8-Pin PFC and PWM Controller Combo# Technical Documentation: FAN4803 PFC/PWM Combo Controller
## 1. Application Scenarios
### 1.1 Typical Use Cases
The FAN4803 is a monolithic integrated circuit designed for high-performance off-line power supplies , combining a Power Factor Correction (PFC) controller and a Pulse Width Modulation (PWM) controller in a single 16-pin package. Its primary use cases include:
* AC-DC Switch-Mode Power Supplies (SMPS): The device is engineered to drive both the PFC boost converter stage and the downstream PWM forward or flyback converter stage from a single controller. This is particularly valuable in applications requiring compliance with international power quality standards (e.g., IEC 61000-3-2).
* High-Power Density Designs: By integrating two critical control functions, it significantly reduces component count and board space compared to using two separate ICs, enabling more compact power supply designs.
* Systems Requiring High Efficiency & Low THD: The FAN4803's average current mode control for the PFC stage ensures near-unity power factor and low total harmonic distortion (THD) of the input current. Its PWM stage utilizes a proprietary technique that provides synchronized leading-edge modulation, minimizing output voltage ripple.
### 1.2 Industry Applications
* Computer & Server Power Supplies: Used in desktop PC, workstation, and server power supplies (e.g., ATX, SSI standards) where high efficiency (80 Plus certification) and power factor correction are mandatory.
* Industrial Power Systems: Provides robust and reliable control for power modules, motor drives, and automation equipment requiring stable DC bus voltages.
* Telecommunications Infrastructure: Suitable for rectifiers and power shelves in telecom systems that demand high reliability and power quality.
* Consumer Electronics: Found in high-end audio/video equipment, gaming consoles, and large-format displays where efficient power conversion is critical.
### 1.3 Practical Advantages and Limitations
Advantages:
* High Integration: Reduces BOM count, saves PCB area, and simplifies design by synchronizing PFC and PWM stages.
* Improved Performance: The synchronized, interleaved operation of the PFC and PWM stages reduces ripple currents on both the input and output capacitors, leading to lower stress and potentially longer component life.
* Comprehensive Protection: Includes features like over-voltage protection (OVP), under-voltage lockout (UVLO), and open-loop detection for enhanced system reliability.
* Reduced EMI: The inherent synchronization and controlled switching transitions can help mitigate electromagnetic interference.
Limitations:
* Design Complexity: While integrated, the circuit design remains complex due to the high-power, high-frequency nature of PFC and PWM conversion. It requires careful attention to magnetics, power switching, and control loop stability.
* Fixed Control Architecture: The control methodology (average current mode PFC, leading-edge modulated PWM) is fixed. Designers needing different topologies (e.g., boundary conduction mode PFC, resonant LLC PWM) must look elsewhere.
* Power Level Constraints: While suitable for medium to high power (typically several hundred watts to over 1 kW), the specific implementation (MOSFETs, inductors, heatsinking) ultimately defines the maximum practical power output.
* Obsolete Status (Note): As a Fairchild Semiconductor (now part of ON Semiconductor) component, the FAN4803 is classified as End-of-Life (EOL) or Not Recommended for New Designs (NRND) . Securing long-term supply may be challenging for new projects.
## 2. Design Considerations
### 2.1 Common Design Pitfalls and Solutions
* PFC Inductor Saturation:
* Pitfall: An undersized or improperly specified
