| The BUCK DC/DC converter is wildly used in the battery charged computers and consumption products. Minisize is required in these products. The improvement of the switching frequency can diminish the converter size. The DC/DC converter is just one seventh as before when the switching frequency is improved from 20KHz to 1MHz. But the switching loss is increased as the switching frequency is improved and so the converter efficiency is decreased. Because efficiency is a main aspect to evaluate the high frequency DC/DC converter, how can higher efficiency be obtained is the important aspect of research.To the ZVT-PWM soft-switching converter, not only the resonant parameters but the input and output voltage and the load can affect the converter efficiency. A detailed research of a typical ZVT-PWM BUCK converter is done in this paper. The loss of the different parts in the assistant circuit of the typical ZVT-PWM BUCK converter is calculated. The ratio of the loss of the different parts in the assistant circuit to the output power is calculated too. The influence of the resonant parameters and the input-output voltage to the converter efficiency is analyzed base the calculation. And the influence of the turn-off loss of the assistant switch to the efficiency of the typical ZVT-PWM BUCK converter is analyzed. The main aspects influence the efficiency are found out and the resonant parameters optimization schemes are brought forward. Due to the deficiency of the typical ZVT-PWM BUCK converter,the design of a new ZVT-PWM BUCK converter is described in this paper. The experimental results and simulation results all approved the improvement measurements can improve the converter efficiency. In the end of the paper, a improved two-phases ZVT-PWM BUCK circuit is brought forward base the same principle.
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