US2822507A - Regulating circuit for energizing variable resistance loads - Google Patents

Description

Feb. 4, 1958 M. J. MULHERN 2,822,507

REGULATING CIRCUIT FOR ENERGIZING VARIABLE RESISTANCE LOADS Filed July 18, 1952 Fig.2.

u w v if I 1 3 f l 2 I TURNS=400 g 3 1 I I FILAMENTS l 1 COLD B:

I l 1 I I RMS LOAD CURRENT Q Inventor: Marvin J-MUIhEFfi is Attornex.

REGULATING CIRCUIT FOR ENERGIZING VARIABLE RESISTANCE LOADS Marvin J. Mulhern, Schenectady, N. Y., assignor to Gem eral Electric Company, a corporation of New York This invention relates to a regulating circuit for energizing variable resistance loads and more particularly to an arrangement for controlling the energization of a load circuit such as the filament of an electronic tube so as to prevent damage thereto during the warm-up period and so as to maintain substantially constant current thereto during normal operation.

The resistance of the filaments of certain electronic tubes varies from a very low value at room temperature to a value substantially in excess thereof as the tube filament is heated to its normal operating temperature. In certain instances, the resistance at normal operating temperature of a tube filament may be as much as four times the resistance of the filament at room temperature. Thus, if full voltage were directly applied to such a filament when cold, an excessive current would flow resulting in probable damage to the filament, or in reduced life of the filament.

A principal object of this invention is to provide an improved regulating circuit for energizing variable resistance loads in such a way as to prevent the application of excessive currents to the load when the resistance thereof is at low values and for controlling the current flow during normal operating conditions.

In accordance with the invention, a saturable reactor having a main winding constructed of two sections magnetically in opposition to each other is arranged in series with'a load circuit so as to supply alternating current thereto. The winding sections of the reactor may be connected in series or in parallel with respect to each other provided their magnetic circuits are in opposition. A pair of control windings which are magnetically coupled with both sections of the main winding are arranged to be energized with direct current. One of these control windings is supplied from a controllable source of direct current of such value that the current supplied through the main winding of the saturable reactor cannot damage the load. The other control winding is arranged to be energized by direct current which is dependent upon the volt-.

age of the load only after the load voltage has reached a predetermined value such as eighty percent of its normal value.

The principle upon which the invention is based is that the average load winding ampere turns of the saturable reactor must be equal to the average control winding ampere turns so long as the saturable reactor is operating in the proportional region.

A comprehensive discussion of the characteristics of saturable reactors can be found in a paper presented by H. F. Storm before the American Institute of Electrical Engineers in May of 1950 and which apears at page 756, vol. 69, part II, of the transactions of the American Institute of Electrical Engineers.

For a better understanding of the invention, reference may be had to the following description taken in conjunction'with the accompanying drawing, in which:

Fig. 1 is a schematic representation of a regulating arrangement embodying the invention;

nited' States Patent Fig. 2 is a pair of load voltage versus load current characteristic curves to aid in understanding the principles of the invention;

Fig. 3 is a schematic diagram illustrating some of the constructional features of the saturable reactor utilized in carrying out the invention.

With reference to Fig. 1, electronic tubes 1 and 2 are provided respectively with filament elements 3 and 4. The filaments 3 and 4 are respectively energized by the secondary windings of transformers 5 and 6. The 'primary windings of transformers 5 and 6 are energized from a secondary winding of a potential transformer 7 whose primary winding is energized from an alternating current source through the switch member 8. Arranged in series with the secondary winding of the transformer 7 are the parallel-connected main windings 9 and 10 of a saturable reactor generally designated by the numeral 11. Saturable reactor 11 is also provided with a pair of control windings 12 and 13 which are arranged so that the magnetomotive forces thereof are in opposition to each other. The saturable'reactor 11 could be physically arranged in any known manner. For example, the main windings 9 and 10 could be disposed on the outer legs of a threelegged core, and the two control windings 12 and 13 could be mounted on the middle leg of the three-legged core. The main windings 9 and 10 could be connected in series if desired, but in either case their magnetic circuits must be in opposition as indicated in Fig. 3.

Control winding 12 is energized through an adjustable resistance 15 from a source of direct current energy indicated at 14 in the form of a conventional rectifier arrangement. The rectifier arrangement 14 is energized from alternating current derived from the secondary winding 16 of the transformer 17 having a primary winding 18. The primary winding 18 of transformer 17 is energized from a secondary winding of a stepdown transformer 19 whose primary winding is arranged to be energized from the alternating current source through the switch 8. Capacitor 20 and a portion of the secondary winding 16 of transformer 17 comprise a voltage stabilizing means which maintains constant voltage output irrespective of variations in the voltage of the alternating current source.

Thus, it will be understood that by suitable adjustment of the variable resistor 15, a desired magnitude of direct current is supplied to the winding 12 so that a predetermined magnitude of current is supplied to the filaments 3 and 4 through the transformers 5 and 6, the saturable reactor 11 being essentially a constant current device which supplies a constant magnitude of current substantially independent of the resistance of the load and determined by the magnitude of the direct current supplied to winding 12. As the filaments 3 and 4 warm up, their resistance increases and the voltage thereacross increases since the current is maintained at a substantially constant value.

In accordance with one feature of the invention, control winding 13 is energized in accordance with the load voltage, and at such time as the resistance of the filaments 3 and 4 reaches a value such as eighty percent of its normal operating value, winding 13 begins to effect control of reactor 11. To this end, a transformer 21 having a primary winding 22 and a secondary winding 23 is connected in parallel with the primary windings of the 'transformers 5 and.6, and a rectifier arrangement 24 is arranged to be energized from a secondary winding 23.

Connected across the direct current output terminals of the rectifier 24 is a smoothing capacitor 25 and a bias resistor 26. The voltage across the bias resistor 26 is I unidirectional conducting device 28 and the resistor 29. From the circuit described thus far, it will be understood that the various elements could be selected and adjusted so that no current would flow through the winding 13 until after the voltage of the load and, hence,'the voltage of the secondary winding 23 of the transformer 21 reaches a predetermined value. At such time as the voltage of the load increases to a predetermined value, a current then begins to flow through the control winding 13, the rectifier 28 being effective to prevent reverse fiow of current through winding 13 when the load voltage is below the above-mentioned predetermined value. b

In accordance with a feature of the invention, the magnetomotive force of the winding 13 is arranged so as to oppose the magnetomotive force of the winding 12. Thus, during the initial portion of the warm-up period, the .winding 12 and the main windings 9 and 10 act as a constant current device-to supply substantially constant current to the filaments 3;and-4. Thereafter, when the resistance of these filaments increases to some amount such as to eighty percent of its normal value, then a current begins to flow through the control winding 13, the magnitude of which increases as the magnitude of the load voltage increases. Since the winding 13 opposes the magnetizing action of the winding 12, the eifect of the winding 13 is to tend to reduce the voltage across the load and also the current thereto.

The particular operation of the circuit described above will be more fully understood from Fig. 2. In Fig. 2, two curves are plotted of load voltage against load current, one .curve being for control ampere turns of 509 such as might be efiective with only winding 12 energized,

i. e., with control winding 13 deenergized, and the other.

being'for control ampere turns of 400 such as might be the effective-net ampere turns when both opposed control windings are energized. Thus, from Fig. 2, it will be understood that approximately 159 percent load current could ,be drawn with the filaments cold and with control ampere turns of 500. As the load is warmed up, 100 percent load is achieved with the filaments hot due to the reduction in net ampere turns due to the opposing effect of winding 13 and winding I12.

From the above description, it will be understood that by the invention the magnitude of current is limited initially due to the saturable reactor 11 acting as an essentially constant current device and thereafter the loadcurrent is reduced due to the regulating effect of thedwinding 13'which is responsive to the voltage of the loa ,In ordertop'revent an excess current from being supplied to the filaments 3 and t at the instant the switch 8" is closed, a relay 30 is, provided having its normally closed contacts 31 connected across the primary windings of the transformers 5, 6 and 21. Thus, it is impossible to supply an excess current to the filaments 3 and '4 so long as the short circuit maintained. Shortly after the switch 8 is closed and at such time as the high inrush current will have diminished to a safe value, the timedelay relay 32 closes its contacts 33 so as to energize the coil of relay 3t) thereby to cause the contacts 31 to be opened'and'the short circuit removed from across the primary windings of the transformers 5, 6 and 21.

'While' I have described and shown a particular embodiment of the invention, I'do not wish to be limited;

theretoand intend in the appended claims to cover all such changes and modifications asfall within the true spint and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a source of alternating current, a load connected thereto, a saturable reactor having a main winding constructed of two magnetically opposed sections, said winding being in series with said load, a pair of control windings magnetically coupled with both of said sections of said main winding, an energizing circuit independent of said load for supplying controllable direct current to one of said control windings so as to maintain the current to the load at a predetermined value, and circuit means coupled to said-load and responsive to the load voltage for supplying direct current to the other of said control'windings for values of load voltage in excess of a predetermined value.

2. In combination, a source of alternating current, a load connected thereto, a saturable reactor having a main winding constructed of. two magnetically opposed sections, said winding being in series with said load, a pair of control windings magnetically coupled with both of said sections of said main winding, an energizing circuit coupled to said source and independent of said load for supplying controllable direct current to one of said control windings, and circuit means coupled to said load and responsive to a quantity which is representative of the load voltage for supplying direct current to the other of said control windings, the magnetomotive force of said control windings being in opposition and the resistance of the load being, substantially greater when at normal operating temperature than when at ambient temperature, and means in said circuit means to prevent the flow of current to said other control winding when the load voltage is ;below a predetermined value.

3. An arrangement for regulating the supply of current to the filament of an electronic tube, comprising a source of alternating current, a-load including a filament of an electronic tube connected thereto, a saturable reactor hav- :ment for energizing one of said control windings, so as to tend to maintain a substantially constant current to said filament irrespective of'the resistance thereof, a source of direct reference voltage, means in circuit with said alternating current-source andsaid load for deriving a voltage proportional to the load voltage, and uni-directional conducting means for connecting the other of said control windings between said-source of direct reference voltage and said voltage derivation means, said uni-directional conductingmeans being poled in a direction to enable the flow of current-through said other control winding only when said derived voltage exceeds said direct reference voltage.

4. The arrangement as defined in claim 3 further com prising means normally short circuiting said load and said voltage deriving means to prevent supply of overcurrent thereto, and time-delay means for disabling said shortcircuiting means when the resistance of said filament has attained a predetermined value.

Referenccs Cited in the file of this patent UNITED STATES PATENTS 2,278,151 Runaldue Mar. 31, 1942 2,331,411 Mila'rta ,Oct. 12, 1943 2,549,782 Engleman Apr. 24, 1951

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