US2447616A - Electronic power generation - Google Patents

Description

A 1948. s. LAPPIN ETAL 2,447,616

' ELECTRONIC POWER GENERATION Filed April '7, 1945 ATTORNEY Patented Aug. 24, 1948 Lester S. Lappin, Camden, and Robert'F. Holt z,

Merchantville. N. J., assignors to Radio Corporation of America, a corporation of Delaware Application April 7 1945, Serial No. 587,176

This application discloses a new and improved means for generating high frequency power.

A general object of the present invention is to improve high frequency power generators for industrial and similar purposes.

A more particular broad object of the present invention is improved means of dielectric heating of non-conducting materials.

Power generators of the nature involved here known in the prior art include an electron discharge tube in a regenerative oscillation circuit. In many instances the regeneration circuit includes a tank circuit inductance through which the direct current for the tube anode flows. These power generators are satisfactory in many cases, but are of limited application for various reasons, many of which flow from the presence of the direct current and/or voltage in the tank inductance. For example, the tank circuit inductance in many cases is in or adjacent the load or material being worked on, so that the operator or operators are sufficiently near thereto to be endangered by the high voltage and/or currents involved.

Moreover, in many of these known systems inductive coupling between the tank circuit and the load is used, and in many cases these arrangements operate unsatisfactorily because this 9 Claims. (c ase-4s) circuit arrangement wherein the direct current is eliminated, thereby reducing the danger to which the operator is exposed. To attain this object, we provided a regenerative generator of the Colpitts type with two tubes and a tank circuit wherein blocking and coupling capacity is used between the anodes of the generator tubes and the tank circuit to keep direct current and voltage out of the tank circuit. l

A further object of the invention is to provide a radio frequency power generator suitable for wide use in the industrial heating art, and one I irrespective of thenature of the material orload sort of coupling to the load causes trouble of various natures. For example, a phenomenon known as frequency skip is often encountered. By this it is meant that the oscillation generator might operate intermittently atits operating frequency and shift erratically to other frequen-. cies not satisfactory for the use at hand.- Furthermore, where inductive coupling is used on loads of certain material fullpower output is unattainable. This may occur where the dielectric load is of low power factor or where loads of high impedance are being worked on or big masses are adjacent the output bushings or'terminals of the system. Thus in many. known systems the operators are exposed to the-high direct current potentials and voltages of; thebeing worked on. To attain this object we provided a direct coupling or shunt feed from the tank. to the load to eliminate frequency skip and otheroperational defects of the nature mentioned above. v t v a: The blocking capacities available for couplin g the anodes to the tank circuit blow up or burn outbecause-of capacity limitations at high frequency. In other words, there are notavailable condensers which will carry the load involved satisfactorily. To overcome'this limitation we use two condensers'in parallelas blocking condensers between'the anodes of the tube and the tank circuit. Then due to lack of uniformity in condenser manufacturing we found that the division of current and power through the blocking condenser would become unequal and again one of the condensers would fail throwing the entire load on the remaining condenser which would also fail; This unequal distribution or division of current in the condensers takes place and is believed to be due to variations in the condenser characteristics and structure, some of which variations are as follows. One condenser may have more ,ca-. pacity-reactancethan the other-so that-there is a tendency for one condenser to carry more than its share of the load. Another cause mayresult from the fact that in one condenser the inductive reactance may almostequal the capacitive reactance so that this condenser is of substantially zero impedance to the high frequency power being supplied to the tank and this condenser assumes more of the, load than the other, and since its arrangement and {dimensions are in general the sameas the other it heats up or fails otherwise,

To overcome the above defects we include in series with the two blocking condensers inductive reactance which is large as compared to the reactance of the condensers. This inductive reactance then provides such a large part of the total reactance of the parallel connections that any inequalities in the reactances of the two condensers are swamped out and are ineffective to cause one of the condensers to assume more than its share of the load.

The power generator of the present invention is to operate at various frequencies. intheembodiment tested and found highly satisfactory the generator operates at 2, 5 and megacycles. To facilitate this operation a novel arrangement of tank circuit tuning condensers has been provided which permits ready adjustment of the tank circuit tuning to the several frequencies at which it is desired to operate.

Although it is believed that our invention will be understood from the description given above, a detailed description of the manner in which our objects are attained and the advantages derived.

therefrom will now be given. In this description, reference will be made to the attached drawings whereinthe singlefigure illustrates the essential elements of a power generator arranged in accordance with our invention. The circuit diagram of the drawings is basicand'it will beobvi-ous to those skilled inthe-ar't that the practical embodiment which we found highly satisfactory includes many refinementsand operating circuit elements not shown, being not'a part of the" subject matter claimed. For example, in the drawings the metering circuits, control circuits, electrode'sup ply rectifier circuits, and filament heating" circuits, or portions thereof at least, are omitted. Y lnthe drawings two electron discharge devices VI' and V2 have their control grids and'anodes coup ed in a parallel circuit. of the Colpitttype for theproduction of radio frequency power by regenerative generation of oscillations. The grids of the two tubes are coupled together by parasitic damping impedances including inductances'Ll and L2 shunted'byresistors RI and R2. The anodes are tied together and connected by the blocking condensers O8 and C9- to theterminals of an inductance' L3, a point of which is connected to one-end of the tank circuit inductance L4. The othenend of theinductance L4 is coupled (in the switch position shown) by condensers C'G to a point intermediate parasitic damping .inductances and resistances LIRI, L2R2. A point on thetankinductance L4 is coupled by a choking inductance L5 to ground, thus preventingthe accumulation of a static charge in the tank coil, providing additional protection to the operator. Direct current for the anodecircuits of the tubes VI and V2 is supplied from a source not shown by way of a radio frequency choke RFC connecting the anodes to a posmvetermmm on the source, the negative terminal of which is conhected to'giound and to the cathode of tube V! b'y resistorR3 and resistor R4 and to the cathode of V2" by resistor R3 and R5. The direct current g rid circuit includes radio frequency choke L6, resistance-R6 and a branch Rlto the cathode of tube vl andabranch R5 to the cathode -of tube V2. 'Thbias results from tube current through the" gri resistance R6.- A'inetei' Ml denotes the grid current intensity.- The cathodes may be heated by alternating current supplied through transformers T2 and TI. Qscillations are generatedby virtue of the fact that the tank circuit terminus connected to-the' anodesandgnds o reactanceof C8 and cs in an embodiment which proves satisfactory, is 8 ohms and the inductive reactances (external and internal) are comparable to the capacitive reactance resulting in an extremely low net reactance. If the stray inductive reactances of the two capacitors are not equal the net .un'balance may be relatively great resulting ina considerable current unbalance and overheating of C8 or C9. The balance coil L3 is connected in series with each capacitor and the mutual inductance thereof is of such a magnitudethat its reactance in each branch is large as compared to the stray inductive reactances and variations in the stray reactances have relativly-sinall effect with respect to unbalancing thecurrents through the two condensers.

Th load or output circuit including the leads 2t and the output plugs 26, is directly coupled to the tank inductance L4 so that frequency instability (frequency skip or jumping) is held to a minimum in all cases including the case where the output works on a load of low power factor.

As stated above the power generator is to oper'ate at several frequencies, in the embodiment developed at'frequ'encies of 2, 5 and 10 megacy'cles'. To permit such operation an improved tank circuit is provided. The tank circuit comprises inaddition to the capacity within the tubes between the plate and cathode, etc, and between theplates and ground, the inductance L4 and condenser C2, the COIIdIISGlSC5, C6 and C'B.

For high frequency operation (10 megacycles in the; present embodiment) the plate end of the tankcircuit istuned by the tube internal capacity and the stray capacitive between plates and ground, etc, and M. For low and medium frequency operation condenser C2 is added byconnecting the same betweenthe plates and cathode. The'g rid capacity for the high frequency operation (lomegacycles) includes in addition to the capacity in the tube between the grid and cathode the variable condenser C5 and the fixed condenser C6. 'Then the condenser CB is the grid blocking (coupling) condenser through which the feedback takes place. Forthe low and medium frequency ope-ration condenser CB is put in shunt with C6 and-o5 and condenser C! is switched in as the grid coupling condenser. .The choke coils RFC andILG are changed to a value appropriate for eacl'ioperating' frequency. The condenser C5 is such-that withqCfi connected in parallel thereto and C2 out of'the circuit the tank may be tuned to the highest frequency, i.e., 10 megacycles, with G21 included in-the plate end of the circuit and G6 in-shunt'with C6 and C5, with C1 acting as the-coupling condenser the tank circuit may be tuned to the medium or lowoperating frequencies, i.e., ,2"or 5 megacycles. Although it will be readily understood that the circuit element dimensions and-values depend on the operating frequencies and that my invention is not limited to particular circuit element dimensions and values, in one embodiment which operated very satisfactorily the-circuit elements were as follows:

The tubes and V2 are type RCA892R.

RI=100 ohms R2=100 ohms R3=0.2 ohm R6=2560 ohms Ll=1 turn 2" dia. at mc., 2 turns 2" dia. at

2 and 5 mc.

L2=1 turn 2" dia. at 10 mc., 2 turns 2" dia. at

2 and 5 mc.

L3=5 turns 1 /2" dia. approx.

L4=to tune to appropriate frequency with given capacity L6=self-resonant at approx. operating frequency C2=.0004 microfarads approx.

05:.00056 microfarads C6=500 microfarads approx.

C6=625 microfarads approx.

C'!=.003 microfarad C8=.0D2 microfarad 09:.002 microfarad What is claimed is:

1. In apparatus for electronically generating oscillatory power for industrial and like purposes, an electron discharge device having an anode, a cathode and a control grid, coupled in regenerative circuit including inductive reactance and capacitive reactance in parallel, the parallel reactances being coupled at one end to the anode of the device and at the other end by feedback coupling to the control grid of the device, direct current blocking condensers connected in parallel in the coupling between the anode of the device and said one end of said parallel reactances, and. means for equalizing the current through the said blocking condensers comprising conductors coupled by mutual inductance in series with the parallel blocking condensers. 2. In apparatus for electronically generating oscillatory power for industrial and like purposes, an electron discharge device having an anode, a cathode and a control grid, coupled in regenerative circuit including inductive reactance and capacitive reactance in parallel, the parallel reactances being coupled at one end to the anode of the device and at the other end by feedback coupling to the control grid of the device, direct current blocking condensers connected in parallel in the coupling between the anode of the device and said one end of said parallel reactances, and means for equalizing the current through the said blocking condensers comprising a winding in series with each of said blocking condensers.

3. In apparatus for electronically generating oscillatory power for industrial and like purposes, a plurality of electron discharge tubes each having an anode, a cathode and a control grid parallel coupled in a regenerative circuit including a tank circuit having inductive reactance and capacitive reactance in parallel, the parallel reactances being coupled at one end to the anodes of the tubes and at the other end by feedback coupling to the control grids of the tubes, direct current blocking condensers connected in parallel in the coupling between the anodes of the tubes and. said one end of said parallel reactances, and means for equalizing the current through the said blocking condensers including a winding in series between adjacent ends of the parallel blocking condensers so that each blocking condenser has a portion of said inductance in series therewith in the parallel connection.

4. In apparatus for generating oscillatory power for industrial purposes, an electron discharge device havingan anode, a cathode, and a control grid, coupled in a Colpittscircuitincluding parallel inductance and capacity coupled at one end to the anode and at the other end by feedback connection to the control grid, direct current blocking condensers in the connection between the anode and said one end of said tank circuit, and means for equalizing the current through the said condensers comprising a balancing inductance coupling the tank end terminals of said condensers together with a point on the balancing inductance connected to said one end of said tank circuit.

5. In apparatus for generating power for industrial purposes, an oscillation generator of the Colpitts type comprising at least one electron discharge tube having an anode, a cathode and a control grid, a tank circuit connected by parallel blocking condensers to the anode of said tube and by a feedback condenser to the control grid of said tube, the purpose of said blocking condensers being to prevent direct current from flowing in said tank circuit and to feed oscillatory power from the tube to the tank circuit, and means for preventing unbalanced reactance of the parallel condensers from causing failure of one thereof including inductance in parallel between the tank terminal ends of said blocking condensers and said tank circuit.

6. Apparatus for generating oscillatory power for industrial and like purposes, at least one electron discharge tube having an anode, a cathode, and a control grid, a parallel tank circuit comprising inductance and at least the capacity inherent between the tube electrodes, a connection between a point on the inductance of said tank circuit and the cathode of said tube, a connection between one terminal of the tank circuit and the anode of the tube, a feedback coupling between the other terminal of the tank circuit and the control grid of the tube whereby oscillatory energy is developed in the tube when the electrodes thereof are energized, means for blocking the flow of direct current in said tank circuit when the electrodes are energized including a pair of condensers each having a terminal tied together and to the anodes of said tubes, and a blocking condenser reactance balancing inductance connected at its terminals to the other terminals of said blocking condensers and at a point intermediate its terminals to the said one end of tank circuit.

'7. In an oscillatory power generator, an electron discharge device having an anode, a cathode and a control grid, coupled in regenerative circuit including inductive reactance and capacitive reactance in parallel, the parallel reactances being coupled at one end to the anode of the device and at the other end by feedback coupling to the control grid of the device, direct current blocking condensers connected in parallel in the coupling between the anode of the device and said one end of said parallel reactances, and means for equalizing the current through the said blocking condensers comprising conductors coupled by mutual inductance in series with the parallel blocking condensers.

8. In combination, a pair of condensers of substantially equal capacity, a connection directly connecting a pair of terminals of said condensers together, a coil connected to and between the other terminals of said condensers, and conductors connected to said direct connection and to the midpoint of said coil whereby alternating annexe.

7 current fed from; ones conductor to; the other-does not: produce harmful .unequak current flow through said condensera.

9: In; apparatus for generating powen for in? dustrial purposes,v an; election dischargedevice having an. anode; a cathode: and a control grid, ci-ncuits: including: a tankz'cincuit coupling the an: ode, cathode and control; grid of said. device in. a regenerative oscillation generating circuit; said. tank circuit comprising parallel am inductor and a capacitor inciudi'ngr at least the inherent capacity" between device electrodes,. at source of direct current potential connected: between the anode and cathode of said" device, andmeans for preventing dinec't current potential from. appearmg" in. said tank v circuit includingy inlthe couplings between thev anode ofi said device and said. tank circuit, a pairof capacitors, said capacitors each having a terminal tied to the anodeoffsaiddevice and a second inductor connected between" the REFERENCES CITED The following references are of records inthe file of this patent:

UNITED STATES PATENTS Number Name Date 1,110,550 Hewitt Sept.,15,-1914 1,946,746 Kemp Feb..13,v1934: 2,001,277 Lewis May- 14, 1935 2,145,124 Mead, Jr Jan. 24-, 1939; 2,282,968 Kenefake May 1 2-, 1942 2,288,364 McArthur June 30", 19,42

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