Abstract: This paper introduced a current-controlling pulse width-modulating switch power, which took BUCK transformation as the main circuit, and took UC1842 as the core. And analyzed its principle and carried on experiment, then used it in the field. The result of practice showed that this switch power has many advantages, such as fast frequency response, high adjusting rate of voltage and high adjusting rate of load, stable output of voltage and small ripple. It is a practical switch power with reliable performance.