A non-isolated converter design with time-multiplexing control topology for un-binned high-power LEDs in parallel operation for off-grid solar-PV streetlamps

Battery-operated Light Emitting Diodes (LEDs) are often arranged in parallel strings in a lighting fixture due to the high voltage gain required in case of a series type connection. Yet, current sharing is prevalent in the parallel configuration due to the large forward voltage tolerance of high-power LEDs resulting in uneven light output and premature failure when they are “overdriven”. Current-matching techniques in practice involve complexity, high cost and reduced efficiency. In this paper, a Single Inductor Multiple Output (SIMO) parallel string LED driver with time multiplexing control which takes advantage of the inability of the human eye in visual perception of high-frequency operation in order to time-share the operation of individual strings is proposed. This shall greatly reduce the component count and complexity with less than 5% current mismatch. Soft start, dimming and shutdown features are achieved for enabling off-grid solar photovoltaic (PV)-based lighting. Also, the availability of the system is increased by introducing a LED failure protocol which has been validated by simulation and hardware implementation.