TND series single-phase high precision automatic AC regulator is composed of contact voltage regulator, sampling controlling circuit, servo motor and electrical operating unit, etc. When the voltage fluctuates because of main voltage unsteady or the customer load varied, the sampling circuit enlarges the voltage changeable signal, drive the servo motor to adjust the position of carbon brush of the contact voltage regulator, then the output voltage is stable. High precise degree, easy to adjust, less waste, and long working time, allowed momentary overload 1.6 times rated capacity. It is an ideal AC voltage stabilizing supply largely used in the place required stable voltage supply, such as home, industrial and mining establishment, government agency, researching agency, and laboratory, etc.