Generator - Internal Circuit Diagram

As with most vehicle ac generators, there is only minimal residual magnetism in the field (rotor) windings. To compensate for this and to achieve high current output at low engine speed, the field is excited by battery voltage supplied to the generator at the 'IG' terminal.

To control the level of field excitation and ultimately, generator output, the voltage supplied to the field (rotor) is controlled by the voltage regulator.

The voltage regulator senses (at the 'B' terminal) battery terminal voltage, which within limits is proportional to the state of charge of the battery. The regulator then adjusts the supplied voltage between the 'IG' terminal and the regulator 'F' terminal (a continuously variable process) to maintain the 'B+' output at a constant level.

If the field were not controlled, the 'B+' output would rise to a level which could damage bulbs and ECMs. The regulator compares the output voltage to an internal voltage reference circuit to achieve the controlled output of the generator.