2EMI solutions: Passive filter Conventional EMI solutions depend on passive filter using inductors and capacitors:Inductors: CMC, DMCCapacitors: X-cap, Y-capThere are limitations when using passive filters:Inductors: Large size and high conduction lossCapacitors: leakage current specifications
3Active EMI cancellation IC WT6001: An effective EMI solution – Y-cap booster A patented technology developed in PowerELab.An SO-8 IC WT6001 developed with W2.Equivalent to a Y-cap with very large value within the EMI concerned frequency range only.No boosting effect in the leakage current test concerned frequency range (50 – 800Hz).Greatly reduce the common mode inductor size and requirements.Reduce converter size and improve conversion efficiency.Provide effective and efficient EMI solution.Built-in electrical surge protection which can easily pass the EN and EN immunity standard.
4Applications: Replace passive Y-cap Replaced by Y-cap boosterLISN
5Effect measurable by oscilloscope when using Y-cap booster Noise voltage across Y-cap inswitching converterNoise voltage across Y-cap boosterin switching converterMore application examples can be found in the datasheet of WT6001
6Practical application examples The original EMI filter design cannot pass the EN55022 class B limit.Filter component:2 x 20mm high mu toroid for common mode filters2 x 0.15uF X – cap1 x 1n Y1-cap connected between primary and secondary
7Practical application examples: Original filter schematic It is a commonly used filter configurationL2B is wound with many turns which intends to suppress the low to mid-frequency common mode noise. Its leakage inductance together with C1 also provides differential mode noise filteringL1B is a single layer, bi-filer wound common mode choke for high frequency common mode noise filtering
8Practical application examples: EMI measurement Y-cap: From 1n to 3n3DM noiseImproved but not enoughCM noiseFailure was identified to be caused by:Insufficient leakage inductance of the common mode choke for DM noise attenuation.The two common mode choke cannot effectively block out the common mode current.Further increase of Y-cap can reduce CM noise but fail to meet leakage current specifications.
9Practical application examples: Solution using Y-cap booster Y-cap booster is used to replace the primary to secondary Y-capAfter using the Y-cap booster, L2B is replaced by a small differential mode filter and L1B is reduced to a 9mm toroid with only a few turns to tackle the high frequency common node noise. The test results pass the required limit lines
10Practical application examples: Filter comparison: Before and After... Failed design even with morecost, loss and bigger size for thefilterPassed design using Y-cap booster with much smaller filter size that saves cost, power and space
11Another practical application examples: Filter comparison: Before and After... Original EMI solution using passive filterin ATX converterNew EMI solution using Y-cap boosterin ATX converter
12ConclusionY-cap booster breaks the relationship between the Y-cap values and leakage current requirement.Greatly reduce product design period and resources.It can be applied to any position with conventional Y-cap.Significantly reduce the size and loss of common mode choke implies higher power density and efficiency.EMI less sensitive to transformer winding capacitance implies more rooms for improving transformer coupling.Very suitable for equipment required low leakage current like medical equipment.
13Active Diode – An easy to use and high efficiency rectifier suitable for all converters Stringent requirements of nowadays converters:Compact sizeLow heat generation and high conversion efficiencyHigh output power and output currentLow cost………!!!Conventional technologies cannot meet the requirements!!
14Synchronous rectifier Use MOSFETs to replace diode rectifiers.State of the Art 30V SCKAverage 30V SO8 MOSFET9 m0.24 VAKAK7.8 m
15Synchronous rectifier Provides low conduction loss.Can operate at higher high current without heatsink.SCK 2.8W 10AMOSFET 0.7W 10A
16Synchronous rectifier Usage not limited to converters with high profit margin.Price of nowadays low RDSon MOSFETs comparable to schottky diodes using the state of the art technology.Provide even lower converter cost because of reduced heatsink, more output power, higher conversion efficiency…..Emerge in low cost converter like adaptors, standard open frame converters, ATX …… .
17Synchronous rectifier ADADProblematic for some conventional topologiesSpecial and sometimes complicated driving circuits SRare needed for different topologiesPerformance sensitive to transformer leakageinductance and operating conditionsConverter cannot be paralleled – Reverse currentPoor efficiency at low loadLimited input voltage rangeSimple circuitDiscontinuous mode is allowedGood low load efficiencyConverter can be paralleledHigh conversion efficiencyWorks just like a diode
18Active diode – Operating principle KAA1N1N2N3N4N1 is the current sense windingN2 provides MOSFET driving signalsA1 driver circuit (IC WT6002)N1 N3 & D1 form energy recovery circuitN4 & D2 form reset circuitD1D2
19Active diode – Operating principle Voltage across winding N2 orgate drive voltage Von of SRdepends on ratio of N2 to N3and voltage VoToffIiAKN1N2N3N4D1D2A1VonVN2Voltage source Vocan be any voltagesource in a converter,e.g. output voltageVoVN3VoVN4
20Application of Active Diode in different topologies ++f+CoV+oMagneticFreewheelVinResetSRCoVo-SVin--Flyback SRSForward SR-FlybackForward
21Application of Active Diode in different topologies +S++1CSR1SC11CV1SR1CoooVin-Vin+SR2-S2CSC2SR2V-22L-of2Half Bridge centre tapCurrent Doubler
22Application of Active Diode in different topologies SR1+CVoo-ISINand many others….SR2Resonant converter
23Successful application of Active Diode in converter products AD on 150W ACDCAD on 120W ACDCAD on 1.5 V 200 A ACDCAD on 50W ACDCAD on 300W ACDCAD on 60W ACDCAD on 100W DCDC
24Conclusion A new “Active Diode” technology is presented. A kind of current driven synchronous rectifier technology that provides high conversion efficiency and eliminates many conventional synchronous rectifier application problems.Patented technologies.An Active Diode driver IC WT6002 for easy implementation of the technology.Well proven by many converter product design.
25ReferencesLiu, J.C.P.; Poon, F.N.K.; Xuefei Xie; Pong, M.H.; current driven synchronous rectifier with energy recovery sensor Power Electronics and Motion Control Conference, Proceedings. PIEMC The Third International , Volume: 1 , 2000, page(s): vol.1Xuefei Xie; Liu, J.C.P.L.; Poon, F.N.K.; Man Hay Pong; Current-driven synchronous rectification technique for flyback topology, Power Electronics Specialists Conference, PESC IEEE 32nd Annual , Volume: 1 , 2001, Page(s): vol. 1Xuefei Xie; Liu, J.C.P.; Poon, F.N.K.; Man Hay Pong; A novel high frequency current-driven synchronous rectifier for low voltage high current applications, Applied Power Electronics Conference and Exposition, APEC Sixteenth Annual IEEE , Volume: 1 , 2001, Page(s): vol.1Liu, J.C.P.; Xuefei Xie; Poon, F.N.K.; Pong, B.M.H.; Practical solutions to the design of current-driven synchronous rectifier with energy recovery from current sensing, Applied Power Electronics Conference and Exposition, APEC Seventeenth Annual IEEE , Volume: 2 , 2002, Page(s): vol.2Xuefei Xie; Joe Chui Pong Liu; Poon, F.N.K.; Man Hay Pong; A novel high frequency current-driven synchronous rectifier applicable to most switching topologies, Power Electronics, IEEE Transactions on , Volume: 16 Issue: 5 , Sep 2001, Page(s):Xie Xuefei; Liu, J.C.P.; Poon, F.N.K.; Pong, B.M.H.; Two methods to drive synchronous rectifiers during dead time in forward topologies, Applied Power Electronics Conference and Exposition, APEC Fifteenth Annual IEEE , Volume: 2 , 2000, Page(s): vol.2US patent "Current driven synchronous rectifier with energy recovery" patent number 6,134,131US patent “Self-driven synchronous rectifier by retention of gate charge” patent number 6,377,477US patent “Current driven synchronous rectifier with energy recovery using hysterisis driver”, patent number 6,597,587