In this paper a fully soft switching bidirectional DC-DC converter is proposed. All semiconductor devices are soft switched while its control circuit remains PWM. This condition is achieved only by one auxiliary switch. So, the proposed topology has less complexity in comparison with other similar structures. The energy conversion through the proposed topology during Buck and Boost modes is highly efficient due to achieve soft switching condition. The auxiliary circuit operates once during each switching cycle. The converter is analyzed and a 250 W laboratory prototype of the proposed converter is constructed. The experimental results are presented and confirm the theoretical analysis.