US2468087A - Thermionic valve circuits - Google Patents

Description

April 26, 1949.

M. LEVY THERMIONIC VALVE CIRCUIT Filed Jan. 18, 1944 r w m w P co/vrkoz 1/077 F/ 6.3 TW MAX.

Patented Apr. 26, 1949 opt msiiiiimf wits cnimis Mauricerll ioise .ilcyriiLondffoii strata; si l fl i by me sne assignments, to'Int'ernational Standare El edt ric' Corporatimi," New York, N. Y.', a';

corporation of D In Great Britain J5 7 Claims." (01: e o-2% rents" of such valve eirciiits lare how; er fre g- (iiiehtly Obtaiiie'dfr'd'm riaifiiig current supplythe'vdltage or which is rarely cori stant and in"s1ic h'af case f'the' stabilisation of the circuit can be efiec'ted rather more simply by an arrangement" controlled by the voltage variations of the alternating supply itself. In this way,:.a'1s'o; the'cornbiriedefiects of all the variable siippli'es derived from the main source maybe simultaneously clealt'with; v

According to the invention, therefore, there is provided an'arra'ngefner'it for stabilising the operatien. of an electric Wave'transl'atingqr generatf' ing device vvhichin'cludes' one'or'morethermionic valves supplied with" biierating potentials and currents froman alternating current sourc'e'lof variable voltage; c'oniprisiiigmeansffor deriving from the source'a unidirectionalcontrol voltage .varying in aceord'ancewiththe voltage var'iatiens of the source and means-for ap lying the control voltage to the device in such'a'inanner aud ender its performance substantially independent of th'eJsaid voltage'variations; I

According to another aspect, the invention comprises an electrmal circuit arrangement coinprising an alternating'current source oi variable voltage, means for deriving" therefro'ni appro priate operating voltages'and currents for a'w'ave translating or generating circuit" containing thermionic valves; and means for applying to one orumore of the valves a unidirectional control voltage adapted to vary inaccorda'n'ce with the voltage variations'of the source in such" manner rendered substantially independent of the said voltage variations; v

The invention will be described Withrefere'nc'e to ,the accompanying drawing; in which? Fig. 1 shows a block schematic diagram" to eii plairi the'principle of the'inve'ntion;

Fig. 2, shows a a schematic circuit diagram or an embodiment; and v,

Fig. 3 shows diagrams to explain the opera- =ti'onlof Fig. 2." a I Fig.1 shows'in block'schematic form the'prin .thatthe.characteristics of the valvecircuitaie ciple of the invention. A loadcirc'uit' which ma be an amplifier, oscillator, meantime, or any other type of circuit employing thermionie valves; is suppliedwith operating p'otentialsjfrom an alternating current main supplytransformer PT through a power unit PU containing approfpriate rectifying and smoothing arrangern nts'. This unit may be of any suitable known type, and may provide any number of diifrent voltages and currents whichmay'be necessary.

voltage 0" f the mainsupply will usually besubjc'tto Variations from'time'to time, which" may quite commonly reach -10%, and generally siich variations ca'usei corresponding variations in the characteristics or performance of the" load Circuit" L. For ex'ampleg'ii this circuit isan 'ainpli fier, the gain will usually increase or decrease when the supply voltage increases or decreases, the: relation being approximately linear for moderatevariations of the supply voltage. Sinjlilarly if the'lo'ad circuit is an oscillator, the fr e"- 'quency'and/tr the outpiitcurrent or voltage may vary in a similar sort of way, w

To compensate for the effect of these vari'a' tion's,'a unidirectional control voltage varying; in accordance with the mainsupply voltage varijt'ionsis; derive dfrom the transformer PT andis applied to the load circuitin'suc'ha manner to counteract the changes produced by the inaiii supply variations; One preferred method'is to apply the control voltage to a grid of cheer m re 6f the valves in the load circuit L in a man similar to that described in thepatent refer ed to" above; In this' case it isnecessary to arrange so" that the control voltag varies in oiipdsi't'e sense to'the'rriaih su'pfilyvtita'ge; 1 v In Fig. l the control voltage 1) is obtained means of the control unit CU which issup'pl'iegl with an alternating voltage V1 fromi th'etraiis through n'on' tube N (or other suitable s discharge tube) and is connected th'rbiiglriare sistan'ce R3 to the positive terminal of a source resistance potentiometer formed by the resistances R1 and R2 connected in series across the transformer PT (Fig. 1), so that an alternating voltage V4, which is a known fraction of V1, is applied through the condenser C1, to the anode of the diode.

The load on the diode D comprises the series connected resistances R4, R and Re, the condensers C2 and C3 being provided for smoothing purposes according to well known principles. The

resistance R6 is provided with an adjustable tap from which an appropriate control voltage '12 may be obtained for application to the load circuit L (Fig. 1)

The action of the circuit of Fig. 2 will be understood from the diagram shown in Fig. 3. curve A indicates the alternating voltage applied to the diode; the line V4 represents the maximum positive amplitudes of A, and is supposed to vary between the limits V4 max. and V4 min. represented by the corresponding dotted lines. The cathode voltage V3 is represented by the chain dotted line. and should be chosen to be a little less than V4 min.

When the instantaneous positive voltage of the curve A exceeds the value V3, the condenser 01 charges through the diode in such a manner as to reduce the anode potential so that it becomes negative to the cathode. If the capacity of the condenser C1 and the total resistance R4+R5+R6 be chosen so that the time constant of the circuit is large compared with the period of the alternating current supply, the condenser will not be able to discharge appreciably between the successive positive loops of the curve A.

The condenser C1 will accordingly acquire a difference of potential substantially equal to V i-V3, and the terminal connected to the anode will be negative; and it is from this difference of potential that the control voltage 22 is derived.

The function of the diode is primarily to charge the condenser, and it can be disregarded from the point of view of the control voltage since it passes no current except just at the tips of positive loops of the A curve. There is thus applied to the resistances R4, R5, Re a continuous voltage V4-V3, derived from the condenser in series with an alternating voltage V4 derived from the resistance R2, and the current due to this alternating voltage is substantially shunted away by the condensers C2 and C3. If R2 be chosen small compared with R4+R5+R6, then the maximum available value of 12 (which is the voltage drop across R6) is very nearly equal to and moreover is of opposite sign to V4V3 as indicated by the plus and minus signs in Fig. 2.

In order to assist in the choice of appropriate elements for the circuit of Fig. 2, the following particulars of a practical circuit are given for illustration. It will of course be understood that other values of the elements may be used in other circumstances.

In this particular case the alternating voltage The V1 was 280 volts R. M. S., the peak amplitude being therefore about 400 volts. The variation of the supply was i10%. The high tension voltage V2 derived from V1 in the power unit was 250 volts i10%.

The resistances and condensers in the circuit of Fig. 2 had the following values:

R1, R3 and Re megohm 1 R2 d0 0.2 R4 and R5 do 0.5 C1 microfarad 0.01 C2 and C3 d0 0.2

The neon tube produced a constant voltage difference of 70 volts and the current flowing through it was about 180 microamperes.

The diode D can be very small, adapted for a current of the order of 1 milliampere, for example such as may be used in television apparatus. Actually in the circuit of Fig. 2, the current which flows through the diode will be much less than 1 milliampere.

It will be seen that with the above values, the maximum amplitude V4 is :18 volts, so that the potential acquired by the condenser C1 varies from 18 to 2 volts. Neglecting R2 in comparison with R4+R5+Rs, it will be seen that the maximum available value for the control voltage '0 varies from 9 to 1 Volts.

It will be seen that the load on the power supply is negligible. The current taken from the transformer PT is less than 300 microamperes (R. M. S.) and that taken from the high tension supply at voltage V2 is less than 300 microamperes.

It will be noted that in this circuit, the supply voltage is stepped down by means of the potentiometer to a value such that V4 min. is only slightly greater than the voltage V3 determined by the neon tube. The variations are stepped down in the same ratio. If therefore, two or three, similar neon tubes be used in series, a smaller step down ratio of 5 :2, or 5:3, may be used, so that the variations are doubled, or trebled. The corresponding range of the maximum values of 11 will be l8 to -2 volts and -27 to 3volts.

With V2=250 volts, more than three neon tubes of course cannot be used, but it will be evident that if a higher value V2 is employed, four or more such tubes become possible. The maximum number of neon tubes is determined by the requirement that there must be at least '70 volts available for each. For other types of gas filled tubes, the fixed voltage may of course be different from 70 volts.

The arrangement of the smoothing circuit (which in Fig. 2 comprises the resistances R4, R5 and condensers C2 and C3) can be varied according to known principles in any desired way, or a non-dissipative wave filter could be used if preferred, though this would be much more bulky and expensive than the simple arrangement shown. However, for any smoothing or filtering arrangement used, the same control voltage will be obtained if the total load resistance is made equal to R4+R5+Rs.

It is to be noted, also, that any other convenient means may be used for stepping down the alternating voltage V1 to V4. For example, the resistances R1 and R2 could be replaced by a suitable step-down transformer; or in Fig. 1, the control unit could be connected to an appropriate tap on the secondary winding of the transformer PT.

Furthermore, in Fig. 2 the diode D could be replaced, if desired, by some other kind of rectifier such as a copper oxide or selenium rectifier connected so that the forward direction is from the condenser 01 to the neon tube N, or by a triode or other valve biassed to the cut oif so that it operates as a rectifier in substantially the same way as the diode D.

It is to be pointed out that the control voltage 0 can be reversed in sign if desired by inverting the diode D (or other equivalent rectifier) and reversing the voltage V2; the circuit operates as described above except that the condenser C1 will now be charged with the opposite polarity, and the charging is performed by the negative loops of the wave A (Fig. 3) instead of by the positive loops. This requires that the source of the voltage V2 should have the positive terminal connected to ground; and if this is not permissible for the power unit PU, the voltage V2 may be obtained from a separate source.

It will be observed that the control unit shown in Fig. 2 does not require any modification to be made to the power unit PU nor in general to the load circuit L, which will usually already have terminals conveniently adapted for applying a bias to the control grids or other grids of the various valves.

What is claimed is:

1. An electrical circuit comprising a source of alternating voltage of variable amplitude, a first rectifier means connected across said source for obtaining a first unidirectional voltage, a load supplied by said rectifier means including at least one thermionic valve having an anode and oath ode connected across said first rectifier means,

means for comparing said first unidirectional voltage from said first rectifier means with at least a portion of said alternating voltage to produce a voltage diiference corresponding to the variable peaks of said alternating voltage, a second rectifier means for rectifying said voltage difference to obtain a second unidirectional voltage in accordance with the peaks of one polarity, and means for applying said second unidirectional voltage to a control electrode of a thermionic valve of said load in the proper phase and amplitude to nullify the efiect of variations of the voltage from said source by means of the fluctuations of said second unidirectional voltage and to render the output of said load substantially independent of variations from said source.

2. A circuit according to claim 1, in which said comparing means include a condenser controlled by a voltage proportional to said alternating voltage and by said first unidirectional voltage to produce a voltage difierence therebetween.

3. A circuit according to claim 1, wherein said comparing means include a condenser controlled at one terminal by a potential derived from said alternating voltage and at the other by a potential derived from said first unidirectional voltage, at least one gas discharge tube, said tube being supplied with current derived from said first unidirectional voltage both said condenser and said gas tube being serially connected with said second rectifier means.

4. A circuit according to claim 1, wherein said comparing means include a condenser controlled by a voltage proportional to said alternating voltage and by said first unidirectional voltage to form a voltage difierence therebetween, said second rectifier having an input circuit including said condenser and a gas discharge tube, said tube being supplied with current derived from said first unidirectional voltage, and having an output circuit including a resistance load, and means for applying at least a part of said resistance load to bias the thermionic valve of said load.

5. A circuit according to claim 1, wherein said comparing means include a condenser controlled by said alternating voltage and said unidirectional voltage to produce a voltage difference therebetween, said second rectifier means having an input circuit including said condenser and in series therewith at least one gas discharge tube, said tube being supplied with current derived from said unidirectional voltage, and an output circuit including a resistance load, means for smoothing said resistance load, and means for applying at least a portion of the smoothed resistance load to bias a thermionic valve of said load.

6. A circuit according to claim 1, wherein said comparing means including a condenser controlled by a voltage proportional to said alternating voltage and by said first unidirectional voltage to produce a voltage difiference therebetween, said second rectifier means having an input circuit including said condenser and an output circuit controlling the input circuit of a thermionic valve of said load, said condenser being arranged to be charged by the positive peaks of one polarity and said second rectifier means being arranged to produce a second unidirectional voltage of negative polarity.

7. A circuit according to claim 1 in which said comparing means includes a condenser controlled by said alternating voltage and said first unidirectional voltage to form a voltage difierence therebetween, and said second rectifier means includes a diode having an anode circuit and a cathode circuit, a gas discharge tube connected in said cathode circuit and connected to be supplied with current from said first unidirectional voltage, said anode circuit being connected through said condenser to said source of alternating voltage, and a resistance connected between said anode and cathode for developing thereacross said second unidirectional voltage.

MAURICE MOISE LEVY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,010,881 Numans Aug. 13, 1935 2,035,125 Grant, Jr. Mar. 24, 1936 2,173,497 Schlesinger Sept. 19, 1939 2,232,856 Idle Feb. 25, 1941 2,276,672 Roberts Mar. 17, 1942 2,392,416 Scrensen Jan. 8, 1946

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