Electronic Ballast Control IC# Technical Documentation: FAN7532 Power Factor Correction (PFC) Controller
## 1. Application Scenarios
### 1.1 Typical Use Cases
The FAN7532 is a critical-mode (transition-mode) Power Factor Correction (PFC) controller IC designed to shape the input current waveform to match the input voltage waveform in AC-DC power supplies. Its primary use case is as the control core in a boost converter topology placed between the bridge rectifier and the main DC link capacitor.
Core Functionality: It drives an external MOSFET switch to control the inductor current in a boost PFC pre-regulator, ensuring the input current is sinusoidal and in phase with the input voltage. This is achieved using a multiplier-based control approach with a zero-current detection (ZCD) pin to maintain critical conduction mode (CrM) operation.
### 1.2 Industry Applications
The FAN7532 is deployed across industries requiring compliance with harmonic current limits (e.g., IEC 61000-3-2) and high power efficiency.
* Consumer Electronics: LCD/LED TV power supplies, desktop computer ATX/SFX power supplies (typically for units >75W), gaming consoles, and audio amplifiers.
* Industrial Equipment: Programmable logic controller (PLC) power modules, motor drives with auxiliary power supplies, and LED lighting drivers for high-bay or industrial fixtures.
* Telecommunications: AC-DC rectifiers and power shelves for networking equipment and servers.
* Appliances: High-power SMPS in air conditioners, refrigerators, and washing machines.
### 1.3 Practical Advantages and Limitations
Advantages:
* High Power Factor: Enables designs to achieve PF >0.99, ensuring compliance with international regulations.
* Critical Conduction Mode (CrM): Operates at the boundary between continuous and discontinuous conduction. This eliminates the reverse recovery loss of the boost diode, improving efficiency, especially at high line voltages.
* Integrated Protections: Includes robust over-voltage protection (OVP), under-voltage lockout (UVLO), and open-loop protection, enhancing system reliability.
* Low Start-up Current: Consumes typically 50 µA during startup, reducing stress on the startup circuitry.
* Multiplier-Based Control: Provides good linearity and a stable, clean current waveform.
Limitations:
* Frequency Variation: In CrM, the switching frequency varies with input voltage and load (highest at low line, full load). This complicates EMI filter design as the noise spectrum is not fixed.
* High Peak Currents: At low input voltages and high power, the peak inductor and switch currents can be significantly higher than the average input current, requiring components rated for higher stress.
* Power Range: Best suited for low to medium power applications (typically up to 300-400W). For higher powers, continuous conduction mode (CCM) controllers are often preferred for lower peak currents.
* Gate Drive: The totem-pole output provides a peak source/sink current of ±500 mA, which is sufficient for most MOSFETs in its power range but may require a gate driver for very large MOSFETs or very high switching frequencies.
## 2. Design Considerations
### 2.1 Common Design Pitfalls and Solutions
* Pitfall 1: Unstable ZCD Signal. A noisy or improperly scaled zero-current detection signal can cause erratic switching, leading to high THD or audible noise.
* Solution: Use a dedicated ZCD winding on the boost inductor (recommended) or a high-voltage resistor divider from the boost diode anode. Include a small RC filter (e.g., 100 Ω, 100 pF) at the ZCD pin to suppress noise, ensuring the ZCD pin voltage stays within its absolute maximum rating (-0.
