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A Novel AC-to-DC Adaptor with Ultra-High Power Density and Efficiency

Fig. 1. The proposed adaptor circuit.
In recent years, the world's engineers and researchers have moved the power industry forward significantly by paying more attention to developing ac-to-dc adaptors with a higher power density and efficiency. However, consumers are never satisfied and always expect to have a more compact, smaller size, and higher efficiency ac-to-dc adaptor. This paper, therefore focuses on further enhancing power density and efficiency. In order to greatly heighten the power density and efficiency, this paper proposes a two-stage topology composed of a bridgeless boost converter followed by a LLC converter, which is shown in Fig. 1.

The bridgeless boost converter converts the time-varying line voltage to a stable dc bus voltage, VBUS, and deposits the energy on the bulk dc bus capacitor, CBUS, while it also regulates both the dc bus and output voltage, VO. Moreover, by applying a harmonics injection control on a bridge-less boost converter can further reduce the required bus capacitance, while the power density can be enhanced accordingly. On the other hand, the LLC converter is operated as a dc transformer (DCX) to step-down VBUS to the desired VO, while it also provides the electrical isolation in order to comply with the safety regulation. In this way, both the high power density and high efficiency can be achieved.

The prototype is shown in Fig. 2, the dimension is 1.47 in3 (6636.510 mm3). The primary GaN devices are PGA26E19BV from Panasonics Inc for both the bridgeless boost converter and the LLC DCX. The line frequency devices of the bridgeless boost converter are STL57N65M5, and the secondary-side SR devices are EPC2023. By increasing the switching frequency above MHz with the GaN devices, the transformer, EMI filter and output filter size are significantly reduced, while about 44.22W/in3 (exclude case) power density can be achieved. On the other hand, the total efficiency of the proposed ac-to-dc adaptor circuit is about 94%. Fig. 3 shows a comparison of the state-of-art adapters and the proposed solution; it can be observed that both efficiency and power density are significantly improved.

Fig. 2. The prototype of 65W ac-to-dc adapter.
Fig. 3. Comparison of state-of-art adapters and the proposed solution.