US2655615A

US2655615A - Television circuit

Info

Publication number: US2655615A
Application number: US169643A
Authority: US
Inventors: Seldin Leon
Original assignee: Allen B du Mont Laboratories Inc
Current assignee: Allen B du Mont Laboratories Inc
Priority date: 1950-06-22
Filing date: 1950-06-22
Publication date: 1953-10-13
Anticipated expiration: 1970-10-13

Description

SPEAKER PICTURE uaa VERTICAL DEFLECTION YOKE Fig. I

SOUND CIRCUITS DEFLECTION YOKE z I|- CATHODE RAY L. SELDIN TELEVISION CIRCUIT CIRCUITS Filed June 22, 1950 VERTICAL DEFLECTION SOUND CIRCUITS PICTURE AND SYNC SEPARATOR CIRCUITS HORIZONTAL DEFLECTION INVENTOR. .LEON SELDIN ANTENNA Oct. 13, 1953 P W X ATTORNEYS FREQUENCY IN KILOCYCLES F lg. 2

Patented Oct. 13, 1953 2,655,615 TELEVISION CIRCUIT Leon Seldin, River Edge, N. 1., assignor to Allen B. Du Mont Laboratories, a corporation of Delaware Inc., Clifton, N. 1.,

Application June 22, 1950, Serial No. 189,843

Claims. (01. sis-2'1) This invention relates to television apparatus and more particularly to means for accelerating and deflecting electrons in the beanrof a cathoderay picture tube Horizontal deflection current for a television cathode ray picture tube has been obtained heretofore by combining a drive tube, a magnetic deflection yoke, and a damper tube. The high voltage impulse which occurs during beam retrace has been rectified to produce an accelerating potential for the second anode of the cathode ray tube. The coupling between the drive tube, the deflection yoke, and the rectifier has usually been a transformer or an autotransformer.

Transformers and autotransformers are expensive and require careful control of such characteristics as coupling coeilicients, self-resonant frequencies of the separate windings, and mutual resonances between the windings in order to prevent undesirable variances in performance of the assembled television apparatus. Control of these characteristics in production quantities is diflicult because of variations in the size of wire used in the windings of transformers and autotransformers.

It is an object of the invention to provide an improved deflection circuit and second anode power supply.

It is among the further objects of the inven- I tion: to provide an inexpensive combined deflection circuit and second anode supply eliminating the requirement for a transformer or an autotransformer for coupling between the drive tube, the deflection yoke and the rectifier tube, to provide a deflection circuit in which the essential characteristics of all components are readily controlled, to provide an anode supply having low internal impedance, to provide an anode supply in which variations in second anode current cause a minimum of deflection distortion.

In accordance with the invention, a drive tube, a damper tube and a deflection yoke are connected in parallel, and a tuned inductance couples these parallel elements to the high voltage rectifler.

In the drawings:

Figure 1 is a diagram, partly in schematic and partly in block form, of a receiver embodying the invention; and

Figure 2 shows a set of curves of voltage versus frequency to illustrate the operation of the invention in part. I

Referring to Figure 1, a periodic horizontal drive signal illustrated at II, characteristic of receivers or the prior art, is derived from the 2 horizontal deflection generating circuits and applied to input electrodes of drive tubes it and I4. The plates of the drive tubes are directly connected to a horizontal deflection yoke I! for a cathode-ray picture tube l1 and to a cathode of a damper tube ll. Small resistors It and II are placed in series respectively with each or the drive tube plates to prevent parasitic oscillations. The damper tube It is oriented so that it is in direct current series with the drive tubes l3 and It. A choke coil 23 connects the common junction of the deflecting coil and associated elements to a source II of positive voltage. The low impedance end oi the deflection yoke I6 is connected to the common junction of an adjustable bypassed resistor 28, which serves as a horizontal centering controLand a fixed resistor 28, connected to.the junction of the plate of the damper tube is and a bypass capacitor 29. The distributed capacitances and capacitances-toground of the active elements are shown in dashed lines as a capacitance 32.

A step-up inductor 33, tunable by means of a slug, connects the deflection elements comprising the drive tubes l3 and II, the yoke l8 and damper tube II, to a tuning capacitor 31 and to a high voltage capacitor 38. The high voltage capacitor 38 couples the inductance 33 to a pair of series high voltage rectifier tubes fl and 42. The cathode of one rectifier tube 42 is connected to the second anode terminal 48 of the picture tube ll across a high voltage bypass capacitor ll and through a filter resistor 40. The capacitance-toground of the second anode of the cathode-ray tube II which, in combination with the fllter resistor it, removes alternating components from the second anode supply, is shown in dashed lines as a capacitance 49.

The operation of the circuit is as follows: The drive signal l2, having as a repetition rate the i'requency of horizontal deflection, periodically cuts oflf the drive tubes i3 and I4, causing the voltage 52 of the horizontal deflection yoke II to gopositive. The horizontal yoke resonates for a half cycle with the capacitance-to-ground 32. At the end of the half cycle, the damper tube ll begins to conduct, preventing further oscillation of this part of the circuit, The voltage I2 across the deflection yoke causes a sawtooth current to flow through the yoke, as is desired for linear horizontal deflection of the cathode-ray beam.

The voltage 52 may be considered to becomposed of a fundamental component at the horizontal deflection frequency of 15.75 kilocycles per second and of second, third, and higher harmonic components at frequencies which are integral multiples of that frequency. The amplitude of each harmonic diminishes from the fundamental, which has a component peak amplitude of approximately 15.'7 per cent or the peak-to-peak voltage 52, to the eleventh harmonic at 173.25 kilocycles per second which has component peak amplitude or approximately 1 per cent. Harmonics higher than the eleventh may be neglected.

The step-up inductor 33 has an inductance value considerably higher than that of the deflection yoke 16 and is tuned to 32.6 kilocycles per second, slightly higher than the 31.5 kilocycles per second frequency or the second harmonic of the voltage 52. In this condition the inductor 33 is partially series resonant with the capacitor 31, which, with the capacitance-toground of dissociated elements, may be considered to form a total input capacitance-toground of the recti flers 4| and 42.

In figure 2 there is a family of response curves, showing as a function of fre uency, the ratio of the voltage across the capacitance-to-ground 31 (E2) to a single fre uency voltage El across the deflection yoke it, this latter voltage corresponding to the component voltages of the wave 52 at the frequencies at which they occur. In particular, the highest curve, which is discontinuous at the frequency of tuning, represents a condition in which no current is drawn by the cathode-ray tube, and no appreciable losses occur in the other parts of the circuit. At low frequencies there is no change of voltage between El and E2. This is substantially the condition at the fundamental deflection ferquency where the circuit may be considered to? be a simple low-pass filter. As resonanceis approached, E2 becomes considerably higher than El until in the preferred circuit at the second harmonic frequency of 31.5 kilocycles per second, there occurs a step-up of approximately 15 times. At the third and higher, harmonic frequencies, no appreciable voltage E2 occurs.

Thecurves

55, 56, 51 and 58 show responses in which the circuit is progressively more heavily loaded. It is seen by the relative positions of the curves that loading does not appreciably affect the value of E2/El at the second harmonic frequency 31.5 kc./sec. until a certain critical loading is reached, as indicated by the curve 56. Loading 01' the circuit beyond this point causes loss in E2, as indicated by the curves 5'! and 58. This relationship between loading and E2 is one of the reasons for the low output impedance of the second anode supply 01' the invention, asdistinguished from the prior The portion of the circuit comprising the capacitors 38 and H, and the rectifiers II and I2, is one form of a voltage doubling circuit, but its purpose is not merely to obtain increased voltage output. Choice of this particular circuit allows the capacitors 38 and II to be charged at opposite peaks of the voltage wave, thus increasing detector efliciency. In addition, the doubler circuit permits a greater ratio to exist between the capacitance 31 and the distributed capacitance of the step-up inductor 33. This permits greater efficiency of the step-circuit so that the frequencies of resonance and of second harmonic may be kept further apart. By this detuning, the series resonant step-up circuit in the absence of load is reactive. In this condition a resistive load adds vectorially to the reactive series impedance, so that there is negligible loss of voltage untilthej-"above mentioned critical loading is reached.' As a result, for loads below the critical amount, there is a, low efiective output impedance of the second anode supply, which is desirable.

In the embodiment shown, the choice of the second harmonic for the reactive series resonance represents an optimum design condition.

In order to operate with low output impedance as shown by the

curves

54, 55, 56 of Figure 2, it is necessary that the Q of the coil 33 be sufflciently high. Within given cost and space limitations, a high Q coil can be best obtained at harmonic frequencies higher than the fundamental. On the other hand, if the coil 33 is reactively resonant at a harmonic frequency higherthan the second, thedeflection circuit is coupled too closely to the rectifier circuit, causing undesirable interaction between the circuits.

The choice of resonance on the high side of second harmonic frequency rather than on the low side is preferred. Although, as has been shown, there is little change in the amplitude of E2 before the critical loading point is reached, there is a change of phase of the current flowing through the inductor,33 with variations in load current. If this current is in the wrong phasal relation with'the diode current, it can out off the diode circuit temporarily, causing an undesirable picture condition known as "folding, in which bands extending vertically through the picture are compressed in a horizontal di rection. The correct phasing is obtained by resonating the circuit above the second harmonic frequency, and "folding is thereby avoided.

A feature of my invention lies in the position of the capacitor 38 in the circuit. In circuits of the prior art it has been customary to connect the anode of the rectifier tube directly to a source of positive potential, without the use of a blocking capacitor. In the circuit of my invention, the capacitor 38 prevents the flow of direct current from the source 24 through the rectifier to the connector 48. In case of accidental human contact with this connector 48, the capacitor 38 prevents dangerous shock currents from flowing. I

In the embodiment shown, heater power for the rectifler tubes is supplied by direct current sources. Alternatively, several turns of 'high voltage wire might be disposed adjacent to the choke 23, to supply alternating current energy tothe rectifier heater. It is inadvisable to draw heater power from the step-up coil 33, or from any other part of the high voltage circuit, since such power losses will appear as lowered Q of the circuit, which will result in poor regulation of the second anode supply.

What is claimed is:

1. In a television receiver, a cathode-ray picture tube comprising an acceleration electrode, a cathode-ray deflection means, a source of repetitive deflection signals connected to said deflection means to deflect the cathode-ray beam in said tube, inductance and a capacitance connected in series and connected to receive energy from said source of deflection signals, said combination of inductance and capacitance being tuned to be resonated by said repetitive deflection signals, and rectifier means connected between said acceleration electrode and the junction of said series-connected inductance and ca- 1 paoitance, whereby said electrode receives enersy derived through said rectifier means from 5 said series-connected inductance and capacitance.

2. The apparatus of claim 1, said series-connected inductance and capacitance being tuned to resonate in accordance with the repetitive rate of said deflection signals.

3. The apparatus of claim 1, said series-connected inductance and capacitance being tuned to resonate at a harmonic of the repetition rate 01' said deflection signals.

4. The apparatus of claim 1. said series-connected inductance and capacitance being turned to resonate at a frequency slightly higher than a harmonic of the repetition rate of said deflection signals.

5. The apparatus 01 claim 1, said cathode-ray deflection means comprising a magnetic coil, and

deflection energy to said coil, a diode damper tube connected in parallel with said coil, a series combination of inductance and a first capacitance connected to receive energy from said source of signals, a second capacitance having a terminal thereof connected to the junction of said inductance and said first capacitance, a rectifier device connected between the remaining terminal of said second capacitance and the remaining terminal of said first capacitance, and a second rectifier device connected between said remaining terminal of said second capacitance and said accelerator electrode.

LEON SELDIN.

References Cited in the flle of this patent UNITED STATES PATENTS Number Name Date 2,188,647 Busse Jan. 30, 1940 2,482,737 Shaw Sept. 20, 1949 2,523,108 Friend Sept. 19, 1950 2,538,857 Schade Jan. 2, 1951 2,541,918 De Mers Feb. 13, 1951