474,607

PATENT SPECIFICATION

Application Date: April 29, 1936. No. 12117/36

Complete Specification Left: March 24, 1937.

Complete Specification Accepted: Oct. 29, 1937.

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PROVISIONAL SPECIFICATION

Improvements in or relating to Electric Smoothing Circuit Arrangements

We, ALAN DOWER BLUMLEIN, a British subject, of 32, Audley Road, Ealing, London, W.5, and ERIC LAWRENCE CASLING WHITE, a British subject, of 32, The Rise, Hillingdon, Middlesex, do hereby declare the nature of this invention to be as follows:-

This invention relates to circuit arrangements for smoothing high tension voltage supplied to electrical apparatus and has particular reference to high tension supply circuits for thermionic valves. It is desirable that the output impedance of the smoothing circuit should be low and one object of the invention therefore is to provide a smoothing circuit which will supply a constant high tension voltage and will present a low resistive impedance to the apparatus supplied.

According to the present invention, apparatus is supplied with direct current from a source connected in series with a thermionic valve, the grid of which is maintained at a positive potential with respect to the negative terminal of the source of supply, said potential being caused to follow potential variations of the source of supply derived from an impedance connected across the source of supply. The impedance may take the form of an ohmic resistance or such a resistance connected in series with a gas discharge tube having the property of providing a substantially constant voltage for a varying current passing through it and provided with tapping points of different potential.

In order that the nature of the invention may be more clearly understood, two smoothing circuit arrangements embodying the invention will now be described by way of example.

Thus, in one circuit arrangement a potentiometer resistance is connected directly across the terminals of the source of supply to be smoothed and an adjustable tapping point is coupled through a condenser and leak resistance having a time constant of the order of eight seconds, to the grid of a triode valve having a bias resistance inserted in the cathode lead. The anode of this valve is connected through a resistance to the positive terminal of the source of supply and a condenser and leak resistance having a time constant of the same order as that of the preceding coupling, serve to couple the anode to the grid of a second triode valve. A source of positive potential is inserted between the lower end of the leak resistance and the negative line.

A resistance is also inserted in the cathode lead of this second valve, the anode of which is connected directly to the positive terminal of the source of supply. A connection is taken directly from the cathode of this valve to the grid of a third valve, the anode of which is directly connected to the source of supply while the cathode is connected directly with the positive terminal of the load to be supplied. The negative terminal of the load is directly connected with the negative terminal of the source of supply.

The resistance in the cathode lead of the second valve ensures that the potential of the grid of the third valve will be maintained at a positive potential with respect to the negative terminal of the source and that this potential will vary with that between the grid and cathode of the second valve. Assuming that the impedance of the source is low compared with the anode impedance of the third valve, this valve will present to the load to be supplied an impedance approximately equal to the inverse of its slope.

In operation, any sudden increase of potential at the tapping point in the potentiometer will cause an increase of anode current in the first valve and a consequent decrease in the anode potential. The potential of the grid of the second valve is thus also reduced and because the cathode of this valve is directly connected with the grid of the third valve, the potential of this last mentioned grid will also be reduced. It will be understood that as this grid is controlling directly the current from the source though the third valve to the load terminals automatic compensation for variations in the source of supplying can be effected. The tapping point on the potentiometer is of course selected to ensure that controlling voltage is taken from the most effective point to ensure that impulsive changes of the potential of the source of supply will not cause corresponding impulsive variation of the voltage at the load terminals.

If the source of supply is more prone to slow changes in potential than to impulsive changes in potential, this condition can be corrected by using batteries instead of condensers and leak resistances for coupling the first and second valves. The battery replacing the first coupling condenser serves to determine the working point on the characteristic of the first valve with reference to the tapping point on the potentiometer. The battery replacing the condenser coupling the first and second valves mainly controls the direct current potential of the output terminals because it determines the bias potential on the grids of the second and third valves.

In another circuit arrangement, the potentiometer comprises an ohmic resistance connected in series with one or more neon discharge tubes connected across the source to be smoothed. It is known that gas filled discharge tubes have the property of giving a substantially constant voltage for varying currents passing through them and this property is utilised in the circuit being considered. A single tube having a number of electrodes arranged at different points within the length of the tube may be used, connections being taken from the separate electrodes to external points.

The junction between the resistance and the neon tube is connected directly to the cathode of a triode valve the grid of which is controlled by a potential derived from a tapping point in a resistance connected at one end to a point of constant potential in the neon tube and at the other end to a tapping point in a resistance connected directly across the source of supply this tapping being taken from point which yields a potential approximately equal to that taken from the neon tube. The connection to the neon tube may be made to a point in a resistance joining an end electrode to an intermediate electrode.

The anode of the triode valve is connected through a resistance to the positive terminal of the source of supply and a connection is taken from the end of this resistance nearest the anode, through two decoupling resistances in series to the grid of a second triode valve. A decoupling condenser is connected in the usual manner between the point of connection between the decoupling resistances and the negative terminal of the source of supply. The anode of the second triode valve is connected directly with the positive terminal of the source of supply and the cathode of this valve is connected directly to the positive terminal of the load. The negative terminal of the load is connected directly with the negative terminal of the source.

It will be understood that under normal constant voltage conditions of the source of supply there will be no variation in potential of any given point on the resistance connected across the supply. The tapping point in the resistance connecting the neon tube to the resistance across the source of supply may therefore be changed without altering the potential applied to the grid of the first triode valve and consequently without altering the anode current of this valve. The potential applied to the grid of the second valve is thus also unchanged. The potential of the grid of the first valve will therefore only vary when there is a variation in the potential drop along the resistance connected across the source due to variations in the source of supply. The anode current of the first valve will for example, increase when the potential drop along that resistance increases due to a rise in the potential of the positive terminal of the source of supply and the consequent decrease in anode potential will be applied to the grid of the second valve, so counteracting the tendency to an increase of the anode potential of this valve and a corresponding increase of potential at the positive terminal of the load.

It will be understood that the provision for decoupling in order to prevent high frequency oscillations from being set up may be made in the first circuit described and other variations may be made within the scope of the invention.

Dated this 28th day of April, 1936.

F. W. CACKETT,

Chartered Patent Agent.

COMPLETE SPECIFICATION

Improvements in or relating to Electric Smoothing Circuit Arrangements

We, ALAN DOWER BLUMLEIN, a British subject, of 32, Audley Road, Ealing, London, W.5, and ERIC LAWRENCE CASLING WHITE, a British subject, of 32, The Rise, Hillingdon, Middlesex, do hereby declare the nature of this invention and in what manner the same is to be performed, to be particularly described and ascertained in and by the following statement:-

This invention relates to circuit arrangements for smoothing high tension voltage supplied to electrical apparatus and has particular reference to high tension supply circuits for thermionic valves. It is desirable that the output impedance of the smoothing circuit should be low and one object of the invention therefore is to provide a smoothing circuit which will supply a constant high tension voltage and will present a low resistive impedance to the apparatus supplied.

In connection with circuit arrangements for compensating for fluctuations in supply voltages for thermionic valve apparatus, it has been proposed to employ thermionic valves in series with the source of supply and a load, and to provide means for controlling the internal impedance of the thermionic valves in dependence upon variations in current taken by the load. In the Specification of Patent No: 446,294, it is proposed to connect a resistance across a load supplied from thermionic rectifiers through a regulating valve and to control the regulation by an amplified voltage derived from said resistance.

According to the present invention, a circuit arrangement for smoothing variations in potential of a source of direct current supply includes a regulating thermionic valve connected in series with the source of supply and a positive load terminal and means for maintaining the control grid of said thermionic valve at a positive potential with respect to the negative terminal of the source of supply, said potential being subject to variation from a superimposed potential which is derived from an impedance connected across the source of supply on the supply side of said regulating valve, said superimposed potential being caused to vary with but in opposite sense to said variations in potential of the source of supply. The potential of the grid of the regulating valve is caused to vary to such a degree as to compensate for the variation in potential of the anode of the regulating valve so as to provide a substantially constant voltage at the load terminals.

In a particular circuit arrangement embodying the invention, variations in potential of the source of supply set up in said impedance are applied to the grid of a second thermionic valve, the output of which controls the potential of the grid of said regulating valve connected in series with the source of supply. A third valve arranged between said regulating valve and said second valve has a resistance connected in its cathode lead, said resistance having a value such that the potential of the cathode of the third valve varies with that of its control grid. The cathode of the third valve is connected directly to the grid of the regulating valve may follow directly variations in potential of the cathode and grid of said third valve.

In an alternative circuit arrangement embodying the invention, potential variations setup across a first resistance connected across the source of supply are applied to the control grid of a valve, the output of which controls the grid potential of said regulating valve, a further resistance connected in series with a gas discharge device across the source of supply being utilised to provide a point of constant reference potential with respect to a tapping point in said first resistance.

In order that the invention may be more clearly understood and readily carried into effect, two smoothing circuit arrangements embodying the invention will now be described by way of example with reference to the accompanying drawings in which:

Figure 1 shows one form of circuit including a resistance connected directly across the source of supply, and providing compensating potentials to a valve circuit, and

Figure 2 shows an alternative form of circuit in which a gas discharge device is connected across the source of supply in series with an ohmic resistance.

Referring to Figure 1 of the drawings, a potentiometer resistance 1 is connected directly across the terminals 2 and 3 of a source of supply the voltage of which it is desired to smooth, and an adjustable tapping 4 is coupled through a condenser 5 and leak resistance 6, having a time constant of the order of eight seconds, to the grid of a triode valve 7, having a bias resistance 8 inserted in the cathode lead. The long time constant of the condenser and resistance combination 5 and 6 is chosen to enable slow variations in potential to be transmitted to the grid of valve 7. The anode of the valve 7 is connected though a resistance 9 to the positive terminal 2 of the source of supply, and a condenser 10 and leak resistance 11 together having a time constant of the same order as the condenser 5 and resistance 6, serve to couple the anode of the valve 7 to the grid of a triode valve 12. A source of positive potential 13 is inserted between the lower end of the leak resistance 11 and the line 14 connected to the negative terminal 3.

A resistance 15 is connected in the cathode lead of the valve 12, the anode of which is connected directly to the positive terminal 2 of the source of supply. A connection is taken directly from the cathode of the valve 12 to the grid of a valve 16, the anode of which is directly connected to the terminal 2, while the cathode is connected directly to the positive terminal 17 of the load to be supplied. The negative terminal 18 of the load is directly connected through the line 14 to the negative terminal 3 of the source supply.

The resistance 15 in the cathode lead of the valve 12 is provided in order that the potential of the grid of the valve 16 will be maintained at a positive potential with respect to the negative terminal of the source of supply, and this potential will vary with that between the grid of the valve 12 and the negative terminal of the source. Instead of a single valve 16, several valves connected in parallel and feeding one or more loads may be employed. Provision for decoupling may be made in order to prevent high frequency oscillations from being set up.

In operation of the circuit, any sudden increase of potential at the tapping point 4 in the potentiometer 1 will cause an increase of anode current in the valve 7, and a consequent decrease in the potential of the anode of this valve. The value of the resistance 9 connected in the anode lead of valve 7 must be such that increase in the potential at the positive terminal 2 will cause a decrease in the potential of the anode of valve 7. Thus if the resistance 9 is of too small a value the rise of potential of the anode of the valve 7 due to an increase of the positive potential at the terminal 2 might be greater than the drop in potential of the anode due to an increase in the anode current of the valve consequent upon an increase in the positive potential applied to the grid of the valve from the tapping point 4. The decrease of the potential of the anode of the valve 7 is accompanied by a decrease in the potential of the grid of the valve 12, and because the cathode of this valve follows the potential of its grid and is directly connected with the grid of the valve 12, and because the cathode of this valve follows the potential of its grid and is directly connected with the grid of the valve 16, the potential on the grid of the valve 16 will also be reduced. It will be understood that as this grid is controlling directly the potential on the load terminals 17 and 18, automatic compensation for variations in the source of supply operating on the anode of valve 16 can be effected. The tapping point 4 on the potentiometer 1 is of course selected to ensure that controlling voltage is such as to neutralise the effect of anode potential variations on valve 16 so as to ensure that impulsive changes of the potential of the source of supply will not cause corresponding impulsive variation of the voltage at the load terminals. The function of valve 12 is to provide a low impedance to valve 16 in case this latter valve should pass grid current. If there is no risk of 16 passing grid current, valve 12, and resistance 15 may be omitted, the top of 11 being connected to the grid of 16.

If it is desired to maintain the load voltage for slow as well as rapid changes of supply potential, batteries may be used instead of condensers and leak resistances for coupling the grids of valves 7 and 12. The battery replacing the coupling condenser 5 serves to determine the working point on the characteristic of the valve 7 with reference to the tapping point 4 on the potentiometer 1. The battery replacing the condenser 10 mainly controls the direct current potential of the output terminals because it determines the bias potential on the grids of the valves 12 and 16, the battery 13 and leak resistances 6 and 11 being omitted.

In the circuit arrangement of Figure 2, a potentiometer comprising an ohmic resistance 19 connected in series with a neon discharge tube 20 is connected across the terminals 2 and 3 of the source the voltage of which is to be smoothed. It is known that gas filled discharge tubes have the property of giving a substantially constant voltage for varying currents passing through them and this property is utilised in the circuit being considered. A single tube having a number of electrodes arranged at different points within the length of the tube is shown. The junction between the resistance 19 an the neon tube 20 is connected directly to the cathode of a triode valve 21, the grid of which is controlled by a potential derived from a tapping point 22 in a resistance 23 connected at one end to a point 24 of constant potential in the neon tube 20 and at the other end to a tapping point 25 in a resistance 26 connected directly across the source of supply, this tapping being taken from a point which yields a potential approximately equal to that taken from the neon tube. The connection to the neon tube is made to the point 24 in a resistance 27 joining two electrodes of the tube.

The anode of the triode valve 21 is connected through a resistance 28 to the positive terminal 2 of the source of supply and a connection is taken from the end of this resistance nearest the anode, through two decoupling resistances 29 and 30 in series to the grid of a triode valve 31. The considerations which apply to the choice of the value of resistances 9 in Figure 1 apply also to the resistance 28 which, in Figure 2, determines not only the voltage at the anode of the valve 21, but also, in conjunction with resistances 29, 30, the voltage of the grid of valve 31. A decoupling condenser 32 is connected in the usual manner between the point of connection between the decoupling resistances and the negative terminal 3 of the source of supply. This decoupling condenser serves only to remove the compensating effect for very high frequencies where the source can be adequately smoothed by small condensers so that the compensation is unnecessary. This decoupling condenser prevents the valves from oscillating at high frequencies (for example, one megacycle). The resistance 30 prevents oscillation of the valve 31 at yet higher frequencies. The anode of the valve 31 is connected directly with the positive terminal 2 of the source of supply and the cathode of this valve is connected directly to the positive terminal 17 of the load. The negative terminal 18 of the load is connected directly with the negative terminal of the source.

It will be understood that under normal constant voltage conditions of the source of supply there will be no variation in potential of any given point on the resistance 26 connected across the supply. The tapping point 22 in the resistance 23 connecting the neon tube 20 to the resistance 26 connected across the source of supply may therefore be changed without altering the potential supplied to the grid of the valve 21 and consequently without altering the anode current of this valve. The potential applied to the grid of the valve 31 is thus also unchanged. The potential of the grid of the valve 21 will therefore only vary when there is a variation in the potential drop across the resistance 26 due to variations in the potential of the source of supply. The anode current of the valve 21 will, for example, increase when the potential drop across the resistance 26 increases due to a rise in the potential of the positive terminal 2 of the source of supply and the consequent decrease in anode potential will be applied to the grid of the valve 31 so counteracting the tendency to an increase of the anode potential of this valve and a corresponding increase of potential at the positive terminal of the load.

A further valve may be inserted between the anode of valve 21 and the grid of valve 31 in the same manner as valve 12 in Figure 1. This further valve will provide a low impedance towards the grid of 31 in case grid current flows.

The neon tube 20 shown in Figure 2 may be replaced by a battery, the potentiometer 27 being taken from the positive terminal of the battery either to a tapping or to the negative terminal of the load, to which also the negative terminal of the battery is connected. When a battery is used, the resistance 19 may be omitted, and in this case the cathode 21 is connected to a point in the battery. A tapping point 24 will still be made in the potentiometer 27 now connected across the battery. The battery, like the neon tube provides a reference potential.

As a further modification the anode cathode path of a triode may replace the resistance 19, the neon tube being omitted and the potentiometer 27 extending from the cathode of this additional valve to the negative terminal of the supply, and serving as a load to the extra valve and to valve 21 as well serving as a potentiometer. The grid of this extra valve is held at a positive potential with reference to the negative supply which potential is in effect the reference potential. For this purpose a bias battery may be inserted between the grid of the extra valve and the negative terminal of the supply. The cathode of the extra valve which is connected to the cathode of valve 21 provides a low impedance reference potential for the cathode of valve 21 and for the top of the potentiometer 27.

Both the circuits shown serve to provide compensation for sudden or transient voltage changes and in the case of Figure 2 also, for slowly varying changes, such changes being effective upon the grid of the regulating valve or valves to annul the effects of changes of anode potential on this valve. It will be seen in the case of Figure 2, that there are direct current connections between the resistance 19, neon tube 20 and the valve 21 and between that valve and the valve 31. The control potential for balance (to annul changes in output voltage) must be opposite in sense to the change of anode voltage and approximately EQUAT. HERE times that change in voltage, where µ is the amplification factor of the regulating valve or valves. In the case of compensation for slowly varying changes in the supply voltage as provided for in Figure 2, it is necessary to provide a reference voltage to which part of the supply voltage may be compared and the regulation effected in accordance with this comparison.

Having now particularly described and ascertained the nature of our said invention and in what manner the same is to be performed, we declare that what we claim is:-

  1. A circuit arrangement for smoothing variations in potential of a source of direct current supply including a regulating thermionic valve connected in series with the positive terminal of the source of supply and a positive load terminal, and means for maintaining the control grid of said thermionic valve at a positive potential with respect to the negative terminal of the source of supply, said potential being subject to variation from a superimposed potential which is derived from an impedance connected across the source of supply on the supply side of said regulating valve, said superimposed potential being caused to vary with, but in opposite sense to, said variations in potential of the source of supply.
  2. A circuit arrangement according to Claim 1, wherein the potential of the grid of the regulating valve is caused to vary to such a degree as to compensate for the variation in potential of the anode of the regulating valve so as to provide a substantially constant voltage at the load terminals.
  3. A circuit arrangement according to Claim 1 or 2, wherein the voltage variations in the source of supply are applied to the grid of a second thermionic valve having a load impedance in its anode circuit, and wherein the potential of the anode of said second valve controls the potential of the grid of the regulating valve.
  4. A circuit arrangement according to Claim 3 wherein a third thermionic valve is inserted between the anode of the second valve and the grid of the regulating valve, the grid of the regulating valve being connected directly to the cathode of the third valve.
  5. A circuit arrangement for producing a substantially constant voltage at the terminals of a load fed from a source of direct current supply, including a regulating thermionic valve or valves connected in series between the positive terminal of the supply and the positive load terminal, means for maintaining the grid of said regulating valve or valves at a positive potential with respect to the negative load terminal, said potential being subject to variation from a superimposed potential which is derived from an impedance connected across the source of supply on the supply side of said regulating valve of valves, said superimposed potential being caused to vary with, but in opposite sense to, the supply voltage by a second thermionic valve, the grid of which is controlled in accordance with the difference of potential between the whole or a portion of the supply voltage and a reference potential.
  6. A circuit arrangement for smoothing variations in potential of a source of direct current supply including a regulating thermionic valve or valves connected in series with the source of supply and a positive load terminal, means for maintaining the control grid or grids of said regulating valve or valves at a positive potential with respect to the negative terminal of the source of supply, potential variations in the source of supply set up in a potentiometer resistance connected across the source of supply on the supply side of said regulating valve or valves, said potential variations being applied to the grid of a second thermionic valve output of which controls the grid potential of said regulating valve, a source of reference potential being arranged between the cathode of said second thermionic valve and the negative terminal of the supply.
  7. A circuit arrangement according to Claim 5, wherein said reference potential is provided by a battery or is a potential across a glow discharge tube.
  8. A circuit arrangement according to Claim 5, wherein said reference potential is the potential between a cathode of a valve and the negative terminal of the supply, the grid of the valve being maintained from a voltage source at a positive potential with reference to the negative terminal of the supply.
  9. A circuit arrangement according to any one of Claims 5, 6 or 7, wherein the grid of regulating valve is controlled from the anode of the second valve.
  10. A circuit arrangement according to any one of Claims 5, 6, or 7, wherein a third valve is connected between the anode of the second valve and the grid of the regulating valve, the grid of the regulating valve, the grid of the regulating valve being connected directly to the cathode of the third valve.
  11. A circuit arrangement for smoothing variations in potential of a source of direct current supply substantially as described with reference to Figure 1 or Figure 2 of the accompanying drawings.

Dated this 23rd day of March, 1937.

F. W. CACKETT,

Chartered Patent Agent.

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Leamington Spa: Printed for His Majesty’s Stationery Office, by the Courier Press. – 1937.