Patent ID: 7538513

Claim:
A step motor drive circuit comprising: a first transistor pair comprised of a first transistor and a second transistor; a second transistor pair comprised of a third transistor and a fourth transistor; a fifth transistor connected in parallel with the first transistor; a sixth transistor connected in parallel with the third transistor; output terminals for connection to respective drive terminals of a step motor to supply signals to the step motor in a state of rotating the step motor and in a state of braking the step motor; and driving means for rotating the step motor in a predetermined direction by supplying an alternating signal to the step motor by alternately driving the first transistor pair and the second transistor pair to an ON state in a state of rotating the step motor and driving the drive terminals of the step motor to a same level by driving the first and the third transistors to an ON state and driving the second and the fourth transistors to an OFF state in the state of braking the step motor; wherein the driving means drives the fifth transistor to an ON state when the first transistor is driven to the ON state in the state of rotating the step motor, drives the fifth transistor to an OFF state when the first transistor is driven to the ON state in the state of braking the step motor, drives the sixth transistor to an ON state when the third transistor is driven to the ON state in the state of rotating the step motor, and drives the sixth transistor to an OFF state when the third transistor is driven to an ON state in the state of braking the step motor; and wherein when driven to the OFF state in the state of braking the step motor, the fifth transistor and the sixth transistor function as protecting transistors that protect the first, second, third and fourth transistors from static electricity generated during operation of the step motor drive circuit.