Wu Zhaohui

A two-dimensional flow sensor using integrated silicon spreading-resistance temperature detectors

A simple silicon two-dimensional (2D) flow sensor for the measurement of both flow direction and speed is described. By integrating two couples of silicon spreading-resistance temperature (SRT) sensors in two perpendicular directions on the surface of a silicon chip, this sensor can detect flow speed and flow direction φ in a full range of 360°. Experimental results confirm theoretical analysis that the output of the sensor increases with the square root of the flow velocity, and the outputs in the two perpendicular directions are proportional to sin φ and cos φ, respectively. The effects of sensor layout are also discussed. With complete oxide isolation for the SRT sensors, the flow sensor could achieve higher sensitivity by operating above the intrinsic temperature of silicon (∼150 °C), or could be used to detect fluid flow at a temperature as high as 300 °C.

Design of a novel AC LED driver with no current glitch based on soft switching operation

In this paper, a novel design on AC LED driver with no current glitch for multiple-string LEDs is presented. The LED driver can run LEDs directly from a pulsating voltage obtained by rectifying an AC voltage without any other AC-DC converter. In order to avoid current glitch due to hard switching operation, negative feedback control is used and the driver operates on a soft switching mode. Without AC-DC converter and complicated control circuit, the driving system is suitable for integration and the driver can be designed on a simple chip. Simulation results show that the lifespan is prolonged, and the quality of lighting and the efficiency of the system are improved because of no more current glitch. The proposed AC LED driver was fabricated in 1 um SPDM 5V40V700V BCD process. The measured results show that the efficiency is about 91% and the power factor is 98.5% under 3.3W 220V∼50Hz condition.