LED driving circuit with stand-alone photovoltaic power

This research proposes an LED driving circuit with stand-alone photovoltaic (PV) power. A bi-directional converter is incorporated to adequately distribute powers among the solar-cell panel, the battery and the LED lamp according to the sunshine intensity, the battery state-of-charge as well as the load requirement. By matching the voltage-current (V-I) characteristic curves, the capacities of the solar-cell panel and the battery are specified to mostly operate the solar-cell panel around the maximum power point. The proposed LED driving circuit is applied to a scenario of the traffic light application. The solar-cell panel is operated near the maximum power point, providing the LED power and delivering the excess energy to the battery. If the light intensity is not strong enough for the solar-cell panel to generate full power required by the load, the battery sets will compensate for the shortage. To verify the theoretical analyses of the LED driving circuit, a laboratory system is set up for experimental tests. The tested results demonstrate that the system can perform the designated functions in accordance with different states. The measured efficiencies are always over 88%.