Abstract:
The present application claims a compact low cost topology solution of a ballast for a discharge lamp that can provide both high power factor and low total harmonic distortion with fewer components than prior art. The topology provides the feature of a low crest factor and quick start that increase both the lamp life and the number of starts for the product. By using Bipolar Junction Transistor instead of Field Effect Transistor as the main switches and also a lower value electrolytic, the cost and size are considerably reduced.

Description:
BACKGROUND OF THE DISCLOSURE 
     The present application is directed to electronic lighting systems, and more particularly to an integrated bridge inverter circuit used in connection with a discharge lamp. 
     Existing single-stage high-power factor electronic ballasts designed for discharge lamps, such as integral compact fluorescent lamp applications, have various drawbacks including an undesirably limited zero-voltage switching range, a high unnecessary component stress during operation and starting. Existing systems also have undesirably high crest factors and high harmonics&#39; content, which prevents products from compliance with International Electro-technical Commission (e.g., IEC-61000-3-2) standards. Such lamps are also bulky and limit its usage in space sensitive applications. 
     One existing electronic ballast which may be used for discharge lamps is a self-oscillating high-power factor electronic ballast as taught by Wong, U.S. Pat. No. 5,426,344. The Wong circuit, and other ballasts in the art, use input bridge circuit portions and inverter circuit portions which are distinct and separate from each other. The Wong approach produces a crest factor of 2.0 or higher. The crest factor, alternately referred to as peak-to-RMS (Root Mean Square) ratio is a measurement of a waveform, calculated from the peak amplitude of the waveform divided by the RMS value of the waveform. Crest factor is a parameter that has direct impact on a lamp&#39;s life. 
     A disadvantage of the Wong approach is it produces a high bus-voltage stresses, such as the voltage across a capacitor, which requires use of high voltage-rated transistors. A further disadvantage of the Wong approach is it requires a large EMI filter to moderate the discontinuous nature of the input current existing prior to the input diode bridge. The high-peak currents, which have higher high frequency current content, need to be filtered out by the input EMI filter. A further disadvantage of existing ballasts such as Wong et al., is a high current stress on the switch transistors and resonant components. 
     Another related patent is Chen, U.S. Pat. No. 6,417,631 by the same first inventor. This topology has eliminated many prior single stage power factor correction (PFC) circuit drawbacks, however, it still uses a larger number of components than a conventional compact fluorescent lamp (CFL), and requires the use of more expensive FET switches. 
     SUMMARY OF THE DISCLOSURE 
     The present application overcomes the shortcomings of existing prior art. 
     An advantage resides in employing a circuit which uses fewer components such as a capacitors, inductors, diodes, and uses less expensive Bipolar Junction Transistors instead of field effect transistor (FET), and thus also has a low cost to produce and to operate. 
     An advantage resides in the circuit having a combination of a high power factor, a low total harmonic distortion, low crest factor and an extended zero-voltage switching range. 
     A still further advantage resides in a low component stress on the parts during the starting and operating of the light unit, resulting in longer life of the ballast. 
     A still further advantage is that the design is extremely compact. 
     Still other features and benefits of the present disclosure will become apparent from reading and understanding the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an illustration of a schematic circuit diagram of an embodiment of the present application. 
         FIG. 2  is an illustration of a schematic circuit diagram of an embodiment of the present application. 
         FIG. 3  is a graphical presentation of a useful result of the performance of an embodiment of the present application. 
         FIG. 4  is a graphical presentation of a useful result of the performance of an embodiment of the present application. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to  FIG. 1 , a schematic circuit  100  of one embodiment of the present application is presented. The legend  101  to the circuit  100  is also presented. The circuit  100  comprises an AC power source  110  located next to a fuse  112  that leads into a junction  113 . One branch of the junction leads to a filter and the other branch goes to an EMI inductor  116  followed by a junction  121 . The filter is comprised of a capacitor  114  and a resistor  115  in series, and is followed by another junction  117  that leads to the other terminal  111  of the power source and a second branch which leads to another terminal  125 . Both terminals  121  and  125  are on opposite ends of a capacitor  123 . In an alternative embodiment, it is possible for line  129  to be wired directly to point  121 . In an alternative embodiment, it is possible for the line  127  to be wired directly to point  125 . 
     The inductor  116  side junction  121  connects to an outer loop line  127  that leads to a capacitor  197 . This junction also connects to the capacitor  123 , to another capacitor  131 , and to the middle of one side of a four-diode bridge  130 , between the diode  133  and the other diode  134 . Capacitor  131  and diode  133  both connect to inner loop  139 , while diode  134  is connected to inner loop  149 . In an alternative embodiment, capacitor  131  may be moved to other points in the circuit such as but not limited to be in parallel with diode  133 ,  134  or, diode  135  and  136  and the like. In an alternative embodiment, there could be no capacitor or more than one capacitor connected in parallel with diodes  133 ,  134 ,  135  and  136 . 
     In an alternative embodiment, the diodes  133 ,  134 ,  135 ,  136  may be collectively or individually removed and replaced by a pair of ultrafast recovery diodes, wherein an ultrafast diode has similar specifications to a regular diode, but has a 25 nanosecond or faster recovery. In still further embodiment, the diodes  133 ,  134 ,  135 ,  136  can be integrated in one package. 
     The non-inductor side junction  125  is connected to the capacitor  123  and an outer loop  129 , which leads to a capacitor  199 . In an alternative embodiment, the lamp  193  is connected to junction  125  since the capacitor  199  and lamp  193  are connected in series. The junction  125  is also connected to the middle of the other side of a four-diode bridge  130 , between the diode  135  and the other diode  136 . Capacitor  131  and diode  135  are both connected to inner loop  139 . Diode  136  is connected to inner loop  149 . 
     Both inner loop  139  and  149  connect to opposite ends of an energy storage capacitor  137  and connect to a second common line  163 . The portion of the common line  163  closest to inner loop  139  contains two resistors  141 ,  143  in series followed in series by a line  160  which lies between the inner loop  139  and  149 . A line  147  is connected between the resistor  143  and the resistor  141 . This line  147  connects to the central line  160 . The central line  160  contains a diode  145  between the resistor  141  and the line  147 . 
     The central line  160  continues on and connects to a winding  154 , that is electrically coupled to an inductor  183 , a resistor  155  and the base terminal  151  of a transistor  150 . The transistor  150  is comprised of the B or base terminal  151 , the C or collector terminal  152 , and the E or emitter terminal  153 . The central line  160  also connects to another resistor  156  and the E or emitter terminal  153  of the transistor  150 . The collector terminal  152  of this transistor  150  connects to the inner loop  139 . 
     On the opposite side of the central line  160 , connected to the same line as the resistors  141 ,  143  a line connects a diac (diode for alternating current)  165  to a capacitor  161 . The other side of the capacitor is connected to the inner loop  149 . After the diac, a line connects the diac diode to a junction, with one side of the junction connected to a resistor  175  and a winding  176  also electrically coupled to an inductor  183 , connects to the inner line  149  and to circuit ground  177 . The other side of the junction is connected to the base terminal  171  of a second transistor  170 . The second transistor  170  is comprised of the base terminal  171 , the collector terminal  172 , and the emitter terminal  173 . The central line  160  also connects to another resistor  156  and the emitter terminal  153  of the transistor  150 . The collector terminal  172  of the transistor  170  is connected to the central line  160  and the emitter terminal  173  of the transistor  170  is connected to a resistor  174 , which is then connected to the inner loop  149 . The inner loop  149  connects to a capacitor  189  and to the central line  160  at a junction point  178 . 
     The two inductors  183 ,  185  are connected in series and one side connects to the junction point  178  and the other connects to the portion  187  of the outer loop bridge  196  that follow the capacitor  197 . The junction  187  is also connected to a lamp  190 , by way of a line  191  to the A terminal  192  of the lamp  193 . The C terminal  194  of the lamp  193  assembly is connected by another line  195  to the portion of the inner loop  198  that follows the capacitor  199 . In an alternative embodiment, the junction  187  is connected to the capacitor  199  and then to the lamp  193 , because the capacitor  199  and lamp  193  are connected in series. 
     The four-diode bridge only conducts one at a time at the switching frequencies of the inverter circuit when it is not on the peak changing. The diodes  133  and  136  are alternately on and off during one half cycle, while diodes  134  and  135  are on during the other half of the cycle of the line cycle. The capacitor  197  also serves to provide the high frequency feedback. Similarly the capacitor  199  also forces the diode to operate at high frequencies due to feedback. 
     With the new topology, in the circuit arrangement, the Rk-a and Rk-b circuit&#39;s base drivers  154  and  176  are derived from inserting the Rk-c primary winding  183  in series with the input of the resonant tank circuit. A tank circuit, also called a resonant circuit, provides the energy to start and operate the lamp. The two secondary windings, Rk-a  154 , and Rk-b  176 , in opposite phase, are connected to the driver of the two Bipolar Junction Transistor bases. The two Bipolar Junction Transistors are connected in series and in half bridge configuration. In this configuration, the primary winding not only senses the lamp&#39;s current, but also the resonant current from capacitor  197 . Since both the branch of the circuit  197  and the lamp  199  are connected to the input bridge, the line voltage modulates the effective capacitor values for the capacitors  197  and  199 . As the instantaneous line voltage varies, the effective capacitor for capacitors  197  and  199  vary with it. Therefore, the current to the input of the resonant tank changes. The base drivers that sense from the input current to the resonant tank amplifies differences over a half line cycle, as a result the crest factor of the lamp is higher in the range of 1.8 to 2.0 which has negative impact on lamp life. In addition, with large variation of the operating frequency over the half line cycle, it is difficult to maintain zero voltage switching of the Bipolar Junction Transistors and consequently the temperature of the parts are high and life of the product is low. 
     The other drawback of this drive arrangement is that as a lamp approaches end of life, the cathode may overheat and the cathode would open. However, the inverter will continue to provide the energy to the lamp and generate an even higher temperature around the cathode. 
     The high frequency operation of the input bridge circuit performs at over 20,000 hertz. The high frequency circuit produces a low total harmonic distortion, also called THD, and high power factor. Unlike a conventional design, this design also will provide the advantage of having a smaller integral lamp profile that will fit in most existing fixtures. The existing high power factor ballasts include a separate power factor correction stage, with additional components, that result in larger complexity, higher price and larger size for the circuit. 
     This circuit design may also use a small value electrolytic that may assure the continuous lamp current conduction, so the unwanted lamp turn-off phenomena is avoided at each cycle that can significantly affect the lamp life. The value of the electrolytic capacitor is sized just big enough to accomplish this feature, but not too big which can hurt the size and cost. The use of Bipolar Junction Transistor switches  150  with the driver circuit, will give a low cost solution for the overall design. This design provides better performance such as high PF and low THD than do existing ballasts approaches, and contains fewer components which help with the manufacturing process, compact size and lower cost. 
     The topology has the feature of using fewer components to achieve premium features like high PF and low THD, all in a compact size. This topology is the same size of the overall lamp like an regular, non-power factor corrected, compact fluorescent lamp. In this disclosure two versions of low cost Bipolar Junction Transistors based electronic ballast circuits are presented. In both circuits, the mean operating frequency is designed at about 100 Khz which is much higher than the conventional circuit operated at about 40 Khz for the size consideration of the magnetic and capacitors. 
     With reference to  FIG. 2 , schematic circuit diagram  200  of one embodiment of the present application is presented. The diagram  200  shows a new improved base drive arrangement for the new inverter circuit. The device  200  comprises an AC power source  210  located next to a fuse  212  that leads into a junction  213 . One branch of the junction leads to a capacitor  215  the other followed by a junction  221 . The capacitor  215  is followed by another junction  217  that leads to the other terminal power source  211  and a second branch which leads to another terminal  225 . Both terminals  221  and  225  are on opposite ends of a capacitor  223 . In an alternative embodiment, line  229  may be wired directly to point  221 . In an alternative embodiment, the line  227  may be wired directly to point  225 . 
     The inductor  216  side junction  221  connects to an outer loop bridge line  227  that leads to a capacitor  297 . This junction also connects to the capacitor  223 , to another capacitor  231 , and to the middle of one side of a four-diode bridge  230 , between the diode  233  and the other diode  234 . Capacitor  231  and diode  233  both connect to inner loop  239 , while diode  234  is connected to inner loop  249 . In an alternative embodiment, capacitor  231  may be moved to other points in the circuit such as but not limited to be in parallel with diode  233 ,  234  or, diode  235  and  236  and, the like. In an alternative embodiment, there could be no capacitor or more than one capacitor connected in parallel with diodes  133 ,  234 ,  235  and  236 . 
     The non-inductor side junction  225  is connected to the capacitor  223  and an outer loop bridge  229 , which leads to a capacitor  299 . In an alternative embodiment, the lamp  293  is connected to junction  225  since the capacitor  299  and lamp  293  are connected in series. The junction  225  is also connected to the middle of the other side of a four-diode bridge  230 , between the diode  235  and the other diode  236 . Capacitor  231  and diode  235  are both connected to inner loop  239 . Diode  236  is connected to inner loop  249 . In an alternative embodiment, capacitor  231  may be moved to other points in the circuit such as but not limited to other lines  227 ,  229 , between diodes  233 ,  234  or between diodes  235 ,  236  and the like. In a still further embodiment, the diodes  233 ,  234 ,  235 ,  236  may be collectively or individually removed and replaced by at least one ultrafast diode. 
     Both inner loops  239  and  249  connect to opposite ends of a capacitor and connect to an central line  260  in between the inner loops  239 ,  249 . The portion of the common line  263  closest to inner loop  239  contains two resistors  241 ,  243 , in series followed in series by a line in between inner loops  239  and  249 . Line  247  is connected between the resistor  243  and the resistor  241 . This line  247  connects to the central line  200 . The central line  260  contains a diode  245  between the resistor  241  and the line  247 . 
     The central line  260  connects to an winding  254 , a resistor  255  and the base terminal,  251  of a transistor  250 . The transistor  250  is comprised of the base terminal  251 , the collector terminal  252 , and the emitter terminal  253 . The central line  160  also connects to another resistor  256  and the emitter terminal  253  of the transistor  250 . The central line  160  also connects to another resistor  256  and the emitter junction  253  of the same transistor  250 . The collector terminal  252  of this transistor  250  connects to the inner loop  239 . 
     On the opposite side of the central line  260 , connected to the same line as the resistors  241 ,  243  is connected a line that is connected to a diac  265  and to a capacitor  261 . The other side of the capacitor is connected to the inner loop  249 . After the diac, a line runs to a junction, with one side of the junction connected to a resistor  275  and winding  276 , connects to the inner line  249  and to circuit ground  277 . The other side of the junction is connected to the base  271 , base of a second transistor  270 . This transistor  270  is comprised of the B or base terminal  271 , the C or collector terminal  272 , and the E or emitter terminal  273 . The central line  260  also connects to another resistor  256  and the collector terminal  273  of the transistor  270 . The collector terminal  272  of the transistor  270  is connected to the central line  260  and the emitter terminal of the transistor  273  is connected to a resistor  274 , which is then connected to the inner loop  249 . The inner loop  249  connects to a capacitor  289  and to the central line  260  at a junction point  278 . 
     The central line  260  is connected to an inductor  283  in series which connect to the portion of the outer loop  296  that follow the capacitor  297 . The central line  260  is also connected  287  to a lamp unit  290 . The lamp unit  290  comprised of a cathode  291  with a filament  292  with a wattage rating  293  such as, but not limited to, 15 Watts. The lamp unit  290  also contains a second cathode  295  comprised of another filament  294 . Both filaments  292 ,  294  are connected together in series with a primary winding  288  and a capacitor  285 . The filaments of the second lamp  295  are linked by a line  298  to the bridge  229 . In an alternative embodiment, the junction  287  is connected to the capacitor  299  and then to the lamp  293 , because the capacitor  299  and lamp  293  are connected in series. 
     The primary winding Rk-c of the base drive transformer  288  is connected in series with the capacitor  285  and two cathode resistors  292  and  295  and then in parallel with the lamp. Since, lamp voltage changes inversely to the lamp current, hence, the drive current which goes through the primary drive transformer is also inverse to the lamp current. The operating frequency over the half line cycle is also less varied compared to the  FIG. 1  circuit because of the negative feedback of the drive characteristic. Therefore, the crest factor of the lamp in the new circuit is substantially lower (1.5 to 1.65). The low crest factor will extend the lamp life. This also provides a more effective means to maintain the zero voltage switching for the Bipolar Junction Transistor, increase the ballast efficiency and low temperature on the switching devices. 
     Because the primary winding of drive transformer is now inserted in series with the cathodes of the two lamps, in the event of one cathode reaching and lamp life, the circuit will automatically stop operation avoiding overheating of the lamp cathode. 
     With reference to  FIG. 3 , the waveform produced by the current application  300  demonstrates the functionality of the circuit presented in  FIG. 1 . The X-axis  310  represents time in five milli-second increments, while the Y-axis  320  represents the variation in voltage measured in volts and the variation in current measured in amps. The waveforms for the connector to emitter voltage  330 , the Bipolar Junction Transistor&#39;s corrector current  340 , the lamp&#39;s current  350  and the input current  360  are each presented. 
     The legend of the graph  370  contains average values for the respective waveforms. For the connector to emitter voltage  330  as displayed in the graph legend, the value is 300 milliAmps per division  372 . For the Bipolar Junction Transistor corrector current  340 , the average value is 100 Volts per division  374 ; for the lamp&#39;s current  350 , the scale is 300 milliAmps per division  376 ; and for the input current  360 , the scale is 20 milliVolts per division  378 . The lamp&#39;s current waveform  350  of the lamp has a higher and longer sustained peak  380 , followed by a trough  385 , followed by a smaller and less sustained shorter peak  390 , followed by a deeper trough  395 . Here the peak  380  that is longest in duration is also highest in peak. 
     With reference to  FIG. 4 , the waveform produced by the current application  400  demonstrates the functionality of the circuit presented in  FIG. 1 . The X-axis  410  represents time in 5 milli-Second increments, while the Y-axis  420  represents the variation in voltage measured in volts and the variation in current measured in amps. The waveforms for the connector to emitter voltage  430 , the Bipolar Junction Transistor&#39;s corrector current  440 , the lamp&#39;s current  450  and the input current  360  are each presented. 
     For the connector to emitter voltage  430  as per the legend on the graph, the value is 300 milliAmps per division  472 . For the Bipolar Junction Transistor&#39;s corrector current  440 , the scale is 100 Volts per division  474 ; for the lamp&#39;s current  450 , the scale is 300 milliAmps per division  476 ; and for the input current  460 , the scale is 20 millivolts per division  478 . The lamp&#39;s current waveform  450  has a small and sustained peak  480 , followed by a small trough  485 , a higher but less sustained peak  490 , and a deep trough  495 . Here the peak  480  that is the longest in duration is also the lowest in peak. 
     A comparison of the lamp current waveform  350  on  FIG. 3  with the lamp current waveform  450  in  FIG. 4  demonstrates the reduction in crest factor. In  FIG. 3 , the sustained peak  380  is higher than the short peak  390 . In  FIG. 4 , the sustained peak  480  is lower than the short peak  490 . Similarly, in  FIG. 3  the deep trough  395  is deeper than the  FIG. 4  deep trough  495 . The peak being of lower height and the troughs being shallower demonstrates the reduction of the crest factor and also demonstrates a useful, concrete and tangible result of the present application. 
     The disclosure has 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 invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.