US2423815A

US2423815A - Thermionic gas-filled rectifier circuit

Info

Publication number: US2423815A
Application number: US466651A
Authority: US
Inventors: Ramsay Henry Thomas
Original assignee: MO Valve Co Ltd
Current assignee: MO Valve Co Ltd
Priority date: 1941-11-05
Filing date: 1942-11-23
Publication date: 1947-07-08
Anticipated expiration: 1964-07-08
Also published as: GB602234A

Description

Patented July 8, 1947 THERMIONI C GAS-FILLED RECTIFIER CIRCUIT Henry Thomas Ramsay, Hatch End, England, assignor to The M-O Valve Company Limited,

London, England Application November 23, 1942, Serial No. 466,651 In Great Britain November 5, 1941 This invention relates to circuit arrangements comprising a thermionic gas-filled rectifier of grid control type wherein the thermionic cathode is separated from the anode by a labyrinth, and a control electrode separate from the cathode and the anode, wherein the main discharge between cathode and anode from lines L, L is started by making the control electrode so much positive to the cathode that a subsidiary discharge passes between those electrodes, and produces ions in such a position and in such an amount that they enable the main discharge to start between the cathode and anode.

It is important to distinguish circuit arrangements of this type from those wherein the rectifier is of the kind in which the function of the grid is substantially the same as that of the control grid in a vacuum triode, namely to co-operate with the anode in establishing at the surface of the thermionic cathode a field sufficiently great to permit a large proportion of the electrons emitted from the cathode to leave the neighbourhood of the cathode. Accordingly the foregoing description of my improved type will be explained further.

The term labyrinth is defined as a baffle or shield arrangement such that the starting of an ion-forming discharge from the cathode is substantially independent of the potential difference between anode and cathode. A necessary condition for such independence is that no straight line can be drawn from anode to cathode that does not intersect a conductor that is negative to the anode during the starting period. A straight line passing through an aperture in a grid is not to be held to intersect the grid. But this condition is not sufiicient. A sufiicient condition alone is that, if the anode and cathode potential is held constant and the control electrode is made progressively more positive to the cathode, the potential of the control electrode at which an ion-forming discharge first occurs (evidenced by a very sharp rise in the current between control electrode and cathode) is substantially independent of the anode-cathode potential. This proves that the anode and control grid do not co-operate in the starting of the first ion-forming discharge. The anode potential is efiective only in converting this first discharge into a discharge between anode and cathode in virtue of the introduction of ions into the labyrinth.

It may be noted also that the two types difier greatly in the power that has to be supplied in operation to the control electrode. In the type 7 Claims. (Cl. 315261) in which the control grid operates as the control grid of a vacuum triode, the power has to be sufficient only to raise the potential of the control grid; it is determined by the capacities I of the electrodes and is generally of the order of a milliwatt. In the type to which the invention relates the power supplied has to be sufficient to provide an ion-forming discharge and generally is of the order of a watt. In circuit arrangements of the type specified there must be eificient deionisation of the labyrinth in the interval between two main discharges. An ob ject of this invention is to provide in circuit arrangements of this type means for promoting such deionisation.

The electrode that is bombarded by positive ions during the deionisation period will sputter to some extent. Any sputtered matter that reaches the thermionic cathode will tend to impair its eificiency. The life of the cathode may be maintained at a reasonable value by limiting the negative potential imposed on the bombarded electrode or the positive ions flowing to it, and thus limiting the sputtering. But then the deionising effect of that electrode is also limited. A further object of the invention is to provide means for preventing much of the sputtered material from reaching the cathode.

Another object of this invention is to provide improved gas-filled thermionic rectifiers capable of use in the improved circuit arrangements.

Further objects and advantages of the invention will be apparent from the following description of three embodiments thereof, given by way of example with reference to the accompanying drawings, in which:

Figures 1 and 2 show respectively the relevant 5 parts of two difierent rectifiers in axial section, together with certain circuit elements represented diagrammatically, and

Figure 3 shows a modified circuit arrangement capable of use with the rectifier shown in Figure 2.

In the rectifier shown in Figure 1, the same structure serves both as the control electrode and as the auxiliary electrode that operates to withdraw positive ions from the labyrinth, I is the thermionic cathode, 2 the anode, 3 is a tubular or cup-shaped metal shield surrounding the cathode and connected to the cathode. The auxiliary or control electrode is made up of a tubular electrostatic shield member 4 round the anode, a metal tube 6, and a control member or plate 5 spaced from and covering the end of the tube 6 within the tubular shield 4; the

parts

4, 5, 6 are electrically connected, and are maintained normally negative to the cathode by a bias source of E. M. F. 1 acting through a choke 8 and a lead l3. The plate acts as a bafiie and is the main operative element of the labyrinth forcing the electrons to, follow a circuitous path in traveling from cathode to anode. These parts shield the cathode completely from the potential of the anode. The current to be rectified is, of course, applied to the lead lines L, L.

To start the discharge, a pulse of positive potential, generated from a source 9 of any of the mechanical or electronic types well. known in the art, is applied to the auxiliary electrode through a resistor I 9; the choke 8 prevents the shortcircuiting of the pulse through the battery. An ion-forming discharge is thus started between the cathode and the auxiliary electrode, the current being limited by the resistor in. The ions produced by this discharge are within the potential field of the anode 2 and enable the main discharge to flow from the anode around the edge of the control plate 5 and through the electrostatic shield by way of the tube 6. When the discharge has been extinguished by reduction of the alteri nating potential being rectified, the timing is such that the pulse is removed and the auxiliary electrode is therefore negative and collects the residual positive ions. There is nothing to prevent matter sputtered from the

parts

5 and 6 in Fig. 1 from reaching the cathode; consequently it will be understood that the negative potential at which they may be maintained is limited.

In Figure 2, the numerals I, 2, 3, 4, 5, I, 8, 9 represent parts corresponding to those. similarly denoted in Figure 1; but there is no tube 6 projecting into the tubular member 3. On the under side of the plate 5 is a plate II insulated from it. This plate II, which serves as a baffle, i connected to. the. tubular shield 4 by a resistor [2 to a point on which, intermediate between its ends, the pulse generator Sis connected.

The discharge is started as before by a. pulse from 9 making 4, 5 and. II all positive. The ions produced in the vicinity of the electrode II are within the potential field of anode 2 and therefore the main discharge between anode 2 and cathode l starts. When the main discharge is extinguished by reduction ofthe potential being, rectified, the full deionising current can flow. to the negative tubular shield 4 and the plate 5; but material sputtered from them is prevented from reaching the cathode by the baffle plate II. On the other hand the baffle plate II has the. resistance l2 in series with it, and the deionising current to it is limited so that there is no objectionable amount of sputteringfrom ions landing on it. Of course the deionisation is lessrapid inside the tubular heat shield 3 than inside the tubular shield 4; but so long as deionisation is sufiicient, somewhere in the path through the labyrinth between anode and cathode the desired result is achieved.

Figure 3 shows a modification of the circuit of Figure 2. In this modification the partsd, 5 are always negative; the positive pulse is applied by the pulse generator 9to the plate I I, which acts as the control electrode, through the resistor [2A. In thisarrangement more power has to. be supp ied. by he nerato 9 n der to s ar the discharge.

I c aim:

1. In rectifier circuits, a gas tube having. an. anode, a cathode, an auxiliary electrode and a.

tubular metal cylinder surrounding said auxiliary electrode, said auxiliary electrode and cylinder being positioned between the cathode and anode and adapted to screen the cathode completely from the anode potential, means for applying a sufficiently low voltage between the saidauxiliary electrode and said cathode to prevent flow of electrons from the cathode to the auxiliary electrode and means for applying an intermittent positive voltage across said auxiliary electrode and cathode sufiicient to produce a flow of electrons from the cathode thereto.

2. In rectifier circuits, a gas tube having an anode, a cathode, an imperforate control electrode and a tubular metal cylinder surrounding and spaced from said control electrode, said control electrode and cylinder being positioned between the cathode and anode and adapted to screen the cathode completely from the anode potential, means for applying a negative bias voltage between the said control electrode and said cathode to prevent flow of electrons from the,

cathode to the control electrode and means for applying an intermittent positive voltage across said control electrode and cathode sufficient to produce a flow of electrons from the cathode thereto;

3. In rectifier circuits, a gas tube having an anode, a cathode, an imperforate control electrode and a tubular metal cylinder surrounding and spaced from said control electrode having a fiange projecting inwardly under said control electrode, said control electrode and cylinder being positioned between the cathode and anode and adapted to screen the cathode completely from the anode potential, means for applying a negative bias voltage between the said control electrode and said cathode to prevent flow of electrons from the cathode to the control electrode and means for applying an intermittent positive Voltage across said control electrode and cathode suificient to produce a flow of electrons from the cathode thereto.

4. In rectifier circuits, a gas tube hav ng. an

' anode, a cathode, an imperforate control electrode and a tubular metal cylinder positioned between said cathode and anode and adapted to.

shield thepotentialof the anode completely from said cathode and incompletely from the space.

adjacent the control electrode, whereby the anode potential exerts no force on the, electrons adjacent the cathode and a substantial forceon the electrons adjacent said control; electrode, means for biasing said control electrode negative to said cathode and means for applying an intermittent positive voltage acrosssaid control elec-.

trode and cathode sufiicient to produce a momentary flow of electrons to said control electrode ,for ionizing the space adjacent thereto by. collision with gas atoms to start a discharge between the anode and cathode.

5.. In rectifier circuits, a gas tube having. an anode, a cathode, an imperforate control, electrode, a tubular metal cylinder around and spaced from the control electrode, a second metal cylinder of lesser diameter than the control electrode and spaced therefrom, said control electrode and cylinders shielding the potential of the anode completely from said cathode and incom- "pletely from the space around the control electrode, whereby the anode potential exerts .substantially no forceon the electrons adjacent the cathode and a substantial force on the electrons adjacent said control electrode, means for biasing said control electrode negative to said cathode and means for applying a positive voltage pulse across said control electrode and cathode sulficient to produce a momentary flow of electrons to said control electrode for ionizing the space adjacent thereto and thereby starting the discharge between the anode and cathode.

6. In rectifier circuits, a gas tube having an anode, a. cathode, two imperforate and insulated electrodes between the cathode and anode barring direct electron travel between the cathode and anode, a metal cylinder around and spaced from said imperforate electrodes, said cylinder having a flange projecting between the cathode and the imperforate electrodes, an impedance connected between said imperforate electrodes, means for applying a negative bias voltage between one terminal of said impedance and said cathode, and a positive pulse-forming device connected between the cathode and an intermediate point in said impedance.

7. In rectifier circuits, a gas tube having an anode, a cathode, two imperforat-e and insulated electrodes between the cathode and anode barring direct electron travel between the cathode 6 and anode, a metal cylinder around and spaced from said imperforate electrodes, said cylinder having a flange projecting between the cathode and the imperforate electrodes, a resistance connected between said imperforate electrodes, means for applying a negative bias voltage between one terminal of said resistance and said cathode, and a positive pulse-forming device connected between the cathode and an intermediate point in said resistance.

HENRY THOMAS RAMSAY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,227,829 I-Iansell Jan. 7, 1941 2,145,088 Kobel Jan. 24, 1939 2,113,392 Baruch Apr. 5, 1938 2,100,196 Lowry Nov. 23, 1937 1,702,785 Leblanc Feb. 19, 1929