A flyback converter with no input capacitance operating in discontinuous conduction mode inherently provides a high power factor. The schematic shown in Figure above takes this approach and adds an output current limit to form a high power LED driver. The circuit description below highlights the key circuit differences between this and a standard fly back converter.To prevent large voltage transients due to AC line inductance or surges, a clamp circuit consisting of C4, D5 and R3 limits the DC bus voltage to a safe value. Once in steady state, the capacitor is effectively decoupled from the circuit by D5 so as to not impact Power Factor (PF). Resistor R3 provides a discharge path for C4.
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