This application note introduces the frequency modulation feature of the L4981B version PFC controller, which can effectively reduce the EMI of the power factor correction circuit.
This document describes the frequency modulation feature of the L4981B Power Factor Correction (PFC) controller. The technique uses Pin 16 (FREQ-MOD) to dynamically change the switching frequency, which helps spread the noise spectrum over a wider range and reduces peak energy associated with electromagnetic interference (EMI). This approach aids in meeting RFI norms such as EN60555 and VDE0871B.
It spreads the noise spectrum over a wider range to reduce the peak of the associated energy and help meet EMI requirements.
Pin 16, which is named FREQ-MOD in this version, is used to perform the frequency modulation function.
It is defined by connecting pin 16 at the rectified mains through a resistor, using a specific formula involving the programming current resistor and oscillator components.