Classic PFC (Power Factor Correction) converters usually have three sensors: input voltage, input current and output voltage. Instead of using these three measures to calculate the duty cycle, precalculated duty cycles can be stored in a memory. With this memory, the system only has to synchronize with the ac mains and apply the duty cycles, at least for nominal conditions. This paper shows several methods to accomplish this synchronization, using an ADC or a voltage comparator. Results show that PFC can be achieved using simple synchronization methods and precalculated duty cycles.