472 Lecture 6 buck boost cuk

472 Lecture 6 buck boost cuk - Lecture 6 Buck boost and Cuk...

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Lecture 6 Buck boost and Cuk converters • Analysis and design of buck boost converter • Cuk converter EEE 498/591 – Raja Ayyanar
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+ Buck-boost converter i L + _ v L V in S 1 D 1 i C I o _ V o D q A A C R L + _ i in + 1 o in VD = - Input-output relationship for Buck-boost ( )( ) ( ) 10 1 in s o s in o T V DT VD V D +- - = =- q A 1 0 t DT S ( 1-D ) T S v L -V o V in 0 • Step up as well as step down depending on D • Negative output (with respect to input ground) • Isolated version - flyback converter popular at ~100 W power level EEE 498/591 – Raja Ayyanar
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Selection of L 0 v L -V o V in i L 0 L I D • L selected such that inductor current ripple is about 10-20% of its max. avg. • Design for worst case condition • CCM considerations Peak-peak ripple in inductor current DT S Consider the T OFF interval ( ) 1 L o S I LV DT D = - () 1 oS L VD T L I - = D I in +I o EEE 498/591 – Raja Ayyanar
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i C 0 Selection of C -I o I in • Choose C based on RMS current requirement ( capacitor RMS current can be larger than load current ) • Verify if specification is satisfied with the chosen C and ESR values o V D () 2 2 , , 1 substitute, 1 1 CRMS o in o in o II D I D ID I D D D =+ - = - = - due to capacitive impedance Consider the ON interval o oS o V T V C D D= t EEE 498/591 – Raja Ayyanar
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472 Lecture 6 buck boost cuk - Lecture 6 Buck boost and Cuk...

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