DE1161358B - Arrangement to protect cathode ray tubes against screen destruction - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Boarding school Kl .: HOIj

German KL: 21g-13/40

Number:
File number:
Registration date:
Display day:

F 34729 VIII c / 21g
August 19, 1961
January 16, 1964

Arrangements for protecting cathode ray tubes are known which serve to prevent destruction of the screen by the impact of the undeflected electron beam when one of the To prevent deflection device. This is generally done by switching a beam controlling one Electrode at a potential that prevents the beam from striking the screen. One uses z. B. in receiver circuits a rectifier stage coupled to the line deflector, which a positive bias voltage for an acceleration electrode or from the deflection voltage Control electrode of the cathode ray tube generated. To avoid an additional beam control must this DC voltage can be smoothed by a capacitor circuit with a high time constant. In the event of failure of the tilting device, the potential of the controlling electrode drops in the negative direction, so that the beam current is suppressed to the screen.

This circuit, which is simple in itself, has the disadvantage that slow fluctuations in the tilt amplitude, which may not be noticed in the picture, at the same time on the intensity or focus of the Can act and cause a disturbing fluctuation in brightness. On the other hand, it is often desired to change the potential of the control electrode with a control voltage.

However, the high time constant and the limit potential of the rectifier path may be necessary for this obstructive.

Furthermore, protective circuits for cathode ray tubes are already known in which the Voltages taken from deflection devices are used by means of two diodes or two Transistors generate a voltage which releases the beam current during the path to the cathode ray tube to switch. If a tilting device fails, the cathode ray tube is then blocked. This one Circuits, however, have the disadvantage that changes in the breakover voltages or the saturation voltages of the diodes or transistors cause a change the bias of the Wehnelt electrode of the cathode ray tube. This The disadvantage is to be avoided if the protective circuit only emits a voltage in the event of a fault, while in normal operation only independent of fluctuations in the tilting devices or the switching elements the normal bias of the cathode ray tube is effective.

The object of the invention is to provide a simple protective circuit which, using very few switching elements, has an effective arrangement for protecting
Cathode ray tubes against screen destruction

Applicant:
TV G. mb H.,
Darmstadt, Am Alten Bahnhof 6

Named as inventor:

Dipl.-Ing. Christian Schubert, Darmstadt

complete protection of the tube against failure of the tilting devices ensures, but also offers the possibility of briefly reducing the potential of the controlling electrode to regulate or to control with blanking pulses. In addition, the tipping power withdrawn should be as small as possible so as not to affect the linearity of the deflection.

Therefore, in an arrangement for the protection of cathode ray tubes, in particular image recording tubes, against burning of the screen, in which, in the event of failure of a deflection device, an electrode controlling the beam is switched to a negative potential preventing the beam from striking the screen and a DC voltage obtained by rectifying the deflection voltage is used for this purpose , the voltage is fed according to the invention to a capacitor, the charging voltage of which blocks a diode which is biased by a DC voltage U _b via a resistor so that during normal operation the sum of the bias voltage U _b and the rectified voltage U _{k is} greater than the operating voltage Ug of the controlling device Electrode is. Two such rectifier circuits are advantageously connected to one another in such a way that one is fed by the vertical deflection voltages and the other is fed by the horizontal deflection voltages and, if one of the tilting devices fails, the beam is prevented from impinging on the screen by opening one of the biased diodes. In the event that only a very small amount of deflection energy is available for the protective circuit, the pulse voltage or the direct voltage obtained from the pulses can be amplified with a transistor stage and the reverse voltage required to bias the diodes can thereby be obtained.

The question of which electrode of the cathode ray tube the reverse voltage should be applied to,

309 779/166

Claims (1)

3 4 depends on the type of tube used and the method is now more negative than its anode, so that at the the associated circuit. For example, in the case of the control electrode, a voltage between the auxiliary voltage U ₁ , Picture display tubes apply the reverse voltage to the and the bias voltage U ₁ , lying voltage Wehnelt electrode to be placed in the tube. When the picture appears. In the event that der'Widerstand 17 very high-recording tubes If it is advantageous if the target voltage is 5 ohmic, the potential of the auxiliary voltage to switch, for example by setting the voltage U _b on the controlled electrode in the case of super orthicons. In order to The beam is sent to the network connected to the storage electrode immediately after the failure of the a reverse voltage of about -5 volts. Locked in this tipping device. The time constant of this In case the potential of the electrode on the ganges depends on the size of the capacitors 7 Cathode-facing side so negative that the io and 10 and the resistors 9, 12 and 17 from. Of the Beam can no longer reach the screen. In ahn- energy consumption of this circuit is Licher way one can with Vidikonen with a turn of high-resistance silicon diodes very low and relatively low voltage the potential of the signal depends on the desired response time of the Lower the electrode so far that the beam does not switch. can achieve more. In all these cases, if only very little breakover voltage of the circuit according to the invention is available, an amplifier stage can be used to switch the electrode in question during normal operation, as shown in FIG. 2 is shown. operating capacitively and resistively remains under little load. Here are the on the capacitors 7 and 10 generated so that they can be controlled with any control voltage th voltages via resistors 8 and 11 to the. 20 base electrodes of transistors 13 and 14 applied; In the following, on the basis of FIG. 1 and 2 the control voltage is explained in more detail for the diodes 18 and 19 in exemplary embodiments of the invention. the same way as in the previous example-led by these shows. The DC voltage required for this, F i g. 1 a protective circuit which works only with diodes and which is removed from the capacitors 7 and 10 and ² 5 only needs to be just large enough that FIG Saturation controlled power level is used. will. The electrode in FIG. 1 shown in this example. 1, 1 and 2 are two transducers, on whose beam tube is a superorthicon tube, which contains the pulse voltages of the vertical and a bulb 16, a mesh electrode 15 in the primary side. This Horizontalablenkgerätes are created. The two 30 network electrodes are located during normal operating outputs of the transformers are each connected to approximately zero potential and needs to be connected to the capacitor C with the rectifiers 3, 4 or 5, 6 to prevent the impact of the cathode ray, which are polarized in this way that with one the screen can only be made negative by 5 volts. Symmetry point connected capacitors 7, 10 The auxiliary voltage required for this circuit are charged unpositiv to U _k. The capacitors 35 gen ± U _b therefore only need the size of a resistor 9 and 12 is connected in parallel. That'll be 6 to 10 volts. In the case of Fi g. 2 are but the point of symmetry is polarized reversely with the negative pole of one of the diodes 3, 4 and 5, 6, since connected to the auxiliary voltage source - U _b . The circuit opening the transistors 13 and 14 a negative also contains two diodes 18 and 19, which is needed with their voltage. Cathodes with the cathodes of the aforementioned 40. In both embodiments were for Diodes 4 and 6 are connected while their rectification of the breakover voltage is two in series Anodes are used on that control electrode of the cathode-lying diodes 3, 4 or 5, 6. These Radiation tube are applied, which is used for the suppression circuit to generate a high voltage of the beam current is determined. This control electrode is advantageous. In special cases, however, the is via a high resistance 17 with a 45 diodes 3 and 4 and the capacitors C omitted Bias battery —U _g connected. For that will. In the exemplary embodiment according to FIG. 1 Correct operation of the circuit is now important, the use of the following circuit elements is appropriate- that during normal operation the sum of the auxiliary voltage is moderate. U _b and the rectifier voltage iU _k greater than the capacitor C 1 Mf Operating voltage U _{g of} the controlling electrode is. 50 ^ j - _{n 1} · »« This is explained in more detail using an example. When the capacitor 7 ■ U ₅ I Mt predetermined operating voltage of the controlling elec- capacitor 10 0.1 Mf trode U _{g is} -30 volts and a blocking of the resistor 20 is 220 kΩ Beam by lowering this operating voltage to resistor 21 220 kß -40VoIt is desired, the auxiliary voltage should 55 wi / Wotonri π nvn z. B. U _b -4OVoIt and the rectified voltage be about +15 volts, so that the condition 15 ^{Dlode 3} OA 258 - 40> - 30 is fulfilled. In this case the result is diode 4 OA 258 the protective effect of the circuit if the diode 5 OA 258 fails Tipping devices as follows. Initially, the positive 60 diode holds 6 OA 258 tive bias of the cathode of diode 18 or 19 _{diode 18} \ \ \ \ \ [[\ \ \ \ \ \ [[\ _s 33 _(silicon) compared to the operating voltage U ₁ , as a result of the open, _ "" _r ". _y . , charge of the capacitor 7 or 8 the blocking of this ^{Dlode w b} ^ (aawxaa) Diode upright. The operating potential of the control electrode is therefore only determined by the voltage U ₁ . 6 ₅ Patent Claims: But does that fall on the capacitor? or 10 lying 1st arrangement for the protection of cathode ray direct voltage due to failure of one of the tilting devices tubes, in particular image pickup tubes against away, so one of the diodes 18,19 opens, since their ka. device by switching an electrode controlling the beam to a beam preventing the impingement of the screen z. B. more negative potential, characterized in that pulse voltages taken from a deflection device are rectified and charge a capacitor, the charging voltage of which blocks a diode, which is supplied via a resistor with a DC voltage U _b in such a size that during normal operation the sum of the Bülfss voltage U _b and the rectified voltage U _{k is} more positive than the operating voltage of the controlling electrode U _g . 2. Arrangement according to claim 1, characterized in that the capacitor voltage or Pulse voltage is increased by an amplifier. 3. Arrangement according to claim 1 or 2, characterized in that in a superorthicon tube as the controlling electrode, the one on the side of the screen facing away from the cathode Net (15) is used. Considered publications:
German Auslegeschrift No. 1 032 424,
1062348. 1 sheet of drawings 309 779/166 1.64 © Bundesdruckerei Berlin