Critical Conduction Mode PFC Controller# Technical Documentation: FAN7930 CCM PFC Controller
Manufacturer : FAIRCHILD (ON Semiconductor)
Component : FAN7930
Description : Critical Conduction Mode (CrM) Power Factor Correction (PFC) Controller
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## 1. Application Scenarios
### Typical Use Cases
The FAN7930 is a specialized controller IC designed for building Power Factor Correction (PFC) pre-regulator stages . Its primary function is to shape the input current drawn from the AC mains to be sinusoidal and in phase with the input voltage, thereby achieving a high power factor (typically >0.95). It operates in Critical Conduction Mode (CrM) , also known as Transition Mode (TM).
* Standalone PFC Boost Converters : The most direct application is a boost converter topology placed between the bridge rectifier and the main DC-DC conversion stage. It elevates the rectified AC voltage to a stable, higher DC bus voltage (e.g., 400V) while correcting the power factor.
* Front-end for Switched-Mode Power Supplies (SMPS) : It is universally employed as the first power processing stage in medium-to-high power AC-DC adapters, LED drivers, and server/telecom power supplies to meet regulatory standards for harmonic current limits (e.g., IEC 61000-3-2).
* Motor Drives and Inverters : Used in the input stage of variable frequency drives (VFDs) and uninterruptible power supplies (UPS) to improve grid-side power quality and reduce input current distortion.
### Industry Applications
* Consumer Electronics : High-power gaming consoles, all-in-one PCs, and large-screen LCD/LED TV power supplies (>100W).
* Computing & Telecom : Server power supplies, blade server modules, and telecom rectifiers where efficiency and compliance are critical.
* Industrial Equipment : Power supplies for industrial automation, control systems, and test/measurement equipment.
* Lighting : High-brightness, high-power LED drivers for commercial and industrial lighting fixtures.
* Appliances : High-end air conditioners, washing machines, and other appliances with motor drives or high-power electronics.
### Practical Advantages and Limitations
Advantages:
* High Power Factor : Enables compliance with stringent international harmonic standards.
* Reduced Component Stress (CrM Operation) : Operates at the boundary between continuous and discontinuous conduction modes. This ensures the boost diode turns off at zero current, eliminating reverse recovery losses and enabling the use of a standard, cost-effective diode instead of a more expensive SiC Schottky.
* Variable Frequency Operation : Switching frequency varies with line voltage and load. At high line voltage and light load, frequency increases, which can sometimes aid in meeting EMI filter size requirements.
* Integrated Protections : The FAN7930 includes crucial safety features like Over-Voltage Protection (OVP), Open-Loop Protection (OLP), and Under-Voltage Lockout (UVLO).
* Low Start-up Current : Minimizes losses in the start-up circuitry.
Limitations:
* Frequency Variation : The variable switching frequency complicates EMI filter design, as the filter must be effective across a wide frequency range.
* Peak Current Limitations : CrM operation results in high peak switch currents, especially at low line voltage and full load. This increases conduction losses and requires a power MOSFET with a higher current rating and careful thermal management.
* Power Range : Typically best suited for applications in the 75W to 300W range. At very low power, frequency becomes impractically high; at very high power, peak currents become excessive.
* Audible Noise Risk : The variable frequency can, under certain light-load conditions, enter the audible range (
