US2695985A - Gas tube power supply - Google Patents

Description

Nov. 30, 1954 G. W. BAIN, JR

GAS TUBE POWER SUPPLY Filed Jan. 5, 1951 INVENTOR EEDEEEWBAIN,.JH.

ATTORNEY United States Patent GAS TUBE POWER SUPPLY George William Bain, Jr., Raritan Gardens, New Brunswick, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application January 3, 1951, Serial No. 204,106

6 Claims. (Cl. 321-38) This invention relates to improvements in electrical power supply systems, and particularly to a power supply system utilizing gaseous electron tubes.

In a copending application of E. 0. Johnson, Serial No. 203,949, filed January 2, 1951, and assigned to the assignee of the present invention, there is described a regulated power supply system capable of handling large amounts of current with low voltage losses. The power supply described in said copending application includes a gaseous electron tube wherein the tube gas is ionized by a current separate from the work circuit current drawn through the tube.

It is a general object of the present invention to provide an improved power supply system utilizing such a gaseous electron tube.

A more specific object of the invention is the provision of an improved gas-tube-rectifier type power supply system adapted to operate at relatively high voltages without danger of inverse current fiow between the main tube electrodes.

In accordance with the invention, the foregoing and other related objects and advantages are attained in a system wherein an alternating voltage which supports an ionizing discharge in a gas tube rectifier is applied to ionizing electrodes in the tube in out-of-phase relation to the alternating voltage which is rectified by the tube. With this arrangement, it is possible to operate the system at higher voltages than could otherwise be tolerated without inverse current flow.

A more complete understanding of the invention can be had by reference to the following description of illustrative embodiments thereof, when considered in connection with the accompanying drawing, wherein:

Fig. 1 illustrates a gas tube rectifier system arranged in the manner described in said copending Johnson application,

Fig. 2 illustrates a gas tube of a type suitable for use in the systems of Figs. 1 and 3, and

Fig. 3 illustrates a full wave rectifier system arranged in accordance with the principles of the present invention.

In order to illustrate the problem with which the presentinvention is concerned, there is shown in Fig. 1 of the drawing a gas tube rectifier system arranged in accordance with the teachings of the above-mentioned copending Johnson application. In the circuit of Fig. 1, a transformer 11 has a primary winding 13 to which alternating voltage can be supplied from any suitable source (not shown). The anode 28 of a gas tube 26 is connected to one end of the transformer secondary winding 15. The other end of the secondary winding 15 is connected to a main cathode in the tube 26 through a capacitor 22, and to an auixiliary cathode 34 through a current limiting resistor 27. The gas tube 26 also is provided with a control electrode 38 between the anode 28 and main cathode 30. This control electrode 38 is connected to the tap 31a of a potentiometer 31 which is in shunt with the capacitor 22.

The structural details of a typical tube such as the tube 26 are shown in Fig. 2. A tube of this type is described more fully and claimed in the copending application of E. 0. Johnson, Serial No. 185,745, filed September 20, 1950, and assigned to the assignee of the present invention.

In the tube shown in Fig. 2, a gas tight envelope 26 is provided with a cathode 30. A U-shaped control electrode or grid 38 and a U-shaped anode 28 partially surround the cathode 30. The grid 38 comprises a plurality of parallel wires 39 which are supported in spaced relat1on. The anode 28 may be a sheet metal element.

Opposite the open ends of the grid 38 and the anode 28 there is mounted a cylindrical focusing electrode 23 provlded with an elongated slot 25 facing the open ends of the grid and anode structures. An auxiliary cathode 34 is mounted coaxially within the focusing electrode 23.

A tube having a structure such as that shown in Fig. 2 can be operated as follows:

If a voltage greater than that required to ionize the gas in the tube is applied between the auxiliary cathode 34 and the anode 28, a current will flow which will ionize the gas in the tube. As a result, a highly conductive mixture or plasma of ions and electrons will be created within the tube envelope. The focusing electrode 23 is effective to concentrate the ionizing current, making it possible to obtain high plasma densities with very small amounts of current or power. With the tube gas ionized to create plasma in the manner just described, it becomes possible to pass a relatively high current between the main cathode 30 and the anode 28 with a voltage drop which may be of the order of 0.1 volt or less. Furthermore, it becomes possible to control this main cathode-anode current by means of a control electrode 38, disposed in the space path as shown.

In the system of Fig. 1, during positive half cycles of anode voltage ionizing current will flow from the auxiliary cathode 34 to the anode 28, ionizing the tube gas. This will allow current to flow from the main cathode 30 to the anode 28 during the same half cycles of anode voltage, causing the capacitor 22 to become charged substantially to the peak voltage across the secondary winding 15. The effective impedance between the anode 28 and the main cathode 30 will be regulated by the control electrode voltage. Since the control electrode voltage will be determined by the voltage across the capacitor 22, regulatory action will be provided by the control electrode 38.

While a system of the type shown in Fig. 1 is suitable for many applications, there is a possibility that inverse current will flow between the anode 28 and the main cathode 30 during negative half cycles of anode voltage if the output voltage is large enough to cause ionization of the tube gas during negative half cycles of anode voltage. That is, during negative half cycles of anode voltage, the main cathode 30 will be positive with respect to the auxiliary cathode 34 by an amount substantially equal to the voltage across the capacitor 22. If this voltage is greater than the gas ionizing voltage, ionizing current will flow from the auxiliary cathode 34 to the main cathode 30. This current will provide a conductive plasma in the tube 26 and greatly increase the possibility of inverse current flow between the anode 28 and the main cathode 30. Therefore, the voltages utilized in a system of the type shown in Fig. 1 must be such that the output voltage will be less than the gas ionizing voltage or must be such that the peak inverse anode voltage will be less than that at which inverse current will flow through the tube when the gas is ionized.

In Figure 3 of the drawing, there is shown a gas tube power supply system arranged in accordance with the invention to reduce the likelihood of inverse current flow by preventing ionization. of the tube gas during negative half cycles of anode voltage. While the principles of the invention are disclosed as applied to a so-called full wave rectifier system, it will be obvious as the description proceeds that the principles of the invention are equally applicable to systems of the half-wave rectifier type.

The system of Fig. 3 comprises a transformer 10 having a primary winding 12 adapted to be connected to an alternating voltage source (not shown). The secondary winding 14 of the transformer 10 is connected at opposite ends to the anodes 28 of a pair of gas filled tubes 26, 26a. The tubes 26, 26a are provided with main cathodes 30, control electrodes 38, and auxiliary cathodes 34.

The main cathodes 30 are connected together and are both connected to the center tap 14a of the secondary winding 14 through a capacitor 40 and through ground.

If the auxiliary cathodes 34 were to be returned to the transformer secondary center tap 14a, the gas in each tube 26, 26a would be ionized on alternate positive half cycles of anode voltage. This ionization would permit electron current to flow from the main cathodes to the anodes and the capacitor 40 eventually would become charged substantially to one half of the peak-to-peak voltage across the secondary winding 14. This would mean that when the anode voltage of either tube went through a negative half cycle, the anode would be negative with respect to the main cathode by an amount substantially equal to the peak-to-peak secondary voltage. At the same time, the main cathode would be positive with respect to the auxiliary cathode by an amount substantially equal to the voltage on the capacitor 4%).

Therefore, in the hypothetical situation just assumed, it can be seen that the voltage developed across the capacitor 40 would be rather critical. If this voltage were large enough to cause current flow between the auxiliary and main cathodes during negative half cycles of anode voltage, then the tube gas would be ionized at all times and the possibility of inverse current flow through the gas tubes would be greatly increased, as was previously explained.

In accordance with the invention, the output voltage at which the system can operate is substantially increased by arranging the circuit so that the voltage between the auxiliary cathode and the main cathode in each tube will decrease substantially during the intervals of inverse anode-main cathode voltage. For example, as shown in Fig. 3, the auxiliary cathodes 34 can be connected to receive alternating voltage in out-of-phase relation to the anode voltages. Thus, the auxiliary cathode 34 and anode 28 of the tube 26 are connected to opposite ends of the transformer secondary winding 14. The auxiliary cathode 34 and anode 28 of the tube 26a similarly are connected to opposite ends of the transformer secondary winding 14. Current limiting resistors 27 are provided in each of the auxiliary cathode circuits to suitably limit the auxiliary discharge currents.

When alternating voltage is applied to the transformer primary winding 12, the tube anodes 28 alternately will receive a voltage of sign opposite to that of the voltage applied to the auxiliary cathodes 34. The tubes 26, 26a alternately will be ionized, allowing current to flow from the main cathodes 30 thereof to the anodes 28. This current will develop across the capacitor 40a voltage substantially equal to one half of the peak-to-peak voltage across the transformer secondary winding 14.

During the half cycle following conduction in either of the tubes 26, 26a, the voltage at the auxiliary cathode TI 34 thereof will be positive with respect to the anode voltage, and will be substantially equal to the main cathode voltage. Therefore, no ionizing current will flow in either tube during the negative anode voltage half cycles, and the system can be operated at relatively high voltages without danger of inverse current flow through the gas tubes.

In order to regulate the output voltage of the system shown in Fig. 3, the control electrodes 38 are connected to the movable tap 42a of a potentiometer 42 in shunt with the capacitor 40. With this arrangement, the voltage at the control electrodes 38 will change relative to the main cathode voltages in response to any change in the system output voltage, and will thereby cause a change in the impedance between the main tube electrodes 28, 30. This change in impedance will be in the proper direction to compensate for the change in output voltage.

If desired, an additional capacitor 44 and inductor 46 can be connected with the capacitor 40 to form a filter for eliminating ripple from the unidirectional output voltage at the terminals 48.

As was previously mentioned, either of the gas tubes 26, 26a could be eliminated from the system of Fig. 3 to provide a half-wave system without materially changing the operating principles.

What is claimed is:

1. A power supply system comprising a transformer having a primary winding and a secondary winding, a

gaseous electron tube having a main cathode electrode, an anode electrode, an electrode for controlling current flow between said main cathode and anode, and an auxiliary cathode from which ionizing current can be drawn to one of said electrodes, a load circuit connected between said main cathode and said auxiliary cathode, said anode and said auxiliary cathode being connected to opposite ends of said secondary winding, and a connection from said control electrode to said load circuit.

2. A power supply system comprising a transformer having a primary winding and a center-tapped secondary winding, a pair of gaseous electron tubes each having a main cathode electrode, an anode electrode, an electrode for controlling current flow between said main cathode and anode, and an auxiliary cathode from which ionizing current can be drawn to one of said electrodes, said anodes being connected to opposite ends of said secondary winding, said auxiliary cathode of each said tube being connected to the anode of the other tube, an output circuit connecting both said main cathodes to said secondary winding center tap, and means to control the voltage at both said control electrodes as a function of the voltage developed in said output circuit.

3. In a power supply system, in combination, a gaseous electron tube having a plurality of electrodes, an alternating voltage source, means including said source and a first pair of said electrodes for passing an ionizing current through said tube, and means including said source and a second pair of said electrodes for passing a separate current through the gas so ionized, said electrode pairs having one common electrode, said pairs being permanently connected to receive oppositely phased voltages from said source.

4. In a power supply system, in combination, a pair of gaseous electron tubes each having a main cathode electrode, an anode electrode, and an auxiliary cathode from which ionizing current can be drawn to one of said electrodes, means to connect permanently said anode and said auxiliary cathode of each said tube in out-of-phase relation to an alternating voltage source, and a circuit to connect both said main cathodes to said anodes.

5. A power supply system comprising a pair of gaseous electron tubes each having a main cathode electrode, an anode electrode, an electrode for controlling current flow between said main cathode and anode, and an auxiliary cathode from which ionizing current can be drawn to one of said electrodes, means to connect said anode and said auxiliary cathode in each said tube to an alternating voltage source in out-of-phase relation, a circuit to connect both said main cathodes to said anodes, and a connection from both said control electrodes to said circuit.

6. A power supply system comprising a transformer having a primary winding and a center-tapped secondary winding, a pair of gaseous electron tubes each having a main cathode electrode, an anode electrode, and an auxiliary cathode from which ionizing current can be drawn to one of said electrodes, said anodes being connected to opposite ends of said secondary winding, said auxiliary cathode in each said tube being connected to the anode in the other tube, and a circuit connecting both said main cathodes to said secondary winding center tap.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 783,482 Thomas Feb. 28, 1905 832,363 Bodde Oct. 2, 1906 1,197,686 Thomas Sept. 12, 1916 1,390,727 Schenkel Sept. 13, 1921 1,612,547 Stoekle Dec. 28, 1926 1,627,231 Chafiee May 3, 1927 2,248,626 Herskind July 8, 1941 FOREIGN PATENTS Number Country Date 192,095 Great Britain Jan. 25, 1923

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