US2467695A - Current rectifier tube - Google Patents

Description

April 19, 1949. PONTE CURRENT RECTIFIER TUBE Filed May 2; 1947 3L rg. 1

I I'm aviar- Manx/ owns 5 Ma, y 9%} I (feats Patented Apr. 19, 1949 UNITED- STATES PATENT OFFICE CURRENT-'RECTIFIERiTUBE Maurice Ponte, Paris, France, assignoritoxflompagnie Generale de Telegraphic SansFiLaeorporation of France 3 Claims.

Rectifier tubes of the so-called cold cathode type, or of the arc type, are at present divided into two classes, which are distinguished one from the other by the method of producing the ionisation which allows the discharge to pass through the tube iorat least a fraction of the :time during which the anode is positive.

In one class of these tubes, ionisation is maintained continuously by an auxiliary arc, generally at low tension, which is struck between the mercury and an electrode located near the oathode. The instant at which the discharge starts can be controlled by a grid; the potential applied to this electrode acting either [by virtue of its amplitude or according to its phase relationship tothe anode potential. This class comprises the thyratron rectifiers which are now well known.

In another class, are the rectifiers known as Ignitrons in which there is no auxiliary are; striking or starting of the discharge is effected at'the required instant during the cycle by means of an ionisation produced by a local discharge between a semi-conducting electrode J dipping in the mercury C: Figure 1 shows diagrammatically one of these tubes in which C is the mercury cathode, A the anode; the grid G is, in reality, only a screen which can be used for quick deionisation of the space enclosed in the tube.

The advantage of ignitrons over rectifiers of the first class resides chiefly in the fact that ionisation is present only at the required instant and disappears during that portion of the cycle in which the anode is negative. This property considerably decreases the risk of a flash-back of the arc, i. e. the formation of a cathode spot on the anode. The construction of the tubes is also simplified and their efiiciency is increased.

However, the construction of the striking electrode is delicate; control of the phase of the starting are at the surface of separation between the semi-conductor and the mercury, which must not wet it, is effected by means of devices which are rather complicated. On the other hand, owing to the very nature of this principle of starting, the

cathodes are necessarilyliquid, which, in practice,

limits the choice of the material of which this electrode can be made-it must, in fact, be mercury,

The present invention provides another solution for the construction of rectifier tubes, in which the instant of the striking i determined by the actual inception of an ionisation in the tube and in which the said ionisation disappears when the anode voltage becomes negative. This solution is also applicable to any gaseous atmosphere, thus extending the range of manufacture and use cry-such tubes.

In principle; accordin'gIto-the invention, ionisation is produced by the effect of r a high-frequency by an'inductance h'the tube lights up, often very violently. This is the phenomenon known by the name of discharge without electrodes. It is advantageous Ito use fairly "short waves, such as metre. wavesbut'this condition is not essential.

The phenomenon aforesaid affords the possibility of producing-ionisation in a gas by the action of asourceof high-"frequency. If the amplitude o'fthe hlgh frequency current which circulates in the coil 'L' (Figure 2) takes the form shown in Figure3, which shows its variation as a function of time, the ionisation of the gas will take a similar form: for example, the frequency of the pulses may be fifty cycles per second, and theuduration of each pulse may be adjusted within vwide'limi'ts: the ionisation in the tube B will have the samecharacteristics, except for the time of (lo-ionisation.

According to -the invention, the rectifier tube shown diagrammatically 'in Figure 4, which com prises a catho'de'Cof liquid mercury and an anode A, both of which are located in an insulating envelope-R, provided with an inductance L. This inductance is traversedby'pulses of current produced by a high-frequency generator.

In Figure 5 "there is-shown, as a iunction of time, the-anode'voltage'v and "the amplitude of thecurrent I'whichtpasses through the coil L. The fiovr ofthe high-frequency current of intensity I has the effect ofionising'the gas at'the instant t1 and of thereby causing the current to flow through the rectifier; the flow of current stops at the instant t2 and the ionisation in the tube disappears during the negative portion of the cycle. The current which passes through the rectifier is, therefore, of the shape shown in Figure 5a, the structural details of which are dependent on the circuits connected to the rectifier, in particular on the filter. The shape and the mean value of the rectified current are thus controlled by the position of the instant ii in the cycle.

The supply of current to the coil L may be efiected by very varied means, the only essential condition being that the oscillator should be absolutely non-conducting except during the pulses, so that the rectifier tube shall not be subjected to any high-frequency influence during the time when there are no pulses. The power of the supply to the coil depends upon the dimensions of the space to be ionised, but for the largest tubes it is of the order of one hundred to two hundred watts, so that the method is economical. Furthermore, the high-frequency for the excitation need not be constant, 50 that the simplest circuits can be used, such as those employing self-oscillator valve circuits or even spark generators.

Figure 6 shows a valve circuit in which the coil is supplied by a well-known Hartley self-oscillator, with a wave-length of, say, a few metres. In this circuit, a multi-electrode valve E has, between its grid and plate, an oscillating circuit comprising a condenser K and an inductance S with an intermediate point connected to earth. In series with the inductance S is the ionisation coil L surrounding the rectifier R. A blocking condenser B connects the anode of B to the oscillating circuit. The anode supply for the exciting valve E may be any one of the types of pulsating supply which are now well known: one simple arrangement can be obtained by using an oscillater of the blocking oscillator type, supplied by the actual supply voltage F of the rectifier, with transformers T and T' and a circuit D for controlling the phase of said supply, which may be of any type. Between the output terminals U and U of the rectifier and the cathode C there is interposed a choke-capacity filter W. More elaborate circuits may be used if necessary,

The construction of the tube is thus simplified since, according to the invention, the ionisation means may be outside the tube; said tube may moreover be provided with the well-known auxiliary electrodes, such as anode screens or the electrodes which accelerate de-ionisation at the beginning of the negative cycle.

Finally, it should be noted that the invention is applicable with any gas.

In the case of very high power rectifier tubes, the usual present day practice is to employ tubes which are maintained permanently in an evacuated condition. The invention is also applicable to this type of tube. In an embodiment shown in section (elevational and plan views) in Figure '7, the actual body of the rectifier M is made of insulating material (glass, ceramic material, or the like) and is provided with a pumping tube. It is, however, advisable for the inside of the tube to be at a definite potential. To this end, the body M is lined internally with a metallic electrode P which is of the shape of a, cylinder slit along a generatrix: the effect of the ionising coil L thus remains practically unchanged by the presence of this metallisation.

In another embodiment, shown in Figure 8, the ionising convolution or convolutions L are actually inside the rectifier. It is, however, desirable, in this case, for the convolution not to be directly in the ionised atmosphere: in a preferred form of the invention, it is embedded in an insulating material Z, the surface of which is at a potential which is defined by a split metallic electrode P similar to that of the embodiment of Figure '7. Both the ends (or, it may be, only one end) of the inductance L are (or is) brought out with the necessary insulation, it being possible for the body of the tube to be entirely metallic in this embodiment,

Although, in its preferred form, the invention has been described as using the field of a coil, it is possible, without exceeding the scope of the invention, to use other influences, as for instance, that of a high-frequency pilot arc between two electrodes located in the tube, or any other means available to the expert.

I claim:

1. In an electric arc discharge apparatus having auxiliary firing means, a device for preventing flashback comprising in combination: the said apparatus, constituted by a casing having a cathode, an anode and an ionizable gaseous medium therein, and by a winding in inductive relationship with said medium; an impulse discharge generator connected to said winding and adapted to produce therein very short impulses repeated at low frequency for initiating an arc spot on said cathode; a source of alternating current adapted to supply current simultaneously to the anode circuits of said apparatus and generator, and means for continuously adjusting the phase of the impulses in accordance with the anode current of said apparatus, the adjustment limits being so arranged that the current in said winding remains constant and nil over an interval of time overlapping sufficiently on the interval corresponding to the negative alternacy of the anode current of said apparatus for all harmful ionization to be suppressed during said second interval.

2. In a device according to claim 1, an electric arc discharge apparatus wherein the said casing is of insulating material and is provided with an inner jacket constituted by a cylindrical metallic electrode, the said winding being arranged around said casing.

3. In a device according to claim 1, an electric arc discharge apparatus wherein the said Winding is enveloped in an insulating mass arranged on the interior surface of said casing, said mass being provided on its side opposite to said casing with a slotted cylindrical metallic electrode.

MAURICE PONTE.

REFERENCES CITED UNITED STATES PATENTS Name Date Spencer May 2, 1944 Number

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