L-R approximation of a phase-controlled LCpCs resonant converter to study the dynamic response as a LED lamp driver

This paper presents the dynamic study of a phase-controlled resonant converter suitable to drive high-brightness light emitting diode (LEDs) lamps. The output current is controlled, at constant switching frequency, through the phase displacement, Ψ, of the control signals of each class D section of the resonant inverter stage. To deal with the study of the transfer function of Ψ to output current, the envelope model of the resonant network is reduced to an equivalent L-R circuit. The approximate closed form of the transfer function is obtained using the new reduced-order envelope model. The model predicts that the current gain is set by the resonant inverter stage. On the other hand, the bandwidth is mainly defined by the output filter and the LEDs' dynamic resistance, providing the whole system with excellent dynamic behavior. A 120W prototype has been built to validate the study.