Solar LED circuit diagram



The goal of this work was to create most efficient constant current boost driver operational from single cell Li−Ion battery recharged from solar module. Savings and the environment quality are a concern. This solar LED circuit diagram describes implementation of the CAT4139, a dc−dc step−up converter that delivers an accurate constant current for driving serial LED string in solar LED lamp.

Battery cell is charged during daylight, when average voltage on solar module (SOLAR+ pin) is around 4.2 V. Charge current at solar module output varies proportionally to incident light and charging is controlled by incorporated protection battery circuit. SOLAR+ voltage switches on transistor T1 and its collector voltage disables the CAT4139.

When ambient light is decreased and voltage on SOLAR+ pin is below threshold given by base−emitter voltage of T1, the CAT4139 driver is enabled and supplies constant current to LED string (T1, R5, R1 circuit is used to invert voltage coming from solar module.).

 During night, battery is being discharged. D2 is used to prevent from reverse current flow from battery to solar module. The constant LED current is given by value of R4 resistor (in this case, 0.3 V/3.3 = 0.091 A.




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