1 EET 423 POWER ELECTRONICS -2Prof R T Kennedy
2 POWER INDUCTORS Prof R T Kennedy
3 THIN INDUCTOR LOW PROFILE CONVERTERProf R T Kennedy
4 INDUCTOR TYPES MOLDED INDUCTOR AIR CORED INDUCTOR ‘AIR’ CORED INDUCTORTOROIDAL INDUCTOR The molded inductor is marker brown-black-black-gold, meaning 10 x 100 μH, or 10 μH, with 5% tolerance. Other inductor types are often unmaked, with value indcated on packaging materials only. Prof R T Kennedy
5 SELECTING INDUCTORS Converter Currents waveforms operation mode• Parameter Selection inductor specification Inductor Losses Construction Type coil v chip Inductors Electromagnetic Interference (EMI / EMC) shielded v non shielded inductors Prof R T Kennedy
6 BUCK-FORWARD CONVERTER CURRENTINDUCTOR CURRENT IL,M IL,m IL,av = Iout t Prof R T Kennedy
7 INDUCTOR RIPPLE CURRENTINDUCTOR CURRENT IL,M IL,m IL,av = Iout t SELECT L: BASED on pk-pk RIPPLE Prof R T Kennedy
8 BUCK & FORWARD OPERATION MODESELDOM DCM increased capacitor requirements multiple outputs poor cross regulation Prof R T Kennedy
9 HIGHER RIPPLE-DC RATIO SMALLER RIPPLE-DC RATIOINDUCTANCE VALUE Ein = 2.7 V V Vout = 1.5 V fsw = 3 MHz Iout = 800 mA L = 1 mH HIGHER RIPPLE-DC RATIO > LOSSES SMALLER RIPPLE-DC RATIO > SIZE Prof R T Kennedy
10 constant inductor voltageIL t J constant inductance constant inductor voltage Prof R T Kennedy
11 IL t L excess resistance less efficient Prof R T Kennedy
12 inductor current exceeds IsatIL t L peaky current reduced L inductor current exceeds Isat Prof R T Kennedy
13 TYPICAL INDUCTOR SPECIFICATIONDESIGN LIMITING FACTORS TEMPERATURE RISE EFFICIENCY due to CORE & WINDING LOSSES CORE SATURATION Prof R T Kennedy
14 INDUCTOR LOSSES SKIN EFFECT PROXIMITY EFFECT WINDING (COPPER) COREHYSTERESIS DC (DCR) AC (ACR) EDDY CURRENT SKIN EFFECT PROXIMITY EFFECT Prof R T Kennedy
15 TYPICAL INDUCTOR SPECIFICATIONProf R T Kennedy
16 DC WINDING (COPPER) LOSSINDUCTOR DC RESISTANCE DC WINDING (COPPER) LOSS Prof R T Kennedy
17 DC RESISTANCE v TEMPERATUREProf R T Kennedy
18 INDUCTOR AC RESISTANCESKIN EFFECT due to eddy currents produced by the ac current add to the outer conductor current subtract from the inner conductor current frequency increase majority of the current flows on the surface Prof R T Kennedy
19 AC RESISTANCE: SKIN EFFECTcurrent density Prof R T Kennedy
20 AC RESISTANCE v FREQUENCYProf R T Kennedy
21 INDUCTOR AC RESISTANCE v FREQUENCYCoilcraft LPO AC RESISTANCE LOSSES Prof R T Kennedy
22 AC v DC RESISTANCE Prof R T Kennedy
23 COMPARATIVE LOSSES Prof R T Kennedy
24 INDUCTOR SELF RESONANT FREQUENCYat which inductor winding inductance resonates naturally with winding distributed capacitance Prof R T Kennedy
25 INDUCTANCE v CURRENT Prof R T Kennedy
26 INDUCTANCE v CURRENT Prof R T Kennedy
27 SATURATION CURRENT v TEMPERATURE25 oC 85 oC Prof R T Kennedy
28 CORE SATURATION reduced inductance increased noiseProf R T Kennedy
29 INDUCTOR RATED CURRENTRATED CURRENT: smaller of saturation and RMS Prof R T Kennedy
30 Isat >> DATASHEET SPEC !!!!Prof R T Kennedy
31 INDUCTOR TEMPERATURE RISEProf R T Kennedy
32 FARADAY’S VOLT-TIME INTEGRALINDUCTOR VOLTAGE V1 t1 INDUCTOR CURRENT t2 V2 t I m I M T current start and finish at same value EQUAL AREAS Prof R T Kennedy
33 ‘IDEAL’ BUCK ANALYSIS CCM VOLT-TIME INTEGRAL APPROACHINDUCTOR VOLTAGE IL Ein -Vout VL area A area B -Vout Dsw T Dfwd T t Prof R T Kennedy
34 INDUCTOR CURRENT WAVEFORMSCCM or DCM operational mode component current stress capacitor ripple current output voltage ripple converter efficiency closed loop regulation performance Prof R T Kennedy
35 INDUCTOR CURRENT v INDUCTANCEDswT Dfwd T Iout Ein-Vout -Vout VL IL t REDUCTION in L constant duty cycle Prof R T Kennedy
36 INDUCTOR CURRENT v INDUCTANCEincreased Isw,max Ifwd,max IC,ripple Vout,ripple REDUCTION in L DswT Dfwd T Iout Ein-Vout -Vout VL IL t constant duty cycle Prof R T Kennedy
37 INDUCTOR CURRENT Prof R T Kennedy
38 variable duty cycle INDUCTOR CURRENT Dsw > 0.5 IL Dsw= 0.5 IoutIL t Iout Dsw = 0.2 Dsw = 0.5 Dsw = 0.8 Dsw > 0.5 Dsw < 0.5 Dsw= 0.5 Prof R T Kennedy
39 LOAD (R) INDEPENDENT INDUCTOR CURRENT DOWNSLOPE UPSLOPE IL tt Prof R T Kennedy
40 INDUCTOR PEAK-PEAK RIPPLE CURRENTProf R T Kennedy
41 CCM-DCM BOUNDARY Prof R T Kennedy
42 CCM-DCM BOUNDARY boundary Prof R T Kennedy
43 CCM-DCM BOUNDARY CCM boundary DCM Prof R T Kennedy
44 CCM-DCM BOUNDARY L Dsw fsw constant CCM CCM / DCM determined by R DCMINCREASE R ‘light loading’ DCM to ensure a desired CCM does not transfer to DCM specify a minimum load current (maximum R) avoid open circuit operation Prof R T Kennedy
45 CCM / DCM determined by LCCM-DCM BOUNDARY R Dsw fsw constant CCM CCM / DCM determined by L DECREASE L DCM to ensure a desired CCM does not transfer to DCM design for CMM at lowest inductance including L v I Prof R T Kennedy
46 CCM / DCM determined by fswCCM-DCM BOUNDARY R Dsw fsw constant CCM CCM / DCM determined by fsw DECREASE fsw DCM to ensure a desired CCM does not transfer to DCM design for CMM at lowest frequency Prof R T Kennedy
47 CCM / DCM determined by DswCCM-DCM BOUNDARY L R fsw constant CCM CCM / DCM determined by Dsw DCM to ensure a desired CCM does not transfer to DCM design for CMM at lowest duty cycle DECREASE Dsw Prof R T Kennedy
48 DCM lower control range LINE & LOAD REGULATION DCM CCMProf R T Kennedy
49 DCM lower control range LINE & LOAD REGULATION DCM CCMProf R T Kennedy