An electronic watch includes a motor including a coil, a driver controlled to an ON state for supplying a driving current to the coil and an OFF state for not supplying the driving current, a driver controller configured to control the driver to the ON state or the OFF state depending on a value of a current flowing through the coil, and a polarity switcher configured to switch a polarity of the driving current when a prescribed condition is satisfied after detecting that an ON time, which is a duration of the ON state of the driver controller, reaches a maximum.

The present invention provides a driving circuit capable of appropriately switching to a high-torque mode and a high-efficiency mode. The present invention relates to a driving circuit and a driving method for a stepping motor, and an electronic machine using the same. A back electromagnetic force detection circuit detects a counter EMF generated in a coil of a stepping motor. A revolution count detection circuit generates a revolution count detection signal representing the revolution count of the stepping motor. A determining circuit generates a determination signal that is asserted if the revolution count detection signal is stable across multiple consecutive cycles. A current value setting circuit generates a current setting value indicating a target value of a coil current. The current value setting circuit sets the current setting value to a predetermined value in a period in which the determination signal is negated, and adjusts the current setting value according to the counter EMF in a period in which the determination signal is asserted. A constant current chopper circuit generates a pulse modulation signal that modulates by way of having a detection value of a coil current approach close to a target value of the current setting value.

Excitation position is changed in accordance with an external clock. The state of a full bridge circuit including four transistors connected to a coil of a stepping motor, is controlled in accordance with the excitation position. At the time of transition from the excitation position at which coil current that flows in the coil is nonzero to the excitation position at which the coil current is zero, a switch is made to (i) the inverse state where the on or off state of each of the four transistors before the transition is inverted, and then a switch is made to (ii) the off state where all the four transistors are off.

The present invention optimizes a current setting value within a short time. The present invention relates to a driving circuit and a driving method for a stepping motor, and an electronic machine using the same. A current value setting circuit generates a current setting value. A constant current chopper circuit generates a pulse modulation signal, which pulse-width modulates by way of having a detection value of a coil current flowing through a coil approach close to the current setting value. A logic circuit controls a bridge circuit connected to a coil of a stepping motor according to the Pulse modulation signal. The current value setting circuit sets the current setting value to a predetermined full-torque setting value in a first period after rotation starts, reduces the current setting value by a predetermined method to a predetermined second setting value less than the first setting value in the following second period, and switches to a high-efficiency mode and adjusts the current setting value by means of feedback control.

There is provided a driving circuit for a stepping motor, including: a counter electromotive force detection circuit configured to detect a counter electromotive force generated in a coil; a current value setting circuit configured to generate a current set value based on the counter electromotive force; a constant current chopper circuit configured to generate a pulse-modulated signal which is pulse-modulated so that a detected value of a coil current flowing through the coil approaches a target amount based on the current set value; and a logic circuit configured to control a bridge circuit connected to the coil according to the pulse-modulated signal, wherein the driving circuit is configured to output the current set value to outside or to access the current set value from the outside.

A stepping motor includes: a rotor; and a stator including an opening accommodating the rotor, a first side yoke extending from the opening in a first direction, a second side yoke extending from the opening in a second direction that is a direction opposite to the first direction, and one or a plurality of coils magnetically coupled to the first side yoke or the second side yoke. Assuming a direction orthogonal to the first direction and the second direction is defined as a third direction, a first recess is formed in an outer circumference of the stator at a position rotated from the third direction toward the second direction by a prescribed first angle and a second recess that determines a stable resting position of the rotor is formed at a position rotated from the second direction toward the third direction by a prescribed second angle.

A stepping motor includes: a rotor; and a stator including an opening accommodating the rotor, a first side yoke extending from the opening in a first direction, a second side yoke extending from the opening in a second direction that is a direction opposite to the first direction, and one or a plurality of coils magnetically coupled to the first side yoke or the second side yoke. Assuming a direction orthogonal to the first direction and the second direction is defined as a third direction, a first recess is formed in an outer circumference of the stator at a position rotated from the third direction toward the second direction by a prescribed first angle and a second recess that determines a stable resting position of the rotor is formed at a position rotated from the second direction toward the third direction by a prescribed second angle.

A direction setting pin DIR receives a direction signal ROT that indicates the rotational direction of the stepping motor. A clock pin CLK receives a clock signal CLK that indicates the rotational direction of the stepping motor. A logic circuit generates a first internal signal and a second internal signal that respectively indicate the states of the first H-bridge circuit and the second H-bridge circuit according to the direction signal ROT and the clock signal CLK. When the clock signal CLK remains in a predetermined state for a predetermined judgment time, the logic circuit transits to a predetermined mode.

A direction setting pin DIR receives a direction signal ROT that indicates the rotational direction of the stepping motor. A clock pin CLK receives a clock signal CLK that indicates the rotational direction of the stepping motor. A logic circuit generates a first internal signal and a second internal signal that respectively indicate the states of the first H-bridge circuit and the second H-bridge circuit according to the direction signal ROT and the clock signal CLK. When the clock signal CLK remains in a predetermined state for a predetermined judgment time, the logic circuit transits to a predetermined mode.

Provided is a motor drive circuit capable of driving a stepper motor even if the load on the stepper motor varies. A motor drive circuit has a first drive circuit that outputs a first drive signal to the driver; a second drive circuit that outputs a second drive signal to the driver; a controller that controls the first drive circuit and second drive circuit. The first drive circuit is configured to output a first drive signal based on the current value of current flow of a coil of a stepper motor. The second drive circuit is configured to output multiple types of second drive signals that differ by the supply time of drive current supplied to the coil. Based on a result of driving by the first drive circuit, the controller selects the type of second drive signal the second drive circuit outputs.