US2354483A - Voltage variation compensator - Google Patents

Description

July 25, 1944.

Original Filed Aug. 20, 1938 8 VOLTS R. E. SCHOCK VOLTAGE VARIATION COMPENSATOR gir- UNI-CONTROL/ WTI I t 01/ TFI/ T 250- COMPEMMTO HES/570E 3moentor fiaberilifgckocfi',

Gttorneg Patented July 2 5,v

VOLTAGE VARIATION COMPENSATOR Robert E. Schoclr, River-head, N. Y., assignor to Radio Corporation of America, a corporation oi Delaware Original application August 20, 1938, Serial No. 225,911. Divided and this application August 29, 1940, Serial No. 354,631

3 Claims. (Cl. 179-171) This invention relates to a new and novel circuit method of compensating for supply voltage variations in vacuum tube amplifiers, oscillators, recording devices, and other types of apparatus requiring constant voltages.

This application is a division of my copending application Serial No. 225,911, filed August 20, 1938, now Patent No. 2,281,205, granted April 28, 1942.

An object of this invention is to provide an improved system of voltage compensation or regulation.

Another object of this invention is to improve the voltage regulation of both an alternating current and a direct current type of amplifier.

Still another object of this invention is to improve the voltage regulation of a vacuum tube oscillator and other apparatus requiring constant voltages. Ihave found that although voltage compensation devices are old in the art, it often becomes necessary that the output of amplifiers and the output frequency of oscillators be independent of variations in their supply voltage. This requirement involves either regulation of the supply voltage or some method of compensation within the amplifier or oscillator circuit for the effect of supply voltage variation. Some of the more common methods of compensation as known in the prior art either involve batteries which are maintained at a voltage high from the common ground or they involve excessive supply voltages.

The improved features and operation of my invention will best be understood by referring to the accompanying drawing, in which:

Fig. 1 is a circuit showing the principle of operation involved in this method of voltage compensation;

Fig. 1a is an alternative arrangement of a circuit, similar to that of Fig. 1, except that a separate voltage supply source is connected to the cathode lead;

Fig.2 is a circuit diagram similar to that of Fig. 1, except that a tetrode type of tube is used instead of a triode;

Fig. 3 is a circuit diagram of this invention similar to that of Fig. 2, except thata potential divider is connected across the screen voltage supply, rather than across the plate or anode supply as in the prior circuits;

Fig. 4 is a circuit dia ram of an amplifier of this invention as applied to a recording device.

Referring now in detail to Fig. 1 of the drawing, the principle of operation involved in this novel circuit arrangement is shown'wherein the electron discharge device or triode tube 2 has connected in its plate circuit a current meter or milliammeter l to indicate the current drawn in the plate circuit and has a voltmeter 3 connected between its grid and cathode to indicate the bias voltage applied-to the tube. The cathode obtains voltage for the purpose of compensating for plate supply changes from a voltage divider or potentiometer R which is connected across the plate supply 5. Any further grid voltage necessary to give proper bias,- as indicated by the voltmeter 3, may be applied by a voltage supply device 6 connected in series with the grid cathode circuit at terminals is as in Fig. 1, or as an other alternative circuit arrangement, as shown by Fig. 1a, the voltage supply device 6 may be connected in series withthe cathode lead at terminals i8. The voltage supply device 6 which is inserted in series with the input or grid circuit, is connected to supply either positive or negative potential, as may be required to prothereto is at a position R on the voltage divider R, then, if the plate supply voltage increases, the voltage on the cathode increases simultaneously by the amount R"/R oi the plate supply voltage change. Ordinarily, increasing the plate supply voltage would increase the plate current indi cated by current meter 4, if there were no compensation, but in this circuit the simultaneous increase of voltage on the cathode compensates for the plate supply increase, since increasing the cathode voltage positively effectively biases the grid negative so that the tube draws less current. Since changing the' voltage on the cathode eflectively changes the voltage on the grid, only a small fraction of the total plate supply voltage need be applied to the cathode to give compensation. Increasing this fraction (R/R) above this amount will cause over-compensation so that a plate supply increase causes the cathode voltage to increase enough to actually decrease the plate current, and vice versa, for plate supply decrease. Placing a fraction of the plate supply voltage changes'on the cathode of tube 2 has necessarily placed a fraction oi! the plate supply voltage on the cathode and caused 2 the cathode to become positive with respect a the grid. If this voltage, as indicated by the grid bias voltmeter I, is not enough to give the voltage necessary for the correct bias, additional,

bias may be obtainedfrom a voltage supply device O placed in the grid circuit at terminals II, as in Fig. 1,- or from a voltage supply device 8 placed in the'cathode circuit at terminals it as in Fig. 1a. If this voltage is more than is required for correct bias, a bucking voltage may be obtained from the voltage supply device 6 inserted in the cathode lead at terminals ll, as in Fig. 1a, to buck the cathode voltage down to that required for a correct bias, or positive voltage may be applied to the grid by placing voltage supply device 8 in the grid circuit at terminals ll, as in Fig. 1. It will be noted that voltage supply device t is merely a representation of a convenient circuit for supplying voltage of either positive or negative polarity as desired, and is not limited to this particular form.

The amount of plate supply voltage change needed on the cathode for complete compensation depends on the gain of the tube, since it is this change on the cathode, multiplied by a gain of the tube, which gives compensation in the plate circuit. Therefore, the amount of plate supply voltage change necessary on the cathode for 49, ll, 41 and I! and hence on the plate and screen, would in the absence of any compensation, cause more plate current to be drawn through the milliammeter, giving an erroneous reading on that meter; tapped across a portion of this divider (59) it receives a portion of the voltage increase positively, across the divider simultaneously, with the screen and plate; This increase of positive potential on the cathode is efiectively the same as an increase of negative potential on the grid which, of course, has the effect of decreasing the plate current drawn by the tube, thus compensating for the compensation will vary with difierent tubes and increase of positive potential on the plate and screen.

With this particular tube, under the operating conditions of this circuit, the cathode tap on forms the plate and screen voltage divider forthe tube when the switches S1, S2 and S: are in position 5. The switches 81, 8a and S: are in position 2.5 when the 2.5 milliampere scale of the recording milliammeter is being used, and in position 5 when the 5 milliammeter scale of the a recording milliammeter is being used.

and thus prevent serious degeneration and loss of overall gain of the amplifier. It should be noted in connection with the circuit diagram shown in Fig. 1 that if there is a hum on the plate. supply, the compensation will compensate forqathis'a'lso in the same manner inwhich it compensates for slow variations'in supply voltage.

Thecircuit arrangement shown in Fig. 2 is generally-similar to that of Fig. 1, except that a tetrode tube is used instead of a trlode. However, if the tetrode plate and screen supply are separate, it may be desirable to connect the compensating voltage divider R across the screen supply, as is shown in Fig. 3, rather than across the plate supply indicated in Fig. 2, since the plate output of the tetrode tube is relatively independent of the plate supply variations as compared with the screen supply variations. In either case, the principleof operation remains the same as is mentioned above in connection with Figs. 1 and 1a. Here again, bias may be obtained of correct polarity and amount by inserting voltage supply device 6 in either the grid or cathode circuits, as shown in Figs. 1 and 1a, respectively.

Referring now to Fig. 4 of the drawing, an amplifier circuit is shown which is particularly adapted for feeding signal voltages to a recording milliammeter. This amplifier comprises input terminals til which are connected to a 1.5 megohm resistor ll and a variable .5 megohm resistor 42 having an arm 43 which connects to the input grid of a type 6L6 screen grid tube 44, the output or plate circuit of which is connected to terminals 45 and "of the amplifier.

meter.

To illustrate the action of the supply voltage compensator, assume that the switches 81, S: and S: are in the 2.5 position. Assume that the plate and screen. supply voltage increases positively. This increase across the divider resistors Terminals 45 and 5a connect to a recording milliam- The heater is connected to an 8-volt supply 46.

By adjusting the variable sooo ohm resistor marked Zero adjust, the voltages across the recording milliammeter may be so balanced that no current flows in the milliammeter. This adjustment is made with no signal on the input terminal so that the meter reads zero with no input voltage. In other words, a reverse cun'ent is drawn through the meter and the zero adjust resistor. This reverse current is adjusted to an amplitude equal to that of the plate current of tube 44 under conditions of no signal input. Now,

a signal of positive polarity placed onthe input will cause the tube to draw more plate current in proportion to the intensity of this said signal and this current will register on the recording milliammeter.

Although only a few circuit arrangements have been shown employing this novel type 01' voltage compensation, it is to be distinctly understood that this invention is not to be limited to the modification shown as its principle of operation is capable of being applied to other circuits.

What is claimed is:

1. An amplifier circuit including a potential divider having a plurality of tapping points thereon, said potential divider being connected across a direct current supply source, said source being subject to variations in voltage, a thermionic discharge tube having acathode, a control grid, a screen grid and a plate, an input circuit connected from said control grid to the negative end of said divider, said cathode, screen grid and plate being connected to points of successively higher positive potential along said divider, the

connection to said plate passing through an output circuit, a connection from the positive end of said divider to said plate through a variable resistor to balance out the current flow through said output circuit in the absence of potential across said input circuit, the resistance or the portion of said divider between said negative end and said cathode connection being so related to However, since the cathode is.

assesss 3 the resistance of the whole of said divider that a change in voltage across said divider causes such similar change of potential applied to said cathode that the plate current in said tube is maintained constant.

2. An amplifier circuit including a plurality of resistors connected in a Y iormation. each of the arms of the said Y being of diflerent resistance and each having a plurality oi tapping points thereonto form. a pair of potential dividers having a portion in common, a source of direct current having its negative end connected to the base of said Y, a thermionic discharge tube having a cathode, a control grid, a screen grid and a plate, an input circuit connected from said control grid to said negative end. said cathode being connected to the junction 01' said Y, said screen grid and said plate being selectively connectable to successively further remote points on one or the other of the arms 0! said Y, the connection to said plate passing through an output circuit, means for selectively connecting the positive end of said source to either arm of said Y, a connection from the positive end of said source through a variable resistor to said plate,

'the resistance of the leg or said Y being so proportioned to the resistance of the whole of each of said potential dividers that a change in voltage of said source causes such similar change of potential to be applied to said cathode that the plate current in said tube is maintained constant.

3. An amplifier circuit including a plurality of resistors connected in a Y formation, each or the arms or the said Y being of diiterent resistance and each having a plurality of tapping points thereon to form a pair of potential dividers having a portion in common, a source or direct current having its negative end connected to the 10 base of said Y, a thermionic discharge tube hav ing a cathode, a control grid, a screen grid and a plate. an input circuit connected from said control grid to said negative end, said cathode being connected'to the Junction of said Y, said screen grid and said plate being selectively connectable to successively further remote points on one or the other of the arms of said Y, the connection to said plate passing through an output circuit, means for selectively connecting the positive end 0! said source to either arm of said Y, the resistance or the leg of said Y being so proportioned to the resistance of the whole or each of said potential dividers that a change in voltage of said source causes such similar change or potential to be applied to said cathode that the plate current in said tube is maintained constant.

ROBERT E. SCHOCK.

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