Abstract：Switching power supply is now developing towards high-frequency soft-switching and high power

density，the volume of magnetic components is greatly reduced，and the excitation inductance of transformer no

longer meets the assumption of large excitation inductance in traditional analysis. Under this background，the

influence of the weak excitation inductance on the full-bridge circuit was analyzed，and proposed that the fullbridge

circuit can achieve autonomous soft-switching through the charging and discharging of the capacitor under

the condition of the weak excitation inductance. The autonomous soft-switching of the full-bridge converter can be

realized when the duty ratio is large. Through principle analysis and calculation，relationship between the charge

and discharge of the switch body capacitance and the inductance current and the time constant was obtained，and

the above principle through simulation were verified . Finally，an experimental platform with a working frequency

of 200 kHz was built to verify the above analysis and simulation results.

      Key words：weak excitation inductance；full-bridge DC-DC converter；soft-switching