Motor control device and motor control method

1 . A motor control device comprising:

a signal identifying unit including an optical isolator that converts an electrical signal supplied via a terminal to which an external device is connected and a switch that opens a connection circuit connected to the terminal; and

an overvoltage detecting unit configured to turn off the switch when a voltage applied to the connection circuit is greater than a threshold voltage,

wherein the signal identifying unit further includes a detection voltage setting circuit that is provided closer to the optical isolator than the switch and connected in parallel to a primary circuit of the optical isolator.

2 . The motor control device according to claim 1 , wherein the switch is switched to an on state when there is no control signal for the switch generated by the overvoltage detecting unit and is switched to an off state when there is a control signal for the switch.

3 . The motor control device according to claim 1 , wherein the signal identifying unit includes a detection voltage setting circuit that sets a voltage to which a primary circuit of the optical isolator responds, and

wherein the switch is provided in the connection circuit between the terminal and the detection voltage setting circuit.

4 . The motor control device according to claim 1 , wherein the switch is an optically isolated MOSFET that is connected in series to a primary circuit of the optical isolator.

5 . The motor control device according to claim 1 , wherein the detection voltage setting circuit includes:

a first constant-voltage circuit that defines an insensible voltage range of a primary circuit of the optical isolator; and

a first impedance element for limiting a current of the primary circuit of the optical isolator.

6 . The motor control device according to claim 1 , wherein the overvoltage detecting unit includes:

a second constant-voltage circuit that defines the threshold voltage; and

a second impedance element for limiting a current which is generated with a voltage greater than the threshold voltage.

7 . The motor control device according to claim 1 , wherein the switch includes an optically isolated MOSFET, and

wherein the overvoltage detecting unit detects a voltage which is generated during voltage limitation at a position closer to the terminal than the optically isolated MOSFET.

8 . The motor control device according to claim 1 , wherein the signal identifying unit includes:

the optical isolator configured to cause a primary circuit to detect an electrical signal supplied via the terminal to which the external device is connected and to cause a secondary circuit to output a logical signal corresponding to the result of detection;

a detection voltage setting circuit configured to limit a voltage which is applied to the primary circuit; and

the switch that is provided to open or close a connection circuit between the terminal to which the external device is connected and the primary circuit in accordance with a control signal.

9 . A motor control method that is performed by a motor control device in which an optical isolator that converts an electrical signal supplied via a terminal to which an external device is connected and a switch that turns off a connection circuit connected to the terminal are provided, the motor control method comprising:

detecting using a voltage setting circuit that is provided closer to the optical isolator than the switch and connected in parallel to a primary circuit of the optical isolator, and

turning off the switch when the voltage applied to the connection circuit is greater than a threshold voltage.