DRIVING DEVICE OF SEWING MACHINE MOTOR

PURPOSE:To electrically conducting the current of quantity corresponding to each operating state to a phase winding at the electric conduction time corresponding to each operating state of acceleration/deceleration and a constant speed of a sewing machine motor, so that an overload is not applied by controlling the electric conduction time, and also, controlling the electric conduction quantity of the phase winding in accordance with a deviation of a rotating speed and a speed command from the outside. CONSTITUTION:The above driving device is provided with an electric conduction control part 9 for controlling an electric conduction time of an AC motor M by an electric conduction circuit 7, and a current limiting circuit 11 for limiting the electric conduction quantity of the electric conduction circuit 7. The electric conduction control part 9 controls rotation of the AC motor M by controlling the electric conduction time to each phase winding Lu, Lv and Lw. At the time of acceleration of the AC motor M, when a current flowing through the phase windings Lu-Lw exceeds the maximum allowable current value IH in a turn-on period of an electric conduction control signal Spwm, a distributor 22 turns off transistors Trx-Trz which are turned on at that time, and decreases the current flowing through the phase windings Lu-Lw by a current limiting signal Sli (High level) from the current limiting circuit 11.