US2498986A - Circuit arrangement for electric discharge devices - Google Patents

Description

Feb. 28, 1950 R. H. DUN-N ET AL A 2,498,986

CIRCUIT ARRANGEMENT FOR ELECTRIC DISCHARGE DEVICES Filed April 29, 1949 2 Sheets-Sheet 1 In ventors (GLAND HARRIS DUN/Y y PETER W- LEN/V0)! Attorney Feb. 28, 1950 R.H. DUNN ET AL 2,498, 9 8'6 CIRCUIT ARRANGEMENT FOR ELECTRIC DISCHARGE DEVICES Inventors KOLAND flARk/S ou/v/v B E ER W. LEN/{0X Wan/(4 Attorney Patented Feb. 28, 1950 v messes I cmomrmnndncnmnnrronaccommonrscnmon DEVICES:

Roland Harris Dunn and Peter William Lennox, London, England; .assignors: to International standardzElcc,

trio Corporation, NewYork; N. 12,.

a'corporationjofnelaware. i I Anmiccti nasin- 29, 1949, Sci-n1. No. 90,325

charg tu es. andv is a continuation. in i ar-t oi the application of M; S. Mcwh rbori R- Dunnond. P. W; lennox, Serial No;- 74A,009',. filed April 2.5, 1947'. I

In. order to render such a tube conducting the gap. between the control electrode and cathode. Taking a particular well :kno struct-ion as an example; so lonsgas; they tential is 130 volts or more, the-minim; .tion current produced we voltage .volts between control electrode and su-flicient to cause current. to flow between anode and cathode.

It is well known to connect-suchtubes in a chain. The catho do of each tube is: connected to ground; over a resistance havinga condenser" in parallel therewith. and a point on thisgiresistance is onnec ed to the; control electrode otgthe next tube, thev values being. so chosen that uvhen one tube is conducting: a potential (if-about. 35. volts.

.is. impressed betweenithe control electrode and cathode of the suoceediostube.

This is: insuflicientto ionisethe gap) between the two electrodes.- Implflses are-applied between the.- contnol electrodes and gr und of al.- the: tubes of 5110.11 polarity as to impresszan additional. po-

-on the control. electrodes; oil all. tubes simultancously. This; potential, added: to: the potential impressed. on a control. electrode; from: the pre- "ceding. tube that is conducting is sufli'cient to ionise the. gap between the; control: electroderand cathode.

The problem sometimes. crises of impressing a desired potential; such. as the primin potential of volts mentioned above, on the control electrode of a principal tube omywhen'ftwo or'i'nore ther tubes, referred to as additional. tubes, are 1 conducting at the same ti The present invention provldes circuit or.- rangement in which gas-filled cold" cathode tubes are employed, each tube having at-fleast a com "ti-o1. electrode and a cathode and in. which said tubes are so connected that a desired biassing potential will only be applied. to thekcontro'l electrode of; a." principai. tube. when a. pfiedetermined number of similar additional tubes have been brought into conducting: condition; said additional tubes being rendered. conducting in any desired order, comprising. a principal tube,

a plurality of similar additional tubes,. the cathode of each of said additional tube being individually connected. to ground throll h ..a c u n ai ow resistancesconnection between a point on each 01'. said low sis-tattoo. circults and the control electrode of said principaltube over. respective rectiflers, the valuesofsaid low resistance,. the characteristics of said. rec 'fie s. nd the direction. in which they areicon; tedin the circuit, and the potentials: applied to the several electrodes-of all saidtubes being.

so selected that only a relatively small potential is applied to the control electrode ofsaid principal tube until all said additional tubes have been rendered conducting, whereupon said dosired'jbiassing potential is impressed on said controligri'd. 1 v

The invention will be better understood from the; following description taken in conjunction with the accompanying drawings in which- Fig; 1 represents an embodiment of the invention employing only'three tubes I Fig. 2' is a. diagram showing as an equivalent circuit the essential features of Fig. 1.;

Fig; 3" is a diagram showing a more general'- ised' form of-the circuit of Fig; 2; and

Fig; 4 representsan embodiment of" the invention employing. si-x'tub'es;

Referring to theFi'g, 1, there are shown three tubes. I 2 and 3- of the same kind. Each tube isa three electrode gas filled tubefhaving a cold cathode, a. control electrode and an anode; The control electrode is represented as an arrowhead and the Cathode. as a small circle,' the cathode beingtthe right hand electrodefif "ther'palr in the case of all three tubes. The anode 0! each tube is: assumed to be connected to a positive source of 130" volts. When any tube, e. g. .I becomes conducting the voltage drop across the junction pointhetweenrectiflcr 4 and resistance 1 is: connected over .a resistance 9 to. the control electrode. or. tube 2,. The reverse resistance of rectifier .6 isabout .20. megohms and the resistancesl IV and .8. together: are about /2 megohm.

The. potential. drop impressed. between-control so clectr.ode and cathode ofitube. 2 is. therefore only v; become conducting even when an impulse i s .,ap

a vfew volts and. is insufilcient. to. cause. tube .2. to

plied to conductor. Hi, connected to the. control electrodeofth-is tube 2.

Suppose now that instead oftube I, tube .3 becomes. conducting, The current in this tube pa ses through resistances. 1i] and .8; to ground and. also through resis nee 1. reotificrpdandne- .sistancel to ground; -i in the-i rwarddi ctionthrough the. rectifier c The resistance orrectifier in the forward in Fig. 1.

rection is about 30,000 ohms, so that resistance 1 is large with respect thereto and the potential at the junction point between resistance 1 and rectifier 6 due to the current rise in the tube.

3 only is only a few volts. The fact that tube 3 is conducting is insuflicient to causetube' 2 to become conducting when an impulse occurs on conductor l0. v

Now consider the case in which .both. tube i and tube 3 are conducting. Neglecting for a points. The relatively low resistance to ground of points [2 and i3 is represented by resistances I1 and I8 corresponding to the ground connections through resistances 4 and 5 in the case of tube l and 8 and II in the case of tube 3 as shown in the Fig.1;

The-equivalent circuit of Fig. 2 corresponds with that shown in Fig. l but is in fact a special moment the connection through rectifier 6 and resistance 1, the junction point between resist-J ances 4 and 5 is at the same potential, volts,

as the junction point between resistances II and 8. The connection between these two points over rectifier-6- and resistance. 1 does not therefore disturb the potential gradient and thejunction point between rectifier 6 and resistance T is also at 35 volts positive potential and this is impressed upon the control electrode of tube 2.

-The effect therefore of both tubes I and 3 being conducting is to cause the control gap of tube 2 tobe ionised on the arrival of the next impulse on conductor l 0.

i It can readily be seen that by'suitable selection of the values of the fixed resistances and the values of the reverse and forward resistances of the rectifiers it is possible to arrange that the conditions in which the control gap. of a final tube becomes ionised on the receipt of an impulse ing' tubes have been rendered conducting. The only relevant efiect of any tube becoming conducting is that-current passes across the anodecathode path. If the cathode is connected to earth (or the negative terminal of the source of positive potential applied to the anode) through a predetermined number of preceding tubes having become conducting, it is only necessary to consider the potentials at the tapping points re- ,ferred to above associated with a numberv of similarly connected tubes such astubes i and. 3

In Fig. 2 there is shown diagra'rnmatically an arrangement which represents the relevant conditions in Fig. 1. v point [2 can. be .consid. ered to be the junction'between resistances 4 and j5.of Fig. 1 and point l3 corresponds similarly to the junction between resistances 8 and II. Re-

,sistance l6 represents resistance 1 of Fig. 1, land-point l'4 represents the control electrode of Resistance 9 of Fig. 1 is omitted from the equivalent circuit shown in Fig. 2 as it plays no part in the circuit for applying potential detube 2.

rived from pointslZ and I3 to point l4 and is only required to limit the current passing over the controlgap of tube 2 after ionisation has .been set up.

The purpose of this circuit is therefore to impress a potential bias on point 14 (where point I4 is of. high resistance to ground), when potenis only obtained when three, four or more precedtial is applied to both points l2 and I3 which" points havea relativelylow resistance to ground, ;but' not tofimpress any appreciable potential bias on point l4 when'thereis no-potential applied to forward resistance.

case of a more general circuit which is shown in Fig. 3 and-thejpperation of the circuit of Fig. 2 will be betterunderstood, after the operation of the circuit of Fig. 3 has been explained.

' The only difference between Fig. 3 and Fig. 2 is that in Fig. 3 resistance l6 has been replaced by a rectifier I9 having -the same characteristics as rectifier I5.

Considering 'FigIB, it is evident that if there is no potential applied'to either point l2 or l3 no potential can b'e developed at point I4. When however a positive potential is applied to point I2 with point l3 remaining at ground potential rectifier I5 is biassed by the potential at point 1-2 to its backward or high resistance direction,

thus causing the circuit to act as a high ratio potential divider from points l2 and i3 to' point I 4. A small residue potential will appear at point I4 but as this biasses rectifier H! to its forward or'low resistance direction the-potential at point I4 is of negligible value. Q

It is evident of course that exactly the same effect will be obtained if positive potential is applied to point l3while point 12 is held at ground potential.

' When however an equal potential is applied to points l2 and I3 it is evident that this same potential will appear at point M, which is of high resistance to ground. It can immediately be seen that further points corresponding to 12 and 13 can be connected through rectifiers similar to rectifiers l5 and 19 to the common point 20 and that provided any one of the points I2, l3 or corresponding points is held at ground potential no appreciable potential will be developed at point 14 when the remaining points l2. 13, etc., are raised to a positive potential. There is of course a limitto the number of connections which can .Jbe made to point 20 determined by the ratio of the backward resistance of the rectifiers to the If n be the maximum'number of rectifiers which can be introduced and R (backward) and R (forward) the resistances of onerectifier then n can be determined from the conditions that must be-greater than R (forward).

Taking the values of '20 megohms for R (backward) and 30,000 ohms for R-v (forward) as quoted by ways .of example earlier in this description this indicates that it would theoretically be possible toconnect over 600 rectifiers to point 20 before the ,.potential developed at point [4 was 'equal to that applied at all the points [2, 13,

etc., except I.

However in order ,to keep the potential at point 14 of. negligible value this number of 600 would have to be very considerably reduced and in practice the maximum number' of rectifiers which it can be seen'that this' isonly a simplified form ofthat; shown in'Fig', 3; Resistance I6 is shown si ter ra t 2 e s. Bil- 3. t "a repl es e e n the desirable value amaose megohms and for R (forward) of 30,000 gohmsj.

as in the example above this gives a value for R I n of about 8,000,000 ohms. It can be seen there-f fore that as this value for resistance |6is hi compared with the forward resistance but low; compared with the backward resistance of rectifier l5 the circuit of Fig. 2 will behave very similarly to that of Fig. 3 described above. Fig. 4 shows an embodiment of the invention in which six cold-cathode tubes are connected up; so that a principal tube can only be rendered conducting when all the other five tubes are already conducting.

The five tubes 2| to 25 inclusive are shown with positive potential applied to the anodes. The control electrodes represented by arrow heads, are shown on the left in all cases, and the tubes can be made conducting by suitable potentials applied to these control electrodes from any source, e. g. potentials desired from the cathode circuits of other similar tubes, impulses from a generator, or potentials from a source such as a battery. The principal tube which is to have potential applied to its control electrode only when the five tubes 2| to 25 are all conducting is tube 26. The cathode of tubes 2| to 25 are connected to ground through resistances 21 to 3| respectively. Rectifiers 32 to 35 are connected between suitable tapping points on resistance. to 3| and a common conductor 31. The rectifiers are arranged so that they present their high resistance to positive potentials developed on the cathodes of the tubes with which they are individually associated. The common conductor 31 is connected to the control electrodes of tube 26. When any of the tubes 2| to 25 are conducting the small current which passes through the associated rectifiers does not result in any appreciable potential being developed on the control electrode of tube 26 so long as at least one of the tubes 2| to 25 is not conducting. Assuming for example that tubes 2|, 22,23 and 25 are conducting but tube 24 is not conducting. Then rectifiers 32, 33, 34 and 3|; will be biassed to their high resistance value and the small currents which pass through these rectifiers will bias rectifier 35 to its low resistance value and pass via part of resistance 30 to ground, so that conductor 31 and the control electrode of tube 26 will be held at a potential not much above ground potential. When however tube 24 becomes conducting in addition to tubes 2|, 22, 23 arid 25 rectifier 35 becomes biassed to its high resistance value and the potential developed at the five tapping points on resistances 21 to 3| appears on the control electrode of tube 26. This potential can be arranged to be suificiently high .to ionise the tube but it is more usually arranged.

to be rather lower than the ionising potential so that the tube will become conducting on the application of an impulse applied to conductor 38. The actual potential developed in conductors 31 when all five tubes 2| to 25 are conducting is determined for any given case by the selection of the tapping points on resistances 21 to 3|.

The arrangements described therefore permit of a principal tube becoming conducting only when a plurality of prerequisite conditions have been fulfilled and have resulted in a plurality of preceding tubes having been made conducting.

While the principles of the invention have been described above in connections with specific embodiments and particular modifications thereof, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the invention.

What is claimed is:

1. Electric circuit arrangement using gas filled cold cathode electric discharge tubes, each tube having at least a. control electrode and a cathode, comprising a principal tube, a pair of similar additional tubes, circuits connecting the oathodes of said additional tubes to ground over individual resistances, an electrical connection from a point on one of said resistances to the control electrode of said principal tube said connection including a rectifier so poled as to offer high resistance to. the flow of current to said control electrode, and a connection from a point on said other resistance over a resistance low compared with the backward resistance of said rectifier to a point between the said rectifier and control electrode, the said resistances being so proportioned that a discharge in one only of said additional tubes will not cause the application of a priming potential between control electrode and cathode of said principal tube for initiating a discharge in said principal tube whilst a discharge in both said additional tubes will cause the application of said priming potential between the control electrode and cathode of said principal tube.

2. Electric circuit arrangement using gas-filled cold cathode electric discharge tubes, each tube having at least a control electrode and a cathode, comprising a principal tube, a plurality of simi-- lar additional tubes, circuits connecting the oathodes or said additional tubes to ground over individual low resistances, electrical connections from similar points on said resistances to a common point over individual rectifiers, each so poled as to oifer high resistance to the flow of current to said common point and an electrical connection between said common point and the control electrode of said principal tube.

3. Electric circuit arrangement comprising a principal tube and a plurality of additional tubes, each of said tubes being gas-filled and having an anode, a control electrode and a cold cathode means for applying potential between control electrode and cathode of said principal tube of insuflicient magnitude to initiate a discharge in said principal tube when no further biassing potential is applied to said control electrode, individual connections from the cathodes of each of said additional tubes to ground over low resistance paths, a source of potential insuficient by itself to cause ionisation of the gas in any of said tubes connected to apply positive potential with respect to ground to the anode of each of said tubes, electric connections between points on each of said low resistance paths over individual rectifiers in the backward direction to the control electrode of said principal tube such that if all said additional tubes are conducting a biassing potential is impressed upon the control electrode of said principal tube suificient together with said first mentioned potential to cause said principal tube to become conducting whereas if any of said additional tubes is non-conducting the potential impressed on the control electrode of said principal tube is too low to be a biassing potential.

ROLAND HARRIS DUNN. PETER WILLIAM LENNOX.

No references cited.

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