This article presents a 48–1 V merged-two-stage hybrid-switched-capacitor converter with a linear extendable group operated point-of-load (LEGO-PoL) architecture for ultrahigh-current microprocessors, featuring 3-D stacked packaging and coupled inductors for miniaturized size, fast speed, and vertical power delivery. The architecture is highly modular and scalable. The switched-capacitor circuits are connected in series on the input side to split the high input voltage into multiple stacked voltage domains. The multiphase buck circuits are connected in parallel to distribute the high output current into multiple parallel current paths. It leverages the advantages of switched-capacitor circuits and multiphase buck circuits to achieve soft charging, current sharing, and voltage balancing. The inductors of the multiphase buck converters are used as current sources to soft-charge and soft-switch the switched-capacitor circuits, and the switched-capacitor circuits are utilized to ensure current sharing among the multiphase buck circuits. A 780-A vertical stacked CPU voltage regulator with a peak efficiency of 91.1% and a full load efficiency of 79.2% at an output voltage of 1 V with liquid cooling is built and tested. The switched capacitor circuits operate at 286 kHz and the buck circuits operate at 1 MHz. It regulates output voltage between 0.8 and 1.5 V through the entire 780-A current range. This is the first demonstration of a 48–1 V CPU voltage regulator to achieve over 1-A/mm $^\text{2}$ current density and the first to achieve 1000-W/in $^3$ power density.

This article presents the design and optimization of a miniaturized 48-V-to-1-V, 240-A linear-extendable group operated point-of-load (LEGO-PoL) CPU voltage regulator module (VRM)— Mini-LEGO —with a volume of 30 mm×11.2 mm × 8.4 mm. The Mini-LEGO converter provides vertical power delivery, and it achieves a peak efficiency of 87.1%, a full load efficiency of 84.1%, and a power density of 1390 W/in $^{3}$ when stepping down a 48 V input voltage to an output voltage of 1 V. The Mini-LEGO offers compact device implementation, simple gate drive circuitry, and a fast regulation-stage switching frequency of 1.5 MHz. The 9-mm-by-9-mm, 4-phase, 20-A-per-phase vertical coupled inductor has a per-phase transient inductance of 10.3 nH, with its coupling reducing the ripple by a factor of six, and a height of 2.5 mm. This vertical coupled inductor structure is designed following a systematic approach to minimizing its height while achieving significant current ripple reduction and maintaining sufficient saturation margin. Thermal simulations are performed to verify the cooling feasibility. A measurement characterization method for vertical coupled inductor structures is introduced and used to characterize the designed vertical coupled inductor.

In this paper, a new single-stage half-bridge (HB) resonant LLC converter additionally employing one resonant capacitor and two relays with one package is proposed, compared with a single-stage HB LLC converter. Moreover, a center-tapped transformer is replaced with a coupled transformer. Since the proposed converter changes the turns-ratio of the coupled transformer using two relays according to low or high input voltage range, it can decrease the range of its needed voltage gain. It means that the proposed converter can be designed with large transformer magnetizing inductance compared with the conventional single-stage HB LLC converter. As a result, the primary conduction and turn-off losses are reduced. Moreover, in low input voltage range, it has smaller total primary wire resistance of the transformer due to parallel connection of the coupled transformer, which decreases its conduction loss. In addition, additionally employed small-sized components can be inserted to the conventional system. To confirm the operation, features, and validity of the proposed converter, universal input with low line (90Vac~132Vac) and high line (180Vac~264Vac) and 16.5V/60W output laboratory prototype targeting laptop adapters with wide-input-voltage range is built and tested.

A new synchronous rectifier (SR) control method is proposed to improve the light-load regulation capability of high-frequency LLC resonant converter. The proposed control method applies the extended SR turn-on time, which results in the negative current flowing through SRs, and the light-load regulation of the LLC resonant converter can be achieved by the negative current. The design guideline of the extended SR turn-on time is presented based on the precise analysis and the equivalent circuit modeling of the LLC resonant converter. In addition, the switching loss and gate driving loss can be reduced because the output voltage can be regulated at low switching frequency. The validity of a proposed control method is confirmed by the experimental results of a prototype converter with 330-380 VDC input and 750 W (12 V/62.5 A) output.

In the standby stage of a server power supply, the flyback converter has been widely used due to its simple structure and low cost. However, since the flyback converter suffers from high voltage stress and a large transformer, it degrades the efficiency and power density of the server power supply. To relieve these drawbacks, this paper proposes a new standby structure where a flyback converter is integrated with a boost PFC converter. The proposed standby structure can relieve the high voltage stress and eliminate the large transformer of the conventional flyback converter because the primary side of the flyback converter is merged with the boost PFC converter. Thus, the proposed structure can achieve high efficiency and high power density in the standby stage. Furthermore, it can help the boost PFC converter achieve a soft switching operation, which results in a high-efficiency PFC stage. As a result, the proposed structure improves the overall efficiency and power density of the server power supply. The validity of the proposed structure is confirmed by a prototype with $100-240V_{rms}$ AC input, 750W PFC output, and 12V/2A standby output.