US2695984A - High-voltage rectifier system - Google Patents

Description

Nov. 30, 1954 J. GIACOLETTO 2,695,984

HIGH-VOLTAGE RECTIFIER SYSTEM Filed Dec. 28, 1950 ATTORNEY United States Patent Ofifice HIGH-VOLTAGE RECTIFIER SYSTEM Lawrence Joseph Giacoletto, Eatontown, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application December 28, 1950, Serial No. 203,071 12 Claims. (Cl. 32132) This invention relates to improvements in high voltage rectification systems, and particularly to an improved rectification system embodying tubes with socalled field emitter cathodes. v

It is known that under suitable conditions electrons can be drawn from a metal surface at or near room temperature to provide emission current in an electron tube (see e. g. Chafee--Theory of Thermionic Vacuum Tubes, first edition, pages 8689). This phenomenon has been adapted especially to high voltage rectification systems where it has certain advantages, since the problems of insulation attendant on the use of heated cathode tubes are eliminated.

In the use of such field emitter rectifiers, two problems have been encountered. First, it is difiicult to obtain a high output current. Second, during operation it is found that field emission deteriorates rapidly. While the exact reason for this deterioration is not clear, it is believed to be due, in part, to bombardment of the field emitter by positive ions during back voltage operation (i. e. when the anode-to-emitter voltage is negative). In the usual case, the emitter electrode is provided with one or more sharp emitter points or similar surfaces having small radii of curvature, in order to obtain the necessary high potential gradient at the emitter. In operation, it is believed that these sharp points or small surface areas are unable to withstand bombardment for any long period of time. Also, as will be shown hereinafter, the field at the emitter is excessive when the circuit first is put in operation, and this may also contribute to the abovenoted rapid decrease in good operating characteristics.

It is a general object of the present invention to pro vide an improved high voltage rectification system.

Another object of the invention is the provision of an improved field emitter type high voltage generator.

A further object of the invention is to provide an improved system for converting low voltage-high current alternating potentials to low current-high voltage unldirectional potentials.

Another object of the invention is to provide an improved field emitter rectifier tube.

In accordance with the invention, the foregoing and other related objects and advantages are attained by provision of an electron tube, combining a field emitter electrode with one or more secondary emitter or dynode electrodes, together with a circuit for operating the tube. As used herein and in the appended claims, the term field emitter is intended to designate an unheated electrode having one or more surfaces with small radii of curvature to establish a high potential gradient at the electrode surface. A secondary emitter or dynode electrode is intended to mean an electrode adapted to emit secondary electrons readily when subjected to bombardment by electrons from some source such as a field emitter electrode. Examples of field emitter and dynode electrodes are given hereinafter. As will be shown, the present invention provides a field emitter tube with much greater current capacity than such tubes normally have, and also allows operation of the tube under voltage conditions such that the field emitter is protected against rapid deterioration.

A more complete understanding of the present invention can be had by reference to the following descrip- 2,695,934 Patented Nov. 30, 1954 tion of illustrative embodiments thereof, when considered in connection with the accompanying drawings, wherein:

Figure l is a schematic diagram of a high voltage rectifier circuit including a field emitter tube arranged in accordance with the invention,

Figure 2 is a schematic diagram of a voltage doubler circuit arranged in accordance with the invention,

Figure 3 is a schematic diagram of a modification of the circuit of Figure 2, and

Figure 4 is a cross-section view of a field emitter tube constructed in accordance with the invention.

Referring to Fig. l of the drawing, there is shown a transformer 10 having a primary winding 12 connected to a source of alternating voltage 14, and a tapped secondary winding 16, having end terminals 18, 20 and an intermediate terminal 22.

Also shown in Fig. l is an electron tube 28, having a collector electrode 26 which is adapted to collect secondary electrons emitted from a dynode electrode 30. The dynode 30 is adapted to emit secondary electrons when bombarded with electrons from a field emitter electrode 32. Details of structure of a typical tube such as the tube 28 are given hereinafter.

To provide an alternating voltage input circuit be tween the dynode 30 and the field emitter 32, the field emitter 32 is connected to the lower end terminal 20 of the transformer secondary winding 16 and the dynode 30 is connected to the intermediate terminal 22 thereof. To provide an alternating voltage input circuit between the dynode 30 and the collector 26, the collector 26 is connected to the upper end terminal 18 through a capacitor 24. The alternating voltage between terminal 20 and 22 is relatively small, being only large enough to provide adequate emission from the field emitter 32 when in the correct polarity. The alternating voltage between terminals 18 and 22 is relatively large, being approximately equal to the desired unidirectional output voltage as is more fully explained in the following paragraphs.

For concreteness, it will be assumed that a positive unidirectional output voltage is required from the system. Accordingly, the junction of the collector electrode 26 and the capacitor 24 is connected to ground. As explained shortly, this.will provide a positive output voltage between an output terminal 34 and ground. Of course, it will be understood that a negative output voltage could be obtained by interchanging the ground connection and the output terminal.

When voltage first appears across the secondary windmg 16 in proper polarity to make the dynode 30 positive with respect to the field emitter 32, electrons will be emitted from the field emitter and will strike the dynode 30. This will cause secondary electrons to be emitted from the dynode. At this instant (assuming that there is no charge on the capacitor 24), there also will be a positive voltage between the collector 26 and the dynode 30, since the connections shown will make the collectordynode voltage be in phase with the dynode-emitter voltage. This will cause secondary electrons to flow from dynode to collector, leaving an increment of positive charge on the ungrounded side of the capacitor 24 (i. e. at the output terminal 34). When the voltage across the secondary winding 16 reverses in polarity, current flow will stop in the tube 28.

During succeeding cycles of operation, the voltage on the capacitor gradually will increase until it becomes substantially equal to the peak voltage between the upper terminal 18 and the intermediate terminal 22 of the winding 16.

The electron multiplication action of the dynode 30 in the tube 28 will provide relatively large total output current with a comparatively small field emitter current. In this way, the low current deficiency previously referred to is overcome. At the same time, the maximum voltage on the field emitter at any time, either forward or back voltage, need be no greater than a few hundred volts because only small field emission current is required. The major portion of the secondary voltage appears between the dynode 30 and the collector 26. This mode of operation is of material benefit in connection with the deterioration problem referred to previously.

For best operation, the field emitter should emit only on the peaks of the positive half cycles of alternating voltage, since the collector-dynode voltage will be positive during decreasing portions of the positive half cycles as the voltage builds up on the capacitor 24. In practice, it is found that the dynode-field emitter voltage at which emission begins is quite sharply defined, being dependant on electrode spacing, electrode structure, etc. Therefore, for any given tube, the peak dynode-to-field-emitter voltage obtained between the intermediate and lower end terminals 22, 20 can be readily adjusted by suitable selection of the tap-point 22 to insure proper operation. By such adjustment, field emission can be restricted to a suitable portion of the positive half cycles ofalternating voltage.

For a properly designed dynode-collector system, only a relatively small voltage is required to collect all secondary electronsfrom the dynode. For this reason a correspondingly small drop in output voltageoccurs when the output current is varied from zero current to full output current. As a result, the output represents a well regulated source under load conditions.

It will, of course, be understood that the invention is not limited to the use of a single stage multiplier. Additional dynodes can be added to the tube '28 where larger output currents are required. For simplicity, single stage multipliers areshown throughout the present application.

In some instances, a higher output voltage may be required than can be obtained conveniently with the basic circuit of Figure l. In Figure 2, there is shown a voltage doubler circuit, embodying the principles of the invention, for generating an output voltage approximately equal to twice the peak voltage developed across the dynode-collector section of the transformer secondary winding.

In the circuit of Figure 2, a first tube 28 and a capacitor 24 are connected to the transformer secondary winding 16 in the same manner as in the circuit of Figure 1. A second tube 36 is provided, having a field emitter 38 connected to the first tube collector 26. A collector 40 in the second tube 36 is connected to the lower terminal 20 of the secondary winding 16 through a second capacitor 42.

A voltage divider, comprisinga pair of resistors 44, 46, is-connected from thefirsttube collector 26 to the second tube collector 40. A dynode-48 in-the second tube 36 is connected to the junctionpoint 50 between the resistors 44, 46.

In the circuit of Figure 2, the secondary winding 16 and the first tube 28 cooperate to build up voltage on the first capacitor 24 in the same manner as in the circuit of Figure 1. That is,'the first tube 28 will conduct current when the upper terminal 18 of the transformer secondary winding 16 is positive with respect to the lower terminal 20. During half cycles of alternating voltage when the foregoing polarity obtains, the second tube field emitter 38 will be positive with respect to its dynode 48, so that no current will flow in the second tube. However, on alternate half cycles (when the upper terminal 18 is negative with respect to the lower terminal 20), the second tube field emitter 38 will be negative with respect to its dynode 48. Therefore, current will flow alternately in the two tubes 28, 36 on alternate half cycles of the transformer output voltage.

As voltage begins to build up across the first capacitor 24, it can be seen that the second tube field emitter 38 and dynode 48 will be driven more negative each time that the conducting half cycle occurs for the second tube. This simply means that the voltage available for operating the second tube 36 gradually will increase, because the increasing voltage across the first capacitor 24 will be added to the voltage across the secondary winding 16. Eventually, the voltage across the second capacitor '42 will build up to be substantially equal to the peak voltage between the secondary terminals 18, 22 plus the voltage on the first capacitor 24.

The voltage divider 44, 46 serves the same purpose for the second tube 36 as does the intermediate terminal 22 for the first tube 28. That is, the junction 50 between the resistors will be at some voltage intermeditae that on the second tube field emitter and collector electrodes 38, 40, so that the second tube dynode 48 can be positive with respect to the field emitter 38 but negative with respect to the collector 40.

The second capacitor 42 in Figure 2 serves as the output storage capacitor. Therefore, the output terminal 34 is connected to this second capacitor rather than to the first capacitor 24 as in the circuit of Figure 1.

In Figure 3 of the drawing, there is shown a modified form of voltage doubler circuit embodying the principles of the invention. In this circuit, the transformer 10 is provided with an auxiliary secondary winding 52, in addition to the principal secondary winding 16. A first tube 28 and capacitor 24' are connected to the secondary winding 16 as in the circuits of Figures 1 and 2. A second tube 36 has a field emitter electrode 38 which is connected to the upper terminal 54 of the auxiliary secondary winding 52, and a dynode electrode 48 which is connected to the lower terminal 56 ofthe auxiliary winding 52. The second tube dynode 48 also is connected to the first tube collector electrode 26. A collector electrode 40 in the second tube 36 is connected through a second capacitor 42 to the lower terminal 20 of the main secondary winding 16 in common with the first tube field emitter 32.

The operation of the first tube 28 in charging. the first capacitor 24 in Fig. 3 is the same as has already been described in connection with the circuits of Figures 1 and 2. Also, as in the circuit of Figure 2, the first tube 28 and the second tube 36 will conduct current on alternate half cycles of transformer voltage. Assume that the upper terminal 18 of the main secondary winding 16 is negative at some particular instant with respect to the lower terminal 20. This will tend to make the second tube dynode 48 negative with respect to-its collector 40,

which is the proper condition for dynode-collector current to flow. Therefore, if the auxiliary winding is connected to the second tube dynode 48 and field emitter 38 in proper fashion to make the emitter 38 negative'with respect to the dynode 48 when the latter is negative with respect to its collector 40, electrons will flow from the emitter 38 and will bombard the dynode 48. For the particular configuration shown inthe drawing, this obviously will result if the upper terminals 18 and 54 of the windings 16 and 52 both swing positive and negative at the same time; i. e. in phase.

When the second tube 36 conducts current, the second capacitor 42 will receive an increment of charge which gradually will build up until the voltage across the second capacitor 42 is substantially equal to twice the voltage on the first capacitor 24. As in the circuit of Figure 2, the second capacitor 42 in Figure 3 serves as the output storage capacitor, and the output terminal 34 accordingly is connected to this second capacitor 42.

It will, of course, be understood that the auxiliary winding 52 in Figure 3 need not be a high voltage winding like the principal secondary 16, but is merely required to develop sufiicien't voltage to ensure field emission from the field emitter 38. By extension of the circuit shown either in Fig. 2, or Fig. 3 additional voltage multiplication can be obtained by the addition of field emitter rectifier tubes.

In any of Figures 1, 2 or 3, the alternating. voltage supplied to the system may have either a relatively low or high frequency without changing the principles of operation. So-called radio frequency oscillators can be used in connection with the rectification systems shown herein with satisfactory results.

Before proceeding to a description of the structural details of the tube shown in Fig. 4, it is well to consider certain requirements imposed by the high voltage involved. These requirements might besummarized briefly as:

(a) Elimination of exposed mica supports.

(b) Curved corners to reduce corona.

(c) Long'leakage paths.

(d) Low capacitance between collector and dynode electrodes.

(e) Location of field emitter so as to be shielded from large electric fields.

(f) Electrode construction so as to provide electric field focus of electrons.

The tube shown in Fig. 4' comprises an evacuated envelope 28, having mounted therein an. inverted cupshaped metallic support 19, the open lower end of which is flared outwardly and terminates ina'rolledtlip .21. The

cup-shaped member 19 is supported by a lead-in conductor rod 23 which passes' through a glass seal 25 inside a metal cylinder 27 which passes through and is sealed to the glass envelope wall.

A circular wire 32 of very small diameter, say 0.001 inch, is radially displaced from the cup-shaped support 19, and is .supported therefrom in any suitable manner, as by a plurality of wires 32a spaced from each other. One end of each of the wires32a is soldered to the wire 32 and the other end of each of the wires 32a is soldered to the outer surface of the support 19. The circular wire 32 constitutes a field emitter electrode. Thewire field emitter 32 has a circular cross-section 321), as shown in the cross-sectional view of Fig. 4, thereby defining the transverse curvature of the surface of the wire field emitter 32 by a relatively small radius of curvature, say 0.0005 inch. This radius of curvature is the radius of the circular cross-section 32b.

A generally bell-shaped electrode 30 extends from the lower end of the cylindrical support 27, and has a rolled lip 31 at the bottom open end thereof. The bell-shaped electrode 30 is composed of (or has an inside surface coating of) a material, such as copper berylium or silver magnesium, capable of emitting secondary electrons in relatively large number upon electron bombardment thereof. The dynode 30 extends downwardly a sufficient distance to surround the field emitter 32 so as to be readily bombarded by electrons from the field emitter.

In the lower end of the envelope 28, there is provided a cup-shaped electrode 26, supported on a metallic lead-in rod 29 which extends through a glass-to-metal seal 33 in the envelope wall. The upper open end of the electrode 26 also terminates in a rolled lip 35, and provides an electron collector electrode facing the dynode 30 to receive secondary electrons therefrom.

As shown by dotted lines in Fig. 4, primary electrons emitted from the field emitter wire 32 will strike the inner surface of the dynode 30, causing secondary electrons to flow therefrom to the collector 35.

The rolled lips 21, 31, 35 provide curved corners to reduce corona. The lip 21 on the support 19 also aids in focussing the secondary electrons from the dynode 30 onto the lip 35 of the collector 36. Also, the lip 21 and associated flange 37 on the lower end of the support 19 shield the field emitter 32 from the large electric field between dynode and collector. In addition, the location of the field emitter and dynode lead-in conductors 23, 27, respectively, at an end of the envelope 28 opposite from the collector lead-in 29 provide long leakage paths between the points of greatest voltage difference, While the relatively large spacing between the principal surface areas of the dynode 30 and the collector 26, provides low capacitance therebetween.

It can be seen that the present invention provides a simple and efficient high voltage rectification system, and one that avoids many of the limitations encountered in prior art field emitter rectifier systems.

What is claimed is:

1. In a system for deriving unidirectional voltage from an alternating voltage source, in combination, an electron tube having a field emitter electrode, a dynode electrode and a collector electrode, a capacitor, a circuit connecting said dynode electrode to said collector electrode through said capacitor and including means to apply between said dynode and collector electrodes a first alternatin voltage derived from said source, a circuit connecting said field emitter electrode to said dynode electrode and including means to apply between said field emitter and dynode electrodes a second alternating voltage in phase with said first alternating voltage, and means connected across said capacitor to derive said unidirectional voltage.

2. The combination defined in claim 1 including a transformer having a primary winding and a tapped secondary winding, said first and second named means comprising separate portions of said secondary winding.

3. In an alternating voltage rectifying system. in combination, a capacitor, an electron tube having a field emitter electrode, a dynode electrode and a collector electrode, an alternating voltage input circuit connecting said dynode electrode to said collector electrode through said capacitor, a second alternating voltage input circuit connecting said dynode electrode to said field emitter electrode, and means connected across said capacitor to derive a unidirectional voltage.

4. In an alternating voltage rectifying system, in -com= bination, first and second electron tubes each having a field emitter electrode, a dynode electrode and a collector electrode, first and second capacitors, a first alternating voltage input circuit connecting said first tube dynode electrode to said first tube collector electrode through said first capacitor, a second alternating voltage input circuit connecting said first tube field emitter electrode to said first tube dynode electrode, a third alternating voltage input circuit connecting said second tube dynode electrode to said second tube collector electrode through said first and second capacitors, and a fourth alternating voltage input circuit connecting said second tube dynode electrode to said second tube field emitter electrode.

5. The combination defined in claim 4 including a transformer having a primary winding and a tapped secondary Winding, said first and second circuits comprising sections of said secondary winding.

6. The combination defined in claim 4 including a transformer having a primary winding and first and second secondary windings, said first and second circuits comprising sections of said first secondary winding, said third circuit comprising said first secondary winding, and said fourth circuit comprising said second secondary winding.

7. In a high voltage rectifier system, in combination, a source of alternating voltage, a capacitor, a first electrode adapted to emit secondary electrons upon electron bombardment thereof, a source of electrons for bombarding said first electrode and comprising a second cold electrode spaced from said first electrode and adapted to emit electrons by field emission upon establishment of a potential difference between said electrodes, a third electrode spaced from said first electrode to collect electrons emitted from said first electrode, a transfer circuit serially connected across said voltage source and including said capacitor and the space path between said electrodes, and connections from each said electrode to points of different potential on said voltage source.

8. A system for converting alternating voltage to unidirectional voltage, said system comprising an alternating voltage source, a transformer having a primary winding connected to said voltage source and having a secondary winding, said secondary winding having end terminals and an intermediate terminal, a capacitor connected to one of said end terminals, an electron tube having a first electrode connected to the other of said end terminals, said first electrode comprising a field emitter electrode, a second electrode in said tube adapted to emit electrons upon bombardment thereof with electrons from said first electrode, said second electrode being connected to said intermediate terminal, and a third electrode in said tube for collecting electrons emitted from said second electrode, said third electrode being connected to said capacitor to provide a series circuit comprising said secondary winding, said capacitor, and the space path between said second and third electrodes.

9. In an electron tube, in combination, an open-end cup-shaped electrode and an open-end bell-shaped electrode, said electrodes being disposed with said open ends facing each other, one of said electrodes having an inner surface constituted of material adapted to emit electrons readily upon bombardment thereof with electrons, and a third cold electrode constituting a source of bombarding electrons for said one electrode, said third electrode comprising a member disposed inside said one electrode adjacent said inner surface, said third electrode having a surface of small radius of curvature adapted to establish a high potential gradient thereon.

10. The combination defined in claim 9 wherein said pair of cup-shaped members terminate at the open ends thereof in rolled lips.

11. The combination defined in claim 9 including a member electrically shielding said third electrode from the other of said pair of electrodes.

12. A field emission rectifier tube comprising a pair of cold spaced electron emitter electrode, one of said electrodes comprising a field emitter electrode having a surface of relatively small area adapted to establish a high potential gradient thereon, the other of said electrodes comprising a bell-shaped dynode electrode having an inner surface facing said small area surface, said other electrode surface being constituted of material adapted to emit secondary eectronsreadilyllllpon electron1 bolnibadrdci References Cited in the file of this patent ment thereo an an electron co ector e ectro e s iel e from said small area surface and disposed to collect UNITED STATES PATENTS secondary electrons emitted from said other electrode Number Name Date surface, 5 1,559,460 Ruben Oct. 27, 1925 2,036,069 Morrison Mar. 31, 1936 2,184,910 Farnsworth Dec. 26, 1939- 2,202,823 Bennett June 4, 1940 2,216,729 Bennett Oct. 8, 1940

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