US2688713A

US2688713A - Rectifier tube

Info

Publication number: US2688713A
Application number: US312348A
Authority: US
Inventors: Malter Louis
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1952-09-30
Filing date: 1952-09-30
Publication date: 1954-09-07
Anticipated expiration: 1971-09-07

Description

S P 7, 5 L. MALTER RECTIFIER TUBE Filed Sept. 30, 1952 Patented Sept. 7, 1954 UNITED S TATES PATENT O FF I CE RECTIFIER Louis Malter, Princeton, N. J iassignor .to .Radio -Corporation of America, a corporation vo'f'Dela- "ware Applicationseptembcr 30,319.52, :Serial No. 312,348

10'Claims.

1 .Thisinventionrelate to gaseous dischargedevices .and particularly to .gaseous discharge devices thatare used for purposes .of rectification. If .a vacuum type of dischargedevi'ce, ortube,

.is used .for purposes of .rectificationla large applied potential is required to overcome the-space charge efiect when the tube is conducting. As

-is wellknown, the space charge eifectmaybe essentially eliminated by inserting a. gaseous filling in the tube. The gaseous filling willionize when the tube conducts and will thus 'form a highly conductive plasma within the tube. The plasma .is a region of very high, but essentially equal,

concentrations .ofiree electrons andpositive ions.

Due to .the'high mobility o'fthep-lasma electrons and the absence of net space charge, the plasma is an excellent electrical conductor. Thus the gaseous discharge type of .device has the advantageof eliminatingthespace charge eifects'when related to a .vacuum type of discharge device.

Even though thegaseous type ofdischarge device has considerable advantage over a'vacuum' type .ference in potential between the cathode and anode during the conductive period for *a given load current, and is required 'to maintain the plasma 'in-the tube. One of the reasonsfithat the arc drop occurs is that the plasma will .li'fiuseoif 'tovarious electrodes and insulating members and -will thus require additional i'ree electrons and positive ':ions to be generated to replace those that are lost. Aifurther reason for the arc drop :is the recombination of electrons Band positive -1ons.

One methodto .overcomeasome of the troublesome effects of :the .arc drop is to separate the ionizing discharge from the work or load :current path through the tube. uVh'en this LiSad'OIlB the a-plasma, may :be generated 'by :an auxiliary discharge while the load :current .circu'it of the tu'be is-serving its useful purpose more efficiently.

Several methods have been devised to=separate thesetwo functions, ire. C1 thei'unction of providing electronswith sufficient energy to generate 0 ions for sustaining the plasma, and (2) the function of providing"the electrici'ield neededfor-pull- 'ing a given anode current through the'tube, "and thus achieve a more efficient "gaseous rectifying tube. The reasonthat a more "efficient gas tube is developed whenlthe two functionsare separated is that the potential needed for-drawinganelectron .current is small (as compared to *.the ;potenti-al required .to maintain the discharge, thus :the most eflicient voltage magnitude may be utilized when :the iunctions are separated. All of these .methods that have been devised :for separating these functions have required a direct current potential to provide the electrodes with sufficient energy to produce a sustained ionization. The 'fact that.a direct -current has been required to sustain the .plasma has many disadvantages. One of .the principal disadvantages is that when the device is -.to be .used for rectification .purposes asdirect current source must be .available.

It is therefore .an object vof .this invention to provide anew and novel gas discharge device that will overcome the requirementlof a direct-current source and willpermit the separationof the above mentionedfunctions.

It is a further-object of this invention 'to provide a new and novel gaseous discharge device that maybe used for purposes of rectification Wiherein all of the electrodes are energized with an alternating current source.

"It 'isa still further object of this invention .to provide .a new and noveltgaseous dischargedevice that 'will separate the functions of sustaininga conductive plasma and drawing -a load current "with all of theelectrodes'ibeing energized with an "alternating current source.

.It is astillfurther object of this invention .to "provide a knew and :novel "rectifying device of the gaseous idischarge type wherein the plasma is 'm'ainta'inedbyalternating current.

It is :a still further object of this invention to provide a novel apparatus including a gas discharge device and circuit "therefor wherein "the elements of "the discharge device .are energized Withan alternating current source to produce a sustained plasma throughout the device.

Tn accordance "with the general aspects 'of this invention thereis provided a-neWan'd-novel gaseous discharge "device embodying 'a construction wherein'allpffthe electrodes are energized "by an alternating current source and wherein'the'function of ionizing the gaseou filling is separated from the load currentpath through the .device. 133? means of this separation of functions within the devi'ce'that is operated with an alternating current-"the arc drop along the load current path is greatly reduced while a sustained ionization is generated "by means of an alternating current. 'One specific embodiment "of this "invention "is 'a pair of "auxiliary cathodes that will discharge between each other during both the forward and inverse half cycles.

These and other features and advantages will best be understood from the following description of the illustrated embodiments when read in connection with the accompanying drawings wherein similar reference characters designate similar parts throughout the several views and in which:

Figure 1 is a sectional view of a gaseous discharge device, which may be used for the purpose of half wave rectification, made in accordance with this invention;

Figure 2 is a transverse sectional view of Figure 1 taken along line 2-2 of Figure 1;

Figure 3 is a cross sectional view of a gaseous discharge device made in accordance with this invention that is adapted for full wave rectification;

Figure 4 is an example of a circuit diagram for the one-half wave rectifying device shown in Figures 1 and 2;

Figure 5 is an example of a circuit diagram for the full-wave rectifying device shown in Figure 3;

Figure 6 is a sectional view of a modification of the gaseous discharge device shown in Figures 1 and 2 and is especially adapted for one-half wave rectification; and

Figure 7 is a circuit diagram which may be used with the device shown in Figure 6.

Referring now to Figures 1 and 2, there is shown a gaseous discharge device comprising a sealed envelope 8 containing an ionizable medium G. Any suitable media may be utilized. The pressure for any particular embodiment will be in accordance with its specific electrode geometry and spacings but is not at all critical and may be varied over wide ranges. A number of tubes of the type under consideration have been found to operate satisfactorily with a filling of helium of a pressure of approximately 750 microns. However, as is well known, other media and other pressures may be used, c. g. pressure which lie in any range between approximately 100 microns and several millimeters of mercury. The envelope 8 has the usual reentrant stem III to support the various elements.

Inside of the envelope 8 is an anode I2 which is shown as tubular in shape. This specific shape of the structure is not critical, although it does offer certain advantages for ion trapping, etc. Surrounded by the anode I2 is a main cathode I4 which may be of the conventional oxide coated type. Also within the anode I2 are two auxiliary cathodes I 6 and I8 which also may be of the conventional oxide coated type of thermionic cathode. These elements are supported, as is shown more clearly in Figure 2, by end micas 2!] and 2I, which are held in place by end rods 22.

In operation of this device a potential difference sufficiently high to cause ionization of the gaseous filling is applied between the auxiliary cathodes I6 and I8. I prefer to apply an alternating current otential between these electrodes so that a battery supply or a similar source will not be required. When this potential is applied, one of the cathodes will act as an anode during one-half of the cycle and then when the cycle reverses the other cathode will act as an anode during the balance of the cycle. By means of using these two cathodes, that are energized by an alternating current source, the gaseous filling of the tube is continuously ionized for all practical purposes, thus forming a continuous conductive plasma. Of course there is a period of time, when the cycle is changing, when no electrons are provided to produce the ionization i. e., when the potential difference between the auxiliary cathodes is less than the ionization potential. However, this slight time will not be suflicient to permit deionization so that the ionized gaseous atmosphere i. e., the plasma, will continuously be present.

The plasma, which occupies the space throughout the inside of the envelope 8, behaves like a low impedance conductor. Furthermore, due to the essential equality therein of charges of opposite signs no electron space charge effects are present. Due to the fact that the plasma is a low impedance conductor, there is effectively connected between the main cathode I4 and the anode I2 a low impedance conductor that conducts electrons when the anode I2 is positive with respect to the main cathode I4.

When the ionization producing discharge function is separated from the work discharge function the potential applied to the work circuit electrodes may be much smaller than the ionization potential of the gaseous filling and thus it has been found that very small voltages can be rectified in a very efiicient manner. The potential applied to a work circuit may exceed the ionization potential provided the dro in a load resistor is sufficiently great so that the potential across the main electrodes does not exceed the ionization potential. This condition can always be satisfied by making the auxiliary discharge current sufiiciently large provided that one has not exceeded the emission capabilities of the main cathode.

The specific arrangement of the various electrodes is not particularly critical although this arrangement does offer some definite advantages. With the anode I2 surrounding all of the oathodes, and closed on the ends by micas 20 and 2 I, a partial ion trap will be formed which will permit more efficient operation of the device. Once the plasma is formed it will not tend to diffuse out of the main discharge region to the various other structures in the tube. When desired the

end insulating members

20 and 2| may be constructed of a conductive material and connected to the anode I2 which will be a complete ion trap. When this is done, i. e. the members 20 and 2I are constructed of metal some insulators are provided for the cathodes to insulate them from the anode I2.

The particular location of the auxiliary cathodes I6 and I8 with respect to the main cathode I4 is also not particularly critical. The primary purpose of the auxiliary cathodes I6 and I8 is to provide the conductive plasma between the main cathode I4 and the anode I2. Any arrangement of the auxiliary cathodes that will produce a plasma that is continuous, for all practical purposes, will be acceptable and is contemplated by this invention.

In Figure 3 there is shown a device that is adapted for full wave rectification purposes. In this embodiment of the invention the envelope 8 contains a pair of

anodes

24 and 25. The pair of

anodes

24 and 25 enclose the main cathode I4 as well as the pair of auxiliary cathodes I6 and I8. The specific cathode structures may be the same as was described in connection with Figures 1 and 2. The primary purpose is to provide a sustained lasma between the main cathode I4 and the

main anodes

24 and 25.

The

main anodes

24 and 25 enclose the cathodes and are supported by insulating members and 2| and support rods 22 as in Figure 2. Here again the insulating

members

20 and 2| may be constructed of a conductive material and thus made a part of the anodes. The main anodes 24 and are spaced apart, as shown in Figure 3, or some type of insulating material may be inserted between the two anodes.

Figure 4 is a circuit diagram utilizing this invention for the purpose of half-wave rectification for the device shown in Figure 1. An al-- tcrnating current is applied to the auxiliary cathodes I 6 and I8 by means of the auxiliary input transformer 32. A current limiting resistor 3|] is connected in the circuit as shown. The alternating current applied to the auxiliary cathodes l6 and I8 is sufficient to cause ionization of the gaseous filling G to thus form the conductive plasma.

The potential that is to be rectified is applied to the main cathode [4 by means of the main input transformer 34. Connected between the anode l2 and one side of the secondary of main input transformer 34 is a conventional filter circuit consisting of capacitor 36, inductor 38 and capacitor 40. Connected to the output of the filter circuit is the load designed as L. Some acceptable values for the filter circuit are 20 mfd for the

capacitors

36 and 40, and 10 henries for the coil 38. These values are not intended to be controlling but merely representative of values that are acceptable for eificient operation at 60 cycles.

The potential to be rectified may be of any desired magnitude and the only limitation will be when a glow discharge takes place from the anode IE to the main cathode l4. The approximate voltage at which the glow discharge will take place in a device of this type is of the order of hundreds to thousands of volts depending upon many factors including the type of gaseous filling, the electrode geometry etc. The reason that thousands of volts may be rectified by the device is that a much greater portion of the applied voltage will appear across the load L. The potential magnitude limitation being when the voltage across the electrodes is sufficient to cause an inverse glow discharge. When the potential between the cathode l4 and the anode I2 exceeds the ionization potential the device will continue to function as a rectifier however, the two functions will combine and as in a conventional gas rectifier the efiiciency of the device will decrease. Under normal operating conditions the potential between the electrodes will not exceed the ionization potential due to the fact that the main portion of the potential applied to input transformer 34 will appear directly across the load L.

Figure 5 shows a circuit diagram that is adapted for full Wave rectification when utilizing the device shown in Figure 3. The circuit elements that are similar to those shown in Figure 4 will not be described in detail. The main input transformer 34 is a conventional transformer with the secondary having a center tap to allow connection to the filter circuit and the load. Since the operation of this circuit is similar to that of Figure 4, further discussion is not deemed necessary.

Figure 6 shows an embodiment of this invention which is used for the purpose of half-wave rectification. The envelope 8 contains a main anode I2 enclosing main cathode l4, auxiliary cathode l8 and auxiliary anode 28. In this embodiment, as in the other embodiments, the par-' ticular electrode arrangement is not critical. The operation of the main cathode I4 and main anode l2 is similar to that described in connection with Figures 1 and 2 and will not be described in great detail in relation to this figure. The plasma producing electrodes, i. e., the auxiliary electrodes, consist of auxiliary cathode l8 and auxiliary anode 28. The auxiliary electrodes function as a conventional gas diode when connected to an alternating current source.

In order to have a plasma within the device when the main circuit conducts some timing or phase shifting arrangements must be made between the two circuits. With respect to time, as long as the auxiliary electrodes discharge be fore the main electrodes the device will function as desired. In other words the auxiliary electrodes discharge and produce the conductive plasma a short time before the main electrodes conduct. The auxiliary electrodes may conduct for a longer period of time than the main electrodes. In the alternative, when the auxiliary electrodes and the main electrodes conduct for the same period of time, the auxiliary electrodes conduct an instant before the main electrodes and thus form the plasma, the desired operation will take place. When this is done the plasma will not have suflicient time to diffuse out of the main path before the end of the conductive portion of the cycle in the main path.

Figure 7 is a circuit diagram that utilizes the device shown in Figure 6 for the purpose of full wave rectification. In this figure the circuit elements are the same as described in connection with Figure 4 and so willnot be described further. When desired some type of timing, or phase shifting, device may be inserted in the main and/or auxiliary input circuits to insure that the various groups of electrodes will conduct at the proper time.

I claim:

1. Rectifier apparatus comprising a gas discharge device, said gas discharge device comprising an envelope containing an ionizable medium, a cathode and an anode in said envelope defining a main current path, means for forming and maintaining a plasma substantially throughout said path including at least one auxiliary thermionic cathode in said envelope and a source of alternating current potential, and said auxiliary cathode being directly connected electrically solely to said source.

2. Rectifier apparatus operable when connected solely to a source of low frequency alternating current potential comprising a gas discharge device, said gas discharge device comprising an envelope containing an ionizable medium, a cathode and an anode in said envelope defining a main current path, means for forming and maintaining a plasma along said path including at least one auxiliary thermionic cathode in said envelope and a source of alternating current potential, and said auxiliary cathode being directly connected electrically solely to said source.

3. Rectifier apparatus comprising a gas discharge device, said gas discharge device comprising an envelope having an ionizable medium therein, a thermionic cathode and an anode in said envelope defining a main current path, a source of low frequency alternating current potential, electrode means for forming and maintaining a plasma substantially throughout said path including at least one auxiliary thermionic cathode in said envelope, and said'auxiliary thermionic cathode being directly connected electrically solely to said source.

4. A gas discharge device, comprising a sealed envelope having an ionizable medium therein, a hollow anode and a thermionic cathode defining a main current path, means for forming and maintaining a plasma along said path including at least one auxiliary thermionic cathode, said anode surrounding said cathode and said means, all of said electrodes being adapted to be energized directly by an alternating electrical current.

5. A gas discharge device operable solely by an alternating electrical current, comprising a sealed envelope having an ionizable medium therein, anode means and a thermionic cathode defining a main current path, electrode means for forming and maintaining a plasma along said path including at least one auxiliary thermionic cathode, and said anode means substantially surrounding said cathode and said electrode means.

6. A gas discharge device comprising a sealed envelope having an ionizable medium therein, a hollow anode and a thermionic cathode defining a main current path, a pair of auxiliary thermionic cathodes for forming and maintaining a plasma along said path, said anode surrounding all of said cathodes.

7. A gas discharge device comprising a sealed envelope having an ionizable medium therein, a pair of elongated semi-circular shaped anodes and a thermionic cathode defining a pair of main current paths, a pair of auxiliary cathodes for forming and maintaining a plasma substantially throughout both of said paths, and said anodes substantially surrounding all of said cathodes.

8. A gas discharge device comprising a sealed envelope having an ionizable medium therein, a hollow anode and a thermionic cathode defining a main current path, an auxiliary thermionic cathode and an auxiliary anode for forming and maintaining a plasma along said path during the interval of time when said path is conducting, and said anode surrounding all of said electrodes.

9. A gas discharge device comprising a sealed envelope having an ionizable medium therein, a pair of elongated semi-circular shaped anodes and a thermionic cathode defining a pair of main current paths, a pair of auxiliary thermionic cathodes for forming and maintaining a plasma substantially throughout said paths, said anode substantially surrounding all of said cathodes, insulating means between said pair of anodes, said main cathode being coaxial with said anodes, said cathodes being aligned with the middle cathode being said main cathode, and said auxiliary cathodes arranged on a line perpendicular to a line through said insulating means and said main cathode.

10. A gas discharge device comprising a sealed envelope having an ionizable medium therein, a tubular anode and a main thermionic cathode defining a main current path, a pair of auxiliary thermionic cathodes for forming and maintaining a plasma substantially throughout said path, said anode surrounding all of said cathodes, and insulating members abutting the ends of said anode and said cathodes.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,863,702 Smith June 21, 1932 2,158,564 Meier May 16, 1939 2,409,717 Slack et al Oct. 22 1946 2,450,475 Hansell Oct. 5, 1948 2,578,571 Meier Dec. 11, 1951