GB2108337A - Starting circuit for multiple fluorescent lamps - Google Patents

Abstract

Two or more fluorescent lamps (11, 12) are connected in electrical series combination, one cathode of each lamp being connected to that of another lamp (13, 14). An end of each remaining cathode (16, 19) of the combination is respectively connected to one of a pair of input electrical power terminals (17, 18), one of the latter connections being via a ballast inductor (21). A starter switch (23) is connected across the other ends of the remaining cathodes, and one or more secondary windings (24) on the ballast inductor are respectively connected across the interconnected cathodes to supply preheating current. The circuit causes simultaneous starting of the lamps, with a single starter switch. <IMAGE>

Description

SPfltC!FlCKflON Starting circuit for multiple fluorescent lamps The invention is in the field of cathode preheat circuits for starting a plurality of fluorescent lamps of the cathode preheat type. Such lamps operate in a circuit which provides heating current through the cathodes for a few seconds until they are hot enough to emit electrons without damage to their electron emission material, whereupon the circuit turns off the preheat current and starts a gas dischage between cathodes.

Atypical cathode preheat fluorescent lamp circuit comprises a ballast connected in series combination with the lamp, this series combination being connected across a pair of electrical power input terminals. Typically, an end of one of the lamp cathodes is connected to one of the input terminals and an end of the other cathode is connected via the ballast to the other input terminal. The ballast may be a reactor (such as an inductor and/or capacitor) or resistor. A starter switch, such as the well known glow-starter switch, is connected across the remaining ends of the cathodes. When electrical power is applied to the input terminals, the starter switch closes, thus completing a current circuit through the cathodes whereby the cathodes become heated to electron-emissive temperature.The starter switch then opens, and a discharge occurs between the cathodes causing the lamp to emit light and function in its normal operating mode.

Many fluorescent light systems employ two fluoroscent lamps, and two starters respectively connected across the lamps, such as is disclosed in Figure 4 of US paten; a 241 386 to Doolay. Each starter functions to preheat the cathodes and start the lamp to which it is connected. Due to normal manufacturing variances in dimensions and other conditions, starter switches vary up to several seconds in ihe length of time they are closed before opening to start the lamps. Thus, in a two-lamp system, one lamp may start up to several seconds after the other lamp starts, thus causing a "flicker" effect that is annoying to many people and which gives an impression of defective lamps of circuit.

In accordance with the present invention there is provided a fluorescent lighting system of the cathode preheat type, comprising a plurality of fluorescent lamps connected in electrical series combination with a cathode of each lamp being interconnected with a cathode of another lamp, a pair of electrical power input terminals, means connecting an end of each of the remaining lamp cathodes respectively to said input terminals, one of the latter connection means including a ballast inductor, a starter switch connected across the other ends of said remaining lamp cathodes, and one or more secondary windings coupled to said ballast inductor and respectively connected across said interconnected cathodes, said starter switch and secondary windings functioning to provide preheat current to said cathodes priorto starting of the lamps.

The circuit advantageously provides substantially simultaneous starting of the lamps using a single starter switch, the starter switch preferably being a glow-starter switch.

In the accompanying drawing, by way of example only, the single figure is a schematic circuit diagram of a fluorescent lighting system embodying the invention.

As shown in the drawing, a plurality of fluorescent lamps 11, 12 are connected in series combination, one cathode 13 of lamp 11 being interconnected in electrical parallel with one cathode 14 of the other lamp 12. Alternatively, the cathodes 13, 14 can be interconnected in series. An end of the remaining cathode 16 of lamp 12 is connected to a terminal 17 of a pair of electrical power input terminals 17, 18 and an end of the remaining cathode 19 of lamp 11 is connected to the input terminal 18 via a ballast comprising an inductor 21 and capacitor 22. As is well known, the capacitor 22 is provided if a "lead" circuit is desired, and is omitted if a "lag" circuit is desired, in which case the inductor 21 is connected between the cathode 19 and the terminal 18. In a "lead" circuit the current leads the voltage in their phase relationship.

A starter switch 23 is connected across the remaining other ends of the cathodes 19, 16, and a secondary winding 24 on the ballast inductor 21 is connected in parallel with the interconnected cathodes 13,14. A conventional starting capacitor 26 is connected across one of the lamps 12, for aiding the starting of the other lamp 11; lffh(3n this lamp starts, the lamp 12 starts immediately.

The starter switch 23 may be o-i any suitable conventional type, such as 3 well known gzow-starter switch as represented in the drawing and compris ing an envelope containing an ionizable gas such as argon or neon and a pair of nornn.a; open switch contacts of which one is a bimetal strip which deforms to close the contacts when heated by a glow discharge of the gas.

The circuit functions as follows. When suitable electrical a-c voltage is applied to the input terminals 17, 18 this voltage is applied across the contacts of the starter switch 23, via inductor 21 and cathodes 16, 19, causing a glow discharge in the starter gas between the electrodes, which heats the bimetal contact causing it to deflect and close the switch contacts. While the starter switch is closed, a current path is established through the inductor 21 and cathodes 16, 19. This current is a value, such as about 0.65 amperes, to "preheat" the cathodes 16, lSto electron emissivetemperature in a short time such as about one second.At the same time, current induced in the secondary winding 24 of the inductor 21 causes the cathodes 13, 14 to "preheat" in a short time, such as about one second, to electron emissive temperature. While the starter switch 23 contacts are closed, there cannot be a glow discharge therein, and the bimetal contact cools and reverts to its normally open position, thus opening the switch contacts whereupon the line a-c voltage is across the series-connected lamps 11, 12. As explained above, the starting capacitor 26 shunts the lamp 12 causing all or a large part of the line voltage to be across the lamp 11, causing a discharge current to flow in the @amp between its cathodes 13, 19 and the lamp lights in normal operating manner.As soon as the discharge occurs in iamp 11, the voltage across the lamp reduces and the lamp 12 starts immediately, in insell known manner. Thus both lamps appear two light simultaneously, in a pieasing manner as corn pared to the above described two starter multiple lamp circuit which can cause the amps to stare at different times causing an annoying flicker effect and conveying an impression of faulty lamps or circuit.

While the lamps 11, 12 are operating, their current, and the current in the ballast inductor 21, is relatively lower (such as about 66%) than the cathode preheat current and only a smaller amount of voltage is induced ;n the secondary winding 23 and hence an insignificant amount of current is provided by winding 24 tc -te cathodes 43, 14. Thus, the system efficiency is improved because little heating @@@ent power is arpiied to the cathodes du ing operation.

More than two lamps may be connected in series, utilising the principles of the inventi@n, using a single starter 23 across the outermost cathodes and employing additional secondary windings 24 connected to preheat the additonal pairs of parallel-connected lamp cathodes. Additional starting capacitors 26 would be provided for the additional lamps in wel@ known manner.

The voltage characteristics of the lamps and the a-cinput voltage at terminals 17, 18 should be chosen for proper operation of the system. For example, the lamps 11, 12 may each be a 34 watt low energy lamp for an input voltage at terminals 17, 18 of standard 220 volts or 277 volts, It is only with the use of these 48" low energy type lamps that satisfactory two lamp starting can be achieved at the mentioned line voltages. Furthermore, the ratio of lamp volts to open circuit volts should not exceed 0.3 to a assure the e starting reliablity. F-or relatively lower input voltages at terminals 17, 18, relatively lower voltage lamps would be used, such as 20 watt lamps.

The invention has been found to achieve its desirable objectives, of providing simultaneous staring of fluorescent lamps in a multiple lamp system and thus avoiding the annoying flicker effect ene its accompanying connotation of defective lamps or circuit, by means of a simple and inexpen- sive circuit having a single starter switch and one or more secondary windings on the inductive ballast which provide preheatcurrentto parallel-connected lamp cathodes.

While preferred embodiments and modifications of the invention have been si,own and described, various other embodimente and modifications there of will become apparent to persons skilled in the art and will fall within the scope of the invention as defined in the following claims.

Claims (8)

1. A fluorescent lighting system of the cathode preheat type, comprising a plurality of fluorescent lamps connected in electrical series combination with a cathode of each lamp being interconnected with a cathode of another lamp, a pair of electrical power input terminals, means connecting an end of each of the remaining lamp cathodes respectively to said input terminals, one of the latter connection means including a bailast inductor, a sta@te@@witon connected across the other ends of said remaining lamp cathodes, and one or more secondary wind- ings coupied to said ballast inductor and res@ective- ly connected across said interconnected camodes, said starter switch and secondary windings functioning to provide a preheat current to said cathodes prior to starting of the lamps.

2. A lighting system as claimed in clam 5, in which said starter swiwn- is a glow switch type.

3. A lighting system as claimed in claim 1; in which said secondary windings provide a substantially lower amount of current to said interconnected cathodes when said lamps are operating than the value of said preheat current.

4. A lighting system as claimed in calm, including a starting capacitor connected across one of said lamps.

5. A lighting system as claimed in claim 4, including a capacItor connected in series with said ballast inductor.

6. A lighting system as claimed in claim 1, in which said interconnected cathodes are in electircal parallel.

7. A lighting system as claims@ in claim 1, in which said Interconnected cathodes are in electrical series.

8. A lighting system substantially as nerein described with reference to the accompanying drawings.