the B-H characteristics of the core materials and the system operational specifications. The general reluctance relationships are that the tertiary leg must be saturated by the primary magnetomotive force acting on the system alone while the shunt and primary legs do not saturate. At the same time, the maximum coercive foce existing in the shunt and primary legs must be less than the coercive force of the core at saturation flux density, while the maximum coercive force of the tertiary leg must be greater than the coercive force of the core at saturation flux density. These conditions insure that the primary magnetomotive force drives the tertiary leg well into saturation. Preferably, the coupling of flux from the tertiary to the primary leg is made close to unity in order to maximize flux coupled to the unsaturated tertiary leg. Additionally, the net reluctance change of the primary circuit as between the saturated and unsaturated conditions in the tertiary leg is kept low so that the primary current does not increase substantially when the tertiary leg saturates. To that end, the magnitude of the reluctance presented by shunt leg 99 is minimized at the same time that the already-mentioned conditions still are met. Other constraints on the core dimensions are satisfied by meeting the requirement that the flux in the primary leg due to the tertiary magnetomotive force be a minimum while the cross-sectional areas of both the primary and shunt legs are large enough to prevent saturation.

Capacitor 105 is of a value sufficient to store energy in an amount to supply both the energy dissipated in tertiary core 98 and the energy demands of the cathode-ray tube load, including dissipation in multiplier 90 and in the other associated circuitry such as the illustrated focus control network. However, when the load is substantially increased, the stored energy in capacitor 105 becomes insufficient to cause the tertiary core hysteresis to be completely traversed when energy is returned from the capacitor to the tertiary winding. Consequently, the tertiary voltage then becomes much lower in amplitude as well as unsymmetrical, as a result of which the operation of the tertiary magnetic circuit ceases to function and no longer is able to supply the energy demands of the load. Such operational drop-out provides short-circuit protection for the system. Even under short-circuit load conditions imposed on tertiary winding 89, the peak current in primary winding 63 does not increase substantially. This occurs because the short circuit of the tertiary winding produces a tertiary magnetomotive force and flux in opposition to that provided by the primary winding. As a result, most of the primary flux is returned to the primary circuit through the shunt leg and hence provides isolation between the tertiary load and the primary supply. That is, the system affords overload protection for the primary driving source.

It will be observed that the described cathode-ray tube high-voltage supply system serves to optimize high voltage regulation characteristics while yet maintaining simplicity of the horizontal deflection system and without requiring any significant design changes in the design of the television receiver itself. It produces a well defined square-shaped tertiary output pulse. The system exhibits minimum ringing during scanning intervals while at the same time producing a flat positive peak during retrace in order to produce a linear relationship between high voltage and current. In addition, the substantial breadth of the output pulses enables charging of the capacitors in multiplier 90 for a substantial por tion. of the time available. At the same time, the output impedance presented by tertiary winding 89 is very low as a result of the saturation so as to maximize the voltage transfer to multiplier 90 by reason of the resulting small charge time constant. The combination of the ferro-magnetic effect and the substantial degree of saturation in the tertiary core results in the presentation of a constant peak-to-peak voltage to multiplier 90. More- 7 over, the high voltage regulation exhibited by the system is substantially independent of at least reasonably small B+ supply voltage variations.

While a particular embodiment of the present invention has been shown and described, it is apparent that changes and modifications may be made therein without departing from the invention in its broader aspects. The aim of the appended claims, therefore, is to cover all such changes and modifications as fall within the true spirit and scope of the invention.

1 claim:

1. In a cathode ray tube high-voltage supply system in which sawtooth-shaped current pulses are developed in a first transformer winding in order to produce a scanning waveform in a deflection yoke on said cathode ray tube, in which energy developed as a result of magnetic field collapse in said deflection yoke is utilized to produce high-voltage output pulses in a second winding and in which the load coupled to said second winding requires a broad generally-square pulse shape, the improvement comprising:

a first closed magnetic circuit non-saturating in response to development of said sawtooth-shaped pulses or in the presence of said energy and including a first ferromagnetic core upon which said first winding is wound;

a second closed magnetic circuit saturating in response to said energy and including only a portion of said first core together with a second ferromagnetic core upon which said second winding is wound;

and a capacitor, included in said load, coupled across said second winding and having a value enabling current cycles in said second winding to coincide with current cycles in said first winding sufficiently that said collapse initiates saturation reversal in said second core.

2. A system as defined in claim 1 in which said load includes a voltage multiplier having capacitance chargeable by said output pulses and in which the magnetization characteristic of said second core is selected to optimize charging of said capacitance after each appearance of said sawtooth-shaped pulses.

3. A system as defined in claim 1 in which said second core is proportioned magnetically to develop said output pulses for optimized application to said load while effecting minimal effect upon the shape of said sawtooth pulses.

4. A system as defined in claim 1 in which said capacitor is of a value to store energy from said output pulses in an amount sufficient to drive said second core into saturation during the return of energy from said capacitor in the intervals between said output pulses.

5. A system as defined in claim 1 in which the value of said capacitor and the magnetic characteristic of said second core are selected such that said second core exhibits one complete traversal of its hysteresis loop for each cycle of said sawtooth-shaped pulses.

6. A system as defined in claim 5 in which the amount of energy exchanged between said capacitor and said second core is sufficient to maintain the degree of peak saturation of said second core substantially the same both during said output pulses and in the interval therebetween.

7. A system as defined in claim 1 in which the magnetic reluctance of said portion is substantially smaller than that of the remainder of said first core, and the cross-sectional area of said portion is sufficiently large to prevent its saturation in response both to said developed energy and to energy exchange between said capacitor and said second core.

8. A system as defined in claim 1 in which said portion is unsaturated in response to energy in said system while said second core saturates in response to exchange of energy with said capacitor.

9. A system as defined in claim 1 in which the maximum coercive force existing in said first core is less than the coercive force of said second core at saturation flux density, and the maximum coercive force of said second core is greater than the coercive force of said first core at the saturation flux density.

10. A system as defined in claim 1 in which the value of said capacitor is sufficient to store energy from said output pulses in an amount ample to return to said second core energy equal to energy dissipated therein together with energy required by said load.

11. A system as defined in claim 1 in which said second core saturates at approximately the middle of the current cycle, following which saturation said capacitor discharges and then is charged in the reverse direction.

12. A system as defined in claim 1 in which said capacitor is alternately charged in opposing directions, and in which said second core alternately becomes saturated in reverse directions.

13. A system as defined in claim 1 in which said second winding exhibits a value of inductance, during unsaturation of said second case, sufficiently high to prevent any significant discharge of said capacitor into

Claims

1. In a cathode ray tube high-voltage supply system in which sawtooth-shaped current pulses are developed in a first transformer winding in order to produce a scanning waveform in a deflection yoke on said cathode ray tube, in which energy developed as a result of magnetic field collapse in said deflection yoke is utilized to produce high-voltage output pulses in a second winding and in which the load coupled to said second winding requires a broad generally-square pulse shape, the improvement comprising: a first closed magnetic circuit non-saturating in response to development of said sawtooth-shaped pulses or in the presence of said energy and including a first ferromagnetic core upon which said first winding is wound; a second closed magnetic circuit saturating in response to said energy and including only a portion of said first core together with a second ferromagnetic core upon which said second winding is wound; and a capacitor, included in said load, coupled across said second winding and having a value enabling current cycles in said second winding to coincide with current cycles in said first winding sufficiently that said collapse initiates saturation reversal in said second core.

13. A system as defined in claim 1 in which said second winding exhibits a value of inductance, during unsaturation of said second case, sufficiently high to prevent any significant discharge of said capacitor into said second winding.