US2373165A - Unidirectional power supply - Google Patents

Description

Patented Apr. 1Q 1945 f 1 U UNETED dlfilifid P'lhld'i' EFF-"WE V UNIDmECTIONAL POWER SUPPLY Madison Caweln, ltort Wayne, Incl, osclgnor to Farnsworth Television and Radio Corporation, a corporation of Delaware Application January 11, 1943, Serial No. $11,916 I 6Claims. (Cl.171-97) This invention relates'to apparatus for generating direct current energy and particularly to apparatus for deriving high unidirectional voltages for use with cathode ray tubes.

According to conventional practice in the use of cathode ray tubes it is necessary to apply to certain of the electrodes of such a tube, unidirectional voltages of the order of several kilovolts. It hasbeen proposed to rectify the periodic pulses of high potential resulting from the sudden current decay of a saw-tooth wave for the purpose of obtaining these high voltages. Typical ap paratus of this type is disclosed in United States of the tube on inductance.

excitation for the oscillator is provided by another Patent No. 2,051,372 granted to Philo T. Famsworth on August 13, 1936. By reason of certain limitations of the saw-tooth generator in the.

Farnsworth system, the oscillator generates sawtooth waves having certain deficiencies. Not only is the current wave generated by the Farnsworth oscillator of limited amplitude, but the rate of change of the current from its maximum to its minimum valu is such to effect the generation .of a wave limited in its maximum frequency.

' ray tube apparatus to be mounted in aircraft, it

is important that the apparatus be made as light as possible. Accordingly, it should include a minimum number of iron core transformers and the filter condensers should be as small as possible.

An object of the present 'invention, therefore, is to provide an improved high unidirectional voltage power supply derived from apparatus which produces saw-tooth waves.

Another object of the invention is the provision of a higher unidirectional voltage power supply than heretofore obtainable and by means of lighter weight apparatus.

High voltage generating apparatus 01 the type disclosed by Farnsworth in the patent referred to has been modified by substituting a. beam power tube for the tctrode used by Farnsworth. The substitution or the beam power tube for the tetrode produced results which were considerably beyond the scope of any reasonable expectancy and effected materially different and improved results over those previously obtainable with the original Farnsworth apparatus. There was found to be a substantial increase in the magnitude of the generated saw-tooth current. The current doses} from its maximum to its mini-. mum value was found to be at a substantially higher rate, thereby enabling the generation of a higher frequency wave.

In accordance with the present invention there is provided an oscillator for generating periodic currents oi saw-tooth wave form which includes an electronic device of the beam power type. There is connected in the anode or output circuit Regeneration or selfinductance loosely coupled to the above inductance. other inductance is connected in the control grid or input circuit of the tube. ductances are poled so that an increase in the anode culrent will apply a positive potential of such magnitude to th grid that the internal impedance oi the tube is reduced to a relatively low value. A source of positive potential of predetermined magnitude is connected to the screen grid of the tube in series with an impedance. Such an oscillator functions to generate a periodic wave of substantially saw-tooth form. Frequencies of the order of hilocycles per second may be obtained so that the coupling between the input and output circuits may be effected without the use of an iron core. Periodically, with the relatively rapid decay of the generated wave from its maximum to its minimum value, there is produced at the anode of the tube a pulse of high voltage and of positive polarity. These high voltage pulses are rectified bye. tube of the diode type and filtered. The resulting high voltage direct current may be applied to certain 01 the electrodes of a cathode ray tube.

For a. better understanding of the invention. together with other and further objects thereof. reference is had to the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

In the accompanying drawing:

Fig. 1 is a circuit diagram of a high voltage generator embodying the present invention; and

Fig. 2 is a series of curves characteristic of voltages appearing in some of the circuits of Fig. 1.

Referring now more particularly to Fig. 1 o! thedrawlng, the generator embodying the p ent invention comprises an oscillator for the seneration of saw-tooth waves and a rectifier. The oscillator includes a beam power tube it having a cathode H, a control grid l2, a screen grid 13, beam-forming elements I t and an anode it. The

The intive terminal of the battery ll.

28 and 2! are by-passed to ground by condensers cathode H is connected internally oi the tube to the beam-forming elements. Externally, the cathode is connected through a resistance It to the negative terminal of a source of direct current energy such as battery H. The negative terminal of the battery is also connected to ground. The anode l5 of the tube is connected. through an inductance l8 which forms the primary winding of an air-core transformer I9. The other terminal of the primary winding is is connected through resistance 2n and 2i to the posi- The resistances 22 and 23. The control grid 12 of the tube is connected through an inductance 24, forming a secondary winding of the transformer IS to the negative terminal of the battery H. The screen grid [3 of the tube is connected through a resistance 25 and resistances 243 and 2i to the positive terminal of the battery 57.

The anode iii of the tube i8 is also connected .to the anode of the diode rectifier tube 26.

Heater current for the cathode of the rectifier tube is derived from an auxiliary Winding 27 on the transformer IS. The cathode of the rectifier tube is connected to a shaping circuit including a series pararllel connection of resistances 2B, 29 and 3t, and a condenser 3!. The output of the rectifier tube 26 which is derived from the cathode is then connected through a relatively 1 small filter condenser 32 to ground. Across the terminals of the condenser 32 is connected a voltage divider comprising resistance 33 and 3t and a potentiometer 35. The maximum voltage obtainable from the voltage divider is appl ed to the second anode 36 of a cathode ray tube 37 by a connection to the upper terminal of resistance 33. An intermediate unidirectional voltage, derived from the slider element 38 0f the potentiometer i applied to the focusing electrode 39 of the cathode ray tube. The control grid 40 and the cathode ii of the cathode ray tube may be connected respectively to terminals t2 and $3 for the application of signaling voltages.

Considering now the operation of the apparatus illustrated in Fig. 1, reference will be made to certain observable characteristics of the oscillator before considering a suggested theory of operation which will be offered subsequently. Ac-

7 cordingly, the voltages which are known to exist at'certain times in the variou circuits associated with-the elements of the beam power tube will be referred to. Such voltages are illustrated by the curves of Fig. 2.

ondary winding 24 i also introduced into the control grid circuit. During periods of current increase in the primary winding the positive potential is of suiilcient magnitude to predominate over the negative potential and to thereby render the control grid sufficiently positive to reduce the impedance of the tube It to a relatively low value. During periods of current decrease in the primary winding a negative potential derived from the secondary winding is in 'oduced into the control grid circuit which, in itself, is suiilcient to increase to infinity the impedance of within the tube 10.

the tube 10. There is also provided a positive bias for the screen grid I3 which is or predetermined minimum magnitude depending upon the value of the resistance 2f), 21 and 2'5 and the voltage of the battery ll.

A cycle of operation will be assumed to start with the closing of the cathode-to-anode path Current starts to flow in the series circuit comprising the battery l'l, resistances 2! and 2D, the transformer primary winding lo, the space current path of the tube Hi, and the resistance H3. The impedance of the anode-to-oathode path within the tube constitutes the major part of the resistance portion of the circuit. Consequently, the impedance of resistances It, 20 and 2| may be neglected for the present purpose. By reason of the inclusion of cathode ll of the beam power tube H] is becoming more positive, as indicated by the curve it of Fig. 2. At the same time, the potential applied to the screen. grid l3 or the tube is becoming increasingly positive, as indicated by the curve 65. Concurrently with these voltage changes, the voltage of the anode lb of the tube remain at a substantially constant negative value, as indicated by the curve 58. Also the potential applied to the control grid 12 similarly remains at a substantially constant value which is positive, as indicated by the curve ill. These -'conditions exist for a period of time which, it has been found, is determined primarily by the ratio of the inductance external 01 the tube it to the internal resmance of the tube, included in the series anode to-cathode circuit of the tube. The current increase between the cathode and anode of the tube ill suddenly stops and'a sharp decrease in this current ensues. A complete interruption of the current flow is effected in considerably less time than in prior art devices, such as the Farnsworth oscillator.

At this point the anode voltage rises momentarily to a sharp positive peel: indicated by the curve 48. This high voltage pulse is produced by the steep wave front portion of the saw-tooth wave; The amplitude of this peak is considerably in excess of the voltage of the battery ll. Also, at this time, the potential of the control grid (2 i momentarily reduced to a high negative value which is in excess of the negative biasing effected by the self-biasing resistance It. This momentary negative potential is represented by the curvew'it.

7 period of time that the cathode-to-anode current is interrupted. The potentials of the tube elements then revert to their initial polarities and values, resulting in the reclosing of the oathode-to-anode path within the tube In and the repetition of the described cycle.

From the curves of Fig. 2, it is seen that, during the major portion of the cycle, the control grid potential has a substantially uniform value while the cathode potential has an increasing value. It is readily seen, therefore, that the pogenerated current wave.

,Tube it T1 I aevaios form, as indicated by the curve iifi.

The frequency of the current wave produced by the oscillator embodying the present invention, is determined primarily by the ratio of the external inductance represented by the primary winding It of the transformer 19, to the internal resistance of the tube HI. These frequency-determining facilities are substantially different from the facilities provided for a similar purpose in the oscillator disclosed in the Farnsworth patent referred to. In the Farnsworth oscillator, the frequency control is eflected by adlusting the value of the grid leak resistance connected from the control grid to ground. In the oscillator, in accordance with the present invention, variation in the frequency of the generated current wave may be eifected conveniently by varying the value of the resistance I! which thereby changes the bias of the control grid it. Thus, the internal resistance oi the tube is changed, thereby altering the inductance-to-resistance ratio or the cathode-to-anode series circuit. It has been found that the actual impedance of the primary and secondary transformer windings It! and 24 respectively, are not at all critical for the successtul operation of the oscillator.

The value of the resistance determines the amplitude of the high peaks or pulses of anode voltages produced by the operation 01' the present oscillator, and also controls the speed of the The latter control determines the time required for the generated current wave to change from its maximum to its minimum value. It has been found that for every design of an oscillator of this type there are certain optimum values of impedance and positive potential connected to the screen grid i3. "The apparatus connected in the manner described and illustrated in Fig. 1, has been found to give satisfactory results for the purposes described when using circuit elements and constants in accordance with the following table. The oscillator frequency is approximately 100 irilocycles per second and the direct current voltage is approximately 1500 volts. i

It is believed that a fuller appreciation of the marked distinction of the oscillator included in the present invention over prior art oscillators may be derived from a consideration of the following suggested theory of operation. It seems evident from a study of the curves of Fig. 2, that the interruption of the cathode current, once it is started, is accelerated at such a high rate that the current cut-oil is relatively absolute. The acceleration is apparently caused by the negative impulsive potential of the controlgrid 12, as indicated by the peak 49. This potential is developed by the regenerative coupling of the transformer windings Ill and 24 in response to the slight lessening of the rate of increase of the oath- -ode current. Up to a certain point, this rate oi increase is constant. As the cathode current starts to increase, it is seen from the curve 45 that the potential of the screen grid I3 is at its lowest value. This is probably due to the deflection of a large number of electrons toward the screen grid at this time. As the cathode current increases, the potential of the cathode also increases, as evidenced by the curve 44. The po-- tentials of the beam-forming electrodes it also increase similarly since they are connected internally of the tube to the cathode H. It appears likely that, as the potentials of the beamforming electrodes increase, the number of electrons which are deflected toward the screen grid decreases at the same rate until the potential of the screen grid reaches a value at which a part of the electron beam strikes the beam-forming electrodes. This action initiates interruption of the cathode current which then, because of the regenerative action of the device, completely ceases substantially instantaneously.

By use of the apparatus arranged in the manner described, it is possible to obtain advantageous results which have hitherto been impossible to obtain. The use of the beam power tube in the oscillation generator produces larger cur rents of saw-tooth wave form. The change of the saw-tooth wave from its maximum to its minimum value is accomplished in a shorter time than heretofore possible, thereby producing a steeper 12A6 Resistance i6 100 ohms Battery i? 250 volts Primary winding i3 25 miiiihenries; 500 turns Resistances re and El 1000 ohms Condensers 22, 23 and 2| .005 microfarad Secondary winding 21s---- 1 millihenry; 100 turns Resistance 25 600!) ohms Tube 28 12H6 /2) Heater winding 21 10 turns Resistance 28 -s e 0.1 megohm Reslstances is, it and 3t 0.47 megohm Condenser 32 250 micromicrofarads Resistance 33 0.94 megohm Potentiometer 8t 0.2 mesohm wave front of this portion of the saw-tooth wave.

These two effects permit the generation of higher frequency saw-tooth waves and also produce higher voltage anode pulses. By reason of the higher frequencies obtainable it is possible to secure adequate regenerative coupling between the input and output circuits of the oscillator tube without the use of an iron-core transformer. Also, the higher frequency waves require the use of much smaller filter condensers. The higher frequency waves, together with the higher voltage anode pulses, permit the production of a higher voltage direct current. The ultimate effect of all of these improved results is the production of a higher unidirectional voltage by the use of extremely light weight apparatus.

ifhile there has beencleecribed what is at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modification may be made therein without departing from the invention, and it is, therefore, aimed. in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A unidirectional voltage supply system comprising, an oscillator for generating currents of saw-tooth wave form, said oscillator including an electronic device having input and output circuits and a predetermined normal internal resistance, an external circuit coupled to said output circuit including an inductance, an external circuit coupled to said input circuit including a the ratio of said output circuit inductance to said internal resistance, and means including a rectiller directly coupled to said output circuit for producing currents of saw-tooth wave form, said oscillator including a beam power tube having input and output circuits and an auxiliary electrode connected to the positive terminal of said low voltage source, said primary winding being connected to said direct current supply source and to said output circuit, said secondary winding being connected to said input circuit, and unidirectional conducting means directly coupled to said output circuit for converting the voltage pulses produced by the steep wave front portions of said saw-tooth wave to a unidirectional voltage.

3. A unidirectional voltage supply system comprising, a direct current supply source, a magnetically coupled oscillator for producing currents of saw-tooth wave form, said oscillator including .a beam-power tube having input and output circults and an auxiliary electrode connected to the positive terminal of said direct currents supply ;source, a primary inductance connected to said direct current supply source and to said output 'circuit, a secondary inductance regeneratively coupled to said primary inductance, said secondary inductance being connected to said input circuit, and means connected to the output circuit of said tube and including a filter condenser for converting the voltage pulses produced by the steep wave front portions of said saw-tooth wave to a unidirectional voltage.

4. A unidirectional voltage supply system comprising, a direct current supply source, an oscillator having inductively coupled input and output circuits for producing currents of saw-tooth wave form, said oscillator including a beam-power tube having a cathode, an anode, a control grid and an ,auxiliary electrode, means for maintaining said electrode at a positive potential, an output circuit inductance connected to said direct current sup- ,ply source and to said cathode and said anode,

an input circuit inductance regeneratively cou-' circuit inductancev being connected-to said'cath ode and said control grid, means connected to 'said anode for rectifying th voltage pulses, produced by the steep wave front portions 0! said saw-tooth wave, and a condenser connected to filter said voltage pulses to-produce a unidirectional voltage.

5. A unidirectional voltage supply system comprising, a direct current supply source, an oscillator having inductively coupled input and output circuits for producing currents of saw-tooth wave form, said oscillator including a beam-power tube having a cathode, an anode, and two grid electrodes, a connection from the positive terminal of said direct current supply source to a first one of said grid electrodes. an output circuit inductance connected to said direct current supply source and to said cathode and said anode, an input circuit inductance loosely coupled regeneratively to said output circuit inductance, said input circuit inductance being connected to said cathode and the second of said grid electrodes, a rectifier connected to said output circuit for conducting the voltage pulses produced by the steep wave front portions of said saw-tooth wave, and a condenser connected to said rectifier for filtering said voltage pulses to produce a unidirectional voltage.

6. A unidirectional voltage supply system comprising, a direct current supply source, an oscillator having inductively coupled input and output circuits for producing current of saw-tooth wave form, said oscillator including a beam-power tube having a cathode, an anode, a control grid and a screen grid, a connection from the positive terminal of said direct current supply source to said screen grid, an output circuit inductance connected to said direct current supply source and :pled to said output circuit inductance, said input 7 to said cathode and said anode, an input circuit inductance loosely coupled regeneratively to said output circuit inductance, said input circuit inductance being connected to said cathode and

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