Precise constant-current control regulates accurate output current across changes in input voltage and output voltage. The operating frequency is proportionally changed by the output voltage to guarantee DCM operation with higher efficiency and simple design. FL7732 provides protection functions such as open-LED, short-LED and overtemperature protection. The current-limit level is automatically reduced to minimize the output current and protect external components in short-LED condition.

This application note presents practical design consideration for an LED driver employing Fairchild Semiconductor PWM PSR controller FL7732. It includes designing the transformer, selecting the components, and implementing constant current regulation. The step-by-step design procedure helps engineers design a power supply. The design procedure is verified through an experimental prototype converter. Figure 1 shows the typical application circuit of primary-side controlled flyback converter using FL7732 created in the design example.

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