Switch Mode Power Supplies Use of Transformers for Electrical (DC) Isolation Safety – Isolate output voltages from Electrical Grid Multiple Reference ( “ground”) Potentials Voltage Matching – Large difference between voltage levels of power source and converter outputs. Feedback must traverse isolation boundary 1.Separate winding for feedback 2.Optical isolation Gate Drive V dd

Transformer Converter Types: Flyback Converter – Derived from Buck-Boost Forward Converter - Derived from Buck Full Bridge – Derived from Buck

Flyback Converter  (t) i p (t) i s (t)  i p (t) + V in - + V out - i L (t) Buck-Boost Converter  (t) i s (t) (Assume CMM) (Assume CCM)

Flyback Converter (cont) Same as Buck-Boost

Flyback Converter (cont) Same as Buck-Boost

+ V in - + V out -

+ V out,1 > V out,2 < 0 - Feedback Multiple Secondaries