Non-isolated topologies for high step-down offline LED driver applications

In this paper, two non-isolated DC-DC converter topologies suitable for offline Light-emitting Diode (LED) driver applications are presented. The output voltage for such applications is generally less than 42 V DC to satisfy LED lighting system requirements. Isolated converters are normally used for this higher step-down (170V-42V/15V DC) operation. However, an isolation transformer introduces increased complexities in the implementation of feedback and control. Dedicated passive or active circuitry is also required to mitigate the energy in the leakage inductance. The proposed topologies are non-isolated and hence are much simpler in implementation. The converters are suited for two nominal step-down conversions - (1) 170V-42V DC, (2) 170V-15V DC operation while maintaining a reasonable duty cycle and efficiency. Their operation is described in detail. Both the converters can be controlled to achieve active power factor correction. Simulation results with relevant parasitic are presented to verify the claimed step-down conversions.