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One three-transistor push-pull (TTPP) converter is proposed in this study. In this TTPP converter, an extra transistor is inserted between the input power supply and midpoint of two primary windings. On the secondary side, a saturable inductor and an extra freewheeling diode are employed. Adopting the proposed pulse-width modulation method for three power switches, two original transistors can achieve zero-voltage-switching (ZVS) easily in a wide range of load current, the extra transistor can also realise ZVS assisted by the saturable inductor. Each operation mode of the proposed TTPP converters is discussed in detail. The soft-switching conditions are explained. One 83.3 kHz, 800 W prototype has been built. Its peak efficiency reaches 94.87%. The experimental result is provided to verify the analysis.

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This study introduces a new active-clamped current-fed push-pull dc-dc converter for renewable energy conversion applications. The proposed converter conserves small input current pulsation, high-voltage conversion ratio, zero-voltage switching (ZVS) and zero-current-switching operation for primary switches and rectifier diodes, respectively, over a large load range. Also, the additional active clamping circuit serves to suppress the voltage spike across all primary switches, as well as assists in achieving ZVS operation. So, the low-voltage switches with low on-state resistance can be adopted. These features can reduce switching loss, voltage stress, transformer turns ratio and diode reverse-recovery effect. More importantly, similar characteristics can be obtained with minimised switches compared with the reported converters that enable to reduce the cost and improve the reliability. Detailed steady-state operation, analysis, performance comparison, experimental results and loss breakdown of the proposed converter are fully discussed in this study. Finally, a 520 W prototype verifies the theoretical analysis.

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