Charge current control for LLC resonant converter

This paper proposes a charge current control method for LLC resonant converter where the total charge of the switch current is compared with the control voltage to modulate the switching frequency. Since the proposed control method uses resonant current for only a half switching cycle together with duty cycle balancing circuit, the circuit can be implemented easily with analog circuit. The charge control makes the system single pole system allowing easy compensation design. Since the charge of the switch current is proportional to the average input current over each switching cycle, it also allows constant power limit. The proposed method has been implemented and tested on a 225W LLC resonant converter.