US2468878A - Frequency reducer - Google Patents

Description

FREQUENCY REDUCER Filed July 19, 1945 2 Sheets shee't l f //8 y /5 /6 6; LOAD INVENVTOR. HEN/FY M HUGE ATTORNEYS.

i' iiay 3 1949. H, M HUGE 2945339373 FREQUENCY REDUCER Filarl July 19, 1.945 2 Sheets-Sham 2 INVEN TOR. HEN/P) M. HUGE M VIM.

AT TO/PNEYS.

Patented May 3, 1949 UNITED STATES PATENT OFFICE 15 Claims.

This invention deals with magnetic frequency reducers, and particularly with a self-starting arrangement for generating an even subharmonic of the energizing frequency through the use of biased saturable magnetic core means.

The invention constitutes an improvement over the subject matter of my U. S. patent application, Serial No. 485,832, filed May 6, 1943, now Patent 2,418,640, issued April 8, 1947. The present application describes a frequency reducer having in one form a leakage-reactance structure for protection against overloads, and utilizing an improved biasing arrangement.

It is an object of this invention to generate an even subharmonic of the frequency of an alternating current source by utilizing a biased saturable magnetic core structure.

Another object of this invention is to produce a self-starting subharmonic generator in which the self-starting of the oscillations is assured in spite of widely varying operating conditions.

Another object of my invention is to use rectifiers to supply biasing current for the saturable magnetic core of a subharmonic generator and to control the biasing current in response to biasing requirements.

Still another object of my invention is to protect a subharmonic generator against overloads through tne use of a leakage reactance core structure together with an improved winding arrangement.

An additional object is to increase the audible components in the output voltage of a subharmonic generator, and to maintain the audible level with variations in load.

Other objects and a better understanding of my invention may be obtained by referring to the following specification and claims together with the accompanying drawings in which Figure l is the schematic diagram of one em bodiment of my invention with my improved biasing arrangement applied to a common-core subharmonic generator. 4

Figure 2 is the schematic diagram of a modified subharmonlc generator, with a common core structure provided with a leakage reactance arrangement for overload protection and utilizing a biasing circuit differing from that shown in Figure 1,

Figure 3 shows a common-core subharmonic generator having overload protection and having a harmonic generating circuit for introducing audible components in the output voltage, and

, Figure 4 shows an embodiment of my invention utilizing two separate saturable inductances to replace the three-legged core construction 0! the other figures.

The frequency reducers made according to my invention make use of biased saturable magnetic core means and a winding arrangement having primary and secondary terminals. The winding arrangement is approximately balanced,

'so that when an alternating voltage is applied to the primary terminals, relatively little voltage of the applied frequency appears across the secondary terminals. Conversely, when the voltage is applied to' the secondary terminals, relatively little voltage of the applied frequency appears across the primary terminals. This relationshipis known in the art as a conjugate relationship between primary and secondary terminals, and may be achieved by combining opposing magnetizing forces in a three-legged core as in Figures 1, 2 and 3, or by combining opposing voltages in serially connected windings as is done in Figure 4. I

In operation, the magnetic bias of the saturable core means is applied in such a manner that the impedance looking into the secondary terminals is substantially symmetrical, while the impedance looking into the primary terminals is unsymmetrical.

The primary impedance becomes unsymmetrical because on one half of a cycle, the alternating current aids the unidirectional biasing flux and highly saturates the core, while on the other half cycle it opposes the biasing flux; hence, when a symmetrical voltage Wave is applied, an unsymmetrical current wave is produced.

In the secondary circuit, the impedance remains substantially symmetrical because each half cycle of secondary alternating current aids the biasing flux in one portion of the core and opposes it in the other portion. When the bias is provided by direct current, the direct current is applied at the primary terminals to produce this result.

In operation a suitable capacitor is connected to the secondary terminals and an alternating .voltage is applied to the primary terminals.

With appropriate circuit constants, I have found that when alternating voltage is applied as shown in Figure 1 the capacitor very readily excites subharmonic oscillations of one-half the source frequency. The subharmonic oscillations thus produced require no starting transient or shock of any kind, and therefore are termed selfstarting. The unidirectional biasing flux impressed on the saturable core, conditions the frequency changer for the self-starting production of even subharmonics and particularly of an output frequency equal to one-half the energizing frequency. The conversion of power from the fundamental frequency to the subharmonic frequency is accomplished by the superposition of the fundamental and subharmonic fluxes in the biased saturable magnetic core members as in the device described in my U. S. patent application Serial No. 485,832, filed May 6, 1943 now Patent Number 2,418,640, of April 8, 1947.

With more particular reference to Figure 1, there is shown a three-legged saturable magnetic core structure 18, having primary windings i2 and i3 on its outer core members and secondary winding E5 on its central core member. Capacitor ii is connected across winding i5 and the load is supplied from a portion of winding i5 terminated at tap it, which is located to supply the desired voltage to t1 e load.

Primary windings i2 and [3 are connected in series with each other and energized from the alternating current source it]. The rectifier bridge ii is connected in series with windings l2 and it to supply them with direct current to bias the saturable magnetic core [8. The rectifier bridge l! is supplied with alternating current from winding it which is wound on the same core member as primary winding 12.

The primary windings i2 and i3 are polarized to magnetize the outer members of the core l8 and to produce opposing magnetizing forces in the central core member Shis arrangement produces a conjugated relationship between the primary circuit comprising windings l2 and, i3 and the secondary circuit comprising winding i5.

in operation the subharmonic nur; circulates through the central core member and through both outer core members, while the flux of the energizing frequency circulates chiefly through the two outer core members. Because of the conjugate arrangement, it is possible to interchange the prim ry and, secondary circuits without changing the method of circuit operation. Falls, the capacitor it could be connected to the windings and and the source Hi and rectifier it connected to tne winding 35 without changing the essential properties of the arrangement. It is not necessary to change the location of the rectifier energizing winding 54 when the primary and secondary circuits are thus interchanged because it is coupled to both the primary and secondary circuits in both arrangements.

The method of energizing rectifier ii which is shown in Figure 1 is highly eiiective in producing consistent circuit operation under widely varying load conditions and wide variations of the voltage of source As previously mentioned, the outer core members carry flux both of the energizing frequency and of the subharmonic frequency, so the voltage induced in winding i 4 has components of both frequencies.

The rectifier i i might be supplied with voltage only from source it and still supply biasing current to satisfactorily'operate the subharmonic generator under many operating conditions. With such an arrangement, however, I have found that when the voltage of source 10 is abnormally high, the biasing current becomes excessive and the subharrnonic oscillations may not always be self-starting, particularly if they are stopped by an overload condition. When the voltage of source i0 is abnormally low, there may be insufficient biasing current and the application of heavy loads on the output circuit may cause the oscillations to cease or become intermittent.

According to my invention, both of these dlfflculties are overcome, and the correct biasing current is maintained over widely varying conditions of load and input voltage. This is accomplished by energizing the rectifiers II with subharmonic voltage in addition to voltage from source I0. A suitable arrangement for energizing the rectifiers with both voltages is shown in Figure 1, in which the winding 14 is wound on one of the outer core members in which subharmonic and fundamental frequency flux are both circulating.

Because of the saturation of the core, the subharmonic voltage tends toremain relatively constant in spite of variations of the voltage of source l0, and therefore acts to minimize variations of biasing current which are produced by source voltage variations. Furthermore, in case the oscillations are stopped by an overload, there is a reduced voltage applied to the rectifier ii and the self-starting of the oscillations upon removal of the overload is assured.

This improved biasing arrangement has a further action in that it tends to unbalance the circuit slightly, so that some voltage of the source frequency is applied to capacitor iT, helping to initiate oscillations in the secondary circuit. The unbalanced condition may be adjusted to its optimum value by varying the relative number of turns in windings i2 and i3, but I have found that highly satisfactory results can be obtained by making winding l2 with the same number of turns as winding II.

In the circuit of Figure 1, the alternating current from source in flows through the rectifier i i. I prefer to provide suiiicient biasing current so the current through the rectifier will not be forced to reverse. If the voltage supplied by winding 14 is too small, the rectifier bridge ii may have impressed on it a high reverse voltage from source ill and be damaged. In such a case, a capacitor could be provided to by-pass the alter nating current. Such a capacitor would. be connected across the direct current terminals of the rectifier bridge ii.

In the preferred biasing arrangement shown in Figure 1, a by-pass condenser is not needed, and in fact not desirable. There is a tendency for the rectifier bridge ii to act as a half-wave rectifier of the current of source iii, and when the application of load on the secondary circuit increases the primary current, it also tends to increase the biasing current. An increase of biasing current under these conditions is desirable since it increases the ability of the subharmonic generator to carry load without stopping the subharmonic oscillations.

The benefits obtainable with my improved biasing arrangement are not limited to the biasing circuit shown. To those skilled in the art, other methods of connecting the rectifier bridge H in the primary circuit will be apparent. Some of these methods are described in my U. S. patent application, Serial Number 485,832. Specifically, it is not necessary for the direct current to flow through the source 10, but the circuit shown provides a simple and economical assembly and is preferred whenever the flow of direct current through the alternating current source does not produce difllculties.

One biasing circuit which does not pass direct current through the alternating current source I0 is shown in Figure 2. This figure also shows a leakage reactance core structure-for protecting the generator against overloads.

The biasing arrangement shown in Figure 2 makes use of a separate pair of windings, 33 and It on the outer members of core it. These windings are connected in series in the same polarity as the primary windings l2 and I3 and therefore constitute a primary circuit of the frequency changer. windings 33 and 34 are supplied with direct current for biasing the core i8. They are energized from the rectifier I I through the blocking inductance 30, which limits the flow of alternating current through the biasing circuit. Because of the balanced character of the circuit, there is relatively little subharmonic voltage in the primary circuits, and the inductance Il may be relatively small and still satisfactorily block the higher frequencies in the circuit.

The rectifier II is supplied with alternating current from a pair of taps 3| and 32 located on the primary windings l2 and I3 respectively. The relative amounts of windings l2 and i3 included between these taps determine the relative amounts of source voltage and subharmonic voltage which are applied to the rectifiers II. For example, if equal amounts of windings l2 and I3 are included, the voltage applied to the rectifier H will be of the frequency of source l0. Differences in the turn numbers introduce subharmonic voltage in the rectifier supply.

The overload protection system shown in Figure 2 is an improvement over the leakage-reactance arrangement shown in U. S. Patent No. 2,179,386, issued November 7, 1939, to C. P. Stocker. In Figure 2, the magnetic shunt members 20 and 2| provide a leakage reactance between the secondary winding i5 and the output winding IS. The shunt members and U are preferably constructed to provide small air gaps in their magnetic circuits, so that under light loads on output winding l9 relatively little of the subharmonic flux is diverted away from winding l9. As the load increases, the magnetizing force of the load current causes more of the subharmonic flux to flow through the leakage flux path presented by members 20 and 2|.

windings 28 and 29 on the shunt members 20 and 2! are connected in series with output winding l9, and when energized by the load current serve to aid in the diversion of flux away from the output winding. In addition, the voltage induced in windings 28 and 29 subtracts from the output voltage so that the diversion of a relatively small amount of flux away from the output winding results in a larger drop in output voltage and hence a larger drop in the loading of the converter. This action is highly effective in protecting the converter against overloads because it permits an appreciable portion of the subharmonic fiux to flow through the winding is under all load conditions, even when the output is short circuited. By permitting subharmonic flux to flow through the closed saturable flux path of the core structure l8 instead of forcing it all through the leakage flux paths, the normal operation of the converter is maintained under overload conditions, and the overload protection circuit acts to maintain the subharmonic oscillations at a reduced level, utilizing the saturable properties of the entire magnetic core structure l8.

The voltage of the source frequency which is induced in windings 28 and 29 is in opposite polarity in the two windings and therefore need not appear in the load voltage. Alternatively, windings 28 and 29 may be connected in parallel,

' effectively preventing the flow of fundamental flux through the leakage members 20 and 2|, while permitting the subharmonic flux to circulate as previously described.

Figure 3 shows a modification of the arrangement of Figure 2 with several circuit elements added for the purpose of introducing audible components in the output voltage. The biasing arrangement ,of Figure 3 is similar to that of Figure 1, with rectifier ii receiving its alternating current supply from winding l4 andsupplying direct current to the primary windings I2 and I3.

The overload protection arrangement of Figure 3 is, in effect, similar to that of Figure 2, although the windings 28 and 29 on the leakage flux members are omitted in Figure 3. They are replaced by a portion of secondary winding i5 terminated at tap 2B. The load is supplied from output winding is through the portion of winding IS, with the voltage from winding [5 opposing that from the output winding. In operation, this combination produces an effect similar to that described in connection with Figure 2, so that on a short circuit some subharmonic flux can still circulate through the closed flux path surrounded by winding l9.

Under some conditions, it may be preferable to provide less protection against overloads in order to maintain a more nearly constant output voltage under normal load conditions. When this is true, the reluctance of the leakage flux paths through shunts 20 and 2| may be increased to a point where heavy overloads will cause the subharmonic oscillations to cease. Even under these conditions, my improved overload protection arrangement provides advantages in maintaining stabilized converter operation under heavy loads and in assuring self-starting of the oscillations after they are stopped by overloads. As previously mentioned the ability of the converter to self-start its oscillations is greatly improved by the biasing arrangement shown, in which both 'subharmonic voltage and fundamental frequency voltage are rectified to supply biasing current for the magnetic core.

Saturable inductance 25 is connected in series with capacitor I! in Figure 3. The subharrnonic current flowing through the capacitor ll sharply saturates the inductance 25 and in so doing generates high order harmonics of the output frequency, The capacitor 24 in parallel with inductance 25 provides a local resonant circuit for the desired harmonics and increases their generation.

When the frequency changer is used to supply ringing current for telephone exchanges, the high order harmonics are often needed to supply ringing tone to signal the calling subscriber that ringing current is being supplied to the number he is calling. When relatively little audible tone is needed, the capacitor 24 may be omitted.

The harmonics generated by inductance 1 25 appear initially across secondary winding [5, and to some extent across output winding i9. When load is applied, however, the flux produced by the harmonics tends to flow through the shunt members 20 and 2i and the harmonic voltage across output winding I9 would rapidly diminish if it were not maintained by capacitor 23. I have found that by connecting capacitor 23 to one end of winding [9 and to a suitably located tap 21 on winding [5 it is possible to maintain a relatively constant audible tone level across the load. The windings are preferably polarized so that the action of capacitor 23 aids the normal harmonic voltages appearing across winding l9.

If the saturable inductance 25 has too high an impedance it may prevent the self-starting oi the subharmonic oscillations. The unbalancing action of the biasing supply winding ll tends to reduce this difiiculty, but in some cases it may be desirable to further adjust the unbalance oi the structure by altering the number of turns on winding H or winding 13.

Although mention is here made of an unbalanced condition, it is to be understood that the structure of the frequency changer is substantially balanced, and relatively little unbalance is required to produce the effects described. The fact that the primary and secondary circuits provide a substantially balanced or conjugate combination is best demonstrated by noting that relatively little current or voltage of the source frequency appears in the secondary circuit, that is, the circuit of capacitor ii.

The circuit of Figure 4 is that of an embodiment of my invention utilizing two saturable cores 35 and 3G to replace the three-legged core structure i3 shown in Figures 1, 2, and 3.

The operation of the circuit of Figure 4 is, for practical purposes, the same as that of Figure 1, except that inductance 33 in series with the load in Figure 4 provides overload protection not provided in Figure l. The primary windings i2 and is in Figure 4 are wound on the saturable magnetic cores 35 and 36 respectively. These primary windings are connected in series to the source through the D. 0. terminals of recti- 11cr 5.".

Rectifier ii is supplied with alternating cu:- rent from winding wound on core 35 with primary winding E2. The winding 54 is coupled to both the primary and secondary circuits, as in Figure 1 and it supplies both subharmonic voltage and fundamental voltage to the rectifier ii.

The secondary circuit of Figure 4 comprises windings and on cores and 35 respectively. The secondary winding are polarized oppositely the primary windings so that the enarrangement is a substantially balanced combination, with voltage of primary frequency being substantially balanced out of the secondar rcuit.

Capacitor it is connected in a closed circuit with the secondary windings El and 38, and ex cites the subharnionic oscillations in the secondary circuit. In operation, both the cores 3.. and 38 are magnetized with both fundamental and "ubharinonic and, as previously mentioned, w ding i is excited by both frequencies.

The load is supplied from a portion of the secondary circuit, including portions of both windand The tap l and ii are located supply the desired output voltage of the subharmonic frequency. By including equal portions oi windings and 38, an output voltage of substantially the same wave shape as the voltage across capacitor is provided.

My invention has been described herein as being applied to specific types of balanced or conjugate circuits comprising saturable magnetic core means, but other similar arrangements may also be used. For example, the biasing arrangement described herein may be substituted in the circuits shown in my U. S. patent application Serial No. 485,832, for the biasing arrangements shown therein.

Although I have described my invention with a certain degree of particularity, it is to be under- 8 stood that the present disclosure has been made only by way of example, and that numerous modifications in the details of construction and the arrangement of the parts may be made without departing from the scope of the invention as hereinafter claimed.

I claim as my invention:

1. A frequency changer adapted to be energized by a source of alternating current and to generate a frequency which is an even subharmonic oi the frequency of said source, said generator comprising a three-legged magnetic core structure, first and second winding means on the first and second legs of the core structure, said first and second winding means being connected in series with each other and adapted to be energized by said source to produce opposing magnetizing forces in the third leg of the core structure, a rectifier connected in series with the first and second winding means to supply direct current thereto, a rectifier energizing winding on the first leg of the core connected to said rectifier, third winding means on the third core leg, and a capacitor connected to the third winding means.

2. In combination, a magnetic core structure having a plurality of members, a plurality of windings on the core structure, comprising primary and secondary circuit means, the primary and secondary circuit means being in a substantially balanced relationship to each other, a capacitor connected in a closed circuit with the secondary circuit means, biasing means for producing a unidirectional fiux in the core structure to modify the impedance of said primary circuit means so that said impedance offers a greater opposition to one half of an alternating current cycle than to the other half of the cycle, output winding means on the core structure inductively related to the secondary circuit means, leakage reactance means providing leakage reactance between the output winding means and the secondary circuit means, and load circuit means including the output winding means and at least a portlon of the secondary circuit means, said load circuit means being adapted to supply a load with subharmonic voltage from the output winding means and an opposing subharmonic voltage from secondary circuit means.

3. In combination, a magnetic core structure having first, second and third members, first and second windings on the first and second members, said first and second windings being connected in series and polarized to produce opposing magnetizing forces in the third member, means for energizing said first and second windings from a source of alternating current, biasing means for producing unidirectional fiux in the first and secand members, a third winding on the said third member, a capacitor connected in a closed circuit with the third winding, a fourth winding on the said third member, leakage fiux means providing leakage reactance between the third and fourth windings, and an output circuit including the fourth winding and at least a portion of the third winding.

4. In combination, a magnetic core structure having first, second and third members, first and second windings on the first and second members, said first and second windings being connected in series and polarized to produce opposing magnetizing forces in the third member, means for energizing said first and second windings from a source of alternating current, biasing means for producing unidirectional fiux in the first and second members, a third winding on the third member, a capacitor connected in a closed circuit with the third winding, a fourth winding on the third member, leakage flux means providing leakage reactance between the third and fourth windings, winding means on the leakage flux means,

and an output circuit including said winding means and said fourth winding.

5. A frequency reducer adapted to be energized by an alternating current source and to supply an output voltage of a frequency which is an even subharmonic of the source frequency, comprising in combination, a magnetic core structure having a plurality of members, a plurality of windings on the core structure, comprising primary and secondary circuit means, theprimary and secondary circuit means being in a substantially conjugate relationship to each other, a capacitor connected in a closed circuit with the secondary circuit means, a rectifier connected to the primary circuit means to supply direct current thereto, output winding means inductively related to the secondary circuit means, and leakage reactance means providing leakage reactance between the output winding means and the secondary circuit means.

6. In combination with a frequency reducer having primary and secondary winding means arranged on a magnetic core structure having a plurality of sa'turable members, with a capacitor connected to the secondary winding means, with output winding means on the core structure and with leakage reactance means providing leakage reactance between the output winding means and the secondary winding means, tone circuit means for supplying harmonic voltage to the output winding means, said tone circuit means comprising saturable inductance means connected in series with said capacitor, and capacitive coupling means coupling the output winding means to the secondary winding means.

- 7. In combination with a frequency reducer having primary and secondary winding means arranged on a magnetic core structure having a plurality of saturable members, with a first capacitor connected to the secondary winding means, with output windin means on the core structure and with leakage reactance means providing leakage reactance between the output winding means and the secondary winding means, tone circuit means for supplying harmonic voltage'to the output winding means,- said tone circuit means comprising a saturable inductance connected in series with the first capacitor, a second capacitor connected substantially in parallel with the saturable inductance, and capacitive coupling means coupling the output winding means to the secondary winding means.

8. In combination with a magnetic frequency reducer having primary and secondary winding means arranged on a magnetic core structure having a plurality of members, an overload pro-- tective arrangement comprising in combination, output winding means on the core structure inductively related to the secondary winding means, leakage reactance means providing leakage reactance between the output winding means and the secondary winding means, and a load circuit including the output winding means and at least a portion of the secondary winding means, and adapted to supply an output voltage of a reduced frequency from the output winding means and an opposing voltage of the reduced frequenc from the secondary winding means.

9. In combination with a magnetic frequency reducer having primary and secondary winding means arranged on a magnetic core structure having a plurality of members, an overload prw tective arrangement comprising in combination, first output winding means on the core structure inductively related to the secondary winding means, magnetic shunt means providing leakage reactance between the first output winding means and the secondary winding means, and second output winding means on the magnetic shunt means connected in series with the first output winding means and polarized to supply 'an output voltage opposed to the voltage supplied by the first output winding means.

10. A magnetic frequency changer comprising magnetic core means having a plurality of members, primary and secondary winding means on the core means, means for energizing said primary Winding means from an alternating current source, at least one of said windin means comprising a plurality of portions on different members of the plurality of magnetic core members, polarized to produce substantially cancelling voltages in the other of said winding means, a rectifier adapted to supply direct current to at least a portion of the primary winding means, a rectifier energizing circuit connected to the rectifier and coupled to both the primary and secondary winding means, and a capacitor connected in a closed circuit with the secondary winding means.

11. A magnetic frequency changer adapted to be energized by a source of alternating current and to supply an output voltage of a frequency which is a subharmonic of the source frequency, said frequency changer comprising magnetic core means having a plurality of core members, primary and secondary winding means on the core means, means for energizing said primary winding means from an alternating current source, at least one of said winding means comprising a plurality of portions on different members of the plurality of magnetic core members, said portions being polarized to produce substantially cancelling voltages in the other of said winding means, a rectifier connected in series with the primary winding means to supply direct current thereto, a rectifier supply circuit adapted to supply the rectifier with subharmonic voltage and with voltage of the source frequency, a capacitor connected in a closed circuit with the secondarywinding means and means for supplying a subharmonic output voltage from said secondary winding means.

12. In combination with a self-starting frequency reducer adapted to supply an output frequency which is an even subharmonic of its energizing frequency, and comprising magnetic core means having a plurality of core members with primary and secondary winding means thereon forming a substantially balanced conjugate combination, unbalancing means for assuring the self-starting of subharmonic oscillations in the secondary winding means, said unbalancing means producing a residual unbalanced condition in the substantially balanced conjugate combination for introducing primary voltage in the secondary winding means.

connected in series, adapted to be energized by said source, and polarized to supply opposing fluxes to the third member, a rectifier connected in series with the first and second windings to supply direct current thereto, a third winding on the third member, a capacitor connected in a closed circuit with the third winding, a saturable inductance connected in series with the capacitor for introducing harmonics in the voltage across the third winding, and a fourth winding on the first member connected to the rectifier to supply rectifier with alternating current, said capacitor being supplied with a relatively small voltage of the source frequency to aid in initiating selfstarting oscillations oi one-half the source frequency through said capacitor.

14. A magnetic frequency changer comprising a magnetic core structure having a plurality of members, a plurality of windings on the members, comprising primary and secondary winding means in substantially conjugate relationship to each other, a rectifier adapted to supply direct current to at least a portion of the primary winding means, a capacitor connected in a closed circuit with the secondary winding means, output winding means inductively related to the secondary winding means, magnetic shunt means providing leakage reactance between the secondary and output winding means, and a rectifier supply circuit connected to the rectifier and adapted to be energized from both the primary and secondary winding means, said primary winding means being adapted to be energized by a source or alternating current.

15. A subharmonic generator adapted to be energized by a source of alternating current and to generate a irequency which is an even subharmonic of the irequency or said source. said generator comprising magnetic core means, a primary circuit and a second circuit. said primary and said secondary circuits comprising at least three windings on said core means, said primary circuit being adapted to be energized by said source for magnetizing said core means, said primary and secondary circuits being disposed to provide a substantially conjugate relationship therebetween, biasing means adapted to supply unidirectional current to said primary circuit, said primary circuit and said biasing means exciting at least a portion oi said magnetic core means to a saturated condition, said biasing means comprising a rectifier and circuit means for energizing said rectifier with voltage of the source frequency and with subharmonic voltage, and a capacitor connected to the secondar circuit, said capacitor in cooperation with said primary and secondary circuits and said magnetic core means exciting subharmonic oscillations in the secondary circuit when the said at least a portion of said core means is saturated by the combined effect of said biasing means and said primary circuit.

HENRY M. HUGE.

No references cited.

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