An AC/DC PFC converter, comprising: an AC input; a rectifier; a half bridge inverter comprising a first switch and a second switch, wherein an output is defined from a switch node between the first and second switches; an LLC resonant circuit (20, 24, 26, 27) coupled to the output, the LLC circuit being arranged to provide an electrical feedback parameter (vC); and a control circuit (62, 64) for generating a gate drive signal for controlling the switching of the first and second switches in a self-oscillating manner in dependence on the electrical feedback parameter, wherein a high gate drive signal turns on the first switch and turns off the second switch and a low gate drive signal turns off the first switch and turns on the second switch, wherein the control circuit is configured to determine a first time duration for an on-time of the first switch and to determine a second time duration for an on-time of the second switch, such that the first time duration and the second time duration together result in a defined desired duty cycle of said switch node, and wherein the control circuit further comprises an integrator (80, 82, 84) for: integrating a first constant value until the control circuit detects that the electrical feedback parameter reaches a threshold value in order to provide the first time duration; and subsequently integrating a second constant value of opposite sign to the first constant value to provide the second time duration. an AC input; a rectifier; a half bridge inverter comprising a first switch and a second switch, wherein an output is defined from a switch node between the first and second switches; an LLC resonant circuit (20, 24, 26, 27) coupled to the output, the LLC circuit being arranged to provide an electrical feedback parameter (vC); and a control circuit (62, 64) for generating a gate drive signal for controlling the switching of the first and second switches in a self-oscillating manner in dependence on the electrical feedback parameter, wherein a high gate drive signal turns on the first switch and turns off the second switch and a low gate drive signal turns off the first switch and turns on the second switch, wherein the control circuit is configured to determine a first time duration for an on-time of the first switch and to determine a second time duration for an on-time of the second switch, such that the first time duration and the second time duration together result in a defined desired duty cycle of said switch node, and wherein the control circuit further comprises an integrator (80, 82, 84) for: integrating a first constant value until the control circuit detects that the electrical feedback parameter reaches a threshold value in order to provide the first time duration; and subsequently integrating a second constant value of opposite sign to the first constant value to provide the second time duration. integrating a first constant value until the control circuit detects that the electrical feedback parameter reaches a threshold value in order to provide the first time duration; and subsequently integrating a second constant value of opposite sign to the first constant value to provide the second time duration.