US2829334A - Current regulator - Google Patents

Description

April 1, 1958 R. J. MURNIGHAN 2,829,334

CURRENT REGULATOR Filed Deo. 1, 1955 2 sheets-sheet 1 RICH-ARD JOSEPH MURNlGHAN BY cxx ATTORNEY April 1, 195s Filed Deo. 1, 1955 2 Sheets-Shea?l 2 f lfc 22 Q o/FFEEEA/cs 9N /QMP/F/ER.

INVENTOR.

RCHRD JOSEPH. MURNIGHAN BY j a u ATTORNEY United Sttes Patent CURRENT REGULATOR Richard Joseph Murnighan, Westwood, N. J., assignor to Vitro Corporation of America, Verona, N. J.

Application December 1, 1953, Serial No. 395,481 2 Claims. (Cl. 323-22) My invention relates to electronic power regulating devices and more particularly relates to current regulating devices.

In many electronic applications, it is necessary to supply a relatively constant current from an unregulated power source to a load whose impedancevaries during operation. When the percentage of current regulation is relatively high, say on the order of many conventional devices are available for this purpose. However, as far as is known to me, such devices are not available for applications requiring a much lower percentage offregulation; i. e., on the order of 0.1% or less. g

Accordingly, it is an object of the present invention to provide a new and improved current regulating device of the character indicated.

It is a further object to provide a new and improved current regulator incorporating a non-linear circuit element which exhibits a relatively large change in voltage when the current flowing therethrough changes by a small amount.

Still a further object is to provide a new and improved current regulating device whose percentage of current regulation is on the order of 0.1% or less and whose current can be varied from zero to a predetermined maximum without adversely effecting the degree of current regulation.

These and other objects of my invention will either be explained or will become apparent to those skilled in the art when this specification is studied in conjunction with the accompanying drawings wherein:

Figure 1 illustrates the invention in simplified form;

Figure 2 illustrates the invention in more detail; and

Figure 3 illustrates a modification of the invention shown in Fig. 2.

Briefly stated, my invention contemplates ay current regulating device for supplying an extremely well regulated current to a load whose impedance varies during operation. Such a load, for example, can be the magnet of a mass spectrometer, whose resistance changes as current ows through the winding of the magnet and raises the temperature thereof. The winding is connected in series with the anode-cathode path of an electric discharge tube, which can be a triode but is preferably a tetrode or pentode, and is also connected in series with a non-linear, thermally stable, low heat capacity element which exhibits large voltage changes for small changes in current iiow therethrough. This element, for example, can be a conventional incandescent dial lamp. The entire series circuit is connected between the terminals of a direct voltage power source. A constant reference voltage, which can be adjusted to any convenient value, is provided to establish the desired current iiow through the winding. The voltage developed across the non-linear element is compared with the reference value, and the difference between the above two voltages is supplied to the control grid of the tube to control the current there- 2,829,334 Patented Apr. 1, 1958 through in such a manner that the difference voltage is reduced to zero.

Referring now to Fig. 1, an unregulated direct voltage with the polarity indicated is impressed across terminals 6. A series circuit consisting in the order named of a load 1 subject to variations in its impedance, a triode 2 and a conventional incandescent dial lamp is connected across terminals 6. A source 4 of direct reference voltage has its positive terminal connected in common with the negative terminal of terminals 6. The negative terminal of source 4 is connected through lead 9 to a first imput of differential amplifier 5. The voltage developed across lamp 3 appears at junction point 7 and is supplied through lead 8 to a second input of amplifier 5. The output of amplifier 5 is supplied through lead 10 to the control grid of triode 2.

An incandescent lamp, due to its high operating ternperature, has a resistance which is virtually unaltered by changes in ambient temperature and hence is thermally i Operation of this circuit is as follows. The reference voltage is set to a value which establishes the correct amount of current flow through the circuit. At this point, the voltage across the lamp and the reference voltage are equal and opposite and hence cancel. The control grid of triode 2 is biased to a suitable value for the correct current through a standard biasing arrangement (not shown) included in amplifier 5. As the load impedance changes, the current through lamp 3 changes; the voltage appearing at junction 7 changes sharply. At this point, a difference voltage (i. e., the difference between the reference voltage and the lamp voltage) is produced which is amplified and supplied to the control grid of triode 2 to restore the current flow to the desired value.

This circuit has a percentage regulation on the order of 3%. This percentage is quite low as compared to conventional apparatus; however, it was discovered that the regulation was adversely affected by variation in the various operating voltages, variations in the reference voltage and variations introduced by the triode itself. The operation of the circuit is predicated on the assumption that small voltage changes across the triode will not appreciably change the triode current. For normal operation, this assumption is reasonable; for very low percentage current regulation, however, this assumption is not accurate.

Accordingly, the circuit shown in Fig. 2 was developed. The reference voltage is derived from voltage divider network connected across a regulated voltage source 20. Source 20 also supplies operating voltages to amplifier 5. Amplifier 5 is provided with a polarity inverter to invert the polarity of the reference voltage before it is compared with the lamp voltage. Triode 2 is replaced by a beam power tetrode 2', which is a quasi-constant current device. Load 1 is the winding of a magnet of a mass spectrometer. Current flow through the winding heats the winding and its resistance changes. The necessary current correction thus required is performed in the same manner as Fig. 1. However, despite the use of unregulated load supply voltage, this circuit has a much lower percentage regulation; on the order of one part in one thousand. Of course, a pentode also acts as a constant current source and can be substituted for tetrode 2' without changing the operation of the circuit.

However, despite this very low regulation, variations 3, inv thesupply-volt-age still have adverse" effects: More# over, the screen voltage for the tetrode is supplied from source 20. The consequent interaction is such as to prevent adjustment' of' the' load current to zero, anv adjustment that is required for many applications. In addition, the interactionalso adversely affects regulation.

The circuit shown in Fig. 3 obviates. these difficulties. The screen voltage for tetrode 2 is supplied from an isolated source which, for example, can be a battery 24. The operating potential produced across terminals 6 is supplied from a regulated'source 23.

yThis circuitr has anextremely low regulation; on the order-of one part in ten thousand. It is highly stable and, by inserting additional tetrodes in parallel with.

tetrode'Z", this regulationcan be maintained over a wide range'of current values rangingupward from zero.

While I havedescribed the invention in the preferred forms'shown, it will be understood that modifications may be made within the scope and sphere of the invention as defined in the claims which follow.

I-claim:

l. A current regulator comprising first,.second and third direct voltage sources, said first and secondsources beingl regulated; a load including a control windingsub ject to resistance variations; an incandescent lamp provided with rst and second terminals; an electricdischargetube provided with an anode lconnected to one` end of said winding, a cathode connected to said flrst .termina1,.a screen gridconnected ftosaid third sourcegfvanda control grdg'mcans coupling said' other end of the -Winding and the second terminal of said lamp to said rst source; a diterential ampliier provided with rst and second inputs and an output, said amplifier being coupled to said second source to receive operating potential directly therefrom througha circuit unaffected by current flow through the electric discharge tube and incandescent lamp, the first input being coupled to said cathode; means coupled to said second source to derive a reference voltage therefromgpmeans to supply said reference voltage to said second amplier input, said amplifier yielding at its output a. control voltage.representingithe difference between said reference voltageand the voltage developed across said lamp; and means to supply said control voltage to said control grid in a direction to oppose changes in the current owing in said load.

2. The current regulator set forth in claim 1 wherein said. tube is a beam power tctrode.

References Cited in the file of thispatent UNITED STATES PATENTS 2,210,394 Braden Aug. 6, 1940 2,551,407l Alder May 1, 1951 2,640,962 Gray June 2, 1953 OTHER REFERENCES

Images