A 6.78 MHz resonant wireless power transfer (WPT) system with a 5 W fully integrated power receiver is presented. A conventional low-dropout (LDO) linear regulator supplies power for operating the ...circuit in the power receiver. However, as the required operating current increases, the power consumption of the LDO regulator increases, which degrades the power efficiency. In order to increase the power efficiency of the receiver, this work proposes a power supply switching circuit (PSSC). When operation starts, the PSSC changes the power source from the low-efficiency LDO regulator to the high-efficiency step-down DC-DC converter. The LDO regulator operates only for initialization. This chip has been fabricated using 0.18 μm high-voltage bipolar- CMOS-DMOS (double-diffused metal-oxide-semiconductor) (BCD) technology with a die area of 2.5 mm x 2.5 mm. A maximum power transfer efficiency of 81% is measured.
This paper presents an analysis of magnetic resonance coupling effects that can be considered for realizing a wireless power transfer (WPT) system. In this study, numerical analysis is applied to ...investigate the power transfer characteristics affected by coil inductance and placement. The simulations and experiments, using various coils and positions, are conducted to find the optimum power transfer condition. The experiment shows that the frequency bandwidth of the wireless power transfer at the optimum coupling condition is enlarged to 0.73 MHz and the transfer efficiency is maintained at over 80%.
This paper presents a wireless power transfer system for mobile devices. To achieve high efficiency in the receiver circuit, an optimal switching frequency is required. Through experimental analysis, ...we suggest the optimal efficiency of a receiver circuit. The switching frequency of this receiver circuit can vary from 500 kHz to 13.56 MHz. The received power has a range of 0 to 5 W, and it has a maximum efficiency of 81%. This circuit was fabricated with a 0.18 μm BCD process, and it occupies an area of 2.5 mm × 2.5 mm.
A shunt-series mixed resonant coupled structure for the wireless power transfer (WPT) applications is proposed. If the coils are designed to have proper inductance values, the power transfer ...efficiency depending on distance has proportional relation only to the shunt capacitors. It enables that the proposed structure facilitates tracking the maximum WPT efficiency according to distance. In the experiment, two pairs of resonant square coils on PCB with different turn ratio (5/10 turn) are compared for 6.78 MHz operation. Both coils have almost same maximum WPT efficiency by optimizing the series and shunt capacitors. But the 10-turn coil only demonstrates aforementioned relation. The proposed structure with 10-turn coil shows that the efficiency of 77.7 % is achieved at a distance of 30 mm.
In this study, simulations and experiments on wireless power transfer (WPT) in a multi-coil environment are conducted under the conditions of multiple battery charging. A series-arrayed 4-coil system ...comprising one WPT system and three identical WPT systems placed in parallel are investigated in this work. We show that low-frequency wireless power transfer is affected by multiple coils placed in parallel within a confined area. The power transfer efficiency at low frequencies can be degraded by 20% as compared to that of a single WPT system.
Through various cases of inverter layout, the change in the propagation delay time (tPD) in the ring oscillator that consists of inverters can be analyzed. In this paper, an inverter layout technique ...for tPD minimization is presented. Through the case-by-case layout, to reduce the tPD, we propose that layout engineers should reduce the input and output node length. The proposed technique post-simulated in a 0.18um CMOS process achieves maximum 7.318% reduced tPD compared to the basic inverter layout.
A wide locking-range frequency divider with programmable input sensitivity is presented in this paper. The frequency divider consists of two D flip-flop-based current mode logic latches and a current ...control circuit. The current control circuit adjusts the current ratio of the sampling pair and the latching pair, while the total current is maintained as a constant. The current control circuit enables the self-oscillation frequency to be adapted to the input frequency. As a result, the divider has wide locking range below -10 dBm input level. The proposed frequency divider is implemented in 0.18 um standard CMOS technology, and the measurement results show a 169% frequency locking range of between 0.5 and 6 GHz at an input power of - 10 dBm while consuming 7.2 mW from a 1.8 V supply voltage.
This study presents the design and implementation of a 6.78 MHz wireless power transfer (WPT) system that uses magnetically coupled resonance for 5 W mobile phone charger applications. For a resonant ...WPT system, one of the most significant design issues is the power receiver because of its resonant characteristics. A compact resonant-type power receiver is required for high efficiency and robustness. To realise a compact size, a fully integrated 5 W power receiver that includes an on-chip AC-DC converter and a DC-DC converter is implemented. A protection circuit that operates only during initial power-up is proposed to protect the power switches in the receiver. The proposed receiver was implemented using a 0.18 mu m bipolar-complementary metal-oxide-semiconductor-double-diffused metal-oxide-semiconductor process with a die area of 3.5 mmx3.5 mm. The measured maximum power transfer efficiency of the receiver and peak efficiency of the system was 81 and 51%, respectively.
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