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FAIRCHILD AN-6083 Dual PWM Combination Controller High Integration Data Manual User Guide

Summary

Elevate your AC/DC designs with the FAN6791, a highly integrated Dual-PWM Combination Controller crafted for developing high-efficiency smart power supplies. This application note provides deep technical guidance for electrical engineers and designers looking to optimize converter performance. The manual covers critical design elements, including advanced startup circuitry, specialized two-step UVLO protection, proprietary green-mode functionality, and system integration best practices. Learn how to achieve maximum reliability while minimizing standby power consumption in your next generation of electronic products.

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www.fairchildsemi.com

AN-6083 Highly Integrated, Dual-PWM Combination Controller

Introduction

This application note shows the step-by-step process to The FAN6791 is designed for the power supplies to achieve design a high-performance power supply which includes a high efficiency. The highly integrated FAN6791 dual-PWM flyback converter for standby power and a single forward combination controller provides several features to enhance converter for main power. Design considerations and the performance of converters. To minimize standby power mathematical equations are presented, as well as guidelines consumption, a proprietary green-mode function provides for a printed-circuit-board (PCB) layout. off-time modulation to linearly decrease the switching frequency at light-load conditions. With the internal high-

The complete power-supply circuits shown in Figure 1

voltage startup circuitry, the power loss due to bleeding

demonstrate the FAN6791’s ability to manage high-output

resistors is also eliminated. The built-in synchronized slope

power while complying with international requirements

compensation of FAN6791 achieves stable peak-current-

regarding AC line quality.

mode control. The proprietary internal line compensation ensures constant output-power limit.

Figure 1. Typical Application

© 2008 Fairchild Semiconductor Corporation www.fairchildsemi.com Rev. 1.0.2 • 3/11/09

Page Summary Contents For FAIRCHILD AN-6083 Dual PWM Combination Controller High Integration Data Manual User Guide

Page 1 www.fairchildsemi.com AN-6083 Highly Integrated, Dual-PWM Combination Controller Introduction This application note shows the step-by-step process to The FAN6791 is designed for the power supplies to ...
Page 2 AN-6083 APPLICATION NOTE Startup Circuitry When the power is turned on, the internal current source 6m A (typically 2.5m A) charges the hold-up capacitor C6 through a startup resistor RHV. During the ...
Page 3 AN-6083 APPLICATION NOTE function internally. The frequency variation ranges from Remote On/Off around 61KHz to 69KHz for a center frequency 65KHz. The frequency hopping function helps reduce EMI emis...
Page 4 AN-6083 APPLICATION NOTE effective, highly efficient, compact flyback power supply VOUTRB R FB operating in CCM without additional external components. The positive ramp added is: R1 SLOPE SLOPEV wher...
Page 5 AN-6083 APPLICATION NOTE Open-Loop Protection FAN6791’s OCP & SCP are based on the detection of feedback signal on FBPWM pin. As shown in Figure 15, when over current or short circuit occurs, FBPW...
Page 6 AN-6083 APPLICATION NOTE The turn ratio is given as: Lab Note Before modifying or soldering/de-soldering the power PRI VOUT OUT (10) supply, discharge the primary capacitors through the SEC (12 SEC (1...
Page 7 AN-6083 APPLICATION NOTE Printed Circuit Board Layout High-frequency switching current/voltage makes PCB GND3→2→1→4: Potentially better for ESD testing layout a very important design issue. Good PCB l...
Page 8 AN-6083 APPLICATION NOTE Figure 16. Layout Considerations © 2008 Fairchild Semiconductor Corporation www.fairchildsemi.com Rev. 1.0.2 • 3/11/09 8
Page 9 AN-6083 APPLICATION NOTE Reference FAN6791 — Highly Integrated, Dual-PWM Combination Controller AN-6741 — Flyback Power Supply Control with the SG6741 AN-6932 — Applying SG6932 to Control a PFC and Fo...

Manual Details

Brand Integration
Pages 9
File Size 343.30 KB
Published May 29, 2026
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Frequently Asked Questions

How does the FAN6791 maintain stable output under varying Line quality?

It utilizes proprietary internal line compensation and built-in synchronized slope compensation for stable peak-current regulation.

What mechanism protects against short circuits or open-loop conditions?

The device incorporates a special two-step UVLO/OLP mechanism to greatly reduce average input power during fault conditions.

How is the minimum power-on delay time calculated?

It is determined by $t = D_{ON} / (C imes V)$, where V is the turn-on threshold voltage and $D_{ON}$ is the internal timing constant.