The FAN7529 is an active power factor correction (PFC) controller for boost PFC applications that operates in critical conduction mode (CRM). It uses the voltage mode PWM that compares an internal ramp signal with the error amplifier output to generate MOSFET turn-off signal. Because the voltage-mode CRM PFC controller does not need rectified AC line voltage information, it saves the power loss of the input voltage sensing network necessary for the current-mode CRM PFC controller. FAN7529 provides many protection functions, such as over-voltage protection, open-feedback protection, overcurrent protection, and under-voltage lockout protection. The FAN7529 can be disabled if the INV pin voltage is lower than 0.45V and the operating current decreases to 65A. Using a new variable on-time control method, THD is lower than the conventional CRM boost PFC ICs.