This Low Dropout
Voltage (LDO) control is a variation of the previously posted 12V LDO control. It is optimized for charging a 6V lead-acid battery with a 9V solar panel.
Minimum voltage drop is less than 1V. It uses a simple differential amplifier and series P channel MOSFET linear regulator. Voltage output is adjustable. It may also be applied in two or four cell lead-acid applications (4V & 8V).
The input voltage exceeds the input voltage by 0.9V when charging at the maximum rate—the lower, the better. Low Dropout
Voltage (LDO) is the catch phrase for anything under approximately 2V.
Current limiting is provided by the solar panel—it is not a commonly understood fact that the solar panel tends to be a constant current device. For this reason, a solar panel can withstand a short circuit. Therefore, the control does not need current limiting.
Circuit Solar Charge Control
To set the voltage, disconnect the battery and connect a 470Ω dummy load resistor across the output. The resistor is necessary to shunt potential MOSFET leakage current as well as the green LED current. The battery must be disconnected because the output voltage of the control cannot otherwise be set below actual battery voltage.