J.-J. Chen

Interleaved LLC series converter with output voltage doubler

A parallel LLC series resonant converter with output voltage doubler is presented in this paper. The interleaved pulse-width modulation (PWM) technique is adopted to reduce the ripple current on input and output capacitors. The capacitance of input and output capacitors can be reduced. The high current stress drawback of conventional LLC resonant converter is overcome by the proposed converter. Thus the adopted converter can be applied for high output current applications. Based on the series resonant behavior, all power switches are turned on at zero voltage switching (ZVS) and the rectifier diodes can be turned off at zero current switching (ZCS). Thus the switching losses on power semiconductors are reduced. In the output side, the voltage doubler topology is adopted for high output voltage applications. Compared with the conventional LLC converter, the advantages of the proposed circuit are low ripple currents on input and output terminals, small size and light weight of transformer, and low conduction losses on power semiconductors. In this paper, the principle of operation, steady state analysis and design consideration of the proposed converter are provided and discussed. In order to validate the proposed converter, the laboratory experiments with 24V/40A output for server power supply were provided.

Analysis and implementation of a bidirectional ZVS dc-dc converter with active clamp

A bidirectional ZVS DC-DC converter with active clamp topology is proposed. The proposed converter is based on the forward converter with center-tapped rectifier at the transformer secondary side. Active clamp topology is used in the forward converter to achieve ZVS feature of power switches and to regulate the output voltage at the desired value. The proposed converter has the advantages of high efficiency and simple circuit configuration. The operating principle, system analysis and design example are described and discussed in detail. Finally, the experimental results of the proposed converter are provided to verify the theoretical analysis.

Active-clamp ZVS converter with step-up voltage conversion ratio

This paper presents a new isolated dc/dc converter with zero-voltage turn-on switching (ZVS) of power switches and zero-current turn-off switching (ZCS) of diodes. In conventional flyback converter, the main drawbacks are high voltage stresses on power devices large transformer size, and serious reverse recovery current which resulted in high voltage spike across output diode. To solve these problems, buck-boost type of active-clamp circuit is connected in parallel with the primary winding to clamp the voltage spike across the power switch, recycle the energy stored in the leakage and magnetizing inductances of transformer and realize the turn-on ZVS by utilizing the leakage inductance and output capacitance of switch. The leakage inductance and the resonant capacitance on the secondary side are resonant to allow the output diodes turn-off at ZCS. Thus the switching losses and thermal stresses of the switches and diodes are reduced, the output diode has no reverse recovery problem, and voltage stresses of the output diodes are clamped to the output voltage. Experiments conducted on a laboratory prototype rated at 270W are provided to verify the effectiveness of the proposed converter.

Analysis of a new ZVS converter with output voltage doubler

A novel zero voltage switching (ZVS) converter with output voltage doubler is presented. The output voltage doubler is used on the output side to achieve the boost type of voltage conversion ratio. Active-clamping technique is adopted to realize the ZVS turn-on of all switches, release the energy stored in the transformer leakage inductance and limit the voltage stresses on power switches. The ZVS function is achieved at the commutation stage of two complementary switches. The proposed circuit has no large output inductor such that the adopted circuit has simpler structure, lower cost and no effective duty loss. The voltage stresses on output diodes are clamped at the output voltage. The circuit configuration, operation principles and design consideration are presented. Finally experimental results based on a 300W prototype are provided to verify the effectiveness of the proposed converter.

Active-clamping dual resonant converter

A dual resonant converter using active clamp circuit is presented in this paper. The active clamp circuit is employed to limit the voltage stress and create zero-voltage-switching (ZVS) turn-on feature for power switches. Moreover, the dual resonant tanks are composed by the leakage inductors and resonant capacitors to achieve zero-current-switching (ZCS) turn-off mechanism for diodes at the secondary side of transformer. Hence, the reverse-recovery problem can be eliminated. The operational principles, design consideration and realization are discussed. Finally, experimental results from a 400W prototype are presented to confirm the effectiveness of the proposed converter.

Implementation of a zero voltage switching Sepic-Cuk converter

This paper presents the system analysis and implementation of a soft switching Sepic-Cuk converter to achieve zero voltage switching (ZVS). In the proposed converter, the Sepic and Cuk topologies are combined together in the output side. The features of the proposed converter are to reduce the circuit components (share the power components in the transformer primary side) and to share the load current. Active snubber is connected in parallel with the primary side of transformer to release the energy stored in the leakage inductor of transformer and to limit the peak voltage stress of switching devices when the main switch is turned off. The active snubber can achieve ZVS turn-on for power switches. Experimental results, taken from a laboratory prototype rated at 300W, are presented to verify the effectiveness of the proposed converter. I. Introduction Modern

Analysis of integrated buck-flyback ZVS converter

This paper presents the system analysis and circuit implementation of a soft switching converter based on buck-flyback topology to have a large voltage step-down between the output and input sides. Compared with the conventional buck converter, the proposed converter has wide turn-on period so that the lower output voltage can be achieved. An active snubber circuit is connected in parallel with the main switch to achieve zero voltage switching (ZVS). The resonance is based on the output capacitance of power switch and resonant inductance at the transition interval between the main and auxiliary switches. Therefore, the turn-on switching losses of power switch are reduced. The circuit configuration, system analysis, and design consideration of the proposed converter are presented in detail. Finally, experimental results based on a laboratory prototype with 240 W rated power are provided to verify the effectiveness of the proposed converter.

Interleaved PWM active-clamping buck-type converter

An interleaved pulse-width modulation (PWM) zero voltage switching (ZVS) converter is presented in this paper. Two converter modules with interleaved PWM scheme are used in the proposed circuit to achieve load current sharing and reduce the ripple currents on the input and output capacitors such that the size of the output choke and capacitor are reduced. For each module, two buck-type dc-dc converters with only two switches are used to reduce the current rating of transformer winding and share the load current. Two buck-type converters in each module use the same switching devices to regulate the output voltage. The ZVS turn-on of the switches is achieved by utilizing the transformer leakage inductance and output capacitance of switches. Thus the switching losses of the proposed converter are reduced. Experiments based on a 660W prototype are provided to verify the theoretical analysis and the effectiveness of the proposed converter.

Implementation of an interleaved ZVS forward converter

A parallel zero voltage switching (ZVS) forward converter with half-bridge topology is presented in this paper. Two converter modules are connected in parallel in the output side to share the load current. In the primary side, two converter modules use the same power switches so that the semiconductor devices are reduced in the proposed converter compared with the conventional interleaved half-bridge converter. The asymmetrical pulse-width modulation (APWM) is used to regulate the output voltage and realize the ZVS turn-on of switches at the transition interval. The voltage stress of switches is clamped at the input source voltage. The system analysis, operation principle and design consideration of the proposed converter are presented. Finally experimental results based on a laboratory prototype are provided to verify the effectiveness of the proposed converter.

Implementation of a parallel ZVS forward converter with less power switches

A parallel ZVS (Zero Voltage Switching) forward converter is proposed to achieve load current sharing, output ripple current cancellation and conversion efficiency improvement. Two forward converters are connected in parallel to achieve interleaved PWM operation. Thus the ripple currents on the output side are partially cancelled each other so that the size of output chokes and capacitor is reduced. Only two switches are used in the proposed converter instead of four switches in the conventional parallel ZVS forward converter. Therefore, the proposed converter has less power switching devices. An active snubber is connected between two power transformers to absorb the energy stored in the leakage and magnetizing inductances of transformers, to limit voltage stresses across switches, and to realize the ZVS turn-on of all switches. Thus the conversion efficiency is improved by the soft switching operation of switching devices. Finally, the performance of the proposed converter is evaluated on a 480W (24V/20A) laboratory prototype.