Abstract:
A new innovative concept in AC/DC cell that transfers energy to the output side directly from the input line, rather than from the storage capacitor in power factor correction (PFC) cell during the period that the line voltage exceeds a preset value. The new concept is based on providing additional winding coupled to the DC/DC transformer connected to the rectified input side to provide a path for the energy transfer from the line to transfer to the output directly (Boost cell) or to be stored in the output transformer (Flyback cell).

Description:
This application claims the benefit of Provisional Application No. 60/308,746 filed Jul. 30, 2001. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to new Power Factor Correction (PFC) alternating current/direct current (AC/DC) power supplies and more particularly to those power supplies in which the energy transfers directly from the input line to the output during any period that the input line voltage exceeds a preset value and this invention claims the benefit of priority from United States Provisional Application Serial No. 60/308,740 filed Jul. 30, 2001. 
     BACKGROUND AND PRIOR ART 
     A number of national and international standards require that the harmonics of the line current of electronic equipments be limited to certain specified levels. The typical prior art approaches for meeting these requirements are set forth in the patent literature as follows: 
     U.S. Pat. No. 5,434,767 to Batarseh, et al.; U.S. Pat. No. 5,636,106 to Batarseh, et al.; U.S. Pat. No. 5,844,787 to Fraidlin, et al.; U.S. Pat. No. 6,266,256 to Lehnert, et al.; and, U.S. Pat. No. 6,044,002 to Van Der Wal, et al., however, each are without an additional winding connected to the rectified input side and not arranged to transfer energy to the output directly during the time when the line voltage exceeds a preset value. 
     Additional background art includes: U.S. Pat. No. 5,508,903 to Alexndrov, et al.; U.S. Pat. No. 5,903,446 to Huillet, et al.; and, U.S. Pat. No. 6,097,614 to Jain, et al. which are each to a DC/DC cell (not for a PFC AC/DC cell); and, U.S. Pat. No. 6,046,914 to Lauter which uses the additional winding connected with the Boost inductor as a voltage feedback sensor to alleviate the voltage across the bulk capacitor. 
     Thus, it appears from the prior art teachings known to the inventors that the approaches for meeting the harmonics requirements of the line current are either: 
     1) to add a power factor corrector ahead of the isolated direct current/direct current (DC/DC) cell section of the switching mode power supply (Two-Stage Scheme); or, 
     2) integrate the function of power factor correction and isolated DC/DC conversion into a single power stage (One-Stage Scheme). 
     Unfortunately, both of these prior art approaches are characterized by a major disadvantage in that they have inherent low efficiency due to the fact that energy is processed twice during its transferring process. This results in very high switching losses in the main switch. 
     SUMMARY OF THE INVENTION 
     It is an important object of this invention to provide a new energy transfer concept to improve the efficiency of power factor correction AC/DC cells. 
     It is a further object of this invention to reduce the high switching losses of the main switch. 
     According to the invention, there is a power factor cell constructed ahead of the current-fed DC/DC conversion cell, and an additional winding coupled to the DC/DC transformer is connected to the rectified input side and arranged to transfer energy to the output directly during the line voltage exceeds preset value. Therefore, the efficiency of the cell can be improved considerably due to the reduced power processing time. 
     According to the invention, the power factor cell can operate both in continuous current mode (CCM) or discontinuous current mode (DCM). The power factor correction cell and current-fed DC/DC cell cell can share a common switch with single control loop or use different switches with separate control loops. 
    
    
     Other features, objects and advantages of the invention will become apparent from the following detailed description when read in connection with the accompanying drawings. 
     BRIEF DESCRIPTION OF DRAWINGS 
     Details of the invention, and of preferred embodiments thereof, will be further understood upon reference to the drawings, wherein: 
     FIG. 1 illustrates a schematic illustrative of the invention. 
     FIG. 2 a  indicates the input line current and line voltage waveforms, respectively, during period I when the line voltage is lower than the preset value; and during period II when the line voltage exceeds the preset value. 
     FIG. 2 b  shows in the upper trace the average current flowing through the additional winding, while the lower trace shows the average current flowing through the DC bus fed winding. 
     FIG. 3 a  shows, in period I, the currents flowing, respectively, through the secondary winding (upper trace), through the DC bus fed winding (middle trace) and through the additional winding (lower trace). 
     FIG. 3 b  shows, in period II, the currents flowing, respectively, through the secondary winding (upper trace), through the DC bus fed winding (middle trace) and through the additional winding (lower trace). 
     FIG. 3 c  is the experimental results wherein waveform: a is the input current; b is the input line voltage; c is the current flowing through the additional winding; and, d is the DC bus fed winding. 
     FIGS. 4 a ,  4   b ,  4   c ,  4   d ,  4   e  and  4   f  are schematic circuit diagrams of Boost, Sepic, Buck-Boost, Cuk, Buck and two-switch Buck Boost PFC cells, respectively. 
     FIG. 5 a  shows the single stage Flyback cell with the additional energy transferring winding. 
     FIG. 5 b  is a schematic that uses the Flyback transformer to replace the Boost inductor in FIG. 5 a.    
     FIG. 5 c  shows the single stage Forward cell with the additional energy transferring winding. 
     FIG. 5 d  is a schematic that uses the Flyback transformer to replace the Boost inductor in FIG. 5 c.    
     FIG. 6 a  shows the single switch series/parallel forward cell with the additional energy transferring winding. 
     FIG. 6 b  is a schematic that uses the Flyback transformer to replace the Boost inductor in FIG. 6 a.    
     FIG. 6 c  shows the single switch series/parallel Flyback cell with the additional energy transferring winding. 
     FIG. 6 d  is a schematic that uses the Flyback transformer to replace the Boost inductor in FIG. 6 c.    
     FIG. 7 a  shows an additional energy transferring winding added to the cell that combines the Buck PFC cell and serial/parallel forward cell. 
     FIG. 7 b  is a schematic that uses the Flyback transformer to replace the Boost inductor in FIG. 7 a.    
     FIG. 7 c  shows an additional energy transferring winding added to the cell that combines the Buck PFC cell and serial/parallel Flyback cell. 
     FIG. 7 d  is a schematic that uses the Flyback transformer to replace the Boost inductor in FIG. 7 c.    
     FIG. 8 a  shows an additional energy transferring winding added to the cell that combines a Boost PFC cell and two switch Forward cells. 
     FIG. 8 b  is a schematic that uses the Flyback transformer to replace the Boost inductor in FIG. 8 a.    
     FIG. 8 c  shows an additional energy transferring winding added to the cell that combines a Boost PFC cell and two switch Flyback cell. 
     FIG. 8 d  is a schematic that uses the Flyback transformer to replace the Boost inductor in FIG. 8 c.   
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Before explaining the disclosed embodiments of the present invention in detail, it is to be understood that the invention is not limited in its application to the details of the particular arrangements shown since the invention is capable of other embodiments. Also, the terminology used herein is for the purpose of description and not of limitation. 
     Refer now to FIG. 1 which shows a block diagram schematic of the invention. This power factor corrected switch mode power supply of the invention has a power factor correction (PFC) cell  90  followed by a current fed DC/DC cell cell  92 . The AC line power  100  applied to the input terminals is rectified by the four-diode bridge  102  before the input of PFC cell  90 . One terminal of the additional winding  120  coupled with the DC/DC transformer  114  is connected to the rectified output side of bridge  102  through a diode  112 . The other terminal of  120  is connected directly to the DC/DC stage, normally connected to the power switch  110 , shared with DC-DC stage. In this latter circuit, the extra winding  120  will be blocked by diode  112  when the output voltage of rectifier  102  is less than a preset value. The preset voltage is a value which is defined by the ratio of the nember: of windings  120  divided by the number of windings  114  times the voltage across the capacitor  108 , i.e. (N 120 /N 114  V 108 ) When the output voltage of rectifier bridge  102  exceeds this preset value, winding  120  will power the output  124  through the coupling winding  116 , and winding  114  will be blocked. Since the output of input rectifier  102  is delivered to the output  124  directly, without being buffered by the capacitor  108 , the efficiency is improved since the energy process time is reduced. 
     FIGS.  2 ( a ) and  2 ( b ) and FIGS.  3 ( a ) and  3 ( b ) show the simulated waveforms for the input current and voltage, respectively, of the hybrid energy transfer cell of the invention. As shown, the energy transfer to the output is done in a hybrid mode: when the line voltage is lower than the preset value (Period I), which is proportional to the voltage of storage capacitor  108 , the storage capacitor will power the output side through the winding  114 ; and, when the line voltage exceeds the preset (Period II), the input power is directly transferred to the secondary side through winding  120 , as shown in FIG.  2 ( b ) and FIG.  3 ( a ) and FIG.  3 ( b ). FIG.  2 ( b ) indicates the averaged current flowing through  114  and  120  in one line cycle, FIGS.  3 ( a ) and ( b ) show the current flowing through  114  and  120  in each switching cycle in period I and II, respectively. Changing the turn ratio of additional transformer winding  120  with respect to the primary winding  114  of the DC/DC transformer can adjust the areas I and II, and substantially adjust the energy share that is transferred to the output directly. Because energy is delivered to the output directly from the line input during II period, without passing the buffering storage capacitor, the efficiency will be improved due to the reduced power processing time. 
     Refer now to FIG.  3 ( c ) for the resulting experimental results which show that the energy is transferred to the output side directly when the line voltage exceeds the preset value. 
     Referring to FIGS.  4 ( a )- 4 (f), there is shown therein schematic circuit diagrams of some known (Prior Art) widely used PFC cells with the common designations, i.e., FIGS.:  4   a  is “Boost”;  4   b  is “SEPIC”;  4   c  is “Buck-Boost”;  4   d  is “Cuk”;  4   e  is “Buck”; and,  4   f  is a two-switch “Buck Boost”, respectively. All of these practical PFC cells can be improved in its effectiveness according to this invention by transferring its input energy directly to the output side. In the subsequent description of these PFC cells, the several components have commonly identified and using a suffix which indicates the particular figure, e.g. rectifier bridge  202   a  is found in FIG. 4 a  whereas rectifier bridge  202   b  is found in FIG. 4 b.    
     Referring now to FIG. 4 a  in the Boost PFC cell, the AC energy enters at input nodes  200   a , rectified by bridge  202   a  with the rectified output flowing through inductor  204   a  and then to diode  206   a  with a branch to switch  210   a.    
     Referring now to FIG. 4 b  in the SEPC PFC cell, the AC energy enters at input nodes  200   b , rectified by bridge  202   b  with the rectified output flowing through transformer  204   b  and then to diode  205   b  with capacitor separated branches to switch  210 b and the coupling winding of transformer  204   b.    
     Referring now to FIG. 4 c  in the Buck-Boost PFC cell, the AC energy enters at input nodes  200   c , rectified by bridge  202   c  with the rectified output flowing through bridge inductor  204   c  with output diode  206   c  and switch  210   c.    
     Referring now to FIG. 4 d  in the Cuk PFC cell, the AC energy enters at input nodes  200   d , rectified by bridge  202   d  with the rectified output flowing through transformer  204   d  with its windings capacitatively connected and with the rectifier bridge  202   d  output also bridged with diode  206   d  and switch  210   d.    
     Referring now to FIG. 4 e  in the Buck PFC cell, the AC energy enters at input nodes  200   e , rectified by bridge  202   e  with the rectified output passing across switch  210   e  and then flowing through inductor  204   e  with the rectifier bridge  202   d  output bridged with diode  206   e.    
     Referring now to FIG. 4 f  in the two-switch Buck Boost PFC cell, the AC energy enters at input nodes  200   f , rectified by bridge  202   f  with the rectified output passing across switch  210   f  and then flowing through inductor  204   f  with the rectifier bridge  202   d  output bridged with diode  206   f  and the inductor output branching into a diode and a second switch bridging diode  206   f.    
     All of these practical PFC cells can be improved in its effectiveness according to this invention by transferring its input energy directly to the output through a current fed DC/DC cell cell. As are schematically illustrated in the following FIGS. 5,  6 ,  7 , and  8 . 
     FIGS. 5 a  to  5   d  show schematic circuit diagrams of combining a single stage isolated power factor corrected power (PFC) supply topologies reflecting the improvement disclosed in this invention using the Boost PFC cell. 
     In FIG. 5 a , the schematic shows the specific topology of combining a Boost PFC with a Flyback transformer modified according to the invention by providing extra winding  320 . As shown therein the AC input  300  is applied to rectifier  302 , and the rectifier output is connected to inductor  304 , diode  306 , switch  310  and capacitor  308 , indicating a Boost PFC cell. The output of PFC cell is fed to the DC/DC cell, constituted by buffer capacitor  308 , switch  310 , Flyback transformer  314 ,  316  and output circuitry  324 . Extra winding  320  and diode  312  is parallel connected with the Boost inductor  304 . 
     In FIG. 5 b , the schematic shows the specific topology of combining a Boost PFC with a Flyback transformer modified according to the invention by providing extra winding  420 . As shown therein the AC input  400  is applied to rectifier  402 , and the rectifier output is connected to transformer winding  404 , diode  406 , switch  410  and capacitor  408 , indicating a Boost PFC cell. The output of PFC cell is fed to the DC/DC cell, constituted by buffer capacitor  408 , switch  410 , Flyback transformer  414 ,  416  and output circuitry  424 . Extra winding  420  and diode  412  is parallel connected with the winding  404 . Winding  434 , which is coupled with  404 , is serially connected with diode  436  and thereafter is parallel connected with the output load  440 . 
     In FIG. 5 c , the schematic shows the specific topology of combining a Boost PFC with a Flyback transformer modified according to the invention by providing extra winding  520 . As shown therein the AC input  500  is applied to rectifier  502 , and the rectifier output is connected to inductor  504 , diode  506 , switch  510  and capacitor  508 , indicating a Boost PFC cell. The output of PFC cell is fed to the DC/DC cell, constituted by buffer capacitor  508 , switch  510 , forward transformer  514 ,  516  and output circuitry  524 . Extra winding  520  and diode  512  is parallel connected with the Boost inductor  504 . 
     In FIG. 5 d , the schematic shows the specific topology of combining a Boost PFC with a forward transformer modified according to the invention by providing extra winding  620 . As shown therein the AC input  600  is applied to rectifier  602 , and the rectifier output is connected to transformer winding  604 , diode  606 , switch  610  and capacitor  608 , indicating a Boost PFC cell. The output of PFC cell is fed to the DC/DC cell, constituted by buffer capacitor  608 , switch  610 , forward transformer  614 ,  616  and output circuitry  624 . Extra winding  620  and diode  612  is parallel connected with the winding  604 . Winding  634 , which is coupled with  604 , is serially connected with diode  636  and thereafter is parallel connected with the output load  640 . 
     Referring to FIGS. 6 a  to  6   d , the schematic circuit diagrams illustrate the invention by showing the incorporation of an additional winding to the topologies combining a Boost PFC with serial/parallel forward and Flyback cell cells, respectively. 
     In FIG. 6 a , the schematic shows the specific topology of combining a Boost PFC with a serial/parallel forward cell modified according to the invention by providing extra winding  720 . As shown therein the AC input  700  is applied to rectifier  702 , and the rectifier output is connected to inductor  704 , diode  706 , switch  710  and capacitor  708 ,  728 , indicating the Boost PFC cell. The output of PFC cell is fed to the DC/DC cell, constituted by buffer capacitor  708 ,  728 , switch  710 , diode  726 ,  730 , Flyback transformer  714 ,  716 ,  718  and output circuitry  724 . Extra winding  720  and diode  712  is parallel connected with the Boost inductor  704 . 
     In FIG. 6 b , the schematic shows the specific topology of combining a Boost PFC with a serial/parallel forward cell modified according to the invention by providing extra winding  820 . As shown therein, the AC input  800  is applied to rectifier  802 , and the rectifier output is connected to Flyback transformer winding  804 , diode  806 , switch  810  and capacitor  808 ,  828 , indicating a Boost PFC cell. The output of PFC cell is fed to the DC/DC cell, constituted by buffer capacitor  808 ,  828 , switch  810 , diode  826 ,  830 , Forward transformer  814 ,  816 ,  818  and output circuitry  824 . Extra winding  820  and diode  812  is parallel connected with the Boost inductor  804 . Winding  834 , which is coupled with  804 , is serially connected with diode  836  and thereafter is parallel connected with the output load  840 . 
     In FIG. 6 c , the schematic shows the specific topology of combining a Boost PFC with a serial/parallel Flyback cell modified according to the invention by providing extra winding  920 . As shown therein the AC input  900  is applied to rectifier  902 , and the rectifier output is connected to inductor  904 , diode  906 , switch  910  and capacitor  908 ,  928 , indicating a Boost PFC cell. The output of PFC cell is fed to the DC/DC cell, constituted by buffer capacitor  908 ,  928 , switch  910 , diode  926 ,  930 , forward transformer  914 ,  916 ,  918  and output circuitry  924 . Extra winding  920  and diode  912  is parallel connected with the Boost inductor  904 . 
     In FIG. 6 d , the schematic shows the specific topology of combining a Boost PFC with a serial/parallel Flyback cell modified according to the invention by providing extra winding  1020 . As shown therein the AC input  1000  is applied to rectifier  1002 , and the rectifier output is connected to Flyback transformer winding  1004 , diode  1006 , switch  1010  and capacitor  1008 ,  1028 , indicating a Boost PFC cell. The output of PFC cell is fed to the DC/DC cell, constituted by buffer capacitor  1008 ,  1028 , switch  1010 , diode  1026 ,  1030 , Flyback transformer  1014 ,  1016 ,  1018  and output circuitry  1024 . Extra winding  1020  and diode  1012  is parallel connected with the Boost inductor  1004 . Winding  1034 , which is coupled with  1004 , is serially connected with diode  836  and thereafter is parallel connected with the output load  1040 . 
     The schematic circuit diagrams with added winding to the topologies combining a Buck PFC and a serial/parallel Forward and Flyback cell cells, are shown in FIGS. 7 a  to  7   d , respectively. 
     In FIG. 7 a , the schematic shows the specific topology of combining a Buck PFC with a serial/parallel Forward cell modified according to the invention by providing extra winding  1120 . As shown therein the AC input  1100  is applied to rectifier  1102 , and the rectifier output is connected to inductor  1104 , diode  1122 , switch  1120  and capacitor  1108  and  1128 , indicating a Buck PFC cell. The output of PFC cell is fed to the DC/DC cell, constituted by buffer capacitor  1108 ,  1128 , switch  1110 , diode  1126  and  1130 , Forward transformer windings  1114 ,  1116  and  1118  and output circuitry  1124 . Extra winding  1120  and diode  1112  is inserted between the switch  1110  and positive output of rectifier  1102 . 
     In FIG. 7 b , the schematic shows the specific topology of combining a Buck PFC with a serial/parallel forward cell modified according to the invention by providing extra winding  1220 . As shown therein the AC input  1200  is applied to rectifier  1202 , and the rectifier output is connected to Flyback transformer winding  1204 , diode  1222 , switch  1220  and capacitor  1208  and  1228 , indicating a Buck PFC cell. The output of PFC cell is fed to the DC/DC cell, constituted by buffer capacitor  1208  and  1228 , switch  1210 , diode  1226 ,  1230 , Forward transformer windings  1214 ,  1216  and  1218  and output circuitry  1224 . Extra winding  1220  and diode  1212  is inserted between the switch  1210  and positive output of rectifier  1202 . Winding  1234 , which is coupled with  1204 , is serially connected with diode  1236  and thereafter is parallel connected with the output load  1240 . 
     In FIG. 7 c , the schematic shows the specific topology of combining a Buck PFC with a serial/parallel Flyback cell modified according to the invention by providing extra winding  1320 . As shown therein the AC input  1300  is applied to rectifier  1302 , and the rectifier output is connected to inductor  1304 , diode  1322 , switch  1320  and capacitor  1308 ,  1328 , indicating a Buck PFC cell. The output of PFC cell is fed to the DC/DC cell, constituted by buffer capacitor  1308  and  1328 , switch  1310 , diodes  1326  and  1330 , Flyback transformer windings  1314 ,  1316  and  1318  and output circuitry  1324 . Extra winding  1320  and diode  1312  is inserted between the switch  1310  and positive output of rectifier  1302 . 
     In FIG. 7 d , the schematic shows the specific topology of combining a Buck PFC with a serial/parallel Flyback cell modified according to the invention by providing extra winding  1420 . As shown therein the AC input  1400  is applied to rectifier  1402 , and the rectifier output is connected to Flyback transformer winding  1404 , diode  1422 , switch  1420  and capacitors  1408  and  1428 , indicating a Buck PFC cell. The output of PFC cell is fed to the DC/DC cell, constituted by buffer capacitors  1408  and  1428 , switch  1410 , diodes  1426  and  1430 , Flyback transformer  1414 ,  1416  and  1418  and output circuitry  1424 . Extra winding  1420  and diode  1412  is inserted between the switch  1410  and positive output of rectifier  1402 . Winding  1434 , which is coupled with  1404 , is serially connected with diode  1436  and thereafter is parallel connected with the output load  1440 . 
     FIGS. 8 a  to  8   d  show the schematic circuit diagrams resulting from the addition of an additional winding to the topologies combining a Boost PFC and two switches forward and Flyback cell cells, respectively. 
     In FIG. 8 a , the schematic shows the specific topology of combining a Boost PFC with a two switches forward cell modified according to the invention by providing extra winding  2020 . As shown therein the AC input  2000  is applied to rectifier  2002 , and the rectifier output is connected to inductor  2004 , diode  2006 , switch  2010  and capacitor  2008 , indicating a Boost PFC cell. The output of PFC cell is fed to the DC/DC cell, constituted by buffer capacitor  2008 , switches  2026  and  2028 , diodes  2030  and  2032 , Forward transformer windings  2014  and  2016  and output circuitry  2024 . The additional winding  2020  and diode  2012  are inserted between low side switch  2026  and positive output of rectifier  2002 . 
     In FIG. 8 b , the schematic shows the specific topology of combining a Boost PFC with a two switches forward cell modified according to the invention by providing extra winding  2120 . As shown therein, the AC input  2100  is applied to rectifier  2102 , and the rectifier output is connected to Flyback transformer winding  2104 , diode  2106 , switch  2110  and capacitor  2108 , indicating a Boost PFC cell. The output of PFC cell is fed to the DC/DC cell, constituted by buffer capacitor  2108 , switch  2126 ,  2128 , diode  2130 ,  2132 , Forward transformer  2114 ,  2116  and output circuitry  2124 . The additional winding  2120  and diode  2112  are inserted between low side switch  2126  and positive output of rectifier  2102 . Winding  2134 , which is coupled with  2104 , is serially connected with diode  2136  and thereafter is parallel connected with the output load  2140 . 
     In FIG. 8 c , the schematic shows the specific topology of combining a Boost PFC with a two switches Flyback cell modified according to the invention by providing extra winding  2220 . As shown therein the AC input  2200  is applied to rectifier  2202 , and the rectifier output is connected to inductor  2204 , diode  2206 , switch  2210  and capacitor  2208 , indicating a Boost PFC cell. The output of PFC cell is fed to the DC/DC cell, constituted by buffer capacitor  2208 , switch  2226 ,  2228 , diode  2230 ,  2232 , Flyback transformer  2214 ,  2216  and output circuitry  2224 . The additional winding  2220  and diode  2212  are inserted between low side switch  2226  and positive output of rectifier  2202 . 
     In FIG. 8 d , the schematic shows the specific topology of combining a Boost PFC with a two switches Flyback cell modified according to the invention by providing extra winding  2320 . As shown therein the AC input  2300  is applied to rectifier  2302 , and the rectifier output is connected to Flyback transformer winding  2304 , diode  2306 , switch  2310  and capacitor  2308 , saying Boost PFC cell. The output of PFC cell is fed to the DC/DC cell, constituted by buffer capacitor  2308 , switch  2326 ,  2328 , diode  2330 ,  2332 , Flyback transformer  2314 ,  2316  and output circuitry  2324 . The additional winding  2320  and diode  2312  are inserted between low side switch  2326  and positive output of rectifier  2302 . Winding  2334 , which is coupled with  2304 , is serially connected with diode  2336  and thereafter is parallel connected with the output load  2340 . 
     The foregoing teaching of the invention clearly shows that the invention improves the efficiency along with high power factors and the reduction of harmonic distortion of the currents in the output of AC/DC power supplies. 
     While the invention has been described, disclosed, illustrated and shown in various terms of certain embodiments or modifications which it has presumed in practice, the scope of the invention is not intended to be, nor should it be deemed to be, limited thereby and such other modifications or embodiments as may be suggested by the teachings herein are particularly reserved especially as they fall within the breadth and scope of the claims here appended.