By analyzing the pulse transformer and ideal drive electric current wave, we try to improve the rate of changing-over, discuss the damped oscillation, point out existing circuit design error, and working a new circuit design which can reduce the common circuit circulation and switch loss.

The mathematical essence of damped oscillation is researched with the qualitative theory of differential equation from the odd characters of the plane autonomous system.

The damped oscillation wave is expressed to harmonics in the Fourier series,the loss resistance of inductor and capacitor are measured when the first harmonic and the harmonics which replacing the damped oscillation wave are applied to the RLC series circuit.