US2459177A - Direct-current amplifier - Google Patents

Description

Jan. 18, 1949. F. L. MOSELEY ET AL 2,459,177

DIRECT CURRENT AMPLIFIER Filed March 5, 1945' 2 Sheets-Sheet 1 VWv N Q E II Q q k x;

I IN V EN TOR.

lam/m- 1. Maxim By [law ASP/Z: Q QM Jan. 18, 1949. F. L. MOSELEY ET A].

DIRECT CURRENT AMPLIFIER Filed March 5, 1945 2 Sheets-Sheet 2 Kill I] IIIIIII Patented Jan. 18, 1949 DIRECTrCURRENT AMPLIFIER FrancisL. Moseley, Osborn, and. Lloyd J'. Perper,

Dayton, Ohio Application March 5,- 1945,.Seriai No. 581,018

(Granted. under the act of'March 3, 18.83., as

2 Claims.

The invention described herein may be manufactured and used by or for theGovernment-f'or governmental purposes, without the payment to 1150i any royalty thereon.

The present invention relatesto. D. C. ampli-- fiers, and is particularly usefuliin. amplifying a low direct current voltage of low power to one of high power.

An object of the invention is to invert weak direct current, amplify the resultant 'A. 0., and

then rectify this A. C. to a resultant direct current of greater power to actuate controls, indicators or any mechanical or electrical. device requiring more voltage or power than wasavailable in the original input.

A further object is to provide such an amplifier which will utilize simple components, be inexpensiveto manufacture and adaptable to mass production technique.

A still further object is to'provide such an amplifier which will have automatic gain stability as well as centering stability'so that spurious output without input is eliminated.

Another object is to provide such an amplifier which is free from ground connections-so as to be easily adaptable to all types-f circuits Where amplification of D. C. is desired, particularly in airborne recording and control applications where the 28 volt battery voltage may be used without special regulation 01' step-up to a higher voltage for the plate circuits.

These and other objects willappear throughout the. specification and will be vvparticularly pointed out in the claims.

Referring to the drawings. wherein like numerals denote like parts,

Fig. lis aschematic diagramyof thev circuit I employedin the amplifier; and,

Fig. 2 is a block diagram illustrating the func reedifor. rectification. Negative.ieedbaclt.isremp amended 30, 1928; 370 0. G. 757) ployed in the various stages of the amplifier to maintaingain stability.

The amplifier isparticularly adaptable to the extremely low power outputs of. aircraft instruments, receivers and controls. For instance, it has proved effective when used with a crosspointer instrument landing indicator, the full scale'output voltage of which is of the order of 150 millivolts. This voltage after amplification to 2 volts in the present amplifier was applied. to operate the stylus of a graphic recorder. In another application the' same voltage of the'crosspointer landing indicator after amplification is used to actuate automatic lpilotcontrols and re-- lays for automatically flying and landing aircrafts.

The amplifier may be employed ina wide range of" power applications and for many other purposes than herein disclosed and it is understood therefore thatno limitation. in the embodiment or details of the disclosure is intended other than ascontained in the claims appended hereto. By way of illustration, to describe an embodiment of the invention, the D. C.v input is first filtered through a filter network to remove any undesir able A. C. ripple and thev input is controlled through a series step attenuator in the incrementsdesired. The desired amount of input resistors are also included to'avoid loading the line and any reductionin. gain therefrom may be compensated by additional amplification.

The: amplifierpreferably. shown includes in its circuit a. transformer input coupling and the secondaryofthis transformer is coupled to the grid of; thefirsttube of. the amplifier, the output of which may be resistively or. capacitively coupled to: several additional amplifier stages. Degenerative-zfeed'back between amplifier stages provides a high degree: of stability and linearity of am- 'plification.

.As-will bezobservedfroma study of. the. schematicdrawing, no balancing circuit is included orj necessary. The zeroposition cannot be unbalancedordrift. That is, withzero input there must depend onia steady, D. C. supply voltage, or

tube; characteristics. for. stability; and freedom 7 from drift. are employed to minimize effects of variable ele- Both current and voltage feed back ments which may be present. The output of the amplifier power tube is derived from the cathode circuit but could equally well be taken from the plate circuit.

The output vibrator forms an output switch through an output transformer. This arrangement permits making and breaking of the output switch in synchronism with the input vibrator, also acting as a make-and-break switch,,in several ways. For instance, the contacts maybe mounted on the same reed so as to be synchronized mechanically, or they may be separately mounted with their respective vibrating reeds electrically synchronized. Thus, even thoughthe 'schematic drawing depicts the two vibrators spaced ateither end of the circuit, in actual use it will be found highly efficient to mount the contacts on a single vibrating reed by proper insulation, and thereby provide a compact unit employing a single vibrator coil.

circuit, and. chokes 5i ,and52; are employed to' filter toutunwmhted powerv supply ripple.

Thus it is seen that considerable powermay be derived through the novel amplifierwith a very small input signal or control voltage and -withgood linearity characteristics wherein the voltageoutput is directly proportional tothe volt- In the drawings, the low input D. C. voltage which is to be amplified is introduced from the a receiver or other source through input terminals ill, reversing switch H and through a stepped attenuator l2 to a pair of vibrator contacts I? age input. There is no necessity for a centering control because zero D. C. signal input gives zero A; C. signal when inverted by the vibrator, and

must give zero signal output when rectified. This 'novel arrangement, due to its freedom from bucking and balancing tube circuits provides such-"a degree of centering accuracy that instruments may be calibrated and voltages may be measured directly 'with gi'ull confidence, in'the which invert the input D. C. voltage-toA C.;

thencethrough transformer coupling 14 which is preferably center tapped to couple the pulsed. -A. C. to the first amplifier tube i5.v Any other conventionaltype of coupling can housed in place .of transformer I l. The A. C. voltage is impressed on grid ll of tube' [5 for amplification,

and the output is successively grid-coupled to,

the succeeding stages-of amplifier tub-es l8, I9, 26 and power tube 2|. Interstagecouplingis illustratecl through capacitators 22, 23, 24 and 25.

Amplifier'tubes. l8, Hi, 20, 2| are operated as Class A amplifiers and inverse feed back is em: ployed at each stage to improve linearity of output. Again, this desirable feature-may be provided or omitted, depending on the degree of gain, stability, or linearity of output required.

Resistors 2t, 21, 28 also form part of the interstage coupling inconventional mannen- Inverse feed back is applied to the individual stages through resistors 29, 30, 3! that is, a portionof the output of tube 18 is applied to its gridinput 32, and similarly tubes lii'and Zll feed back a portion of their respective output to their grid input; Current feedback is provided, through cathode resistors 33, 34, 35, 36 and; outputvload 42. .Gricl bias is maintainedthrough grid resistors 3'5, 38, 39, 40 in conventional manner The power output of. power tube 25 isshown for illustration purposes, as derived through its cathode M and transformer 44. The filtering network such as condensers 53,- 54 and inductance may also be provided to filter out unde sired output ripple.

The-output of transformer 44 is fed to the output vibrator 45 where rectification of the A.,C.

takes place in synchronism with the input of vibrator I3, by center tapping the secondary of the output transformer M. Phasing of the amplifier is adjusted through proper values of :ca pacitanoes and resistances in the circuit so that the output A. C. to the output contacts in vibrator $5 is in phase with the A. C. at the input contacts of vibrator I3. Extraneous power for amplifying the low voltage is injected into the plate circuit of the amplifier tubes through terminals 45 and switch 41. The power supply feeds'the vibrator coil 48- which actuate's'the reed Y claimed is:

accuracy of the measurements. The output may be. varied by pr'oport'ioning. the gain components so as to obtain a logarithmic or other desired type of-gain; Initial design 'ofthe components will determine the type .of gain. 1 a

The input circuit of thi'samplifieris completely isolated from the output circuit and-there is consequently no likelihood .for the output circuit voltage .to' float above groundat the power supply voltage level and thereby damage circuit compo- I nents or prevent accuracy of operation. U

I This amplifier permits the utilization of standard localizer andglide pathradio equipment for automatically landing aircraft. In such application a preferred methodis to employ la separate amplifier for the-glide path receiver voltage source and for the localizer. receiver. voltage source. And when these units are used in -combination ,withthe rate circuit systems of'landing such as are described in-copending application Number 545,l73,filed July 15,1944, now abandoned, and application Number 542,594, filed June 28 1944, the aircraft controls canbe made to respond to the localizer and glide path beams with a fidelity that human pilots admittedly have been unable to duplicate.

Having thus described the invention, .what "is 1. An amplifier system for amplifying low level direct current voltages to high level direct current voltages, comprising a multi-stage-alternatin current tube amplifier and biased togoper-ate as a class A amplifier, a vibrator having a vibrat ing reed with av pair of spaced contacts "between which the reed vibrates, an input circuit for said amplifier having a. transformer'whos'e-primary winding is connected across said vibrator contacts, the reed of the vibrator being connected in series between the direct current sourceto. be

amplified, and the electricmidpoint of said pri-' mary, winding, whereby zeroalternating current voltage appears in the output of theainplifier when zero direct current voltage'is at said input,

another vibrator'having a vibrating reed a'nd a pairof spaced contacts between which the reed vibrates, means coup said other vibrator to the output of said amplifier for full waverectification, the vibratory armature-of the first-mentioned vibrator being conductively-isolated from 5 direct current ground in the absence of direct REFERENCES CITED current input Voltages and the input terminals The following references are of record in the of the system and the output terminals of the s system being effectively isolated from each other file thls patent with respect to the passage of direct current, 5 v UNITE!) STATES PATENTS 2. An amplifier system according to claim 1 in Number Name Date which each stage of said muiti-tube amplifier has 1,423,156 Espenslchied Sept 5 1922 i plate circuit back-coupled to its grid circuit 2,114,298 Gunn Apt 19' 1938 for alternating current feedback. 2,133,670 SChuchmann Oct. 18, 1938 FRANCIS MOSELEY- 2,190,317 Holst Feb, 13, 194

LLOYD PERPER- 2,297,542 Eberhardt Sept. 29, 1942

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