A Highly-Integrated 20-300V 0.5W Active-Clamp Flyback DCDC Converter with 76.7% Peak Efficiency

Abstract

There is a growing need for compact and energy efficient high-voltage (HV) DCDC converters with input voltages >100V for low-power applications up to 500mW. This includes loT and smart-home, supplied from the ac mains, as well as auxiliary supplies for power converters in electrical vehicles and in the field of renewable energy that operate from HV DC-link. Discrete state-of-the-art power supplies are not efficient at light loads below 500mW and are relatively large in size, Fig. 1. They typically use a passive-clamp flyback (PCF) topology (Fig. 1 bottom right) with large external components, such as power switches (Q <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</inf> ), HV capacitors <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(Cc)$</tex> , the output diode <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{D}_{\text{out}}$</tex> , and a transformer <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\top$</tex> with up to several millihenries of inductance. The passive clamp topology also suffers from losses due to the leakage inductance <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$L_{\text{lk}}$</tex> and the hard switching of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{Q}_{\mathrm{M}}$</tex> . Non-isolated HV DCDC converters with dedicated power topologies [1] achieve good power densities but are not suitable for applications that require galvanic HV isolation. Active clamp flyback (ACF) converters (Fig. 1 bottom left) allow for galvanic isolation while keeping switching losses low. However, ACF designs [2], [3] are usually optimized for high output power and still require large external components. Further, their complex control limits the light-load efficiency. This paper presents a low-power-optimized ACF IC that benefits from integration in a 180nm HV SOI technology. It offers a fully integrated power stage and provides a robust and time-precise control at faster switching speed and more compact size. This way, high light-load efficiency and good power density are achieved.