Electronic Ballast Controller# Technical Documentation: FAN7544N Power Factor Correction Controller
Manufacturer : FAIRCHILD SEMICONDUCTOR (ON Semiconductor)
Component : FAN7544N
Type : Critical Conduction Mode (CRM) Power Factor Correction (PFC) Controller IC
Package : 8-Pin DIP (Dual In-Line Package)
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## 1. Application Scenarios
### Typical Use Cases
The FAN7544N is a dedicated controller IC designed for building boost-type Power Factor Correction (PFC) pre-regulators . Its primary function is to shape the input current drawn from the AC mains to closely follow the sinusoidal waveform of the input voltage, thereby achieving a high Power Factor (PF > 0.99 typical) and low Total Harmonic Distortion (THD < 10% typical).
Primary Use Cases Include:
* AC-DC Switch-Mode Power Supplies (SMPS): Used as the front-end PFC stage in power supplies requiring compliance with international harmonic current standards (e.g., IEC 61000-3-2). This is its most common application.
* Standalone PFC Modules: Incorporated into modular power solutions that provide a regulated, high-voltage DC bus (typically ~400V) for downstream DC-DC converters.
* Lighting Systems: Employed in high-power electronic ballasts for HID lamps and high-brightness LED drivers to improve grid efficiency and meet regulatory requirements.
* Industrial Motor Drives & UPS Systems: Used in the input stage to reduce harmonic pollution on the AC line and improve the overall efficiency of the system.
### Industry Applications
* Consumer Electronics: High-end desktop computers, gaming consoles, large-screen LCD/LED TVs, and audio amplifiers.
* IT & Telecom: Server power supplies, telecom rectifiers, and network equipment power modules.
* Industrial Equipment: Programmable Logic Controller (PLC) power supplies, automation system power units, and welding equipment.
* Lighting: High-power street lighting, stadium lighting, and industrial lighting power supplies.
### Practical Advantages and Limitations
Advantages:
* High Power Factor: Enables designs to easily exceed regulatory requirements for harmonic current emission.
* Critical Conduction Mode (CRM) Operation: Also known as Transition Mode (TM). This ensures the boost inductor current returns to zero on every switching cycle (Zero Current Switching - ZCS at turn-on). This minimizes switching losses in the boost diode and reduces reverse recovery issues, leading to higher efficiency, especially at lower power levels.
* Simplified Design: The CRM control method inherently provides input voltage feedforward, simplifying the control loop compensation compared to fixed-frequency Continuous Conduction Mode (CCM) controllers.
* Internal Start-up Timer: Reduces external component count.
* Low Start-up Current: Minimizes stress on the start-up circuitry.
* Over-Voltage Protection (OVP): Protects the system from output overvoltage conditions.
Limitations:
* Power Range: Best suited for low to medium power applications (typically up to 300W-400W). At higher power levels, the peak currents in CRM become very high, increasing conduction losses and EMI, making CCM controllers more suitable.
* Variable Frequency: The switching frequency varies with input voltage and load. It is highest at the zero-crossings of the AC line and lowest at the peak. This complicates EMI filter design, as the filter must be effective over a wide frequency range.
* Audible Noise Risk: At light loads, the switching frequency can drop into the audible range (<20kHz), potentially causing inductor or ceramic capacitor whine.
* Higher RMS Currents: Compared to CCM, CRM operation results in higher RMS currents for the same output power, which can necessitate larger
