Won-Sup Chung

Triangular/square-wave generator with independently controllable frequency and amplitude

A triangular/square-wave generator with current-controllable frequency and amplitude is presented. The generator utilizes operational transconductance amplifiers as switching elements. A prototype circuit built with commercially available components exhibits less than 2% nonlinearity in its current-to-frequency transfer characteristic from 1 to 10 kHz and -150 ppm//spl deg/C temperature coefficient of frequency over 15/spl deg/C to 35/spl deg/C. The circuit also displays wide sweep capability and good linearity of current to amplitude. The application of the circuit to a current-controllable saw-tooth waveform generator is also presented.

A self-driven active clamp forward converter using the auxiliary winding of the power transformer

This study proposes a new self-driven active clamp forward converter eliminating the extra drive circuit for the active clamp switch. The converter used the auxiliary winding of the power transformer to drive the active clamp switch and a simple RC circuit to get the dead time between the two switches. The operation principle was presented and experimental results were used to verify theoretical predictions. A 100-W (5 V/20 A) prototype converter that only exhibited 1.5-turn winding number in the auxiliary winding was sufficient to drive the active clamp switch on the input of 50 V. Finally, the measured efficiency of the converter was presented and the maximum efficiency of 91% was obtained.

Pulsewidth Modulation Circuits Using CMOS OTAs

This paper presents three pulsewidth modulation modulators using CMOS operational transconductance amplifiers. They consist of a ramp integrator and current-tunable Schmitt triggers. Prototype circuits built using discrete components exhibited that their duty cycles are linearly controllable. Because of their simple structure, the proposed modulators can be easily fabricated in a monolithic integrated circuit.

Current-controllable monostable multivibrator using OTAs

A monostable multivibrator with current-controllable pulse width and height is presented. The circuit utilizes three operational transconductance amplifiers (OTAs) as switching elements. Two of them compose a Schmitt trigger and the other forms an integrator. The theory of operation is presented and experimental results are used to verify theoretical predictions. A prototype circuit built with commercially available components exhibits less than 4.4% nonlinearity in its current-to-pulse width transfer characteristic from 200 to 1600 /spl mu/s and 20 ppm//spl deg/C temperature coefficient of width over 0/spl deg/C to 75/spl deg/C. The circuit also displays good linearity of current-to-pulse height and 1200 ppm//spl deg/C temperature coefficient of height.

A Resistance Deviation-to-Pulsewidth Converter for Resistive Sensors

A resistance deviation-to-pulsewidth converter is presented for interfacing resistive sensors. It consists of a ramp integrator, two resistance-tunable Schmitt triggers, and two logic gates. A prototype circuit built using discrete components exhibits a resolution as high as 14 bits and a linearity error less than plusmn0.06% when the output pulse is counted by a 10-MHz clock signal. The proposed circuit is applied to measure the temperature difference with the platinum resistance temperature detectors. The measured conversion sensitivity of the temperature difference-to-pulsewidth converter is 5.74 mus/degC, and its linearity error is less than plusmn1% in the temperature difference range of 0degC to 100degC.

A temperature difference-to-frequency converter using resistance temperature detectors

A novel temperature difference-to-frequency (TD/F) converter using two platinum resistance temperature detectors (RTDs) has been developed. The resistance difference of two RTDs is converted into a DC current to control the simulated inductor, which is designed so that its inductance is inversely proportional to the square of the current. The simulated inductor forms the resonant circuit of a Colpitts oscillator and hence the oscillation frequency becomes directly proportional to the resistance difference. A conversion sensitivity of 16 Hz/ degrees C and a residual nonlinearity of less than 2% over the temperature difference range of 35 degrees C to 155 degrees C are obtained by the prototype converter which oscillates at 667 Hz at a 51 degrees C temperature difference. The minimum detectable temperature difference is estimated to be +or-0.013 degrees C. The power dissipations in the RTDs are about 2 mu W. The proposed converter, except for the RTDs, can be fabricated in a monolithic IC form by scaling the component values. >

A linear operational transconductance amplifier for instrumentation applications

A linear operational transconductance amplifier (OTA) is described that consists of a linear transconductor and a translinear current gain cell followed by three current mirrors. The proposed circuit has superior linearity and temperature characteristic when compared with the commercially available OTA. A prototype circuit with a transconductance of 50 mu S has been built with discrete bipolar transistors producing a linearity error of less than +or-20% over an input voltage range from -0.8 to 0.8 V. The prototype OTA circuit also exhibits a transconductance that is linearly dependent on a bias current varying over four decades with a sensitivity of 1 S/A. >

A Color Temperature and Illuminance Controllable LED Lighting System

This paper presents an LED lighting system with an LED color control algorithm that can independently change its color temperature and illuminance. To show the validity of the proposed algorithm, it is proven that its solution always exists. The proposed algorithm was applied to the control of an LED module that is composed of red, green, blue, and white (RGBW) LEDs. Its color temperature variation ranged from 3,500~7,500[], and its illuminance ranges from 500~1,500[lux]. Within these range, the color temperature and illuminance deviations are as low as [%] when the junction temperature of LEDs are maintained at 40[]. In the range of 30~70[], the measured illuminance and color temperature deviations are as low as 2.1[%] and 3.6[%], and the compensated ones are as low as 1[%] and 0.49[%], when the desired illuminance and color temperature are 1,000[lux] and 6,500[], respectively.nyang.ac.kr).

Experimental Identification Method for Small-Signal Analysis of Smart Power ICs

Smart power integrated circuits (ICs), as the combination of control and power functions on a single chip, enable the production of more miniaturized systems. This paper presents an experimental method for the small-signal frequency-response analysis of smart power ICs in switch-mode power supplies. In this method, the switching-duty-cycle output of a power IC is converted into a digital signal by using two high-speed counters during each switching period, and the power ICs control input signal is simultaneously converted into a digital signal by an analog-to-digital converter. After processing the data of the duty-cycle output and the control input, not only the transient response but also the frequency response of the power IC can be obtained. Using least square identification, the smart power ICs transfer function is finally synthesized from the measurement data. This analysis method, referred to as sampling the transient responses and frequency responses of power ICs, can efficiently provide reliable and accurate transfer functions whether the switching frequency of a power IC is jittered or frequency modulated. The experiments using different power ICs were presented herein to validate the analysis method. The results were discussed, and the effectiveness and practicality of the method were verified.

A bridge resistance deviation-to-time interval converter for resistive sensor bridges

A bridge resistance deviation-to-time interval converter is presented for interfacing resistive sensor bridges. It consists of two voltage-to-current converters, two current-tunable Schmitt triggers, a ramp integrator, and two logic gates. A prototype circuit built using discrete components exhibits a conversion sensitivity amounting to 4527.8µs/Ω over the resistance deviation range of 0-2Ω and a linearity error less than ± 0.01%.