DE2252967A1 - CIRCUIT ARRANGEMENT FOR INTERRUPTING THE POWER SUPPLY TO A TUBE IN THE TELEVISION RECEIVING DEVICES IN THE EVENT OF POWER OVERLOAD - Google Patents

Description

LOEWE OPTA GMBH October 25, 1972

1 Berlin 46 Ma / He - P 882

Teltowkanalstr. 1-h

Circuit arrangement for interrupting the power supply to a picture tube in television receivers in the event of power overload

The invention relates to a circuit arrangement for interrupting the energy supply a cathode ray tube in electronic picture display devices in the event of power overload, especially in television receivers with thyristor horizontal deflection circuits.

With conventional tube deflection stages, one Power overload is almost impossible, as the beam power is due to the relatively large Generator internal resistance of the high voltage source is limited. Show a different behavior on the other hand, deflection circuits equipped with semiconductors, in particular thyristor deflection circuits; they can deliver several times the power into the picture tube. Because of this, it is well known Jet current limiting circuits used to prevent a power overload of the picture tube. Such beam

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Current limiting levels are usually as Threshold switches designed to deflect the excess beam current.

It has been found that these beam current limiting circuits do not offer absolute protection against the disturbances known as a result of excessive beam current. Through a Excessive beam currents in the picture tube are e.g. self-destruction or degradation of the cathode, pulling the image mask forward and / or destroying the luminous surface and destroying it the rectifier cascade in the high-voltage part cannot be ruled out, as in the latter case the power loss is too high. Other defects can occur in the event of an overload in the Video transistor or the video amplifier stage occur as soon as the base circuits and Burn off the decoupling resistors. These possible errors occur especially when in the circuit is defective or the beam current limiting circuit does not work, because long-term values of the beam current of more than 10 mA are achieved. It is therefore advisable to independent of known jet current limiting circuits, when a defined beam current threshold is exceeded, the energy supply to interrupt the picture tube at such a point on the device that even the

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steering generator including the high voltage generator is completely switched off and an automatic restart after it has been eliminated Error is enabled.

According to the invention it is provided for this purpose that in Deflection circuit, preferably before the horizontal deflection circuit, shunted with one controllable power gate is arranged, which has a control circuit depending on a behind the high-voltage generator tapped information from the beam current when exceeding a defined beam current threshold conductive and short-circuits the supply circuit. Switching off the power supply of the horizontal deflection stage on the input side prevents that an energy is given off to the components endangered by beam current overload will·

In a further embodiment it is provided that the information tapped from the jet stream after rectification, fed via a resistor to a filter capacitor for image-frequency filtering and integrated and compared with a reference voltage, and that via the control circuit when the reference voltage is exceeded by the information from the beam current Ignition current to the ignition electrode of the current gate

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in the shunt of the deflection circuit flows and the shunt opens, so that the deflection electronic circuit is short-circuited.

In another embodiment, the invention provides that the tapped from the jet stream Information after rectification via a resistor to a capacitor for frame rate Sieving fed and integrated in this and fed to a threshold switch, which when a defined threshold value is applied, which is directly proportional to the beam current threshold value is, through-t and the control circuit opens, whereby the power gate in the shunt and the deflection circuit short-circuited will.

So that the energy supply is not interrupted in the event of brief beam current peak errors is, the time constant of the filter element is chosen so that the threshold switch responds or the reference voltage is only exceeded when at least the tube is overloaded while the image is running.

In a preferred embodiment of the invention it is provided that the threshold switch is off a series connection of a drawing diode and a

i 0 9 8 2 0 / ■■ J ■> 2 2

There is a diode arranged in the forward direction, which is connected to the base of a switching transistor the control circuit is connected, the when the Zener voltage and the diode forward voltage of the integrated ignition voltage are exceeded switches through to the ignition electrode of the current gate in the shunt.

The invention is particularly suitable in connection with a thyristor horizontal deflection circuit with an input-side return thyristor, which is connected in parallel to the deflection unit and thus the current gate is shunted to short-circuit the supply current can form. The ignition electrode of this thyristor is in a manner known per se with a transistor control stage connected, via which the applied to the control electrode of the input transistor Ignition pulses for commutation are switched through. The flyback thyristor is thus used for two different tasks. On the one hand, he leads the normal way Ignition pulses the commutation of the horizontal deflection circuit and on the other hand is used to short-circuit the consumer current. One Current overloading of this thyristor is usually ruled out because it is natural Current limitation is given by the internal resistance of the voltage source.

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To simplify the structural design and the restriction to only a few components is a further embodiment of the invention the input switching transistor at the same time as a switching element for the threshold value switch and is used for this Zwock with its base not only with the ignition pulse generator, but also via the Zener diode line connected to the circuit for the information tapped from the beam current.

In a total coordination of the circuit it is provided that the control circuit consists of one capacitively coupled to the ignition electrode via the collector, in an emitter-base circuit arranged pnp transistor consists, which via a collector resistor with an npn-doped Input switching transistor is connected, whose emitter is connected to ground and whose Basis on the one hand with the ignition pulse generator and on the other hand with the cathode of the diode of the Zener diode line is connected via the Zener diode is connected to the filter capacitor,

According to a further feature of the invention, the overload protection circuit is provided with a device e main fuse, e.g. a reusable one electronic fuse in the power rectifier part, coupled, which takes the entire energy

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Supply interrupts j so that the return » thyristor blocks automatically and when the supply current is switched on again for as long remains locked and triggered normally. can, until the protection circuit with renewed responds to an error that has not been rectified. One in the main circuit is preferred for this purpose used electronic fuse that can be switched off on the AC side a rectifier and a charging and / or smoothing capacitor connected in series for this purpose exists, where between the rectifier ■ and the charging and / or smoothing capacitor in A controllable current gate is connected in series, which depends on the faulty commutation of the Return transistor blocks and via a lift connection by charging the charging and / or smoothing capacitor when the return thyristor is blocked becomes conductive again ο

The invention is described below in two exemplary embodiments explained in more detail with reference to the drawing.

In the drawing, %

Fig. 1 is an incompletely shown Thyrxstor Horizontalablenkschalttsng with an overload protection device and ■

/ 04

Fig. 2 shows an indicated thyristor horizontal deflection circuit with a detailed overload protection circuit shown, via which the ignition pulses for commutating the return thyristor are fed in at the same time.

The circuit arrangement shown in Fig. 1 consists of a thyristor horizontal deflection circuit with an input-side return thyristor circuit 1 consisting of a return thyristor 2 and a diode 3 connected with opposite polarity to this and with a parallel thyristor circuit h, which consists of a reverse thyristor arranged opposite the thyristor There is a trace thyristor 5 and a diode 6 connected in parallel with opposite polarity thereto. On the output side, the deflection circuit is terminated with a primary winding of a high-voltage transformer as a shunt inductance and a tangent correction capacitance 8 arranged in series therewith. The horizontal deflection circuit is inductively-transformer-connected via the secondary winding 11 of the high-voltage transformer to the symbolically represented picture tube 12, the base point of the secondary winding 11 being connected to ground via a resistor 13. The measurement information that can be tapped off at the resistor 13 is transmitted to an integration

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member 14 supplied, which is shared with one formed overload protection circuit belonging threshold switch 15 is connected to the depending on a defined beam current threshold becomes effective when a proportional voltage is applied to the integration element 14 and switches an ignition current through to the ignition electrode of the thyristor 2, causing it to open and shorts the deflection circuit. Through the Short-circuit current speaks a fuse, not shown, preferably a voltage-dependent, automatically reclosable electronic fuse, so that as a result of the anode voltage collapse, the return thyristor 2 and are triggered normally by the ignition pulses 16 when the device is switched on again unless the fault has not been eliminated and the protective circuit responds again.

In Fig. 2 is also a thyristor horizontal deflection circuit with a flyback thyristor circuit 1 from a flyback thyristor 2 a diode connected with opposite polarity 3, a trace thyristor 4 with a trace thyristor 5 and one in opposite polarity direction switched diode 6 and a primary winding 7 arranged on the output side Tangent correction capacitance 8 shown. The power supply is provided by the voltage source

- 10 -

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1θ tL ·, via the series inductance 9 and the storage capacitance 10. The secondary winding 11 is connected via the connection A via the rectifier cascade, not shown, to the symbolically drawn picture tube. The bottom point of the secondary winding, on the other hand, is connected to ground via a measuring resistor 13 'from which the measurement information for the protective circuit is tapped. The beam current-dependent measurement information is fed to a series capacitance 19 and a diode 20 connected in the reverse direction and connected to ground. This diode capacitance combination is intended to ensure that only the positive half-wellons are stored in the filter capacitor 22 connected to ground via the resistor 21. With this filter circuit, a Zener diode 23 is connected to the cathode Zk, which is connected to the cathode on the one hand via a resistor 25 to ground and on the other hand to the base of an input switching transistor 26, via whose base the ignition pulses 16 for commutation are also fitted. The npn-doped input switching transistor 26 is connected to ground via the emitter and via the collector and a series resistor 27 to the base of a further transistor 28 which is pnp-doped. This transistor 28 is arranged in a base-emitter circuit, the emitter being connected to a po-

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sensitive voltage source U _x ,., and the base over

Yy i

the base resistor 29 are connected. The collector is applied via a "resistor 30" Ground and is capacitive via a capacitor 31 to the ignition electrode of the return thyristor 2 coupled. In the normal operating state, the thyristor horizontal deflection circuit is via the Transistors .26, 28 by the applied ignition pulses controlled and the return thyristor 2 commutiei ^ t.

The measurement information applied to the measuring resistor 13 is connected to ground via the capacitor 19 and the diode 20. The positive DC voltage present is integrated in the filter circuit 21. As soon as the voltage exceeds the Zener voltage 23 and the forward voltage of the diode 2k , the input switching transistor becomes conductive. This also controls the transistor 28, so that from U_. An ignition current flows to the ignition electrode of the return thyristor 2 during the period of the complete charge reversal of the capacitor 31, whereby the return thyristor switches through and only blocks again when the fuse in the power supply unit has briefly switched off the device, so that the anode voltage at the return thyristor collapses. When the device is switched on again, the protective circuit remains ineffective if the defect has been rectified and only responds when the picture tube is overloaded again.

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Claims (1)

LOEWE OPTA GMBH October 25, 1972 Berlin k6 Ma / lie - P 882 Teltowkanalstr. 1-4 Claims 1.) Circuit arrangement for interrupting the energy supply a picture tube in case of power overload, especially in television receivers with thyristor horizontal deflection circuits, characterized in that that in the deflection circuit, preferably before the horizontal deflection circuit, a shunt with fiinem controllable power gate (2) is arranged, this via a control circuit depending on a tapped behind the high-voltage generator Information from the beam current when a defined beam current threshold is exceeded becomes conductive and shorts the supply circuit. 2. Circuit arrangement according to claim 1, characterized in that the information tapped from the beam current after rectification via a resistor (21) a filter capacitor (22) is integrated and compared with a reference voltage, and that via the control circuit when the reference voltage is exceeded by the information from Beam current an ignition current to the ignition electrode of the current gate in the shunt of the deflection current 409820/0422 circle flows, creating the diversion circle is short-circuited. 3. Circuit arrangement according to claim 1, characterized in that the information tapped from the beam current after rectification via a resistor (21) fed to a filter capacitor (22) for image-frequency filtering and integrated therein which is connected to a threshold value switch which, when a defined Threshold value j, which corresponds to the beam current threshold value is directly proportional, switches through and controls the control circuit, so that to the Ignition electrode of the current gate in the shunt an ignition current flows, whereby the deflection circuit is short-circuited. km circuit arrangement according to claim 2 or 3 »characterized in that the time constant of the filter element (21,22) is selected so that the threshold value switch (23» 24) only responds or the reference voltage is only exceeded then, n when at least there is a power overload of the picture tube (12) for the time of an image sequence. 409820/0422 ~ v - 5 · Circuit arrangement according to claim k , in conjunction with claim 3, characterized in that the threshold value switch consists of a series connection of a Zener diode (23) and a diode {2h) arranged in the forward direction, which is connected to the base of a switching transistor (26) the control circuit are connected, which shunted through an ignition voltage to the ignition electrode of the Strointore when the sum voltage from the Zenor voltage and the diode forward voltage is exceeded by the beam current information. 6. Circuit arrangement according to one of the preceding claims, in preliminary connection with a Thyristor deflection circuit with a flyback thyristor, characterized in that the current gate is shunted by the return thyristor (2) is formed whose ignition electrode is directly or indirectly connected to a known, at the control electrode of an input switching transistor (26) applied transistor control stage is connected, via which the ignition pulses for commutation are switched through. 7. Circuit arrangement according to claim 6, characterized in that 409820/042 / Γ the base of the input switching transistor (26) is connected via a diode (2k) and a Zener diode (23) to a filter circuit (21, 22) for the information tapped from the beam current. 8. Circuit arrangement according to claim 7 »characterized in that the control circuit consists of a capacitively coupled via the collector to the ignition electrode, arranged in the emitter-base circuit pnp transistor (28), which via a collector resistor (2.7). is connected to an npn-doped input switching transistor (26) whose emitter is connected to ground and whose base is connected on the one hand to the ignition pulse generator and on the other hand to the cathode of the diode (Zk) of the Zener diode path, which is connected to the filter capacitor (22). 9. Circuit arrangement according to one of the preceding claims, characterized ge indicates that a reclosable fuse element in the power supply circuit of the horizontal deflection circuit is used, which briefly interrupts the supply circuit, whereby the Return thyristor (2) blocks. 409820/042 10. Circuit arrangement according to claim 9 »characterized in that that the electronic fuse is arranged within the power rectifier part and from a rectifier and a charging and / or smoothing capacitor connected in series with this consists in a television receiver, and that between your rectifier and a controllable current gate connected in series to the charging and / or smoothing capacitor is that, depending on the desired false triggering, the supply current flow . / locks and shunted by charging of the charging and / or smoothing capacitor when the thyristor (2) is blocked dos deflection circuit is opened again. 409820/0422