EET 423 POWER ELECTRONICS -2 Prof R T Kennedy POWER ELECTRONICS 2

IDEAL TRANSFORMER MAGNETIC DEVICE ELECTRICAL ISOLATION FUNCTION: TRANSFER ENERGY SCALE CURRENT and VOLTAGE TRANSFER NO ENERGY STORAGE Prof R T Kennedy POWER ELECTRONICS 2

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 Kennedy POWER ELECTRONICS 2

TRANSFORMER PARASITICS Prof R T Kennedy POWER ELECTRONICS 2

TRANSFORMER LIMITATIONS LOW FREQUENCY core saturation SMPS FREQUENCIES core loss Prof R T Kennedy POWER ELECTRONICS 2

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 b core losses reduce with temperature increase core saturation saturation flux density reduces with temperature increase leakage inductance Prof R T Kennedy POWER ELECTRONICS 2

FLYBACK CONVERTER TRANSFORMER Prof R T Kennedy POWER ELECTRONICS 2

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 Kennedy POWER ELECTRONICS 2

FORWARD CONVERTER TRANSFORMER Prof R T Kennedy POWER ELECTRONICS 2

LEAKAGE INDUCTANCE EFFECTS Prof R T Kennedy POWER ELECTRONICS 2

FLYBACK TRANSFORMER Magnetising Current is important in flyback transformers (& inductors) represents Energy Storage requirements Leakage Inductance is a parasitic Prof R T Kennedy POWER ELECTRONICS 2

FERRITE CORE TOROIDAL TRANSFORMER Prof R T Kennedy POWER ELECTRONICS 2

Prof R T Kennedy POWER ELECTRONICS 2

REDUCE LEAKAGE INDUCTANCE Prof R T Kennedy POWER ELECTRONICS 2

Prof R T Kennedy POWER ELECTRONICS 2

LOW OUTPUT VOLTAGE HIGH OUTPUT CURRENT Prof R T Kennedy POWER ELECTRONICS 2

OUTPUT CURRENT SHARING Prof R T Kennedy POWER ELECTRONICS 2

HIGH EFFICIENCY Prof R T Kennedy POWER ELECTRONICS 2