US3143701A

US3143701A - Stabilization circuit for arc lamps

Info

Publication number: US3143701A
Application number: US809485A
Authority: US
Inventors: Lester F Bird
Original assignee: Engelhard Hanovia Inc
Current assignee: Engelhard Hanovia Inc
Priority date: 1959-04-28
Filing date: 1959-04-28
Publication date: 1964-08-04
Anticipated expiration: 1981-08-04

Description

Aug. 4, 1964 L. F. BIRD STABILIZATICN CIRCUIT Foa ARC LAMPS Filed April 28, 1959 M v. w B w n e e ,k my ,Wm wx. X d. m C `f a il. fr mm M l. L ma ll/l m.

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United States Patent O This invention relates to a stabilization circuit for arc lamps and, more particularly, for high pressure arc lamps of the compact type. *A y It has been found from life tests on high'pressure arc lamps of the compact type `that unnecessary instantaneous current demands from the electrodes considerably shorten the life of such lamps. Accordingly, circuits which maintain lamp voltages at the lowest value despite variations in line voltage yield the best useful life for the lamp. With the usual ballast for the arc composed of a .constant series reactance, there is no compensation for varyingrsupply voltages and the life of the lamp is relatively short. Such arrangements also have the obvious drawback that light from the lamp will flicker with supply voltage variations.

It is further noted that prior circuits which have been effective for accomplishing this purpose have generally been unnecessarily expensive in the provision of. heavy dutyregulator circuits having anV unnecessarily broad range of regulation.

Y Therefore, it is the principal objectof this invention to provide an improved operating circuit for arc lamps, in which the power supplied to the lamp is maintained substantially constant. As a result, the useful life of the lamp is greatly increased. As a further advantage, the light output remains independent of variations in the supply voltage.

In accordance with an illustrative embodiment of the invention, stabilization for arc lamps is obtained by the use of an inductive ballast of which the impedance is regulated automatically as a function ofthe supply voltage. This is accomplished by means of a pair of saturable reactors, the power winding of each reactor being connected to receive one half-wave of the supply current. In order to vary the impedance of these power windings, two magnetic fields are applied to the magnetic core of each-reactor. The first magnetic field has a Vconstant magnetic force above that required for the impedancce at which optimum supply current conditions prevail. The magnetic force of the second field is weaker and a function of the supply voltage; it is applied to Vthe core in opposite polarity with respect to the first field. By superposition both fields act combined upon the core to automatically adjust the impedance, and therefore maintain the voltage at the arc lamp at a substantially constant value.

In practice, each reactorcore carries two control windings of which the rst receives a constant direct currentY signal while the second control winding is energized by a direct current signal which is a function, of the supply voltage. Since control windings of saturable reactors must necessarily be energized by direct current, two reactors are required, whereby the power Winding of each reactor is associated with a rectifier. Each winding receives one of the half-waves of the supply current or a portion thereof as this is the case when an additional, constant impedance is connected in parallel with respect to the power windings.

In accordance with a feature of the invention, the heavy duty inductive ballast of an arc lamp is shunted by a magnetic amplifier having a power capacity which is a fraction of that of the ballast. In addition, control signals which are the resultant of a constant signal combined in opposition with a variable line voltage signal are applied to change the impedance of the shunt magnetic amplifier. e

The foregoing arrangements have the advantage of providing regulation for an arc lamp by the addition of an inexpensive light duty magnetic amplifier in parallel with the main ballast of the arc lamp circuit. Furthermore, excellent regulation is provided without changing the desired inductive character of the series ballasting circuit for the arc lamp.

In accordance with another feature ofthe invention the ballast for an arc lamp includes two saturable magnetic cores, and circuitry for applying two magnetic fields to each core. The first field has aconstant magnetic forcey higher than that required for optimum current supply to the lamp. The second, weaker magnetic'fieldfvaries with the supply voltage and is applied to thecores in opposite polarity with respect to the first fieldto increase the irnpedance of the ballast as the line voltage increases.

The invention will be further illustrated by reference to the accompanying drawing which is a circuit ,diagram of one embodiment of the invention..

The arc lamp 10, which may be a high pressure arc lamp of theY compact type, is supplied from an alternating current source through the leads Y12 and 14 and a constant inductive ballast 16. The

power windings

18 and 20 of a pair of saturable reactors 22 and`24 are connected in parallel with the ballast 16, and therefore with each other, to form an additional, variable ballast. The

rectifiers 26 and 28,y each associated with one of .the

power -`windings 13 and 20, respectively, eliminateone half-wave from the corresponding winding. p l

In4 order .to varypthe-,impedance in the

windings

18 and 20 for increasing orv decreasing the totalballast in,

the supply circuit/the` reactor 22 is provided with two i

control windings

30 and 32. In a similark mannen'con- Variation of the impedance in the power windings as a function of the supply voltage is obtained by means of i direct current signals through the control windings, whereby each half-wave ofthe total` supply current is separately subjected to this correction. Since the impedancein the

power windings

18 and 20 is an inverse kfunction of the degree of. magnetic saturation in the

cores

38 and 40, av

decrease in saturation andrtherefore an increase in impedance must be obtained from an increase` in supply` voltage. This is accomplished, in accordance with the invention, by applying aconstant magnetic field to the

cores

38 and 40, the force of this field exceeding that required for optimum current supply' to the lamp 10.` For this purpose, the

control windings

30 and 34 are energized by a sufficiently strong,lconstant direct current signal which may be obtained from any suitable .current source. In practice, the required current is` preferably derived fromthesupply lines 12 and L14 over' taps 42 and 44, a voltage stabilizer 46, which may comprise a saturable reactor 48 andA a loading capacitor 50, and a full'- wave bridge-,type rectifier 52.

The second, weaker direct current signal, which lmust be a function of the supply voltage, is obtained by means of taps 54 and 56, through a transformer 58 and a secondA Patented Aug. 4, 1964- been shown as being wound in the opposite sense. Obviously, the same effect can be obtained, eg., by reversing the polarity of one of the rectifiers.

From the foregoing it will be understood that the cores 38` and 40 are subjected'to the action of a differential magnetic field which is the result of the comparatively greater magnetic force generated by the constant current signalv flowing through

windings

30 and 34, diminished b'y the opposed magnetic force at any particular instant and obtained from the second

pair'of control windings

32 and 36. In practice, and in order to obtain a large operating range, it has been found advantageous to provide a current in the

windings

30 and 34 about twice as strong as the average or optimum current in the

windings

32 and 36. In operation, a decrease in line voltage and therefore in the signal current through

control windings

32 and 36 results in an increase of magnetization in the The impedance then decreases to permit more current to flow through the

power windings

18 and 20 and through the-lamp. With increased linevoltage, conditions are reversed, that is, with an increase in line voltage, inagnetization in the cores decreases to increase the impedance inthe power windings. Less current in the supply circuit flows` through the lamp and the desired result ofrpower stabilization is obtained. In this regard it will be noted that the magnetic fields set up by the constant current signal in the

windings

30 and 34 prevail over the varyingu supply signal fields generated by the

coils

32 and 36; that is true at any particular instant. In each case, the resulting differential magnetic field therefore has the polarity of the first mentioned field and varies as an inverse -function of the supply signal through the

windings

32 and 36.

In -one particular example, the supply voltage had a nominalvalue of 115- volts and actually variedA from about 100 volts to 130 volts. The resulting variable control voltage at the secondary of the transformer 58 varied from Vmm when the line voltage was 100 volts. to Vmm when the line voltage was 130 volts. The constant biasing voltage at the output of the circuit 46 was equal to Vmax., the maximum value of the variable control voltage. Now, withy the constant biasing and yvariable control signals Vbeingapplied in opposition to the magnetic amplifier, they cancel out when the line voltage is at the maximum value of 130 volts. Under these conditions the impedance of the magnetic amplifier is high and essentially no-` current flows through it, When the Vline `voltage drops to 100 volts, however, the differential bias saturates the magnetic amplifier and its impedancedrops sufficiently to maintain the arc lamp voltage at a substantially constant level. The minimumimpedance of the magnetic amplifier is thereforev several times that of the, ballast 4, and the power handling capacity of the magnetic amplifier is only a minor factor of that of the ballast.

The subject matter of thisr application is related to that' disclosed in co-pending applicaion Serial No. 781,222, filed December 18, 1958, now abandoned.

It will be` obvious to those skilled in the art that many modifications may be made within the scope ofthe present invention without departing from the spirit thereof, and the invention includes all such modifications.

What is claimed is: v

1'. An automatically regulated ballast circuit comprising alternating current input means connectable to a current supply, a ballast connected in series in the input means, a pair of saturable reactors having. power windings, the ballast including the power windings, means for directing one half-wave `of the supply current through the power windings of one reactor, means for directing the other half-wave of the supply current through the power windings of the other reactor; each reactor having a core and first and second control windings; means for supplying a first, stabilized direct currentvsignal to the first control winding of each reactor for magnetically biasing both cores equally and beyond the saturation degree required for optimum current supply conditions; means for deriving, from the alternating current supply, a second direct current signal which is a function of the supply voltage; and means for supplying said second signal to the second controlV winding of each reactor for opposing, equally in each core, the saturation produced by the first stabilizedy direct current signal in the first control winding with the second signal.

2. An automatically regulated ballast circuit compris` ing alternating current input means connectable to a current supply, a ballast connected in series in the input means, a Vpair `of Isaturablel reactors having power windings, the ballast including` the power windings, means for directing one half-wave of the supply current through the power windings of one reactor; means lfor directing the other half-wave of the supply current through the power 1 windings of the other reactor; each reactor having a core o f each reactor for opposing, equally in both cores, theA and firs-t and second control windings; means Afor supply-y saturationproduced by the first stabilized directk current signal inthe first control windings. I

3. An automatically regulated ballast circuit comprising alternating current input means connectable to a current supply, a ballast connected inseries in the input means, the ballast comprising an inductance having com` paratively. low impedance land the power windings of a dual magnetic amplifierof comparatively high impedance,

each winding being connectedin parallel with-said inductance; a pair of rectiers oppositely poledrelativeto each other and each associated with one of the said pair ofv power windings, the du-al magnetic amplifier having i' trol windings of each core to increase the two cores, a pair of control windings being associated with each core; circuitry includingA a stabilizer and a first bridge- Ytype full-wave rectifier for deriving-a first, constant direct current signal from said power Isupply means; means for applying said first signal to one of the control windings of each core tol decrease the impedance in the power windings below the impedance level for optimum current supply conditions; circuitry including a transformer and a second full-wave bridge-type rectifier for deriving, from the alternating current supply,` atsecond direct current signal which is a function of the supplyrvoltage.; andmeans for applying said Isecond signal to the other conthe power windings.

References Cited in -the file of this patent UNITED STATES PATENTS 2,399,377 vPanna et a1. Apr. so, 1946 2,786,968 Kabak Mar. 26,v 195,7 2,926,287 Bird Feb. 23, 1960 impedance in

Claims

1. AN AUTOMATICALLY REGULATED BALLAST CIRCUIT COMPRISING ALTERNATING CURRENT INPUT MEANS CONNECTABLE TO A CURRENT SUPPLY, A BALLAST CONNECTED IN SERIES IN THE INPUT MEANS, A PAIR OF SATURABLE REACTORS HAVING POWER WINDINGS, THE BALLAST INCLUDING THE POWER WINDINGS, MEANS FOR DIRECTING ONE HALF-WAVE OF THE SUPPLY CURRENT THROUGH THE POWER WINDINGS OF ONE REACTOR, MEANS FOR DIRECTING THE OTHER HALF-WAVE OF THE SUPPLY CURRENT THROUGH THE POWER WINDINGS OF THE OTHER REACTOR; EACH REACTOR HAVING A CORE AND FIRST AND SECOND CONTROL WINDINGS; MEANS FOR SUPPLYING A FIRST, STABILIZED DIRECT CURRENT SIGNAL TO THE FIRST CONTROL WINDING OF EACH REACTOR FOR MAGNETICALLY BIASING BOTH CORES EQUALLY AND BEYOND THE SATURATION DEGREE REQUIRED FOR OPTIMUM CURRENT SUPPLY CONDITIONS; MEANS FOR DERIVING, FROM THE ALTERNATING CURRENT SUPPLY, A SECOND DIRECT CURRENT SIGNAL WHICH IS A FUNCTION OF THE SUPPLY VOLTAGE; AND MEANS FOR SUPPLYING SAID SECOND SIGNAL TO THE SECOND CONTROL WINDING OF EACH REACTOR FOR OPPOSING, EQUALLY IN EACH CORE, THE SATURATION PRODUCED BY THE FIRST STABILIZED DIRECT CURRENT SIGNAL IN THE FIRST CONTROL WINDING WITH THE SECOND SIGNAL.