FAIRCHILD AN-9750 High-Performance Factor Flyback Converter for LED Driver with FL7732 PSR Controller
Summary
Maximize efficiency and simplify circuit design for professional LED drivers using this comprehensive application note. This resource guides engineers through designing primary-side controlled flyback converters utilizing the FL7732 PWM controller, ensuring robust constant current regulation and high power factor correction. The manual provides detailed, step-by-step procedures covering ideal DCM operation, advanced protection circuits (Open/Short-LED), and linear frequency control for reliable performance across diverse load conditions. Ideal for electrical designers developing next-generation LED lighting power supplies with minimal components and maximized reliability.
Page 1 Text Content
www.fairchildsemi.com
AN-9750 High-Power Factor Flyback Converter for LED Driver with FL7732 PSR Controller
efficiency and simple design. FL7732 provides protection
Introduction functions such as open-LED, short-LED and over-
temperature protection. The current-limit level is
This highly integrated PWM controller, FL7732, provides
automatically reduced to minimize the output current and
several features to enhance the performance of low-power
protect external components in short-LED condition.
flyback converters. The proprietary topology enables
simplified circuit design for LED lighting applications. By This application note presents practical design consideration using single-stage topology with primary-side regulation, a for an LED driver employing Fairchild Semiconductor LED lighting board can be implemented with few external PWM PSR controller FL7732. It includes designing the components and minimized cost, without requiring an input transformer, selecting the components, and implementing bulk capacitor and feedback circuitry. To implement high constant current regulation. The step-by-step design power factor and low THD, constant on-time control procedure helps engineers design a power supply. The utilizes an external capacitor connected at the COMI pins. design procedure is verified through an experimental prototype converter. Figure 1 shows the typical application
Precise constant-current control regulates accurate output
circuit of primary-side controlled flyback converter using
current across changes in input voltage and output voltage.
FL7732 created in the design example.
The operating frequency is proportionally changed by the output voltage to guarantee DCM operation with higher
Figure 1. Typical Application Circuit
© 2011 Fairchild Semiconductor Corporation www.fairchildsemi.com Rev. 1.0.3 • 5/15/12
Page Summary Contents For FAIRCHILD AN-9750 High-Performance Factor Flyback Converter for LED Driver with FL7732 PSR Controller
Manual Details
| Brand | Fairchild |
|---|---|
| Pages | 13 |
| File Size | 435.57 KB |
| Published | July 07, 2026 |
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Frequently Asked Questions
What protective features does the FL7732 controller include?
The FL7732 provides open-LED, short-LED, and over-temperature protection functions.
Why is Discontinuous Conduction Mode (DCM) preferred for flyback converters?
DCM operation is preferred because it allows better output regulation in primary-side control.
How does the controller achieve constant current regulation?
It uses ® TRUECURRENT technique to compare the estimated output current against an internal reference voltage, adjusting the MOSFET duty cycle accordingly.
What benefit does using the FL7732 single-stage topology offer for LED drivers?
It allows simplified circuit design with few external components and minimized cost.