US3004209A - D.c. regulator and control circuit - Google Patents

Description

Oct. 10, 1961 K. J. KNUDSEN 3,004,209

D.C. REGULATOR AND CONTROL CIRCUIT Filed May 1, 1957 INVENTOR. Knud .J. Knudsen 3,004,209 DJC. *AND CONTROL .Knnd d. Knudsen, Middlebury, 'Gonm, nssignor to iiewis Engineering #OompanmrNaugatuck, Conn.,- a corpora- .tiontof Connecticut Filed gday 1', 1957, \Ser. .No. 656,422

Claims. 1323-42) This invention'relatcs to electrical regulators for maintaining voltages constant, and more particularly to low- ,power 'D.-'C. voltage regulators.

An object of the invention is to provide a novel and improved transistor and crystal diode type D.-C. voltage regulator adaptable for use with normally constant .loads, which regulator counteracts, by means ofa variable voltage drop, variations in the supply voltage so as to hold the voltageapp'lie'd to a load within very narrow limits.

Another object of the invention is to provide an improved ED.-C. voltage regulator as a'bove set forth, which employs a load-carrying drop resistor of nominal resistance in the circuit ,prov'idingthe counteracting effect on the Voltage variations in the supply.

A further object of the invention is to provide a novel and improved D.-C. voltage regulator with load-carrying drop resistor as characterized, wherein the counteraction of the voltage variations follows the effecting of disproportionate variable auxiliary 'load currents in .thesaid drop resistor.

Yet another object of the invention is .to provide .an improved 'D.-'C. voltage regulator having a .transistor, crystal diode and drop resistor as above outlined, wherein the variable load=current .is eifected by a variable auxiliary loading .imposed .by the transistor .output .circuit, and wherein the transistor input. circiiitrecivessignals which are responsive -to the variations in .the voltage of the supply.

.A -feature of the invention resides in the,provision .of .an improved, 'transistor-.typeD.lC. voltage regulatoremp'loying .a load-carrying drop resistor, wherein any .rise or ran in the supply voltage .causes .a-flisproportionate change .in a relatively smaller voltagctdrqp across the load-carrying ilrop. resistor, thereby .toefr'ect compensation .for .such change which is either-equal .-.or,proporftiona'l and oppoitedhercto under all normal-operating conditions.

A further ob'ject -of invention is to ;-.provide .an improved .pyrometer Lbridge .having novel and effective .col'dijunct'ion control orscompensation which is not-only very simple but extremely effective in reducing error .caused by the .cold ,junction of zthettherrnooouple.

Another feature .of the invention resides in the provision of aniimproved pyrometer bridge with novel cold junction .compensat'ion, :wherein, ineigpensive :and .:readily available metals .are .used-in the .legs of the bridge, ;to ettect the compensation.

Still .another. object .of .the .-invention .is zto provide a pyrometer Lhridgerhaving .novel .and improved cold junction compensation s tilizinginenpensiveand readily available metals .to constitute .compensatingmesistors, wherein the correctresistance values maylbereadily-and accurately determined 11y relatively simple formulae.

-Otherfeatures and advantages :willhereinafter appear. Tln the accompanying .drawing, .the single .figure is a schematic circuit .diagram .of the novel .D.-C. voltage regulator and compensated ,pyrometer bridge, :as @rovided by the invention.

Referring .now .to the drawing, .there is shown .a dottedhlock outlineindicated at .10,.a,pyrometer.bridge .Ply 1(not shown) which ,may .be connected .to -.a .trans- 3,004,209 Patented Oct. 10, 1961 "ice having a common positive terminal or cathode 20, thereby to effect full-wave rectification of the secondary output at a voltage somewhat 'less than half that of the second-' ary coil. To smooth out the ripple .in the rectified voltage, a filter capacitor 21 is provided, connected be- ;tween the positive supply terminal 20 and a ground 22. The above transforming and rectifying means for the voltage supply may also have a resistor 23 connected to the positive terminal 20, to provide for adjustment of the voltage valueas required by the bridge .load. The voltage :between the output terminal wire 2.4 .of the resistor 23 and the ground is thus available for supplying the bridge load referred to and located in the broken outline 10, such voltage 'being subiect to variation because of variations in the voltage applied .to..the input terminals '12, .13 of the transformer.

-In accordance with the .present invention 1 provide a .novel and improved D.-.C. voltage control .or regulator unit having ,a transistor and a .crystal .diode, which unit is characterized by the inclusionof .a drop resistor-and a variable auxiliary loading circuit connected .to the fixed main load. The said drop resistor ismade tocarry load currents. changing disproportionately with variations in thesupply voltage, wherebyits changing, relatively small voltage drop automatically compensates .for said variations so .as .to maintain .a constant voltage .at .an ;output terminal of the resistor, for energization of .the bridge circuit. As shown, this loadrcarrying resistorris indicated at 25 .in the figure, and has one terminal connected with the wire '24,.and .a second or output terminal connected 'to1a wire.26'the voltage of which -.(.with.respect.to ground) is maintained substantially constantdespite .fluctuations within aspecifiedrange'in the voltage :appliedto .the input terminals '12, 13 of the {transformer ,11. The resistor 25 is also termed a second .drop resistor, in -the appended claims.

In attaining such constant voltage at {the terminal -.or wire 26, I pass variable current .throughthe dropresistor 25 by means oiauxiliaryloadingimposedzby atransistor 27 having a base 28, collector ,2Q,.andemitter .30. ZI -he transistor 27 .may be advantageously .of .the :type classi- .fied as 'NPN, connected so .that .its .emitter is -.common to both the output circuit of the transistorand the ,input circuit thereof. .I connect the transistor output circuit so as.to effect an auxiliary loading through the drop .resistor 25, such loading varying automatically in responseto variations in the voltage applied -.to the trans- .former terminals 12, .13 by virtue of :a signal voltage impressed on the transistor input circuit, .which signal voltage changes with the voltage applied .to the .transformer.

By'this invent-iontheltransistor 27 and the circuitthereof are arranged in a novel manner, inconjunction-with a 'crystal-diode-and otherdrop resistors, to effect such variable auxiliary loading for the purpose specified. Ac-

cordingly, as. shown, 'I-'connect the emitter 30 to a ground .said variable'manner. The above connections constitute :the output :or auxiliary loading circuit of :the transistor 27. ilhe resistor 34 serves ito :establish a constant power dissipation on the transistor, effecting -.operation which is .-.free efromtcreep due to :local temperature change of the base The transistor input circuit, ihereinafter also 36, in accordance with this invention, by the provision of a crystal diode 40 connected between the wires 37 and 24 with its polarity opposing current flow from the wire 24 to the ground 38. Considering that the supply line comprising the resistor 23 and wire 24 is positive and that the grounds are negative, the crystal diode 40 is so connected as to operate under reverse breakdown, by having its positive terminal or cathode connected with the wire 24. The crystal diode 40 thus acts as a reference, in the manner of voltage regulator tubes, and will exhibit a substantially constant breakdown voltage across its terminals.

I have found that with a voltage output of 28 at the wire 20, and using a 500 ohm value for the resistor 36, a fairly constant voltage of 7.4 may be produced across the terminals of the crystal diode 40. In consequence of this, variations in the voltage applied to the transformer input terminals 12, 13 will cause the relatively smaller voltage drop across the resistor 36 to vary disproportionately. I have further found that by making the resistor 34 similar in value to the resistor 36, and by making the series load carrying resistor 25 so as to have a value of ohms, in

conjunction with the constant main load represented by the bridge circuit, it is possible to obtain at the output terminal 26 of the resistor 25 a very constant voltage measured to ground.

This is accomplished as follows: Changes in the supply voltage applied to the terminals 12, 13 of the transformer -11, causing the said disproportionate changes in the relatively smaller voltage drop across the resistor 36, will provide a varying input signal for the transistor 27 which thereby varies the auxiliary load effected by the output circuit thereof which is connected to the drop resistor 25. *The said loading is such that a disproportionate current change occurs in the resistor 25 with changes in voltage at the terminals 12, 1-3, and such current change is so termed because percentagewise it is greater, for voltage increments at the terminals 12, 13, than the percentages represented by the increments.

Expressed in another way, a rise in voltage at the terminals 12, 13 will not only cause an increase in current through and voltage drop across the resistor 25 by virtue of the main bridge load (which is fixed), but there will also be an additional current through and voltage drop across the resistor 25 due to a disproportionate increase in the loading provided by the output circuit of the transistor 27. This latter increase in loading is of such value that it will maintain at the output terminal 26 of the drop resistor 25 a substantially constant voltage with respect to ground. Moreover, this regulating action also occurs where the supply voltage applied to the terminals 12, 13 drops. When a voltage drop occurs, the loading imposed through the resistor 25 by the transistor output circuit decreases disproportionately with the voltage drop,

thereby lightening the load applied to the output terminal 26 of the dropping resistor 25, with the result that the voltage of the terminal 26 is still maintained constant.

It will be understood that the voltage of the signal applied to the transistor input circuit comprising the base 28 and emitter 30 is determined by the rectifier output voltage at the wire 20 in conjunction with the values of the dropping resistor 36 and the resistor 23 in series with the rectifier output. Where the voltage of the terminal 20 is in the neighborhood of 28 volts, signal voltage across the resistor 36 will be somewhat less than 20 volts, as- 1 suming a voltage drop across the diode 40 of 7.4 and a voltage drop across the resistor 36 of approximately 0.5 volt.

From the foregoing it is seen that I have provided a novel, extremely simple and effective D.-C. voltage regulator comprising in conjunction with the transistor 27 and crystal diode .40, the dropping resistor 25 carrying the load current, such regulator compensating for changes in the voltage applied to the transformer input terminals 12, 13 in a manner that a constant voltage exists at the output terminal 26 of the resistor 25, with respect to ground. Relatively few components are employed, and such components are characterized by mechanical ruggedness, and great electrical and mechanical reliability. Moreover, the sizes of the components are very small, so that the entire voltage regulator need occupy only an extremely small space.

For the purpose of compensating for variations in the functioning of the transistor 27 and diode 40 due to temperature variations, I provide in the main. load circuit a temperature-compensating resistor 42, which advantageously may be formed of nickel having a resistance value of 65 ohms or so, such resistor having one terminal connected with the wire 26 and delivering current at its other terminal or wire 43 to the bridge circuit. I have found that with this circuit it is possible to interchange both the transistor and diode and still retain regulator integrity over a very wide range of operation.

The present improved D.-C. regulator as above set forth is advantageously employed in a pyromcter system for temperature indications and control, and for such use a thermocouple 45 may be provided, being made subject to the temperatures being measured or controlled. The thermocouple 45 is connected with a resistance bridge 1 circuit having novel cold junction compensation as provided by the invention, such circuit being enclosed in the broken outline 10. The bridge circuit shown has supply terminals or wires 46 and 47, the latter being connected to a ground 48. Two legs of the bridge may comprise resistors 49 and 50 having approximately 2,600 ohms and 2,585 ohms respectively, such resistors being connected to the terminal 46. The resistor 50 may be connected to a servo-controlled potentiometer resistance 51 of approximately 16 ohms, over which a sliding contact 52 passes, such contact being driven by a servo motor.

By this invention the two remaining legs of the bridge comprise respectively a resistor 55 of constant temperature coetficient of resistance, and two series-connected resistors 56 and '57. The resistor 55 may be of an alloy known commercially as Constantan, or an alloy known as Karma, whereas the resistors 56 and 57 are respectively nickel and copper. The Constantan resistor 55 may have a resistance value of 3.4282 ohms, the nickel resistor 56 may have a resistance value at 30' C. of 1.1868 ohms, and the copper resistor 57 may have a resistance value at 30 C. of 2.2414 ohms. By this organization of the resistors 55, 56 and 57 comprising the remaining two legs of the bridge, I obtain an effective cold junction compensation by which the error introduced in the indications of temperature, and in the control, is maintained at a. very low value throughout a wide range of temperatures, the

latter for example being as great as from plus 80C. to

minus 70" C. With such organization a zero error may be had at the said temperature extremes and also at zero degrees C., with an error at points in between of less than A of a degree C., this being a theoretical value. Be-

tween temperatures of minus 55' C. and plus :120' C. a

maximum error of 34 of a degree C. would be obtained. In actual conditions of production, this error would be increased slightly, and a maximum error of one degree C. throughout the entire range could be expected.

Included in the two second-mentioned legs of the bridge is, of course, a portionof the'potentiometer resist ance '51, and also portions of a calibration resistor 60 'of constant temperature coeflicient of resistance. The resister 60 may for example have a value of 36 ohm, and

may (constitute i the resistance \element :of a potentiometer having :a contact #61 -.connected do :the ground .wire 47 mi .theabridge. :shown, .the resistor 60 is'conneated with thearesistors 35 and 57,'soias1o be :includedfin the bridge legs. Adjustment-of the contact 61 of the potentiometer resistor 60 (enables the bridge -to be adjusted -:for zero indication on a meter included in series with .the thermocoupletleads 63-and 64 f thethermocouple 45. :I-hav'e :iound that, in conjunction with the ab'ove set forth coldjunction compensation, the thermocouple lead 63 may 'be advantageously formed of an alloy known commercially astAlumel, and the lead- 64 formed ofa-metal alloy known commercially zas Chromel. Ihe Alumel lead 63 is connected to a tterminal :or junction 7 2 disposed between the resistors :49 -and 56 .as shown, and the -Chromel lead is connected to acoldijunction -terminal 65 to which there is also connected-a copper lead 66,the'latter :going to a-coil 67 or a DJC. instrument movement of the DArsonval type. Theremaining terminal of thecoil 67 is connected by a wire-'68 *with the potentiometercontact 52.

Whilethe valuesof the-resistors '55 and '56 and 57 have been given to four decimal places, obviously from a practical standpoint-it is=not necessary to adhere rigorously to the last figures. The resistor values as shown maybe obtained by=use-o'f the *following formulae:

where H=Difierential millivolts between +80 C. and-0 C. L=Diiferential millivolts between -70 C..and 0 C. A=Nickel sample resistance at 80 C. in ohms -B=Niekl-sample resistance at 0 C. in ohms C:Niclte'lsample resistance at -7 0 C. in ohms D -Goppersample resistanceat 80C. in ohms E=Copperrsample resistance-at 0 Grill ohms F =Copper sample resistance at --70 C. in ohms X =Bridge nickel at 0 C. in ohms Y=Bridge copper at 0 C. in ohms Z=Bridge Constantan at 0 C. in ohms In finding errors at intermediate points, in the temperature range, the eoetficient for the sample nickel is taken as X /B and for the copper Y/E.

From temperature versus resistance measurements, the following values were found for the Constantan, nickel and copper used for the resistors 55, 56, 57 and 60.

X =Nickel in ohms=1.1868 Y=Copper in ohms=2.24l4 Z =Constantan in ohms=3.25 62 It will be understood that the bridge circuit and thermocouple as above set forth function in the following manner: After the bridge first has been properly balanced, the temperature of the thermocouple 45 will be translated into a potential and nulled by an opposite potential existing between the junction 72 of the bridge and the potentiometer contact 52, such nulling bridge potential being obtained by suitable adjustment of the contact 52. Thereupon, the position of the potentiometer contact 52 will be indicative of the temperature to which the thermocouple 45 is subjected. Changes in the thermocouple temperature will results in changes in the potential generated thereby, requiring readjustment of the potentiometer arm 52 to effect a nulling of the thermocouple The new position of the potentiometer arm 52 to effectuate this nulling will thereupon be indicative of the new temperature of the thermocouple 45.

Initial adjustment of the bridge is eifected in the following manner; The thermocouple 45 is placed in ice, and the potentiometer 60 adjusted to obtain a zero indication on a meter inserted in the thermocouple leads.

:It will be understood that the contact resistance atthe potentiometer 60 has insignificant effect on the balance of the resistance bridge circuit. Since such contact resistsauce is part of aresistaneetof over 1000 :ohmsand the currents in the two bridge arm circuits 'which :determine she proper voltage .:relation between points 72 .and 51 tremain .practically constant for 'contact resistance vari- -ations of approximatelyphrs oriminus .1 ohm, the-contact resistance of the 'potentiometeriarm '52 controlled by the servo motorihas no influence, since n'o current flows .at 'balance.

,For the purpose of adapting the bridge circuit for difierent diodes and transistors having commercial vari ations, a rheostat or adjustable resistance 75 may be provided, connected to-the bridge input terminal 46 and to the output terminal 43 of =1he temperature-compensating nickelresistor '42. The rheostat 75 may have a movable contact or slider 76, as indicated, 'toefiect a control of the current flowing through :the resistance bridge.

-It will be now seen that I ihave provided, for a =pyrometer type of temperature indicator and control, a simplitied and etie'ctivesnovel and improved D.-C. voltage regulator and resistance bridge having novel and effective cold-junction compensation, whereby the temperature indications'and control are accurate within specified, narrow limits over -a wide range of temperatures. The organization as above provided is relatively simple 'in'its construction, requiring but small space and being characterized by stability 'and reliability b'oth from the mechanical standpoint and the el'ectricalstandpoint.

Variations and modifications may be made within the :scopeof the claims and portions of the improvements may be :used without others.

-I claim:

1. In a voltage control circuit, a transistor having a base, an emitter and a collector; a first voltage-dropping resistor connected-'between the baseandemitter; a rectifier and two resistors aIbseries-connected in the order'named,

the rectifier being connected do said base and the end resistor of the series being connected tothe'collector, said end resistor, collector and emitter comprising an auxiliary load circuit; supply and main load circuit leads connected respectively to the ends of that one of the series-connected resistors which is joined to the rectifier so as to bridge the said resistor, the load circuit lead being more remote from the rectifier than the supply circuit lead by the value of the said bridged resistor; and additional supply and main load circuit leads connected with each other and to the auxiliary load circuit having the said emitter.

2. The invention as defined in claim 1 in which the said dropping resistor and the said end resistor have relatively high values commensurate with each other.

3. The invention as defined in claim 1 in which the rectifier comprises a crystal diode characterized by a substantially constant voltage drop across it when a varying D.-C. potential of greater value is applied thereto, having a polarity tending to cause reverse current fiow through the diode.

4. In a voltage control circuit, a transistor having a base, an emitter and a collector; a first drop resistor having a pair of terminals, said drop resistor being connected across the base and emitter; a circuit including a diode having terminals and resistor means series-connected to said diode, said circuit being connected across the base and collector with the diode disposed between the said resistor means and base; a supply circuit for applying a D.-C. potential to those terminals of the said first drop resistor and diode which are remote from each other, the said resistor means including a second drop resistor connected to said supply circuit; and a loading circuit connected to the emitter and to a point on said second drop resistor removed from the supply circuit connection thereto, said second drop resistor having a value such that changes in the voltage drop across it are substantially equal to changes in the D.-C. potential of the supply circuit.

5. The invention as defined in claim 4 in which the said resistor means includes an additional resistor of relatively high value as compared with said second drop resistor, said additional resistor and first drop resistor being of commensurate values.

6. In a D.-C. voltage control, a supply circuit having a series dropping resistor; a load circuit connected to the supply circuit to receive energy therefrom; a variable loading means including a transistor having an output circuit connected across the load. circuit to augment the load applied to the supply circuit; and signal circuit means connected across the supply circuit ahead of said dropping resistor, supplying the input circuit of said transistor with .a signal potential varying with the potential of said supply circuit whereby a rise of supply potential will impose a disproportionately greater loading on the supply circuit and effect a disproportionately greater drop through the dropping resistor, thereby to maintain the load voltage constant, said signal circuit including a resistor bridging the transistor input, said transistor output circuit including a resistor, both said resistors having relatively high values commensurate with each other and said series dropping resistor having a value constituting a small fraction of the value of said two resistors; and another series dropping resistor connected in the supply circuit ahead of both said first-mentioned dropping resistors and said signal circuit means.

7. The invention as defined in claim 1 in'which there is an additional series dropping resistor connected in the supply circuit lead ahead of the one series-connected resistor which is joined to the rectifier.

8. In a voltage control circuit, a transistor having a base, an emitter and a collector; a supply circuit for providing a D.-C. voltage which is susceptible of variation; a voltage drop means connected across said circuit, having series-connected components one of which is connected to one side of the supply circuit and manifests a constant drop with changes in current therethrough and the other of which manifests a changing drop with changes in current thercthrough, the emitter and base of said transistor constituting the input circuit thereof and being connected with said other component to receive an input signal varying with the voltage drop across said other component, said base being also connected with the said one component, the collector and emitter of the transistor constituting the output circuit thereof; a load-carrying resistor connected to the said one side of the supply circuit; means connected with the load-carrying resistor, providing an auxiliary load circuit through the transistor via the said emitter and collector thereof, said auxiliary load circuit being energizable from the supply circuit through said load-carrying resistor, and the input signal to said transistor being independent of the voltage drop through said load-carrying resistor, said load-providing means including a drop resistor in the auxiliary load circuit, connected to the load-carrying resistor and to the said collector whereby changes in the voltage drop across said loadcarrying resistor are substantially equal to changes in the D.-C. voltage of the said supply circuit; and a main load circuit having a constant load, connected to the common junction of the said load-carrying and drop resistors and to the said emitter.

9. The invention as defined in claim 8 in which the said other component comprises a high-resistance drop resistor, and in which the drop resistor in the means completing the load circuit comprises a high-resistance resistor, said high-resistance resistors having values commensurate with each other and greatly in excess of the value of the said load-carrying resistor.

References Cited in the file of this patent UNITED STATES PATENTS 2,372,432 Keizer Mar. 27, 1945 2,751,550 Chase June 19, 1956 2,759,142 Hamilton Aug. 14, 1956 2,850,694 Hamilton a Sept. 2, 1958

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