Abstract:
A compact fluorescent lamp (CFL) ballast driver includes first, second and neutral AC voltage terminals, a full wave rectifier between the first AC voltage terminal and the neutral AC input terminal, and a separate branch between the second AC voltage terminal and the neutral AC input terminal. A resonator circuit includes at least two inductors and provides its output voltage to a CFL lamp. The driver includes a first state detector circuit to monitor the first AC voltage terminal, and a second state detector circuit to monitor the second AC voltage terminal. The first and second state detector circuits activate respective first and second switches. The first switch shunts one inductor of the resonator circuit, and the second switch shunts another inductor of the resonator circuit. The driver can be housed in a CFL having a capper, a three-way lamp base adjacent to the capper and an arc tube.

Description:
BACKGROUND 
     A typical incandescent three-way lamp produces three levels of light intensity (i.e., low, medium, and high) using two lamp filaments within the same optical housing. The two filaments are typically of different wattages. For example, one lamp filament can be a low wattage filament, and the other filament can be a high wattage filament. 
     Conventionally, these two filaments are connected in parallel to the lamp base. The lamp base itself has two contacts and a neutral contact. Each of the filaments operates at full voltage when activated. 
     Proper installation of the three-way lamp is achieved by using a three-way lamp socket, which has three contacts instead of the usual two for a single filament lamp. This third contact is typically off center in the bottom of the socket, and makes contact with the second filament circuit. 
     The three-way lamp is controlled using a three-way switch, which itself has four positions. Starting from the ‘off’ position, the switch can sequentially connect power to one filament (typically the lower wattage filament,), then the other filament, and then both filaments. 
     A standard compact fluorescent lamp does not typically provide three levels of lighting when connected to a three-way switch. Instead the standard compact fluorescent lamp can be modified to include two different arc tubes in parallel to the lamp base, where each of the arc tubes operates at full lumen output when activated by the three-way switch. This dual arc tube solution requires two ballasts, one to drive each of the arc tubes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a block diagram of a conventional compact fluorescent lamp (CFL) ballast circuit; 
         FIG. 2  schematically depicts a conventional CFL ballast circuit; 
         FIG. 3  depicts a block diagram of a three-way CFL ballast circuit in accordance with embodiments; 
         FIG. 4  schematically depicts a three-way CFL ballast circuit in accordance with embodiments; and 
         FIG. 5  depicts a three-way CFL in accordance with embodiments. 
     
    
    
     BRIEF DESCRIPTION 
     In accordance with embodiments, a ballast driver provides three-way level control of the compact fluorescent lamp (CFL) lumen output. The driver can include a CFL ballast, which has an autotransformer as the main inductor. The driver also can include a sensor and a switch network. The sensor is configured to detect the output level selection made by a user. The switch is responsive to the detected output level selection and connects taps of the autotransformer to the CFL based on the detected selection. In one implementation, the driver can be built by discrete components. 
     In accordance with embodiments, the CFL ballast driver can be housed within a capper of a compact fluorescent lamp. The CFL includes a lamp base including an exterior surface having first and second line voltage contacts and a neutral line voltage contact, an arc tube located distal from the lamp base, and a capper located adjacent to the lamp base. 
     DETAILED DESCRIPTION 
       FIG. 1  depicts a block diagram of conventional CFL ballast circuit  100 . The conventional ballast circuit includes full wave rectifier stage  110  with a buffer capacitor. Starter circuit  120  charges a capacitor to a threshold voltage of a diac, which when conducting provides input to a half bridge (H-bridge) circuit. DC/AC inverter  130  generates a high frequency signal for the fluorescent lamp. The DC/AC inverter circuit includes resonant circuit  132  and inductor  134 , which generates an amplified voltage to trigger fluorescent lamp  140  to ignite. 
       FIG. 2  schematically depicts conventional CFL ballast circuit  200 . Circuit  200  is an implementation of the block diagram depicted in  FIG. 1 . A full wave rectifier formed by diodes D 5 , D 6 , D 7 , D 8  conditions AC input line voltage from terminals T 1 , T 2  into a DC voltage. Capacitor C 2  buffers the output of the full wave rectifier. 
     The starter circuit starts the H-bridge circuit that provides a voltage to the CFL during each half cycle of the line voltage. Capacitor C 1  charges to the threshold voltage of diac D 2  through resistors R 2 , R 3 . Capacitor C 1  discharges through diac D 2  to the base of solid state switch Q 2 . Diode D 1  prevents capacitor C 1  from getting charged on the threshold voltage of diac D 2  again for every second half-period (which is when solid state switch Q 2  is conducting). 
     A DC/AC inverter generates a high frequency (about 50 kHz) AC signal for the fluorescent lamp. As the starter circuit triggers solid state switch Q 2  into conduction, current starts to flow from positive supply voltage Vdd through capacitors C 5 , C 6 , C 7 , inductors L 5 , L 3  and solid state switch Q 2  to negative supply voltage Vss. Inductors L 1 , L 2 , L 5  are coiled on the same saturable ring core transformer, where inductor L 5  is the primary winding and inductors L 1 , L 2  are secondary windings. This ring transformer generates the base-emitter voltage for solid state switches Q 1 , Q 2  to control the H-bridge circuit. 
     When current flows through inductor L 5 , voltage gets induced on the base of solid state switches Q 1 , Q 2  with opposite polarity. Solid state switch Q 2  stays opened, solid state switch Q 1  is closed until the ring core gets saturated. After saturation of the ring core, solid state switch Q 2  closes, and current stops flowing through inductor L 5 . This stop of current flow causes an opposite polarity voltage on the secondary windings (inductors L 1 , L 2 ), which causes solid state switch Q 1  to open, with solid state switch Q 2  remaining closed until the next saturation of the ring core. This process is repeated about every 20 us (i.e., about 50 kHz), producing a square wave with about a 50% duty cycle applied to the output of the half bridge (the emitter of solid state switch Q 1 , and the collector of solid state switch Q 2 ). 
     The resonant circuit includes inductor L 3  and capacitor C 7 . The values of inductor L 3  and capacitor C 7  are calculated to have a resonant frequency equal to the frequency of the square wave. Without an ignited CFL XL 1 , the quality factor of the resonant circuit is very high. When current starts to flow through the resonant circuit, an amplified voltage starts to appear on the terminals of capacitor C 7 . After a few periods this voltage reaches the ignition voltage of the CFL, and CFL XL 1  ignites. Once the CFL ignites, the resonant circuit&#39;s quality factor decreases causing inductor L 3  to function as a choke. 
       FIG. 3  depicts a block diagram of three-way CFL ballast circuit  300  in accordance with embodiments. CFL ballast circuit  300  includes AC input  305  with three terminals. These three terminals are connected to a three-way switch (not shown) located, for example, in a lamp socket. The three-way switch is operable by a user to select the output level of the CFL. The three-way switch has four positions. Starting from the ‘off’ position, the switch can sequentially connect power to a first terminal of AC input  305 , then to another terminal, and then to both terminals. The third terminal of AC input  305  is the neutral line. 
     The three-way CFL ballast can include rectifier and buffer capacitor  310 . The rectifier stage can be a full wave rectifier. In accordance with embodiments, rectifier stage is expanded to include additional rectifiers (e.g., diodes) in a separate branch to accommodate the additional input line. Starter circuit  320  charges a capacitor to a threshold voltage of a diac, which when conduction provides input to an H-bridge circuit. DC/AC inverter  330  generates a high frequency signal for the fluorescent lamp. The DC/AC inverter circuit includes resonant circuit  332  and inductor  334 , which generates an amplified voltage to trigger fluorescent lamp  350  to ignite. 
     CFL ballast circuit  300  includes state detector circuit(s) and switches  340 . The state detector circuits are implemented to determine the state of the three-way switch in the fixture. The switches (e.g., relay drivers and relays) control the choke inductor on the output of the H-bridge, which increases and/or decreases the voltage driving CFL lamp  350 . 
       FIG. 4  schematically depicts three-way CFL ballast circuit  400  in accordance with embodiments. Three-way CFL ballast circuit  400  is an implementation of the block diagram depicted in  FIG. 3 . A full wave rectifier formed by diodes D 3 , D 4 , D 5 , D 6 , D 7 , D 8  conditions AC input line voltage from terminals T 1 , T 2 , N into a DC voltage. Capacitor C 2  buffers the output of the full wave rectifier. 
     The starter circuit starts the H-bridge circuit that provides a voltage to the CFL during each half cycle of the line voltage. Capacitor C 1  charges to the threshold voltage of diac D 2  through resistors R 2 , R 3 . Capacitor C 1  discharges through diac D 2  to the base of solid state switch Q 2 . Diode D 1  prevents capacitor C 1  from getting charged on the threshold voltage of diac D 2  again for every second half-period (which is when solid state switch Q 2  is conducting). 
     A DC/AC inverter generates a high frequency AC signal (about 50 kHz) for the fluorescent lamp. As the starter circuit triggers solid state switch Q 2  into conduction, current starts to flow from positive supply voltage Vdd through capacitors C 5 , C 6 , C 7 , inductors L 5 , L 3 , L 6 , L 7  and solid state switch Q 2  to negative supply voltage Vss. Inductors L 1 , L 2 , L 5  are coiled on the same saturable ring core transformer, where inductor L 5  is the primary winding and inductors L 1 , L 2  are secondary windings. This ring transformer generates the base-emitter voltage for solid state switches Q 1 , Q 2  to control the H-bridge circuit. 
     When current flows through inductor L 5 , voltage gets induced on the base of solid state switches Q 1 , Q 2  with opposite polarity. Solid state switch Q 2  stays opened, solid state switch Q 1  is closed until the ring core gets saturated. After saturation of the ring core, solid state switch Q 2  closes, and current stops flowing through inductor L 5 . This stop of current flow causes an opposite polarity voltage on the secondary windings (inductors L 1 , L 2 ), which causes solid state switch Q 1  to open, with solid state switch Q 2  remaining closed until the next saturation of the ring core. This process is repeated about every 20 us (i.e., about 50 kHz), producing a square wave with about a 50% duty cycle applied to the output of the H-bridge (i.e., the emitter of solid state switch Q 1 , and the collector of solid state switch Q 2 ). 
     In accordance with embodiments, the resonant circuit includes inductors L 3 , L 6 , L 7  and capacitor C 7 . Inductors L 3 , L 6 , L 7  are implemented as an autotransformer. The taps of the autotransformer are switched into the resonant circuit based on the detected state of the three-way switch. The values of inductor L 3 , L 6 , L 7  and capacitor C 7  are calculated to have a resonant frequency equal to the frequency of the square wave. Without an ignited CFL XL 1 , the quality factor of the resonant circuit is very high. When current starts to flow through the resonant circuit, an amplified voltage starts to appear on the terminals of capacitor C 7 . After a few periods this voltage reaches the ignition voltage of the CFL, and CFL XL 1  ignites. Once the CFL ignites, the resonant circuit&#39;s quality factor decreases causing inductors L 3 , L 6 , L 7  to function as a choke inductor. 
     The value of the choke inductor is modified by switching inductors L 6 , L 7  in and out of the circuit based on the setting of the three-way switch in the fixture. Based on the three-way switch status, relays K 1 , K 2  are opened and/or closed. When closed the corresponding inductor is shunted from the resonant circuit. Diodes D 9 , D 10 , resistors R 7 , R 8  and capacitors C 9 , C 10  form two half wave rectifiers that provide power to the relays. 
     For example, starting with the three-way switch in the off position, there is no AC input line voltage on either of terminals T 1 , T 2  ( FIG. 4 ). Operation of the three-way switch can connect line voltage to a first terminal (i.e., either of terminals T 1 , T 2 ), then to a second terminal (i.e., the other of terminals T 1 , T 2 ), and then to both of terminals T 1 , T 2 . With line voltage connected to the first terminal, the corresponding half wave rectifier provides DC voltage to its relay, which in turn shunts out a portion of the autotransformer winding (i.e., one of inductor L 6 , L 7 ) from the resonant circuit. With line voltage connected to the second terminal, the corresponding half wave rectifier provides DC voltage to its relay, which in turn shunts out a different portion of the autotransformer winding (i.e., the other of inductor L 6 , L 7 ) from the resonant circuit. With line voltage present on both of terminals T 1 , T 2 , both relays are activated and both portions of the autotransformer are shunted from the resonant circuit. In this manner, CFL XL 1  is provided with three voltage levels and produces three different lumen output levels. 
       FIG. 5  depicts three-way CFL  500  in accordance with some embodiments. Three-way CFL  500  includes lamp base  510 , which includes two AC line voltage input contacts and a neutral contact on an exterior surface of the lamp base. When three-way CFL  500  is installed into a three-way socket, these contacts electrically mate with corresponding contacts in the three-way socket. Also included in the three-way CFL are capper  520  and optical housing  550 . Housed within optical housing  550  is CFL arc tube  540 . A three-way CFL ballast circuit in accordance with embodiments can be housed within capper  520 . 
     Three-way CFL  500  is depicted as having the form of a conventional incandescent lamp. However, other implementations of three-way CFL  500  having different forms are within the scope of this disclosure. In accordance with embodiments, three-way CFL  500  need not include optical housing  550 . 
     Although specific hardware and methods have been described herein, note that any number of other configurations may be provided in accordance with embodiments of the invention. Thus, while there have been shown, described, and pointed out fundamental novel features of the invention, it will be understood that various omissions, substitutions, and changes in the form and details of the illustrated embodiments, and in their operation, may be made by those skilled in the art without departing from the spirit and scope of the invention. Substitutions of elements from one embodiment to another are also fully intended and contemplated. The invention is defined solely with regard to the claims appended hereto, and equivalents of the recitations therein.