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In this paper, a novel transformer-less interleaved four-phase high step-down conversion ratio dc-dc converter with low switch voltage stress is proposed. In the proposed converter, the new capacitors switching circuits are combined with interleaved four-phase buck converter in order to get a high step-down conversion ratio without adopting an extreme short duty ratio. Based on the capacitive voltage division, the main objectives of the capacitors switching circuits in the converter are both storing energy in the blocking capacitors for increasing the voltage conversion ratio and reducing voltage stresses of active switches. This will allow one to choose lower voltage rating MOSFETs to reduce both switching and conduction losses, and the overall efficiency is consequently improved. In addition, due to the charge balance of the blocking capacitor, the converter features automatic uniform current sharing characteristic of the interleaved phases without adding extra circuitry or complex control methods. The operating principle and steady-state analyses of the voltage gain are discussed. Finally, a 400-V input voltage, 24-V output voltage, and 500W output power prototype circuit is implemented in the laboratory to verify the performance.