US2164538A - Gas discharge tube and circuits - Google Patents

Description

July 4, 1939. w. L. Malen v GAS DISCHARGE TUBE AND CIRCUITS Filed Dec. 29, 195'? Discharge sans Discharge INVENTR. l

W/LBER L. ME/ER Patented July 4, 1939 UNITED STATES GAS DISCHARGE TUBE AND CIRCUITS Wilber L. Meier, North Arlington, N. J., assignor,

by mesne assignments, to Radio Corporation of America, New York, N. Y., a corporation of Delaware Application December 29, 1937, Serial No. 182,188

8 Claims.

My invention relates to electron discharge devices, more particularly to such devices of the gaseous type and circuits therefor.

In certain conventional grid controlled gas discharge tubes, not only is a rather high voltage between plate and cathode necessary to cause the tube to break down and pass current, but also the grid though effective in controlling the initiation of the arc-like discharge, is ineffectivey after the discharge starts in stopping the discharge unless very high' negative potentials are applied to the grid which for most purposes is impractical. The tube is usually shut off by removing the anode voltage. This of course limits the application of tubes of this kind.

In my copending application No. 141,411 filed May 8, 1937 and assigned to the same assignee as the present application, I describe andclaim a gas discharge tube in which the discharge can be easily controlled and the discharge started and stopped at will. I'he described tube makes use of a magnetic field for controlling the discharge.

While the tube described in the above noted application is applicable to many uses it is particularly suitable for converter apparatus for vtransforming a low voltage direct current supply to a low or high voltage oscillatory or intermittent current supply. The transformation of a low voltage direct current source of supply t0 a low or high Voltage oscillatory or intermittent current supply can be accomplished by the use of a vibrator, as in the power paci.: of automobile radio receivers. In many applications however, the vibrator is objectionable because of the short life of the contacts, sticking of the contacts, and the like, and because of the spark or arc that may occur. Gaseous tube oscillators may be used, but in the usual case, especially at low frequencies, expensive and bulky inductances and condensers are required.

It is therefore the principal object of my invention to provide a device for transforming or converting a low voltage direct current supply to a low or high voltage oscillatory or intermittent current supply emciently by means of a circuit using a gas discharge tube, particularly the type of tube described in my co-pending application noted above, in which vibrating contacts and the other objectionable features noted in this kind of device are eliminated.

The tube described and claimed in my copending application comprises a cathode and anode, both contained within an envelope containing a gas which may be ionized at a very low voltage, for example caesium vapor, the caesium vapor being maintained ionized at voltages as low as 1.5 to 3 volts. The envelope closely surrounds the electrodes and positioned on the outside of the envelope is an electromagnet which (Cl. Z50- 27) produces a eld transverse to the gas discharge between the cathode and anode. With the 10W voltages used between the cathode and anode, preferably not more than 15 volts, I- am able with a moderate magnetic iield to extinguish the gaseous or arc discharge between the electrodes. This tube lends itself particularly to a circuit which I have invented for converting lowpotential direct currents to pulsating or alternating currents of either high or low voltage.

Brieytheconverter circuit made in accordance with my invention includes a tube of the type described in my copending application having in series with it a load and a source of low voltage supply. The electromagnet for controlling the discharge through the tube` is connected in series with a second gas discharge tube and a condenser, thus forming an oscillatory circuit through the second gas discharge tube. One side of the condenser is directly connected to the negative side of the source of voltage supply and the other side of the condenser connected through a resistor to the positive side. The condenser and resistor arrangement provides a so-called time constant circuit which provides a pulsating or oscillating current output from a direct current supply in which the ratio of the time of current iiow to the time of no current new can be adjusted to any value. The discharging of the condenser through the electromagnet and the second gas discharge tube when the second gas discharge tube breaks down shuts ofi: the current in the output of the iirst gas discharge tube and hence through the load. The condenserv then charges up again and the process is repeated to produce a pulsating current in the output of the rst tube of any desired low frequency Within limits.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims, but the invention itself will best be understood by reference to the following description taken in connection with the accompanying drawing in which Figure l is a vertical section of an electron discharge device described in my co-pending application noted above, Figure 2 is a transverse section taken along line 2-2 of Figure l, Figure 3 is a graph showing the plate voltageplate current characteristics of the tube shown in Figures l and 2, and Figure 4 is a diagram of a tube and circuit made according to my invention for converting low voltage direct current to alternating or pulsating current of high or low voltage in the output of the tube.

The tube shown in Figures 1 and 2 comprises an envelope i0 containing a gaseous atmosphere, for example caesium vapor, ionizable at low voltage to provide a gaseous discharge, and closely surrounding the enclosed electrodes. The cathode II is provided with the coated ns I2 and heater I3, the cathode being surrounded by and connected to heat shield I4. The anode I5 receives the electrons emitted from the cathode Il. Acontrolelectrode I 8in the form of a cylinder surrounds the anode and extends toward the cathode. Voltages from 4 to 14 volts are applied between the electrodes, this voltage being preferably below that at which destructive cathode bombardment by ions takes place, but great enough to cause ionization and a gas discharge. Caesium vapor will ionize at very low voltages to permit a gas discharge between the electrodes within the tube. On the outside of the tube place electromagnets I6 for producing a field transverse to the gas discharge. When the electromagnets I6 are energized to produce a moderate strength field the arc discharge can be easily extinguished so that the anode current can be readily reduced to zero. To conserve the heat which is necessary to maintain the caesium vaporized the envelope I0 may be surrounded by insulating coating I1. The tube may also be placed within an evacuated container. A

The anode voltage-anode current characteristics of a tube made according to my invention are shown in Figure 3. As the magnetic field is increased in strength, as indicated by curves a, b, and c, the breakdown voltage and voltage required for maintaining the discharge increases. As indicated by curve c, if a magnetic held of sufficient intensity is produced transverse to the arc stream between the cathode and anode, for a given load, as represented by the straight line extending at an angle between thevoltage and current axes, a condition can be produced whereby breakdown will not only not occur but that a discharge can be extinguished after it has once been started. Thus, if a voltage Em is applied between the cathode and anode so that there is a current of the value represented by the intersection of curve a and the load line, if a magnetic field, which will produce the characteristic line c is applied between the cathode and anode, the arc discharge will be extinguished. The magnetic eld causes the electrons and the ions of the arc stream to be vdeiected out of the path between the cathode and anode and to recombine on the wall of the tube or on an auxiliary electrode provided for this purpose. This in effect increases the resistance of the tube so that the applied voltage cannot maintain thel are or gas discharge. This characteristic is made use of in the operation of circuits made according to my invention and using the tube described above.

An example of a tube made according to my invention includes a cathode having a diameter of about .250, which is also the diameter of an anode disc spaced 2 mm. away, the length of the cathode being .75", The diameter of the heat shield is .260". Voltages from 6 to 9 Volts are applied between the cathode and anode and the tube is operated at a temperature ranging from 140 to 250 C. although wider temperature ranges are possible. The envelope closely surrounds the electrodes to keep the heat losses at a minimum and permit the magnetic eld to be concentrated in the space between the electrodes. If it is desired to establish the magnetic field more easily, auxiliary electrodes made of magnetic material may be placed inside the envelope. Residual magnetism of the magnet may be neutralized by means of small neutralizing winding on the magnet so that the residual eld is reduced to zero or an auxiliary electrode positioned close to the cathode may be used to establish a low current discharge.

A circuit embodying my invention is shown in Figure 4 and includes ln addition to the first gas discharge tube I0 made according to Figure 1, a source of anode potential I9 which may also serve as the heating source for the heater I3 of. cathode II. The load 2D is connected between anode I5 and the positive side ofpthe voltage source. It may be the primary of a transformer or some other load. The means for controlling the discharge through tube I0, and hence through the load 20, includes electromagnet I6 in series with the gas discharge tube 2I, having a cathode 22, grid 23 and anode 24, and the condenser 25 bridged by the resistor 26. The condenser 25 and electromagnet I6 form an oscillatory circuit when a discharge takes place through the tube 2l. One side of the condenser is connected to the cathodes of the tube and to the negative side of the voltage source I9. The other side of the condenser is connected through resistor 21 to the positive side of the source of voltage i9. The control electrode I8 of the rst gaseous discharge tube is connected through a resistor 28 to a point between the anode of the second gas discharge tube and the electroinagnet i5.

The circuit may be controlled by a switch 29. Closing of the switch 29 permits condenser 25 to charge up through resistor 21, the value of which may be adjusted to vary the time that it takes to charge condenser 25. At the same time tube lll starts conducting, permitting current through load 20. As the condenser charges, the voltage on the anode 24 rises until the breakdown voltage on the tube is reached. The condenser then discharges through the tube through the electromagnet I6 energizing the magnet I6 to generate a magnetic eld to shut on? the discharge through the rst gas tube I0. Due to oscillatory action of condenser 25 and electromagnet l, which forms the inductance, the anode voltage of. tube 2l at the end of the discharge period becomes negative with respect to the cathode. This of course stops the discharge through the tube 2l and at the same time causes the voltage on the grid I8 of tube I0 to be negative so that current cannot flow through the tube Il). The condenser at the end of this period, however, again becomes charged from a negative value to a positive value and at the same time the voltage on the grid rises to a point which permits tube IIl to breakdown, which point is determined by the tube construction and the amplification factor of the grid, and current is again through the tube I0 and the load 2D. This current continues until tube 2| again breaks down, thus the cycle is repeated. Changing the resistance 21 varies the time that the tube I0 conducts and during which current flows through the load 20. The grid 23 of tube 2I is connected to resistor 26, the position changing the breakdown characteristic of the tube 2I so that a longer or shorter period elapses during which the condenser 25 may be charged. A gas tube which does not have a control grid could also be used in place of tube 2l in the circuit.

While I have indicated the preferred embodiments of my invention of which I am now aware and have also indicated only one specific application for which my invention may be employed, it will be apparent that my invention is by no means limited to the exact forms illustrated or the use indicated, but that many variations may

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