US3235770A - Pulse starting device using a special pulse transformer having integral capacitance - Google Patents

Description

1966 H. WATTENBACH PULSE STARTING DEVICE USING A SPECIAL PULSE TRANSFORMER HAVING INTEGRAL CAPACITANCE Filed Dec. 27, 1962 A w w w M W1. w 0 n m J .IH/VI l [I 0 0 m a A Z21: f w I E L x r H v a 7 m f n mf m v 4 w m, wfl (k l mmW 5 5 5 22 L m w m a F a L F IL I IIIII ll- W {M 4 3 4 Z\ 5 A 5 f, a E 2 .2 x 4 L 5:1 m: g g E F W 1TWVTT1TOT-I Hans L. Wa tflre ach I-Iis A lrlrcrneg United States Patent 3,235,770 PULSE STARTING DEVlCE USING A SPECIAL PULSE TRANSFORMER HAVING INTEGRAL CAPACITANCE Hans I... Wattenbach, Cleveland Heights, ()hio, assignor to General Electric Company, a corporation of New York Filed Dec. 27, 1962, Ser. No. 247,632 2 Claims. (Cl. 315239) This invention relates to a pulse starting device particularly useful for starting lamps where the required ignition voltage is much higher than the operating voltage.

The terminal voltage required for starting high pressure are lamps may be several times the voltage at which the lamp normally operates. An example of a lamp where such conditions are carried to the extreme is a socalled metal vapor alumina lamp which utilizes an envelop of polycrystalline alumina ceramic. The high melting point of the alumina ceramic (over 1900 C.) allows construction of a high current density lamp having a small diameter but this increases the breakdown voltage of the lamp and makes starting very difficult. Thus one alumina ceramic lamp wherein the interelectrode distance is 50 to 60 millimeters and the inner diameter of the ceramic tube is 6 millimeters, when filled with argon or xenon to a pressure of about 20 millimeters at room temperature, has a starting voltage of about 1800 volts peak. When a metal vapor such as cesium or sodium is added, the starting voltage decreases to a value of approximately 1100 volts peak. In normal operation, this lamp may operate at currents from 6 to 12 amperes with a voltage drop from 120 to 50 volts, the lamp wattage being about 600 watts.

In my copending application Serial No. 247,631 filed of even date herewith, entitled Starting Circuit for Discharge Lamps and assigned to the same assignee as the present invention, I have described and claimed a new and improved pulse starting circuit particularly suitable for the above lamp. That circuit includes a pulse transformer having a primary and a secondary winding, a pair of condensers which may be referred to as the charge .and discharge condensers, and a pulse switching element which is suitably a spark tube. The secondary of the pulse transformer is connected in series with the lamp in the output or load circuit of a conventional ballast. One condenser is connected across the ballast output circuit to form a charging circuit, and the other condenser is connected in series with the spark tube and the primary of the pulse transformer across the ballast output circuit to form a discharging circuit.

The object of the present invention is to provide an improved pulse starting device in accordance with the principles elaborated in my aforementioned copending application which is simpler and more economical to mass produce.

A feature of my invention is a reduction in the number of parts by utilizing a pulse transformer construction where integral or built-in capacities are used for the condensers required by the circuit.

According to my present invention, the pulse starting device comprises a pulse transformer constructed of sheets of conductive foil and insulating film wound on a magnetic core such as a ferrite rod. A continuous conductive foil, which may be referred to as the main foil, forms the primary and secondary windings, a tap being provided at an appropriate place corresponding to the junction between primary and secondary turns. Auxiliary conductive foils are juxtaposed against the primary end of the main foil in such a way that between the primary and the auxiliary foils two capacities are obtained which can be used for the charge and discharge con- Patented Feb. 15, 19fi6 densers in the pulse starting circuit. The insulating film thus serves both as insulation between the conductive foil turns of the pulse transformer and as dielectric material for the built-in capacities.

For further objects and advantages and for a better understanding of the invention, attention is now directed to the following description of a preferred embodiment, to be read in conjunction with the accompanying drawing. The features of the invention believed to be novel are more particularly set forth in the appended claims.

In the drawing wherein like symbols denote corresponding elements throughout the several figures:

FIG. 1 is a schematic diagram of a starting circuit embodying the invention.

FIG. 2 is a schematic diagram explanatory of the construction of the pulse transformer.

FIGS. 3a and 3b are developed edge and plan diagrams respectively of the pulse transformer.

FIGS. 4a and 4b are side and end section views respectively of the assembled pulse transformer.

The starting and operating circuit for a metal vapor lamp illustrated in FIG. 1 is generally similar to those described and claimed in my copending application Serial No. 247,631, filed of even date herewith, entitled Starting Circuit for Discharge Lamps and assigned to the same assignee as the present invention. It includes a ballast having input terminals 1, 2 for energization from the usual -120 volts, 60 cycle alternating current supply and output terminals 3, 4 across which, in a conventional circuit, the lamp would be connected. In this circuit, however, a pulsing device is connected across terminals 3, 4 and it in turn has output or lamp terminals 5, 6 across which the metal vapor alumina lamp'7 is connected. The function of the ballast is to regulate the lamp operating current and it will therefore include series impedance; it may also include transforming means to step up the line voltage. The illustrated ballast is a high reactance autotransformer 8 comprising a primary winding 9 and loosely coupled secondary winding 10 connected in series with the primary across ballast output terminals 3, 4. The leakage reactance of the secondary Winding serves in effect as a series impedance which regulates the lamp discharge current during normal operation. Terminals 2, 4 and 6 are all conductively joined and need not be physically distinct.

The starting device or pulsing circuit 11, shown enclosed within the dotted rectangle, comprises a pulse transformer 12 having a primary winding 13 and a secondary winding 14 which is connected between terminals 3 and 5. Thus the secondary winding 14 and the lamp 7 are connected in series across ballast output terminals 3, 4. Included in the pulsing circuit are a pair of capacitances C C preferably of equal value or rating. One capacitance, C is connected across ballast output terminals 3, 4 to form a charging circuit. The other capacitance, C is connected in series with a pulse switching element, shown as a spark tube 15, and primary winding 13 of the pulse transformer, across the ballast output terminals to form a discharging circuit,

In the operation of the circuit, when an A.-C. voltage is applied to terminals 1, 2, capacitor C charges or discharges as it follows the open circuit secondary voltage of ballast 8. The capacitance or value of capacitor C is small enough that there is substantially no resonant effect with the inductance of ballast 8. In other words, the capacitive reactance of capacitor C is much higher than the inductive reactance of reactor 8 so that the voltage across capacitor C follows substantially the line voltage. However the voltage across capacitor C cannot change so long as spark tube 15 is not conducting. Thus across the electrodes of the spark tube there exists the difference in the instantaneous values of voltage across capacitances C and C The breakdown voltage of the spark tube is selected to be within the peak value of the secondary open Circuit voltage provided by the ballast at terminals 3, 4. Therefore the breakdown voltage of the spark tube is exceeded at every half-cycle whereupon it conducts current with a maintaining voltage of 10 to 15 volts. At this low voltage, the spark tube is able to transfer high current pulses and only a small part of the pulse energy is dissipated internally. The spark tube may be compared to a very fast switch wherein the time required for turn-on is about 10 second. After each oscillatory discharge of the condensers, the spark tube extinguishes; it fires again at the next half cycle.

Upon breakdown of the spark tube, a current pulse passes through primary winding 13 of the pulse transformer (discharging capacitor C and charging capacitor C During the next half cycle, the current How is in the opposite direction and the charges on the capacitors are likewise reversed. The current pulses produce voltage pulses of a duration between 1 and 10 microseconds and of a peak voltage of about 2000 volts in the secondary 14 of the pulse transformer. These pulses are delivered to the lamp in series with the secondary open circuit voltag of ballast 8 and cause initial ionization and eventually the starting of the lamp. After the lamp has started, the open circuit voltage of the ballast decreases to the operating voltage of the lamp which is lower than the break down voltage of the spark tube, so that the generation of pulses ceases.

The pulse starting device of my present invention, as schematically indicated in FIG. 2, is electrically equivalent to that of my aforementioned copending application described above and the difierence arises in the construe tion of the pulse transformer into which the capacitors are combined. Instead of using conventional wire for the turns of the pulse transformer, I substitute thin metal bands or foil for the conductor along with insulating film and both are wound together on a magnetic rod. In addition I provide two auxiliary windings in such a way that two distributed capacities are developed between the primary turns and the auxiliary turns, These distributed capacities then serve as capacitive elements C C in the starting circuit and eliminate the need for separate condensers. In FIG. 2, the auxiliary windings are indi cated at 16, 17 and the distributed capacitances are indicated at C and Ca the external circuit connections are made to tap points w, x, y, z.

The actual physical construction of the pulse trans former will be readily understood by reference to FIGS. 3a, 3b. The magnetic core of the transformer is a cylinder 18 of magnetic material such as ferrite. The ferrite rod acts as a transformer core with a large air gap. A suitable material for the metal foil is copper foil one mil thick; for the insulating film, one mil thick polyethylene terephthalate (Du Pont Mylar) may be used. Over the first part of the winding designated A and correspond ing to the secondary turns 13 of the transformer, insulating film 19 and metal foil 20 are rolled together on the ferrite rod, The result is a spiral winding with the turns insulated by film 19; tap w provides a connection to the end of the secondary winding and corresponds to lamp terminal tap at provides a connection to the junction of secondary and primary turns and corresponds to load circuit terminal 3. Over the next part B1, an extra insulating film 21 is added below original insulating film 19, and two insulating films 22, 23 are added above metal foil 20. These additional insulating films extend uninterruptedly from beginning to end of the primary winding, that is, over both parts B1 and B2. In addition a metal foil 24 is added to extend only over part B1; it provides auxiliary turns 16 and distributed capacity C0 Tap y is provided at the beginning of metal foil 23 to permit a circuit connection to be made to capacitance C0 Tap y corresponds to common terminal 4, 6 which complements both load circuit terminal 3 and lamp terminal 5.

4. Over portion B2, another metal foil 25 is provided with tap z at its beginning; metal foil 25 provides auxiliary turns 17 and distributed capacitance Cc As seen in the drawing, spark tube 15 is connected between tap z and tap y corresponding to the common terminal.

After the bands of metal foil and insulating film have all been wound tightly on the core, the assembly may be dipped in a resin such as an epoxy resin which is then allowed to set in order to cement the various layers together. The side appearance of the finished pulse transformer with spark tube connected between taps y and z is shown in FIG. 40:; an end section view without the spark tube is shown in FIG. 4b.

As an example of a pulse transformer in accordance with the invention, one intended to operate with a ballast having an open circuit voltage of 200 to 270 volts is constructed as follows: the core is a ferrite rod, 7 centimeters long by 2 centimeters in diameter; the metal foil is copper foil 1 mil thick and 6 centimeters wide; the insulating film is polyethylene terephthalate 1 mil thick and 7 centimeters wide. With 150 turns in the secondary, its inductance is 1.35 millihenries; with 20 turns in the primary its inductance is .025 millihenries. Capacity Cc; is 0.13 microfarad, and CC2, 0.15 microfarad. In operation, the pulsing circuit provides a peak pulse voltage of 2800 volts and a peak pulse current of 2.5 amperes; the pulse duration is 1.5 microseconds and the pulse repetition rate is 1 pulse per half cycle, that is, pulses per second on a 60-cycle supply.

My invention thus provides a pulse transformer having a pair of built-in capacitances which can be used in a pulsing circuit to start discharge lamps requiring a high starting voltage. The metal foils and insulating film can be machine wound on a ferrite core and the inherent simplicity of the device makes its manufacturing cost very low. The arrangement in addition makes for ruggedness and low cost.

While a specific embodiment of the invention has been illustrated and described in detail, it is intended as exemplary and not in order to limit the invention thereto. The scope of the invention is to be determined by the appended claims which are intended to cover any modifications falling within its spirit.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A pulse starting device for insertion in an electric discharge lamp operating circuit of the kind including ballasting means energized by alternating current and supplying to a load circuit terminal a regulated current for an electric discharge lamp requiring a starting voltage higher than the open-circuit voltage of said ballasting means, comprising a pulse transformer including a magnetic core having wound thereon conductive foils with their turns insulated from each other, said foils being wound flat turn upon turn on said core and including one main foil provided with an intermediate tap forming a load circuit terminal and determining a primary winding portion on one side thereof and a secondary winding portion on the other, the outer end of said primary winding portion forming a lamp terminal, a first auxiliary foil extending along and wound with the primary winding portion but insulated therefrom to provide an integral capacitance to the end of said primary winding portion near said load circuit terminal, a second auxiliary foil extending along and wound with the primary winding portion beyond said first auxiliary foil but insulated therefrom to provide an integral capacitance to the outer end of said primary winding portion, a common terminal complementing both said load circuit terminal and said lamp terminal and connected to said first auxiliary foil, and pulse switching means connected between said second auxiliary foil and said common terminal.

2. In combination, an electric discharge lamp operating circuit including ballasting means energized by alternating current and supplying to a load circuit terminal a regulated current for an electric discharge lamp requiring a starting voltage higher than the open-circuit voltage of said ballasting means, a pulse transformer including a magnetic core having wound thereon conductive foils with their turns insulated from each other, said foils being wound fiat turn upon turn on said core and including one main foil provided with an intermediate tap connected to said load circuit terminal and determining a primary winding portion on one side thereof and a secondary winding portion on the other, the end of said primary winding portion constituting a lamp terminal, a first auxiliary foil extending along and wound with the primary winding protion but insulated therefrom to provide an integral capacitance to the end of said primary winding portion near said load circuit terminal, a second auxiliary foil extending along and wound with the primary winding portion beyond said first auxiliary foil but References Cited by the Examiner UNITED STATES PATENTS 2,509,005 5/1950 Lord 3l5239 2,521,513 9/1950 Gray 315243 2,536,580 1/1951 Spurr 333-70 JOHN W. HUCKERT, Primary Examiner.

JAMES D. KALLAM, Examiner.

D. E. PITCHENIK, Assistant Examiner.

Claims (1)

1. A PULSE STARTING DEVICE FOR INSERTION IN AN ELECTRIC DISCHARGE LAMP OPERATING CIRCUIT OF THE KIND INCLUDING BALLASTING MEANS ENERGIZED BY ALTERNATING CURRENT AND SUPPLYING TO A LOAD CIRCUIT TERMINAL A REGULATED CURRENT FOR AN ELECTRIC DISCHARGE LAMP REQUIRING A STARTING VOLTAGE HIGHER THAN THE OPEN-CIRCUIT VOLTAGE OF SAID BALLASTING MEANS, COMPRISING A PULSE TRANSFORMER INCLUDING A MAGNETIC CORE HAVING WOUND THEREON CONDUCTIVE FOILS WITH THEIR TURNS INSULATED FROM EACH OTHER, SAID FOILS BEING WOUND FLAT TURN UPON TURN ON SAID CORE AND INCLUDING ONE MAIN FOIL PROVIDED WITH AN INTERMEDIATE TAP FORMING A LOAD CIRCUIT TERMINAL AND DETERMINING A PRIMARY WINDING PORTION ON ONE SIDE THEREOF AND SECONDARY WINDING PORTION ON THE OTHER, THE OUTER END OF SAID PRIMARY WINDING PORTION FORMING A LAMP TERMINAL, A FIRST AUXILIARY FOIL EXTENDING ALONG AND WOUND WITH THE PRIMARY WINDING PORTION BUT INSULATED THEREFROM TO PROVIDE AN INTEGRAL CAPACITANCE TO THE END OF SAID PRIMARY WINDING PORTION NEAR SAID LOAD CIRCUIT TERMINAL, A SECOND AUXILIARY FOIL EXTENDING ALONG AND WOUND WITH THE PRIMARY WINDING PORTION BEYOND SAID FIRST AUXILIARY FOIL BUT INSULATED THEREFROM TO PROVIDE AN INTEGRAL CAPACITANCE TO THE OUTER END OF SAID PRIMARY WINDING PORTION, A COMMON TERMINAL COMPLEMENTING BOTH SAID LOAD CIRCUIT TERMINAL AND SAID LAMP TERMINAL AND CONNECTED TO SAID FIRST AUXILIARY FOIL, AND PULSE SWITCHING MEANS CONNECTED BETWEEN SAID SECOND AUXILIARY FOIL AND SAID COMMON TERMINAL.

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