In an aircraft electrical system, excitation current for the alternator is supplied by which circuit?

• A. Voltage regulator circuit
• B. Battery bus
• C. Ignition switch circuit
• D. DC circuit

Answer: (D)

The field windings of the alternator must be fed with direct current to establish the magnetic field that drives AC generation. That excitation current comes from the DC side of the airplane’s electrical system—the DC circuit. The voltage regulator’s job is to modulate how much of that DC field current is sent to the field windings to keep the system voltage within limits, but the actual source of the excitation is the DC circuit (typically tapped from the battery bus).

So, although the regulator influences the amount of field current, the excitation path itself is a DC circuit, not an AC path or an ignition circuit.