US2467840A - Direct-current transformer - Google Patents

Description

April 1949. e. E. MALLINCKRODT 2,467,840

, DIRECT CURRENT TRANSFORMER Filed Dec.- 20, 1946 23 I 28 2- MW IW M "2?" Patented Apr. 19, 1949 UNITED 'STATES '7 Claims.- (Cl. 323--27) This invention relates to transformers, and

1 with regard to certain more specific features, to

step-down transformers for direct current.

Among the several objects of the invention may be noted the provision of apparatus for a transforming direct current of one'voltage into direct current of another voltage; the provision of a transformer of the class described which in-- volves no make-and-breaksystems either of the vibrating contact or oscillating circuit varieties; the provision of a transformer of this class which will safely handle a supply circuit potential of relatively high value and provide a relatively large step-down ratio to a work circuit potential of-lower values; and the provision of a simple of various possible embodiments of the inven-.

tion is illustrated,

Fig. 1 is a diagrammatic layout of the invention, being taken on line I--I of Fig. 2; and

Fig. 2 is a horizontal section. taken on line 2--2 of Fi 1.

Similar reference characters indicate corresponding parts throughout the several Views of the drawings.

Referring to the drawings, there is shown at numeral l a highly evacuated and hermetically sealed envelope or manifold which may be composed of any suitable material for the purpose, such as, for example, heat-resistant glass tubing such as Pyrex, of about 3 in. bore. Within an indented end 5 of this envelope is located a thick end closure composed, for example, of steel of about 4 in. diameter and about /2 in. thick.

cathode 3 which is heated to electron emissivity high-potential D. C. primary supply circuit I1. This circuit is supplied from a high-potential D. C. source (not shown) of 100,000 v., for example. The anode I5 constitutes a relatively The glass tube I is flanged at I 9, underneath which it is ground and lap-fitted to the face of the anode I5. It is held down by means of a clamp ring 22, the latter being fastened by studs 26 threaded into the anode I5. Grease or other sealing compound in the lap-joint thus formed provides an hermetic seal. Air is ex hausted from the tube I by means of an exhaust port 2 connected with a suction line l which is welded to the anode at collar 6.

Between the anode I5 and the cathode 3 is a relatively thin partition or shield 2 I, composed, for example, of a thin foil of beryllium approximately .0025 in. thick or aluminum approximately .002 in. thick. This is located about 2 cm. from the inner surfac of the anode I5 and is only slightly less in diameter than the bore of tube I. The partition 2| is in the desired secondary low-potential D. C. load or Work circuit 23.

Mounting of the partition foil 2i is accomplished by providing three glass insulators 8A, 0B and 8C affixed in holes through the anode I5. These insulators support a conducting ring I0 to which the foil 2| is peripherally attached. Through one insulator 8A passes a return lead from the secondary circuit 23. This is connected to ring I0. Through part of insulator BB passes a lead from a negative grid bias circuit I2 to a suppressor grid I i close to the inner surface of anode I5. The grid circuit I2 is supplied by.

means of a 45 v. battery 28, for example. Insulator 8C functions only as a third sup-port for the ring I0 of partition 2|. In order hermetically to seal the insulators, each .is fused to a glass nipple I6 into which is fused its respective lead and which in turn is fused to an alloy collar I8. Each collar is in turn soldered to the outside of the anode I5. Such hermetic sealing constructions are common and further detailed description is therefore unnecessary.

The distance from the foil 2I to the cathode 3 is of the order of 9 inches and may b as low as 1 inch. The length of the indentation 5, for proper insulation, is of the order of 2 feet. The dimensions hereinbefore given are for the stated 100,000 v. potential in the primary circuit Ill and for a 5,000 v. to 10,000 v. potential in the secondary circuit 23. In view of the above, there will be a potential field gradient throughout the 9-in.'distance between the cathode 3 and ace-mic electrons will have their maximum energy in the vicinity of the anode it, which, as will be seen, is the reason for placing the partition 2| close to said anode Hi.

Operation is as follows, referring to a primary electron (negative charge) driven from the cathode 3. Because anode i5 is always positive relatively to the cathode 3, as indicated by the solid plus and minus signs thereon, this primary electron is driven as suggested by the .line of arrows 33 and arrives with near maximum energy of approximately 100,000 electron volts at the foil 2|. Here it dislodges a multiplicity of secondary electrons (negative charges) which under the ratio of 100,000 v. to say, 5,000 v. in secondary 23, will be of the order of twenty electrons (maximum). This is suggested by the fan-shaped group of arrows 35. The foil at this time is relatively minus with respect to the anode l5, since it lies between it and the cathode 3. This is indicated by a solid minus sign on the side of the secondary circuit 23 connected with the foil 2!. (If the secondary potential is to be 10,000 v., then the number of electrons dislodged will be ten, maximum.) The twenty released electrons are driven from the thin foil 2! toward the thick anode i5.

Thus, under the assumed starting conditions the anode it will initially be relatively positive with respect to the foil 2|, and these conditions are shown by the solid plus and minus signs, as stated. The reason for this stated sense of initial polarities is the direction of the field potential gradient in the envelope i when no current is flowing in the apparatus.

The twenty electrons arrive at the anode l5 and immediately build up thereon a negative charge (as suggested by the dotted minus sign) to the extent of reversing the polarity of the secondary load circuit 23, as indicated by the dotted plus sign on said secondary circuit.

Under these conditions the anode I5 is still positive relatively to the cathode 3. But under the operating conditions the anode I5 is relatively negative with respect to the foil 2i and that only is what said dotted plus and minus signs indicate.

Although the secondary electrons 35 bombard the anode iii, its thickness prevents the dislodgment of any more electrons, except possibly a few stray ones on its inner surface which are driven baclt by means of the suppressor grid It, that being the purpose or" this grid. That is, this anode is substantially non-emissive.

In view of the above, it will be clear that the operating polarities of the load circuit 23 are the reverse of its initial polarities under starting conditions. This, so far as circuit 23 is concerned, results in a. potential gradient between the anode l5 and foil 2| which is inverse to the potential gradient in circuit li between the cathode 3 and the anode it. Thus operating conditions of the primary circuit and of the load circuit are established and maintained.

Regarding the voltage to be maintained in the load circuit ilii, this will preferably be such as will allow an optimum number of the secondary electrons 35 to reach the anode i5. This, under the conditions to be maintained in the case of the present example, will be something between ten and twenty per primary electron striking the foil. The conditions to be maintained will be clear when it is noted that the number of electrons dislodged from the thin foil 2! is constant for a. given voltage and current in the primary circuit I? and for a given full thiclmcss. These secondary electrons represent the available current which may be tively low potential in the circuit 23. This would also result in excessive heating of the anode l5 and perhaps its destruction, due to the secondary electrons striking it with full velocity and energy. Thus the voltage of the load circuit 23 cannot be reduced indefinitely. 0n the other hand, if the a negative charge on the anode I5 is allowed to build up too high a value, all flow of secondary electrons 35 will be stopped and the action of the transformer will cease. Under such conditions there is also danger of overheating the foil 2| by reason of forcing back to it too many of the electrons 35. The operating voltage value of the load circuit 23 should therefore be carried at a value which will produce neither of said limiting conditions.

The minimum heating of anode l5 and maximum power from the secondary circuit are obtained by operating the secondary circuit at as high a voltage as possible. above which the current would drastically drop, due to the inverse potential field forcing back too many of the electrons 35, and above which there would be the stated danger of forcing back too many of the electrons into the thin foil 2|. By operating at said maximum power there is avoided the possibility that by reducing the voltage too much in the load circuit, there'may not be enough inverse field applied against the oncoming electrons to slowv them down sufficiently to prevent overheating of the thickanode [5. Since power is a product of volts and amperes, if the voltage were reduced too much the electric power in circuit 23 would also be reduced, and this reduction in electric power would manifest itself as undesirable heat in the anode 15. Thus the maximum power to be withdrawn in the secondary circuit is determined by said desirable voltage maintained in the secondary circuit which lies somewhere between the above-mentioned two limits (between 5,000 v. and 10,000 v.) in the present example.

Thus it may be seen that the secondary circuit, including all apparatus therein, must have impedance-current drop equal to the above-mentioned optimum operating voltage, or, IZ=V, which may lie between 5,000 v. and 10,000 v. The circuit load and impedance is designed for this result.

The above description is in terms of one primary electron emitted from the cathode 3, but it will be understood that the action is on an average the same for each electron emitted. and that the number of electrons subject to the operation described is a function of the amperes flowing in the primary circuit 11.

Returning to the characteristics of the thin foil or shield 2|, its thickness depends upon (1) the desired step-down ratio, and (2) the voltage in the primary circuit.

Regarding the factor (1) of the step-down ratio, assuming a given primary voltage, the

thicker the coil the higher will be the step-down ratio. Thus, for example, if it were desired to change the voltage ratio from 100,000 v. to 2,000 v. (instead of the stated 100,000v. to between 5,000 v. and 10,000 v.) the aluminum foil thickness would need to be greater than the stated .002 inch. As another example, if it werev desired to step down 2,000,000 primary volts to between 10,000 and 15,000 secondary volts,.the

thickness of the foil might be greater than approximately .2 in. of aluminum.

Regarding the factor (2) of the voltage in the primary, the thickness of the foil for a given secondary voltage is a function'oi the primary voltage. As an example,- for a primary voltage of approximately 1,000,000 to be stepped down to approximately 5,000 to 10,000, approximately .1 in. of aluminum foil thickness might be required. As to the vacuum to be maintained in the envelope I, this should be good enough to permit emcient electron flow in the tube and to. establish adequate vacuum dielectric strength; but it will be understood that if a known, so-called cold cathode is used, some gas may be introduced.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As many changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter containedin the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sence.

I claim:

1. An electric D. C. transformer comprising an electron tube having an emissive cathode and a substantially non-emissive anode in a relatively high-voltage D. C. circuit, an emissive shield in said tube between the cathode and the anode adapted to be bombarded on one side by primary electrons moving from the cathode toward the anode, said shield emitting under said bombardment multiple electrons on its other side toward the anode, said shield and anode being connected into a D. C. work circuit.

2. An electric D. C. transformer comprising an electron tube having an electron-emissive cathode and a substantially non-emissive anode, both in a relatively high-voltage D. ('3. circuit, said anode being relatively positive with respect UNITED STATES PATENTS Number Name Date 1,732,050 Jobst Oct. 15, 1929 2,158,564 Meier May 16, 1939 2,192,506 Ruben Mar. 5, 1940 2,294,782 Jacobsen Sept. 1,- 1942 to the cathode, an emissive shield in said tube between the cathode and the anode positioned to be bombarded on its side adjacent the cathode by primary electrons from the latter and being thin enough to emit secondary electrons on its side adjacent the anode to build an electron charge on the latter which becomes relatively negative with respect to said shield, said shield and anode being connected to a relatively lowvoltage D. C. work circuit supplied by secondary electrons under the electron voltage which exists between the anode and the shield.

3. Apparatus made according to-claim 2 in which said shield is composed of a. solid sheet of aluminum of the order of several thousandths of an inch thick.

4. Apparatus made according to claim 2 in which said shield is made of a solid sheet of beryllium oi the order of several thousandths of an inch thick.

5. Apparatus made according to claim 2 in which said tube includes a control grid for the cathode.

6. Apparatus made according to claim 2 in which said tube includes a suppressor grid for the anode. v

7. Apparatus made according to claim 2 in which said tube includes a control grid for the cathode and a suppressor grid for the anode.

- GEORGE E. MAILINCKRODT.

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

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