US2597980A - Electric circuit comprising electric discharge device - Google Patents

Description

y 1952 J. M l. FERGUSON ETAL 2,597,980

ELECTRIC CIRCUIT COMPRISING ELECTRIC DIESCHARGE DEVICE Filed Dec. 19. 1949 2 SHEETS-SHEET 1 INVENTORS JOHN ll. FERGUSON CLIFFORD BROWN AT T ORNEYS May 27, 1952 J. M I. FERGUSON ET AL ELECTRIC CIRCUIT COMPRISING ELECTRIC DISCHARGE DEVICE Filed Dec. 19. 1949 2 Sl-EETS-SHEET 2 It /\l INVENTORS: JOHN M. FERGUSON CLIFFORD BROWN.

FIG. 2.

BY 6% 76M ATTORNEYS Patented May 27, 1952 ELECTRIC CIRCUIT COMPRISING ELECTRIC DISCHARGE DEVICE John McIntyre Ferguson and Clifl'ord Erown,

Stafford, England, assignors to: The English Electric Company Limited, London, England, a

British company Application December 19, 1949, Serial No: 1 38,884

In Great Britain December 31, 1948 This invention relates to electrical pulse generating circuits.

An object of the invention is to provide a pulse generating circuit suitable to serve as a radar modulator and to handle pulse powers up to the order of 10 megawatts and more.

In carrying the invention into efiect, a pulseiorming network is charged through a step-up transformer from a source of alternating current having frequency equal to that of the pulserepetition required, and is discharged by a pulse of very heavy current through a load and through a discharge tube of the mercury pool type. This discharge is immediately preceded by another heavy current discharge through the tube.

Fig. l of the accompanying drawing illustrates diagrammatically a pulse generating circuit which embodies the invention in preferred form. This circuit is employed as pulse modulator in a radar transmitter. Fig. 2 illustrates the wave forms at various points in the circuit of Fig. 1.

The network is a pulse-forming network which is alternately charged, relatively slowly, from an alternating current generator l2 and discharged, very rapidly, through a load [3.

The frequency of the alternating current generated by generator [2 is equal to the repetition frequency required for the pulses, which may be about 500 cycles per second. At this frequency, network It! presents impedance which is substantially a capacitance. It is charged from generator I2, during part of a cycle thereof, through a step-up transformer II and a choke 26, and it reaches a potential of about 20 kilovolts.

The discharge path for the network It comprises in series the load [3, represented as a resistance, and the arc path from anode M to cathode |5 of a mercury pool discharge device. The discharge ofthe network l0 takes the form of a square-wave pulse of very heavy current, say about 500 amps, subsisting for about one or two microseconds.

The mercury pool discharge device is provided with an igniter l6 supplied with current from a direct current source 21 of about 100 volts, this current being under control of a push-button l1 and limited by series resistor 28.

The direct current source 2'! also supplies current through choke 29 and resistor 31 to an excitation anode l8. This current is limited by resistor 31 to about 5 amps, and maintains a steady excitation are from anode 8 to cathode j 3 Claims. (01. 250-27) 15 after the igniter has been operated. byv pushbutton ll.

In order to avoid the danger that the excitation are may be quenched when network I0 is discharged, a further anode I9 is arranged to discharge a condenser 20 during the period covering the instant when discharge of network 10 is to occur.

Condenser 20 is charged substantially linearly ;from a direct current source 2| through a large inductance 22. Once in every cycle of alternating source 12, condenser 20 is discharged by a heavy current flowing through inductance 23 and the path between anode l9 and cathode I5. The

discharge is initiated, about 50 microseconds in advance of the instant for discharge of network I 0, by application of a firing pulse to control grid 24 which covers anode l9. Inductance 23 and condenser 20 are so proportioned that the discharge current will have the form of a half sine wave of duration about microseconds and peak value about amps. About the instant when this current reaches its peak, a firing pulse is applied to control grid 25 which covers anode l4, and the very rapid discharge of capacitance to through load 13 then occurs.

The firing pulses for the control grid 24 are derived from a small alternating current generator 30 which is coupled to generator I2 and produces alternating current of the same frequency. The output of generator 30 is applied through a phase shifter 3| to a pulse generator 32, from which firing pulses are applied over bias source 33 to control grid 24. Phase shifter 3| can be adjusted so that these firing pulses occur when network I0 is charged and ready for discharge.

The firing pulses for the control grid 25 are applied from a pulse generator 34 over bias source 35. Pulse generator 34 is controlled from pulse generator 32 through time delay network 38,

which can be adjusted to give the desired interval between the firing pulses on control grids 24 and 25.

In Fig. 2-

Wave form Vl2 represents the 500 cycles per second sine wave voltage generated by the generator l2 of Fig. 1.

Wave form V24 represents the voltage of control grid 24 relative to cathode [5.

Wave form V20 represents the voltage across condenser 20.

Wave form Ii 9 represents the intermittent half sine wave discharge currents from anode Is. The time scale is exaggerated relative to that of wave forms V12, V24, V20, because the duration OFFICE of each of these discharges from anode I9 is only about 100 microseconds.

Wave form V25 represents the voltage of control grid 25 relative to cathode l5.

Wave form-y represents the voltage between anode H and cathode l5.

Wave form IIS represents the current pulses through load l3; and as each of these has .a duration of only about two microseconds, the time scale is'exaggerated even more than that of wave form I19.

In the method of operating the apparatus which has been described, the'discharge between anode l4 and cathode I5 is timed to occur when" that between anode l9 and cathode I5 is near its peak. Alternatively, however, the discharge between anode l4 and cathode 15 may be timed to occur at any time up to 100 microseconds later than this.

What we claim as our invention and desire to secure by Letters Patent is:

1. An electrical pulse generating circuit com prisingan electric-discharge tube having a mercury poolcathode a first anode provided with a first controligrid, and a. second anodeprovided with a second controlgrid; aload, .a first capacitance, a path for discharging said first capaci" tance through said load and through the arc path betweerrsaid first anode and said cathode by a'veryheavy current subsisting fora period of the order of microseconds upon the appiiea= tion ofafiring pulse tosaidfirst control grid;

an" alternating current source-and a step-up transformerarrangedto charge said first capacitance; a second capacitanceconnected in series forms a substantially sinusoidal half-wave subsisting for a period of the order of hundreds of microseconds, and means to apply a firing pulse to-said first control grid at a time within a period of loo-microseconds commencing during said heavy current discharge.

2. A circuit according to claim 1, wherein the electricdischarge tube is provided with means to maintain a continuous excitation arc therein.

'3. A circuit according to claim 2, wherein the electric discharge device is provided with an igniter for initiating-the excitation are.

JOHN MCINTYRE FERGUSON. CLIFFORD BROWN.

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

UNITED STATES PATENTS Number Name Date 2,242,948 Gulii ksen d- May 20 1941 2,288,554- Smith June 30; 1942 2,458,574 Dow Jan. 11, 1949 2,498,257

Douma Feb. 21, 1950

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