US2025093A - Inductance device - Google Patents

Description

Dec. 24, 1935. w p COTTER ET AL, 2,025,093

INDUCTANCE DEVICE Filed Oct. 26, 1952 ATTORNEY Patented Dec. 24, 1935 UNITED stares FATi'i'i FFEQE field, Mass Bosch ration of New York assignors tion, Springfield, ltiiass, a corpoto United American Application October 26, 1932, Serial No. 639,599

3 Claims.

This invention relates to improvements in inductance devices, and more particularly when employed in the low pass network of a radio power supply unit, as a eactor.

The object of this inventn is to provide a reactor which automatically assumes a maximum value of apparent inductance over a wide range of direct current through the reactor.

Another object of this invention to provide an inductance whose value remains more nearly constant under a direct current flow of wide variation.

Another object is to enlarge the direct current carrying capacity or rating of an inductance without havin the value thereof drop to a point so low that it becomes useless as a filter element in radio power systems.

Still a further object is to provide an inductance having rigid elements but with a core so designed to present the effect of having a variable air gap, which changes .vith the degree of core saturation.

Other objects and improvements will become apparent when the following description is read in view of he drawing and diagrams in which:

Fig. 1 shows a side elevation of an inductance device according to our invention; Fig. 2 is a side view of same; Fig. 3 is a diagram showing the variation of effective A. C. inductance value with the load current; and Fig. t presents an outline of one method of using our invention.

The same numerals identify the same parts throughout.

It is well known in the art that reactors may be designed for efiicient operation at specified values of direct current in the winding. For example, an iron core reactor may be designed with an airgap which will give a maximum value of apparent inductance at one particular value of direct current. However, for lower values of direct current the apparent inductance is not as high as it would be if the airgap were made smaller. Also for higher values of direct current the apparent inductance is not as high as it would be if the airgap were made greater.

In this design of radio power supply systems the object desired is to attain stable output voltage under fluctuating current drain and at the same time maintain the values of the filter elements, or the LC ratio relatively constant, in order to remove the hum producing fluctuations of the rectifier output. There is no difficulty in designing an effective filter section containing the inductance and capacitance necessary to make it effective at the hum frequency provided the current drain from the system is constant. In certain practice the current drain is not constant, for the tubes draw cu rents in proportion to the constantly fluctuating volume level of the program. This can es a changing direct current 5 through the windings of the inductance or filter choke, and results in a varying degree of magnetization in the core thereof. Under severe current conditions the core becomes saturated, the effective reactance of the choke to the A. C. component of the rectifier output becomes very low, and a poor filter .g action results. The effective A. C. inductance of the choke changes with the degree of magnetic saturation and the net r ult, when combined with a fixed amount of c acity, is a circuit in which the element relation and therefore the filtering effectiveness varies widely.

In lov. pass filters as used in radio power sup ply systems, values of capacity and inductance '20 are chosen which will have a cut-off at some frequency below that of hum. The product of these two factors should remain constant in order to retain any given cut-ofi frequency. It is obvious, therefore, that if the value of inductance drops while the capacity stays constant, the cutoff frequency will be raised and a larger percentof hum component will pass through the filter. We propose to remedy this state by providing an inductance or choke whose efiective A. C. inductance remains more constant under a wide variation in current how, and whose general effectiveness does not drop severely when subjected to heavy current.

To explain the function and utility of the invention reference is first made to Fig. 4 wherein l ndicates the primary of an alternating current transformer and 2 a vacuum tube rectifier having a cathode 3 and a pair of anodes 4. The cathode 3 is heated by current from a coil 5 inductively related to the coil i and one pole of the cathode is connected to a lead 5. The anodes 4 are each united to a separate extremity of a secondary coil inductively related to the coil l and the numeral 8 indicates another lead united to the mid-point of the coil 1. In the line of the conductors 5 and H is an inductance 9 according to our invention and the two leads II and 8 are bridged by a condenser it.

To obtain proper filtering and voltage regulation the inductance is made as shown in Figs. 1 and 2, wherein the numerals i2 and i2a indicate the two sides of a magnetic frame having ends l3 and a transversely extending portion M in the middle which serves as a core for the turns of a coil l5. The side l2, ends l3 and middle portion I4 are made in one piece laminations in the form of an E, while the side We which bridges the faces of the ends I3 and middle portion i4 is separately constructed and is of variable cross section as indicated in Fig. 2. For example, the side l2a will be of varying width and comprises portions at, b, c and d, the portion (1 making contact with the surface of the ends I3 and middle portion it, while the portions or sections 1), c and d, which are rigid with section a, are separated from the terminal face of the ends 13 and portion i 4, by air gaps of progressively greater extent. The entire magnetic circuit of the coil l5 can, of course, be laminated and all of the parts will be rigidly secured to one another. 7

The efiect of a magnetic circuit, such as shown in Figs. 1 and 2, is illustrated in Fig. 3, wherein the curves a, b, c and (1 indicate the relation between the product of the current and number of turns of the coil to the inductance L for each of the sections a, b, c and d. The values of the effective A. C. inductance L are plotted as ordinates and the values of the product of the number of turns and current are plotted as abscissas so that it will be seen that the inductance drops as the ampere turns increase. The line [6 represents the combined or resultant effect.

When a small D. C. current is passed through the winding E5, the magnetic fiux is substantially confined to the core section a. When the current is increased, the flux is shifted toward the stepped sections b, c and :1 according to the proportionate current intensity. This action gives the effect of altering the airgap and the reluctance of the magnetic circuit to suit the needs of the momentary current intensity. Thus the tolerance of the choke to what would ordinarily be overload currents is materially increased, likewise the drop in A. C. inductance value usually associated therewith is substantially reduced, and the inductance is maintained automatically in proper relation to the D. C. current flow to produce eificient regulation.

This invention is highly satisfactory in practice, is inexpensive to build, and is of smple construction. The performance and characteristics are certain, and all likelihood of functional derangement is avoided.

While we have shown and described our invention as applied to a particular system and as embodying the various devices indicated, changes and modifications therein will be obvious to those skilled in the art and our object is therefore to cover all such changes and modifications as fall within the true spirit and scope of our invention.

What we claim is:

1. In a radio power supply device, the combination of a rectifier and a filter circuit connected to the output of said rectifier, said filter circuit including a series connected inductance and a condenser connected across said circuit at the output side of said inductance, said inductance comprising a winding around a laminated core, said core being formed with paralleled stepped airgaps therein of successively differing lengths.

2. In a radio power supply device, the combi nation of a rectifier and a filter circuit connected to the output of said rectifier, said filter circuit including a series, connected inductance and a condenser connected across said circuit at the output side of said inductance, said inductance comprising a winding around a laminated core, one side of said core being formed with paralleled stepped airgaps therein of successively increas-r ing extent.

3. In a radio power supply device, the combination of a rectifier and a filter circuit connected to the output of said rectifier, said filter circuit including a series, connected inductance and a condenser connected across said circuit at the output side of said inductance, said inductance comprising a winding around a laminated core, said core having paralleled stepped airgaps of successively increasing extent formed in a horizontal side thereof.

WILLIAM F. COTTER. MARION E. BOND.

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