US3361954A - Direct current triode voltage regulator - Google Patents

Description

Jan. 2, 1968 c. o. JORGENSEN 3,

DIRECT CURRENT TRIODE VOLTAGE REGULATOR Filed Aug. 30, 1965 l3 10 LOAD I LOAD n aoovoc '4 SOURCE CLINTON o. JORGENSEN INVENTOR.

AGENT United States Patent Calif., assignor to Bristol, Pa, a corpora- ABSTRACT OF THE DISCLOSURE A direct current, common cathode triode voltage regulator connected across the load in which the conduction of the triode is responsive to an adjustable negative biasing source and also to feedback from the anode of the triode through a parallel RC circuit.

This invention relates to improved voltage regulators and more particularly to improved triode voltage regulators for use with direct current power supplies.

In much of the contemporary electronic equipment, it is generally recognized that changes or fluctuations in operating voltages frequently have an adverse effect on the performance characteristics of such equipment. For example, in electronic switching devices such as multivibrators it is common practice to supply both the load and voltage-sensitive timing circuits from the same power source. Switching action produces abrupt and at times wide ranging load changes which causes substantial supply voltage fluctuations and corresponding variations in switc ing periodicity. Thus, when precision switching periods are desired, it becomes necessary to regulate operating voltage levels to within narrow limits usually determined by the degree of precision required.

' Apparatus for regulating DC supply voltages appear in several forms. One well known means includes vacuum tube type voltage regulators. Output voltage regulation by this means is frequently accomplished by employing gasfilled VR (voltage regulator) tubes in combination with other elements in the regulating circuits. Generally, the VR tubes have a standard operating threshold fixed at such values as 75, 90, 108 or 150 volts DC, thereby limiting the choice of operating voltage levels and causing the user to frequently compromise on the selection of load design parameters. Moreover, these tubes in themselves are known to be incapable of regulating a 300 volt DC power supply any closer than about 1.5 to 3% of the supply voltage. Closer regulation may be had by cascading the VR tubes or employing zener diodes in the regulating circuits. This is done at the expense of increased complexity, unreliability and cost of manufacturing such devices, in addition, to retaining the aforementioned limitations on choice of operating voltage levels.

It is, therefore, an object of this invention to provide for an improved voltage regulator having a lower equivalent source impedance for use with a direct current power supply.

Another object of this invention is to provide an improved triode voltage regulator having a selectable operating voltage level yet capable of maintaining its output voltage Within narrower limits than comparable prior art devices.

Another object of this invention is to provide a simple, versatile, reliable and inexpensive triode voltage regulator having good regulating characteristics.

Still another object of this invention is to provide an improved triode voltage regulator having a grounded cathode thereby eliminating a biased heater supply and improving safety of operation with respect to potential differences between cathode and heater.

These and other objects and advantages will become apparent from the following description taken in connection with the accompanying single figure drawing which shows an embodiment of the invention.

Briefly, this invention contemplates achieving the foregoing objects by employing a triode amplifier tube as a voltage regulator in shunt with the load in a circuit where triode conduction is established initially from an adjustable biasing source and varied responsive to output voltage changes by the control grid in opposition to changes in load current. This action maintains essentially a constant current flowing from a DC power source through a voltage dropping resistor to both a variable load and the anode of said triode. The regulated output voltage is taken across the anode and cathode, the latter being grounded for safety of operations.

Referring to the drawing, there is shown a schematic diagram of a triode voltage regulator circuit for achieving the foregoing objects. Twin triode 10, a medium mu Class A1 amplifier tube such as an RCA 5687, is employed as voltage regulator for a 300 volt DC source 11. A triode having a singular electrode structure, or alternately one having high mu characteristics, may also be used. Where the particular triode chosen has dual electrode structures as in the circuit illustrated, their respective anodes, control grids and electron-emitting cathodes are connected for parallel operation. For this reason, these elements will be referred to below in the singular.

The anode of triode 10 is connected through voltage dropping resistor 12 to the positive side of 300 volt DC source 11 at input terminal 19. The electron-emitting cathode is connected to a grounded conductor which joins negative source input terminal 20 to output terminal 17. The heater, not shown, is connected to an unidentified voltage source. The control grid of triode 10 is connected to the juncture of resistors 13 and 14 which form a voltage divider in a grid biasing and control network. The opposite end of resistor 14 is connected to biasing source which for convenience has been designated a minus volts DC, although voltages as low as minus 50 volts DC may be employed. Resistor 13 is shunted by compensating capacitor 15 and its remaining end is connected to the anode of triode 10. Terminals 16 and 17 are respectively connected to the anode and ground across which the regulated output appears. Load 1 is connected across output terminals 16 and 17 through series load resistor 18. Additional loads identified as Load it connected through series load resistor Rn may also be connected across the output terminals up to the capacity of source 11.

A mode of operation will be described after first assuming, for example, that triode 10 is in fact an RCA 5687; the nominal regulated output voltage at terminal 16 is +200 v. DC; that Load 1 and Load 12 are multivibrators varying between 10 and 20 ma. and 2 and 20 ma., respectively, at random, coincident intervals. Other circuit components are: capacitor 1550 pf and the resistance values of resistors 12-21200 ohms, 13-220,000 ohms, l i-140,000 ohms, Iii-8,200 ohms, and RN8,200 ohms, respectively. It will be understood that these values are for illustrative purposes and are not to be construed as limiting in any sense.

In operation, the grid of triode 10 is responsive to both an adjustable biasing voltage for pre-selecting a nominal anode voltage level and to changes in anode voltage for maintaining this voltage level within narrow limits. Initially, let it be assumed that Load 1 is operating in its stable state and resistor 14 in the grid biasing and control network is adjusted to produce about 14 volts bias on the grid. This establishes nominal triode conduction and permits a charge on capacitor 15 to accumulate to a particular value. Triode conduction causes a nominal current to flow through resistor 12 which hereinafter will be referred to as regulator current. Both regulator current and eXternal load current pass through resistor 12 and their sum normally remains essentially constant and reduces source 11 voltage from +300 v. DC to a nominal +200 v. DC at the anode of triode 10. Under steady supply and load current conditions, this maintains both grid and anod voltages at steady values and maintains the output voltage across terminals 16 and 17 within narrow limits.

A reduction in triode conduction takes place when grid bias is lowered to a greater negative value by adjusting resistor 14, or upon receiving a downward fluctuation in source 11 voltage level which lowers grid bias reference. Consequently, either condition decreases the current flow through resistor 12. Adjustment of resistor 14 has the effect of raising the nominal anode voltage to a value higher than the +200 volt level. The reduction in current flow through resistor 12 reduces the voltage drop thereacross and substantially offsets the downward fluctuation in source 11 voltage level, thereby maintaining anode and output voltages at the nominal level. The opposite action takes place when triode conduction is increased by opposite adjustment of resistor 14 or an upward fluctuation in source 11 voltage level.

When load current increases, for example, by the sudden switching of Load 1 from its stable to its unstable state, the load current flowing through resistor 12 begins to increase. This is accompanied by a slight increase in voltage drop across resistor 12 which has a tendency to lower the anode voltage below the +200 volt level while lowering grid bias at the junction between resistors 13 and 14 below -14 volts. T riode conduction decreases as does the regulator current flowing through resistor 12, thus initiating a regulatory action which tends to maintain essentially the original current flow in, and voltage drop across, resistor 12. Because of the anode feedback connection to the grid and the transconductance characteristics of triode 10, the regulatory action stabilizes when anode voltage reaches about +1995 volts and grid voltage at about 14.2 volts. The degree of regulation may be improved by employing a higher mu triode if the range of current variation is smaller. Thus, it will be observed that grid voltage varies directly proportional to anode voltage and in effect inversely proportional to load current to maintain the output voltage at terminal 16 within a narrow limit of the nominal +200 volt level.

It should be noted that when load current suddenly increases, a momentary dip in output voltage would slowly occur because of reduced triode conduction which is accompanied by a change in grid-to-cathode capacitance charge. However, this dip is essentially prevented by the action of compensating capacitor 15 which supplies current to instantly readjust the grid-to-cathode capacitance charge to a new level.

Further increases in load current, as for example by the initiation of Load n concident with Load 1, produces a corresponding increase in current flowing through resistor 12. As previously mentioned, this will cause a decrease in grid voltage which in this instance is driven to below 14.5 volts. Again this decreases both triode 10 conduction and the regulator portion of current flowing through resistor 12 and restores anode voltage to about a volt less than the nominal +200 volt level. Theoretically, the output voltage can be maintained at about the +200 volt level while load current increases until triode 10 ceases to conduct current. Thereafter, the total current flowing through resistor 12 increases instead of remaining essentially constant and causes the anode voltage to decrease proportionally thereto.

Operation during a reduction in load current takes place under opposite conditions from the foregoing. For example, as Load 11 is removed from output terminals 16 and 17, anode voltage rises from a level of about +199 volts a d grid voltage rises from below 14.5 volts, the

latter causing triode 10 to conduct more heavily and increase the regulator current portion of current flowing through resistor 12. This increase in regulator current substantially oifsets the reduction in load current flowing through resistor 12 and raises the anode voltage toward the nominal +200 volt level. As load current drops 011 this action continues until the original nominal output voltage level is attained.

Under the foregoing conditions, this simple voltage regulator circuit provides a regulation of between /s% and /2 of the supply voltage across output terminals 16 and 17 when using an RCA 5687 as triode 10. Closer regulation is of course obtainable by using a higher mu triode having adequate maximum power and current ratings. This is because of the greater sensitivity provided by the higher ratio of anode current changes to grid voltage changes. Further, while reference has been made to a nominal output voltage of 200 volts DC, other voltage levels may be had within the limits of triode 10 by adjusting the value of resistor 14 to a new value as desired.

Moreover, it should be noted that because triode 10 is acting as a shunt regulator rather than a series regulator and the fact that its cathode is grounded, operational safety and reliability are improved with respect to voltage differences that otherwise would exist between cathode and heater. Many tubes are limited to volts or less cathode to heater rating. Therefore, a separately biased heater voltage source would be required for higher voltages. This detracts from the ease of utilizing a simple voltage regulator with a varying source and load and further emphasizes the advantages offered by this invention.

Although the present invention has been described with a certain degree of particularity, it is understood that changes may be made in circuit details without departing from the spirit and scope of the invention as hereinafter claimed.

What is claimed is:

1. A voltage regulator for a direct current supply system having a DC source connected in a circuit to a load, said voltage regulator comprising:

a voltage dropping resistor connected in series between said source and said load;

a triode vacuum tube having medium to high mu characteristics and an anode, grid and an electron emitting cathode, said anode and said cathode being connected across said load;

biasing means including an adjustable source of a negative voltage connected to said grid for causing substantial tube conduction and corresponding anode current flow through said voltage dropping resistor t establish a nominal output voltage level as desired during the absence of said load; and

means for supplying a control voltage to said grid, said means including a resistor and a capacitor connected in parallel between said grid and a point between said anode and said voltage dropping resistor for automatically maintaining a substantially constant voltage drop across said voltage dropping resistor.

References Cited UNITED STATES PATENTS OTHER REFERENCES RCA Receiving Tube Manual, High Voltage Regulator Circuit, 1961, p. 51 relied on.

JOHN F. COUCH, Primary Examiner.

A. D. PELLINEN, Assistant Examiner.

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