The system setup based on Zeta topology is shown in Fig. 6 (a), where lead acid battery specification is 12 V 100 Ah, and LED module consists of 15 pieces of Philips Lumileds Luxeon LXK2-PB12-L00. The prototype of LED driver shares the same controller as that of solar charger shown in Fig. 6 (b), where the SAS charges the same battery through Sepic-based charger circuit.
The LED driver in Fig. 6 (a) works at constant current control mode. In conventional
implementation of constant current driving, the practical LED driving current is sensed and compared with the current reference, and the error signal is processed by a proportional and integral (PI) type current regulator. In Zeta-based driver, another type of current regulator is studied and implemented based on digital hysteresis control, as is shown in Fig. 7, where ILED is practical driving current of LED module, Iset is current reference, ΔIth1 is threshold of current adjustment, and ΔIth2 is larger threshold that ΔIth1 for determining the perturbation steps (ΔD2 > ΔD1) of DQb.