DE1056175B - Circuit arrangement for dynamic sharpness correction for electrostatically focused cathode ray tubes - Google Patents

Description

With cathode ray tubes, especially with television picture display tubes, In general, there is the problem, the luminous point on the whole fluorescent screen get sharp. This problem arises from the fact that the radius of curvature of that circle the center of which lies approximately in the middle of the deflecting means and the focal point on its circular arc moves, is smaller than the radius of curvature of the fluorescent screen. This results in, that the luminous point, which is generally sharply focused in the center of the line or the image degenerates into a light spot with increasing deflection. There is thus the task of Compensation of the sharpness error along a line caused by the less curved screen is caused to provide suitable means to the normally too shallow depth of field balance. This can be achieved by a displacement with the deflection of the electron beam the sharpness is enforced in such a way that the luminous point is always sharp at all points of the grid is focused. With electrostatically focusing cathode ray tubes is for this purpose, starting from the center point, a focusing voltage that increases towards the edge necessary. The problem outlined above is known, and solutions to this have already been found Problem. The invention shows a particularly simple approach for the case that for the deflection of the cathode ray a transformer tilting device is used, which is particularly the case with televisions is common.

According to the invention, the focusing voltage is obtained in that at the base of the transformer, on which the capacitor to obtain the DC voltage from the flyback pulses (Bcoster capacitor) is connected, a transformer is connected via an isolating capacitor and a suitable proportion of the DC voltage is tapped via an adjustable resistor and through the transformer of this direct voltage, the alternating voltage superimposed on the booster voltage, rotated by 180 ° in phase, is added additively in such a way that the focusing grating of Cathode ray tube is supplied with a control voltage variable over the line length, wherein this control voltage is dimensioned so that the resulting luminous point on its whole way the screen is always fully focused. The invention thus turns on in a simple manner The necessary control voltage is derived from the voltage sources present in the television set. It is beneficial to provide a ferrite core for the transformer, d; i for such ferrite cores (lit · losses at the occurring high frequencies

Circuit arrangement

for dynamic sharpness correction

for electrostatically focused

Cathode ray tubes

Applicant:

Max Grundig,
Fürth (Bay.), Kurgartenstr. 37

Ewald Börjes and Richard Otto, Fürth (Bay.),
have been named as inventors

are lower than, for example, with sheet iron. The transmission ratio of the named transformer can preferably be 1: 1, but can also depending on the picture tube to be controlled grow. In order to change the circuit arrangement to the one to be used when changing tubes To be able to adapt the tube type, it is advantageous to design the coupling of the transformer so that it can be changed and thereby to create the possibility of setting the necessary gear ratio accordingly. On the other hand, the alternating voltage can also be used at different, suitably selected taps the secondary winding can be removed.

The operation of the circuit arrangement according to the invention is based on the drawing, which represents an example of maintenance, explained in more detail. In the drawing are all for the operation of the device necessary but unimportant for the explanation of the invention switching elements for the sake of clarity omitted.

In FIG. 1, the lower end of the line transformer 1 is denoted by 2. At this connection point 2, the charging capacitor 3 is connected, which is used to obtain the DC voltage from the Line return pulses are used (booster capacitor). This capacitor 3 is used in a known manner the DC voltage is fed to the line deflection circuit via terminal 4. Also, ah will be the Point 5, an additional DC voltage is also connected in a known manner. It is natural too possible, the booster voltage for other purposes to be used in the device.

TOi 508/166

Claims (4)

1 056 4 75 A potentiometer 7 is connected to the aforementioned base point 2 via a resistor 6. The direct voltage for the focusing electrode of the cathode ray tube is taken from this in a manner known per se. The remaining alternating voltage is discharged via the discharge capacitor 8. In the circuits known up to now, the potentiometer 7 is only used to adjust the sharpness in small areas of the screen, primarily in the center of the image. According to the invention, the primary winding 10 of a transformer 11 is connected to point 2 via a capacitor 9. The secondary winding 12 of the transformer 11 lies in the line running from the potentiometer 7 to the focusing electrode 13 of the cathode ray tube. At point 2 there is a voltage which is composed of a direct voltage and a superimposed alternating voltage. The direct voltage corresponds to the booster voltage generated at the booster capacitor. 2a. For example, a direct voltage of about 750 volts is present at point 2, on which an alternating voltage of about 150 Vss originating from the deflection voltage is superimposed ? 11 just the bills supply voltage component. At point 14 between capacitor 9 and primary winding 10 there is then a voltage as shown schematically in FIG. 2b. A possible retroactive effect of the CL element 10-9 is kept negligibly small by a suitable choice of the transformer. A very high number of turns must be provided in the coil, so that coL is very large. The transmission ratio should generally be 1: 1, but can fluctuate depending on the cathode ray tubes and can also be 1: 1.5, for example. About the potentiometer 7 is the base point 15 of the secondary winding 12, the transformer 11 for the normal. Sharpness adjustment necessary DC voltage component supplied. The AC voltage parts of the voltage at point 15 are derived through the capacitor 8. The transformer 11 rotates in a manner known per se, the phase of the alternating voltage by 180 °. At point 16 behind the secondary winding 12 of the transformer 11 there is therefore a voltage distribution as shown schematically in FIG. 2 c. The resulting voltage consists of a direct voltage component on which an alternating voltage is superimposed, so that the total voltage increases as a function of the deflection of the electron beam from a maximum through a minimum to a further maximum. This voltage therefore has the form necessary to control the focusing electrode, since the focusing voltage must become higher with increasing deflection in order to keep the focal point permanently on the screen. Since the additionally added alternating voltage at the minimum of this voltage or during the passage through the negative half-wave, the voltage below the for focusing, 5! tion in; The DC voltage required in the middle of the screen drops, it is necessary to set a basic DC voltage on potentiometer 7 that is about half the peak voltage of the superimposed AC voltage than when focusing without ίο dynamic correction. Obtaining the focus control voltage according to the invention from the booster voltage with the help of the phase rotation of the transformer 11 and the easy adaptability to changing tubes with the help of the variable coupling or tapping of the transformer 11 and the potentiometer 7 thus provides a threading improvement in the reproduced image. The circuit arrangement according to the invention is in itself independent of the special design of the line deflection stage, the connection of the deflection coils, the high voltage generation, etc. It can also be retrofitted without difficulty in existing television sets. P Λ T E N T A N S P R 0 C H E: 1. Circuit arrangement for dynamic sharpness correction for electrostatically focused cathode ray tubes, especially in television receivers, in which a transformer tilting device is used to deflect the electron beam, characterized in that at the base of the tilting transformer, at which the capacitor to obtain the DC voltage from the return pulses (booster capacitor ) is connected, a transformer is connected via an isolating capacitor, the secondary winding of which is in series with one of. -Adjustable DC voltage derived from the same base point feeds the focusing electrode. ■
■ :. '' . 2: Circuit arrangement according to Claim 1, characterized characterized in that the coupling of the transformer or the tap on the secondary winding is changeable. 3. circuit arrangement according to claim 1 or 2, . characterized in that a ferrite core is used for the transformer. 4. Circuit arrangement according to claim 1 or one of the following claims, characterized in that the on the potentiometer at the base ^; : the DC voltage tapped from the flyback transformer is selected to be approximately half the peak voltage of the AC voltage component higher than with uncorrected focusing. '"· . : .- Publications considered: German patent specifications No. 743 753, 829 469. 1 sheet of drawings © 909 508/166 4. 59