This paper proposes a novel single-phase ac to high voltage dc converter based on Cockcroft-Walton cascade rectifier with only adding one bi-directional switch and one boost inductor. This paper also derives a new method of circuit representation for Cockcroft-Walton cascade rectifier, which simplifies the equivalent circuit and is convenient for simulation. Compared with conventional Cockcroft-Walton rectifier, the proposed converter provides half-wave symmetric and low-distorted line current, adjustable power factor at the ac source, and regulated dc output voltage. Unit power factor is achieved by the average-current method and the dc output voltage is regulated by a PI compensator. Moreover, this paper employs a digital signal processor to implement a digital controller for operating the proposed converter and a prototype with 500 w rating is implemented for test. Both simulation and experimental results demonstrate the validity of the proposed converter.