US2826734A - D.-c. cold-cathode tube voltage regulator - Google Patents

Description

March 11, 1958 M. MILLER 2,826,734

D.-C. COLD-CATHODE TUBE VOLTAGE REGULATOR,

Filed July 1, 1952 2 Sheets-Sheet 1 'INVENTOR MYRON MILLER ATTORNEYS March 11, 1958 M. MILLER 2,826,734

D.C. COLD-CATHODE TUBE VOLTAGE REGULATOR Filed July 1, 1952 2 Sheets-Sheet 2 FIG.3.

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[so 140 I30 120 I0 BATTERY VOLTAGE INVENTOR MYRON MILLER ATTORNEYS United States Patent Ofilice D.-C. COLD-CATHODE TUBE VOLTAGE REGULATOR Myron Miller, Silver Spring, Md., assignor to the United States of America as represented by the Secretary of the Navy Application July 1, 1952, Serial No. 296,779

Claims. (Cl. 323-17) (Granted under Title 35, U. S. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention comprises novel and useful improvements in voltage regulators and more particularly pertains to a cold-cathode type D.C. voltage regulator.

Cold-cathode tubes have a substantially constant voltage drop over a wide range of current and consequently can be utilized as voltage regulators. One such arrangement utilizes a cold-cathode tube in series with a regulating resistor across a D.-C. voltage source to be regu lated. Such an arrangement produces a substantially constant voltage output which appears across the coldcathode tube and which output potential is determined by the conduction potential of the tube. A plurality of cold-cathode tubes may be connected in series to produce a regulated output voltage which is a multiple of the individual tube conduction potential.

The breakdown potential of cold-cathode tubes is greater than the conduction potential thereof and consequently special provision must be made for igniting the tubes when a plurality of tubes are connected in series and the supply voltage being regulated does not exceed the combined breakdown potentials of the tubes, Additionally, in some applications in which the load is continuously connected to the regulator so that load current begins to flow through the regulator circuit when the regulator is connected to the D.-C. voltage source, the drop across the regulating resistor due to the flow of load current therethrough further reduces the voltage applied to the cold-cathode tubes and further increases the prob lem of igniting the tubes.

An important object of this invention is to provide a cold-cathode tube D.-C. voltage regulator in which the tubes are automatically ignited upon connection of the voltage regulator to the D.-C. voltage source being regulated.

Another object of this invention is to provide a coldcathode tube D.-C. voltage regulator which requires low power for operation.

A further object of this invention is to provide an automatically igniting cold-cathode tube voltage regulator which will ignite under load on low supply source voltage.

Still another object of this invention is to provide a cold-cathode tube D.-C. voltage regulator which will not be extinguished due to sudden load surges.

Other objects and many of the attendant advantages of this invent on will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

Fig. 1 is a schematic view of one form of cold-cathode tube voltage regulator;

Fig. 2 is a schematic view illustrating a modified form of voltage regulator;

Fig. 3 is a schematic view illustrating a further modified form of voltage regulator; and

2,825,734 Patented Mar. 11, 1958 Fig. 4 is a curve illustrating the variation in output voltage with decreasing supply potential.

Reference is now made more specifically to Fig. 1 of the drawings. A pair of cold-cathode tubes 10 and 11 respectively having plates l2, l3, grids 14, 15 and cathodes 16, 17 are diode connected in a series circuit with each other and with regulating resistor 18. Certain types of cold-cathode tubes have a substantially constant conduction potential as the control gap current is varied over a Wide range and have a substantially uniform breakdown potential which exceeds the conduction potential. In order to effectuate ignition of series connected cold-cath ode tubes from a D.-C. supply source B having a nominal output voltage which is less than the combined breakdown potentials of the series connected tubes, a resistance 19 is provided in shunt with tube 10. When the D.-C. voltage source B is connected to the regulator circuit as by switch S potential is applied to tube 11 by way of resistors 18 and 19 causing tube 11 to ignite, thereby reducing the potential drop thereacross to the conduction potential of the tube.

A load 21 is connected across the voltage regulator tubes by way or" an R.-C. filter circuit comprising ballast resistor 22 and condenser 2.3, which filter circuit serves to prevent load surges from extinguishing the voltage regulator. Since the starting load current [including the charging current of condenser 23] begins to flow when the voltage regulator is connected to supply source B there is a voltage drop across resistor 18. In order to cause both voltage regulator tubes to fire even when the supply voltage exceeds the sustaining voltage of tube 11 and the breakdown voltage or" tube 10 by only a few volts, a series R.-C. circuit comprising resistor 24 and condenser 25 is provided in shunt with resistor 18. The capacitance of condenser 25 is made large so that the voltage drop thereacross is small during the interval in which conduction is successively established in tubes 11 and 10. The series resistor 24- is provided to prevent the rapid discharge of condenser 1.5 which would tend to extinguish the regulator tubes 10 and 11, and is made small as compared to the resistance 18. Thus, during a transient period after connecting the voltage regulator to the supply source B the series circuit including resistor 24 and condenser 25 effectively shunts the resistor 18 by a relatively low impedance path, thereby reducing the voltage drop thereacross. Thus, resistor 18 may be chosen to have a large value to provide proper regulation with low power requirements, and yet the regulator tubes will be automatically ignited since resistor 13 is shunted during the interval in which tubes 10 and 11 are being ignited. Resistor 19 is chosen to have a large value to reduce the power loss thereacross to a small value during normal operation of the regulator.

Alternatively, a fuse may be utilized in lieu of condenser 25, the fuse being chosen to have a rating such that it will rupture when the voltage regulator tubes are ignited, at which time the combined components of the load current and regulator current which flows therethrough exceeds the rated amperage of the fuse. Use of a fuse, however, precludes refiring of the regulator tubes in the event they are extinguished before the supply source voltage B drops below the minimum value at which firing of the regulator tubes can be effected.

The regulator illustrated in Fig. 2 is similar to that of Fig. 1 and includes a supply source B which is adapted to be connected, as by switch S across the series cir cuit comprising regulating resistor 33 and cold- cathode tubes 31 and 32 which are diode connected in series with each other. Tube 31 is lay-passed by a high impedance resistor 34, and resistor 33 is shunted by an R.-C. firing circuit comprising series connected resistor 35 and condenser 36. The load 37 is coupled across the regulator .by the drop across conditions, the regulator can be -fire under connit' tubes by way of a filter circuit cornrising ballast resistor 38 and condenser 39. A resistor L is connected in shunt with resistors 33 and As is apparent, the resistor lfl reduces the voltage drop across resistor 33, due to the flow of load current and the charging current of condenser 39. In this manner, tubes 3i and 32 may be caused to ignite on an even lower differential between the supply voltage B and the composite conduction potential of tube 32 and the breakdow potential of tube 31. Al though the regulated voltage appearing at terminal 42 does not follow the combined conduction potentials of tubes 31 and 32 as closely as in the embodiment illustrated in Fig. l, by proper choice of the values of resistors 33, 38 and 41 the degree of regulation can be made high. Further, for a given supply potential, the voltage at point d2 is varied only by the fraction of the change in the sustaining voltages of tubes 31 and 32. Since the conduction potential of cold-cathode tubes is substantially constant only over an intermediate portion of the range of control gap currents, the resistor 41 improves the linearity of the regulated output voltage at very low and very high values control gap current.

The embodiment illustrated in 3 comprises a pair of cold-cathode tubes 51 52 which are diode connected in series with each other and with a regulating resistor 53. Tube 51 and resistor are shunted by a high impedance resistor 54 whercb voltage from the supply source B is applied to tube o2; when the voltage regulator is connected thereto a" switch S thereby causing tube 52 to ignite. Re ance 54 is made very high so as to reduce the power c am under normal operating conditions and condenser is connected shunt with tube 52.. The condenser 55* is chosen to have a small value so as to beco as charged r pidly upon connection of the regulator to the power sup; y. Condenser 55 thus serves to supply a portion of the initial surge of current through tube 52 upon ignition thereof, and therefore reduces the voltage drop act s resistor which would tend to cause the tube to extinguished. A series do cuit comprising resistor 56 and condenser 57' is connected across cord-cathode tubes and the load 63 is connected to the regulo .y of a 11-0. circuit comprising ballast resistor denser A resistcr 63 is connected resistors and di The resistor 63 supplies a porti to load current to load 63 and also a portion of the or 3 current of'condenser Thus, by proper choi the values of resistors 53, 61 63, the drop .or 53 can be made small so as to permit ignition of tubes 51 and 52 when the differential between the supply source potential and the composite cor" -otential of tube 52 and breakdown potential of tuo From the foregoing it is a cathode tube regulator circuits ments, provision is made a one of the pair of series o ned thereby readying the non-cond the embodiments illustrated i made for shui ing the regulat pedance path A r a prec connecting the regulator to the s reducing the voltage drop during the aforementioned interva ducting regulator tube can be i potential which 875C mue for firing. In and 2, provision is ors by a low imrval after c reg lating resistor s that the non-conply source 1e composite tion potential of he t ignited r gulator tube breakdown poten viding the shunt across r ating c n comes conductively inerttive l uct ng tube.

r which beoperating omatically urce potential and high regulating resistor impedance. In this manner a highly regulated output voltage is obtained with comparatively low regulator power consumption and from a low potential source.

It has been further ascertained that a continuously connected shunt across the regulating resistor and the output filter resistor is effective to reduce the potential drop across the regulating resistor to perm-it automatic ignition of both cold-cathode tubes at low supply source potentials.

As is apparent from Figs. 2 and 3, before the coldcathode tubes become conducting, the relative magnitudes of the component of the load current which flows through the regulating and ballast resistors and the component which flows through the resistor in shunt therewith is determined by the relative impedances of the parallel paths. The drop across the regulating resistor before the regulator tubes become conducting can thus be made small so that the tubes will automatically ignite on low supply source potentials. However, after conduction through the tubes is established, the regulator tubes exercise a controlling effect on the current l'low through the parallel paths, and the output potential of the regulator is then, to a great extent, determined by the conduction potential of the cold-cathode tubes. Further, the provision of the shunting resistor reduces the variations in the regulated output voltage due to variations in the conduction potential of the cold-cathode tubes.

The voltage regulator tubes become extinguished at a relatively lower supply source potential than is necessary to ignite the tubes. The regulator then effectively drops out of the circuit and the output voltage is determined by the supply source potential and the drop across the regulating resistor and output filter resistor. Since the regulator continues operation when the differential between the supply source potential and the conduction potential of the regulator tubes is small, the output voltage rise when the tubes become extinguished is not large, and for some tubes may be within the permissible range of output voltage.

Fig. 4 is a curve illustrating the variations in output voltage as the supply potential decreases. The initial portion of the curve between points A and B indicates the regulated output voltage when the regulator is in operation. The line B, C constituting the voltage rise when the regulator drops out, and the line C, D indicates the output voltage variation after the voltage regulator drops out.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore understood that Within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed as new and desired to be secured by letters Patent of the United States of America is:

1. A voltage regulator for maintaining a substantially constant voltage between the terminals of an electrical device supplied from a variable potential direct current source comprising, in combination, a pair of cold-cathode tubes each having a control gap; a first series circuit adapted to be connected across the source to be regulated and including said cold-cathode tubes and a regulating resistor; and a second series circuit having a connection in common with said regulating resistor and adapted to interconnect said tubes 'ith said source at said common connection; said second series circuit including an impedance element connected to provide a conductive path shunting one of said tubes and having an impedance which is high as compared to the control gap conduction potential of said one of said cold-cathode tubes to thereby elfectuate ignition of theother of said tubes in response to connection of said regulator to the source to be regulated, and low impedance circuit means in shunt with said regulating resistor for by-passing said regulating resistor with a low impedance path during the interval in which conduction is established in said cold-cathode tubes.

2. A voltage regulator for a variable potential direct current source comprising a first series circuit including a pair of cold-cathode tubes and a regulating resistor adapted to be connected across the source to be regulated, a second series circuit including a ballast resistor and said pair of cold-cathode tubes adapted to be connected to a load circuit, and means for igniting said coldcathode tubes in response to connection of said first series circuit to the source to be regulated, said igniting means including an impedance element in shunt with one of said tubes and means connected to said regulating resistor for reducing the potential drop across said regulating resistor due to the flow of load current through the regulator.

3. A voltage regulator for a variable potential direct current source comprising a first series circuit including a pair of cold-cathode tubes and a regulating resistor adapted to be connected across the source to be regulated, a second series circuit including a ballast resistor and said pair of cold-cathode tubes adapted to be connected to a load circuit, and means for igniting said cold-cathode tubes in response to connection of said first series circuit to the source to be regulated, said igniting means including an impedance element in shunt with one of said tubes and means including an impedance element in shunt with said regulating resistor and said ballast resistor for reducing the potential drop across said regulating resistor due to the flow of load current through the regulator.

4. A voltage regulator for a variable potential direct current source comprising a first series circuit including a pair of cold-cathode tubes and a regulating resistor adapted to be connected across the source to be regulated, a second series circuit including a ballast resistor and said pair of cold-cathode tubes adapted to be connected to a load circuit, and means for igniting said cold-cathode tubes in response to connection of said first series circuit to the source to be regulated, said igniting means including an impedance element in shunt with one of said tubes and means including a series R.-C. circuit in shunt with said regulating resistor for reducing the potential drop thereacross for a predetermined time interval after connection of the regulator to the source to be regulated.

5. A voltage regulator for a variable potential direct current source comprising, in combination, a first series circuit including a pair of cold-cathode tubes and a regulating resistor adapted to be connected across the source to be regulated; a second series circuit including a ballast resistor and said pair of cold-cathode tubes adapted to be connected to a load circuit; and means for igniting said cold-cathode tubes in response to connection of said first series circuit to the source to be regulated; said igniting means including an impedance element in shunt with one of said tubes, means including an impedance element in shunt with said regulating resistor and said ballast resistor, and a series R.-C. circuit in shunt with said regulating resistor for reducing the potential drop across said regulating resistor for a predetermined time interval after connection of said regulator to the potential source to be regulated.

6. A voltage regulator device including a pair of input terminals energized from a voltage source to be regulated and a pair of output terminals for applying the derived regulated voltage to a utilization circuit, one terminal of each of said input and output terminals being connected to form a common terminal; a pair of coldcathode tubes connected in series circuit relation to define a high potential terminal and a low potential terminal with said low potential terminal being connected to said common terminal; and an impedance circuit interconnected between the other terminals of said input and output terminals and having an intermediate terminal connected to said high potential terminal for igniting said cold-cathode tubes in response to current applied to said input terminals from the voltage source to be regulated whereby the voltage appearing at the output terminals is thereby regulated; said impedance circuit including a first impedance element connected to provide a conductive path shunting one of said tubes and to apply an igniting potential to the other of said tubes, a second impedance element for applying an igniting potential to said one of said tubes a predetermined interval of time after ignition of said other of said tubes, a third impedance element interconnected between said intermediate terminal and said other terminal of said output terminals and characterized by the property of directly varying its impedance in accordance with the variations in current flowing therethrough, and voltage dropping means connected to said second impedance element for reducing the potential drop thereacross due to the flow of current through said tubes.

7. The device of claim 6, wherein said voltage dropping means comprises a series R.-C. circuit connected in shunt with said second impedance element.

8. The device of claim 6, wherein said voltage dropping means comprises a resistor connected in shunt with said second and third impedance elements.

9. The device of claim 7, wherein said first impedance element is connected in shunt with said second impedance element and said one of said tubes; and further including a capacitive reactance connected across the anode-cathode circuit of said other of said tubes.

10. The device of claim 6, wherein said voltage dropping means comprises a resistor connected in shunt with said second and third impedance elements, and a series R.-C. circuit connected across said second impedance element.

References Cited in the file of this patent UNITED STATES PATENTS 2,524,325 Mentzes Oct. 3, 1950 2,554,800 Steiner May 29, 1951

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