An 81.0% Peak Efficiency, 1.0W/cm³ Miniaturized 5V/1A AC-DC Converter Using a Highly-Integrated Primary-Side Active Clamp Flyback Controller with Adaptive Frequency and Zero-Voltage Switching

This paper seeks to reduce the physical size of 5W isolated AC-DC converters, which is increasingly important for smart building and internet of things applications that require small devices integrated with wired power. Prior works on primary-side regulation (PSR) flyback converters [1]–[3] (Fig. 1) eliminate signal isolation blocks to increase power density at 5V/1A, shrinking the converter in [1] to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$17.496\text{cm}^{3}$</tex> with a peak efficiency of 78.2%. However, PSR converters require lower frequency and larger magnetizing inductance <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\mu \mathrm{m})$</tex> in the trans-former <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(&gt; 700\mu \mathrm{H})$</tex> due to switching loss. A flyback with secondary-side regulation (SSR) achieved zero-voltage switching (ZVS) with a volume of 48 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$6\text{cm}^{3}$</tex> for 60 W with a smaller <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$210\mu \text{HL}_{\mathrm{m}}$</tex> (Fig. 1) [4]. Further reduction in the transformer size requires a higher switching frequency, but the efficiency of the SSR is limited by leakage inductance <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\mathrm{L}_{1\mathrm{k}})$</tex> and switching frequency [5]. Active clamp flyback (ACF) systems (Fig. 1) [6], [7] enable up to 220kHz operation with full system using ZVS by reusing the energy in the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{L}_{1\mathrm{k}}$</tex>. Most prior ACF systems target higher output power (>30W) and have larger volume (e.g., 24.32cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> [6]). In addition, compared to the SSR, extra components are required for ACF switching operation [4]. There remains a need for 5V/1 A ACF converters with smaller volume from reducing the transformer size and suppressing the number of components.