A Zero-Voltage-Switching Buck Converter with Conduction-Loss-Minimized ZVS Operation and Auxiliary Inductor Transient Reuse Technique Achieving up to 8.3% Efficiency Improvement and 42% Voltage Droop Reduction

Buck converters using zero-voltage switching (ZVS) techniques are widely used to reduce the significant turn-on V-I overlap loss associated with high-voltage (HV) power switches. The primary challenge in ZVS techniques lies in constructing an efficient current path to charge the switching node with minimal additional components and extra loss. Approaches like using negative inductor current from the buck topology [1]–[2] or adding a small resonant branch parallel to it [3] can achieve ZVS, but they lead to large inductor current ripples or continuous resonant inductor current, causing significant conduction losses under heavy loads. To address these losses, various approaches utilizing auxiliary discontinuous inductor currents have been proposed [4]–[8]. In [4]–[5], auxiliary inductors energized by V<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OUT</inf> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$2/3 V_{\text{OUT}}$</tex> gradually introduce current into the main path until it exceeds the load current <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\mathrm{I}_{0})$</tex> and charges the switching node, leading to significant losses at low output voltages and heavy loads. An auxiliary inductor energized by VIN <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\mathrm{V}_{1\mathrm{N}_{-}\text{MAX}}=20\mathrm{V}$</tex> in [6] enables faster charging but creates reliability concerns due to high di/dt current pulses at higher input voltages, requiring large <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mu \mathrm{H}$</tex> -level inductors solely for ZVS, which is inefficient. To balance reliability and cost, reducing the voltage across the auxiliary inductor allows the use of a smaller inductor for ZVS without reliability issues. This is shown in [7]–[8], where an auxiliary capacitor energizes a 30nH auxiliary inductor [8]. However, it remains uncertain whether the conduction loss introduced by the ZVS branch is fully optimized. On the other hand, the limited slew rate of the main inductor current <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\mathrm{I}_{\mathrm{L}})$</tex> continues to pose a challenge in improving the load transient response of hundred-kHz ZVS buck converters, while using an auxiliary inductor solely for ZVS operation seems inefficient and wasteful.