FAIRCHILD SG6902 Application for Controlling a CCM PFC and Flyback PWM Power Supply Data Manual
Summary
The SG6902 is an advanced Green Mode PFC/Flyback PWM Controller designed for building high-efficiency, reliable switching power supplies like 120W adapters. This application note guides engineers through a complete, step-by-step design using interleaved PFC and PWM stages to drastically reduce noise while maximizing efficiency. Key features include automatic green-mode operation, multi-vector control for fast transient response, and comprehensive protections (OVP/UVP, Brownout). It is essential for power supply designers seeking stable performance across varying loads with minimum external components.
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AN-6902 Applying SG6902 to Control a CCM PFC and Flyback/PWM Power Supply Summary Description This application note shows a step-by-step design to a SG6902 is designed for power supplies that consist of boost 120W/24V power adapter. The equations also can be PFC and flyback PWM. It requires few external applied to different output voltages and wattages. components to achieve green-mode operation and versatile
protections and compensations.
Features The proprietary interleave switching synchronizes the PFC
and PWM stages and reduces switching noise. At light
Interleaved PFC/PWM Switching
loads, PFC stage is turned off to save power and the PWM
Green-Mode PFC/PWM Switching switching frequency is decreased in response to the load. No PFC Switching at Light Loads for Power Saving
For PFC stage, the proprietary multi-vector control scheme Innovative Switching Charge Multiplier-divider provides a fast transient response in a low-bandwidth PFC loop. The overshoot and undershoot of the PFC voltage are
Low Startup and Operating Current
clamped. If the feedback loop is broken, SG6902 shuts off
Innovative Switching Charge Multiplier-divider the switching to protect the power supply and its load. Multi-vector Control for Improved PFC Output
For the flyback PWM stage, the synchronized slope
Transient Response
compensation ensures the stability of the current loop. Average-Current-Mode Control for PFC “Hiccup” operation limits a maximum output power during the overload situations.
Programmable Two-Level PFC Output Voltage to
Achieve the Best Efficiency The difference between members of this family are shown in the table below.
PFC Over-voltage and Under-voltage Protections PFC and PWM Feedback Open-loop Protection Parameter SG6902 SG6901A Cycle-by-cycle Current Limiting for PFC/PWM Start Threshold Voltage 16V 12V
Slope Compensation for PWM Minimum Operating Voltage 10V 10V Maximum Power Limit for PWM The Interval of OPFC Lags Behind OPWM at Startup 11.5ms 11.5ms
Brownout Protection
PFC On/Off O X
Over Temperature Protection
OTP O O
Power-on Sequence Control and Soft-start
Soft-Start O O
20-Pin SOP and SSOP Packages
© 2007 Fairchild Semiconductor Corporation www.fairchildsemi.com Rev. 1.2.1 • 5/1/08
Page Summary Contents For FAIRCHILD SG6902 Application for Controlling a CCM PFC and Flyback PWM Power Supply Data Manual
Manual Details
| Brand | Fairchild |
|---|---|
| Pages | 12 |
| File Size | 539.14 KB |
| Published | June 18, 2026 |
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Frequently Asked Questions
How does the SG6902 improve efficiency at light loads?
It employs Green-Mode PFC/PWM Switching, which turns off the PFC stage or decreases the switching frequency to save power.
What features ensure stability and fast response in the PFC stage?
The proprietary multi-vector control scheme provides a fast transient response, while innovative charge multiplier-dividers clamp voltage overshoot/undershoot.
If I break the feedback loop during operation, what happens?
The SG6902 is designed to automatically shut off to protect both the power supply and its load.
Do different models (SG6902 vs SG6901A) have functional differences?
Yes. The SG6902 includes Brownout Protection, which is absent in the SG6901A model.