NCP1200 driver LED circuit

This circuit uses a low-cost, offline constant current source to power multiple LEDs . A full-wave bridge rectifier (VD2 ~ VD3) and filter capacitor C1 provide approximately 160V DC voltage to the conversion circuit IC 1 and its associated components. Resistor R3 changes the bias value for the current sense pin of IC 1, and the 6.2kΩ value allows the use of a 1.2Ω sense resistor for R6. Reducing R6 not only reduces cost but also increases the efficiency of the circuit relative to a higher wattage sense resistor. Capacitor C3 is used to stabilize the current of the feedback network and carries the 400V rated voltage when the LED string is open circuit. The RC network consisting of R5 and C4 provides low-pass filtering to the CS pin.