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Switch Mode Power Supplies. V dd. 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.
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Switch Mode Power Supplies Vdd 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 • Separate winding for feedback • Optical isolation Gate Drive
Transformer Converter Types: • Flyback Converter – Derived from Buck-Boost • Forward Converter - Derived from Buck • Full Bridge – Derived from Buck
Buck-Boost Converter Flyback Converter (Assume CCM) (Assume CMM) Df f(t) + Vin - + Vout - iL(t) ip(t) is(t) ip(t) F(t) is(t)
Flyback Converter (cont) Same as Buck-Boost
Flyback Converter (cont) Same as Buck-Boost
+ Vin - + Vout -
Multiple Secondaries + Vout,1 > 0 - + Vout,2 < 0 - Feedback