US2293468A - Cold cathode rectifier - Google Patents

Description

Aug. 18, 1942. c. T. KNIPP i 2,293,468

COLD CATHODE RECTIFIER Filed Sept. e, 1939 2 Sheets-Sheet 2 Patente d Aug. 18, 1942 4 COLD` CATHODE RECTIFIER Charles T. Knipp, Urbana, Ill., assignor to Board of Trustees of the University of Illinois, Urbana, Ill., a corporation of Illinois Application September 16, 1939, Serial'No. %5,193

7 Claims.

The present invention relates to rectiers, particularly of the electronic or tube type.

The invention aims primarily to provide an improved rectifier characterized by a cold cathode. A rectifier in which the cathode operates in a relatively cold state has numerous advantages over thermionic or filamentary rectifiers in which the cathode must be maintained in a heated state by a filament or the like. For example, the burning out of the filament terminates the life of the tube much short of the life expectancy of the other elements of the tube. Moreover, the thermal energy generated by the filament is largely dissipated as a heat loss. Furthermore, the heated electron emitting surface gradually loses its efiectiveness to emit electrons. These and other disadvantages are avoided in a cold cathode rectifier.

My improved rectifier utilizes certain of the discoveries made by Crookes and Hittorf with reference to the electrical conductivities prevailing within tubes which have been evacuated down to very lowkpressures, these tubes having spaced electrodes sealed therein between which the electrical discharge is drawn. tablished that when these tubes are exhausted down to an extremely rarified or high vacuum stage, known as the Crookes' stage, and are then subjected to a relatively high voltage between the electrodes; a phenomenon in the form of a nonluminous region or dark space develops at or in immediate proximity to the electrode or electrodes which are then functioning -as cathodes. This region became known as the Crookes' dark space, and represents the mean free path of the issuing electrons.

Hittorfs later experiments performed on the Crookes' dark space revealed other related phenomena pertaning to increased resistance to conductivity when the Crookes' dark space is limited in its development or caused to envelope its respective electrode. Crookes and Hittorf did not, however, perceive and apply the potentia1ities of the Crookes' dark space for rectfying alternating Currents.

I have found that by controlling the Crookes' dark space of one of the electrodes, or by establishing an unbalanced relation between the Crookes' dark spaces of different electrodes, a

Very effective rectifying action can be obtained without the employment of a heated cathode or other thermionic agency. This improved cold cathode rectifier comprises a tube or like chamber enclosing a plurality of electrodes preferably Crookes esshroud or equivalent element which limits the development of the Crookes' dark space or approximately encloses this dark space at that electrode. At the Crookes' stage of evacuation of the tube, this barrier or hood prevents that electrode from functioning as a cathode, so that it thereafter functons solely as an anode, for producing the desired unilateral conductivty.

One manner in which my invention may be carried into efiect is illustrated in the accompanying drawings illustrating different specific embodiments of the tube. In such drawings:

Figure 1 is a longitudinal sectional view of one embodiment -employing three electrodes for obtaining full-wave rectification;

Figure 2 is a simple circut diagram illustrating one typical use of the tube; and

Figures 3, 4 and 5 are longitudinal sectional views illustrating other embodiments of the tube.

Referring to Figure 1, the body of the tube ll) is shown as being composed of glass, although it will be understood that it may be composed of other insulating materials, or might even be made of a metal. The electrodes ll, !2 and !3 preferably consist of aluminum rods fused in position in glass seals M, !5 and !6 respectively. The outer ends of the rods carry any suitable connector terminals I'l, !8, and e for making connection with the circuit. The two electrodes l2 and |3 shown as disposed in the lower part of the tube are arranged to function solely as anodes, in consequence of which the electrode H shown in the upper part of the tube is caused to function solely as a cathode. The two lower electrodes are made to function solely as ancdes by the em- -ployment of the above mentioned barriers or hoods in association with said lower electrodes. In the exemplary Construction illustrated in Fgure 1, these take the form of cylindrical glass hoods or envelopes !2' and IS' which substantially enclose the electrodes !2 and 13, in spaced relation thereto. The two hoods are preferably substantially identical, the cylindrcal inner walls of each being spaced substantially uniformly from the cylindrical outer surfaces of their respective electrodes. The closed inner ends of said hoods are also preferably spaced from the consisting of `plain metallic rods or other simple inner ends of their electrodes. The open outer end of each hood preierably extends beyond the bare metal surface of its respective electrode to overlie a portion of the glass seal !5, IG. Any suitable supporting struts, spiders or like arrangement may be employed for supporting the hoods 12', 13' in the above relation to their respective electrodes. In one typical embodiment of the invention, each of the electrodes consists of an aluminum rod of approximately millimeters in diameter, and the radial distance from the surface of such electrode to the irmer walls of its respective hood is approximately 2 centimeters. I wish it to be understood, of course, that the above described arrangements and proportions are merely illustrative and not limitatve.

The tube may be evacuated to the desired clegree by connection with a mercury pump or the like, following which the tube may be permanently closed by a hermetic seal. As alternative procedures, the tube may remain connected with the mercury pump or other exhausting means for intermittent or continuous exhausting during operation; or, after being thus exhausted by the pump, the tube may remain connected with a receptacle formed as a part of the tube and containing charcoal, this charcoal being adapted to absorb gas from the tube when the charcoal is cooled by the action of liquid air or the like. The embodiment shown in Figure 1 illustrates such a receptacle 22 joined to the rectifier H) by the connecting neck portion 23 and containing a mass of charcoal 24. A vessel containing licuid air can be brought up to immerse the receptacle or bulb 22 in the liquid air, thereby bringing the temperature of the charcoal down to a very low point, which results in the charcoal efiectively absorbing gas remaining in the tube. If desired, a stop-cock or the like may be interposed in the connecting neck portion 23, so as to enable the bulb receptacle 22 to be disconnected from the rectifier tube for maintainin the pressure substantially constant in the tube over`1ong periods of time. The Crookes' stage of rarefaction at which satisfactory rectifying action occurs is a vacuum in the ne-ighborhood of .001 mm. Hg or less.

Typical circuit connections for full-Wave rectification are illustrated in Figure 2. Any suitable transformer 26, or connected pair of transv formers, establishing a center tap or split secondary 27, may be employed for supplying the potential to the rectifying tube. The end terminals of the secondary 21 are connected to the two anode electrodes !2 and !3 of the tube. The center tap of the secondary is connected to one side of the direct current load L, and the cathode electrode ll of the tube is connected to the other side of the load L. This load might be an X-ray tube, a Geissler tube, or any other' direct current device, preferably of high potential characteristic. In the Geissler tube illustrated, the anode is indicated at 3i and the cathode at 32. Typical alternating current Voltages which have been rectied in the rectifying tube lil have ranged from 5000 to 25,000 volts, but it will be understood that higher or lower voltage ranges may be employed, depending upon the dimensions of the rectifying tube, etc.

In the operation oi the tube, the existence of a relatively low pressure within the tube is appare-ntly an important factor for securing the desired rectication. For example, if the tube is subjected to its Operating potential When it has only been exhausted down approximately to the Geissler stage (approximately .05 mm. Hg) the alternating discharge passes back and forth between the electrodes about equally well in both directions, the electrodes serving alternately as cathode and anode. In other words, at these gas pressures the glass barrier or hood exerts little or no rectifying action. However, if the vacuum in the rectifying tube is now made higher as by the cl-arcoal-in-liquid-air control) until the Crockes' dark space (i. e., the mean free path of the issuing electrons) reaches to or extends beyond the inside 'chmensions of the glass hoods l2' and l', then the respective electrodes !2 and [3 can no longer function as cathodes, i. e., they serve as anodes only. The discharge through the tube is now unidirectonal, the cut-off being very sharp at the neutral line, With no fringing or feathering out visible in cathode-ray oscillographs. The opening of either one of the two switches 28 or 29 leading to the two anodes !2 and !3 gives half-wave rectification, and this half-wave rectification likewise seems to be perfect, with no fringing or feathering out Visible, and the rectification on one alternation being substantially identical ,with the rectication on the other alternation. Of course, where halfwave rectification is to be performed continuously, a two electrode tube is employed, as hereinafter described. The abruptness with which the rectiiying action starts as the gas pressure in the tube is lowered to the Crooke-s' stage depends on the geometrical accuracy of the hood or hoods l2'-l3'; The radial distance from the surface of each electrode l2-l3 to its glass envelope l2'--l3' should be uniform at all points. such electrons as are projected from the electrodes I 2-l3 leave the surfaces of said electrodes in directions normal or at right angles to said suraces, and it is important that these electrons must not get out of the hoods |2'-l3'. Accordingly, the open ends of these hoods are arranged to extend to or overlie a portion of the glass seal !5-16 at each of said anode electrodes.

Figure 3-il1ustrates another construction of three electrode tube for full-wave rectification.

The two anodes Iza and lsa. enter the tube lo in diametrically opposite relation. The exposed portions of these electrodes extend into a glass cylinder 34, which has a transverse diaphragm or partition 35 of glass or other insulating material disposed in the cylinder 34 intermediate its ends. The resulting structure constitutes a hood for each of the anodes Iza-Isa. This cylindrical hood structure may be mounted by any suitable supporting posts, spider arms or the like, as previously described. surrounding said glass cylinder is the cathode l la, this being in the form of a metallic ring which is spaced circumferentially from the glass sleeve 34 and is disposed equidistant from the opposite ends thereof. A suitable Connector terminal I'la extends from the cathode ring Ha outwardly through a glass seal l4a. The same evacuating methods and apparatus may be employed in connection with this tube as were previously described. The operation of the tube is also the same as previously described.

Figure 4 illustrates a simple form of two electrode tube for effecting half-wave rectication The construction and operation of this tube will be apparent from the preceding description.

Figure 5 illustrates another embodiment of two electrode tube in which a modified construction of hood is employed. This hood structure comprises an insulating sleeve portion 38 spaced radially from its associated electrode, a second insulating sleeve portion 39 likewise spaced radially from the electrode, and an oute' hood 40 which envelopes both sleeve portions 38 and 39. These three portions 38, 39 and 40 may be constructed of glass or any other suitable insuiating material. The open space 4! is preferably in the form of a continuous annular gap between the adjacent ends of the sleeve portions 38 and 39, although, as a modified arrangement, these two sleeve portions may be in the form of a continuous sleeve structure formed with spaced holes 4| located at different points around the sleeve. Where the sleeve portions are separate, the outer sleeve portion 39 and hood 49 can be supported by mounting posts, spider arms or in any other suitable way. The outer hood ta intercepts electrons emitted radially out through the space or openings 41.

While I have illustrated and described what I regard to be the preferred embodiments of my invention, nevertheless it will be understood that such are merely exemplary and that numerous modications and rearrangements may be made therein without departing from the essence of the invention.

I claim:

l. A full-wave cold cathode rectifier comprising a tube having a gas pressure of the order of .001 mm. of mercury, three electrodes extending substantially radially into said tube from different angles, and insulating hoods enveloping two of said electrodes for causing said latter electrodes to function solely as anodes, the inner ends of said hoods adjacent to the third electrode being closed and the outer ends of said hoods being open.

2. A cold cathode rectier comprising a tube having a gas pressure of the order of .001 mm. of mercury, a plurality of electrodes extending substantially radially into said tube from different angles, and an insulating hood enveloping one of said electrodes for causing said latte' electrode to function solely as an anode, the inner end of said hood adjacent another of said electrodes being closed, and the other end of said hood being open.

3. A cold cathode rectifier comprising a tube having a gas pressure of the order of .(301 mm. of mercury, a pair of electrodes extending into said tube from different angles, and an insulating hood enveloping on of said electrodes for causing said latter electrode to function solely as an anode, the inner end of said hood adjacent the other of said electrodes being closed, and the outer end of said hood being open.

4. A full-wave cold cathode rectier conp'ising a tube having a gas pressure of the order of .001 mm. of mercury, three electrodes extending substantially radially into said tube from different angles, and conning structures ccmposed of insulatng material partially enveloping two of said electrodes for causing said latter electrodes to function solely as anodes, the third electrode :being adapted to function as a cathode, said confining structures comprising end hoods and also comprising openings disposed outwardly of said end hoods, said hoods being interposed as barriers between the inner ends of their respective anodes and the inner end of said cathode, said openings permitting electrons to flow from said cathode to said anodes but preventing electrcns emitted by said anodes from having any straight line path of flow from said anodes to said cathode.

5 A cold cathode 'ectifier comprising a tube having a gas pressure of the order of .001 mm. of mercury, a plurality of electrodes extending into said tube from different angles, and a confining structure composed of insulating material partiaily enveloping one of said electrodes for causing said latter electrode to function solely as an anode, another of said electrodes being adapted to function as a cathode, said confinng structure comprising an end hood and also comprising an opening disposed outwardly of said end hood, said hood being interposed as a barrier between the inner end of its respective anode and the inner end of said cathode, said opening permitting electrons to flow from said cathode to said anode, -but preventing electrons issuing from said anode from having any straight line path of flow from said anode to said cathode.

6. An electron device for utilizing Crookes' dark space phenomena to effect cold cathode rectication of alternating Currents, comprising an envelope evacuated to the Crookes' stage of evacuation approximately of the order of .001

of rne'cury, a plurality of electrodes extending into said chamber and adapted for connection with an alternating current circuit of sufiicient potential to create a crookes dark space at each electrode, and insulating hood means housing one of said electrodes for confining the development of the Crookes' dark space at said latter electrode and the mean free path of the electrons issuing therefrom, whereby said latter electrode is caused to function solely as an anode.

7. An electron device 'for utilizing Crookes' dark space phenomena to efiect cold cathode rectification of alternating Currents, comprising an envelope evacuated to the Crookes' stage of evacuaton approximately of the order of .001 mm. of mercury, a plurality of electrodes in said Cham-ber adapted to be energized by an alternating current of sufiicient potential to create a Crookes' dark space at each electrode, and barrier means of insulating material housing one of said electrodes for confining the mean free path of the electrons issuing therefrom, whereby said latter electrode is caused to function solely as an anode, and another of said electrodes is enabled to function as a cold cathode.

CHARLES T. KNIPP.

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