Using the Buck-Boost topology, the circuit shown in Figure above generates a non-isolated constant current (CC) output for driving LEDs. Typical uses include night-lights, neon sign replacements,emergency exit signs or any application utilizing LEDs for lighting.The AC input is rectified and filtered by D1, D2, C1, C2, RF1, and RF2. Two diodes improve both line surge withstand (2 kV) and conducted EMI. Resistor RF1 should be a fusible flameproof type, whereas RF2 can be fl ameproof only.
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