31.10 A Fully integrated 500V, 6.25MHz GaN-IC for Totem-Pole PFC Off-Line Power Conversion

Grid-powered devices such as desktop computers, displays and TVs, industrial power supplies, and 5G infrastructure are experiencing an increasing demand for higher power efficiency and density. Despite the moderate power levels (below 100W), these devices collectively consume over 10 TWh annually. High energy efficiency is key to reducing global energy usage. Flatter screens and smaller desktop computers call for more compact power interfaces. Both goals favor GaN technology due to its low-loss high-frequency switching capability. For grid-powered applications, a power-factor correction (PFC) stage minimizes the reactive power and regulates the $120 / 230 \mathrm{~V}$ AC line voltage to a DC voltage $V_{\mathrm{HV}}=200 / 400 \mathrm{~V}$, as shown in Fig. 31.10.1 (top). A subsequent DC/DC converter converts $V_{\mathrm{HV}}$ to typically 12 to $48 \mathrm{~V}$. Conventional PFC converters use a boost stage combined with a full-bridge rectifier, illustrated in Fig. 31.10.1 (middle left). Such a topology shows limited efficiency with several diodes in the power path [1]. The bridgeless totem-pole PFC converter (TPPFC), Fig. 31.10.1 (middle right), replaces the diodes with transistors significantly reducing losses. Transistors $M_{R H}$ and $M_{R L}$ are switched in sync with the line frequency of $50 / 60 \mathrm{~Hz}$, acting as a rectifier for the $A C$ input. Due to the low switching frequency, they can be implemented using any transistor type with low on-state resistance. During the positive line cycle (Fig. 31.10.1 middle right), $\mathrm{M}_{\mathrm{L}}$ acts as the active switch to energize the inductor L during the duty cycle $D . \mathrm{M}_{\mathrm{H}}$ is the synchronous rectifier guiding the current to the output during the freewheeling phase (1-D). When the line voltage changes polarity, $M_{L}$ and $M_{H}$ exchange roles. Favorable for lower output powers, the presented TPPFC employs DCM regulation [1]. GaN-FETs, inherently free of a body diode structure (see cross-section in Fig. 31.10.2), are ideal for efficient hard-switching of $M_{H}$ and $M_{L}$ in the TPPFC, where use of silicon transistors is not feasible due to reverse-recovery charge related losses.