US2445441A - Rectifier - Google Patents

Description

July 20, 1948. Q KRlEGER 2,445,441

RECTIFIER Filed Dec. 28, 1945 INVENTOR.

BYGard-ner* LKrieger if fwfy Patented July 20, `1948 Gardner n-Krie ger; rincetoxr; N: ilassignor Radio Qorporatiom of America; a. corporation-of Delaware vThis invention relates to cold cathode rectiers and fioie especially to cold cathode gas rectif'ers. It is an object of this invention to provide a cold cathode gasrectiiier having a high inverse voltage characteristic and a moderate starting voltage p @thii oblietswill appear i-nthe following dereferencev being -hd td the drawir'gf,` ih which: e* Y i *1f-he sin'gle figure of the drawing is iai-*section through a rectifier tube involving the invention. The rectifier may have the usual glass envelope l lled with any of the inert gases, but to reduce sputtering it is desirable to use a gas of low molecular Weight, so I prefer to employ neon for this purpose. The pressure is not critical, but it must be in the range of this type of rectifier. This range has been found to be between 50 microns and .5 millimeter for neon and the highest pressure is used to obtain longest life. The electrode 2 acting as cathode in the rectifying half cycle will be designated as the cathode in this description. In the other half cycle it is the anode, but substantially no current flows during such half cycle. The other electrode 3 will, for a similar reason, be called the anode.

The cathode may be made of vario'us inactive conductors, as the rectifying action does not depend upon any special properties of the cathode material. However, since this electrode is subject to sputtering during operation of the tube, which absorbs and depletes the gas, the life of the tube is increased by making the cathode of a material that resists sputtering. Aluminum has been found to satisfactorily meet this requirement. The size and shape of the cathode also are not critical, but it is desirable to make it of such shape that the supporting wires or rods are shielded to prevent them from sputtering. I therefore prefer to make the aluminum in the shape of a cup with the supporting wire 4 attached thereto on the inner surface. Other shapes may be used with other provisions for shielding the supporting wire.

The anode 3 may be any suitable metal, as its character has no effect on the rectifying action. Nickel or nickel alloy Iwill be a satisfactory material. It is preferable to make this electrode in the shape of a wire or tubing. In the embodiment shown in the drawing, the anode 3 is surrounded by an electron-permeable sheath 5, which may be any of a variety of insulation materials. Heretofore proposals have been made to shield the anode completely except for a small orifice opposite the cathode. This is not a dea claims. (CL ci-2715i sirable construction. I have found that the gasA pressure? theI tube: isi vmade lessi critical and the iperatior'rmore:V reliable byhaving manygpaths fr the electrons/through the insuiausor. I have found a',- closeiy woven glass sheath very; factorily' accomplishes this purpose,l but arr irre sulatr' or' a plurality of insulators on the annde 3';Y supplying a rhultipllcityr of` cracks; fissuresl or other openings for:4 producing many electronpaths to the anode have alsof Been'feundf. satis@ factory. The size of the anode is not critical, but EIS have found it desirable to make it of small size. In tubes like the one illustrated in the drawing, the anode has been made about one-eighth of an inch in diameter.

In the diagrammatic connections to the tube I have illustrated a source 6 of alternating voltage with a tapped bleeder resistance 1 for the rectified current supply. To produce suitable operation of the rectler, I have found that the impedance 1 should be relatively high, for example, not less than about one-half megohm. Any impedance above this value will ordinarily be satisfactory. No lters are shown in the drawing as these may be omitted or used, as desired.

The operation of the rectifier may be explained as follows:

When the cathode 2 is negative and the anode 3 positive, electrons from the cathode are projected to the positive electrode at suflicient velocity to bombard secondary electrons from the surface upon which they land. Some of the electrons pass through the interstices of the insulation sheath 5 and land on the anode 3 but, due to the preponderance of glass fiber over the interstices, most of them hit the glass fibers and bombard secondary electrons therefrom in a ratio greater than unity until the sheath attains approximately the potential of the anode 3. Ihese secondary electrons are then attracted to the anode through the interstices. Thus, during the rectifying half cycle described, a multiplicity of electrons are shot from the cathode and these collide with the inert gas molecules and produce positive ions, which are attracted to the negative cathode 2. It is these ions that furnish the greater part of rectified current, the primary electronic current in the opposite direction being small in comparison, as is well known.

On the next half cycle .the anode 3 becomes negative and the Icathode 2 positive. The sheath 5 has a positive potential from the loss of secondary electrons in the previous half cycle that is substantially the same as 4the cathode 2, now anode. Hence, nearly all the potential drop is between the electrode 3 and sheath 5 and there is no substantial collision with gas atoms, as the path is too short. In the space between the sheath 5 and the cup 2 there is very little drop in potential and hence few electrons move to cup 2 in this furthermore be too low for substantial bombardment of electrons, from vthe gas atomsllThere will therefore be no substantial ionic'ecurrent' in this half cycle and, of course, the very small electron current is negligible. In use the tube has a starting voltage of 600 volts and a peak inverse voltage of 4 to 6 kilo volts, below which substantially no inverse current iiows. The tube has beenused'in circuits drawing 10 micro amperes with no apparent limitation on the life yof the. rectifier.. higher currents may be delivered by the rectifier with reduced life.

Having described my invention, what I claim is:- w u 1. In cold cathode rectiflers, an envelope con-A taining an inert gas, a cathode, ananode spaced from the cathode sufhcientlyto provide a path beyond the mean free -path .ofv the electronsfat the pressure of said gasjandinsulating material surrounding theanode all partsv offwhich are spaced less than the mean free path of -the electrons therefrom and-'having a multiplicity of `electron Apaths therethrough,

half cycle and their velocity wouldy 2. In cold cathode rectifiers, an envelope containing an inert gas, a cathode, an anode spaced from the cathode suiiiciently to provide a path beyond the mean free path of the electrons at the pressure of said gas, and a pervious sheath of insulating material surrounding the anode all parts of which vare spaced less than the mean free vpath ,of the' .electrlsr'therefromL v 3. In cold cathode rectiflersj an envelope containing -an 4inert gas of low molecular weight, a Icathode cup of low sputtering metal, an anode rod spaced from said cup suiiiciently to provide a path beyond the mean'free lpath of electrons at I`the pressure of said gas and a woven glass Much V- sheath 'surrounding' said anode rod and in substantial contact' therewith.

GARDNER L. ImIEG-EB.

REFERENCES CITED The following references areV ofvrecord in the file of this patent:

UNITED STATES `PATENTS Name Date' Machlett Jan. 20,V 1931 'Hitchcock July 14, 1931 Hendry May 2, 1933 Spanner Dec. 5, 1939 5 Number

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