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A single-switch quasi-resonant converter is proposed to obtain high efficiency. Using a variable switching frequency control, this converter is continuously operated at the critical conduction mode for soft switching of the power semiconductor switch. By the resonance, the proposed converter reduces the turn-on loss of the switch without additional active switches and alleviates the reverse-recovery losses of the rectifying diodes. Furthermore, the voltage stress of the rectifying diodes due to the output series resonant circuit is clamped to the output voltage. Experimental results for the 48-V/160-W converter at the variable switching frequency are obtained to show the performance of the proposed converter. Index Terms--Quasi-resonant converter, soft switching.

A single-stage single-switch power factor correction (PFC) flyback converter with a synchronous rectifier (SR) is proposed for improving power factor and efficiency. Using a variable switching-frequency controller, this converter is continuously operated with a reduced turn-on switching loss at the boundary of the continuous conduction mode and discontinuous conduction mode (DCM). The proposed PFC circuit provides relatively low dc-link voltage in the universal line voltage, and also complies with Standard IEC 61000-3-2 Class D limits. In addition, a new driving circuit as the voltage driven-synchronous rectifier is proposed to achieve high efficiency. In particular, since a driving signal is generated according to the voltage polarity, the SR driving circuit can easily be used in DCM applications. The proposed PFC circuit and SR driving circuit in the flyback converter with the reduced switching loss are analyzed in detail and optimized for high performance. Experimental results for a 19 V/90 W adapter at the variable switching-frequency of 30~70 kHz were obtained to show the performance of the proposed converter. Index Terms--Power factor correction (PFC), single-stage single-switch converter, variable switching-frequency control, voltage-driven synchronous rectifier (SR).

A step-up dc--dc converter with a resonant voltage doubler is proposed. The proposed converter is composed of an active-clamp circuit and a resonant voltage doubler. The active-clamp circuit, which is controlled by dual asymmetrical pulsewidth modulation of the primary side, reduces the voltage spikes of main switches and limits the voltage stress of the switches as the maximum input voltage. In addition, the resonant voltage doubler of the secondary side provides two resonant-current paths formed by the leakage inductance and the output resonant capacitors, and zero-current-switching turn-off of diodes can be achieved by their resonant current. Thus, the losses of the output diodes due to the reverse-recovery problem can be removed. In addition, the voltage stress of the output diodes is clamped to the output voltage. The operation and analysis of the proposed circuit is presented in detail. To verify the performance of the proposed converter, experimental results are carried out for a 1.2-kW dc--dc converter with a constant switching frequency of 70 kHz. Index Terms--Dual asymmetrical pulsewidth modulation, resonant voltage doubler, step-up dc--dc converter, zero current switching (ZCS).

A bridgeless boost rectifier with low conduction losses and reduced diode reverse-recovery problems is proposed for power-factor correction. The proposed boost rectifier can reduce the conduction losses and alleviate the diode reverse-recovery problems by using a coupled inductor and two additional diodes. Zero-current turn-off of the output diodes is achieved, and the reverse-recovery currents of the additional diodes are slowed down to reduce the diode reverse-recovery losses. All inductive components are realized on a single magnetic core by utilizing the leakage inductance of the coupled inductor. Furthermore, for the use of this topology in the practical design, the linear peak current mode control is employed for the proposed boost rectifier. A detailed analysis and a control strategy are presented. Experimental results for a 300-W prototype are also discussed to show the performance of the proposed boost rectifier. Index Terms--Boost rectifier, diode reverse recovery, power-factor correction (PFC).

A boost converter with high performance and low cost is proposed for power factor correction. The proposed boost converter reduces the reverse-recovery loss of the diode by adding a simple inductor-diode branch paralleled with the output diode. Detailed analysis and experimental results obtained on a 300-W prototype are discussed. Index Terms--Boost converter, power factor correction (PFC).