Voltage Detector (2.7V)# Technical Documentation: KA75270ZTA Power Factor Correction Controller
Manufacturer : FAIRCHILD (Now part of ON Semiconductor)
Component Type : Critical Conduction Mode (CRM) Power Factor Correction (PFC) Controller IC
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## 1. Application Scenarios
### Typical Use Cases
The KA75270ZTA is specifically engineered as a high-performance, low-cost controller for building active Power Factor Correction (PFC) pre-regulators . 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 near-unity power factor (PF > 0.99). This is accomplished by controlling a boost converter topology operating in Critical Conduction Mode (CRM) , also known as Transition Mode (TM).
* Standalone PFC Front-End: The most direct application is as a dedicated PFC stage placed between the AC line input and the downstream DC-DC converter(s) in a switched-mode power supply (SMPS). It boosts the rectified line voltage to a stable, higher DC bus voltage (typically 385-400V DC).
* Integrated PFC+LLC Combo Designs: It is commonly paired with a resonant half-bridge LLC controller (like the FAIRCHILD FAN7621) to create high-efficiency, two-stage power supplies for demanding applications. The KA75270ZTA handles PFC, while the LLC stage provides isolated, tightly regulated output.
### Industry Applications
This IC is a cornerstone component in power supplies subject to regulatory mandates for harmonic current emission and power factor.
1. Computer & Server Power Supplies: Essential in 80 PLUS certified Silver, Gold, Platinum, and Titanium rated SMPS for desktop PCs, workstations, and servers (e.g., ATX, SSI EPS). It ensures compliance with IEC 61000-3-2 Class D harmonic limits.
2. Industrial Power Systems: Used in power modules for factory automation, motor drives, and telecommunications rectifiers where high PF and low Total Harmonic Distortion (THDi) are required for grid stability and reduced infrastructure costs.
3. Consumer Electronics: Found in high-end LCD/LED TV power supplies, gaming consoles, and large audio amplifiers where efficiency and regulatory compliance are critical.
4. Lighting: Employed in high-power LED driver ballasts and electronic ballasts for fluorescent lighting to meet energy efficiency standards like ENERGY STAR and EU Ecodesign.
### Practical Advantages and Limitations
Advantages:
* High Power Factor: Consistently achieves PF > 0.99 across a wide load range.
* Inherent Valley Switching: CRM operation ensures the boost MOSFET turns on at the minimum drain voltage (zero-voltage switching, ZVS), drastically reducing switching losses and EMI.
* Simplified Design: Requires no input voltage sensing or multiplier circuit, reducing external component count and design complexity.
* Internal Start-up Timer: Features a programmable soft-start function to limit inrush current during power-up.
* Robust Protection: Integrates over-voltage protection (OVP), under-voltage lockout (UVLO), and open-loop protection.
Limitations:
* Variable Frequency Operation: In CRM, switching frequency varies inversely with line voltage and load. This complicates EMI filter design, as the filter must be effective across a wide frequency band (from tens of kHz to several hundred kHz).
* Peak Current Stress: The inductor current is triangular with a high peak-to-average ratio. This results in higher RMS current stress on the boost inductor, MOSFET, and diode compared to Continuous Conduction Mode (CCM) PFC, potentially affecting component selection and efficiency at very high power levels.
* Power Range: Best suited for medium power applications , typically up to 250-300W. For
