US2572690A - Rectifying apparatus - Google Patents

Description

Oct. 23, 1951 w. H. BIXBY RECTIF'YING APPARATUS Filed Oct. 19, 1948 5? FIG.

OFF

70 SOURCE 2/ WVENTOR W H. B/XBY ATTORNEY Patented Oct. 23, 1951 RECTIFYING APPARATUS William H. Bixby, Detroit, Mich., assignor to Donald R. Middleton and Stanley M. Hanley, doing business as Power Equipment Company, Detroit, Mich., a copartnership Application October 19, 1948, Serial No. 55,340

8 Claims.

This invention relates to rectifying apparatus and particularly to a rectifier comprising two grid-controlled gaseous discharge devices operating in parallel.

The principal object of the invention is to provide means for initiating conduction at effectively the same instant in two grid-controlled gaseous discharge devices operating in parallel.

A further object of the invention is to provide a new and improved'control system for two gridcontrolled gaseous discharge devices operating in parallel whereby the currents in the two devices,

respectively, are maintained substantially equal.

A characteristic of a grid-controlled gaseous discharge tube is that, in order to start conduction between the anode and cathode, it is necessary to first form an arc discharge between the control grid and the cathode. The grid voltage required for this depends upon the anode voltage and upon the design of the tube. When conduction starts, the grid thereafter loses control until the flow of current between anode and cathode is interrupted, after which it regains control until another breakdown occurs between grid and cathode.

For the successful operation of two such tubes in parallel, for greater rectified output, it is desirable that the tubes become conducting at practically the same instant in the cycle of the supply voltage, and that during the conducting portion of the cycle the current remain substantially equal in two tubes. Assuming the first condition to be satisfied, the latter requirement can be met by means of a center-tapped equalizer coil with one-half of its winding connected in series with one of the tubes and the other half in series with the other tube. Since considerable variation in the critical grid firing voltage is common between tubes of the same type, it is preferable that the voltage applied to the grids of the tubes have a very steep wave front in order to raise the gridcathode voltages of the two tubes, respectively, above the critical firing voltage at the same time. If a circuit for producing an abruptly rising peaking voltage were used for this purpose, the load capacity of the circuit would. of course, need to.

the other tube, that is, the controlling tube, there is impressed a firing voltage which need not be peaked but which may be a voltage obtained from an alternating-current supply source. When the controlling tube is fired and space current begins to flow therein, a voltage is thereby induced in the auxiliary winding which immediately fires the controlled tube. Throughout the rest of the cycle the current is maintained equally divided between the tubes by the well-known action of the equalizer coil.

Under certain circumstances, as hereinafter explained, the auxiliary coil may be dispensed with and the above results obtained by means of the equalizer coil.

The invention is applicable to the operation of two grid-controlled gaseous discharge tubes connected in parallel as a half-wave rectifier, or two pairs of such tubes connected as a full-wave rectifier.

The invention will be more clearly understood from the following detailed description and the accompanying drawing, of which:

Fig. 1 is a schematic view of a half-wave rectifier embodying the invention;

Fig. 2 is a modification of the circuit of Fig. 1; and

Fig. 3 is a schematic view of a full-wave rectifier embodying the invention.

Referring to Fig. l, the grid-controlled gaseous discharge tubes I and 2 are connected in parallel to form a half-wave rectifier for supplying rectified current from an alternating-current source 3 to a load 4. The primary of a transformer 5 is connected to the alternating-current source 3 and its secondary is connected between one side of the load 4 and the midpoint of an equalizer coil 6. The end terminals of the equalizer coil are connected respectively to the anodes of tubes l and 2. The cathodes of the tubes are connected in parallel across the center-tapped secondary l of a heater transformer, the primary of which is omitted from the drawing. The midpoint of the secondary l is connected to the other side of the load 4.

The grids of tubes l and 2 are provided with a negative bias from a potentiometer 8 connected in parallel with a condenser 9 across the output terminals of a bridge rectifier ID, to which alterhating current is supplied from source 3. A firing voltage for tube l is supplied by a transformer H, the primary of which is connected to source 3 and the secondary of which is connected between the grid and cathode of this tube in series with a portion of the biasing potentiometer 8 winding I3 is, in eifect, a transformer having a center-tapped primary.

When at the beginning of a half cycle of the the source 3, the secondary of transformer :5 is applying an increasing positive voltage to the anodes of tubes l and 2, at the .same time the secondary of transformer I! is applying a .posi-' tive voltage to the grid of tube 1. When the latter voltage has sufliciently overcome the negative bias provided by rectifier l9, tube ionizes and becomes conducting its grid-cathode current being limited byresistor l2. Current then flows ,through the upper ,half of the equalizer coil through the-anode cathode space of tube 1, and through the load I! back to the secondary .of

transformer-5. The initiationof current through .theupper half vof coil 3 induces ahigh voltage .in .the auxiliary winding is which is applied .to the grid of ,tube 2. The auxiliary winding is .so designed that this induced YOltage is great .enough to assure the firing of tube ,2, excessive gridcathode current being prevented by resistor i l. Current will then how through the lower half [of the equalizer coil .3, through the anode-cathode space of tube 2, and through the load 4 back to the secondary of transformer 5. Thus conduction is started in tube ,2 at practically the same instant that conduction is initiated in tube I. Thereafter, during the remainder of the cycle of the a t a in urrent s u ce. the curr nt will divide equally between the two tubes, or nearly so, ,due to the balancing action of the equalizer .coil For instance, if the current in tube .I should tend to increase more rapidly than the current in tube 2,.therchoking action of .the upper half of the coil 6 would tend to retard the in-- crease in tube I, while at the same time a voltage would be induced in the lower half of coil 6 which would tend to increase the current through tube 2. In this manner the reciprocal action tends to maintain the two currents approximately equal.

:Inthe operation .of the above circuit it is necessary to adjust the negative bias provided by pctentiometer 55 to a value that will always prevent the firing pf tube 2 until the start .of current tube I.

In Fig, 2 there is shown a modification of the circuitof Fig. 1 wherein the equalizer coil is connected on the cathode side of the tubes instead of on the anode side. Like characters are used to designate the same elements in these figures. As in Fig. 1, alternating-current source 3 ,supplies-power to transformer 5, one end of the secondary being connected to one side of the load 4 and the other end to the anodes of tubes I and 2. In this case the cathodes are separately heated by the center-tapped secondary windings I5 and IE of a heater transformer, the primary of which is not shown. The midpoint of secondary 1315 connected to one terminal of the equalizer coil 6 and the midpoint of secondary i6 is conof a load 29..

4 is supplied by transformer ll. Switch I! in one position connects coil l3 in the grid-cathode circuit of tube 2 and in the other position it excludes the coil.

With switch I! in the down position as shown. this circuit operates in the same manner as that of Fig. lghut has an advantage over th'e former .in the following respect. When, in Fig. 2, current begins to flow through tube l and through the upper half of equalizer coil 6, a voltage is thereby induced in the lower half of the coil whichmakes the cathode of tube 2 more negative with respect to its grid. This voltage therefore aidsin :thefiring-of tube 2. If its magnitude were great enough the auxiliary winding could be omitted entirely. This may be accomplished by operating switch H to the up position, the grid of tube '2 then being connected directly to the negative terminal of the bias supply.

Fig. 3 illustrates an :application of the invention to a full-wave rectifier, in which two tubes .of va typesuch as shown in Figs. 1 and ;:2 .are op.- erated in parallel to .rectifyone Ihalf of the wave and a similar pair of tubes to rectify the ether half. In this figure tubes .24 and .25 are connected :as a full-wave rectifier to supply direct current -to a load 29, .and would ,so operate with tubes 24' and 25' removed .from their sockets. With the two latter tubes in position, however, the .fir'ing. of tube .24 on one .half cycle causes tube 2 3 to fire, these two tubes sharing the load current in parallel. When tube .2 .5 begins to ccnduct, on the next half cycle it causes tube 25' to con.- duct "and these two tubes divide the .lcadrduring this half cycle. Tubes 25 and25 act theref qre as controlling tubes, while tubes :24 and 25' are the controlled tubes.

- Referring first to the .upper half of-Eig'the primary winding of transformer .20 is connected to the alternatin -current source 21. The sec ,ondary is divided into two parts, winding and winding 23. The upper terminal cf-winding 2.21s connected to the anode of tube 2-4 and the lower terminal of winding 23 to the-anode of tube 25.

; The other terminals of the two secondarywindin s are joined together through the upper .half

of an equalizer coil 23, .a conduct-or 27., and the lower half of an equalizer coil 1-26". Conductor :2 is connected through a choke coil "28 to one side The cathodes of tubes 24 and 25 are connected in parallel across :the center-tapped secondary 39 of a heating transformer, the primary of which is not shown, and the center tap is connected to the other side of the loa'd29. A condenser 31 is connected across the output terminals of the rectifier, forming a smoothing filter in combination with-choke coil 28. The grids of tubes Hand 25 are connected respectively to the terminals of .the center-tapped secondaryof a transformer 32, the midpoint of the transformer winding being returned through switch 33 to the cathodes via the center tap-of the secondary winding Current limiting resistors 34 and 35 are connected respectively in the grid-cathode circuits of tubes 24 and 25".

Potentiometer 36 in series with resistor 31, which is shunted by a voltage regulating gas tube 38 and a condenser 39, are connected across the output terminals of the rectifier. Potentiometers .40 and 4| and condenser-A2 are connected in par.- allel across the output terminals of. an auxiliary bridge rectifier 43, which is supplied with alterating current from source 2|. When switch 33 is in the on position it connects the midpoint .of the secondary of transformer .32 to the slider of potentiometer 36, and when in the off position to the slider of potentiometer 4 I.

It will be seen that the portion of Fig. 3 just described constitutes an ordinary full-wave rectifier, employing a single grid-controlled gaseous discharge tube for each half cycle of the alternating current to be rectified. In the lower half of the figure, with exceptions to be noted, tubes 24 and 25 are connected as a similar full-wave rectifier, with its output terminals in parallel with'those of the first rectifier. For convenience, the corresponding elements in this half of the drawing are given the same reference numbers asthose in the upper half, but with the addition of primes to distinguish them. Here the lower terminal of secondary winding 22' is joined to the upper terminal of windin 23 through the lower half of equalizer coil 26, conductor 21, and the upper half of coil 26. The grid of tube 24 is connected to' one end of the auxiliary winding 44, which is in inductive relation to equalizer coil 25, and similarly the grid of tube 25' is connected to one end of the auxiliary winding 44', which is in inductive relation to coil 26'. The other terminals of the auxiliary windings 44 and 44 are connected together and to the slider of potentiometer 40. The cathodes of tubes 24 and 25 are connected in parallel with those of,

tubes 24 and 25.

For the protection of gaseous rectifier tubes of this kind it is generally desirable to delay" conduction after the application of anode voltage until the cathodes have become heated to transformer 20, and with the slider of potentiometer 40 likewise adjusted for non-operation of tubes 24 and 25'. When the switch is turned to the on position after the warm-up period, tube 24 will fire near the start of a half cycle of positive voltage on its anode and grid, and current will begin to fiow through its anode-cathode space, through the load 29, through the upper half of equalizer coil 26, and thence back to the secondary winding 22. The voltage thereby induced in the auxiliary winding 44 will cause tube 24 to begin conducting also, the path of this current bein from secondary winding 22' through the anode-cathode space of the tube, through the load 29, through the lower half of equalizer coil 26, and thence back to the secondary, and through the rest of the half cycle tubes 24 and 24' will operate in parallel and share the load equally through the action of equalizer coil 25; as previously explained for Figs. 1 and 2.

In the same manner, near the beginning of the next half cycle the controlling tube 25 will start conducting and current will flow through its anode-cathode, space, through the load 23, through the lower half of equalizer coil 26', and thence back to the secondary winding 23. The voltage thereby induced in the auxiliary winding 44 will cause tube 25 to fire immediately afterwards, and current will start flowing through its anode-cathode space, through the load 2?, through conductor 21, and through the u per winding 23'.

half of equalizer coil 26' back to the secondary Equalizer coil 26 will then act to maintain equality of the currents in tubes 25 and 25' through the rest of this half cycle, in the manner previously explained.

In the adjustment of the biasing potentiometer 36 it is necessary to make sure that the negative bias is suflicient to prevent either controlled tube from firing ahead of its controlling tube. This bias will then be satisfactory for the warmup period also, i. e., with switch 33 in the "01! position.

When the circuit is operating with switch 33 in the on position, the negative bias for the controllin tubes 24 and 25 provided by potentiometer 36 fluctuates with the output voltage, thus varying the instant of firing. This exercises a regulating effect on the voltage, tending to keep it constant. The purpose of the constant voltage discharge tube 38 connected across .resistor 31 is to concentrate the entire variation in output voltage across potentiometer 35. I In Figs. 1 and 2, for simplicity, the provision of a separate biasing voltage for the warm-up period is omitted, and likewise the voltage regulating feature just mentioned.

What is claimed is:

1. In combination, a first and a second gaseous discharge device each having an anode, a cathode and a control electrode, a center-tapped reactance coil, means for supplying current from an alternating-current supply source to a load through a circuit having two parallel branch paths, each including the space current path of one of said devices in series with one half of said reactance coil, an auxiliary coil in inductive relation to said react-ance coil, a circuit including said auxiliary coil connecting the control electrode and cathode of said second device, and means for impressing upon the control electrode of said first device a potential with respect to its cathode for causing the control of space currentin both of said devices.

2. In combination with a rectifier comprising a first and second gaseous discharge device, each having an anode, a cathode and a control electrode, said devices being connected in parallel paths which are in series with an alternatingcurrent source and a load, a control system for insuring substantially equal division of current in said devices comprising a center-tapped equalizer coil the two halves of which are connected respectively in series with the anode-cathode discharge paths of said devices, an auxiliary coil in inductive relation to said equalizer coil, a circuit including said auxiliary coil connecting the control electrode and cathode of said second device, and means for impressing upon the control electrode of said first device a potential with respect to its cathode for initiating conduction therein and thereby initiating conduction immediately afterwards in said second device.

3. In a rectifying circuit having two parallel branch paths through which currents are transmitted from an alternating-current source to a load, said paths respectively comprising a first and a second gaseous space current rectifying device each having an anode, a cathode and a control electrode, means for controlling the current supplied from said source to said load comprising an inductance device having a first and a second winding, means for connecting respectively different portions of said first winding in the said parallel branch paths, a circuit connecting the control electrode and cathode of said r secondrectifying device including said second rvinding, and a circuit connecting the control electrode and cathode of said first rectifying device including a source of voltage for causing conduction to be initiated in said first device and "thereby causing the initiation .of conduction in said second device. Y

, ,4. In a rectifying circuit having two parallel branch paths through which currents are transmitted from an alternating-current source to a load, said paths respectively comprising a first and a second gaseous space current rectifying device each having an anode, a cathode and a control electrode, means for insuring substantially equal division of current in said rectifying 1 devices comprising an inductance device having afirst :and a second winding, means for connecting1different portions of said first winding respectively between the anodes of said rectifying devices and the said alternating-current source, .a' source of directacurrent biasing voltage, a circuit connecting the control electrode and cathodeof said second rectifying device including said second winding and said source of biasing voltage: and a circuit connecting the control electrode and cathode of said first rectifying device including said source of biasing voltage and a source of voltage for causing conduction to be initiated in said first device and thereby causing the initiation of conduction in said second device. 1 5! In a rectifying circuit having two parallel branch paths through which currents are transmitted from an alternating-current source to a load, said paths respectively comprising a first land a second gaseous space current rectifying device. each having an anode, a cathode and a control electrode, means for insuring substantially equal division of current in said rectifying devices comprising an inductance device having a first and a second winding, means for connecting a first portion of said first winding between the cathode of said first rectifying device and said load and a second portion of said first windins between the cathode of said second rectifying ,device and said load, a source of direct-current biasing voltage, a circuit connecting the control electrode and cathode of saidsecond rectifying device including in series said second windinc. said source of biasing voltage and said secend portion of said first Winding, and a circuit connecting the control electrode and cathode of saidfirst rectifying device including in series said source of biasing voltage, said first portion of said first .winding and a source ofvoltage for causing conduction to beinitiated in said first device andthereby causing the initiation of conduction in said second device.

6. in a rectifying circuit having two parallel branch paths through which currents are trans-,- -rnitted from an alternating-current source to a load,- said paths'respectively comprising a first and a second gaseous space current rectifying device each having an anode, a cathode and a control electrode, means for insuring substantially equal division of current in said rectifying devices comprising a center-tapped inductance coil, means for connecting one half of said coil between the cathode of saidfirst rectifying device and the said load and the second half of said 8 coil between the cathode of said second rectifying device and the said load, a source of direct- .current biasing voltage, a circuit connecting the control electrode and cathode of said second rece ,tifying device including said source of biasing voltage and said second half of said coil, and a circuit connecting the control grid and cathode of said first rectifying device including the first half of said coil, the said source of biasing-voltage and a source of voltage for causing conduction to be initiated in said first device and thereby causing the initiation of conduction in said second device. 1

'1. In a rectifying circuit having two parallel branch paths through which currents are trans-v mitted from an alternating-current source to-a load, said paths respectively comprising a first and a second gaseous space current rectifying device each having an anode, a cathode and a control electrode, means for insuring substantially equal division of current in said rectifying devices comprising an inductance device having a center-tapped first winding and a second Wind ing, means for connecting the two halves ofsaid first winding respectively in the said parallel branch paths, a source of direct-current biasing voltage, a circuit connecting the control electrode and cathode. of said second rectifying device in cluding said source of biasing voltage and said second winding, and a circuit connecting thereontrol electrode and cathode of said first rectifying device including said source of biasing voltage and a source of voltage for causing conduction to be initiated in said first device and thereby causingthe initiation of conduction in said sec-v ond device.

8. In combination, a first and a second gaseous space current device each having an anode, a cathode and a control electrode, means for sup? plying current from an alternatingecurrent source to a load through a circuit having two parallel branch paths, an inductance device having a first and a second winding, means for connecting said windings in said branch paths respectively between a first terminal of said load and said cathe odes respectively, control circuits including said windings respectively for connecting the control electrode and cathode .of said space current de vices respectively, and means for impressing an alternating voltage upon one only of said control circuits tocause conduction to be initiated repeatedly and substantially simultaneously in both said space current devices.

WILLIAM H. BIXBY.

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

UNITED STATES PATENTS Number Name Date 1,995,810 Klemperer Mar. 26, 1935 2,088,474 Haller July 27, 1937 2,134,530 Philpott et a1 Oct. 25, 1938 V FOREIGN PATENTS Number Country Date 445i1 8 Great Britain Apr. 2, 1936

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