Stepper motor valve actuator

For use in controlling a regulated device, the combination comprising:

• power input terminal means arranged for connection to a source of AC power;
• motor means having field coils and a motor shaft;
• means arranged to provide a DC signal;
• switching means connected between said motor means and said power input terminals and to said DC signal means, said switching means being arranged for receiving a first direction control signal and a locking control signal, said switching means being responsive to said first direction control signal for completing a first circuit between said power input terminals and said motor means to apply the AC power to the motor means thereby effecting a rotation of the motor shaft in a first direction, said switching means being further responsive to said locking control signal to apply a DC signal to the motor terminals thereby effecting the locking of the motor shaft in situ in between applications of said first direction control signal, the motor shaft being thereby driven predetermined incremental amounts in accordance with the first direction control signal;
• and
• actuating means operatively coupled to said motor means and arranged for connection to the regulated device, said actuating means being responsive to the motor means for controlling the operation of the regulated device.