This paper describes a boost half-bridge DC-DC converter for photovoltaic system that reduces the input voltage and current ripples by using a 1:1 transformer and an auxiliary capacitor. The 1:1 transformer replaces the boost inductor in a previous boost half-bridge converter. The auxiliary capacitor is connected serially to the secondary coil of the 1:1 transformer, and resonates with the leakage inductance of the 1:1 transformer. The input voltage and current ripples are reduced by setting the switching frequency equal to the resonance frequency between the auxiliary capacitor and the leakage inductance, and by coupling the resonance current to the primary coil of the 1:1 transformer. The proposed converter had input voltage ripple less than 0.2 V-p.p, input current ripple less than 0.81 A(p.p), 5, and power-conversion efficiency higher than 94.5% when the converter was operated at input voltage of 30-50 V, output voltage of 400 V, output power of 30-300 W, and switching frequency of 46 kHz. These experimental results show that the proposed converter is well suited for photovoltaic micro-inverter applications that require a small input capacitor, low input voltage, high input current, high output voltage, and high power-conversion efficiency.