GREEN MODE PWM CONTROL IC# Technical Documentation: FAN7602B Green-Mode PWM Controller
Manufacturer : FSC (Fairchild Semiconductor, now part of ON Semiconductor)
Component Type : Current-Mode PWM Controller with Green-Mode Operation
Primary Function : Primary-side regulation for offline flyback converters in low-power SMPS applications.
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## 1. Application Scenarios
### Typical Use Cases
The FAN7602B is specifically engineered for offline switch-mode power supplies (SMPS) utilizing a flyback topology . Its primary use cases include:
* Low-Power AC/DC Adapters and Chargers : Commonly found in adapters for networking equipment (routers, modems), small consumer electronics (wireless headphones, Bluetooth speakers), and battery chargers for power tools or personal care devices, typically in the 5W to 30W range.
* Auxiliary (Standby) Power Supplies : Provides the low-voltage rail (e.g., 5VSB, 12V) in desktop PC power supplies, televisions, and appliances, where high efficiency at light loads is critical.
* LED Driver Modules : Used in non-dimmable or simple constant-voltage LED drivers for signage, lighting strips, and indicator panels.
* Industrial Control Power Modules : Powers microcontrollers, sensors, and relays in control systems where robust, isolated power from a mains input is required.
### Industry Applications
* Consumer Electronics : Power supplies for set-top boxes, gaming peripherals, and audio equipment.
* IT & Communication : Adapters for fiber-optic network terminals (ONTs), VoIP phones, and security cameras.
* Industrial Automation : Power for PLC I/O modules, HMI panels, and measurement devices.
* Home Appliances : Internal power boards for smart home devices, coffee makers, and air purifiers.
### Practical Advantages and Limitations
Advantages:
* High Light-Load Efficiency (Green Mode) : The controller reduces switching frequency under light-load or no-load conditions, significantly lowering standby power consumption to meet global energy efficiency standards (e.g., ENERGY STAR, EU CoC Tier 2).
* Primary-Side Regulation (PSR) : Eliminates the need for an optocoupler and secondary-side feedback circuitry, reducing component count, cost, and board space while improving reliability.
* Built-in Protections : Integrates multiple protection features including Over-Current Protection (OCP), Over-Voltage Protection (OVP), and Over-Temperature Protection (OTP via external NTC), enhancing system robustness.
* Fixed 65kHz Switching Frequency : Simplifies transformer and EMI filter design.
* Low Startup Current (<30µA) : Enables the use of a high-value startup resistor, improving efficiency at startup.
Limitations:
* Limited Output Power Range : Optimized for low-to-mid power applications. Not suitable for high-power designs (>~60W) where continuous conduction mode (CCM) or other topologies are preferred.
* PSR Accuracy and Transient Response : Voltage regulation accuracy (±5% typical) and load transient response are generally inferior to designs using secondary-side feedback with an optocoupler. Not ideal for applications requiring very tight voltage tolerances.
* Fixed Frequency : Lack of frequency jittering can make it more challenging to meet stringent EMI compliance margins compared to controllers with spread-spectrum features.
* DCM-Only Operation : Designed for Discontinuous Conduction Mode (DCM), which can lead to higher peak currents and potentially larger output capacitors compared to CCM operation at similar power levels.
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## 2. Design Considerations
### Common Design Pitfalls and Solutions
1. Pitfall: Transformer Design for PSR
* Issue : Incorrect transformer auxiliary
