A 2-5MHz Multiple DC Output Hybrid Boost Converter with Scalable CR Boosting Scheme Achievi 1 ng 91% Efficie 1 ncy at a Conversion Ratio of 12
Chen Chen, Jin Liu, Hoi Lee
Abstract
High conversion-ratio (CR) DC-DC boost converters are essential for LED backlighting in smartphone and tablet displays. For realizing a high CR, a conventional boost (CB) converter [1] shown in Fig. 18.7.1 would use a large duty ratio D and thus have short on-time of power switch <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{S}_{2}$</tex> . This not only limits the converter switching frequency <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{f}_{\text{SW}}$</tex> but also results in a large inductor current ripple <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\Delta \mathrm{i}_{\mathrm{L}}$</tex> . As high CR also leads to a large average inductor current <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{I}_{\llcorner}$</tex> under a given output current <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{I}_{0}$</tex> , the power efficiency of the CB converter would be significantly degraded due to enlarged inductor conduction loss with large <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\Delta \mathrm{i}_{\mathrm{L}}$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{I}_{\llcorner}$</tex> . Hybrid boost converters are recently reported. Both converters in [2], [3] add a capacitor path in parallel with the inductor to reduce the inductor current stress, while a two-phase converter in [4] doubles its switching pulse width and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{f}_{\text{SW}}$</tex> through 2-phase operation with 2 inductors. However, compared with the CB converter, their improvements in CR are limited within 2 times. Moreover, output-voltage-rated power transistors that have larger on-resistance and parasitic capacitance are required in prior hybrid boost converters [2]–[4], resulting in higher power losses and inferior performances in high frequencies.