The description of a scheme where all the excitation energy of a synchronous machine is derived from its output terminals through a potential transformer and a thyristor-controlled ac-to-dc converter is presented. The circuit is controlled by a strong feedback loop and performs the functions of both the conventional exciter and an automatic voltage regulator. The excitation energy is supplied in the form of dc voltage pulses of constant amplitude and variable width at constant frequency. The scheme is meant for isolated power supply and requires only a 12-V dry cell for triggering a pair of thyristors. Some experimental difficulties are also discussed. © 1973, IEEE. All rights reserved.