A 4–40 V Input Floating–Ground GaN-Based Buck–Boost Converter With Pre-Charge Function for Enhanced Power Efficiency

Many applications including automotives demand DC-DC power converters that can cover wide input range with improved power efficiency. This paper presents a 4–40 V input, Gallium Nitride (GaN) based non–inverting buck–boost converter incorporating several methods to improve power efficiency. It employs a new floating–ground three-state four-switch topology along with a pre–charge gate driver for the low–side GaN switch, a Dual Duty–Cycle Controller (DDCC) and an Inductor Peak Current (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_LPEAK</i>) adjusting Module (IPCM). The floating–ground technique alleviates the voltage stress on the high–side power switch and minimizes the inductor current ripple Δ<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_L</i>, resulting in reduction of both switching power loss and conduction power loss. Additionally, the floating-ground topology together with a pre–charge gate driver for the GaN switch achieves a precise pre–charging time duration, preventing reverse conduction during the switch dead time. Consequently, the converter optimizes the power efficiency especially in the buck–boost mode (for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V_IN</i> of 10–14 V in design). The DDCC determines precise duration of each state for the three–state operation and maintain seamless transition across different modes. The ICPM enables adjusting <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_LPEAK</i> through indirectly sensing <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_L</i> and the output voltage <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V_OUT</i> followed by the DDCC. With the proposed techniques, the reverse conduction of the low-side switch is minimized, and a 2% peak efficiency improvement is achieved in the buck–boost mode. Operating at 2 MHz covering 4–40 V input to a 24W (12 V and 2 A) output, this buck-boost converter achieves a peak efficiency of 92%.