Patent Grant
8520410
The present invention relates to the field of power supplies. More particularly, the present invention relates to a primary only controlled quasi resonant converter.
There are several power converter topologies that have been developed over the years, which are intended to improve the power density and switching efficiency of power converters. An emerging focus of new converter topologies is to provide a means to reduce or eliminate converter switching losses, while increasing the switching frequencies. Lower loss and higher switching frequency means more efficient converters, which can reduce the size and weight of converter components. Additionally, with the introduction of high speed composite semiconductor switches, such as metal oxide semiconductor field effect transistor (MOSFET) switches operated by pulse width modulation (PWM), recent forward and flyback topologies are now capable of operation at greatly increased switching frequencies, such as, for example, up to 1.0 MHz.
However, an increase in switching frequency can cause a corresponding increase in switching and component stress related losses, as well as increased electromagnetic interference (EMI), noise, and switching commutation problems, due to the rapid switching of the semiconductor switches at high voltage and/or high current levels. Moreover, modern electronic components are expected to perform multiple functions, in a small space, efficiently, and with minimal undesirable side effects. For instance, a conventional voltage converter that provides for relatively high power density and high switching frequencies, should also include uncluttered circuit topologies, provide for isolation of the output or “load” voltage from the input or “source” voltage, and also provide for variable step-up or step-down voltage transformation. In an effort to reduce or eliminate the switching losses and reduce EMI noise the use of “resonant” or “soft” switching techniques has been increasingly employed in the art. The application of resonant switching techniques to conventional power converter topologies offers many advantages for high density, and high frequency, to reduce or eliminate switching stress and reduce EMI. However, the complexity required to provide control to the power switches and the components associated with complex control, create a limited use in commercial applications.
In an effort to reduce or eliminate the switching losses and reduce EMI noise caused by high switching frequencies, “resonant” or “soft” switching techniques are increasingly being employed. Resonant switching techniques generally include an inductor-capacitor (LC) subcircuit in series with a semiconductor switch which, when enabled, creates a resonating subcircuit within the converter. Further, timing the control cycles of the resonant switch to correspond with particular voltage and current conditions across respective converter components during the switching cycle allows for switching under zero voltage and/or zero current conditions. Zero voltage switching (ZVS) and/or zero current switching (ZCS) inherently reduces or eliminates many frequency related switching losses. Several power converter topologies have been developed utilizing resonant switching techniques, such as, for example, U.S. Pat. No. 5,694,304 entitled “High Efficiency Resonant Switching Converters,” to Telefus, et al., (Telefus), which is hereby incorporated by reference; U.S. Pat. No. 5,057,986 entitled “Zero Voltage Resonant Transition Switching Power Converter,” to Henze, et al., (Henze), which is hereby incorporated by reference; U.S. Pat. No. 5,126,931 entitled “Fixed Frequency Single Ended Forward Converter Switching at Zero Voltage,” to Jitaru (Jitaru), which is hereby incorporated by reference; and U.S. Pat. No. 5,177,675 entitled “Zero Voltage, Zero Current, Resonant Converter,” to Archer, (Archer), which is hereby incorporated by reference.
In particular, Henze describes single ended DC-DC flyback topologies for operation at very high switching frequencies, such as 1.0 MHz or greater. In Henze, a plurality of pulse width modulated (PWM) switches are utilized to effect zero voltage resonant transition switching. Jitaru describes variations of known forward and/or flyback converter topologies employing zero voltage and/or zero current resonant techniques. Jitaru specifically describes a forward converter topology utilizing resonant switching techniques to operate at constant frequency. Archer describes zero voltage, and zero current, switching techniques in resonant flyback topologies utilizing a resonant transformer assembly inserted in parallel with either the primary or secondary winding of the main transformer.
The application of such resonant switching techniques to conventional power converter topologies offers many advantages for high density, high frequency converters, such as quasi sinusoidal current waveforms, reduced or eliminated switching stresses on the electrical components of the converter, reduced frequency dependent losses, and/or reduced EMI. However, energy losses incurred during control of zero voltage switching and/or zero current switching, and losses incurred during driving, and controlling the resonance means, are still problematic. For instance, some researchers have implemented an active clamp in conjunction with a resonant converter circuit to realize the benefits of high frequency switching, while reducing its many side effects. See, for example, the United States Patent to Telefus, incorporated by reference above.
An improved switching type power converter known as a quasi resonant tank circuit is described in US. Patent Publication No. 2007-0263415 to Jansen et. al. (Jansen), hereby incorporated in its entirety.
It is well known that MOSFET switches include inherent capacitances that must be accounted for. To that end,
The power converter 200 of
In most single ended power converters such as the flyback converters of
A person of ordinary skill in the art will appreciate that the driving capacitor 236 is in parallel with the secondary resonant capacitor 238 when the auxiliary switch 220 is enabled. As a result, the values of the driving capacitor 236 and the secondary resonant capacitor 238 must be proportional; i.e. one should not be changed without changing the other since doing so would change the effective total resonance capacitance for the tank circuit 201. However, a capacitor of a smaller value cannot drive a capacitor of a higher value. As a result, in high power applications, such as power greater than 10 watts at an output, the auxiliary switch 220 must be larger in order to properly handle increased current flow. As the switch 220 increases in size, parasitic capacitances Crss1 and Ciss1 increase proportionally. As a result, the driving capacitor 236 must be of a higher value. A discrete capacitor of a higher value directly translates to increased size and cost, which can be unacceptable in small form factor products. Regardless of the size and cost, increasing all values may simply be untenable due to increased serial equivalent resistance of the capacitors causing unacceptable decreases in efficiency. To that end, what is needed is a power converter circuit having a quasi resonant tank circuit wherein the circuit driving the auxiliary switch is independent of the auxiliary switch itself.
The instant invention provides a switching type power converter utilizing a quasi resonant tank circuit. A primary switch and an auxiliary switch selectively couple energy storing elements to the tank circuit, thereby changing a resonant frequency. The auxiliary switch is driven by an independent driver having a separate power source, enabling higher power conversion with respect to the prior art listed above while using physically small and cost effective elements, including transistors.
In a first aspect of the invention, a power converter comprises an output transformer, and a resonant tank circuit coupled to the output transformer. In some embodiments, the resonant tank comprises a primary switch for selectively charging a first energy storing element, a second energy storing element in parallel with the first energy storing element, an auxiliary switch for selectively coupling a third energy storing element with the first energy storing element, and a first power source for providing power to the resonant tank circuit. A comparator detect a voltages across at least one of the energy storage elements, and a driver drives the auxiliary switch based on the output state of the comparator. Advantageously, the driver comprises a second power source for providing a power independent of the tank circuit.
In operation, the fact that the driver receives power from a separate power source enables the driver to draw as much current as it needs, and is therefore able to drive an auxiliary switch of any size. The added components of the driver are generally transistors, which are very cost effective and small in form factor, enabling high power output power converters in a small form factor apparatus, able to charge or provide operating power to anything from a cellular telephone to an electric vehicle, depending on the size of the driver. In some embodiments, the second power source is a rectifier coupled to a winding of a power transformer.
The energy storage elements described above are able to be any among a discrete inductor, the inductance of the transformer, discrete capacitors or parasitic capacitors inherent to switches. The switches are able to be MOSFETs, or for higher power applications IGBTs. Preferably, the comparator comprises a capacitor for receiving charge from at least one energy storage element, a first diode for directing current to a pre-driver, a second diode for limiting a reverse current to the at least one energy storage element and a third diode for limiting a reverse current to the pre-driver. In some embodiments, the pre-driver is able to be a MOSFET. The driver is able to be any known or application specific driver to suit a particular application taking into consideration power and efficiency needs, such as a Class A circuit, a Class AB circuit, a Class B circuit, a Class C circuit and a Class D circuit.
In another aspect of the invention, a power converter comprises an output transformer, a first resonance capacitor coupled to the transformer to form a resonant circuit with the primary inductance of the output transformer, a primary switch for selectively charging the first resonance capacitor, and a second resonance capacitor coupled to the output transformer. An auxiliary switch forms a resonant circuit with the primary inductance of said transformer, and a comparator determines an amount of charge on the first resonance capacitor. In order to effectively drive any size auxiliary switch according to the output state of the comparator as determined by the charge on the first resonance capacitor, a driver is provided, wherein the driver comprises an independent power supply. In some embodiments, the comparator comprises a capacitor for receiving charge from the first resonant capacitor and a pre-driver for receiving charge from the capacitor and driving the driver. Diodes may be used to direct current to the pre-driver and away from the resonant capacitor. In some embodiments, the first and second resonant capacitors are able to comprise discrete component capacitors or parasitic capacitors inherent to the switches.
Preferably, the power converter utilizes a switching cycle comprising a first resonant cycle, and a second resonant cycle, wherein energy in the first resonant capacitor is substantially transferred to the second resonance capacitor through the first and second resonant cycles. Generally, the first resonant cycle comprises a higher frequency than the second resonant cycle. In some embodiments, the comparator selectively enables a driver according to the switching cycle, wherein the driver drives the auxiliary switch.
The novel features of the invention are set forth in the appended claims. However, for purposes of explanation, several embodiments of the invention are set forth in the following figures.
In the following description, numerous details and alternatives are set forth for the purpose of explanation. However, one of ordinary skill in the art will realize that the invention can be practiced without the use of these specific details. In other instances, well-known structures and devices are shown in block diagram form in order not to obscure the description of the invention with unnecessary detail.
The comparator 309 and driver 310 for the auxiliary switch 304 are configured such that when the voltage across the primary winding of the transformer 303 is higher than zero, the auxiliary switch will 304 is the on position. The comparator 309 and driver 310 for auxiliary switch 304 are further configured such that when the voltage across the primary winding of the transformer 303 is equal or lower than zero, the auxiliary switch 304 is disabled. Consequently, a first resonance frequency exists for voltages of less than or equal to zero across the primary winding of transformer 303 as a result of the energy exchange between the primary inductance of transformer 303 and the first resonance capacitor 306.
Advantageously, the driver 310 is able to be as powerful a driving device as necessary because it is independent from the comparator 309. In the prior art of
The output of the driver 410 is coupled to the gate of the auxiliary switch 404. Because the auxiliary switch is being parametrically driven by the driver means 410 that is able to provide any necessary drive current, the auxiliary switch 404 is as large as necessary to carry an appropriate current without requiring a change in the value of the capacitor 426. In some embodiments, a protection diode 480 is able to protect from overcurrent conditions. As mentioned above, because the capacitor 426 is no longer driving the auxiliary switch 404, but rather a pre driver switch 433, the resonant capacitor 406 need not be increased in value so that a ratio between the capacitor 426 and the resonant capacitor 406 is maintained, since the value of the capacitor 426 may remain small and still be able to drive a relatively small pre-driver Q5433. The additional cost of the transistors in the driver means 410 and the pre-driver 433 are generally inconsequential compared to the cost of increased values of capacitors as would be required for higher power applications in the prior art of
The resonant tank circuit 401 comprises the primary switch 405, the first resonant capacitor 406, the auxiliary switch 404 having parasitic capacitance (not shown) that serves as a second resonant capacitor, and the primary inductance of the output transformer 403. The auxiliary switch 404 is able to selectively couple the resonant capacitor 406 in parallel with the primary winding of the output transformer 403 thereby selectively switching between a first and a second resonant frequency. For voltages of higher than zero across the primary winding of the transformer 403, the auxiliary switch 404 is in the on position and the second resonance capacitor, the gate to drain capacitor of the auxiliary switch 404, is connected in parallel with the first resonance capacitor 406. Consequently, a second resonance frequency, which is lower in value than the first resonance frequency, exists for voltages of higher than zero across the primary winding of transformer 403 as a result of the energy exchange between the primary inductance of transformer 403 and the first and second resonance capacitors. Additional inductance may be included if desired as a discrete inductor 403A in series with the primary winding of the output transformer 403. Inductance may be reduced by adding a discrete inductor 403B in parallel with the primary winding of the output transformer 403. In the exemplary embodiment of
When the power converter from
After a quarter cycle of the first resonance frequency, the voltage across the primary switch 405 substantially equals to the rectified power and consequently the voltage across the first resonance capacitor 406 and the primary winding of the output transformer 403 is substantially zero. At this moment most of the energy originally stored in the first resonance capacitor 406 is now stored in the inductance of the primary side of the output transformer 403. Also at this moment the auxiliary switch 404 is switched on by the comparator 409 and the driving means 410 for the auxiliary switch 404. As a result of the second resonance between the inductance of the primary winding of the output transformer 403 and the first and second resonance capacitors in parallel, the voltage across the primary switch 405 further increases and consequently the voltage across the first resonance capacitor 406 and the primary winding of the output transformer 403 also increases.
After a quarter cycle of the second resonance frequency, most of the energy stored in the inductance of the primary side of the output transformer 403 is transferred to the first and second resonance capacitors but in opposite polarity and lower amplitude compared to the original start voltage across the first resonance capacitor 406. Such a condition is referred to as a reset condition. As a result of the resonance between the first and second resonance capacitors and the primary inductance of the primary side of the output transformer 403, the voltage across the primary winding and consequently the voltage across primary switch 405 starts to decline.
After a quarter cycle of the second resonant frequency, most of the energy stored in the first and second resonance capacitors is again stored in the inductance of the primary side of the output transformer 403. At that moment the voltage across the first and second resonance capacitors and the primary side of the output transformer 403 is substantially zero. At that moment the auxiliary switch 404 is disabled by the comparator 309 and the driver means 410. After the auxiliary switch 404 is disabled, the resonance continues based on the original first resonance between the inductance of the primary side of the output transformer 403 and the first resonance capacitor 406.
After a quarter cycle of the first resonance frequency, the voltage across the primary switch 405 further falls until it reaches substantially zero. Then, the primary switch is able to be under substantially Zero Voltage Switching conditions. The auxiliary switch 404 also switches under substantially Zero Voltage Switching conditions as a result of the comparator 409 which detects the zero voltage point across the primary winding of the output transformer 403, which coincides with a substantially zero voltage across the auxiliary switch 404.
In operation, a power converter device is able to utilize the benefits of flyback-type without suffering the ill effects of high frequency transients by utilizing a resonant tank circuit as described above. Advantageously, the driver module for one of two switching elements in a tank circuit is independent of a comparator which decides when to enable the switching element to change the resonant frequency of the tank. Because the driver element is independent, and able to derive power from its own power source, for example its own winding and rectifier on a multiple winding transformer, the driver element can be made as powerful as necessary to drive a switching element of any size. In some embodiments, a capacitor and an inductor form the resonance circuit. Alternatively, a capacitor in parallel with the coil of a transformer forms a parallel resonance circuit. In both these types of implementations, the parasitic capacitances advantageously generate a negative current back to the source. Hence, the parasitic capacitances, which are normally problematic for a system, operate as capacitors that store and release energy in conjunction with the resonant tank and the real capacitances. Stated differently, all the components are in a full resonance circuit, including the real or active components, and the parasitic components. Therefore, all or most of the energy generated by the components of the system, including the parasitic components, is transferred either to the load (typically in the low frequency mode), or back to the source (in the high frequency mode).
In particular, the cyclical operation of some embodiments implement a quasi resonant storage tank by the generation of a series of dampening sinusoidal wave forms. Some embodiments further maintain, for the system, an energy equilibrium such that the energy of a high frequency cycle is substantially equivalent to the energy of a low frequency cycle.
While the invention has been described with reference to numerous specific details, one of ordinary skill in the art will recognize that the invention can be embodied in other specific forms without departing from the spirit of the invention. Thus, one of ordinary skill in the art will understand that the invention is not to be limited by the foregoing illustrative details, but rather is to be defined by the appended claims.
| Number | Name | Date | Kind |
|---|---|---|---|
| 4184197 | Cuk et al. | Jan 1980 | A |
| 4273406 | Okagami | Jun 1981 | A |
| 4370703 | Risberg | Jan 1983 | A |
| 4563731 | Sato et al. | Jan 1986 | A |
| 4645278 | Yevak et al. | Feb 1987 | A |
| 4712160 | Sato et al. | Dec 1987 | A |
| 4788626 | Neidig et al. | Nov 1988 | A |
| 4806110 | Lindeman | Feb 1989 | A |
| 4823249 | Garcia, II | Apr 1989 | A |
| 4841220 | Tabisz et al. | Jun 1989 | A |
| 4857822 | Tabisz et al. | Aug 1989 | A |
| 4866367 | Ridley et al. | Sep 1989 | A |
| 4890217 | Conway | Dec 1989 | A |
| 4893227 | Gallios et al. | Jan 1990 | A |
| 4899256 | Sway-Tin | Feb 1990 | A |
| 4901069 | Veneruso | Feb 1990 | A |
| 5065302 | Kanazawa | Nov 1991 | A |
| 5090919 | Tsuji | Feb 1992 | A |
| 5101322 | Ghaem et al. | Mar 1992 | A |
| 5132890 | Blandino | Jul 1992 | A |
| 5235491 | Weiss | Aug 1993 | A |
| 5325283 | Farrington | Jun 1994 | A |
| 5365403 | Vinciarelli et al. | Nov 1994 | A |
| 5373432 | Vollin | Dec 1994 | A |
| 5442540 | Hua | Aug 1995 | A |
| 5673185 | Albach et al. | Sep 1997 | A |
| 5712772 | Telefus et al. | Jan 1998 | A |
| 5790395 | Hagen | Aug 1998 | A |
| 5811895 | Suzuki et al. | Sep 1998 | A |
| 5838554 | Lanni | Nov 1998 | A |
| 5859771 | Kniegl | Jan 1999 | A |
| 5905369 | Ishii et al. | May 1999 | A |
| 5923543 | Choi | Jul 1999 | A |
| 5949672 | Bernet | Sep 1999 | A |
| 6091611 | Lanni | Jul 2000 | A |
| 6188302 | Conway | Feb 2001 | B1 |
| 6191957 | Peterson | Feb 2001 | B1 |
| 6272015 | Mangtani | Aug 2001 | B1 |
| 6275397 | McClain | Aug 2001 | B1 |
| 6323627 | Schmiederer et al. | Nov 2001 | B1 |
| 6385059 | Telefus et al. | May 2002 | B1 |
| 6388897 | Ying et al. | May 2002 | B1 |
| 6390854 | Yamamoto et al. | May 2002 | B2 |
| 6396716 | Liu et al. | May 2002 | B1 |
| 6452816 | Kuranuki | Sep 2002 | B2 |
| 6459175 | Potega | Oct 2002 | B1 |
| 6487098 | Malik et al. | Nov 2002 | B2 |
| 6549409 | Saxelby et al. | Apr 2003 | B1 |
| 6578253 | Herbert | Jun 2003 | B1 |
| 6618274 | Boylan et al. | Sep 2003 | B2 |
| 6650552 | Takagi et al. | Nov 2003 | B2 |
| 6654261 | Welches et al. | Nov 2003 | B2 |
| 6721192 | Yang et al. | Apr 2004 | B1 |
| 6775162 | Mihai et al. | Aug 2004 | B2 |
| 6894461 | Hack et al. | May 2005 | B1 |
| 6899434 | Morishita | May 2005 | B2 |
| 6919715 | Muratov et al. | Jul 2005 | B2 |
| 6989997 | Xu | Jan 2006 | B2 |
| 7035126 | Lanni | Apr 2006 | B1 |
| 7038406 | Wilson | May 2006 | B2 |
| 7102251 | West | Sep 2006 | B2 |
| 7139180 | Herbert | Nov 2006 | B1 |
| 7202640 | Morita | Apr 2007 | B2 |
| 7208833 | Nobori et al. | Apr 2007 | B2 |
| 7212420 | Liao | May 2007 | B2 |
| 7239532 | Hsu et al. | Jul 2007 | B1 |
| 7274175 | Manolescu | Sep 2007 | B2 |
| 7315460 | Kyono | Jan 2008 | B2 |
| 7386286 | Petrovic et al. | Jun 2008 | B2 |
| 7450388 | Beihoff et al. | Nov 2008 | B2 |
| 7499301 | Beihoff et al. | Mar 2009 | B2 |
| 7545256 | O'Toole et al. | Jun 2009 | B2 |
| 7564706 | Herbert | Jul 2009 | B1 |
| 7596007 | Phadke | Sep 2009 | B2 |
| 7701305 | Lin et al. | Apr 2010 | B2 |
| 7924578 | Jansen et al. | Apr 2011 | B2 |
| 8059434 | Huang | Nov 2011 | B2 |
| 8102678 | Jungreis | Jan 2012 | B2 |
| 8126181 | Yamamoto et al. | Feb 2012 | B2 |
| 8134848 | Whittam et al. | Mar 2012 | B2 |
| 8155368 | Cheung et al. | Apr 2012 | B2 |
| 8194417 | Chang | Jun 2012 | B2 |
| 8207717 | Uruno et al. | Jun 2012 | B2 |
| 8243472 | Chang et al. | Aug 2012 | B2 |
| 8369111 | Balakrishnan et al. | Feb 2013 | B2 |
| 8400801 | Shinoda | Mar 2013 | B2 |
| 20020008963 | DiBene, II et al. | Jan 2002 | A1 |
| 20020011823 | Lee | Jan 2002 | A1 |
| 20020036200 | Ulrich | Mar 2002 | A1 |
| 20030035303 | Balakrishnan et al. | Feb 2003 | A1 |
| 20030112645 | Schlecht | Jun 2003 | A1 |
| 20040183510 | Sutardja et al. | Sep 2004 | A1 |
| 20040252529 | Huber et al. | Dec 2004 | A1 |
| 20050024016 | Breen et al. | Feb 2005 | A1 |
| 20050036338 | Porter et al. | Feb 2005 | A1 |
| 20050117376 | Wilson | Jun 2005 | A1 |
| 20050138437 | Allen et al. | Jun 2005 | A1 |
| 20050194942 | Hack et al. | Sep 2005 | A1 |
| 20050225257 | Green | Oct 2005 | A1 |
| 20050254268 | Reinhard et al. | Nov 2005 | A1 |
| 20060002155 | Shteynberg et al. | Jan 2006 | A1 |
| 20060022637 | Wang et al. | Feb 2006 | A1 |
| 20060109696 | Ren et al. | May 2006 | A1 |
| 20060152947 | Baker et al. | Jul 2006 | A1 |
| 20060213890 | Kooken et al. | Sep 2006 | A1 |
| 20060232220 | Melis | Oct 2006 | A1 |
| 20070040516 | Chen | Feb 2007 | A1 |
| 20070051712 | Kooken et al. | Mar 2007 | A1 |
| 20070120542 | LeMay | May 2007 | A1 |
| 20070121981 | Koh et al. | May 2007 | A1 |
| 20070138971 | Chen | Jun 2007 | A1 |
| 20070247091 | Maiocchi | Oct 2007 | A1 |
| 20070247877 | Kwon et al. | Oct 2007 | A1 |
| 20070263415 | Jansen et al. | Nov 2007 | A1 |
| 20080018265 | Lee et al. | Jan 2008 | A1 |
| 20080043496 | Yang | Feb 2008 | A1 |
| 20080191667 | Kernahan et al. | Aug 2008 | A1 |
| 20090034299 | Lev | Feb 2009 | A1 |
| 20090196073 | Nakohori | Aug 2009 | A1 |
| 20090290384 | Jungreis | Nov 2009 | A1 |
| 20090290385 | Jungreis et al. | Nov 2009 | A1 |
| 20100039833 | Coulson et al. | Feb 2010 | A1 |
| 20100322441 | Weiss et al. | Dec 2010 | A1 |
| 20110132899 | Shimomugi et al. | Jun 2011 | A1 |
| 20110261590 | Liu | Oct 2011 | A1 |
| 20120112657 | Van Der Deen et al. | May 2012 | A1 |
| Number | Date | Country |
|---|---|---|
| 4217869 | Aug 1992 | JP |
| 10243640 | Sep 1998 | JP |
| 2000083374 | Mar 2000 | JP |
| 2000253648 | Sep 2000 | JP |
| 2004208357 | Jul 2004 | JP |
| Entry |
|---|
| International Search Report, PCT/US2011/49438, International filed Aug. 26, 2011, 10 pages. |
| EE Times.com- “Teams Claim Midrange Wireless Energy Transfer”, by R. Colin Johnson, 4 pages, Nov. 6, 2007. |
| EE Times.com- “Wireless Beacon Could Recharge Consumer Devices”, by R. Colin Johnson, 3 pages, Nov. 6, 2007. |
| Hang-Seok Choi et al., Novel Zero-Voltage and Zero-Current-Switching (ZVZCS) Full-Bridge PWM Converter Using Coupled Output Inductor, Sep. 2002 IEEE, pp. 641-648. |
| “New Architectures for Radio-Frequency dc/dc Power Conversion”, Juan Rivas et al., Laboratory for Electromagnetic and Electronic Systems, Jan. 2004, Massachusetts Institute of Technology, Room 10-171, Cambridge, MA02139, pp. 4074-4084. |
| “Randomized Modulation in Power Electronic Converters”, Aleksander M. Stankovic, member IEEE, and Hanoch LevAri, vol. 90, No. 5, May 2002, pp. 782-799. |
| “Analysis and Special Characteristics of a Spread-Spectrum technique for Conducted EMI Suppression”, K.K. Tse, et al., Member IEEE, IEEE Transactions on Power Electronics, vol. 15., No. 2, Mar. 2000, pp. 399-410. |
| International Search Report dated 05 Mar. 2012, International Application no. PCT/US2011/059817, International Filing Date: Nov. 8, 2011, 9 pages. |
| Notice of Allowance re. U.S. Appl. No. 12/687,761, filed Jan. 14, 2010, Examiner: Tran, Nguyen, art unit: 2838, 7 pages. |
| Number | Date | Country | |
|---|---|---|---|
| 20120113686 A1 | May 2012 | US |
