US2135006A - Rectifying device - Google Patents

Description

Nov. l, 1938.

T. JURRIAANSE RECTIFYING DEVICE n g--fgf Filed April 19, 1957 [ALT Patented Nov. 1, 1938 PATENT ogFfFlcE nEo'riFYING DEVICE Tom JurriaansaEindhoven, Netherlands, assignor -to N. V. Philips ,Gloeilampenfabriekem Eindhoven, Netherlands Application April 19, 1937, SerialNo'. 137,851 VIn Germany April 21, 1936 My inventionrelates to-A. C. rectifyingdevicea and more particularly to devices Vcomprising an incandescible-cathodeionic rectifying tube.

My invention 'is particularly advantageous rin connection with the rectication of A. C current of medium voltages-having an inverse peakyalue of about 150-1000 volts-and'foi` currents of -from several amperesto 100 amperes Yormore; howe ever it is Vnot limited theretmbut may beu'sed'in connection with other-voltages and currents.v

It is, of course, essentialto prevent back discharges in gaseous rectifying -tubes,"i. e; tubes having a filling of one or more gases, vapors, or a mixture thereof, and much'worli` has been done in this direction, especially in connection withmercury-eatl1ode tubes. Although the use of a gaseous lling at low pressure, for instance 0.01 mm. of Hg or less, will prevent such discharges, this results in a very high voltage drop in the discharge path, which reduces the life of the tube. More particularly, in incandescible-cathode tubes, the life of the cathode is materially reduced by ionic bombardment due to the `high voltage drop in the discharge path, and the cathode had to be made oversize to ensure reasonably long life. On the other hand, if the lling is given a high pressure, for instance 1 mm. of Hg Vor more, to-

the gaseous filling has generally been given a` compromise value which fully met the essential condition 'of preventing back -discharges at the expense of a reduced life of the tube.

The object of my invention is to eliminate the above difliculties and to remove the undesirable eiiect of a low-pressure filling upon the -liie of the tube, while retaining its protective effect against back discharges.

In accordance with the invention, I use -an incandescible-cathode rectifying tube having `a. gaseous filling at a pressure of less than 0101 mm. of Hg even at the emitting surface of the cathode, and provide within the tube a magnetic eld whose lines of force connect the anode and cathode. Y

With such a construction the protection against back discharges 4is not appreciably reduced,` whereas the possibility-ot ionizationl for the discharge is greatly increased in the direction of current flow; due probablyto the extension of the ,electron paths through the magnetic field wherebyithe'possibility of.;e1ectrons colliding with neutral; gasI .moleculesorV gas`4 `atoms is` .greatly (Cl. Z-27.5)

increased. This appears from the fact that there is a decrease in the cathode drop whereby the disintegration of the cathode is reduced and thus the life of the tube'is materially increased. As the cathode kdrop generally constitutes the mainportion of the total voltage drop of the discharge, thus phenomenon is of especial importance.

It is preferable that the discharge path follow as closely as possible the lines of forcev of the magnetic field, as I have found that a considerably larger voltage drop will occur in .the discharge at any point at which the path is caused to deviate from the magnetic lines of force. Furthermore, I prefer to so arrange the electrodes in the magnetic field that substantially the entire discharge path extends within that part of the discharge space which is traversed by the magnetic lines of force. In this manner the efliciency of the arrangement is increased to' the maximum, whereas ami-nimum amount` of magnetic energy is required.

In one embodiment of my invention, as applied to a full-wave rectifying tube, I so arrange the magnetic eldthat the' lines of force traverse the tube envelope at two definite points at which the anodesare disposed, whereas I locate the cathode in the center of the magnetic beam extending between these points, so that the discharge path extends in the direction of the magnetic lines of force. In such arrangement the means for producing the magnetic eld can be Very advantageously provided outsideof the tube, and the magnetic eld can be readily concentrated at the desiredV points of the envelope.

In order that my invention maybe clearly understood and readily carried into effect, I shall describe same more ful-ly with reference to the accompanying drawing, in which:

Figures 1 and 2 are partly sectionized views of full-wave rectifying devices according vto the invention. t

The device illustrated in Fig. 1 comprises a full-Wave rectifying tube 3, a permanent magnet 5, and a rectifying circuit arrangement indicated by 4 and having single-phase A. C. supply terminals and D. C. output terminals.

The tube 3 comprises a closed envelope 8 of vitreous material, an incandescible cathode I, energized in asuitable manner -not shown, and two anodes 2 in the form of metal discs, Afor instance of iron, adjacent the envelope.- Cathode I- and anodes2 are connected to arrangement 4 by means of conductors!! to I2, and as such rectifying. circuits are Well' known' in the art,

further description of same is believed unneces- Sary.

Tube 3 is provided with a suitable gaseous lling, for instance mercury vapor, having during operation a pressure of less than 0.01 mm. of Hg. As shown, a quantity of mercury I3 is provided in a protuberance, formed preferably in a cool portion of the envelope. In some instances it is preferable to artificially cool the portion of the envelope in which the mercury is disposed, for instance by a circulating cooling liquidjin order to maintain the mercury at a temperature which agrees with the corresponding saturation pressure of the mercury vapor within the tube. As such cooling means are well known in the art and do not form part of the present invention, further description or illustration of same is believed tobe unnecessary."

Disposed outside tube 3 with its pole faces in contact with the outer surface of envelope 8 and in line with anodes 2, is a permanent magnet 5. Magnet 5 produces a constant magnetic field whose lines' of force'extend within the tube be-` tween anodes 2, as indicated by the arrowed lines 6. It will be noted that cathode I is disposed centrally within this magnetic field, and that the discharge path between cathode I and anodes 2 closely follows the lines of force of this field. i

It will be noted that cathode I extends perpcndicularly to the lines of force, and thus is intercepted by a maximum number of lines of force, which insures a .minimum voltage drop of the discharge. Furthermore, the lines of force extending between the anodes 2 are located in a space which is materially free from any obstruction which might impede the passage of the discharge along the lines of force extending from the cathode to each anode.

To prevent the possibility of back discharges being caused by particles disintegrating from cathode I and dropping on the anode 2, a screen I of non-magnetic material such as molybdenumV intercepts straight lines drawn from any point on the cathode to the anodes. Two such lines are indicated by I5. v Y,

'It will be noted that the screen 'I is curved to follow the direction of therlines of force, and` thus intercepts only a Yminimum number of thel lines.

Although in Figure 1 a constant magnetic field as produced by a permanent magnet has been shown, an electromagnet may also be used. This is shown in Figure 2 in which the same reference numbers have been used to designate the parts corresponding to those of Figure 1.

In contradistinction to Figure 1 the anodes 22 are not supported by separate anode supports but they are directly welded to circular ferrochromium discs I6 forming part of the envelope 23 of the tube. The two legs I'I ofthe electromagnet are welded to the discs I6 and serve at the same time as lead-in conductors to theanodes 22. The magnetic circuit is completed by pole pieces I8 having a gap I9 between them which prevents the setting up in the glass envelope of thermal stresses which might damage` the tube and insulates the two anode leads from each other. v

The electromagnet windings are connected to a current supply 20 shown `schematically and providing the electromagnet with direct or alternating vcurrent according as to whether a constant or a pulsating magnetic eld is desired.

In fact it is immaterial invvhatr direction the magnetic eld may pulsate, provided it disappears only at the moments at which it can be dispensed with for suitable operation 'of the tube.

Y Under some conditions it is of advantage to use a magnetic field which pulsates with the anode'current in such a manner that the magnetic field disappears during the blocking phase of the Yanode and thereby insures maximum protection against back discharges.

The tubes shown in the figures of the drawing may be used to rectify alternating currents up to rof the order of 1-50 ampere at negative peak voltages of approximately 150 volts or higher.

While I have described my invention in connectionuwith specific examples and applications, I do not wish to be limited thereto but desire the appended claims to be construed as broadly as permissible in view of the prior art.

What I claim isz- 1. A full-wave rectifying device comprising an ionic discharge tube having an envelope, an incandescible cathode, two anodes disposed adjacent the wall of the envelope, and a gaseous llf ing having during operation a pressure less than 0.01 mm. of mercury, and means outside the envelope to produce a magnetic field having lines of force traversing the envelope at points adjacent the anodes and extending between the anodes in a beam, said cathode'being centrally disposed within said beam and spaced from said anodes to form a discharge path following the lines of force thereof.

2. A'full-wave rectifying device comprising an ionic discharge tube having an envelope, an incandescible cathode having amain emission surface, two anodes disposedV adjacent the wall of the envelope, and a gaseous filling having during operation a pressure less than 0.01 mm. o f mercury, and means outside the envelope for producing a magnetic field having lines of force traversing the envelope at points adjacent theV anodes and extending between the anodes in a beam, said cathode being centrally disposed within said beam with the main emission surface extending transversely to lines'of force thereof and being spaced from saidranodes to form a Vdischarge path following the lines of force.

3. A full-wave rectifying device comprising an ionic discharge tube having an envelope, an incandescible cathode, two anodes disposed adjacent the wall of the envelope, and a gaseous filling having during operation a pressure less than 0.01 mm. of mercury, and means outside the envelope to produce a magnetic eld having lines of force traversing the envelope at points adjacent the anodes andextending between the anodes in a beam, said cathode being centrally disposed within said beam and spaced from said anodes to form a discharge path following the lines of force thereof and lying substantially entirely'within the portion of the discharge space traversed by the lines of force.

4. A full-wave rectifying device c'omprisingan ionic discharge tube having an envelope, an in candescible cathode, two anodes Ydisposed adjacent the wall of the envelope, said cathode being spaced from each anode by a distance substantially equalv to the distance between the anodes,

a screen between said cathode and anodes and lo,

cated symmetrically with respect to'a line passing through said anodes, and a gaseous filling having during operation a pressure less than 0.01 mm. of mercury, and means outside the envelope to .produce a magetic field having lines of force traversing the envelope at points adjacent the anodes and extending between the anodes in a beam, said cathode being centrally disposed within said beam to form a discharge path following the lines of force thereof.

5. A full-wave rectifying device comprising an ionic discharge tube having an envelope, two anodes disposed adjacent the wall of the envelope and substantially in a common plane, an incandescible cathode disposed above said plane and symmetrically with respect to said anodes, a screen between said cathode and said plane and located symmetrically with respect to said anodes, said screen intercepting a straight line between any point on said cathode and any point on said anodes, and a gaseous lling having during operation a pressure less than 0.01 mm. of mercury, and means outside the envelope to produce a magnetic eld having lines of force traversing the envelope at points adjacent the anodes and extending between the anodes in a beam, said cathode being centrally disposed within said beam and spaced from said anodes to form a discharge path following the lines of force thereof.

6. A full-wave rectifying device comprising an ionic discharge tube having an envelope, two anodes disposed adjacent the wall of the envelope and substantially in a common plane, an incandescible cathode disposed above said plane and symmetrically with respect to said anodes, a screen between said cathode and said plane and located symmetrically with respect to said anodes, and a gaseous filling having during operation a pressure less than 0.01 mm. of mercury, and means outside the envelope to produce a magnetic field having lines of force traversing the envelope at points adjacent the anodes and extending between the anodes in a beam, said cathode being centrally disposed within said beam and spaced from said anodes to form a discharge path following the lines of force thereof, said screen being curved to follow the lines of force.

7. A discharge tube having electrodes including a cathode, and an envelope having a vitreous portion and metal members sealed therein, and means for producing a magnetic eld within said envelope comprising a coil and a core 'having two portions insulated from each other, each of said portions having one end secured to one of said members.

8. A full-wave rectifying device comprising an ionic discharge tube having an envelope comprising a vitreous portion and two metal members sealed therein, an incandescible cathode, two anodes each secured to one of said metal members, and a gaseous filling having during operation a pressure less than 0.01 mm. of mercury, and means outside the envelope for producing a mag netic eld having lines of force passing through said metal members and anodes and extending between the anodes in a beam, said cathode being centrally disposed within said beam and spaced from said anodes to form a discharge path following the lines of force, said means comprising a coil, and two cores electrically insulated from each other, each core having one end secured to the outer surface of one of said metal members.

TOM JURRIAANSE.

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