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This article proposes an improved isolated four-switch three-level half-bridge dc–dc converter suitable for high-input-voltage applications. The primary switches operate under zero voltage switching (ZVS) for a wide load range, which is accomplished by the inclusion of an auxiliary inductance in the circuit. In addition, the conditions necessary to ensure zero current switching (ZCS) for the output rectifiers are determined. A detailed mathematical analysis is carried out, allowing the proper design of the circuit. Output voltage control and input voltage balance are also investigated in detail. The analyses are validated by experimental tests performed with a 1 kW prototype, operating at 100 kHz, with an input voltage range of 700–800 V and output voltage of 400 V. Efficiency levels up to 96.13% and higher than 90% for the entire output power range of 20%–100% are demonstrated in laboratory.