Masahito Jinno

An Efficient Active LC Snubber for Forward Converters

An efficient active LC snubber for forward converters is proposed in this paper. The proposed active LC snubber can be used to reset transformer and suppress switching surge. Further, by storing surge energy in the proposed active LC snubber and then releasing it to the flyback auxiliary output, the converter can achieve high efficiency. For a forward converter with active LC snubber, 91.02%, the maximum output efficiency can be obtained. Because of the high performance on surge suppression and energy recovery, experimental results show that the output efficiency of this proposed converter is higher than that of active-clamped-based converters. Furthermore, for a synchronous rectification forward converter with this active LC snubber, the maximum output efficiency can be further raised to 94.72%.

Research on the Reverse Conduction of Synchronous Rectifiers

Research on the reverse current phenomenon in synchronous rectifiers (SRs) is presented in this paper. For loss reduction, the SRs composed of metal-oxide-semiconductor field-effect transistors (MOSFETs) have recently been employed to replace the conventional rectifiers with diodes in low-voltage and high-current applications. Because the MOSFETs in the SRs are used as bidirectional switches, reverse current flow will probably occur. The reverse current phenomenon will cause undesired power loss. To clarify the effects of the reverse current on the forward converter with an SR, both the experiment and the analysis are performed. Furthermore, the concepts and methods for dealing with this phenomenon are clearly described in this paper.

Efficiency improvement for SR forward converters with LC snubber

A novel circuit is proposed to alleviate the problems associated with using synchronous rectifiers in forward converters. The proposed circuit employed an LC snubber in the primary side of the converter as opposed to conventional schemes of employing an additional active switch to improve the efficiency. For the proposed forward converter with 40 W output, 91% efficiency at 3.3 V and 4 A output is obtained. In this paper, the circuit operation of this converter is described with the aid of simulation waveforms and the design criteria are also established.

Investigation on the Ripple Voltage and the Stability of SR Buck Converters With High Output Current and Low Output Voltage

Synchronous rectifiers (SRs) composed of MOSFETs have recently been employed to replace the conventional rectifiers with diodes. SRs are widely used in switched-mode power supplies with low output voltage and high output current for efficiency improvement. Owing to the high-efficiency characteristic, it is adequate to use an SR buck converter in a voltage regulator for powering a central processing unit. Normally, such SR buck converter must operate at fairly high switching frequency for miniaturizing a whole circuit and achieving a fast response. However, at the conditions of low output voltage, high output current, and high switching frequency, the influence of parasitic elements to circuit operation will become extremely obvious. Therefore, the design considerations concerning the ripple voltage and the stability of such SR converters should be carefully investigated and clarified. By establishing the equivalent circuit and using a state-space averaged method, the ripple ratio of output voltage and the static and dynamic characteristics of the SR buck converter with nonnegligible parasitic elements are obtained. Thus, the design criteria concerning the output ripple voltage and the stability are clarified.

An efficient active LC snubber for multi-output converters with flyback synchronous rectifier

An efficient active LC snubber for multi-output converters with flyback synchronous rectifier (SR) is proposed in this paper. The proposed active LC snubber can be used to reset transformer and suppress switching surges. Besides, by storing surge energy in the proposed active LC snubber and then releasing it to the flyback SR, the converter can achieve high efficiency. For a forward converter with flyback SR, 90.8%, the maximum output efficiency, can be achieved. Experimental results also show that the output efficiency of this converter with the proposed active LC snubber is higher than that of active-clamped-based converters.

Study on the Reverse Conduction of Synchronous Rectifiers

A study on the reverse current phenomenon in synchronous rectifiers is presented in this paper. For loss reduction, the synchronous rectifiers composed of MOSFETs have recently been employed to replace the conventional rectifiers with diodes in low voltage and high current applications. Because the MOSFETs in the synchronous rectifiers are used as bidirectional switches, reverse current flow will probably occur. The reverse current phenomenon will cause undesired loss. To clarify the effects of reverse current on the forward converter with synchronous rectifier, both the experiment and the analysis are performed in this research

An interleaved single-stage LLC resonant converter used for multi-channel LED driving

In order to simplify circuit complexity, reduce cost and improve system efficiency, this paper proposes an interleaved single-stage LLC resonant converter to drive multi-channel light emitting diodes (LEDs) with high power-factor and current-sharing features. Two derivative buck-boost typed power-factor-correctors (PFCs) with interleaving operation are integrated with an LLC resonant converter to form the presented circuit. The proposed single-stage converter has the features of simple circuit structure, balanced switch currents, low dc-bus voltage, low input current harmonics, and high system reliability. With proper analysis and design, the power switches can turn on with zero-voltage-switching (ZVS), and the output rectifier diodes can turn off with zero-current-switching (ZCS), which results in low switching losses. Additionally, by connecting the primary windings of transformers in series, the current-sharing among all the LED channels can be achieved naturally. Operation principles and circuit analysis are addressed. Finally, a laboratory prototype with 220 Vrms utility-line voltage is implemented correspondingly to verify the validity of the theoretical predictions and the feasibility of the proposed circuit.