Hello everyone ! can you please tell me how this whole circuit is working ? specially these ones, 1.whats happening at LM317's pins(in adjust and out) ? 2. whats the purpose of zener here? 3. purpose of transistor nd how is it working ? last question! how much time it will take to charge that 6v(4.5Ah) battery if we use 12v(3watt) solar panel?