Kai Hui Chen

A Novel Switched-Coupled-Inductor DC–DC Step-Up Converter and Its Derivatives

This paper presents a novel dc-dc converter configuration, which successfully integrates two technologies, including a switched capacitor and a switched coupled inductor, into one converter. By adopting a coupled inductor to charge a switched capacitor, the voltage gain can be effectively increased, and the turns ratio of the coupled inductor can be also reduced. Not only lower conduction losses but also higher power conversion efficiency is benefited from a lower part count and lower turns ratios. The proposed converter is simply composed of six components, which can be further derived to varied converters for different purposes, such as a bidirectional converter. The operating principle and steady-state analysis are discussed in this paper. A 250-W laboratory hardware prototype is completed and verified. The voltage gain is up to 11. The highest efficiency is 97.2%, and the full-load efficiency is kept at 93.6%.

Design of Quasi-resonant flyback converter control IC with DCM and CCM operation

A Quasi-resonant (QR) flyback converter control IC is design and implemented. Flyback converter is applied in small to medium power rating applications mostly, due to low cost and simple circuit topology. The conventional fix frequency operated flyback converter is the most adapted power converter, but the switching losses cause lower conversion efficiency. The flyback converter can be operated in BCM and DCM by quasi-resonant control. The quasi-resonant control utilizes the resonant action between magnetize inductor of transformer and parasitic capacitor of power MOSFET to achieve valley voltage turn-on and reduce the turn on losses increasing the conversion efficiency. The switching frequency increases with reducing load, and the switching losses will cause poor efficiency. Flyback converter operated in BCM and DCM in heavy load condition will lead to higher conduction losses. To improve the conversion efficiency at light load and heavy load condition, the proposed control circuit is integrated with frequency clamp and maximum off-time limit functions.

Analysis and implementation of a DC-DC step-down converter for low output-voltage and high output-current applications

A novel DC-DC step-down converter with interleaved control for low output-voltage and high output-current applications is presented in this paper. The voltage gain of the proposed converter is half of the conventional buck converter with reduced current stresses on power devices and low output-current ripple are reduced. The operating principle, steady-state analysis, and small-signal model analysis are discussed in detailed. Finally, a prototype circuit of the proposed converter with 12-V input voltage, 1.5-V/40-A output is implemented to verify the performance.

Design and implementation of a bidirectional SEPIC-Zeta DC-DC Converter

Bidirectional DC-DC converters are used in many applications when bidirectional energy transfer between two DC buses is needed. This paper presents a bidirectional dc-dc converter with coupled inductor. High voltage conversion ratio is achieved and the leakage-inductor energy is recycled in both discharge mode and charge mode. Also, the switch voltage stress is reduced by the clamping circuit to achieve high efficiency in the proposed converter. An experimental circuit is implemented to verify the feasibility. The conversion efficiency can achieve 94.3% in discharge mode and 92.6% in charge mode.

Non-electrolytic capacitor LED driver with feedforward control

In this paper, the design and implementation of a non-electrolytic capacitor LED driver is proposed. The proposed driver includes a Boost PFC converter as first-stage and a LLC Resonant Converter as second-stage. With feedforward control, the output current ripple can be reduced without electrolytic capacitor, the lifetime of the driver will be increased. In this paper, the operating principles of the LLC resonant Converter with feed-forward control will be discussed. Besides, the optimized design of the proposed control scheme will be discussed, too. Finally, a two-stage non electrolytic capacitor LED driver is implemented to drive 150 W LED load. Experimental results show that the proposed circuit can be operated at 90~264Vrms AC input voltage range and the highest efficiency is 90.4 %. The output current ripple and LED efficacy will be also verified.

Design and implementation of a interleaved single-phase power factor correction Zeta converter

This paper presents a single-phase power-factor-correction (PFC) AC-DC step-up/down Zeta converter. It is operated in discontinuous conduction mode (DCM) to achieve unity power factor and step-up/down DC output voltage. The proposed converter is suitable for universal line voltage (90 ~ 264 V) and wide output power range. The operating principle and steady-state analyses of the voltage gain and the boundary operating condition are discussed. Finally, a 400 W / 200 V prototype sample is built in the laboratory to verify the feasibility and performances of the proposed converter.

Primary Side Control For Flyback Converter Operating in DCM and CCM

Primary side regulation (PSR) technology has the characteristics of lower cost and standby power losses. However, there is no algorithm suitable for discontinuous conduction mode (DCM) and continuous conduction mode (CCM) operations of primary side control for flyback converter because of the difficulty in estimating the output voltage correctly. In this paper, a PSR control algorithm suitable for DCM/CCM flyback converter is proposed and implemented with digital micro controller. The voltage drop on the secondary winding and output diode at CCM operation is compensated by sensing the secondary side current at the instant when primary side switch is being turned-on. The secondary side current is zero at the voltage sensing instant and equal to the current at the instant when primary side switch is being turned-on as flyback operated at DCM. In addition, the proposed algorithm can be used to regulate either the output voltage or current very well. An experimental prototype with 150 W rated power is built to verify the feasibility of the proposed control. Experimental results show that the output voltage can be controlled with error less than 0.25%, and the output current error is less than 5%. The conversion efficiency is up to 92.8%.

Control IC for TRIAC dimming LED driver with quasi-resonant flyback converter

In this paper, a TRIAC dimmable controller for quasi-resonant flyback LED driver is realized. Nowadays, many countries take effort to save energy. Because lighting system takes part of approximately 20% of world energy consumption, by replacing the traditional incandescent bulbs with light-emitting-diode (LEDs), electrical energy can be saved significantly. TRIAC dimmer is commonly used for traditional incandescent bulbs in Europe and America countries. The TRIAC needs a holding current to keep it conducting. The TRIAC will misfire and cause the LED light output flickering when the holding current is insufficient, so that to solve this problem, this thesis proposes a method to estimate the holding current requirement for various TRIACs by detecting the misfiring phenomenon. Then the controller will automatically adjust the bleeder current to meet the TRIACs holding current. Compare to the traditional constant current bleeder circuit, the proposed method can reduce the power consumption on the bleeder circuit significantly. Furthermore, this controller utilizes primary-side quasi-resonant control which can reduce switching loss and improve the efficiency. Finally, this controller is fabricated with TSMC 0.25 μm 60 V CMOS high voltage mixed signal general purpose process and applied to an input voltage of 90∼264 Vrms, output voltage of nominal 40 V, and constant output current of 600 mA/24W hardware prototype to verified the feasibility of the proposed control.

Design of control IC for multiphase interleaved buck converter with alternate phase-shedding

In this paper, a controller for a multiphase interleaved buck converter with alternate phase-shedding is realized. With phase-shedding control, the efficiency at low load condition is improved by turning-on appropriate number of phase(s), but the temperature on the active phase(s) is higher than the off phase(s) that cause the temperature unevenly distribution. To solve this problem, the alternate phase-shedding is implemented in the proposed controller. The phases take turns to provide the load current at low load condition to distribute power to each phase and share the same load as well as improve reliability. The proposed controller would implement interleaved control regardless the number of active phases. In addition, taking advantage of the application of high step-down ratio, the proposed control structure that input current is sensed to control each phase is adopted. The number of components and pins of controller can be reduced. This chip is fabricated with TSMC 0.25um CMOS high voltage mixed signal general purpose process and is tested with an input voltage of 12 V, output voltage of 1.2 V, and output power of 72 W three-phase buck converter to verify the feasibility.

Design and implementation of single-stage LED driver with high frequency pulse

A single-stage LED driver with high frequency pulse is presented in this thesis. The proposed circuit integrates a boost power-factor-correction converter and a half-bridge resonant inverter into a single-stage LED driver. The boost inductor is operated in discontinuous conduction mode to achieve high power factor and low current harmonic distortion. The half-bridge resonant inverter is connected with a full-bridge rectifier to increase the utilization factor of the LED. Furthermore, the effectiveness of the LED equivalent model on the resonant circuit and the light characteristics of the LED with high frequency pulse are also discussed. Finally, a single-stage high frequency pulse LED driver is implemented to drive a 40 W LED module. Experimental results show that the proposed circuit can be operated at 100~120 Vrms and the highest efficiency is 93.14 %.