Xinke Wu

Analysis and Derivations for a Family ZVS Converter Based on a New Active Clamp ZVS Cell

A new zero voltage switching (ZVS) cell is proposed based on the active clamping technique. With a small clamping diode in the cell, the voltage ringing caused by the auxiliary inductor and the parasitic capacitance of the diode is eliminated, and therefore, the circulating loss is minimized. A new ZVS boost converter is presented and analyzed in detail to demonstrate the operating principle of the new ZVS cell. A new family of ZVS dc-dc converters can be derived based on the proposed ZVS cell and typical nonisolated dc-dc converters. A 500 W/190 kHz ZVS boost prototype is made to verify the analysis.

A Simple Two-Channel LED Driver With Automatic Precise Current Sharing

A simple rectifying circuit for an isolated two-channel LED driver without active current-sharing control is proposed. An alternating current source can be used to generate a two-channel LED driver with the proposed rectifying structure. With the proposed H-bridge rectifier and a block capacitor in series with the secondary side winding of the transformer, the currents in two LED strings are shared automatically even for different LED strings with different voltage drops. The operation principle of the rectifier is analyzed with a sinusoidal current source, and it is verified with a series-parallel resonant (LLC) dc/dc converter. This proposed rectifier can be applied to other converters featuring a high-frequency current source link.

A High Efficiency Flyback Converter With New Active Clamp Technique

This paper proposes a flyback converter with a new noncomplementary active clamp control method. With the proposed control method, the energy in the leakage inductance can be fully recycled. The soft switching can be achieved for the main switch and the absorbed leakage energy is transferred to the output and input side. Compared to the conventional active clamp technique, the proposed methods can achieve high efficiency both for heavy-load and light-load condition, and the efficiency is almost not affected by the leakage inductance. The detailed operation principle and design considerations are presented. Performance of the proposed circuit is validated by the experimental results from a 16 V/4 A prototype.

A Precise Passive Current Balancing Method for Multioutput LED Drivers

The multistring LED in parallel is a popular structure in backlight and lighting applications. The current balancing for each string is required to achieve uniform luminance and reliable operation. This paper proposes a simple and precise lossless passive current balancing circuit for multiple LED strings application. With a dc block capacitor in series with the transformer secondary side and the proposed two outputs rectifier structure, the currents of the two outputs can be automatically balanced due to the charge balancing of the capacitor. Compared to the conventional active current sharing technique using switching converter or linear switch, the proposed methods can achieve high efficiency and low cost. The proposed method can be applied to both current-fed topology and voltage-fed topology, which can also be extended to even outputs application. The basic two balanced output structure with a voltage-fed half-bridge topology is analyzed in this paper to show the detailed operation principle. The design considerations for continuous conduction mode and discontinuous conduction mode operations are also presented. Performance of the proposed circuit is validated by the experimental results from a 60 W prototype with 400-V dc input.

A Capacitor-Isolated LED Driver With Inherent Current Balance Capability

This paper presents a capacitor-isolated light-emitting diode (LED) driver with inherent current-balancing capability. Based on a series resonant converter, the resonant capacitor can be used both for safety isolation and the current balancing with the proposed two-output rectifier structure. Compared to the conventional current-sharing technique, the proposed LED driver circuit is simple and has low cost and high performance. Also, the capacitor-isolated structure is more efficient and compact compared to the conventional transformer isolation. The detailed theoretical analysis and design considerations of the proposed circuit are presented. The performance of the proposed circuit is validated by the experimental results from a 60-W prototype with two balanced outputs.

Analysis and Optimal Design Considerations for an Improved Full Bridge ZVS DC–DC Converter With High Efficiency

This paper proposes an improved full bridge dc-dc converter, which can achieve zero-voltage-switching (ZVS) with wide input voltage range and load range. The operation principle of the converter and the optimal design considerations for high efficiency and ZVS range are analyzed. By adding two clamp diodes and two small coupled inductors at the primary side of the transformer, the voltage ringing across rectifier diodes is reduced. Therefore, Schottky diodes can be employed to reduce conduction loss, and high efficiency is achieved. A 1.2-kW/105-kHz prototype was made with an efficiency higher than 95% at full load to verify the theoretical analysis

Optimum Design Consideration and Implementation of a Novel Synchronous Rectified Soft-Switched Phase-Shift Full-Bridge Converter for Low-Output-Voltage High-Output-Current Applications

Optimum design consideration and implementation of a novel synchronous rectified soft-switched phase-shift full-bridge dc/dc converter with a primary-side energy storage inductor for server adapter application is presented in this paper. By employing a primary-side energy storage inductor, the main switches can achieve a soft-switching condition, and there is little reverse recovery loss in the body diodes of a secondary-side rectifier due to relatively slow downslope of the triangular current. Since the output capacitive filter reduces the voltage stress across the rectifiers, the synchronous rectifier with a lower breakdown voltage rate can be utilized to improve the conversion efficiency dramatically. Thus, this converter can obtain relatively high conversion efficiency for some medium-power applications with low output voltage and high output current, such as the server adapter. Several key optimum design considerations of this converter are also presented in detail in this paper. Finally, a 100-kHz, 300-W (12 V/25 A) laboratory-made prototype for a given server adapter application is built up based on the proposed optimum design procedure of this converter to verify all the theoretical analysis and evaluations.

Variable On-Time (VOT)-Controlled Critical Conduction Mode Buck PFC Converter for High-Input AC/DC HB-LED Lighting Applications

For high input voltage (>;264 Vac) ac/dc applications, a buck power factor correction (PFC) converter is a good choice because of its low output voltage, high efficiency, lifetime improvement, and cost reduction by using a low voltage rating (<;200 V) electrolytic capacitor. However, due to the inherent dead angle of the input current, the harmonics of the buck PFC converter are high, which limits its application in lighting systems. In order to make the buck PFC converter meet the harmonics requirements (IEC61000-3-2, Class C) in lighting applications, this paper proposes a variable on-time controller for a critical conduction mode (CRM) buck PFC front-end converter for isolated high-brightness LED applications. By feedforwarding the input voltage and regulating the on-time of the switch, the high-order harmonics can be reduced to meet the lighting system limitations. Experimental results obtained on a 150-W CRM buck front-end PFC prototype show that the efficiency of buck PFC exceeds 96% during the entire line input range (250-530 Vac) at full load, and the current harmonics content can meet the harmonic requirements.

Low Voltage and Current Stress ZVZCS Full Bridge DC–DC Converter Using Center Tapped Rectifier Reset

An improved zero-voltage and zero-current-switching (ZVZCS) full bridge dc-dc converter is proposed based on phase shift control. With an auxiliary center tapped rectifier at the secondary side, an auxiliary voltage source is applied to reset the primary current of the transformer winding. Therefore, zero-voltage switching for the leading leg switches and zero-current switching for the lagging leg switches can be achieved, respectively, without any increase of current and voltage stresses. Since the primary current in the circulating interval for the phase shift full bridge converter is eliminated, the conduction loss in primary switches is reduced. A 1 kW prototype is made to verify the theoretical analysis.

A New Current-Driven Synchronous Rectifier for Series–Parallel Resonant (

A new synchronous rectifier (SR) driving method is proposed using primary current sensing in this paper. Because the magnetizing current of transformer is included in the primary winding of transformer, it cannot be used to generate the driving signals of SRs directly. A current-compensating winding in current transformer (CT) is used to cancel out the magnetizing current and generate suitable driving signals for SR. Therefore, one CT is used to generate two driving signals for two SRs in LLC converter with a center-tapped rectifier. This current-driven method is simple and low cost for high-output-current dc-dc application. A 150-W dc-dc prototype using LLC half-bridge converter with the proposed SR circuit is built up to verify the theoretical analysis.