In this paper

a method of parameter design of LLC converter based on vector diagram is presented.After briefly introducing the basic working principle of LLC resonant converter

the fundamental equivalent circuit of LLC resonant converter is obtained by fundamental wave analysis method.Then

the relationship between the variables in the converter is expressed by vector diagram

which explains the restriction of the gain range of the converter on the values of excitation inductance and resonant capacitance.Finally

combining with resonance

the restriction of excitation inductance and resonant capacitance is explained.The relationship between the lowest switching frequency and the peak voltage of resonant capacitor and the resonant current is used to determine the lowest switching frequency and other circuit parameters conveniently.