US2431902A - Self-regulating high-frequency generator - Google Patents

Description

Dec. 2, 1947. ALB|N 2,431,902

SELF REGULATING HIGH-FREQUENCY GENERATOR I Filed Dec. 28, 1943 OUTPUT 19 17 I! 60 A; POWER Suppl. v 16 00 TPl/ T u... Petr/F152 FEEDEQICK GALB/N,

BY M

60' CATHODE 60w 3 a! Pan E2 ATTORN PowEe J'Npu'r INPUT Patented Dec. 2, 1947 SELF-REGULATING HIGIIfi-FithdfifiNGY GENERATOR Frederick G, Albimii s Angeles} to Radio Corporation of Delaware Applicationl eceniber28, 1943; s'eiialna'i. 5131912? 40mins; (Cl. 250;3

'rmt invention re ates to thermionic oscillators or"ele ctrica1 current generators, and particularly to" control circuits for stabilizing or regulating the input energy'to" an oscillator tube with respect to'the output energy therefrom.

In the industrial application of high frequency oscillators or" generators; the load is varied between zeroto maximum frequently, which is un' like conditions" imposed upon such oscillators when used in radio'broadca'sti'rig systems; Where theiload is'constant, it is only necessary to adjust' the" cathode and grid voltages or feedback voltage'a't the optimum values and the generators" will operate"satisfactorily overlong periods. Where the load on such oscillators isfrequently variedbetween zero an'd'maximum; the cathode emission should always be ample for the maximum" space current required and the cathode heater temperature should be'minimuin for optitube'ecoriemy; Furthermore, for thediighe'st efficiency; the" grid voltage" and current should be the rfia'kirhlirfi allowable when the oscillator" is workihg'iiitoa" full load; Normally however when the load is reduced, the grid voltage" and current will rise above the allowable maximum which will reduce the lifeof the tube as well'ascause possible damage by" overheating.

regulatory means to providethe optimum cathodeheater current in accordance with thespace current fiowing,-and also provides meansforincreasing the grid current to maximum during maximum' load and to decrease the grid voltage and current" as the load decreases; In thismanner, it is unnecessary fortheoperator or his assistant toad-just the grid current and; cathode heater current when changes are made in the oscillator load,-whichas mentioned above, occursfrequently where theoscillator output is used for industrial purposes such as wood gluing, heating of plastics, and-similaruses'. V a i 'I-he-use of feedback circuits in whichaportion of the output energy of" the oscillator is rectified forvarying the amount of energy suppliedto the cathode is well-known; a system of' thistype being disclosed and claimed in G. Jones, Jr., Patent No. 2, 175;694-of October 1Q, 1939. The Jones-invention however, is intendedtomaintain the high frequency output current constant; ir-

respectiveof load; by'varying the-filament power,-

whereas the present invention is for the purpose of;varying-thefilament power in accordance with thevariations in load, theload current being allowed to vary as-required; A novel method and means for varying the cathode heater tempera- Ifhe present invention is directed to automatic 21, ture' withfload changes as well as a means or; controlling the eildv'oltage and currentwitwioaaria i v eda f ,7

The principalflobject" or the nvention; there fore, isto facilitate the application of high f quency energy to" varying loadsover different te s: t f f. f. a a

Another object oflthe' invention is to providean improved high frequenc generator for" in diis'trialuses. v s v v r H A further'obje'et' of" the invention is to provide anim'proved regulatory'systernfor high fi equenoy" est matorswherein the grid voltage and} currentis varied n accordance with 'load va'riationsi A further oloj'ect of; t e inventio'n is'f tel 1 th vid'e an" improved regulatorysystein' for high frequency' oscillators wherein the cathode heater" current? is varied in accordance with load van ations:

A still further" object of the invention is to" provide an' improved high frequency oscillator or generator having a' regulatory circuit forvary ing' the grid feedback voltage and current'and" the" cathode" heater current in" accordance with variations in the load'on the oscillator; A'lthough the novel features" which are he'Fj lieved tobecharacterist'ic of this invention will; be pointed out with particularity in the appended claims; the manner of its org'anization and'the; mode of its operation will be better understood" byreferring' to the following description read conjunction" with the accompanying olr'awin'gs forming'apart'hereoflinwhichr I a n s Fig. 1 is a schefiiatic'ciicuit diagram or a high frequency oscillator" or generator embodying' thel grid voltage and" current regulatory circuit and cathode heating current regulator means of the invention, and

Fig; 2is aschematie circuit diagram ofa) high" frequencyoscillator embodying alternative'meansfor regulatingboththegrid voltage and currentand the cathodeheater power of the invention;

Referring nowto Fig; 1," a triode vacuum tube Sis-shown with ananode 6,' a'- grid T, and a-cathode'BI The anode circuitis connected overeatd-uctoi" H) to the tuning of tank inductance 1 shunted byfixed tuning or tank cond'enser l 3'and variabletuningand'feedback condensers II as" described in: detail'iii my copending" application; Serf No. 492 ,24'S;.fi1ed June 25; 1943; The tan or tuning coil 121's variably coupl ed to an output?- pickup coil l6 to var'y thelQ d: adapted to be connected across terminals l 1, A primary'wind mg I9 of a feedback transformer 20 having a secondary 2| is shown connected in the load circuit.

The normal grid circuit of the oscillator tube 5 is over conductor 24 to the mid-point between variable condensers I4. The radio frequency circuit from grid to cathode includes in order, conductor 24, the grounded half of variable condenser l4, ground, radio frequency transformer secondary 2|, conductor 29, and the filament bypass capacitors 22. A path for the direct current discharge of condenser 14 is provided through radio frequency choke coil 26 and resistor 21 to ground. Anode potential for the tube 5 is supplied from the rectifier 35 over conductor 36, choke coil 31 and the upper portion of tuning coil l2, a by-pass condenser 39 being connected to ground and the end of coil 31. The negative terminal of the rectifier 35 is connected over conductor 4| to ground. The cathode heating energy is obtained from any suitable power supply over transformer 3| and transformer 43, which power supply is also connected to the rectifier 35.

The adjustment of the secondary 21 of transformer 2D is such that with the radio frequency output power from the generator equal to the maximum rating for the apparatus, the optimum grid potential, current, and phase relative to the plate potential are obtained, and consequently the maximum efficiency is realized.

The phasing of the winding 2| is so determined that the potential across its terminals as a result of the load current through primary winding l9 adds to the potential obtained from condenser l4. Thus, the total grid-cathode potential is equal to the sum of these two voltages.

Under conditions of reduced output power, the potential of winding 2| is reduced, thereby reducing the potential of grid-to-cathode. Due to regulation of the anode circuit, when the load is reduced, the potential of condenser M will rise, but the amount of this rise is substantiall less than the decrease of potential of winding 2|. Thus, the net effect of the reduction of the load current is a reduction of grid-cathode potential.

Simultaneous with the above action, the large line current into the anode supply rectifier 35 induces a potential in the secondary circuit of the current transformer 3! adding to the potential obtained from the line to supply the transformer 43. Under conditions of maximum load, the filament potential and current are also maximum and ample for the space current of the tube 5. The reduction of output power causes a reduction in the anode supply rectifier line current, and consequently a reduction of filament power. This regulatory means is particularly applicable to tubes having pure tungsten filaments. It is also desirable for stable operation that the filament emission be above the saturation point for all load conditions. In other words, the filament emission must not be reduced to the condition where the tube output power is impaired due to lack of sufiicient emission. The regulatory means lessens the filament power above the saturation point.

Referring now to Fig. 2 in which a similar oscillator generator is shown, the tube 41 has an anode 48, grid 49, and cathode 58. The other elements of the tuning circuits, such as the coils l2, l6, and 31 and condensers l3, l4, and 39, correspond to the same numbered elements in Fig. 1. In the embodiment shown in Fig. 2, the grid voltage regulating circuit includes a feedback transformer 52 with its variable primary winding 53 and its secondary winding 54. The winding 54 is shunted by a variable condenser 55 for adjusting the phase in Fig. 2. It will be noted that the rectifier 51 supplying anode voltage for the tube 41 over conductor 58 and conductor 59, includes a winding 60 on the center leg of the cathode transformer core 6 l The cathode heating current is obtained from any suitable alternating current power source and impressed on primary winding 64 and then impressed on the cathode 50 from secondary winding 65 on core 6|, the winding 65 being shunted by alternating current circuit condensers 56. Since the plate current flowing through winding 60 varies the coupling between windings 64 and 65, the heating of cathode 50 is controlled by the load on the oscillator. That is, the higher the anode current, the greater the magnetic saturation of the core Bl. Thus, as the load increases and the space current increases, the greater the saturation of the core 61 which reduces the reactance in the transformer and permits a greater transmission of energy from the primary winding 64 to the secondar winding 65. This provides greater emission from the cathode and adequately accommodates the increased load. As the load is reduced, the plate current decreases and the reactance of the transformer increases to decrease the cathode heating current. In this manner, the optimum operating efficiency and economy is provided for the tube 41.

With the above regulatory circuits embodied in an oscillator or generator system, the cutput of the system may be varied between zero and maximum without overheating the system due to increased grid current, while maintaining maximum efiiciency of the system at all times. Since the secondary winding of filament transformer 43 in Fig. 1 has a high radio frequency potential above ground determined by the voltage across winding 2|, the circuit of Fig. 2 is preferred. Furthermore, the saturable transformer system of Fig. 2 is particularly suitable to an anode supply rectifier employing a three-phase supply line, although the modification of Fig. 1 could also be used with a three-phase supply source.

I claim as my invention:

1. An oscillator system comprising a thermionic vacuum tube having an anode, grid, and cathode, an anode-cathode circuit including a tuning inductance, a tuning condenser connected in shunt to a portion of said inductance, and a rectifier, a load circuit including the primary of a feedback transformer, and a grid-cathode circuit including a feedback condenser and the secondary of said feedback transformer, said feedback condenser being connected in shunt to a portion of said tuning inductance and said secondary of said feedback transformer being connected in series with said feedback condenser between said grid and cathode, the total grid-cathode potential being the sum of the feedback condenser voltage and the feedback transformer voltage.

2. An oscillator system in accordance with claim 1, in which means are provided to decrease the feedback transformer voltage with an increase in the feedback condenser voltage, saidmeans causing said feedback transformer voltage to decrease at a higher rate than the feedback condenser voltage.

3. An oscillator system comprising a thermionic vacuum tube having an anode, grid, and cathode, a tank circuit including a truning inductance, a tuning condenser, and a feedback condenser, a load circuit coupled to said tuning inductance, said tuning condenser being connected across a portion of said inductance and said feedback condenser being connected across another portion of said inductance a feed back transformer having a primary winding in said load circuit, an anodecathode circuit including said tuning condenser and said tuning inductance and a grid-cathode circuit including said feedback condenser and the secondary winding of said feedback transformer, the grid-cathode potential being the sum of the voltage across said feedback condenser and the voltage across the secondary of said feedback transformer, the decreases in the voltage in said load transformer being greater than the increases in voltage across said feedback condenser during variations in the output of said vacuum tube.

4. An oscillator system in accordance with claim 3, in which a cathode heating circuit is provided, said circuit including a transformer having a core, said anode-cathode circuit of said vacuum tube also including a winding on said core, variations in the feedback voltage across said feedback transformer varying the current in said transformer core winding to vary the current fed to said cathode.

FREDERICK G. ALBIN.

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

UNITED STATES PATENTS

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