Browsing by Author "Chen, Shih-Min"

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Challenge on compact size DC-DC buck converters with high-speed current sensor and on-chip inductors
(2007)
Chen, Shih-Min
;
Hsieh, Chun-Yu
;
Chen, Ke-Horng
;
電控工程研究所
;
Institute of Electrical and Control Engineering
This paper proposes a compact size DC-DC buck converter toward on-chip inductors and minimized external components. Multi-phase, high switching frequency and pseudo continuous conduction mode (PCCM) techniques [1] achieve the possibility to implement on-chip inductors. The effective inductance is about 20nH. Due to high switching frequency above 20MHz, it is a challenge to have a highly accurate current sense for high performance of converters. Simulation results demonstrate that the accuracy of high-speed current sensor is about 95%. Besides, mode switch between pulse width modulation (PWM) and pulse frequency modulation (PFM) alleviates the limitation of high-speed current sensor in case of light load condition. Compact size design of converter is an advanced technique as a power module for system-on-chip (SOC) designs.
Hardening steels by the generation of transient phase using additive manufacturing
(2019-06-01)
Huang, E-Wen
;
Lee, Soo Yeol
;
Jain, Jayant
;
Tong, Yang
;
An, Ke
In the present work, the tensile properties of 15-5 PH steel fabricated by selective laser melting (SLM) were examined with respect to the transient austenite phase. Compared with the 8%-transient-phase sample, the 18%-transient-phase one shows higher ultimate tensile strength and relatively low yield strength, as well as hardening behavior. We conducted in-situ neutron-diffraction study to examine the microstructure evolution for mechanistic understanding. After applying the external load, most non-equilibrium, retained austenite in the 8% transient-phase sample transforms before the yield strength, whereas in the 18%-transient-phase sample only 50% of the austenite transforms. Accompanying with the phase transformation, a decrease in the dislocation density and the dislocation strain energy-assisted phase transformation of the ferrite phase are found in the 8%-transient-phase sample even before yielding, which, however, is not the case in the 18%-transient-phase sample. The study demonstrates the SLM enables tuning the amount of transient-phase ratio and coherency between phases to realize a mechanical property control for additive manufactured steel.