Abstract:
A fluorescent lamp system including a ballast with primary and secondary windings and a switch for each electrode of the lamp system. Each switch is operable in response to the voltage across its associated lamp after its associated lamp turns on to interrupt the connection of an associated electrode to its associated heater winding and wherein at least one of said heater windings is a portion of the secondary winding.

Description:
BACKGROUND OF THE INVENTION 
     This is an invention in lighting. More particularly it involves an arrangement for conserving power in the operation of fluorescent lamp systems. 
     This application is related to U.S. patent application Ser. No. 629,868, filed Dec. 19, 1990 and assigned to the same assignee as this application. Application Ser. No. 629,868 is hereby incorporated by reference herein. 
     It is desirable to decrease the power expended by fluorescent lamps by shutting off the current to the heater electrodes of such lamps after ignition. In the past a number of arrangements for doing this have been proposed. Some of these use relays (see U.S. Pat. No. 4,661,745 to Citino et al and U.S. Pat. No. 4,954,749 to Crawford). Relays can be noisy and are subject to wear. The use of a filament transformer has also been proposed (see U.S. Pat. No. 4,399,391 to Hammer et al). Arrangements with filament transformers require auxiliary protection against excessive currents which can be developed in case a lamp electrode is damaged and the lamp acts in the manner of a rectifier. 
     SUMMARY OF THE INVENTION 
     It is an object of this invention to provide an improved arrangement for discontinuing heater electrode current flow in fluorescent lamps after the lamps are ignited. 
     One of the features of the invention is that it responds to the decrease in voltage across the lamps of a two lamp rapid start fluorescent lamp system which takes place after lamp ignition. 
     One of the advantages of the invention is that it decouples all of the filaments of a rapid start fluorescent lamp system from the filament windings upon ignition of the fluorescent lamps of the system. This makes a portion of the secondary winding available as a filament winding without the fear of it generating uncontrollable voltage during lamp operation. 
     In accordance with one embodiment of the invention, there is provided a fluorescent lamp system comprising a fluorescent lamp having a pair of electrodes. A ballast is provided for connection to a proper source of voltage. The ballast includes a primary winding and a secondary winding. The ballast when connected to a proper source of voltage, provides a voltage across the lamp. The ballast includes a pair of electrode heater windings. At least one of the electrode heater windings comprises a portion of the secondary winding. A pair of semiconductor switches is provided, each of which connects one of the electrode heater windings to a respective lamp electrode. Control means is connected across the lamp and responds to the voltage across the lamp when the lamp is on to render each of the semiconductor switches non-conductive. The control means responds to the voltage across the- lamp when the lamp is off to render each of the semiconductor switches conductive. 
     In accordance with another aspect of the invention, there is provided a rapid start fluorescent lamp system comprising a plurality of fluorescent lamps each having a pair of electrodes. A ballast is provided for connection to a proper source of voltage. The ballast includes a primary winding and a secondary winding. The ballast, when connected to a proper source of voltage, provides a voltage across the lamps. The ballast includes a plurality of electrode heater windings for applying heating voltage to the electrodes of the fluorescent lamps. At least one of the electrode heater windings comprises a portion of the secondary winding. A plurality of switches are provided for connecting the electrode heater windings to the lamp electrodes. Control means is included which is connected across the lamps and is responsive to the voltage across the lamps when the lamps are on to render each switch non-conductive. The control means is also responsive to the voltage across the lamps when the lamps are off to render each switch conductive. 
     In accordance with a still further aspect of the invention there is provided a fluorescent lamp system comprising a fluorescent lamp having a pair of electrodes. A ballast is provided for connection to a proper source of voltage. The ballast includes a primary winding and a secondary winding. The ballast, when connected to a proper source of voltage, provides a voltage across the lamp. The ballast includes a pair of electrode heater windings. One of said electrode heater windings comprises a part of the primary winding and one of said electrode heater windings comprises a part of the secondary winding. A pair of switches is provided, each connecting one of the electrode heater windings to a respective lamp electrode. Control means is connected across the lamp and responds to the voltage across the lamp when the lamp is off to conduct current which current renders each switch conductive. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     Other objects, features and advantage of the invention will be apparent from the following description and appended claims when considered in conjunction with the accompanying drawing in which: 
     the sole FIGURE is a schematic circuit diagram of one embodiment of the invention in a two-lamp rapid start fluorescent system. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the FIGURE there is shown therein two fluorescent lamps 11 and 13 each having a pair of electrodes 11a, 11b and 13a, 13b, respectively. Electrode 11a is connected across heater winding 15 which forms a part of the secondary winding SE of autotransformer 17. This connection is through triac TR1. Electrodes 11b and 13a are connected through triac TR2 across heater winding 19 of transformer 17. Electrode 13b is connected through triac TR3 across winding 21 which forms a part of primary winding PR of transformer 17. As is typical, primary winding PR is connected by capacitor C1 to secondary winding SE. This combination of elements is connected across lamps 11 and 13 which receives operating voltage therefrom. Such an operating voltage will be supplied when primary winding PR is connected to a proper source of voltage through lines 23 and 25. 
     Starting capacitor C2 is connected across lamp 11 in order for lamp 13 to start first and lamp 11 to follow in sequence thereafter. Also connected across lamps 11 and 13 from terminal A through triac TR3, electrode winding 13b and portion 21 of primary winding PR to line 25 is a circuit comprising sidac S1, resistor R1 and a diode bridge comprising diodes D1-D4. Connected in series across the diode bridge are the inputs 1 and 2 of optical couplers OC1 and OC2. As is well known a photodiode is connected across the input terminals 1 and 2 of optical couplers OC1 and OC2. As is also well known a light activated triac is connected across the output terminals 4 and 6 of each optical coupler OC1 and OC2. In this way optical couplers OC1 and OC2 provide electrical isolation between the diode bridge D1-D4 and the circuitry to which the light activated triacs are connected. These light activated triacs of optical couplers OC1 and OC2 are connected through resistors R2 and R3 to the gates of triacs TR1 and TR2, respectively, to render triacs TR1 and TR2 separately controlled. Signals for the gates of triacs TR1 and TR2 are generated by the voltages across the associated electrode windings 15 and 19, respectively. The main conduction paths of triacs TR1 and TR2 are connected in series with heater windings 15 add 19 and their respective lamp electrodes 11a, 11b and 13a. 
     The control means comprising sidac S1, resistor R1 and the diode bridge formed by diodes D1-D4, as mentioned earlier, is connected directly to the gate of triac TR3 and through electrode 13b of lamp 13 to line 25. With this arrangement an optical coupler is not required for triac TR3. The control means comprising the circuitry containing sidac S1, diode bridge D1-D4 and the optical couplers OC1 and OC2 enable triacs TR1, TR2 and TR3 to provide heating power to the electrodes of lamps 11 and 13 to enable them to ignite, and upon ignition the control means responds to the reduction in the voltage across the lamps to render triacs TR1, TR2 and TR3 non-conductive. 
     In operation, when a proper voltage is applied across lines 23 and 25 to primary PR of autotransformer 17 a pre-ignition voltage is applied across junction A and line 25 sufficient for sidac S1 to breakover and permit conduction through itself, resistor R1 and the diode bridge formed by diodes D1-D4, triac TR3 and electrode winding 13b. As a result, the photodiodes in optical couplers OC1 and OC2 connected in series across the diode bridge emit light and turn on the light activated triacs of optical couplers OC1 and OC2. This enables current to flow from heater windings 15 and 19 through respective resistors R2 and R3 to the gates of triacs TR1 and TR2. As a result, triacs TR1, TR2 and TR3 are rendered conductive and permit heater windings 15, 19 and 21 to provide heating current to electrodes 11a, 11b, 13a, and 13b of lamps 11 and 13. Upon heating sufficiently electrode. 13a and 13b will start conduction in lamp 13 to be followed shortly thereafter by conduction in lamp 11. Upon lamps 11 and 13 conducting the voltage across the lamps and across terminal A and line 25 is no longer high enough to allow sidac S1 to conduct. As a consequence the light emitting diodes of optical couplers OC1 and OC2 no longer have voltage applied to them and can no longer emit light. As a consequence the light activated triacs of optical couplers OC1 and OC2 cease to conduct and no longer provide signals to the gates of triacs TR1 and TR2 which consequently cease conducting. Triac TR3 also ceases conduction when sidac S1 ceases conduction. As a result the electrodes of lamps 11 and 13 are no longer provided with current from heater windings 15, 19 and 21 with the consequent preservation of power which otherwise would be consumed. 
     In a contemplated embodiment, sidac S1 was chosen to have a 300 volts breakover voltage to enable conduction through resistor R1 and diodes D1-D4. Resistor R1 was selected to limit the current through the diode bridge to between 5 and 10 milliamps which met the specification for the photodiodes of optical couplers OC1 and OC2, which were made by Motorola &amp; Harris Semiconductor Co. catalog number MOC3012. Triacs TR1 and TR2 for this embodiment were made by Teccor Co. catalog number Q201E3. Triac TR3 was a Teccor catalog number L201E3. In this embodiment a total savings of about five (5) watts of power was experienced for both lamps. 
     As those skilled in the art will appreciate, while only one type of ballast arrangement has been specifically disclosed herein, the invention described will operate with various other ballast arrangements. 
     It should be apparent that modifications of the above will be evident to those skilled in the art and that the arrangements described herein are for illustrative purposes and are not to be considered restrictive.