Browsing by Author "Lee, Ming-Wei"

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A Battery-Free 217 nW Static Control Power Buck Converter for Wireless RF Energy Harvesting With alpha-Calibrated Dynamic On/Off Time and Adaptive Phase Lead Control
(2012-04-01)
Huang, Tzu-Chi
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Hsieh, Chun-Yu
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Yang, Yao-Yi
;
Lee, Yu-Huei
;
Kang, Yu-Chai
Abattery-free nano-power buck converter with a proposed dynamic on/off time (DOOT) control can achieve high conversion efficiency over a wide load range. The DOOT control can predict the on/off time at different input voltages without a power consuming zero current detection (ZCD) circuit, as well as suppress static power in idle periods. To adapt to the fluctuations in a harvesting system, the proposed alpha-calibration scheme guarantees accurate ZCD over process, voltage variation, and temperature (PVT) in the DOOT to improve power conversion efficiency. Furthermore, the adaptive phase lead (APL) mechanism can improve inherent propagation delay attributable to low-power and non-ideal comparator, thus improving load regulation by a maximum of 30 mV. The test chip was implemented in 0.25-mu m CMOS process with a die area of 0.39 mm(2). Experimental results showed 95% peak efficiency, low static power of 217 nW and good load regulation of 0.1 mV/mA, which are suitable for RF energy harvesting applications.
Automatic Power Monitor (APM) in Switching Charger with Smooth Transition Loop Selector (STLS) for High-energy Throughput System
(2012)
Tsai, Tsu-Wei
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Peng, Ruei-Hong
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Su, Yi-Ping
;
Chen, Ya-Ping
;
Chen, Ke-Horng
This paper proposed a switch-based charger system instead of LDO-based charger for Li-Ion batteries. The automatic power monitor (APM) controls three main power delivery paths to generate five different charging cases. Moreover, with the proposed smooth transition loop selector (STLS), the charging process can transfer smoothly and never oscillate between two consecutive stages. Furthermore, the STLS can bear different batteries with wide built-in resistance variation by adjusting charging factors. The stability analysis proves that the stability of APM loop is guaranteed by only one Type-III compensator. The simulation results ensure the performance of the system controlled by APM even if the power source is unable to provide sufficient power.
Characterizing the interfacial shear strength of graphite/epoxy composites containing functionalized graphene
(2016-08-01)
Lee, Ming-Wei
;
Wang, Tai-Yuan
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Tsai, Jia-Lin
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機械工程學系
;
Department of Mechanical Engineering
This study investigated the interfacial shear strength (IFSS) of graphite/epoxy composites containing functionalized graphene. Epoxy resin together with pristine graphene and functionalized graphene were employed as a matrix in the fiber composites, with graphene loadings in the epoxy matrix of 0.1, 0.3, and 0.5 wt%. The functional groups grafted on the functionalized graphene were characterized through Fourier transform infrared spectra and X-ray photoelectron spectroscopy. The IFSS of the fiber composites were evaluated through microdroplet testing, and the corresponding failure mechanism was examined using scanning electrical microscopy. The experimental results indicated that the IFSS increased with the graphene loadings in the matrix. Furthermore, both functionalized graphene and pristine graphene provided a similar IFSS in the fiber composites. Observation of the failure interface showed that the failure mechanism of the IFSS was dominated by interfacial failure between the fiber and matrix in conjunction with adhesive failure in the matrix. Introducing graphene in the matrix can enhance IFSS by improving the adhesive strength in the interface as well as complicating the crack extension in the matrix. (C) 2016 Elsevier Ltd. All rights reserved.
Mechanical properties of nanocomposites with functionalized graphene
(2016-11)
Lee, Ming-Wei
;
Wang, Tai-Yuan
;
Tsai, Jia-Lin
;
機械工程學系
;
Department of Mechanical Engineering
The research investigated the thermal and mechanical properties of graphene/epoxy nanocomposites. Pristine graphene and functionalized graphene were used as nano-reinforcement in the nanocomposites. The graphene loadings employed in the nanocomposites were 0.1, 0.3, 0.5, and 1.0wt%. The functional groups grafted on the functionalized graphene were characterized through Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). Results indicated that two kinds of functional groups are grafted on the functionalized graphene surfaces: one contains only COOH group and the other contains both COOH and NH2 groups. Moreover, from mechanical and thermal testing, it was found that the nanocomposites with functionalized graphene demonstrate better mechanical and thermal properties than those with pristine graphene. The graphene containing NH2 and COOH functional groups exhibits superior mechanical and thermal properties than the graphene with only COOH functional group. In addition, Young\'s modulus and thermal conductivity of the nanocomposites increase as the graphene loading increases. However, the fracture toughness and tensile strength of the nanocomposites attain peak values when the functionalized graphene loading is 0.1wt%. The effects of the functional groups on the mechanical and thermal properties of nanocomposites were elaborated using molecular dynamics (MD) simulation. It was revealed that the interfacial thermal conductance and normalized interaction energy increase between the functionalized graphene and epoxy matrix, which may be responsible for the enhanced mechanical properties in the functionalized graphene/epoxy nanocomposites.
Reduction of Equivalent Series Inductor Effect in Delay-Ripple Reshaped Constant On-Time Control for Buck Converter with Multi-layer Ceramic Capacitors
(2012)
Chen, Wei-Chung
;
Kang, Yu-Chi
;
Lin, Chia-Ching
;
Chen, Ke-Horng
;
Wang, Shih-Ming
The time constant, which is the product of the output capacitor and its equivalent series resistance (ESR), limits the stability of conventional constant on-time control buck converter. To meet the expected requirements, SP-CAP is mostly used as output capacitor although it deteriorates the performance of converter. On the other hand, the multi-layer ceramic capacitors (MLCC) features low cost and small equivalent series resistance (ESR) and is widely used in commercial power management ICs. However, the stability often suffers from the sub-harmonic problem due to small time constant. This paper proposes a differential-zero compensator with the noise margin enhancement (DZC-NME) technique in constant on-time control buck DC-DC converter with ceramic output capacitor. The proposed DZC-NME technique not only eliminates the limit of large time constant but also tolerates the existence of equivalent series inductor (ESL) effect. Simulation result demonstrates the function and shows smaller output ripple of 10mV and high efficiency of 91 % with ESR which smaller than 1m Omega.
Variable Sampling Slope (VSS) and No-Deadtime Ramp Generator (NDRG) Techniques for Closed-Loop Interleaving Power Factor Correction (PFC) Design with Suppression of Current Mismatch
(2012)
Chen, Chun-Yen
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Peng, Ruei Hong
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Tsai, Jen-Chieh
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Kang, Yu-Chi
;
Ni, Chia-Lung
the proposed interleaving power factor correction (PFC) can effectively reduce the size of the AC-DC converter for portable electronics. Fully integrated variable sampling slope (VSS) technique can provide precise phase regulation under variable line voltage. Besides, the no-deadtime ramp generator (NDRG) records the previous status to modify the sequent on-time value to achieve current sharing for suppressing the total harmonic distortion (THD) and restraining the input current ripple, EMI filter, and the size of input inductor. Therefore, more power can be provided by the proposed interleaving PFC than that of single-phase PFC. Simultaneously, the drawback of the peak current twice than the average current in the Boundary control mode (BCM) can be greatly reduced. The test circuit fabricated in the TSMC 0.5 mu m 800V UHV process shows the highly integrated interleaving PFC can deliver high power of 180W with improved phase regulation precision.