The circuit is composed by two stages, a front-end PFC implementing the L6563 and a resonant DC/DC converter based on the new resonant controller, the L6599.
The PFC stage delivers a stable 400Vdc and provides for the reduction of the mains harmonic, allowing to meet the European norm EN61000-3-2. The controller is the L6563 (U1), working in transition mode and integrating all functions needed to control the PFC and interface the downstream resonant converter. The power stage of the PFC is a conventional boost converter, connected to the output of the rectifier bridge. It includes the coil L2, the diode D4 and the capacitor C9. The boost switch is represented by the power mosfet Q1. The L2 secondary winding (pins 8-10) is dedicated to provide to the L6563 the information about the PFC coil core demagnetization, necessary to the controller for the TM operation. The divider R1, R2 and R14 provides to the L6563 the information of the instantaneous voltage that is used to modulate the boost current, and to derive some further information like the average value of the AC line, used by the VFF (voltage feed-forward) function. This function allows keeping almost independent the output voltage by the mains one. The divider R7, R8, R9, R10 is dedicated to sense the output voltage. The second divider R11, R12, R13 and R28 is dedicated to protect the circuit in case of voltage loop fail.