US2542468A - Electrical regulator - Google Patents

Description

Cn V. BOCCHARELLE ELECTRICAL REGULATOR Filed April 15, 1949 LiggmmkwmwxwwwwxmwQ JNVENToR. 4cfm@ y. .50ccm/mu enanas ses. 2o, resi UNITED 5 STATES PATENT -oFFIIcE U f 2.54am

Carlo V.

Park, Pa., assignor to Applicatim April 13, 1949. Serial No. 87.150

8 Claims. (Cl. 20L-72) The present invention relates broadly to voltage regulators and, more particularly, to passive resistive elements which exhibit al pronounced non-linear relationship between the voltage applied across them and the current flowing through It is well known that in electrical systems which comprise a generator, a power supply, and a load suitably coupled thereto. it is often essential ,to maintain a constant voltage across the `load in the face of varying values of power supply output voltage and load current.

The relation between the load voltage under these varying conditions and the load voltage under predetermined normal conditions is termed regulation, the regulationbeing said to bel good when changing conditions produce little or no change in'load voltage and poor when the opposite is true. It is in this sense that the above terms are used in the subsequent discussion.

When the inherent regulation of an electrical system of the type hereinbefore described is poor, recourse is often had to some type o! voltage regulating device which is ordinarily connected intermediate'tbe power supply and the load, for the purpose o'f improving this regulation.

Such a device may be a so-called non-linear resistor which is characterized in that, over a certain range of values of current flowing therethrough, the voltage across its terminals remains substantially constant. The manner in which such a resistor maintains the load voltage constant is described in more detail hereinafter.

This type of voltage regulating resistor has, in the past, usually taken the form of a carbon-pile regulator which consisted oi' a stack of contacting carbon disks maintained under pressure.

While satisfactory for some applications, this carbon-pile regulator suffered from a. number of serious defects. For example, it was unstable inasmuch as its regulating voltage was subject to unpredictable nuctuations. It was also practically useless at high voltages since it was subject to sparking at the Junctions between adjacent disks with consequent deterioration of the pile.

0n the other hand, a voltage regulating resistor constructed in accordance with my invention is comprised, in general terms, of a single compact column of silicon carbide granules arranged within that column in a manner hereinafter described; The basic features of composition, construction, and of the conduction process which characterize my novel device combine to free it of the defects hereinbefore described. In addition, its regulating lvoltage is readily adjustable and its characteristics capable of complete design.

It is, accordingly. a primary object of my invention to provide a novel voltage regulating resistor.

It is another object of my invention to provide a voltage regulating resistor having readily adjustable regulating voltage.

Still another object of my invention resides in the provision of a voltage regulator which is stable over the operating-rangefor which it is designed.

A still further object of my invention resides in the provision of a voltage regulator which is of simple and sturdy construction. v

Theseand other objects of my invention will become more readily apparent from a consideration of the following discussion in conjunction with the accompanying drawings where Figure l is a schematic representation of an electrical system which comprises a voltage regulator and which will be used to illustrate some of dthe general properties associated therewith: an

Figure 2 is a representation of avoltage regulating resistor embodying my invention.

As has been briefly pointed out in the preceding discussion, voltage regulators are usually inserted intermediate a power supply and its load. This is schematically illustrated in Figure 1 to which more detailed reference may now be had. In this figure. there is showna power supply l0, a voltage regulator il of the non-linear resistive type here under discussion, and a load I2, all connected in circuit relation. It will be understood that while power supply in and load l2 may assume any desired form, they are shown in Figure 1 intheir conventional schematic representation, power supply i0 taking the form of a simple voltage generator G in series with an internal impedance Za, the output voltage thereof being developed across terminals I3 and Il and being equal to the voltage generated by generator G less the voltage drop across internal impedance Zo due to the current flowing therethrough. Load il is represented schematically by an impedance connected to the output terminals of the power supply. The regulator Il is represented as an impedance connected in shunt with the load impedance. The operation o! such a system is so well known that a brief recapitulation here will suflice. The load voltage-which it is desired to maintain constant-will be equal 3 to the voltage across terminals I3 and Il and thus equal to the voltage generated by generator G less the voltage drop due to current flowing through internal impedance'Zc. The regulator, being in parallel with the load, will, of course, have the same voltage applied to its terminals. Current will now through the load and through the regulating resistor, the proportion of the current flowing through each being inversely related to their relative impedance values. An increase in generated voltage above its desired value, due to any cause, will result in an increase in the terminal voltage of the power supply and thereby in the voltage across the load and regulator impedances I2 and II. If the voltage regulator II is operating properly, its effective impedance will tend to decrease in response to the increase in voltage thereacross, thereby drawing increased current from the power supply. This in turn increases the voltage drop across the internal impedance Zo of the supply, thus lowering its terminal voltage until the desired condition of supply and load voltage has been reestablished. The converse phenomenon of course takes place if the generated voltage should decrease. Should the load current, on the other hand, increase (due to a decrease in the value of the load impedance), this would cause increased current drain from the power supply, with attendant increased voltage drop across its internal impedance and lowering of the terminal and the load voltage. This lowering of voltage would also be sensed by the regulator which would again react by increasing its effective impedance, thereby reducing its own current drain on the power supply and compensating for the increased current drain due to the load until the terminal voltage of the supply and, simultaneously, the load voltage are restored to substantially their desired value. Here again a similar reasoning process will explain the converse behavior.

summarizing then, changes in voltage across a regulator of the type under discussion produce non-linearly related changes of current therethrough in the region in which it provides regulation. In fact, in that region, at any rate, a small increase in voltage produces a relatively large increase in current, while a small decrease in voltage produces a disproportionately large decrease in current. This characteristic is used to impart voltage regulation to an electrical system in the manner hereinbefore outlined.

A regulator which operates in the manner hereinbefore described is illustrated, partly in crosssection, in Figure 2, to which more detailed reference is now made. Such a regulator comprises, in general terms, a column of silicon carbide granules collectively designated by reference numeral I5, the arrangement of these granules in the column being discussed in more detail hereinafter. In its preferred form this column is cylindrical in shape and is enclosed `in a closely fitting cylindrical container I6 constructed of some suitable heat-transmissive material such as glass. A solid electrically conductive plug I1 closes one end of the container I6 while pressure is applied to the silicon carbide column, at the other end thereof, by means of a plunger I8 backed by a spring I9. A rigid insulating cylinder may be provided to enclose the entire structure and to provide support for plug I'I at one end and for pressure spring I9 at the other. This cylinder is preferably constructed of two portions 2l and 22 in threaded engagement with each other, this arrangement serving the double purand of providing a ready adjustment of the ten` sion of pressure spring I9, thelatter being accomplished by varying the degree of engagement of the two sections. Both the plunger I8 and plug I1 may be carried through the end walls of the insulating cylinder and terminated in some suitable terminal arrangement such as lugs 23 and 2l for connection to associated circuit elements. It will be apparent that several features of primarily mechanical significance are also found in the preferred embodiment. For example, the conductive plunger is provided with a shoulder 25 which prevents the end of the plunger from being inserted overly far into container I8. A spring retaining shoulder 26 is also mounted on plunger I8 for obvious reasons. 'Ihe inside diameter of insulating cylinder 2li is preferably considerably larger than would be required to contain the silicon carbide column and its immediate container I6. This makes it unnecessary to maintain very close tolerances of either the outside of container I6 or the inside of insulating cylinder envelope 20. If this latter tightly surrounded the former, unnecessarily close tolerances would, on the other hand, have to be maintained therebetween, in order to prevent fracture of container IB.

While these several features are principally matters of mechanical and manufacturing convenience and, consequently, do not constitute essential characteristics of my invention, there are a number of others which have a pronounced effect upon the performance of this regulator in accordance with my invention. It is toward f these significant features that the immediately subsequent discussion is specifically directed.

To begin with, the silicon carbide granules are placed in container I6 loosely, that is, preferably, without an intervening binding material. In addition to that, they are align By aligned it is meant that they are placed in such relative positions as to occupy the least practicable volume for a given weight. This may be accompllshed, for example, if the filling of the envelope is carried out while a strong axial electric field is being applied to the envelope and its contents. Such a field will cause the granuleswhich may be regarded as roughly ellipsoidal in overall appearance and each having several pointedprotuberances-to occupy positions which, on `the average, bring the orientation of their longitudinal axes into coincidence with the field direction and therefore also withthe longitudinal axis of cylindrical container I6. It should be pointed out. in this connection, that the shape of these granules is, ordinarily, highly irregular. lHowever to the naked eye and under low power magnification, they appear as amorphous bodies of the roughly ellipsoidal form hereinbefore described, which are provided with a few pointed protuberances. Since this macroscopic delineation is sufficient to clarify the various features of the invention, the physical description of the granules will be confined thereto. While the basic phenomena of conduction which underlie the principles of operation of such a voltage regulator are not fully understood, it is believed that this orientation of the particles results in statistically bringing,r the points of the protuberances of one into contact with the surface of the adjacent ones, thus establishing an apparently highly desirable form of point-to-surface contact. When the silicon carbide granules are thus aligned, the regulator exhibits considerably improved regulatlon in the sense that there is considerably less change in voltase across it for a given change ln current through it, within the range of application o! the regulator. In addition, this alignment of the granules succeeds in substantially reducing the tendency of a regulator constructed in accordance with my invention to exhibit voltage-current hysteresis, this being a phenomenon characterized in that `the magnitude of the current resulting from increasing the voltage to a predetermined value is different from Ithe magnitude of the current resulty ing from decreasing the voltage to the same value.

' It is clear that such a phenomenon. which, in eilect, makes the regulating characteristic dependent upon the past history of the regulator, may be highly undesirable in many applications, and that its elimination, by' virtue ofthe granule alignment hereinbefore described, constitutes an important feature of my invention. It is apparent that alignment within the meaning of the term as hereinbefore deilned may be obtained by other means than by application of the aforementioned electric field. For example, vibration applied to container i6 may result in the silicon carbide granules settling into the desired pattern, as well as a combination of vibration and application of the electric held. Thus, oniy the aligned relationship of the granules, as opposed to the method by whichthis alignment is attained, ia an essential feature cf my invention.

Attention is particularly directed to the fact that the nature of the container which encloses .theslicon carbide granules plays a significant role the performance of the regulator, inasmuch as its proper choice also tends to reduce the hysteresis etl'ect hereinbefore described. This Lis due to the fact that, if the silicon carbide is enclosed `in a container made of heat insulating material, then the temperature at the previously described point-to-surface contacts between the individual granules becomes a function of the previous history of the regulator. Since this temperature appears to have considerable influence on the conductivity, the latter will also be ailected and voltage-current hysteresis result. 0n the other hand, the provision of a heat transmissive container facilitates the dissipation of heat from these contacts and renders the conductivity of the regulator more nearly independent of its past history. It is on the basis of these considerations that the preferred embodiment. as hereinbefore indicated, comprises a container made of a suitable heat transmissive material.

Although silicon carbide granules tend to take the form of somewhat oblong particles, their size may be made to vary over a considerable range. This size has an important. though indirect, bearing on the regulating characteristics o! my novel regulator. I have found that the regulating voltage is directly proportional to the number of grains per unit height of the column, and

hence indirectly proportional to grain size. Thus it would appear that decreasing the granule size would result in increasing the regulating voltage provided the column height is held constant, and this assertion is borne out by experimental evidence.

The current through the voltage regulator, on the other hand, is roughly proportional to the number .of granules per unit of cross-sectional area. Thus the conductivity of the regulator decreases approximately with the square of the narrow dimension of the granules. From the above, it is clear that it is a simple matter to design a voltage regulator in accordance with;

spring-loaded plunger applied a compressional force of readily adjustable magnitude. This application of pressure may be made to serve an important purpose in connection with my novel regulator in that it may, within limits, control the regulating voltage of the regulator. It will 4be understood that this regulating voltage is primarily a function of the physical dimensions of the silicon carbide column, particularly when considered with reference to the size of the individual granules in the manner hereinbefore described. However, by the application of pressure it is possible to change this regulating voltage to come extent. In general, increased pressure causes lowering of the regulating voltage, it being understood that it is desirable to maintain some ininhnum pressureon the column at all times in order te insure satisfactory contact between in= dividual granules.

Finally, mention shouid be made of a feature which has not been previously treated because it is inherent in the operation oi' my novel type of voltage regulator as described in connection with Figure l.. Reference is had to the fact that some current continuously ows through the regulator regardless of whether the load is open circuited or has some finite value of impedance. 'Ihis current.; termed stand-by current, may constitute a substantial fraction of the total current drawn from the power supply, and it inevitably increases, sometimes prohibitively, the current requirements or such a supply. It is there- Vfore highly desirable to maintain this stand-by current at its minimum permissible value for any given value of desired regulating voltage. Fortunately, this is inherently achieved in the pre ferred embodiment of my invention. Speciilcally. it is the appropriate application of pressure to the silicon carbide column as hereinbefore described, which. simultaneously with its other effects, results in keeping the value of the stand-by current at a. virtual minimum for any particular set of operating conditions.

Although the invention has beendescribed with reference to a single preferred embodiment, its principles have been set forth in sufiicient detail to enable those skilled in the art to design and construct other useful apparatus embodying these principles and adapted for other particular applications. Accordingly, I desire my inventive concept to be limited only by the scope of the appended claims.

I claim:

1. A voltage regulating circuit element comprising: a compact column of silicon carbide granules of roughly ellipsoidal form, the longi tudinal axis of each of said granules being disposed in substantial alignment with the-longitudinal axis of said column, and means for applying a compressional force to said column.

2. A voltage regulating element comprising: a compact'column of aligned siliconv carbide granules and a pair of electrically conductive connectors, one ofsaid connectors contacting one end oi' said column and the other of said connectors contacting the other end of said column.

3. A voltage regulating element comprising: a

. cylindrical container;

anales heat transmissive, electrically non-conductive. a compact column of aligned silicon carbide granules enclosed within said container and a pair of electrically conductive connectors, each of said connectors extending into a corresponding end of said container and contacting the end of said column adjacent said corresponding end ol' said container.

4. A voltage regulating element comprising: a heat transmissive, non-conductive. open-ended cylindrical container; a compact column oi aligned silicon carbide granules enclosed within said container; an electrically non-conductive cylinder spaced from said nrst container; a first electrically conductive plug extending into said cylinder and contacting one end of said column, said plug being provided with a shoulder for retaining said plug in ilxed relation to said cylinder; a second electrically conductive plug extending into said cylinder and contacting the other end of said column. said second plug being provided with a spring retaining shoulder; and a compressed helical spring arranged in concentric relation with said second plug and disposed intermediate said spring retaining shoulder and that wall of said cylinder through which said second plug extends, said spring applying predetermined pressure to said column via said second plug.

5. Apparatus according to claim 4 characterized in that said cylinder is comprised of two longitudinal sections. in adjustably threaded engagement with each other, whereby the degree of compression of said spring may be varied, thereby adjusting the pressure applied to said column via said second plug.

6. A voltage regulator adapted to maintain the voltage across an electrical load, when in shunt circuit relation therewith, substantially constant under varying conditions of supplied voltage and load current, said regulator comprising: an electrically non-conductive, heat ive con- 8 tainsr. a column oi silicon carbide particles longitudinally enclosed by said container, an electrically conductive plug closing one of the narrow ends of said container and intimately contacting said column, a longitudinally insertable, electrically conductive plug closing the other narrow end ci.' said container and intimately contacting said column, and a compressionally adjustable pressure springA backing said insertable plug. whereby the compressional torce exerted on said column by said spring via said insertable plug may be varied.

7. A shunt-type voltage regulator comprised of a, compact column of silicon carbide granules, an electrically non-conductive, heat-transmissive container enclosing said column. and a pair of conductive elements penetrating said container Aso " REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 1,325,889 Curtis Dec. 23, 1919 1,543,083 Marshall June 23. 1925 2,329,085 Ridgway Sept. 7, 1943 FOREIGN PATENTS Number Country Date 27,961 'Great Britain Dec. 12, 1912

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