US2097882A - Power supply circuits - Google Patents

Description

Nov. 2, 1937. w. T. HUDTWALKER 2,097,882

POWER SUPPLY CIRCUITS Filed June 9, 1933 lNVENTOR MLL/AM 7'. #007 [#41622 ATTORNEY from the voltage divider.

Patented Nov. 2, 1937 POWER SUPPLY CIRCUITS Wiliiam T. Hudtwalker,

Richmond Hill, N. Y.,

assignor to Radio Corporation of America, a corporation of Delaware Application June 9, 1933, Serial No. 675,062

1 Claim.

The present invention relates to electrical networks and particularly to networks including thermionic tubes. V

In the usual method of energizing the electrodes of electronic tubes from the power supply mains of the normal alternating current network it is common practice to raise the voltage of the alternating current, rectify the resulting energy and then filter the rectified energy so as to remove the undesirable fluctuating component thereof. The usual set-up in such instances comprises a full wave rectifier the output of which feeds into a filter circuit which is composed of choke coils and condensers. The output of the filter circuit is then impressed across a voltage divider resistance element and the various desired voltages for the energization of the thermionic tubes of a radio receiver or the like are derived In the cases where the energization of thermionic tubes provided with indirectly heated cathodes is contemplated it is common to supply the rectifying and filtering system with current at the same time that the heater element for the indirectly heated cathode of the thermionic tube is energized. In the tubes of thisnature, that is, tubes provided with indirectly heated cathodes, a certain time period elapses after the heating circuit energy is supplied before the cathode assumes its normal action, that is, before the cathode is raised to a tem perature which is sufiicient for electrons to boil off, so to speak. During this time period current obviously does not flow through the thermionic tubes with the result that the voltage built across the filter condensers is greatly increased over the normal voltage and sometimes causes the condensers to break down. devised to, so to speak, delay the energization of the rectifier tubes until after the cathodes of the indirectly heated thermionic tubes assume normal operation. However. in such systems as are now known, various complications arise and it is a fact that the expense of purpose is considerable.

It is an object of the present invention to provide an electrical network whereby the harmful effects of the delay characteristics of a tube provided with an indirectly heated cathode do not affect the filter system in any way harmful to the elements thereof. Another object of the present invention is to provide an electrical network that shall compensate for the increase in voltage during the aforementioned time lag.

The foregoing objects thereto are attained in a and others ancillary preferred embodiment Many systems have been delay circuits for this of the present invention by causing the output current of a rectifier filter system to traverse an More specifically, is provided a current named. conditions, that such characteristics that the potential thereacross: is not the rate of change of current material that very satisfactorily pose is commercially known as across the filter circuit there path meeting the above is, a current path having rate of change of linearly related to therethrough. A answers the pur- Thyrite and is described in the United States Patent #1321742 to McEachron.

Thyrite, above, is a according to the patent referred to material somewhat similar to dry process porcelain throughout the mass of which appear minute particles of conducting material.

The substance is substantially an insulator at low potentials and becomes a continuously better conductor as the current through it is increased.

For a better acteristics of the substance Thyrite understanding of the general charreference is made to an article entitled Thyrite; A New Material for Lightning Arrestors by K. B. Mc- Eachron, appearing in General Electric Review, February 1930, page 92-.- From a reading of the above mentioned article it may be gathered that Thyrite has a characteristic.

The material Thyrite the form of discs each face hyperbolic resistance-ampere is usually utilized in of which is provided with a sprayed metallic coating for contact purposes, however, it should be understood that the shape of the material is not a controlling factor. It should be noted, however, that the resistance of Thyrite varies directly with its thickness but The novel features that are characteristic of the present forth in particularity in the believed to be invention are set appended claim.

will best be understood from the following description of a specific embodiment when read in connection with the accompanying drawing, the

single figure bodiment of of which represents a preferred emthe invention showing the rectifier source of alternating current through the terminals I and 2 associated with the primary 4. A suitable switch 1 is provided for turning the power on and off as desired in customary fashion. One end of the secondary 5 is connected to the anode of a rectifier tube 8 while the other end of the secondary 6 is connected to the anode of rectifier tube 9. The cathodes of the rectifier tubes 8 and B have one side common as shown and are connected to a suitable source of energizing current not shown. The output of the rectifier tubes is taken as is usual in such cases from the center point of the secondary 6 which is the negative side of the output and a point common to the two mentioned cathodes which is the positive side of the output in accordance with the usual conventions.

The positive side of the rectifier output is connected to one end of a voltage divider resistance 12 through a pair of choke coils H! and H while the negative side of the rectifier output is connected to the other end of thevoltage divider resistance 52. While choke coils l0 and H have been shown connected to the positive side of the rectifier output it is to be distinctly understood that they may be just as well connected in the negative side of the rectifier output, and in fact, in some instances, connection in the negative side is desirable. The usual filter condensers l3 and M are provided connected across the positive and negative lines on either side of the choke coil H.

So far it is evident that the system described comprises the usual rectifier and filter circuit. A load adapted to be energized from the output of the filter circuit may comprise a tube of the screen grid type and provided with an indirectly heated cathode. directly heated cathode includes the secondary 5 and a suitable resistance Hi. It should be noted that tube i5 is connected so that the potential on the cathode is higher than the potential on the grid, hence, there is provided a so-called automatic bias for the grid in The anode of the tube is connected to the top of the voltage divider resistance l2 although it may "be connected to any point of resistance l2 de- The heater circuit for the ill-' customary fashion.

readily energized immediately upon the closing of switch I it is obvious that the load which comprises the tube I5 is, in reality, zero with the result that a very much higher voltage exists across the condensers l3, I4 than the voltage existing across these condensers when the whole system is in normal operation. Accordingly, it has been found that the condensers l3 and i4 must be built to withstand this added voltage with the attendant increase in cost and size.

To overcome this drawback there are provided across the two condensers the two Thyrite resistances l! and i8. While two of such resistances have been shown it is obvious that one may be sufficient for the purpose. As connected, the two elements I! and i8 protect the filter condensers l3 and 14 during the interval of time required by the tubes such as IE to warm up and take a load. The two elements l1 and i8 will also protect the network against surges and in addition they have a filtering effect when used in the position shown because the Thyrite elements present a lower impedance with increase of applied potential thus tending to smooth out ripples.

The present invention is of particular importanoe in transmitter apparatus since in such cases the use of a device in which the load is not taken immediately subjects associated equipment to voltage overload.

It is to be understood that the present invention is not limited to the use of Thyrite or an equivalent material since many modifications will at once be apparent to those skilled in the art to which the invention pertains, hence, the invention is not to be limited by the specific exemplifie cations shown for purposes of illustration but only by the prior art and by the spirit of the,

appended claim.

I claim:

A filter circuit for use in connection with power supply systems utilized to energize thermionic tubes provided with indirectly heated cathodes and wherein an appreciable period of time is required for energizing the indirectly heated cathodes, said filter system including a choke and at least one filter condenser, an additional filter means shunted across the filter condenser comprising a device for protecting the filter condenser during the period of time required to energize the indirectly heated cathodes, said device comprising an element composed of a granular material having a hyperbolic resistance-ampere characteristic which is unaifected by variations in the rate of change of voltage applied to the element to produce a flow of current therethrough, the resistance of said element being always substantially the same for a given density of current fiow through it whether the value of the said current density is attained by increasing or by decreasing the current fiow, said additional filter means having a decreasing impedance with increasing applied potential across it whereby the additional filter means operates to smooth out current passing through the filter circuit.

a WILLIAM T. HUDTWALKER.

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