This application note describes the theory of operation and step-by-step design considerations for a power factor correction power supply using the FAN6982 controller
The document describes the FAN6982 as a 14-pin Continuous Conduction Mode (CCM) Power Factor Correction (PFC) controller IC. It employs leading-edge modulation for average current control and includes advanced features such as variable output voltage function, TriFault Detect, soft-start, peak current limiting, and input voltage brownout protection. A typical application circuit is provided where the supply voltage is managed by a standby auxiliary power supply and controlled by the RDY pin for a downstream DC/DC converter.
The text covers the functional description of CCM versus BCM operation, the current and voltage control loops, and the benefits of line feed-forward for maintaining regulation during line transients. It also explains the line voltage sensing circuit, the range function for improving efficiency at light loads, oscillator timing, the RDY function for downstream converter control, and the soft-start mechanism to prevent output voltage overshoot.
| Package Type | 14-pin |
|---|---|
| Operation Mode | Continuous Conduction Mode (CCM) |
| Internal Resistor Value | 5.7kΩ |
| Internal Reference Voltage | 2.5V |
| Brownout Protection Trip Point | 1.05V |
| PFC Startup Threshold | 1.9V |
| FBPFC Threshold for RDY Connection | 96% of 2.5V |
| FBPFC Threshold for RDY Float | 46% of 2.5V |
| Vea Clamp Voltage | 2.8V |
The FAN6982 is commonly used for high-power applications above 300W.
The RDY signal is used for power-on sequence control of the downstream DC/DC converter.
The variable output voltage function reduces PFC output voltage at light-load and low-line conditions to improve light-load efficiency.
It clamps the error amplifier output voltage at 2.8V until the PFC output reaches 96% of its nominal value.