An improved half-bridge LLC converter with magamp auxiliary post-regulator is proposed in this paper. The function of magamp is bypassed when the converter works within low input-voltage range, whereas it operates as an auxiliary post-regulator when the input-voltage is high. By changing the magamp’s blocking time, the dc gain of the converter can be extended accordingly. Hence, the input-voltage range of the converter is extended. The generalized operational principle is analyzed and the design criterion for the magamp is presented. Finally, a 25 V output, 400 W experimental prototype was built and tested for a 160–300 V input-voltage range to verify the feasibility of the proposed method.