US2576100A - Voltage stabilizing system and tube - Google Patents

Description

Nov. 27, 1951 s. c. BROWN 2,576,100

VOLTAGE STABILIZING SYSTEM AND TUBE Filed July 13, 1945 2 SHEETS-SHEET 1 STABILIZED A. C- INP T U g OUTPUT AVALANCHE DISCHARGE moos Fig. 2

- STABILIZED A.C.INPUT OUTPUT 0 r AVALANCHE i 2 SHEETSSHEET 2 s. c: BROWN VOLTAGE STABILIZING SYSTEM AND TUBE .05 MICROAMPERES NEON Nov. 27,

Filed July 13, 1945 m 4 w 6 3 w 2 3 o o 8 2 w 4 2 O O o 2 I Patented Nov.- 27, 1951 23min;

VOL'lPAGE STABILIZING SYSTEM AND TUBE Sanhorn C. Brown, Cambri n, Mass., assignor by mesne assignments to Research Corporation, New York, N. Y., a corporation of New York . Application July 18. 1945, Serial No. 604,953

10 Claims.

The present invention relates to voltage stabilizing systems and apparatus.

Many types of electronic and other electrical devices require a stabilized power supply for proper operation. Instruments such as Geiger- Miiller counters and the electron microscope are representative or those requiring an extremely stable high voltage direct current supply.

Stabilizing arrangements hitherto employed have generally been based on the fact that a coldcathode gas diode, operated under conditions which result in a self-maintaining glow discharge, exhibits a relatively constant potential drop across its electrodes over a moderately wide range of currents. For relatively slmple'low voltage systems, where the stability requirements are not severe, such a' tube, commonly termed a glow discharge or voltage regulator tube, may be arranged in parallel with the load directly across the output 01' a simple rectifier-filter power supply. In such arrangements the glow discharge tube functions as an automatically varying load or bleeder resistance to provide an approximately constant output voltage.

Other arrangements involve the use of a glow discharge tube in conjunction with a high-transconductance triode and one or more high gain amplifier tubes. Changes in output voltage relative to a reference voltage provided by the glow tube are amplified and applied to the grid of the series-connected triode to vary the voltage drop across the latter in a direction tending to restore the output voltage substantially to its proper value.

Systems based on the glow discharge tube are limited in their performance and useful appliestion by the characteristics 01' the glow discharge. Maintenance of the discharge requires currents within the approximate range of five to forty milliamperes, with the result that substantial P wer is dissipated if the applied potential is greater than one or two hundred volts. Furthermore, the tube is relatively sensitive to variations in temperature, so as to afiect materially the voltage stability, particularly in the case of the higher voltage systems employing a large amount amplification. Such systems may require an extended warm-up period when used in conjunction with equipment requiring a relatively high order of stability in the voltage supply.

The present invention is based on the discovery that it is possible, by utilizing discharge phenomena difiering materially from the glow-type discharge, to stabilize with great accuracy relatively high voltages, of the order of several thousand volts, without the use of complicated degenerative amplifier circuits and without appreciable power dissipation in the stabilizing means. For an understanding or the mode of operation of the stabilizing systems oi the present invention, it is necessary to distinguish between th various types of discharge which may occur between electrodes in a gas atmosphere.

The passage of current between the electrodes, under the influence 01' an applied potential, is dependent on the liberation of ions in the electrode gap. At low potentials, no significant amount or ionization takes place as a result of the applied potential}. and consequently no appreciable current flows, unless ions are liberated in the gap by some external source. If such a source of ions is present, as for example from a radio-active or photoelectric source, then the current in the discarge will be proportional to the ionization resulting from said external source. The ionization current-represents a multiplication of the electrons in the field near the anode due to ionization by electron impact. Thus the entire current is carried by individual ion avalanches created by charged particles entering and multiplied by the ionizing field. This region is termed the avalanche region.

As the potential across the electrodes. is increased, the number of ion pairs produced in each avalanche increases rapidly. until a point is reached where a sufiicient quantity of secondary electrons is released to cause temporarily selfmaintaining corona discharges. This region oi temporary currents due to the partially self-maintaining corona is called the intermittent corona region and it is in this region that the Geiger- Milller counter tube operates.

With a further increase in applied potential across the electrodes, the corona discharge becomes continuous, with'high currents and intense ionization, giving a visible .glow. The conventional glow'discharge voltage regulator depends for its operation on the self-maintaining corona or glow discharge.

If the current-voltage characteristic of these three regions is examined, it will be found that in the avalanche region a small change in applied potential results in a very marked change in current carried by the discharge. I have found that this extreme sensitivity to small changes in voltage may be effectively utilized to provide voltage stabilizing system capable of operation with a very high order of stability and of relatively simple construction and arrangement. Since the ionization current, for operation in the avalanche region, is extremely small, the power dissipation in the stabilizing system is so low as to be of no significance even at high voltages. In addition, the operating characteristics of the avalanche discharge are relatively independent of variations in temperature.

It is, therefore-one of the objects of my invention to provide a voltage stabilizing system operating in accordance with principles which differ substantially from conventional systems embodying glow discharge tubes.

It is, more particularly, an object of the invention to provide voltage stabilizing systems and power supplies embodying the same, suitable for both low and high voltage applications, which provide with a minimum of apparatus and*without circuit complications, a high order of stability in the output voltage.

The invention also has as an object the provision of a voltage stabilizing system and tube therefor having novel means for readily and precisely adjusting the magnitude of the stabilized voltage over a relatively wide range.

A further object of the invention involves the provision of a stabilizing tube of novel construction and mode of operation, characterized by very low current requirements and a high order of sensitivity to small changes in applied voltage.

In accordance with these and other objects, one of the features of my invention involves a voltage stabilizing system which is based on the use 01' a special stabilizing tube of the cold cathode, gas diode type wherein the pressure of the gas fill is greater than about 0.5 cm. Hg.

More specifically, a feature of the invention consists of a voltage stabilizing system employthe pressure of the gas fill may be varied to adjust the magnitude of the stabilized voltage over a substantial range.

In the accompanying drawings illustrating the invention, Figs. 1 and 2 are schematic diagrams of representative stabilized power supplies embodying the invention; Fig. 3 is a view of one form of stabilizing tube suitable for use in stabilizing systems of the present invention; Fig. 4 is a modified form of stabilizing tube having provision for varying the gas pressure within; Fig. 5 is a plot of a typical voltage-current characteristic for a stabilizing tube operating in the avalanche region; Fig. 6 is a plot of stabilization voltage in terms of gas pressure for representative gases; and Fig. 7 is a plot illustrative of the performance of a gas diode, operating in the avalanche region, in providing a stabilized output voltage over wide variations in input voltage.

In the stabilized high voltage supply shown in Fig. 1, the stabilizing system is employed in conjunction with a conventional rectifier-filter power supply circuit comprising a transformer [2, rectifier l4, and filter condenser IS. The direct current output voltage, which would, in the absence of stabilizing means, vary over a wide range with changes in the alternating current supply voltage, is stabilized at a substantially constant predetermined value by means of the special stabilizing diode 20. This tube operates in conjunction with a fixed resistance 22 to apply bias voltage to the grid of the series regulating triode 24 and thereby control the potential drop across the latter. For applications where the current requirements are relatively 10w, the regulating triode may advantageously have a high amplification factor rather than high transconductance.

The stabilizing diode, in the embodiment illustrated in Fig. 3, comprises concentric cylindrical electrodes in which the inner electrode 30 forms the anode and the outer shell 32 the cathode.

Glass seals 34 are employed at each end to provide a gas tight closure. Connection to the anode 32 is made by a lead 36 extending through one seal, and a lead 38 provides connection to the cathode shell. If desired, the tube may be provided with a suitable base for socket mounting in accordance with conventional practice.

The nature and pressure of the gas fill, and the ratio of the diameters of the electrodes, determine the voltage at which the diode stabilizes the output of the power circuit. These same factors likewise influence the sensitivity, or steepness of the voltage-current characteristic, such as is illustrated for a typical case in Fig. 5, although sensitivity is dependent to a lesser degree on gas pressure than on electrode ratio and type of gas.

The gas employed may be either a simple gas, such as neon, argon, helium or hydrogen, or an organic gas. It is generally preferable to select a gas that does not require pressures in excess of atmospheric to attain the desired stabilization voltage. The influence of the type and pressure of gas on voltage is illustrated in ,6, where the characteristics for neon, helium, argon and hydrogen are plotted for a typical electrode ratio.

In respect to electrode geometry, it has been found that for concentric cylindrical electrodes, a ratio of diameters of approximately two provides satisfactory stabilization characteristics.-

By way of illustration, a suitable tube having this electrode ratio may have an anode radius of 0.55 cm. and a cathode radius of 1.19 cm.

The avalanche discharge, as has already been indicated, is dependent on the release of ions within the electrode gap from some external source. Under normal conditions, ions are released only upon the chance admission within the electrode region of charged particles from some relatively remote source. The avalanche current under these circumstances is exceedingly small, of the order of 10 amperes or less. At such magnitudes, the value of resistance required at 22 in order to provide a bias voltage for the regulating tube 24 within the proper range of operation tends to approach the grid-cathode leakage resistance of the tube itself.

To avoid this limitation and to increase the stabilization range of the diode, provision is made for increasing the magnitude of the avalanche current. By associating with the tube a source of ionization external to the discharge, the number of ion avalanches for a given potential may be materially increased, so as to provide avalanche currents within the approximate range of 10- to 10- amperes. This permits the use in the grid-cathode circuit, of the regulating tube of a resistor 22 of the order of 10* ohms, a value substantially below that of normal leakage resistance between grid and cathode. In addition, the provision of a large number of ion avalanches serves tomask the eilects of statistical fluctuations in the avalanche current arising from the random nature of the ion release.

The source of ionization which should possess a high order of stability, over considerable periods of time, may be provided in a number of ways. Radioactive disintegration provides a convenient source of charged particles. The radio-active means may be associated with the tube externally thereof, or a radioactive substance may be incorporated within the tube, as by plating radioactive isotopes on the cathode surface. For this purpose, and Fe, each having a half life of approximately five years, have ben found suitable. Alternatively, a radioactive gas may be employed. The invention is not dependent for its operation on radioactive means as a source of ionization, however, as other sources of ionization may be employed such as photoelectrons.

The amount of radioactivity or other source of ionization influences the range of voltage variation over which the diode provides effective stabilization. Since the region of very low avalanche current is not well suited for operation because of the extremely high values of resistance required for the bias resistor 22, the effective range of the tube may be extended as a practical matter only by increasing the magnitude of the avalanche current. In general, an activity which permits avalanche currents up to approximately 0.5 microampere is ample to accommodate variations of one hundred percent in supply voltage, a range considerably in excess of that normally encountered. For variations more nearly comparable to actual conditions, a substantially lower value of avalanche current and correspondingly smaller amount of radioactive material are sufficient. It should be pointed out that the amount of radioactivity does not affect the sensitivity of the diode appreciably, for operation within the useful range.

The effectiveness of the voltage stabilizing system in a particular case is well illustrated in Fig. 7, where output voltage is plotted against input voltage, the input voltage being that presented to the stabilizing system by the rectifierfilter. The argon-filled tube at a pressure of 18 cm. Hg provides an operating point of approximately two thousand volts. The relatively small increase in output voltage for a two-fold increase in input voltage illustrates the sensitivity of response. While the same order of sensitivity is not realized with tubes designed for operation at the lower voltages, below five hundred volts, nevertheless the stabilization provided is highly effective in reducing to a negligible value the effect of normal variations in supply voltage.

The voltage-current characteristic of a typical avalanche diode incorporating a radioactive substance and having an argon fill at a pressure of 18 cm. Hg is shown in Fig. 5. It will be seen that a change in potential of the order of twelve volts,

from approximately 1978 to 2000 volts, produces a twenty-fold change in current, from 0.005 microampere to 0.1 microampere. In passing, it may be noted that this involves a power dissipation within the tube, when operating at the 2000 volt-0.1 microampere point, of only 0.002 watt. This may be compared with a power dissipation of the order of forty watts for maintenance of a glow discharge at the same potential.

It will be noted that no smoothing choke has been illustrated in the stabilized power supply, Fig. 1, since the stabilizing system is itself highly effective in removing ripple. For high-voltage, low-current applications, the stabilizing tube makes possible a still further simplification in the supply system. Such a system is illustrated in Fig. 2, wherein the series-regulating triode likewise functions as a haliwave rectifier. The

stabilizing tube, responding to variations in output voltage at ripple frequency, provides substantial smoothing or filtering as a result of its normal stabilizing action, through control of the bias onthe grid of the combination rectifier-regulating tube. -A filter condenser may be employed across the output for additional smoothing.

The wide variation in the operating point-of the tube with changes in pressure of the gas provides a means for adjusting the magnitude of the stabilized voltage output over a substantial range. For this purpose, a substantial portion of the diode envelope may consist of a flexible bellows 50 (Fig. 4) by which the volume of the envelope, and consequently the pressure of thegas within, may be varied. Expansion and contraction of the bellows is efiected by suitable means such as a screw 52 which may haveindex means associated therewith calibrated in terms of voltage. Such an arrangement permits precise adjustment of the stabilized output voltage without the use of voltage-dividing circuits. A control'range of the order of five hundred volts in the case of a supply nominally rated at two thousand volts may be readily achieved.

To summarize the features of the invention, the distinguishing characteristics of the -.avalanche tube and its mode of operation and manner of utilization may be specifically compared with those of the glow discharge tube. In the firstplace, the avalanche tube operates at gas pressures above approximately 0.5 cm. Hg. and at currents substantially less than 0.1 milliampere, while the glow tube operates at gas pressures of the order of 0.1 mm. Hg and at currenis appreciably greater than 1.0 milliampere. Furthermore, the operating point of the avalanche tube increases with increasing gas pressure, while in the glow tube the converse is true.

The avalanche tube is dependent for continued operation on ionization from an external source, whether or not such source is specifically associated with the tube. In the-glow tube, on the other hand, the discharge, once initiated, provides the ionization for continued operation, the discharge being self-maintaining under the influence of the applied potential. Power dissipation in the avalanche discharge is insignificant; in the glow discharge at potentials over one or two hundred volts it is substantial. Stability of the glow or corona type stabilizer is dependent on the stability of its self-maintaining discharge, and therefore on the stability of the gas and that of the electrode surface, which is under intense ion bombardment. In the-avalanche tube, stability is dependent on anionization source external to the discharge. By using long-period radioactive isotopes as the ionization source, an extremely high order of stability is provided.

While the invention has been illustrated and described as embodied in specific stabilizing and power supply systems and stabilizing tubes, therefor, this has been for the purpose of illustration only, and countless variations in the avalanche tube in respect to electrode geometry, nature and pressure of the gas fill, and ionization source, and in the manner of utilizing the tube in power supply systems may be made without departing from the scope of the invention.

Iclaim:

1. A voltage stabilizing system comprising a power circuit, a grid-controlled regulating tube in series with the power circuit, and means responsive to output voltage for applying a control voltage to the grid of the regulating tube to 7 minimize the'eifect of potential changes in the power circuit, said means comprising a bias resistor and a gas diode in series therewith, said diode operating in the avalanche region.

2. A voltage stabilizing system comprising" a power circuit, a grid-controlled regulating tube in series with the power circuit to control the output voltage thereof, and means for applying a control voltage to the grid of the regulating tube to minimize the effect of potential changes in the .power circuit, said means comprising a bias resistor and a gas diode in series therewith across the output side of the power circuit, the

diode operating in the avalanche region and having associated therewith a source of ionization.

3. A voltage stabilizing system for a power circuit, comprising a grid-controlled regulating tube connected in series with the power circuit to control the output voltage thereof, and means responsive to changes in output voltage for applying a control voltage to the regulating tube to minimize the change, said means comprising a bias resistor and a gas diode in series therewith, said diode being operated in the avalanche region and having associated therewith a source of ionization, and means for varying the gas prasure within the diode to control the magnitude of the stabilized output voltage.

4. A voltage stabilizing system for a power circuit, comprising an electronic regulating tube connected in series with the power circuit to control the output voltage thereof. said tube having an anode, a cathode, and a control grid, and means for applying a control bias to the grid comprising a gas diode, a resistanceconnected in series with the diode across the power circuit with the grid of the regulating tube connected to the junction between diode and resistance, said diode beingoperated in the avalanche region at current magnitudes substantially below the minimum for a self-sustaining discharge, the diode having a radioactive substance associated therewith for increasing the magnitude of the avalanche current.

5. A voltage stabilizing system fora power circuit, comprising an electronic regulating tube connected in series with the power circuit to control the output voltage thereof, said tube having an anode, a cathode. and a control grid, and means for applying a control bias to the grid comprising a gas diode and a resistance connected in series therewith across the power circuit, said diode comprising spaced electrodes within an envelope having a gas fill at a pressure above approximately 0.5 cm. Hg. and having a radioactive substance therein.

6. A voltage stabilizing system for a power circuit, comprising an electronic regulating tube connected in series with the power circuit to control the output voltage thereof, said tube having an anode, a cathode, and a control grid, and means for applying a control bias to the grid comprising a gas diode and a resistance connected in series therewith across the power circuit, said diode comprising spaced electrodes within an envelope having a gas fill at a pressure above approximately 0.5 cm. Hg and having a radioactive substance therein, bellows means in communication 8 f with the diode and forming a portion of the diode envelope, and means for adjusting the bellows volume to vary the gas pressure within the diode and thereby adjust the magnitude of the stabilized output-voltage. r

7. A stabilized power supply comprising a source of high potential alternating current, and common rectification and stabilization means comprising an electronic tube having an anode, a cathode, and a control grid, said tube being connected in series with the source of alternating current to provide both rectification and stabilization via the anode-cathode circuit thereof, and means including a resistor and a gas diode in series therewith, said diode containing a gas at a pressure above approximately 0.5 cm. Hg and operating in the avalanche discharge region to apply stabilizing bias to the control grid of the rectifying and stabilizing tube to provide a voltage-stabilized direct current output of low ripple content.

8. A voltage stabilizing system comprising a supply circuit, a grid-controlled regulating tube in series with the output of the supply circuit, and means responsive to output voltage for applying to the grid of the regulating tube a control potential, said means comprising a bias resistor and a gas diode operating by avalanche discharge, the diode having a gas fill at a pressure above approximately 0.5 cm. Hg, and a source of ionization in association therewith.

9. A voltage stabilizing system comprising a power circuit, a grid-controlled regulating tube in series with said power circuit to control the output voltage thereof, and means for deriving from said output voltage a control potential for the grid of the regulating tube, comprising a bias resistor and a gas diode operating by avalanche discharge and having a gas fill at a pressure above approximately 0.5 cm. Hg.

10. A voltage stabilizing system comprising a power circuit, a grid-controlled regulating tube in series with said .power circuit to control the output voltage thereof, and means for deriving from said output voltage a control potential for the grid of the regulating tube, comprising a bias resistor and a gas diode operating by avalanche discharge and having a gas fill at a pressure above approximately 0.5 cm. Hg, the bias resistor having a resistance such that appropriate control potential is applied to the grid of the regulating tube for diode current less than 0.1 milliampere.

SANBORN C. BROWN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,760,525 Rentschler May 27, 1930 1,747,050 Charlton Feb. 11, 1930 2,318,644 Tubbs May 11, 1943 2,323,857 Trevor July 6, 1943 2,362,769 Parratt Nov. 14, 1944 2,372,432 Keizer Mar. 27, 1945 FOREIGN PATENTS Number Country Date 63,383 Denmark April 1945

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