Solar. - Here is other circuit schematic for solar charger. This is Circuit Schematic 6V Solar Charge Shunt Regulator like in figure 1 below. A shunt regulator technique may be effectively employed in regulating the charging voltage of a lead-acid battery. Although it has a practical power limitation (< 20W or so), it has the notable advantage of being an LDO (low dropout) regulator (zero voltage dropout in this case) - this is in contrast with the typical series regulator that often has a dropout voltage in the order of 1 to 3V.
Circuit schematic like in figure 1 above is Circuit Schematic 6V Solar Charge Shunt Regulator. D10 is a schottky battery isolation diode – it is vital in this application so that the actual battery charge never gets shunted by the regulator. The low forward voltage of D10 (approx 0.25V @ low current) means that the solar panel must generate only 0.25V over the battery voltage. The shunt regulator consists of two transistors (Q1 & Q2) in the composite NPN/PNP connection. This has the current gain of a Darlington with the input characteristics of a bipolar transistor. Q2 dissipates approx. 3.5W, so a small heatsink is required. D2 in series with zener D3 (6.8V) and the Vbe of Q1 make up the voltage reference – when the voltage exceeds 7.45V, Q1 & Q2 turn on so that the current is shunted. I had to trim up the voltage of the zener slightly by adding D2 because the zener was running on the low side. The shunt current path is through D4 through D8 – these diodes dissipate approximately half of the power thus taking it away from Q2. D4 through D8 also drop sufficient voltage to turn on LED D9, thus indicating at least 75% charge level.
The original article : "Circuit Schematic 6V Solar Charge Shunt Regulator"