AS440 is a half wave phase controlled thyristor type AVR and forms part of the excitation system for a brushless generator. The design employs Surface Mount Technology (SMT) for high integration of features in a small footprint AVR. Positive voltage build up from residual levels is ensured by the use of efficient semiconductors in the power circuitry of the AVR. The power and voltage sensing circuits have separate terminals, allowing the excitation power to be derived directly from the stator winding for basic applications or from an auxiliary winding if sustained short circuit performance is required. The AVR is linked with the main stator windings and the exciter field windings to provide closed loop control of the output voltage with load regulation of +/- 1.0%. The AVR voltage sensing terminals continuously sample the output windings for voltage control purposes. In response to this sample voltage, the AVR controls the power fed to the exciter field, and hence the main field, to maintain the machine output voltage within the specified limits, compensating for load, speed, temperature and power factor, of the generator. A frequency measuring circuit continually monitors the generator output and provides under-speed protection of the excitation system, by reducing the output voltage proportionally with speed below a pre-settable threshold. A manual adjustment is provided for factory setting of the under frequency roll off point, (UFRO). This can easily be changed to 50 or 60 Hz in the field by push-on link selection. Over excitation conditions are limited to a safe period by a protection circuit within the AVR. Provision is made for the connection of a remote voltage trimmer, allowing the user fine control of the generator's output. An analogue input is provided allowing connection to the Power Factor controller or other external devices with compatible output. The AVR has the facility for droop CT connection, to allow parallel running with other similarly equipped generators.