US2464704A - Current control circuit - Google Patents

Description

March 15, 1949.

w. B. MARTIN ET AL CURRENT CONTROL CIRCUIT Filed July 12', 1947 In 24 M /9 IIIIIIIIIIIIII! FICLZ INVENTORS Patented Mar. 15, 1949 CURRENT CONTROL CIRCUIT Wade B Martin, Ramsey, N. J and Harry Talberth, Brooklyn, N. Y.

Application July 12, 1947, Serial No. 760,630

.6 Claims.

This invention relates to a current control circuit and, more particularly, to an improved current control starting circuit for firing a fluorescent lamp.

A fluorescent lamp in general comprises a suitable mixture of inert gases contained within an elongated tubular envelope having its interior surface coated with a fluorescent substance. Widely spaced thermionic electrodes of filamentary form are mounted within the tubular envelope near opposite ends thereof. In lighting the lamp, it is first necessary to ionize the gaseous atmosphere within the envelope by heating the lfilamentary electrodes to an electron emitting temperature because at room temperatures the gas will not pass sufficient current for ordinary lighting purposes. This is accomplished by employing a current control starting circuit which permits the flow of a relatively high current through the filamentary electrodes in series to preheat them to the point of electron emission.

When the temperature of the electrodes reaches this point, the current control circuit abruptly interrupts the flow of current thereby causing a relatively high firing potential to be momentarily applied to the electrodes. This ionizes the gaseous atmosphere within the envelope which then serves as a conductive medium for sustaining a current flow between the electrodes at line potential. This line current flow through the gaseous atmosphere between the electrodes generates high intensity radiations within the invisible portion of the spectrum which, as is Well known in the art, excite the fluorescent coating on the interior of the lamp and cause it to fluoresce thereby producing visible light.

In designing a current control circuit for controlling the application of the preheating current and the firing potential, it is necessary that the circuit be designed to allow ample time for preheating the electrodes before causing the firing potential to be applied as otherwise the electrodes would be damaged, the ends of the lamp would be darkened, and considerable flickering and sputtering of the lamp would occur. On the other hand, it is also desirable, for obvious reasons, that a starting circuit should be designed to consume no more time in the preheating period than is necessary to raise the temperature of the electrodes to an adequate emissive temperature. In attempting to strike a balance between insufficient preheating and unduly long preheating, it sometimes happens that a starting circuit will fail to fire the lamp.

Accordingly, it is an object of this invention to provide an improved current control circuit.

It is also an object of this invention to providean improved current control circuit for controlling the application of a firing potential to afluorescent lamp.

Another object of the invention is to provide an improved current control starting circuit for firing a fluorescent lamp smoothly and without flickering or sputtering.

Still another object is to provide an improved current control circuit for effecting the preheating of the filamentary electrodes of a fluorescent lamp the instant that the line voltage is applied to the lighting circuit of the lamp.

A further object is to provide an improved current control starting circuit for eflecting adequate preheating of the filamentary electrodes of a fluorescent lamp and for causing a firing potential to be applied to them.

An additional object is to provide an improved current control starting circuit for causing a firing potential to be automatically and repeatedly applied to the filamentary electrodes of a fluorescent lamp and for automatically deactivating itself in the event the lamp fails to fire after a preassigned interval of time.

These and other objects of the invention are attained by means of an improved current con trol circuit having a heating element constituted by a high resistance which is connected in series with an inductive ballast and the lamp electrodes. This high resistance is normally virtually shortcircuited by a shunt path which includes a resistance wire heating element. The resistance wire heating element is helically wound around the high resistance and both of them are disposed in heating relationship to a normally closed bimetallic switch. As soon as the line current is applied to the lighting circuit of the lamp, the current will immediately flow through the shunt path in the starting circuit and will thereby immediately start to preheat the filamentary electrodes.

During this time, the resistance wire heating element becomes hot and radiates heat to both the high resistance and the bimetallic switch. The bimetallic switch and the resistance wire heating element are so proportioned that the switch will open at about the same time that the electrodes become sufficiently preheated for a discharge to be initiated across the lamp. When the shunt path across the preheated high resistance is thus opened, a high voltage surge is produced across the electrodes by the inductive bal last and the lamp should fire.

If, for various reasons, the lamp fails to fire, the line current now applied to the preheated high resistance will cause it to generate more heat which is radiated to the bimetallic switch causing it to open still further until it engages a second bimetallic switch which also has a resistance wire heating element connected to it in heating relationship. This establishes another virtual short-circuit across the high resistance. vCurrent will now flow through this second shunt 3 path to continue the preheating of the electrodes. During this time, the second resistance wire heating element will become hot and will radiate heat to the second bimetallic switch. Also during this time, the high resistance becomes cool.

Thus, the heating of the second resistance Wire heating element tends to disengage the second bimetallic switch from the first bimetallic switch by moving the former in one direction while, at the same time, the cooling of the high resistance is conducive to disengagement of the two switches by permitting the first bimetallic switch to move in the opposite direction. The combination of these two opposite actions causes the two bimetallic switches to separate quickly opening the second shunt path across the high resistance. This "causes the inductive ballast to produce a second high voltage surge across the electrodes which should fire the lamp.

If the lamp'stillfails to fire, the two bimetallic switches will again move into "engagement with each other "and the sequence of operations described in the preceding paragraph will be repeated until the ambient temperature within the housing structure of the starting circuit rises to a sufiiciently high degree to hold the bimetallic switches in their extreme positions, as is described in "more detail hereinafter, thereby ,preventing further recycling operations.

Tnese'and other features of the invention'are 7 "mo'ie'fully di cussed'in connection with the fol-- lowing detailed description of the drawing in which:

Fig. lis'a schematic circuit diagram of the improved current control circuit, and

Fig. 2 is a front perspective view with the housing structure broken away to 'show'the compact manner in'which the components of the improved current 'c'o'ntrol'starting circuit are assembled.

, In Fig.'1;a fluorescent lamp l containing a suitable mixture of inert gases is shown to be pro- "vided with oppositely disposed filamentary electrod'es2'and 3 near each end thereof. A supply source of the customary domestic potential, such I "as apower line supplying'115 volt 60 cycle current, isjindicated by the reference numeral 4 for operatin'g'the lamp I. Qne side of the power supply source '4 is connected through a suitable ballast impedance, such as a choke coil 5, 'tothe electrode 3. The other side of the power source 4 is "connectable through a manually operable control switch 6'to the electrode 2. The electrodes 2 and 3 are connected in series through a suitable high "resistance 'l'which also functions as a heating element in the current control circuit as is described hereinafter. A current control starting circuit 8 'for'con'trolling the application of both the preheating cur- *remram the firing potential to the electrodes 2 "and 3 is connected across the high resistance I in "shunt relation thereto. This currentcontrol cir- "cuit' 8 includes a resistance wire heating element '9 which is helically 'wou'ndaround' the high resistance has is shown inFig.'2,'forefficiently radiating heat thereto. Ascanfurthe'r be seen in Fig. 2, both the 'highreslstance l and theresiste'nce wire neatin element 9 are disposed in heating relationship to a-'fiei ible bimetallic switch Hi composed of any two suitable metals having dissimilar 'thermalexpansion 'coeiiicients. One end of the "bimetallic switch I is fixedly f mounted at the pbir'it l I.

' Nearthe othen'end of the bimetallic "switch I0,"a metalliccontact rod M' isafiixedto one side thereof byany convenient means, such asq'o'y welding. "Thei-endof the contactirod 14 is bent at an angle for movement against a stop provided by a mounting card indicated schematically at 24.

Another flexible bimetallic switch 16 composed of any two suitable metals having dissimilar thermal expansion coefficients has one end fixedly mounted at the point I! in electrically conductive engagement with one end of the resistance wire heating element 9. A second metallic contact rod I8 is aflixed, as by welding, to the bimetallic switch Hi near its other end for engagement with the first contact rod l4.

When the starting circuit 8 is in an unenergized condition, as is shown in Fig. 1, the contact rods I4 and I8 are in engagement with each other.

'Since the resistance wire heating element *9 "has a much smaller resistivity than that of the high thermal expansion'coeffici'ents has one end'fixedly mounted at the point 20. Theother end-of the switch is is bent-upward at an angle-to form a contact lip 2| 'for engagement with the contact rod Hi. Whenthe starting "circuit 8'is in anum energized condition, as is shown in Fig. '1, the contact lip 2| does not engage the contact rod I4. A'second'r'esistance wire heating element-22 is disposed in heating'relationship to the bimetallic switch l9 and has one end connected-in electrically conductive engagement with the switch I ii at the point 20.

To operate this current control circuit, the manually operable control'switch 6 isfirst closed to apply the line current from "the source 4 to the inductive ballast 5 in series with the electrodes 2 and 3 and the resistance wire heating element 9 in the shuntpath'across thehighresistance i. This flow of currentthrough the electrodes 2 and 3 causes them to become warm thereby partially ionizing the gaseous atmosphere contained within the envelope of the lamp I. At the same time, the fiow of current through the resistance wire heating element 9 causes it to become hot.

The heat thus generated by'theresistance wire heating element 9 is radiated tothe bimetallic switch iii and also to the highiresistanc'e 1 which both become warm dueit'otheir proximity which is more evident in Fig.2. The'bimetallic switch Iii finally becomes so hot that'it bends downward thereby opening the circuitthrough the contact rods M and I8. As was stated above, the resistance wire heating element 9 'and the bimetallic switch in areso proportioned that the contact rods M and I8 willseparate at about th'esarne time that the electrodes '2 and 3 become sufiicie'ntly preheated for a discharge to be initiated across the lamp l'.

The sudden iopening of the-circuit through the contact rods l4 and I8 opens the shunt path across thehigh resistance '1 thereby, in *e'iiect, switching it in series with the inductive ballast Sand theelectrod'es 2 "and 3. 'This resistance 7! has such a high resistivity that the sudden same effect as opening the series circuit"through the inductive ballast 5 and the electrodes 2 and 3.

This interruption causes the inductive ballast 5 to produce a high voltage surge or kick across the preheated electrodes 2 and 3 thereby com pleting the ionization of the gaseous atmosphere contained within the envelope of the lamp I and resulting in the striking of a low voltage are which, when once started, will be sustained by the line voltage with the electrodes 2 and 3 being maintained at a discharge sustaining temperature by the discharge current through the lamp I. A small condenser 23 is connected across the high resistance I to minimize sparking or arcing when the contact rod I4 moves away from the contact rod I8 to open the shunt path across the high resistance I.

During the time that the lamp I remains in operation, a small amount of current will flow through the preheated high resistance 1 to maintain it warm. The heat now generated by the high resistance I is radiated to the bimetallic switch I and keeps it sufficiently warm to maintain the contact rod I4 in an open position approximately midway between the contact rod I8 and the contact lip 2| but not suificiently downward to engage the mounting card 24. The above-mentioned shunt path in the starting circuit 8 thus remains open as long as the lamp I is in operation.

It should be noted that, because of its relatively large mass, the heat inertia of the high resistance I is great. However, this inertia is overcome during the initial attempt to fire the lamp I due to the high resistance I having been first preheated by heat radiated by the resistance wire heating element 9.

In the event that the lamp I should fail to fire, a larger amount of current will flow through the high resistance 1. This current will have a voltage about double that which it would have had if the lamp I had fired. The resistance I will therefore become hotter than it would have been under the conditions described in the preceding paragraph and, due to its proximity as shown in Fig. 2, will radiate a relatively high amount of heat to the bimetallic switch IO. lhe bimetallic switch I 0 now becomes so hot that it bends further downward until its contact rod l4 engages the contact lip 2I to close an auxiliary shunt path across the high resistance I.

Since the resistance wire heating element 22 in this shunt path has a considerably smaller resistivity than the high resistance I, most of the line current will now flow through this path instead of through the high resistance I which will now become cooler and will cease to radiate as much heat to the bimetallic switch In so that it also will become cooler.

This flow of current through the resistance wire heating element 22 causes it to produce heat which is radiated to the bimetallic switch I9 due to their proximity as shown in Fig. 2. This heat tends to cause the bimetallic switch I9 to bend downward. During this time, the cooling of the high resistance I tends to permit the b metallic switch III to cool as was described in the preceding paragraph so that it be ns to bend upward. Due to these simultaneously opposite actions, this auxiliary shunt path is quickly opened to again place the high resistance 1 in series with the filaments 2 and 3. As was stated above. this in effect interrupts the series circuit through the induct ve ba last and the electrodes 2 and 3 due to the high value of resistance I. The high voltage surge now pro- 6 duced by the ballast coil 5 due to this interruption is applied to the preheated electrodes 2 and 3 in another attempt to fire the lamp I.

This sequence of operations is quickly repeated several times if necessary. If the lamp I fails to fire during these operations, the ambient temperature of the air inside the housing structure, which completely encloses the starting circuit 8 as is shown in Fig. 2, finally rises to a point sufi'iciently high to cause all three bimetallic switches l6, Ill, and I9 to bend further downward. The bimetallic switch I9 is free to bend far downward so that its contact lip 2i will be out of engagement with the contact rod I4. The downward bend of the bimetallic switch I0 is arrested due to the bent end of its contact rod I4 hitting against the stop constituted by the mounting card 24. Similarly, the downward bend of the bimetallic switch I6 is arrested due to its bent end striking against the stop constituted by the mounting card 24. Since the distance between the mounting card 24 and the tip of the bimetallic switch It is shorter than the distance between the mounting card 24 and the tip of the contact rod I4, the contact rod l4 will now bend down further than the bimetallic switch I6. This prevents the contact rod I c from coming into engagement with the contact rod M at this time.

Thus, both the main shunt path across the high resistance 1 and the auxiliary shunt path across the high resistance i will now be held open due to the heat inside the housing structure holding the three bimetallic switches I6, l0, and I9 in the downward positions just described. The starting circuit 8 will remain in this condition due to the heat produced by the flow of line current through the high resistance I. With both the shunt paths being thus held open, no further attempt to fire the lamp I will be made until the control switch 6 has been opened to discontinue the fiow of current through the high resistance I and until the ambient temperature within the housing structure becomes sufficiently reduced to permit the bimetallic switches I6, I0, and I9 to move up out of their extreme downward positions.

It is to be noted that the reason for the stops provided by the bent ends of the contact rod I4 and the bimetallic switch I6 hitting against the mounting card 24 is not only to prevent the contact rod I 8 from engaging the contact rod I4 at this time but also to prevent the contact rod I4 from being carried down far enough to engage the contact lip 2I during this period of high ambient temperature.

In Fig. 2, the current control starting circuit 8 of Fig. 1 is shown to be mounted on a card 24 of insulat ng material and is also attached to a base 25 of insulating material. The base 25 together with a cylindrical casing 26 of any suitable material constitute a housing structure which completely encloses the start ng circuit 8. The base 2515 provided with terminals 2! and 28 for facilitating the electrical connection of the starting circuit 8 to the lighting circuit of the lamp I of Fig- 1. It can be seen in Fig. 2 that the high resistance I is connected across the terminals 27 and 28 and that the condenser 23 is also connected across the terminals 2! and 28 in shunt with the resistance I.

The b metallic switch I0 is shown to be bent in the form of a J and is attached to the mounting card 24 at the point I I by any suitable means, such as by a rivet. It is electrically connected to to efficiently radiate heat thereto.

the terminal 28 by a conductor 29 which passes through. an eyelet 33), along the back of the mouhtirg card it, and then through another eyelet 35. The free end of the bimetallic switch iii welded thereto one end of a metallic contact rod M which has its other end bent at an angle for serwing as a stop arm for the purpose discussed above in the description of Fig. l.

The contact rod M is normally in contact with another metallic contact rod l8 welded near one end of the bimetallic switch it. The bimetallic switch it is also bent in the form of a J and is attached to the mounting card M at the point I! in a manner similar to that of the bimetallic switch iii. The other end of the bimetallic switch iii is bent at an angle to serve as a stop arm for the reason described above. The fixed end of the bimetallic switch H has soldered thereto one end of the resistance wire heating element 9 wh ch is helically wound around the Bakelite shell of the high resistance l in order The other end of the resistance Wire heating element 9 is soldered to the conductor 3! which is connected to the terminal 27.

It is to be noted that both the high resistance l and the resistance wire heating element 9 pass through the bend at the bottom oi the bimetallic switch ill in order that the heat which they generate may be more eificiently radiated to the bimetallic switch Hi. It is especially to be noted that, due to the resistance wire heating element ll being superimposed upon and wound around the high resistance 1, the heat generated by the resistance wire heating element El will be efficiently radiated to the high resistance '5 for preheating it as was discussed above in the description of Fig. l.

The bimetallic switch H; has one end bent in the form of a J which is afiixed to the mounting card 2& at the point 28 in a manner similar to that of the bimetallic switch H3. The other end of the bimetallic switch it is bent upward to form a contact lip 2| for engagement with the contact rod i i. If desired, instead of thus bending the end of the bimetallic switch 19, a short section of contact rod material may be soldered along the top edge of the bimetallic switch I9 for performing the same function as the contact lip 2i. resistance wire heating element 22 which has one end soldered to the lead-in conductor 3| and has its other end soldered to the fixed end of the bimetallic switch l9.

In order that the heat generated by the resistance wire heating element 22 will not be effectively radiated to the other bimetallic switches in and iii, the wire 22 is passed from the back of the card M through an eyelet 32, then along the front of the card 26, through another eyelet 33, along the back of the card 24, and then through another eyelet it to the fixed end of the bimetallic switch I9.

The eyelets 32, 33, and 3 4 also perform a spacing function by reason of their rims projecting slightly out from the mounting card 24 and thereby serving to space the wire 22 a short distance away from the mounting card 24 so that it will not become burnt or charred when the wire 22 becomes hot. In addition, these eyelets 32, 33, and 34 also function to absorb some of the excess heat produced by the resistance wire heating element 22.

The J-bend at the fixed end of the bimetallic switch I6 is large enough to provide 'sufilcient The bimtallic switch It is heated by the spacing between'the free end of the bimetallic switch it and the resistance wire heating element 22 so that it will not be efiectively heated thereby. this regard, it should be noted, as was stated above in the description of Fig. 1, that the bimetallic switch It is heated only by the ambient temperature within the housing structure constituted by the casing 26 and the base 25.

It is to be noted that the bimetallic switches Hi, It, and I9 are self-compensating for normal changes in the ambient temperature within the housing structure or for changes in room temperature. This is because such temperature changes will efiect equal movement of the free ends of each of the bimetallic switches l0, l6, and I9 so that their relative positions with respect to each other will remain the same.

It is to be understood that the specific construction described above and shown in the drawing is for the purpose of explaining the nature of this invention and that various modifications may be made therein without departing from the scope of the invention which is to be limited only by the claims appended hereto.

What is claimed is:

1. In combination, a source of electric current, a high resistance, a normally closed main shunt circuit connected across said high resistance, a normally open auxiliary shunt circuit connected across said high resistance, and means for applying current from said source to said high resistance and said main and auxiliary shunt circuits, said main shunt circuit having a normally closed first bimetallic switch connected in series with a first resistance wire heating element helically wound around said high resistance for eficiently radiating heat thereto and disposed in heating relationship to said first bimetallic switch, and said auxiliary shunt circuit including a normally open second bimetallic switch and expediting means for expediting movement of said second bimetallic switch, said expediting means comprising a second resistance wire heating element connected in series in said auxiliary shunt circuit and disposed in heating relationship to said second bimetallic switch for radiating heat thereto.

2. In combination, a source of electric current, a fluorescent lamp having filamentary electrodes, a normally open control switch, an inductive ballast, a high resistance having one end connected to one of said electrodes and having another end connected to another of said electrodes, circuit means for connecting said control switch and said inductive ballast and said high resist ance and said electrodes all in series with said source of current, a normally closed main shunt circuit connected across said high resistance, said main shunt circuit including first and second contact means normally in engagement with each other and connected in series with a first resistance wire heating element adapted to generate and radiate heat upon the closure of said control switch, said second contact means including first bimetallic means, said first resistance wire heating element being disposed in heating relationship to said first bimetallic means for radiating heat thereto, said first bimetallic means being adapted when hot to move said second contact means out of engagement with said first contact means for opening said normally closed main shunt circuit, said inductive ballast being adapted to produce a first high voltage surge between said electrodes upon the opening of said main shunt circuit across said high resistance, said high resistance being adapted to become hot and to radiate heat upon the opening of said main shunt circuit with said control switch closed, said high resistance being disposed in heating relationship to said first bimetallic means for radiating heat thereto, and a normally open auxiliary shunt circuit connected across said high resistance and including third contact means having second bimetallic means connected in series with a second resistance wire heating element disposed in heating relationship to said second bimetallic means for radiating heat thereto, said first bimetallic means being adapted when heated by said high resistance to move said second contact means into engagement with said third contact means for closing said auxiliary shunt circuit across said high resistance, said second resistance wire heating element being adapted to become hot upon the closure of said auxiliary shunt circuit for heating said second bimetallic means, said first bimetallic means being adapted to move said second contact means out of engagement with said third contact means after said auxiliary shunt circuit is closed, said second bimetallic means being adapted when hot to move said third contact means out of engagement with said second contact means for opening said auxiliary shunt circuit, and said inductive ballast being adapted to produce a second high voltage surge between said electrodes upon the opening of said auxiliary shunt circuit across said high resistance.

3. A combination in accordance with claim 9 and comprising in addition a housing structure for completely enclosing said high resistance and both said main and auxiliary shunt circuits, said first contact means including third bimetallic means, and a stop member disposed within said housing structure, all of said three bimetallic means being adapted to move their associated contact means toward said stop member upon an increase in the ambient temperature within said housing structure, said second contact means having a first stop instrumentality adapted to hit against said stop member for holding said second contact means out of engagement with said third contact means, and said first contact means having a second stop instrumentality adapted to hit against said stop member for holding said first contact means out of engagement with said second contact means whereby both said main and auxiliary shunt circuits are held open.

4. A current control starting circuit for an electric gaseous discharge device having a plurality of filamentary electrodes, said starting circuit comprising in combination a high resistance having one end connected to one of said electrodes and having another end connected to another of said electrodes, circuit means including a main shunt path and an auxiliary shunt path for shunting said high resistance, switching means having at least three switch arms for controlling said shunt paths, the first and second of said switch arms being normally in electrically conductive engagement for closing the main shunt path, the third of said switch arms being normally out of electrically conductive engagement with the other two switch arms for opening the auxiliary shunt path, means for causing said high resistance to become hot and to radiate heat to the second switch arm, said second switch arm, being adapted when hot to move into electrically conductive engagement with the third switch arm for closing the auxiliary shunt circuit, said high resistance being adapted to cool and to cease radiating heat to the second switch arm when said auxiliary shunt circuit is closed, said second switch arm being adapted to move away from the third switch arm for opening the auxiliary shunt circuit when heat ceases to be radiated to it by the high resistance, and accelerating means for accelerating the opening of the auxiliary shunt circuit after it has been closed, said accelerating means comprising a resistance wire heating element connected in series with the third switch arm and disposed in heating relationship thereto and adapted to become hot when said auxiliary shunt circuit is closed, said third switch arm being adapted to move away from the second switch arm for opening the auxiliary shunt circuit when heat is radiated to it by said resistance wire heating element.

5. In a current control starting circuit for firing an electric gaseous discharge device having a plurality of filamentary electrodes with means for producing a first high voltage surge between said electrodes for firing said device, circuit means for quickly producing a second high voltage surge between said electrodes in the event said device fails to fire in response to the first high voltage surge, said circuit means including two switch arms of bimetallic material, the first of said switch arms being adapted when hot to move into electrically conductive engagement with the second of said switch arms and when cool to move out of engagement therewith, the second of said switch arms being adapted when hot to move out of electrically conductive engagement with said first switch arm, and heat radiating means adapted to radiate heat to said second switch arm only after said first switch arm has been heated and is beginning to cool.

6. A current control starting circuit for an electric gaseous discharge device having a plurality of filamentary electrodes, said starting circuit comprising in combination a high resistance having its first end connected to a first one of said electrodes and having its second end connected to a second one of said electrodes, 2. first bimetallic switch arm, a first resistance wire heating element having one end connected to said first switch arm and having its other end connected between the second end of the high resistance and said second electrode, a second bimetallic switch arm, a second resistance wire heating element having one end connected to said second switch arm and having its other end connected between the second end of the high resistance and said second electrode, a third bimetallic switch arm having a fixed end and a free end adapted to move into electrically conductive engagement with said first and second switch arms alternatively, and circuit means for connecting the fixed end of said third switch arm between the first end of the high resistance and said first electrode.

WADE B MARTIN. HARRY TALBERTH.

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

UNITED STATES PATENTS Number Name Date 2,356,813 Betz Aug. 29, 1944 2,426,229 McCarthy Aug. 26, 1947

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