Charging system — operating principle [Toyota Camry Vista-V40]

When the key in the ignition switch is in the "ON" ("ON") position, current from the battery flows from the alternator "L" terminal through the voltage regulator to the "E" terminal, and the battery charge indicator light is illuminated. When the engine is started, the output voltage increases as the alternator speed increases. When the output voltage becomes higher than the battery voltage, part of the energy generated by the alternator is used to recharge the battery. At the same time, the voltage at the "L" terminal increases and the potential difference between the battery and the "L" terminal disappears, after which the battery charging lamp goes out. If the output voltage is out of regulation, the voltage regulator transistor changes the voltage so that the alternator voltage remains constant.