Lithium-Ion Charger Controller# Technical Documentation: FAN7564 Power Factor Correction (PFC) Controller
Manufacturer : FAIRCHILD (now part of ON Semiconductor)
Component : FAN7564
Type : Critical Conduction Mode (CRM) Power Factor Correction (PFC) Controller IC
Primary Function : To control a boost converter stage to shape the input current waveform to match the input voltage waveform, achieving a high power factor (typically >0.99) and low total harmonic distortion (THD) in AC-DC power supplies.
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## 1. Application Scenarios
### Typical Use Cases
The FAN7564 is designed as a dedicated controller for building Critical Conduction Mode (CRM) Boost PFC front-end stages . Its primary use case is to be placed between the AC line rectifier and the main DC-DC converter stage in offline power supplies.
* Standalone PFC Pre-regulators : It drives an external MOSFET to control a boost inductor, capacitor, and diode, creating a regulated high-voltage DC bus (typically 385-400V) from a universal AC input (85-265VAC).
* Interleaved PFC Configurations : While the FAN7564 is a single-phase controller, multiple units can be synchronized and phase-shifted to create interleaved PFC stages. This configuration is used for higher power applications (e.g., >500W) to reduce input current ripple, boost inductor size, and improve thermal performance.
* Voltage Follower Operation : It can be configured in a "voltage follower" mode where the output DC bus voltage is not fixed but varies in proportion to the rectified AC input voltage. This improves efficiency at low line conditions by reducing switching and conduction losses, though it requires a downstream DC-DC converter with a wider input voltage range.
### Industry Applications
The FAN7564 is found in a wide range of AC-DC power supplies where compliance with harmonic current emission standards (like IEC 61000-3-2) and high efficiency are mandatory.
1. Computer & Server Power Supplies : From desktop PC ATX/SFX power supplies (250W-600W) to server PSUs, where 80 PLUS certification demands high efficiency and PFC.
2. Industrial Power Systems : Power supplies for factory automation, PLCs, and motor drives that require robust, reliable operation from unstable AC mains.
3. Telecommunications Infrastructure : Rectifiers and power shelves for telecom systems requiring high power density and reliability.
4. Consumer Electronics : High-end LCD/LED TV power supplies, audio amplifiers, and gaming console adapters where size, efficiency, and EMI compliance are critical.
5. Lighting : High-power LED drivers and ballasts for commercial and industrial lighting.
### Practical Advantages and Limitations
Advantages:
* High Power Factor & Low THD : Inherent CRM operation ensures the inductor current reaches zero every cycle, naturally shaping the input current to follow the input voltage sine wave.
* Zero Voltage Switching (ZVS) : The CRM operation allows the external MOSFET to turn on when the drain-source voltage is at a minimum (valley switching), significantly reducing switching losses and improving efficiency, especially at high line voltages.
* Frequency Modulation : The switching frequency varies inversely with the input voltage and load. This spreads the EMI spectrum, simplifying filter design.
* Integrated Protections : Includes over-voltage protection (OVP), open-loop protection, and a disable function, enhancing system reliability.
* Simple Design : Requires fewer external components compared to average current mode control PFC controllers, reducing BOM cost and board space.
Limitations:
* Variable Frequency Operation : The wide variation in switching frequency (highest at low line, full load) complicates EMI filter design across the entire operating range and can cause audible noise
