Green Current Mode PWM Controller# Technical Documentation: FAN7602CMX Green-Mode PWM Controller
Manufacturer : FAIRCHILD (now part of ON Semiconductor)
Component Type : Current-Mode PWM Controller for Offline Quasi-Resonant Flyback Converters
Primary Function : Provides control circuitry for high-efficiency, low-power switch-mode power supplies (SMPS) with minimal standby power consumption.
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## 1. Application Scenarios
### Typical Use Cases
The FAN7602CMX is specifically engineered for quasi-resonant (QR) flyback converter topologies in offline AC/DC power supplies. Its primary use cases include:
* Low-to-Medium Power AC/DC Adapters & Chargers (5W to 30W range): Commonly found in power supplies for consumer electronics such as routers, set-top boxes, monitors, and small appliances. Its green-mode feature is critical for meeting global energy efficiency standards (e.g., ENERGY STAR, EU CoC Tier 2) by minimizing no-load and light-load power consumption.
* Auxiliary/Standby Power Supplies : Used in larger systems (e.g., TVs, desktop PCs, industrial equipment) to generate the low-voltage rail needed for standby or control circuitry, thanks to its low startup current and burst-mode operation.
* LED Driver Power Supplies : Suitable for constant-voltage LED drivers where high efficiency across a wide load range and robust protection are required.
### Industry Applications
* Consumer Electronics : The dominant application area, powering a vast array of household and personal electronic devices.
* Industrial Controls : Provides reliable, isolated power for control boards, sensors, and communication modules, benefiting from its integrated protections.
* IT & Networking Equipment : Powers modems, routers, and switches where high efficiency at both full load and standby is mandated.
* Lighting : Found in LED bulb drivers and external LED power modules.
### Practical Advantages and Limitations
Advantages:
* High Efficiency & Low Standby Power : Quasi-resonant switching reduces switching losses, especially at high line voltage. The proprietary "Green Mode" function dramatically decreases switching frequency under light/no-load conditions, cutting switching and gate drive losses.
* Integrated Protections : Includes built-in Over-Current Protection (OCP) , Over-Voltage Protection (OVP) via the feedback loop, and an internal Over-Temperature Protection (OTP) for enhanced system reliability.
* Low Startup Current (< 30 µA) : Allows the use of a high-value startup resistor, reducing power loss in the startup circuit and enabling faster, more reliable startup.
* Valley Switching (QR Operation) : Turns the MOSFET on at the minimum voltage point (valley) of the drain voltage oscillation, minimizing turn-on switching losses and EMI generation.
Limitations:
* Power Range Constraint : Optimized for low-to-medium power applications (typically < 75W). For higher power levels, other topologies (e.g., LLC, active-clamp flyback) with different controllers may be more appropriate.
* Frequency Variation : The quasi-resonant operation leads to a variable switching frequency that changes with input voltage and load. This complicates EMI filter design compared to fixed-frequency controllers.
* Minimum Load Consideration : In burst mode (green mode) at very light loads, the output voltage ripple may increase. Designs requiring extremely tight voltage regulation at near-zero load may need additional circuitry.
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## 2. Design Considerations
### Common Design Pitfalls and Solutions
1. Pitfall: Unstable Operation or Jittering at Light Load
* Cause : Improper setting of the green-mode threshold or feedback loop compensation near the burst mode entry point.
* Solution : Carefully select the voltage divider ratio on the
