US2874319A - Variable voltage regulator - Google Patents

Description

Feb. 17, 1959 v N, ANTON 2,874,319

" l VRABLE VOLTAGE REGULATOR 'original Filed May 15, 1955 United States Patent' O isclaims. ((21.313-54) This application is a division of my copending application Serial No. 355,342 filed May 15, V1953, now abandoned. v

The present invention relates to the art involving voltage regulator tubes` and is specifically concerned withv improvements in voltage regulator tubes of the corona discharge type.- i A common form of voltage regulator tube includes a within the envelope and consequently varying thev regucathode and an anode in a suitable gas or vapor atmosphere within an' envelope. Under proper pressure, at a predetermined voltage correlated to the materials and dimensions of the electrodes and to the nature and pressure of the'atmospherewithin the envelope, the tube will initiate a corona discharge between the anode and the cathode.` Such a corona discharge is useful in Voltage regulation, since it has a relatively steep voltage-current curve; i. e., a relatively small change in voltage produces a relatively large change in current. This provides a type of voltage regulating action sinceany increase in input voltage increases the discharge current which can be used to create a volt drop in a series resistor so that the voltage across the tube varies only slightly, much less than the change in input voltage. Accordingly, in use, the voltage regulator tube having a predetermined operating voltage is utilizedto regulate the output of a source of voltage which in the absence of regulation would be considerably higher than the `tube operating voltage. By connecting such a tube and aseries resistor across the output of such a circuit', the voltage is limited substantially to the operating voltage of the tube. Any tendency of the circuit4 to increase its output voltage results in an increased dis-` charge through the tube which drags down the Ivoltage to maintain it nearly level in value.V

In the past, voltage regulator tubes of this type were designed and constructed to operate at a single fixed voltage, thereby requiring precise fabrication and assembly of the various component parts, since the particular corona discharge voltage is'determined by the geometry of the electrodes, including their size,I shape and spacing, as well as by the natureof the atmosphere in which the discharge takes place.

According to the present invention, a variable discharge voltage can be obtained and is provided, which permits the' control voltage of a regulated system to be precisely adjusted within the range of variation of the tube. The present invention is further advantageous in providing a voltage regulator tube which is relatively rigid in construction so as to withstand vibration without variation in characteristics, and which is provided with features preventing current leakage or arc-over when used on relatively highvoltages.` It is designed and constructed-of preformed ceramics and precision machined `partspermitting accurate alignment and assembly and creating uniform characteristics in production. For the purpose of permitting `variation in the corona discharge Voltage a? portion of the envelope vis made expansible and contractiblefthereby` varying the pressureof the atmosphere lated voltage.

According to another feature of the present invention, the operation of such voltage regulator tubes is improved by assuring that the tube will ionize and discharge immediately upon attaining the critical voltage for the tube. This produces an important improvement in operating characteristics, for it reduces Ythe differential between the starting voltage needed for assured striking and the' ultimate operating voltage, and it permits the tube to be used consistently with very low current levels, of the order of one micro ampere or less, where prior art tubes were subject to erratic and unstable action with such low current levels. Y p

For this purpose, a radioactive material is inserted within the envelope, whichl continuously emits particles which maintain a slight degree of ionization in the atmosphere within the envelope, thus generating a continuous supply of free electrons. Because of the fact that the ionizatio-n content has been shortened very considerably by the supply of free electrons generated by the radioactive source, it is possibleto permit the input voltage to increase at a verymuch faster rate than would be permissible if the radioactive material had not been added and still fire the tube in the corona region. If the tube did not ionize immediately upon the application of the input voltage, the input voltage could achieve very high values so that when ionization is achieved the current through the tube would be so high that the tube would go into glow discharge rather than corona discharge. This stand-by ionization also assures that the tube will discharge exactly and precisely at its critical voltage, thereby maintaining more accurate regulation Vthan was previously possible. This in turn permits other advantages to be attained, particularly with respect to the maximum discharge current which can be accommodated. Thus, by use of a deliberately oxidized cathode, of relatively low work function, together with a non-oxidizable anode, vthe range of permissible discharge currents and the range of regulation attainable is increased, without too great an increase in required starting voltage.

A These and other advantages of the present invention will become more apparent from consideration of the following description of a preferred embodiment thereof taken lin conjunction with the appended drawing which, in its single ligure, shows a longitudinal cross-sectional view of one form of variable voltage corona discharge regulator tube having axial symmetry.

Referring now to the drawing, the tube of the present invention is formed by a cylindrical cathode 11 having a tubular bore 12 extending axially therewithin and having an enlarged threaded portion 13 intermediate the ends thereof. A ceramic bushing 14 is mounted in the left end ofthe-bore 12 of cathode 11 and has an annular groove 16 within which the end 17 of the cathode 11 is crimped. The bushing 14 has an aperture. 18 permitting the equalization of pressure on both sides thereof. It also contains an axial recess 19 which receives the end 21 of an anode rod or Wire 22. The enlarged portion 13 of the cathode 11 has an annular lip or rim 24 forming an annular recess 26 which engages the enlarged bore of an insulating envelope member 27, preferably of ceramic material, whose end 2S is sealed to the lip 24 atthe annular recess 26, preferably by a fused vacuum seal 29. The envelope member 27 has a reduced-bore section 31 joined to portion 28 by a shoulder 32 which serves to retain a further insulating and preferably ceramic bushing 33 in the right end 34 of the bore 12 of cathode 11. Bushing 33 has aY bore 36 axially thereof which accommodates and surrounds the anode 22, and serves to c onne ionization, as will be described hereinbelow.

` f The anode 22is` mounted in [the end of a metallic anode support 37 by being crimped into the apertured end 38 of the anode support 37. The anode support 37 is also provided with an annular lip 39 intermediate its ends forming an annular recess 41 accommodating the right end 42 of the ceramic envelope member 27. The anode support 37 also has a threaded extension 43 at the right end thereof. The anode support lip 39 is sealed to the ceramic envelope member 27 by suitable fused vacuum seals 44.

The right end of the bore 38 of the anode support 37 is sealed as shown at 46 to a glass exhaust tip 47. A threaded cap 48 engages the threads 43 of the anode support 37 to protect the exhaust tip 47, and also serves as a terminal for the anode electrode. It will be understood that this construction is far superior to the conventional baked-on cap soldered to the anode by conventional uxes, usually found to be corrosive.

Surrounding the cathode 12 is a bellows arrangement 51 which is sealed to the cathode 11 Aat the base 52 of the enlarged portion 13. This bellows 51 has a closed end 53 preferably integral therewith. Accordingly, it will be seen that the envelope of the tube comprises the bellows end 53, the bellows 51, the cathode 11, the ceramic body member 27, the anode support 37 and the exhaust tip 47, all of which are sealed to their respective adjoining elements by suitable vacuum-tight seals.

The bellows end 53 is secured to a metallic externally threaded bushing 54 whose threads 56 engage the internally threaded bushing S4 whose threads 56 engage the internal threads 57 of a metallic member 58 having a closed end 59 and rotatably mounted within a protecting shell 61 which at its right end 62 engages the threads 13 of the body member 11. The member 58 is prevented from longitudinal movement by the peened over end 63 of shell 61 and by the shoulder 64 of shell 61. It will therefore be apparent that by rotating the member 58, as by a screw slot or wrench-head at the end of member 58, bushing 54 is caused to move longitudinally with respect to the cathode 11 and thereby moves the end 53 of the bellows relative to the cathode 11. Since the bellows is part of the envelope of the tube, its movement changes the envelope volume and accordingly varies the pressure of the atmosphere therewithin. As the bellows is compressed to reduce the volume, the pressure is increased and the operating voltage is raised. As the bellows is expanded, the pressure is decreased and the operating voltage is dropped.

The present construction provides excellent rigidity against vibration and against change in electrical characten'stics due to the vibration which might be encountered in use. The anode 22 is constrained at both ends having its end 21 fastened in the recess 19 of the insulating button 14 at the left and having its right end secured to the end 38 of the anode support 37. The cathode 11 is thus ixedly related to the anode 11 despite the regulated voltage adjustment provided. The ceramic body 27 is provided with annular grooves 64 which increase the length of the external resistance path between the rim 24 of the cathode body 11 and the anode lip 39 whereby even at high voltages of the order of 700 voltages or more leakage is inhibited and cannot aect operating characteristics of the tube.

The construction of the present tube also permits it to be readily mounted on a panel, with the adjustment for operating voltage on one side and the electrical connections on the other. Thus, the panel can be clamped lietween sleeve 62 and the enlargement 24 of the `cathode y The various insulating parts such as the member '58, the bushing 14, the bushing 33 and the body member 27 are preferably preformed of ceramic material which makes possible uniform size and electrical characteristics during ,production and eliminates the disadvantages of devitrication and strain that are .common in `the use of i unregulated voltage.

glass envelopes. The anode construction provides excellent electrical connection and mechanical support and eliminates failures which are characteristic of conventional spot-welded assemblies. The various metallic parts can be precisely machined which makes possible the accurate alignment of the anode with respect to the cathode and makes the lengths of anode and cathode uniform in production so that uniform characteristics are experienced.

It will be understood that the tube after having its seals made in conventional manner is exhausted through the exhaust tip 47 and filled with the desired amount and pressure of gas or vapor to form the atmosphere of the tube after which the exhaust tip is sealed olf and protected by the cap 48. The gas or vapor used is preferably one readily ionoizable but chemically inert relative to the electrode materials. The two terminals of the tube are then formed by the cap 48 connected to the anode 22 and the body member 11 and shell 61 connected to the cathode.

In use, a voltage regulator tube of the present type is connected in series with a resistor across a source of The tube is non-conductive and essentially an open circuit until the voltage impressed across it exceeds a predetermined critical value. Thereupon, ionization may begin, forming a corona discharge. However, for such discharge, there must be an initial ionization, since unless at least one free electron occurs in the electric field between the electrodes, no discharge between the electrodes can take place. liance is placed upon the effect of cosmic rays which pervade space and which cause an initial ionization to permit formation of the corona discharge. However, such cosmic rays are a random phenomenon, and may fail to occur at desired instants.

The present invention provides a further feature to insure that the tube is in a condition to initiate a discharge at all times, whereby greater reliability and accuracy of regulations is attained.

According to the present invention, use is made of a radioactive material placed Within the envelope so that the electrons continuously produced by it will facilitate the commencement of the corona discharge and assure that the discharge begins precisely at a fixed value of impressed voltage. This radioactive substance may take a variety of forms. However, because of certain desirable characteristics, it is preferred to use carbon 14 This radioactive substance possesses an extremely long half life, of the order of 5000 years, so that it does not substantially vary its characteristics or its emission during the normal shelf life plus useful life of such tubes. Furthermore, it is stable and readily compounded into simple chemicals which can be readily applied.

A preferred form of carbon 14 utilized in the present invention is as a constituent of barium carbonate. Powdered barium carbonate (containing some carbon 14) is mixed in a lacquer formed by dissolving collodion cotton in amyl acetate. A desirable concentration has been found to be a 3% mixture or dispersal of barium carbonate in this lacquer, thereby forming a paint which canbe applied by brush or dipping as desired. A small spot of this paint may be applied to one of the surfaces of the insulating bushings 14 or 33, preferably between the anode and cathode.

This radio active carbon then continuously emits charged particles into the field between anode and cathode. When-a sufficiently high voltage is applied to these electrodes, the velectric field gradient accelerates these charged vparticles suliiciently to ionize molecules of the atmosphere within the envelope, which in turn ionize other molecules to cause a complete discharge. The use of the radioactive material thus maintains the tube in readiness to discharge as .soon as a sufficient voltage is applied, .andLm'ore precise regulation is thus attained.

Customarily re-.

. delined striking voltage for the device.

' LA ltjwill be understood that carbon-14-is-1merely`oneconvenient form of radioactive element which can be applied, and other radioactive material may be also applied -in the same or other ways within the envelope of the tube. The use of radioactive material in the manner just described reduces instability at low discharge currents, so that low work function materials maybe used, which permit large discharge currents without building up ion sheaths which can interrupt discharge. IAccordingly, as a further feature of the present invention, the cathode is made of a low work function material. Preferably, it is formed of chrome-iron (such as 28% chromium, 72% iron), chromium plated and oxidized, either before or during the baking-out. The anode, in order to provide low forward impedance and to maintain the corona non-oxidizable material, and for this purpose may be plated with rhodium, gold, platinum, or similar noble non-oxidizable materials.

The insulating bushings 14 and 33 also serve an important function with respect to providing a sharply In the tube, the electric field is essentially radial between the cathode and the anode, except for the region at the left tip of the anodeand at the right end of the cathode, where fringing occurs. If these bushings were not present, the resulting ionic discharge would normally follow the electric tield gradient `and would have portions of differing length whose effect would be to broaden out and make somewhat uncertain the speciiic striking voltage for the tube. In particular, such fringing effects vary from tube to tube in production, causing correspond variation in striking voltage. By the interposition of these bushings M and 33, however, the ionic discharge path is limited, since, of course, the ions cannot travel within the insulating material. As a result, the ion flow is maintained essential-ly radial and is separated from the fringe field areas. This confining of ionization results in eX- ceedingly uniform characteristics from tube to tube in mass production and within the same tube from time to time.

It willbe understood that the above description is illustrative only, since many variations and modifications will be readily apparent to those skilled in the art without departing from the spirit ofthe present invention, which is defined solely by the appended claims.

What is claimed as the invention is:

l. A corona-discharge voltage regulator tube comprising a hollow axially symmetrical cathode, an insulating bushing at each er1-d of said cathode and extending thereacross, one of said bushings having an anode-receiving recess centrally thereof and the other having a central bore therethrough, a rod-like anode coaxial with said cathode and having one end seated in said recess and the other passing spacedly through said bushing bore, and means supporting said anode coaxially of and insulatedly with respect to said cathode, said anode-supporting means providing a terminal for said anode, means for sealing said cathode at the end with said one bushing and means for exhausting said cathode through said other bushing bore, whereby ionization within said cathode is confined between said bushings to |avoid fringe effects and provide sharper striking voltages.

2. A corona-discharge voltage regulator tube as in claim l, wherein said last sealing means comprises a bellows having the closed end surrounding a substantial portion of said cathode element, said closed end being opposite said one insulating bushing, said one insulating bushing having a gas-equalizer aperture extending therethrough and said sealing means further including means for variably adjusting said bellows to regulate the operating voltage of said tube.

3. A corona-discharge voltage regulator tube as in claim l having an ionizable atmosphere therein, and a radio- B active substance to initiateridnization thereof upon application of a' critical voltage between said anode and cathode, whereby superior operation of the tube is achieved and a tendency to a termination of a glow discharge is reduced. t

4. A corona-discharge -voltagetube las in claim 2 having an ionizable atmosphere therein, and a radio-active substance to initiate ionization thereof upon application of a critical voltage between said anode and cathode, whereby superior operation of the tube is achieved and a tendency to a termination of a glow discharge is reduced.

5. A corona-discharge voltage tube as in claim 1 having an ionizable atmosphere therein and wherein said anode supporting means have a paint thereon including a radio-active substance to initiate ionization of the said atmosphere.

6. A corona-discharge voltage tube as in claim 2 having an ionizable atmosphere therein and wherein said anode supporting means have a paint thereon including a radio-active substance to initiate ionization of the said atmosphere.

7. A corona-discharge voltage tube as in claim 3 wherein said cathode having a low work function whereby superior low current operation of said tube is achieved and a consequent increase in operating range is accomplished.

8. A corona-discharge voltage tube as in claim 7 Wherein said anode has a surface of a noble element.

9. A corona-discharge voltage tube as in claim 7 wherein said anode surface is formed of a group of elements comprising rhodium, gold -and platinum.

10. A voltage regulator tube comprising a hollow cylindrical cathode element, an insulating bushing at each end of said cathode element, one of said bushings having an anode-receiving recess centrally thereof and the other of said bushings having a central bore therethrough, a rod- `like anode element coaxial with said cathode element and having one end within said one bushing recess and passing through said other bushing bore, a conductive anode supporting element insulatedly sealed to said cathode element adjacent said other bushing, said anode supporting element having an axial bore receiving and supporting the other end of said anode element therein, a glass exhaust ,tip sealed to the outer end of said anode supporting element, and means sealing the end of said cathode element having said one bushing.

1l.' A voltage regulator tube as in claim l0, wherein said last sealing means comprises a bellows, and further including means for variably adjusting said bellows to regulate the operating voltage of said tube.

l2. A voltage regulator tube comprising a hollow cylindrical cathode element, `an insulating bushing at each end of said cathode element, one of said bushings having an anode-receiving recess centrally thereof and the other of said bushings having a central bore therethrough, a rod-like anode element coaxial with said cathode element and having one end Within said one bushing recess and passing freely through said other bushing bore, a hollow insulating element having one end sealed to said cathode adjacent the end with said other insulating' bushing, a hollow conductive anode-supporting element sealed to said insulating element adjacent the other end of said insulating element, said anode-supporting element having an axial bore receiving and supporting the other end of said anode element therein, a glass exhaust tip sealed to the outer end of said anode-supporting element coaxially thereof, and means sealing the end of said cathode element having said one bushing.

13. A voltage regulator tube as in claim l2, wherein said last sealing means comprises a bellows, having a closed end and surrounding a substantial portion of said cathode element, said closed end being opposite said one insulating bushing, said one insulating bushing having a gas-equa1izing-aperture extending therethrough, and

said sealing means further i11c111di1z1g `means for variably adjusting said bellows to Tegulate the operating voltage 8 Brkey ..1.. v.r Nov. 18, 1947 Friedman Y. Sept. 26, 1950 Gerber e July 24, 1951 B'rowr'x Nov. 27, 1951 Cohen Nov. 4, 1952 Kalb May 26, 1953 Pompeo et al, June 9, 1953 Landrey et a1. Sept. 15, 1953 Friedman Oct. 20, 1953 Warmaltz et al Aug. 2, 1955 Hancock Aug. 15, 1955 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 2,874,319 February 17l 1959 Nicholas Anton It is hereb5'Y certified that error appears in theprinted specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, lines 29 and BO., kstrike out internally threaded bushing 54 Whose' threads 56 engage the"; Column w linev lo, for "ionoizable" read iohizable --Lg column 5 line 3.2y for "eorrespomdH read e Corresponding hw.,

Signed and sealed this 2nd day of June 1959a (SEAL) Attest:

KARL AXLINE ROBERT C. WATSON Attesting Oicer Commissioner of Patents

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