LED Driver using LNK454DG

A very simple high efficiency led driver circuit can be designed using LNK454DG controller designed by Power Integrations . This LNK454DG led driver is configured as non-isolated discontinuous flyback converter designed to drive LED strings at voltages of 2.5 V to 3.5 V with an output current of 366 mA The circuit meets both line surge and EMI requirements and the low component count allows board dimensions required for LED candelabra bulb replacement applications. LNK454DG led driver is very easy to be configured and require few external electronic parts.

LED Driver Schematic

Two differential pi (π) filter EMI stages are used with C1, R1, L1 and C2 forming one stage and C2, L2, R2 and C3 the second.The incoming AC is rectified by BR1 and filtered by C1, C2 and C3. The total effective input capacitance, the sum of C1, C2 and C3, was selected to assure correct zero crossing detection of the AC input by the LinkSwitch-PL device and to meet high power factor and low THD. Due to the limited input capacitance (to meet PF) RV1 and VR1 are used to limit component voltage stress during line surges.The LNK454DG device (U1) incorporates the power switching device, oscillator, output constant current control, start-up, and protection functions.

The integrated 725 V MOSFET provides extended voltage margin and ensures high reliability even during line surge events. The device is powered from the BYPASS pin via the decoupling capacitor C5.The rectified and filtered input voltage is applied to one end of the primary winding of T1.The other side of the transformer’s primary winding is driven by the integrated MOSFET in U1. The leakage inductance generated drain voltage spike is limited by an RCD clamp consisting of D1, R3, and C4.Diode D2 is used to protect the IC from negative ringing when the MOSFET is off due to the reflected output voltage exceeding the DC bus voltage, the result of minimal input capacitance to give high power factor.T1 transformer is an SNX R1568 coil from Santronics or some other equivalent .
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