This application note describes a demonstration board based on the transition-mode PFC controller L6563S and presents the results of its bench evaluation. The board implements a 400 W, wide-range mains input, PFC pre-conditioner suitable for ATX PSU, flat screen displays, etc. The chip is operated with fixed off time control in order to use a low-cost device like the L6563S, which is usually prohibitive at this power level. Fixed-off-time control allows continuous conduction mode operation, which is normally achieved with more expensive control chips and more complex control architectures.