12V LDO Solar Charge Controller

This Low Dropout Voltage (LDO) solar charge controller uses a simple differential amplifier and series P channel MOSFET linear regulator ”their compatibility seems like a marriage made in heaven. Voltage output is adjustable. It is mainly intended for charging 12V lead-acid batteries. The input voltage exceeds the input voltage by 1. 25V when char
 12V LDO Solar Charge Controller - schematic

ging at the maximum rate ”the lower, the better. Low Dropout Voltage (LDO) is the catch phrase for anything under approximately 2V. This could potentially be reduced to below 1V by making D3 a schottky rectifier. 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. This control charges the battery at a constant voltage and also maintains a charged battery (float charge). The float charge voltage specification is a little lower than the charge voltage, so to accommodate both voltages, a compromise is reached by simply reducing the voltage slightly ”that is how ALL automotive systems operate. To obtain maximum charge in a 12V battery, set the control to 14 to 14. 6V. Automotive systems further reduce voltage to 13 to 13. 5V in order to accommodate high temperature operation as the battery is usually located in the hot engine compartment ”battery has a negative thermal coefficient of voltage. To set the voltage, disconnect the battery and connect a 1K dummy load resistor to the output. The resistor is necessary to shunt potential MOSFET leakage current as well as the green LED current. R4 and D1 form a 6V shunt zener voltage reference. Q1 & Q2 make up the classic differential amplifier that amplifies the difference...

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