US3275837A

US3275837A - Xerographic charging apparatus

Info

Publication number: US3275837A
Authority: US
Inventors: Joseph J Codichini; Rolf W Eichler; Thomas F Hayne
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1963-01-04
Filing date: 1963-01-04
Publication date: 1966-09-27
Anticipated expiration: 1983-09-27
Also published as: CH460930A; SE314133B; DE1488286A1; FR1385736A; NL302691A; BE642095A; GB1040264A; DE1488286B2

Description

p 1966 J. J. CODICHINI ETAL 3,275,837

XEROGRAPHIC CHARGING APPARATUS 2 Sheets-Sheet 1 Filed Jan. 4, 1963 Fzi: H

/N|/EN7'O]/I?\f. JOSEPH J. CODICH ROLF W. EICHLER THOMAS F. HAYNE BY ATTORNEY p 1966 J. J. CODICHINI ETAL 3,275,837

XEROGRAPHIC CHARGING APPARATUS Filed Jan. 4, 1963 2 Sheets-Sheet 2 I05- I25 v. T 60 CYCLE P F/G. Z

POSITIVE OUTPUT WAVEFORM POSITIVE CORONA THRESHOLD m APP IMATELY 4 o oo VOLTS flZjRO VOLTAGE LEyEL A 7 U V L \NEGATIVE CORONA THRESHOLD V APPROXIMATELY 3700 VOLTS NEGATIVE OUTPUT WAVEFORM O1 +0 T TS-I SR-I Ac INPUT INVENTORS.

TS-2 O JOSEPH J. CODICHINI ROLF w. EICHLER TS-3 G GN THOMAS F. HAYNE.

D. Y F/a'4 fl/g ATTORNEY United States Patent York Filed Jan. 4, 1963, Ser. No. 249,442 3 Claims. (Cl. 307-2) This invention relates in general to xerography and, in particular, to an improved high voltage power supply for use in a xerographic apparatus to provide effective unidirectional power to threshold type loads, such as corona discharge devices.

More specifically, the invention relates to an electrical power supply circuit for providing electrical power to threshold type loads, for example, to supply electrical power to one or more corona discharge devices of the type disclosed in Vyverberg Patent No. 2,836,725.

In the process of xerography, for example, as disclosed in either Carlson Patent No. 2,297,691, issued October 6, 1942, or in Carlson Patent No. 2,357,809, issued September 12, 1944, a xerographic plate comprising a layer of photoconductive insulating material on a conductive backing is given a uniform electric charge over its surface and is then exposed to the subject matter to be reproduced, usually by conventional projection techniques. This exposure discharges the plate areas in accordance with the radiation intensity which reaches them and thereby creates an electrostatic latent image on or in the plate coatmg.

Development of the image is effected with developer material or developers which comprise, in general, a mixture of a suitable pigmented or dyed electroscopic powder, hereinafter referred to as toner, and a granular carrier material, which later functions to carry and to generate triboelectric charges on the toner. More exactly, the function of the granular material is to provide the mechanical control to the powder, or to carry the powder to an image surface and, simultaneously, to provide almost complete homogeneity of charge polarity. In the development of the image, the toner powder is brought into contact with the plate and is held thereon electrostatically in a pattern corresponding to the electrostatic latent image. Thereafter, the developed xerographic image is usually transferred to a support or transfer material to which it may be fixed by any suitable means. After transfer, any toner powder remaining on the xerographic plate is removed.

Since the disclosure of the basic concept of xerography by Carlson, a variety of xerographic reproducing devices are in use, on a commercial basis, for general copying applications of the type normally encountered in business, engineering or law offices. These machines are therefore adapted to operate from a conventional commercial electricial outlet, that is, 110 volt alternating current outlet.

In general, the electrostatic charging of the xerographic plate in preparation for the exposure step, the electrostatic charging of the support surface to effect transfer and the charging of the xerographic plate to aid in the removal of residual toner powder are accomplished by means of corona generating devices whereby electrostatic charge is applied to the respective surface in each instance. For example, an electrostatic charge on the order of 740 volts is applied to the xerographic plate surface in preparation for the exposure step. To effect this charge in preparation for the exposure step, there is imposed on the high voltage wire of the corona charging device, a direct current potential of from 7000 to 8000 volts, depending on the corona threshold potential to the corona discharge device.

Patented Sept. 27, 1 966 Prior art power supply circuits, capable of imposing a high voltage direct current potential to these corona discharge devices from a low voltage alternating current source, have been costly to manufacture and to maintain.

It is, therefore, the principal object of this invention to improve power supply circuits so that the circuit can be manufactured economically.

For a better understanding of the invention, as well as other objects and further features thereof, reference is bad to the following detailed description of the invention to be read in connection with the accompanying drawings, wherein: I

FIG. 1 is a schematic illustration of a xerographic reproducing apparatus having a number of corona discharge devices actuated by a power supply circuit in accordance with the invention;

FIG. 2 is a schematic wiring diagram of a preferred power supply circuit of the invention;

FIG. 3 is a curve showing the output voltage waveform from the power supply circuit of FIG. 2; and,-

FIG. 4 is a schematic wiring diagram of another embodiment of a power supply circuit.

General As shown, the xerographic apparatus comprises a xerographic plate including a photoconductive layer or lightreceiving surface on a conductive backing and formed in the shape of a drum, generally designated by numeral 20, which is journaled in a frame to rotate in the direction indicated by the arrow to cause the drum surface sequentially to pass a plurality of xerographic processing stations.

For the purpose of the present disclosure, the several xerographic processing stations in the path of movement of the drum surface may be described functionally, as follows:

A charging station, at which a uniform electrostatic charge is deposited on the photoconductive layer of the xerographic drum;

An exposure station, at which a light or radiation pattern of copy to be reproduced is projected onto the drum surface to dissipate the drum charge in the exposed areas thereof and thereby form a latent electrostatic image of the copy to be reproduced;

A developing station, at which a xerographic developing material including toner particles having an electrostatic charge opposite to that of the electrostatic latent image are cascaded over the drum surface, whereby the toner particles adhere to the electrostatic latent image to form a xerographic powder image in the configuration of the copy to be reproduced;

A transfer station, at which the xerographic powder image is electrostatically transferred from the drum surface to a transfer material or support surface; and,

A drum cleaning station, at which the drum surface is first charged and then brushed or wiped to remove residual toner particles remaining thereon after image transfer, and at which the drum surface is exposed -to a relatively bright light source to effect substantially complete discharge of any residual electrostatic charge remaining thereon.

The charging station is preferably located as indicated by reference character A in the schematic illustration of the apparatus. In general, the charging apparatus or corona charging device 21 includes a corona discharge array of one or more discharge electrodes that extend transversely across the drum surface and are energized from a high potential source and are substantially enclosed within a shielding member.

Next subsequent thereto in the path of motion of the xerographic drum is an exposure station B. This exposure station may be one of a number of types of mechanisms or members such as desirably an optical scanning or projection system, or the like, designed to project a line copy image onto the surface of the photoconductive xerographic drum from a suitable original.

The optical scanning or projection assembly consists of a copy board in the shape of a drum, hereinafter referred to as copy drum 30, which is adapted to support copy to be reproduced and arranged to rotate in light projection relation to the moving light-receiving surface of the xerographic plate. Uniform lighting is provided by suitable lamps 31 attached to a slotted light reflector 32 mounted adjacent to the copy drum.

A slotted light shield 33, adapted to protect the xerographic plate from extraneous light, is positioned adjacent to the surface of the xerographic plate. A slot aperture in the light shield extends transversely to the path of movement of the light-receiving surface of the xerographic drum 20 to permit reflected rays from the copy drum to be directed against limited transverse areas of the lightreceiving surface as it passes thereunder.

To enable the optical system to be enclosed within a relatively small cabinet, a folded optical system including an object mirror 34, a lens 35, and an image mirror 36, is used in the preferred embodiment of the apparatus.

A document fed through document guides 37 to the copy drum is removably secured thereon by a suitable gripper mechanism for movement therewith in timed relation to the movement of the xerographic drum whereby a flowing image of the copy is projected onto the xerographic drum. The copy is held against the surface of the copy drum until gripped by means of document retaining guides 38. Pressure guides 93 and document guard 41 retain and guide the trailing edge of the document on the copy drum. After the copy is scanned, it is released from the copy drum to 'be transported out of the machine by the copy drum and document feed out rollers 42 through document feed out guide 43.

Adjacent to .the exposure station is a developing station C in which there is positioned a developer apparatus 50 including a developer housing having a lower or sump portion for accumulating developer material 51. Mounted within the developer housing is a driven buckettype conveyor 52 used to carry the developer material previously supplied to the developer housing to the upper portion of the developer housing from where the developer material is cascaded over a hopper chute 53 onto the drum.

As the developer material cascades over the drum, toner particles of the developer material adhere electrostatically to the previously formed electrostatic latent image areas on the drum to form a visible xerographic powder image; the remaining developer material falling off the peripheral surface of the drum into the bottom of the developer housing. Toner particles consumed during the developing operation to form the xerographic powder images are replenished by a toner dispenser 54.

Positioned next adjacent to the developing station is the image transfer station D which includes suitable sheet feeding mechanism adapted to feed sheets of paper successively to the xerographic drum in coordination with the presentation of the developed image on the drum at the transfer station. The sheet feeding mechanism includes a sheet source such as paper tray 60 for a plurality of sheets of a suitable support material, that is, sheets of paper or the like, separator rollers 61 adapted to feed the top sheet of the stack of support material through a guide 67 .to a sheet conveyor mechanism 62 having paper grippers 63 thereon which carry the sheet support material into contact with the rotating xerographic drum in coordination with the appearance of a developed image at the transfer station.

The transfer of the xerographic powder image from the drum surface to the support material is effected by means of a corona transfer device 64 that is located at or immediately after the point of contact between the support m'aterial and the rotating xerographic drum. The corona transfer device 64- is substantially similar to the corona discharge device that is employed at the charging station in that it also includes an array of one or more corona discharge electrodes that are energized from a suitable high potential source and extend transversely across the drum surface and are substantially enclosed with a shielding member. In operation, the electrostatic field created by the corona transfer device is effective to tack the transfer material electrostatically to the drum surface and simultaneously with the tacking action, the electrostatic field is effective to attract the toner particles comprising the xerographic powder image from the drum surface and cause them to adhere electrostatically to the surface of the support material.

As the paper gripper mechanism continues to move forward in its closed circuit, it will strip the support material from the xerographic drum and carry it to a fixing device, such as, for example, heat fuser 70, whereat the developed and transferred xerographic powder image on the support material is permanently fixed thereto.

After fusing, the finished copy is preferably discharged from the apparatus at a suitable point for collection externally of the apparatus. To accomplish this, there is provided a pair of delivery rolls 65 and 66 by means of which the copy is delivered from the machine after it is released by the gripper mechanism. Suitable cam means 68 and 69 are provided at the receiving and delivery stations of the conveyor mechanism, respectively, to actuate the paper grippers at these stations to receive or discharge a sheet of support material.

The next and finatl station in the device is a drum cleaning station E whereat any powder remaining on the xerographic drum after the transfer step is removed and whereat the xerographic drum is flooded with light to cause dissipation of any residual electrical charge remaining on the xerographic drum.

To aid in the removal of any residual powder remaining on the xerographic drum, there is provided a corona prec'leaning device 84 that is substantially similar to the corona discharge device that is employed at charging station A. Removal of residual powder from the xerographic drum is effected by means of a web cleaner device adapted to continuously feed a clean fibrous web material into wiping contact with the xerographic drum, As shown, the web material 55 is taken from a supply roll 81 and transported around a cleaning or pressure roll 82, preferably made of rubber, onto a takeup or rewind roll 83.

Any residual electrical charge remaining on the xerographic drum is dissipated by light from a fluorescent lamp 85 mounted in a suitable bracket above the xerographic drum, a suitable starter and ballast being provided for energizing the fluorescent lamp.

Suitable drive means drive the xerographic drum, the copy drum, the sheet conveyor mechanism at predetermined speeds relative to each other, and to effect operation of the paper separator roll, and the web cleaner mechanism, the latter being driven at a speed or speed whereby relative movement between the xerographic drum and the web material is effected. Suitable drive means are also provided for effecting operation of the conveyor power supply circuit adapted to operate from a con- 1 ventional commercial electrical outlet, that is, a volt alternating current outlet. The power supply circuit consists of a stabilized transformer and modified voltage doubler circuits which provide at least two separate output voltages; one with positive voltage peaks above the effective corona threshold and negative voltage peaks below the corona threshold and the other with negative voltage peaks above the corona threshold and positive voltage peaks below the corona threshold.

The stabilized transformer T, sometimes called a constant voltage transformer, a static magnetic voltage stabilizer, or a ferrosonic voltage stabilizer, is well known in the art and the specific details of the structure of the transformer will not be described in detail herein since it forms no part of the subject invention. Transformers of this type are adequately described in the Radio Engineers Handbook published in 1943 by McGraw-Hill Book Co. Inc. However, it is noted that in this type of transformer, the secondary portion of the magnetic core of the transformer is saturated to provide the stabilizing action, the output voltage has a flat topped wave form which is a distinct advantage for the particular circuit to be described in detail hereinafter. An additional useful feature of the stabilized transformer is that the loose magnetic coupling between the primary and the secondary thereof causes the output current at short circuit to be sharply limited which is of benefit as a safety feature both for personnel and equipment.

Referring now to FIG. 2, the power supply circuit consists of a high voltage transformer, generally indicated by reference T, with a magnetic shunt path MS between the primary winding TP and the secondary winding TS to provide loose magnetic coupling between the primary and the secondary. The primary winding TP of the trans former is connected to a suitable source of electrical power, such as a 110 volt, 6O cycle alternating current outlet.

In the embodiment shown, the secondary winding TS is provided with taps TS1, TS-2, TS-3, TS-4 and TS5. Tap TS is connected to ground which is a return path for the high voltage output at terminals C, T and PC. Capacitor 0-3 is connected to taps TS3 and TS-S and operates in conjunction with the loose magnetic coupling of the transformer to cause the secondary portion of the transformer to magnetically saturate and thereby provide a stabilized transformer secondary voltage.

Tap TS-l of the transformer is connected directly to a capacitor C-ll with a parallel .bleeder resistor R-1. The bleeder resistor R1 is used to discharge the capacitor C-l after input power has been removed from the power supply, so that no terminals remain hot on the power supply after the input power has been removed. The other terminal of capacitor C-l is connected to output terminals C and T and to one end of rectifier SR-l. The other end of rectifier SR-l is connected to tap TS3 of the secondary winding of the transformer.

As shown, the output from capacitor C-l is connected to terminals C and T connected to corona charging device 21 and to the corona transfer device 64, respectively both of these terminals being provided with a positive peak voltage above threshold voltage. With this arrangement, the capacitor C-l is charged on every other half cycle of secondary voltage from the transformer through the rectifier SR1 which blocks opposite half cycles of secondary voltage from discharging capacitor C-l. As a result of this charge on the capacitor 0-1, the output voltage as seen between the terminals C or T and ground is an AC voltage with a DC. bias voltage provided by the charge in capacitor C-ll.

As seen in FIG. 3, the output voltage to the terminals C and T is somewhat square in shape, a result of the output characteristics of the stabilizing transformer. This squared wave shape is more beneficial, as described hereinafter, than a strictly pure sine wave as would normally come from an ordinary high voltage transformer.

A similar circuit consists of the transformer secondary taps T S-2 and TS4, which with rectifier SR-2 connected in series with resistor R2, charges capacitor C-2 connected to the secondary tap TS-2 of the transformer to impose an output potential on the output tap PC, which is a biased negative output voltage. The purpose of the resistor R-2 is to limit current through rectifier SR2 under conditions when the output at the terminal PC or when the corona precleaning device 84 connected thereto is shorted to ground. Under normal operating conditions, the voltage drop across resistor R-2 is almost insignificant.

The reason why a current limiting resistor is used in series with rectifier SR-2 and none is used in series with the rectifier SR-1 is that under PC short circuit conditions, at larger direct current voltage can appear across capacitor C-2, whereas under C or T short circuit conditions, capacitor Cl represents a noticeably smaller alternating currentimpedance and the voltage across the tap TS-l and TS-3 will drop under short circuit C or T conditions due to the loose coupling between primary and secondary coils of the transformer. Also there is little, if any, need to provide a bleeder resistor for capacitor C-2 because the energy stored in capacitor 0-2 is noticeably lower than the maximum allowable energy storage for safety considerations. As shown in FIG. 3, the output wave shape through outlet PC is also a square wave.

The advantage of a square output voltage wave shape for use with corotrons, used in a Xerographic reproducing machine, is that the effective output voltage imposed upon the corona discharge device is a function of the voltage above the threshold during any given cycle. In a xerographic reproducing machine, the peak allowable voltage is limited by the level at which arcing will first occur so that with the squared wave shape, as shown, more power can be delivered at a given peak voltage than could be utilized with a voltage output in the form of a pure sine wave shape.

The operation of the circuit can best be explained by reference to FIGS. 2 and 3. The stabilized transformer (T), with loose magnetic coupling between the primary and secondary, working in conjunction with capacitor C-3 provides a stabilized output voltage so that output voltages will change less than five percent for changes of fifteen percent in input voltage. This, of course, is a necessary requirement for consistent operation in that in the average commercial office, the power input to a xerographic reproducing apparatus from a commercial electrical outlet will vary throughout the normal working day as a result of variations of load imposed upon the electrical circuit within an ofiice building.

Operation of the modified voltage doubler portion of the circuit can be understood more readily if only the positive output section is considered initially "(consisting of the transformer secondary TS, rectifier SR-Z, capacitor C1 and resistor R-l). On half cycles of one polarity, it can be seen that current will flow through the rectifier and charge the capacitor. Resistor R-l is used to bleed the charge from the capacitor so that voltage will not remain at the output terminals for any appreciable length of time after input power has been removed, but the resistance value is high enough so that the resistor has negligible affect on steady state circuit operation. When the secondary voltage reverses polarity, the rectifier will not conduct and the voltage presented to the load will be the sum of the capacitor voltage plus the transformer secondary voltage. The resultant output voltage Wave shape is that of the transformer secondary but with the positive peaks increased in magnitude and the negative peaks decreased in magnitude by the voltage across the capacitor.

It can be seen from the above that the flat topped wave shape from the transformer is not distorted, but rather biased to provide higher peak voltages of one polarity. This will provide a greater amount of energy for the load than a sharply peaked wave form with the same peak value. The value of the flat topped wave form can be appreciated by noting that the effective power available for charging is approximately proportional to the voltage above threshold squared, times incremental time and that the peak value is limited by the spark over voltage level.

Ordinarily, it is desirable to retain the short circuit current limiting characteristics of the transformer. However, the equivalent circuit of the shorted power supply is basically a series connection of the transformer inductance and the capacitor. If the values of inductive and capacitive reactance are nearly equal, the current limiting impedance will be very low. Therefore, since the inductance of the transformer has already been determined by output voltage and stabilization requirements, the capacitor must be chosen to provide either predominantly capacitive or inductive reactance in order to limit short circuit current. The choice will determine the shape of the load regulation curve as follows:

(A) If inductive reactance is chosen, the output voltage will be nearly constant for load currents up to a given value determined by the transformer design and then drop sharply to zero at a short circuit current which may not be more than several hundred percent of rated load current. This will happen because the high reactance of the transformer is produced by a magnetic shunt with a series air gap. The magnetic shunt is between the primary and secondary coils and tends to reduce the coupling between the primary and secondary (or increases the internal reactance of the equivalent circuit) except that at nominal loading, the air gap presents a high reluctance (magnetic circuit impedance) to flux between the coils and effectively provides close coupling between coils. As the secondary (load) current increases, the fiux density will increase in the secondary portion of the magnetic core and thus cause primary current and flux density to increase and the primary and secondary fluxes are in opposition so that the series air gap in the magnetic shunt will not then present so high a reluctance in comparison to the core proper (coupling primary and secondary) and flux will be diverted through the shunt, thus reducing coupling.

(B) I-f capacitive reactance is chosen, the output voltage will drop in a straight line from the open circuit value to zero at a short circuit current value. Since the capacitor is used to limit short circuit current, the transformer secondary voltage will not drop to zero at short circuit because the capacitor will then be the transformer load and an additional short circuit path will exist through the rectifier and a portion of the transformer secondary. Short circuit current through the rectifier will be greater than that for conditions in paragraph (A) by the (inverse) ratio of transformer secondary turns involved in each case. This follows from the fact that the transformer limits secondary flux which is a function of current times transformer turns. Therefore, in order to limit secondary current, it is necessary to add resistance in series with the rectifier (see resistor R-2 and rectifier SR4 in the negative output section of the circuit).

For the application in the xerographic apparatus shown, it is necessary to draw a significant current for two positive corona devices so the current limiting action of the transformer has been chosen for positive outputs as shown in the circuit diagram. The negative output does not require a large current and, in addition, it is desirable to maintain a constant current for expected variations in barometric pressure, temperature, humidity, etc. The steep load regulation curve (nearly a straight line) obtained with capacitive reactance limiting current will provide small variation in load current for'wide variation .of operating conditions so the capacitor C2 is used to limit short circuit current.

As is well known, the corona threshold potential and the corona current from an energized wire are functions of the wire diameter. In the embodiment of the Xerographic apparatus shown, the wire sizes of the corona devices are such that the positive corona threshold potential of the corona charging device 21 and the negative corona transfer device 64 is approximately 4000 volts and the corona threshold potential of the corona precleaning device 84 is approximately 3700 volts. These values of corona threshold potential will vary with variations of temperature and humidity.

In a preferred embodiment of the circuit of the invention, the values of the various elements of the circuit are chosen so that with a 115 volt input to the primary of the stabilized transformer T, the output voltages are as follows:

Output Terminal C and/or T PC Positive Peak (Volts) slooo'iira'iiiiiiihi'fj 5,800

From the above table, it is apparent since the corona threshold potential of both the corona charging device 21 and the corona transfer device 64 is approximately 4000, these devices will only emit positive corona, since the maximum negative peak voltage of 3000 volts is below the threshold potential of these devices. In the same manner, the corona precleaning device 84 Will only emit negative corona since the maximum positive peak potential of 3300 is less than the corona threshold potential of this device.

For other applications, for example, when arcing of a corona wire is desired or can be tolerated, an ordinary transformer may be used in lieu of the stabilized transformer T, as shown in FIG. 4. In this embodiment, the power supply circuit is used to provide a positive peak voltage above threshold voltage to only a single threshold type load, such as corona discharging device 21.

As shown in FIG. 4, this power supply circuit consists of a high voltage transformer, generally indicated T. The primary winding TP' of this transformer is connected to a suitable source of electrical power, such as a volt, 60 cycle alternating current outlet.

The secondary Winding TS is provided with three taps TS-l', TS-2' and TS3'. Tap TS3 is connected to a terminal G connected to ground which is a return path for the high voltage output at the terminal C or to the corona charging device 21, which is connected thereto.

Tap TS-l' of the transformer is connected directly to a terminal of capacitor C-l. The other terminal of capacitor C-l is connected to the output terminal C and to one end of the rectifier SR1. The other end of rectifier SR-l is connected to tap TS-3 of the secondary winding of the transformer.

As shown, the output of capacitor C1 is connected to a terminal C which, in turn, is connected to a corona charging device 21 to provide this device with a positive peak voltage above threshold voltage. With this arrange ment, the capacitor C-1 is charged on every other half cycle of secondary voltage from the transformer through the rectifier SR-l which blocks opposite half cycles of secondary voltage from discharging capacitor C1. As a result of this charge on the capacitor C-l, the output voltage, as seen between the corona charging device 21 and ground, is an AC. voltage with a DC. bias voltage provided by the charge in capacitor C-l.

Although the output of this circuit has been shown as being connected to a corona charging device, this corona charging device was used merely as an example of a threshold type load, it being apparent that other types of threshold type loads could be used in lieu of the corona charging device shown. This high voltage power supply circuit can be used to provide a biased A.C. voltage to an output terminal, the polarity of bias being de-,

terminal with the rectifier polarity as shown in FIG. 4. In addition, it is realized that a conventional transformer having more taps could be used in the manner shown in FIG. 2 to provide both a positive threshold peak voltage and a negative threshold peak voltage to a pair of threshold type loads.

The following significant or novel features are obtained with the new power supply circuitry:

(1) Corona charging (or similar phenomenon) equivalent to that obtained with filtered D.C. from a conventional voltage doubler (previously considered to be the most economical method) is obtained with:

(A) The rectifying element reverse voltage reduced by a factor of approximately four which results in a considerable cost reduction.

(B) The number of power supply components is reduced by one rectifying element and one capacitor per polarized (positive or negative) output. This allows a further cost reduction and causes the power supply to be inherently more reliable.

(C) The total efliciency of the corona emitting circuit is improved by allowing use of more efficient corona devices. That is, it is necessary to use voltages somewhat above the corona threshold for stable corona current and the circuit described provides lower current values (allowing a higher percentage of total corona current to be used for charging, etc.) for a stable corona voltage level.

(D) The rectifying elements are not directly in series with the outputs and thus do not have to pass short circuit current.

As it is well known, the corona threshold potential and the corona current from an energized wire are functions of the wire diameter.

While the invention has been described with reference to the circuit disclosed herein, it is not confined to the details set forth since modifications thereof will be apparent to those skilled in the art. For example, the power circuit disclosed could be used for a single output, either positive or negative, by deletion of that portion of the circuit not required. This application, therefore, is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims.

What is claimed is:

1. A high voltage power supply circuit to provide a positive biased A.C. voltage between a first output terminal and a third output terminal and a negative biased DC. voltage between a second output terminal and said third output terminal, said power supply circuit including a stabilized transformer having primary input terminals adapted to be connected to a source of A.C. potential, and a secondary having multiple taps;

a first capacitor connected from a first tap of said secondary to said first output terminal,

a first rectifier having its anode connected to a third tap of said secondary and its cathode connected between said first capacitor and said first output terminal,

a second capacitor connected between a second tap of said secondary and said second output terminal,

a second rectifier having its cathode connected to a fourth tap of said secondary and its anode connected between said second capacitor and said second output terminal, and

said third output terminal being connected to a fifth tap of said secondary, whereby the positive peak voltage applied to said first output terminal is greater than the negative peak voltage applied to said first outlet terminal and whereby said negative peak voltage applied to said second output terminal is greater than the positive voltage applied to said second output terminal.

2. A high voltage power supply circuit to provide a positive biased A.C. voltage between a first output terminal and a third output terminal and a negative biased DC. voltage between a second output terminal and said third output terminal, said power supply circuit including a stabilized transformer having primary input terminals adapted to be connected to a source of A.C. potential, and a secondary having multiple taps;

a first capacitor and a first resistor connected in parallel with each other from a first tap of said secondary to said first output terminal,

a first rectifier having its cathode connected between said first capacitor and said first output terminal and its anode connected to a third tap of said secondary,

a second rectifier and a second resistor connected in series, the cathode of said second rectifier being connected to a fourth tap of said secondary, and the anode of said second rectifier being connected through said second resistor between said second capacitor and said second output terminal, and

said third output terminal being connected to a fifth tap of said secondary whereby the positive peak voltage applied to said first output terminal is greater than the negative peak voltage applied to said first outlet terminal and whereby said negative peak voltage applied to said second output terminal is greater than the positive voltage applied to said second output terminal.

3. The apparatus of claim 2, including a third capaci tor having one side connected between said third tap of said secondary and said first rectifier and its other side connected between said fifth tap of said secondary and said third output terminal.

References Cited by the Examiner UNITED STATES PATENTS 2,375,458 5/1945 Agnew et a1 307-2 2,965,044 12/1960 Johnson 307-2 3,005,110 10/1961 Elam 321-20 X 3,067,376 12/1962 Kwast 321-20 X FOREIGN PATENTS 642,762 3/ 1937 Germany.

61,197 7/ 1926 Sweden.

MAX L. LEVY, Primary Examiner.

LLOYD MCCOLLUM, MILTON O. HIRSHFIELD,

Examiners.

L. R. CASSETT, T. J. MADDEN, Assistant Examiners.

Claims

1. A HIGH VOLTAGE POWER SUPPLY CIRCUIT TO PROVIDE A POSITIVE BIASED A.C. VOLTAGE BETWEEN A FIRST OUTPUT TERMINAL AND A THIRD OUTPUT TERMINAL AND A NEGATIVE BIASED D.C. VOLTAGE BETWEEN A SECOND OUTPUT TERMINAL AND SAID THIRD OUTPUT TERMINAL, SAID POWER SUPPLY CIRCUIT INCLUDING A STABLIZED TRANSFORMER HAVING PRIMARY INPUT TERMINALS ADAPTED TO BE CONNECTED TO A SOURCE OF A.C. POTENTIAL, AND A SECONDARY HAVING MULTIPLE TAPS; A FIRST CAPACITOR CONNECTED FROM A FIRST TAP OF SAID SECONDARY TO SAID FIRST OUTPUT TERMINAL, A FIRST RECTIFIER HAVING ITS ANODE CONNECTED TO A THIRD TAP OF SAID SECONDARY AND ITS CATHODE CONNECTED BETWEEN SAID FIRST CAPACITOR AND SAID FIRST OUTPUT TERMINAL, A SECOND CAPACITOR CONNECTED BETWEEN A SECOND TAP OF SAID SECONDARY AND SAID SECOND OUTPUT TERMINAL, A SECOND RECTIFIER HAVING ITS CATHODE CONNECTED TO A FOURTH TAP OF SAID SECONDARY AND ITS ANODE CONNECTED BETWEEN SAID SECOND CAPACITOR AND SAID SECOND OUTPUT TERMINAL, AND SAID THIRD OUTPUT TERMINAL BEING CONNECTED TO A FIFTH TAP OF SAID SECONDARY, WHEREBY THE POSITIVE PEAK VOLTAGE APPLIED TO SAID FIRST OUTPUT TERMINAL IS GREATER THAN THE NEGATIVE PEAK VOLTAGE APPLIED TO SAID FIRST OUTLET TERMINAL AND WHEREBY SAID NEGATIVE PEAK VOLTAGE APPLIED TO SAID SECOND TERMINAL IS GREATER THAN THE POSITIVE VOLTAGE APPLIED TO SAID SECOND OUTPUT TERMINAL.