Prof R T Kennedy1 EET 423 POWER ELECTRONICS -2

Prof R T Kennedy2 IDEAL TRANSFORMER MAGNETIC DEVICE ELECTRICAL ISOLATION FUNCTION: TRANSFER ENERGY SCALE CURRENT and VOLTAGE TRANSFER NO ENERGY STORAGE

Prof R T Kennedy3 REAL TRANSFORMER SOME ENERGY STORAGE MAGNETISING INDUCTANCE (WITHIN CORE) minimised by using gapless core minimised by using high permeability core LEAKAGE INDUCTANCE (EXTERNAL to CORE)

Prof R T Kennedy4 TRANSFORMER PARASITICS

Prof R T Kennedy5 TRANSFORMER LIMITATIONS LOW FREQUENCY core saturation SMPS FREQUENCIES core loss

Prof R T Kennedy6 FLYBACK CONVERTER TRANSFORMER BASICALLY MULTI WINDING COUPLED INDUCTOR energy storage in non-magnetic gap energy recoverable DESIGN LIMITATIONS core + winding losses  temperature rise & efficiency fixed  core losses reduce with temperature increase core saturation saturation flux density reduces with temperature increase leakage inductance

Prof R T Kennedy7 FLYBACK CONVERTER TRANSFORMER

Prof R T Kennedy8 FORWARD CONVERTER TRANSFORMER NORMAL TRANSFORMER NO energy storage ideally leakage inductance represents energy stored in non-magnetic regions mutual inductance represents stored energy in core DESIGN LIMITATIONS core losses leakage inductance

Prof R T Kennedy9 FORWARD CONVERTER TRANSFORMER

Prof R T Kennedy10 LEAKAGE INDUCTANCE EFFECTS

Prof R T Kennedy11 FLYBACK TRANSFORMER Magnetising Current is important in flyback transformers (& inductors) represents Energy Storage requirements Leakage Inductance is a parasitic

Prof R T Kennedy12 FERRITE CORE TOROIDAL TRANSFORMER

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Prof R T Kennedy14 REDUCE LEAKAGE INDUCTANCE

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Prof R T Kennedy16 LOW OUTPUT VOLTAGE HIGH OUTPUT CURRENT

Prof R T Kennedy17 OUTPUT CURRENT SHARING

Prof R T Kennedy18 HIGH EFFICIENCY