US2808536A - Cathode ray tube protecting and energizing circuits - Google Patents

Description

Oct. 1, 1957 G;F.. uso ETAL 2,808,536

CATHODE RAY TUBE PROTECTING AND ENERGIZING CIRCUITS Filed Nov. 18, 1954 damage if the electron CATHODE RAY TUBE PROTECTING AND ENERGIZIN G CIRCUITS Application November 18, 1954, Serial No. 469,740 Claims. (Cl. 315-) The invention relates to the operation of cathode ray type electron discharge devices, and it particularly pertains to circuit arrangements for energizing such devices incorporating means protecting them from damage due to faulty operation of the energizing circuitry.

There are a number of different kinds of cathode ray type electron discharge devices in commercial use which, comprise an electron beam forming structure and an electron receiving target upon which the'electrons from the electron beam impinge, and which are subject to beam is not kept in motion by the beam deflecting systems normally causing the beam to scan the target. Nearly all of these electron discharge devices are relatively expensive, in View of which protective circuit means are desirable if not an economic necessity as well. One such electron discharge device for which adequate protection is especially desirable, is the vidicon or photoconductive television pickup tube which has a target of photoconductive material Which is damaged whenever a beam of normal intensity is allowed to remain stationary or partly stationary thereon. That is to say, the photoconductive target will be damaged in the event of failure of either the vertical or horizontal deflection as Well as the failure of both.

There are circuit arrangements known for protecting cathode ray type electron discharge devices in the event of failure :of associated circuitry which can be adapted satisfactorily to almost any of the presently used commercial cathode ray tubesf The circuit arrangement according to the present invention is an improvement in that the energizing potential associated with an electrode for attracting the electrons of the beam to the target is directly dependent on the presence of energy in the beam deflecting system associated with the cathode ray discharge device.

An object of the invention is to provide an improved circuit arrangement for preventing damage to the target of a cathode ray type electron discharge device in the event of failure of associated operating circuitry.

Another object of the inven 'on is to provide a failsafe circuit arrangement for protecting a cathode ray type electron discharge device in the event of failure in the associated circuitry or in the protective circuit arrangement itself.

A more specific object of the invention is to provide a fail-safe circuit arrangement for generating the signal electrode potential of a photoconductive television pickup device which is dependent upon the presence of energy in both the horizontal and vertical beam deflecting systems associated with the device.

The objects of the invention are attained in a protecting and energizing circuit arrangement for a cathode ray type electron discharge device having an electron beam forming structure, an electron receiving target upon which the electron beam from the beam forming structure impinges, and an electron attracting electrode arranged in cooperative relationship with theelectron receiving target.

In such electron discharge devices, the

" ted atent time Patented Oct. 1, test electron attracting electrode cooperates to insure. that the electron beam impinges upon the target in themanner desired under normal operation for the particular type of electron discharge device under consideration and should the potential on the electron attracting electrode be reduced below a certain value the beam current will be cut oit due to space, charge. According to the invention, the energizing potential for the electron attracting electrode is obtained from or is made directly dependent upon the presence of the proper amount of energy in the electron beam deflecting system associated with the electron discharge device under consideration.

In particular, in the circuit arrangement according to the invention there is provideda control system Whic EQQ may include a magnetic amplifying device, an electron discharge device or some other form of controlled electron flow path device which is coupled to one of a plurality of the electron beam deflecting systems to transfer a portion of the energy therein to the control device to condition the latter for operation in response to the presence of energy in the one deflecting system. The control system is also connected to another of the beam defiectingsystems to obtain a portion of the energy therein to produce an output potential only in the presence of energy in all of the beam deflecting systems. Thereafter means are provided to convert the output potential of the control system into the proper form for energizing the electron attracting electrode of the cathode ray type electron discharge device to cause the electron beam to impinge on the target; again only in response to the:

presence of energy in all of the electron beam deflecting systems.

More particularly, the circuit arrangement according to the invention contemplates the use of a controlled electron flow path device having an input circuit coupled to one of the electron beam deflecting systems to transfer a portion of the energy thereat to a bias voltage rectifying device and associated filter network to produce a positive driving potential. This direct driving potential is applied to the input electrode of a controlled electron flow path device or system forming the control system, having a common circuit electrode to which positive energizing potential is applied to render the control system inactive in the presence of only normal energizing potential. electron beam deflecting systems, in the form going pulses, circuit electrodes of the control system to produce positive going potential pulses between the output and common circuit electrodes of that controlled electron flow path system. These output pulses are converted by means of -a rectifying device coupled to the controlled electron flow path system to direct energizing potential for application to the electron attracting electrode of the cathode ray type electron discharge device.

Further according to the invention, a unilateral impedance element is used to render ineffective, or destroy, any positive going pulses that may be obtained from the other electron beam deflecting system. a

Still further according to the invention, electron attracte in-g electrode energizing potential is stabilized in a failsafe manner by means of a unilateral impedance device connected between the potential storage capacitor and a- A portion of the energy in another of the of negative is applied between the input and commoninvention, except perhaps for failure of the positive pulse destroying unilateral impedance element.

In order that the invention may be more clearly understood and readily put to practical use, an express embodiment of the invention, given by way of example only, is described below with reference to the accompanying schematic diagram of a circuit arrangement according to theinvention for use with a photoconductive television pick-up device.

The sole figure shows a circuit arrangementaccording to the invention for use particularly with a photoconductive type television pick-up device or vidicon 10 which comprises an evacuated envelope in which there is located a source of electrons comprisingthe usual heater 13. and a cathode '15 which is arranged with associated beam forming structure to project a beam of electrons in the direction of a beam currentcontrolling electrode 17 A potential somewhatnegative with respect to that on the cathode and of a" value to produce the desired beam intensity is impressed on the controlling electrode 17. A positive potential is impressed on an accelerating electrode 19 to accelerate the electrons through a drift space surrounded by a wall electrode 21 which is maintained at a potential relatively high with respect to that at the cathode 15, which is maintained at fixed reference potential, shown here as ground. The beam is focused and aligned either with electromagnetic focusing and alignmentcoils or a permanent magnet structure having field shunts for alignment (not shown). in the latter. use, variations in wall potential greatly facilitate the adjustment. The electrons in the beam impinge upon a target 23 made of photoconductive material such .as selenium, or various ones of the sulphide, selenide and oxide compounds which are known to be photoconducting. The photoconducting materials themselves, and indeed the targets of such devices themselves, have no eflect on the circuit arrangement of the invention and therefore no further detailed description is given. In the vidicon tube there is a signal electrode 25 in front of the photoconductive target 23. This signal electrode is an electron attracting and collecting electrode which is light permeable, being frequently made of a coating of stannic chloride or stannic oxide coated on the glass envelope of the tube, and arranged in contiguous relationship with the photoconductive electron receiving target 23; It should be understood that the circuit arrangement according to the invention is not limited to use with a cathode ray discharge device of the structure specifically shown and described hereinbefore, but it may be used in conjunction with any of the cathode ray devices in which there is an electron receiving target arranged in cooperative relationship with an electron attracting electrode of general form. Such structures are found in image orthicons having a target mosaic and a decelerating ring or in image iconoscopes having an electron mosaic target and a collector anode in the form aquadag Wall coating or the like. Obviously, those skilled in the artwill suggest means for adapting the circuit arrangement of the invention 'to those other types of tubes wherein the reception of electrons by the target is influenced by another cooperating electron attracting electrode.

The electron beam emanating from the electron beam forming structure is deflected across'the target 23 in a plurality of directions to form a raster under the influence of a plurality of electron beam deflecting systems. These deflecting systems may incorporate electrostatic deflecting plate structures or electromagnet deflecting winding structures, or both, as desired under the circumstances. As shown here the electron beam is deflected in the vertical direction 'by a vertical beam deflecting winding 39 which is coupled to the output winding 32 of a vertical deflecting transformer having an input winding 33 to which vertical deflecting wave energy is applied. In similar manner the electron beam is deflected in the horizontal direction under the influence of a horizontal electron beam deflecting winding 35 coupled to the output Winding 37 of a horizontal deflecting wave transformer having an input winding 38 to which horizontal deflection wave energy is applied.

As long as the electron beam is deflected across the target 23 in both the vertical and horizontal directions no damage will ensue, and the current at the signal collecting electrode 25 will be proportional to the light variations projected onto the target 23 through the transparent signal electrode 25 by means of the usual optical system (not shown). If, however, the beam of a vidicon is prevented from being deflected in either of the two directions, normal energizing potential will cause the target 23 to burn after a short timeinterval. The target material used in present day vidicon tubes is more susceptible to burning than the target material used in other types of tubes so that the electron beam in the vidicon tubes cannot be allowed to sweep back and forth along the same line. While other types of cathode ray tubes may not be quite so susceptible to'damage, the additional protection is often well worthwhile.

According to the invention, the energizing potential for the transparent conducting signal electrode 25 is obtained from the beamdeflecting systems associated with the particular tube 10 under consideration. Energy in the vertical deflection winding 30 is obtained by connections to a vertical energy transferring resistor 41 connected in series with the beam deflecting winding 30 and applied by means of .a coupling capacitor 42 across an input resistor 43 of a driving potential developing controlled electron flow path device shown here as an elec-.

tron discharge tube 44 having an input electrode or grid 45 and a common circuit or cathode electrode 46 between which the grid or input resistor 43 is connected and an output or :anode electrode 47. The amplified energy waveis developed across a load resistor 48 and applied by means of a coupling capacitor 49 and a D.-C. return resistor 51 to a bias voltage rectifier 53. Energy from the vertical deflecting circuit is rectified by the bias voltage rectifier 53 and accumulated in a storage device in the form of a capacitor 55. The accumulated direct potential by way of a resistor 57, which in conjunction with the capacitor 55 forms a filter network, to a control device which may be in the form of a magnetic amplifier device, but is preferably a controlled electron flow path system shown here as an electron discharge system 60. The electron discharge system 60 has an input circuit or grid electrode 61 and a common circuit or cathode electrode 62. The cathode electrode 62 is connected to a point of fixed reference potential by means-of a common circuit or cathode resistor 63 shunted by a cathode bypass capacitor 64. By means of a cathode resistor 65 connected to a point of fixed positive energizing potential the cathode electrode 62 is biased positively with respect to energizing potential on the grid electrode 61 so that the discharge system 6 0 is cut off in the absenceof-any positive potential applied to the grid electrode 61 by way of the storage capacitor 55. As thus far described conduction takes place in the control discharge system 60 when positive potential is applied to the grid electrode 61 but no alternating'output potential is developed at the output or anode electrode 67.

Energy from the horizontal deflecting wi'nding'35 is extracted by means of an energy translating transformer having a primary winding 71 connected in series with the horizontal beam deflecting winding 35 and a secondary winding 73. It should be understood that the energy may be obtained by the use of energy transferring devices shunting the deflecting windings 30, 35, but with magnetic deflection system-s the operation will not be failsafe as with the series connection shown, because in the latter case any interruption in the deflecting windings 30, 35 will stop the flow of current in the energy transferring resistor 41 or the transformer primary 71. With electrostatic deflecting structures,-however, the shunt cit-- cuit arrangement should be used to provide fail-safe operation so that no output energy will be available if for any reason a short circuit exists between the plates of the electrostatic deflecting structure. By means of a coupling capacitor 75 energy in the horizontal circuit is applied to the grid electrode 61 of the control discharge 60 to apply negative pulse energy thereto. Positive pulse energy which might cause the anode potential of the control tube 60 to vary and falsely provide an alternating output is eliminated by the use of a positive pulse destroying device 77, preferably of semiconductor form.

By means of a coupling capacitor 79 connected to the anode electrode 67 of the control device 60 the alternating or pulsed output potential resulting from the energy derived from the vertical and horizontal beam deflecting circuits is applied to a rectifying device shown here as a high vacuum heated cathode type diode 80 where the energy is rectified and accumulated in a storage capacitor '81. A D.-C. return resistor 83 is connected to the anode of the diode 80 and a point of fixed potential, shown as ground. The energy stored in the storage device 81 is applied by means of a voltage divider element '83 having an adjustable arm 84 through a series resistor 85 to the signal electrode 25 associated with the photoconductive target 23 of the vidicon 10.

Further according to the invention voltage regulation may be supplied, if such is desired. The cathode of a regulating diode 87 is connected to a point of regulated positive energizing potential to provide regulated voltage at the signal electrode 25 and also to-block the application'of this regulated positive potential when no alternating potential is obtained at the anode electrode 67 of the control discharge system 60. In normal operation a potential greater than the regulated potential is generated across the storage capacitor 81. This stored potential is reduced to the value of the regulated potential by conduction through the regulating diode 87. -In the event of failure, however, the diode '87 will cease conducting and no potential will be applied to the signal electrode 25.

Whenever the control electron discharge system 60 is cut off due to the applied bias voltage, the negative going horizontal pulses at the grid electrode 61 of the discharge system 60 will not be amplified so that no rectifier unidirectional voltage will appear at the cathode .of the rectifier diode 80. In the event of vertical sweep failure no positive driving potential will be applied to the grid electrode 61 of the discharge system 60 and the latter -will be cut oif.

The values of the components listed below, which were used in an application of the invention to an industrial television camera with satisfactory results, are suggested as examples of circuit components for an initial investigation of practical applications of the invention.

Ref. No. Component Type or Value Vidicon 6198. Transferring resistor. 100 ohms Coupling capacitor 0.1 mt. Grid resistor 1 megohm Drive tube 12AU7. Load resistor 100 kilohms. Coupling capaciton. 0.5 mt. D return resistor... 1 megohm. Drive rectifier 1N34A. Storage capaeiton. 0.1 mt. Grid resistor 390 kilohms. Control tube 12AU7. Cathode resistor 1 kilohm. Cathode bypass 0.1 mi. Blasing resistor 40 kilohms. Coupling capacitor 0.01 mt. Pulse destroying device 1N34A. Coupling capacitor 0.1 mt. Target rectifier 6AL5 Storage capacitor .0 mt. D.-O. return resisto 180 kilohms Voltage divider 500 kilohms Regulating diode 6AL5.

A power supply delivering 300 volts is connected between the points marked with the plus (-1-) sign and the minus sign and volts regulated at the point marked +R. Normally the circuit arrangement of the invention developed -130 volts across the storage capacitor 81 which was reduced to 100 volts by conduction through the voltage regulating diode 87. Obviously other values and potentials will be suggested to those skilled in the art for other applications of the invention.

The invention claimed is:

1. A protecting and energizing circuit arrangement for a cathode ray type electron discharge device having an electron beam forming structure, an electron attracting electrode arranged in cooperative relationship with an electron receiving target upon which the electron beam from said structure impinges, including a plurality of beam deflecting systems arranged about said electron discharge device to deflect the beam to scan said target, a plurality of deflecting wave circuits individually coupled to said beam deflecting systems, a control device having an output circuit at which is produced energy in proportion to potential applied to an input circuit of said device, means connected in circuit with one of said beam deflecting systems to derive a portion of the energy therein, means coupled between said energy deriving means and the input circuit of said control device to render the latter in condition for operation in response to the presence of energy in said one beam deflecting system, means connecting another of said beam deflecting systems to the input circuit of said control device to produce said output potential in response to the presence of energy in all of said beam deflecting systems, and means coupled between the output circuit of said control device and said electron attracting electrode to convert the energy at the output circuit of said control device to energizing potential for the electron attracting electrode of said electron discharge device, thereby to protect said electrode by energizing the same only in response to the presence of energy in all of said electron beam deflecting systems. I

2. A protecting and energizing circuit arrangement for a cathode ray type electron discharge device having an electron beam forming structure, an electron attracting electrode arranged in cooperative relationship to an electron receiving target upon which the electron beam from said structure impinges, including a pair of beam deflecting structures arranged about the path of the electron beam of said electron discharge device to deflect the electron beam to scan said target, a pair of deflection wave translating circuits, an energy transferring device connected in circuit with one of said deflection wave translating circuits and one of said beam deflecting structures, another energy device connected in circuit with the other of said deflection wave translating circuits and the other of said beam deflecting structures, a controlled electron flow path device having input, output and common circuit electrodes, means coupling one of said devices between said input and common circuit electrodes, means coupling a unilateral impedance device between said output and common circuit electrodes controlled electron flow path system having input, output and common circuit elements, a resistor connecting the input element to said unilateral impedance device connected between said uni-lateral impedance device and the common circuit electrode of said controlled electron flow path system, means coupling said input element to the other of said energy transferring devices, a connection between the common circuit element and a source biasing potential, means coupling a rectifying element and a load element in series across the output and common circuit electrodes of said controlled electron flow path system, a storage device shunting said resistive element, and a connection between said electron attracting electrode and a point on the load element of said rectifying device.

3. A target protecting and energizing circuit arrangement for a photoconductive type television pickup device having an electron beam forming structure, ,a photoconductive target upon which the electron beam from said structure impinges and a light permeable signal electrode arranged in contiguous relationship to said photoconductive target, including a pair of horizontal beam deflecting structures arranged about the beam path of said pickup device to deflect the electron beam to scan said target, a pair of deflection wave translating circuits, an energy transferring device connected in circuit with one of said deflection wave translating circuits and one of said beam deflecting structures, another energy transferring device connected in circuit with the other of said deflection wave translating circuits and the other of said beam deflecting structures, a controlled electron flow path device having input, output and common circuit electrodes, means coupling one of said energy transferring devices between said input and common circuit electrodes, a unilateral impedance device and a capacitor connected in series between said output and common circuit electrodes, a controlled electron flow path system having input, output and common circuit electrodes, means connecting the input electrode to the junction between said unilateral impedance device and said capacitor, means coupling said input electrode to said other energy transferring device, a diode element and a resistive element coupled in series across the anode output and common circuit electrodes of said controlled electron fio-w path system, a capacitor shunting said resistive element, and connections between said signal electrode and a point on said resistive element.

4. A target protecting and energizing circuit arrangement for a photoconductive type television pickup device having an electron beam forming structure, a photoconductive target upon which the electron beam from said structure impinges. and a light permeable signal electrode arranged in contiguous relationship to said photoconductive target, including a pair of beam deflecting windings arranged about said pickup device to deflect the electron beam to scan said target, a pair of deflection wave transformers each having an output winding, an energy transferring device connected in series with one of said transformer output windings and one of I said beam deflecting windings, another transferring energy device connected in series with the other of said transformer output windings and the other of said beam. deflecting windings, a controlled electron flow path device having input, output and common circuit electrodes, means coupling one of said energy transferring devices between said input and, common circuit electrodes, a unilateral impedance device and a capacitor connected in series across said output and common circuit electrodes, a controlled electron flow path system having input, output and common circuit electrodes, a resistor connecting the input electrode to the junction between said unilateral device and said capacitor, means coupling said input electrode to the other of said energy transferring devices, a capacitor, a diode element and a resistive ele- '8 ment connected in series across'the anode output and common circuit electrodes of said controlled electron flow path system, a resistor shunting the 'junction of said capacitor and said diode element, a capacitor shunting said resistive element, and a connection between said signal electrode and a point on said resistive element.

5. A target protecting and energizing circuit arrangement for a photoconductive type television pickup device having an electron beam forming structure, a photoconductive target upon which the electron beam from said structure impinges and a lightpermeable signal electrode arranged in contiguous relationship to said photoconductive target including a horizontal beam deflecting winding and a vertical beam deflecting winding arrangedv about said pickup device to deflect the electron beam to scan said target, a horizontal deflection wave transformer having an output winding and a vertical deflection wave transformer having an output winding, a transformer having a primary winding connected in series with said horizontal transformer output and said horizontal beam deflecting windings and having a secondary winding, a resistor connected in series with said vertical transformer output and said vertical beam deflecting windings, an electron discharge device having cathode, control and cathode electrodes, a capacitor coupling said resistor between said control and cathode electrodes, another capacitor and another resistor connected in series between said anode and cathode electrodes, a semi-conductive device and a further capacitor connected in series across said other resistor, an electron discharge system having input, output, a cathode, a grid and an anode, a resistor connecting the grid to the junction between said semi-conductive device and said further capacitor, a capacitor coupling said grid to said secondary winding, a semi-conductive device shunted across said secondary winding, a connection between the cathode and a point of positive energizing potential, a capacitor, a diode element and a resistive element connected in series across the anode and cathode electrodes of said electron discharge system, a resistor shunting the junction of said capacitor and said diode element, a capacitor shunting said resistive element, another diode element having an anode electrode connected to the cathode electrode of the first said diode element and a cathode connected to a point of regulated positive energizing potential and a connection between said signal electrode and a point on said resistive element.

References Cited in the file of this patent UNITED STATES PATENTS 2,098,384 Goodrich Nov. 9, 1937 2,222,426 White et al. Nov. 19, 1940 2,261,776 Poch Nov. 4, 1941 2,444,902 Torsch July 6, 1948 2,687,484 Weimer Aug. 24, 1954

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