J.-C. Hung

Boost Converter With Coupled Inductors and Buck–Boost Type of Active Clamp

This paper proposes an improved boost converter with coupled inductors and buck-boost type of active-clamp feature, PWM control and zero-voltage switching in both main and auxiliary switches. In the converter, the active-clamp circuit is used to eliminate voltage spike induced from the leakage inductor of the coupled inductors. The active switch of the converter can still sustain a proper duty cycle when it operates with a high step-up voltage ratio, reducing voltage stress significantly. A set of passive-clamping circuit is adopted to eliminate undesired resonance between leakage inductor of the coupled inductors and stray capacitor of the boost diode, recovering trapped energy. Thus, conversion efficiency can be improved significantly. A 200 W prototype of the proposed boost converter was built from which experimental results have shown that efficiency can reach as high as 92% and surge can be suppressed effectively.

A single-stage fast regulator with PFC based on an asymmetrical half-bridge topology

This work presents single-stage regulators with power-factor correction (PFC) based on an asymmetrical half-bridge topology. The proposed regulator is formed from a boost converter with two coupled inductors and an asymmetrical half-bridge converter with the synchronous switch technique, and it is controlled with pulsewidth modulation to achieve zero-voltage switching (ZVS). The boost converter is operated in discontinues conduction mode to achieve PFC. With the coupled inductors, input current ripple and power factor can be improved significantly. The proposed regulator has the features of constant-frequency operation, ZVS, and low voltage stress imposed on the active switches. Moreover, the regulator can achieve high power factor, high power density, high efficiency, low switching loss, and low component count, which makes its applications at medium-power levels feasible. Experimental results have verified the discussed features of the proposed regulator.

Boost Converter with Coupled Inductors and Buck-Boost Type of Active Clamp

This paper proposes a boost converter with coupled inductors and buck-boost type of active clamp. In the converter, the active-clamp circuit is used to eliminate voltage spike induced from the trapped energy in leakage inductor of the coupled inductors. The active switch in the converter can still sustain a proper duty ratio when even under high step-up applications, reducing voltage and current stresses significantly. Moreover, since both main and auxiliary switches can be turned on with zero voltage switching, switching loss can be reduced and conversion efficiency therefore can be improved significantly. A 200 W prototype of the proposed boost converter was built from which experiment results have shown that efficiency can reach as high as 92% and surge can be suppressed effectively. It is relatively feasible for applications to fuel cell and battery power conversion

An Active-Clamp Push–Pull Converter for Battery Sourcing Applications

This paper presents an active-clamp push-pull converter for battery sourcing applications. A pair of auxiliary switches, resonant inductors, and clamping capacitors is added to the primary side of the transformer to clamp voltage spike and recycle the energy trapped in the leakage inductors. In the proposed active-clamp push-pull converter, since both main and auxiliary switches can be turned on with zero-voltage switching, switching loss can be reduced and conversion efficiency therefore can be improved significantly. Furthermore, the proposed converter can eliminate potential flux-imbalance problems existing in the conventional push-pull converter. In this paper, a 1 kW active-clamp push-pull converter was implemented, from which experimental results have shown that efficiency improvement and surge suppression can be achieved effectively. It is relatively feasible for applications to battery sourcing converters.

A PSpice model for fluorescent lamps operated at high frequencies

A PSpice circuit model simulating the electrical characteristics of the fluorescent lamp operated at high frequency is proposed. The model is constructed from a two-parameter equation which is derived based on a set of two measurements. This is a readily constructed and a computer simulator oriented model which is suitable for a preliminary design of electronic ballasts. Simulated and experimental results are used to verify the analytical discussions, and, moreover, an electronic ballast design example using the proposed model is presented to further demonstrate its applications.

A PSpice circuit model for low-pressure gaseous discharge lamps operating at high frequency

A simple, but accurate, PSpice circuit model simulating the electrical characteristics of low-pressure gaseous discharge lamp operating at high frequency is proposed. The model is constructed from a two-parameter equation and is suitable for computer simulation and analytic derivation in a preliminary design of electronic dimming ballasts. Simulated and measured results are used to verify the theoretical discussion.

An improved boost converter with coupled inductors and buck-boost type of active clamp

This paper proposes a boost converter with coupled inductors and a buck-boost type of active clamp. In the converter, the active-clamp circuit is used to eliminate the voltage spike that is induced by the trapped energy in the leakage inductor of the coupled inductors. The active switch in the converter can still sustain a proper duty ratio even under high step-up applications, reducing voltage and current stresses significantly. Moreover, since both main and auxiliary switches can be turned on with zero-voltage switching, switching loss can be reduced, and conversion efficiency therefore can be improved significantly. A 200 W prototype of the proposed boost converter was built, from which experiment results have shown that efficiency can reach as high as 92% and surge can be suppressed effectively. It is relatively feasible for low-input-voltage applications, such as fuel cell and battery power conversion.

Generation of pulsed electric fields for processing microbes

This paper first reviews viable microbe processing mechanism and then presents generation of pulsed electric fields for processing microbes. Microbe processing includes food sterilization, waste treatment, pollution control, and medical diagnostics and treatment. To generate pulsed electric fields for achieving sterilization, a generated high dc output voltage is chopped into pulsed waveforms, in which their pulse-width varies from tens of nanoseconds to hundreds of microseconds, period changes from 0.1 to 1 ms, and electric field intensity is from tens to hundreds of kV/cm. In this study, we propose wide pulses stacked with narrow pulses to prevent undesired air breakdown and reduce power consumption. Modified half-bridge series resonant converters are used to generate high dc voltages. They are operated at high frequency, in discontinuous conduction mode and with a PWM control; therefore, its weight and size can be reduced significantly and its efficiency can be correspondingly improved.

A PDM controlled series resonant multi-level converter applied for X-ray generators

This paper presents analysis, design and practical consideration of a pulse-density modulation (PDM) controlled series resonant multi-level converter applied for X-ray generators. The proposed converter is operated at 100 kHz and with a maximum output power of 30 kW. The resonant tank of the converter is operated slightly above its resonance to achieve zero voltage switching and low turn-off loss at switching transition resulting in low loss. With the multi-level configuration, the voltage imposed on the switches is only half of the input voltage. A prototype has been implemented and the experimental results have demonstrated the feasibility of the proposed system.

Development of ZVS single-stage isolated converters with a PFC feature based on asymmetrical half-bridge topology

In this paper, a systematic approach to developing a family of zero voltage switching (ZVS) isolated single-stage converters with a PFC feature based on asymmetrical half-bridge topology is presented. The single-stage converters are developed by adopting the synchronous switch scheme, and they can achieve constant frequency operation, ZVS and low voltage stress imposed on the active switches. Moreover, it can achieve a high power factor, high power density, high efficiency, low switching loss and low component count, which make converter operation at low to medium power levels feasible. In the paper, such converters have been developed, and one of which is designed and implemented to verify the feasibility.