A kind of power conversion circuit, which converts positive voltage into negative one is presented according to the principle of negative voltage charge pump, so the DC output voltage is doubled. Factors affecting the speed and accuracy of MOS switches are fully considered, and a charge pump with MOS switches working in linear region is designed, avoiding the problem of threshold voltage drop. By single positive power supply, a non-overlapping clock is generated skillfully by changing switching threshold voltage of the inverters, to drive the MOS switches correctly with positive and negative voltage. The simulation results based on CMOS 0.35 mum technology show that, at 1 MHz refresh frequency, the circuit converts +1.5 V to -1.5 V, with error less than 0.2%, and setup time less than 20 mus. Besides, the circuit is less limited by the supply voltage and refresh frequency, and is not sensitive to the variations of process.