in this paper, the dynamics of the half-bridge LLC resonant converter are investigated based on the small signal model and a piecewise PI regulation is studied and derived by simulation. Small-signal dynamics of the circuit under consideration contain many factors that may affect regulation accuracy and performance of digitally controlled regulators. The load factor is specifically addressed here. The objective of this paper is to introduce a digital piecewise PI compensation to achieve time-optimal response to an external disturbance such as a step load transient.