Aimed at the puzzle that the first-order load capacitance parameter is difficult to adjust smoothly and continuously, a sort of first-order equivalent circuit was designed to solve the problem. Based on the equivalence on the circuit external characteristics, by means of controlling pulse duty cycle of PWM, through adjusting the current and voltage of the active circuit continuously and smoothly, it could achieve a smooth and continuous adjustment of capacitance parameter. The first-order circuit equivalence was analyzed, and the error analysis showed that, with the increase of switching frequency, the error would be decreased gradually. The comparative study of simulation showed that under the condition of switching frequency being 100 kHz, the duty cycles would respectively be 20%, 50% and 80%, the maximum error respectively would be 1.598×10－3,2.49×10－3and 1.588×10－3,and the equivalent curve is almost the same with the actual curve. The results also showed that it is feasible for designed first-order equivalent circuit, and it provides a new thought to make first-order load capacitance parameter to be adjusted smoothly and continuously.
