Abstract:
A ballast circuit including a charge pump interface circuit is disclosed to provide a method of isolating a switch from a power line used to power a ballast for supplying electrical power to a lamp. In addition, the charge pump interface circuit provides a method to control a discrete dimming ballast circuit which includes one or more inverters. The charge pump interface circuit offers cost advantages because no relays are necessary for isolation of the switch from the lamp electrical power and the dimming ballast circuit can be installed where existing lamps are currently mounted, without the need to add additional wiring.

Description:
BACKGROUND 
   This application claims priority to and the benefit of U.S. Provisional Application No. 60/631,895, filed Nov. 30, 2004, which application is incorporated herein by reference in its entirety. 

   The present disclosure relates to a method of isolating a control signal from a power line using a charge pump circuit. It finds particular application in conjunction with ballast controlled gas discharge lamps and discrete dimming systems and will be described with particular reference thereto. However, it is to be appreciated that the exemplary embodiments of this disclosure are also amenable to other like applications. 
   Many types of dimming ballasts have been proposed that control the arc current of a gas discharge lamp such as a fluorescent lamp. One type includes an external means of heating the cathode to prevent sputtering of the cathodes whenever the arc current is reduced to less than 50% of its rated value. The efficiency of such a dimming circuit falls off as the light intensity is reduced. 
   Multiple ballast dimming systems control fluorescent lamps either in pairs or individually. For example, a three lamp fixture may have a two lamp ballast and one lamp ballast whereby the light intensity can be changed from 33% to 100% of its rated value by turning on a specific ballast. This requires at least two ballasts to cover a 3 to 1 range in brightness, which may increase cost and impact the available space in the fixture. Also, a latching relay is used to turn the ballasts on and off which requires a power supply to activate the relay coil. 
   Dimming systems capable of operation, as described above, are further described in U.S. Pat. No. 6,686,705, issued to Nerone et al., and “A Discrete Dimming Ballast for Linear Fluorescent Lamps”, authored by Haiyan Wang, and these references are hereby totally incorporated by reference. 
   A better system capable of powering a plurality of lamps is desirable from an efficiency perspective and from a packaging and cost perspective. In addition, it is desirable to have a circuit to isolate a low voltage control signal used for activating discrete dimming levels without using external power supplies from the power line voltage, the low voltage control signal selecting individual lamps for a discrete dimming system. 
   BRIEF DESCRIPTION 
   According to one embodiment of this disclosure, a switch circuit is provided, the switch circuit comprising a high frequency oscillator; a first latch; a first, second and third capacitor; and a first diode and a second diode. The first capacitor&#39;s first electrode is operatively connected to the output of the high frequency oscillator, the second capacitor&#39;s first electrode is operatively connected to the anode of the first diode and the cathode of the second diode, the third capacitor&#39;s first electrode is operatively connected to the cathode of the first diode and the input to the latch, and the cathode of the second diode is operatively connected to the third capacitor&#39;s second electrode and the high frequency oscillator common ground. 
   According to another embodiment of this disclosure, a ballast lamp circuit is provided, the ballast lamp circuit, comprising one or more inverters configured to receive power from a single DC power source, each inverter for selectively powering a load and a controller operatively coupled to each of the one or more inverters via an on/off control signal for selectively switching on and off each inverter independently. The controller comprises one or more switch circuits, each switch circuit comprising a high frequency oscillator; a first latch including a first, second and third capacitor, and a first diode and a second diode. The first capacitor&#39;s first electrode is operatively connected to the output of the high frequency oscillator, the second capacitor&#39;s first electrode is operatively connected to the anode of the first diode and the cathode of the second diode, the third capacitor&#39;s first electrode is operatively connected to the cathode of the first diode and the input to the latch, and the cathode of the second diode is operatively connected to the third capacitor&#39;s second electrode and the high frequency oscillator common ground. 
   According to another embodiment of this disclosure, a ballast lamp circuit is provided, the ballast lamp circuit comprising a means for inverting a DC voltage to one or more AC waveforms for selectively driving one or more lamps; a means for isolating one or more switches, the one or more switches selectively controlling the one or more AC waveforms for selectively driving one or more lamps. 
   According to another embodiment of this disclosure, a method of isolating a switch is provided, the method comprising generating a high frequency low voltage AC waveform; operatively connecting the high frequency low voltage AC waveform to a first pole of the switch via a first capacitor; and operatively connecting a second pole of the switch to a second capacitor, the second capacitor serially connected to a first diode and third capacitor, wherein the voltage across the third capacitor increases for each cycle of the high frequency low voltage AC waveform while the switch is closed, until a maximum voltage is obtained, and the first and second capacitor values are selected to provide substantial isolation of the switch from the voltage across the third capacitor and the high frequency low voltage AC waveform. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of one exemplary embodiment including a plurality of inverters. 
       FIG. 2  is a circuit diagram of a switch isolation circuit according to another exemplary embodiment. 
       FIG. 3  is a graph of C3 voltage as a function of inverter cycles. 
       FIG. 4  is a block diagram of another exemplary embodiment including a plurality of inverters and a plurality of low voltage push button switches. 
   

   DETAILED DESCRIPTION 
   With reference to  FIG. 1 , illustrated is a schematic representation of a gas discharge lamp dimming system  10  according to one exemplary embodiment of this disclosure. This dimming system includes a power factor correction (PFC) circuit  12 , two ballast circuits  14  and  18  and two fluorescent lamps L 1   16  and L 2   20  operatively connected to each ballast  14  and  18 , respectively. A controller  22  selectively controls ballasts  14  and  18  to power the lamps L 1   16  and L 2   18 , respectively. 
   Dimming is achieved, for the lamp system  10  illustrated in  FIG. 1 , by selectively illuminating only lamp L 1   16  and only lamp L 2   20 . Full lumen output is achieved by selectively illuminating lamp L 1   16  and lamp L 2   20 . While a two ballast/lamp circuit combination will be described with further detail, this disclosure is not limited to a two lamp operation. For example, three, four, five, six, etc. ballast/lamp combinations are within the scope of this disclosure. As the number of lamps increases, the greater the number of possible dimming modes. In addition, other variations of the dimming system include powering more than one lamp from a single ballast. Multiple lamp operation from a single ballast provides a technique to control multiple dimming modes and full power luminescence of a lamp system. 
   With further reference to  FIG. 1 , a more detailed description of the lamp system is provided. 
   The lamp system  10  is powered by an AC power source (not shown), such as  120  VAC,  277  VAC, etc. depending on the power line voltage availability. A PFC circuit rectifies the AC power and generates a DC voltage which is fed to ballasts  14  and  18  as illustrated. Each ballast inverts the DC voltage to produce an AC waveform to power lamps L 1   16  and L 2   20 . 
   The controller  22  selectively controls ballast  14  and/or  18  to drive lamps L 1   16  and L 2   20 . As previously discussed, dimming can be achieved by illumination of only one lamp. 
   To provide an input signal to the controller  22  for selecting which lamps to turn on and which lamps to turn off, a switch arrangement is incorporated within the controller  22 , according to one embodiment of this disclosure. Techniques for providing a control signal to the controller  22  include a push button switch, toggle switch, relay, logic driven switch, etc., and are within the scope of this disclosure. 
   With reference to  FIG. 2 , a switch circuit  30  according to one exemplary embodiment of this disclosure is illustrated. The switch circuit  30  includes a charge pump circuit to provide acceptable levels of isolation between a user operated switch, and the PFC, ballast, and lamp circuit previously described with reference to  FIG. 1 . The switch circuit  30  is described as being housed within the controller  22  for illustration purposes. However, as will be appreciated by those of skill in the art, the switch circuit  30  can also be housed in an independent enclosure which is operatively connected to the controller  22 . The switch circuit  30  comprises a high frequency oscillator U 1   32 , a logic driven latch  34 , switch S 1   36 , capacitor C 1   38 , capacitor C 2   40 , diode D 1   42 , diode D 2   44  and capacitor C 3   46 . In general, switch S 1   36  activates an output Q of the latch which is operatively connected to a ballast via the controller. The latch output Q signals the controller of  FIG. 1  to turn on a respective lamp via the respective ballast. 
   With further reference to  FIG. 2 , a second switch circuit is illustrated that is operatively connected to the high frequency oscillator U 1   32  and the logic driven latch  34 . The second switch circuit comprises switch S 2   48 , capacitor C 4   50 , capacitor C 5   52 , diode D 3   54 , diode D 4   56  and capacitor C 6   58 . This second switch circuit provides a signal to the latch which sets a control signal  Q . This latch output is operatively connected to a ballast via the controller  22  and turns the lamp and ballast combination off. 
   A more detailed description of the switch circuits and their operation will now be described. In one embodiment, the high frequency oscillator U 1   32  generates a high frequency voltage approximately equal to 100 kHz. Initially, with switch S 1   36  in a normally open position, no voltage is present across capacitor C 3   46  and therefore the logic latch output “on” is not set to turn on a ballast lamp combination. Moreover, initially, with switch S 2   48  in a normally open position, no voltage is present across capacitor C 6   58  and the latch output “off” is not set to turn a ballast and lamp combination off. 
   To provide acceptable levels of switch isolation from the common ground, capacitor C 1   38  and capacitor C 2   40  are selected sufficiently small to provide a relatively large impedance at the power line frequency, ex. 60 Hz. For example, in one exemplary embodiment of this disclosure, the series combination of capacitor C 1   38  and C 2   40  yields a capacitance of only 11 pF if C 1 =C 2 =22 pF. The impedance of this equivalent capacitance is 240 Meg ohms at 60 Hz. Therefore, the amount of current that is capable of passing to earth ground is only 1 uA, well below the UL limits for current flow through a human host. 
   To provide an acceptable switch response time for control of the lamps and provide sufficient noise immunity one exemplary embodiment of this disclosure comprises capacitor C 3   46  equal to approximately 100 nF when the serial equivalence of capacitor C 1   38  and C 2   40 =5 pF-100 pF. More specifically, when capacitor C 1   38  and capacitor C 2   40  equals approximately 22 pF. In general, the ratio of capacitor C 3  to the equivalent capacitance of C 1 +C 2  is approximately four orders of magnitude. Subsequent to switch S 1   36  being depressed, the high frequency oscillator  32  charges capacitors C 1   38 , C 2   40  and C 3   46  during the next positive ½ cycle. It should be noted that multiple cycles of the oscillator are required to charge capacitor C 3  to a sufficient level to provide a logic input voltage sufficient to set the latch output. During the subsequent negative oscillator ½ cycle, diode D 1   42  prevents capacitor C 3   46  from discharging until it can continue to charge during the next oscillator positive ½ cycle. Diode D 2   44  provides a return path for the negative oscillator ½ cycle generated current. 
   With reference to  FIG. 3 , illustrated is a graph  60  representing the voltage  62  across capacitor C 3   46  as a function of inverter cycles. Each inverter cycle, K, corresponds to 5 ms. In other words, the switch operator will be required to depress switch S 1  for a relatively short time to charge capacitor C 3  sufficiently to set the latch output “on”. After the logic latch output “on” is set, it will remain set until the second switch circuit including switch S 2 , sets the latch “off” output. 
   The second switch circuit comprising U 1   32 , C 4   50 , C 5   52 , C 6   58 , D 3   54 , D 4   56 , S 2   48  and the logic latch  34  operates as described previously with reference to the first switch circuit. Together, the combination of two switch circuits, as described heretofore provides a switch circuit and method of operating a switch circuit to isolate a user operated switch, such as a push button switch or other manual/automatic switch, from common ground at acceptable UL standards. In addition, by selecting the appropriate values of capacitors C 1   38 , C 2   40 , C 4   50  and C 6   58 , other isolation standards can be implemented. 
   Other variations of the switch circuit described heretofore comprise selecting a relatively larger value of capacitor C 3   46  to increase the delay associated with setting a latch output  34 . Conversely, a smaller capacitance for capacitor C 3   46  can be selected to decrease the delay if noise considerations are acceptable for reliable operation. 
   Substantially, the method of isolating a switch as disclosed comprises generating a high frequency low voltage AC waveform and operatively connecting the high frequency low voltage AC waveform to a first pole or input of a switching type device, via a sufficiently small capacitance at the power line operating frequency, to isolate the first pole switch at acceptable standards. In addition, a second pole of the switching type device is operatively connected to a second capacitor, similar in size to the first capacitor, the second capacitor serially connected to a third capacitor, via a diode, which is substantially larger than the equivalence of the first capacitor and the second capacitor. This switching method provides a voltage across the third capacitor which increases for each cycle of the high frequency low voltage AC waveform while the switch is closed until a maximum voltage is obtained. The voltage across the third capacitor is used to drive a logic device. 
   In one embodiment of the switching circuit and method as described heretofore, the following components are as follows:
         C 1 =22 pF;   C 2 =22 pF;   C 3 =100 nF;   U 1 =approximately 100 kHz;   D 1 , D 2 , D 3  and D 4  are iN4148 diodes; and   the Latch is a S-R Flip Fop latch.       

     FIG. 4  illustrates another ballast lamp circuit  70  in accordance with one exemplary embodiment. The ballast circuit includes an AC power source  72 , an electromagnetic interference EMI filter  74 , a bridge rectifier  76 , a power factor correction circuit  78 , a bus capacitor  80 , four inverters  82 ,  86 ,  90  and  93 , a controller  100  and four pairs of low voltage push buttons  102 ,  104 ,  106  and  108 . While four inverters are shown in this embodiment, other combinations of inverters are within the scope of this disclosure (e.g. less than four inverters or more than four inverters). Each inverter is coupled to a load  84 ,  90 ,  94  and  98 . The AC power source  72  is filtered through an EMI filter  74  and rectified by the bridge rectifier  76 . The bridge rectifier  76  supplies DC voltage to the power factor correction circuit  78 . The power factor correction circuit  78 , also referred to as a boost converter, provides a DC bus  98  and return line to the bus capacitor and each of the inverters. 
   Each inverter,  82 ,  86 ,  92  and  96 , may be turned on or off by the controller  100  via control signal lines  110 ,  112 ,  114  and  116 , respectively. In other words, each inverter is individually addressable and controllable by the controller. This is accomplished by discrete control signals to each inverter. This allows for the operation of zero to n inverters, where “n” is the number of inverters coupled to the DC bus and common return line (i.e. four inverters in the embodiment shown). For example, where the load on each of the four inverters is a gas discharge lamp, each capable of emitting approximately equivalent light, the ballast lamp circuit  70  is capable of dimming the lighting provided by the lamp fixture to about 75%, about 50% or about 25% by shutting down any of the inverters or the ballast lamp circuit can extinguish the fixture by shutting down all of the inverters. 
   Switching devices, ex. push button switches,  102 ,  104 ,  106  and  108  are operatively connected to the controller  100 . The controller  100  houses four independent switching circuits as illustrated in  FIG. 2 , each switching circuit including two isolated switching circuits as illustrated. Switching device  102  is operatively connected to a first switching circuit, switching device  104  is operatively connected to a second switching circuit, switching device  106  is operatively connected to a third switching circuit and switching device  108  is operatively connected to a fourth switching circuit. 
   The first switching circuit outputs are operatively connected to control line  110 , the second switching circuit outputs are operatively connected to control line  112 , the third switching circuit outputs are operatively connected to control line  114  and the fourth switching circuit outputs are operatively connected to control line  116 . 
   In operation, switching device  102  controls the on/off operation of lamp  84 , switching device  104  controls the on/off operation of lamp  90 , switching device  106  controls the on/off operation of lamp  94 , and switching device  108  controls the on/off operation of lamp  98 . 
   A feature of the exemplary embodiment includes packaging the components of the ballast circuit and controller, excluding the AC power source and loads, in a single enclosure. The enclosure is adaptable to mounting within a gas discharge lamp fixture. The enclosure may be hermetically sealed and/or potted. A number of additional packaging methods for the components of the ballast circuit are available and are known to those of skill in the art upon the reading of this application. 
   The exemplary embodiments have been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the exemplary embodiment be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof. 
   
     
       
             
             
           
             
             
           
         
             
                 
             
             
               Reference Character 
               Component 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               10 
               gas discharge lamp dimming system 
             
             
               12 
               PFC circuit 
             
             
               14 
               ballast circuit 
             
             
               16 
               Lamp L1 
             
             
               18 
               ballast circuit 
             
             
               20 
               Lamp L2 
             
             
               22 
               controller 
             
             
               30 
               switch circuit 
             
             
               32 
               high frequency oscillator U1 
             
             
               34 
               S-R latch, logic latch 
             
             
               36 
               switch S1 
             
             
               38 
               capacitor C1 
             
             
               46 
               capacitor C2 
             
             
               42 
               Diode D1 
             
             
               44 
               Diode D2 
             
             
               46 
               Capacitor C3 
             
             
               48 
               switch S2 
             
             
               50 
               Capacitor C4 
             
             
               52 
               Capacitor C5 
             
             
               54 
               Diode D3 
             
             
               56 
               Diode D4 
             
             
               58 
               Capacitor C6 
             
             
               60 
               graph 
             
             
               62 
               voltage curve 
             
             
               70 
               ballast lamp circuit 
             
             
               72 
               AC power source 
             
             
               74 
               emi filter 
             
             
               76 
               bridge rectifier 
             
             
               78 
               PFC circuit 
             
             
               80 
               bus capacitor 
             
             
               82 
               inverter 
             
             
               84 
               load/lamp 
             
             
               86 
               inverter 
             
             
               88 
               DC bus 
             
             
               90 
               load/lamp 
             
             
               92 
               inverter 
             
             
               94 
               load/lamp 
             
             
               96 
               inverter 
             
             
               98 
               load/lamp 
             
             
               100 
               controller 
             
             
               102 
               push button switch 
             
             
               104 
               push button switch 
             
             
               106 
               push button switch 
             
             
               108 
               push button switch 
             
             
               110 
               control signal line 
             
             
               112 
               control signal line 
             
             
               114 
               control signal line 
             
             
               116 
               control signal line