Motor drive device

A motor drive device includes: an inverter circuit; a drive circuit which receives voltage supplied from a control power source; a first cutoff circuit which cuts off voltage supply from the control power source to the drive circuit; a second cutoff circuit connected between the first cutoff circuit and the drive circuit; a voltage detection circuit which detects a detection voltage corresponding to the voltage supplied from the control power source and which is capable of changing the detection voltage; a comparison circuit which, upon determination that the detection voltage is not within a predetermined range, cuts off the first cutoff circuit; and a diagnosis circuit which diagnoses the first cutoff circuit. The diagnosis circuit causes the comparison circuit to cut off the first cutoff circuit, diagnoses the first cutoff circuit, and upon diagnosing the operation of the first cutoff circuit as being abnormal, cuts off the second cutoff circuit.

CROSS-REFERENCE OF RELATED APPLICATIONS

This application is the U.S. National Phase under 35 U.S.C. § 371 of International Patent Application No. PCT/JP2018/015782, filed on Apr. 17, 2018, which in turn claims the benefit of Japanese Application No. 2017-097340, filed on May 16, 2017, the entire disclosures of which Applications are incorporated by reference herein.

TECHNICAL FIELD

The present disclosure relates to a motor drive device including an abnormal voltage protection circuit.

BACKGROUND ART

A motor drive device which drives a motor has, in addition to the basic function of driving the motor, the protection function of stopping the motor upon abnormality detection so as not to compromise the safety of the motor and a system loaded with the motor drive device.

Abnormal states include a state in which values of various supply voltages supplied to various circuit blocks of the motor drive device become abnormal. Specifically, the abnormal states include: for example, a state in which the supply voltage exceeds the withstand voltage of a circuit component forming the motor drive device or a state in which the supply voltage falls below the operation guarantee range of the circuit component. Breakdown or malfunction of the circuit component of the motor drive device may occur in such abnormal states, compromising the system safety.

Thus, suggested to prevent the breakdown or the malfunction of the circuit component is a technology of monitoring the supply voltage supplied to each circuit block of the motor drive device and executing predetermined protective operation upon detection of an abnormal voltage such as overvoltage or low voltage (refer to, for example, Patent Literature 1 for overvoltage protection). The motor drive device which executes such protective operation will be described with reference to the drawing.FIG. 4is a block diagram illustrating one example of a schematic configuration of a conventional motor controller.FIG. 4illustrates, together with the conventional motor drive device, motor12which is driven by the motor drive device.

As illustrated inFIG. 4, the conventional motor drive device includes: control power source1, voltage monitoring circuit102, cutoff circuit103, pulse width modulation (PWM) signal generation circuit8, drive circuit9, and inverter circuit11. A drive signal is supplied from drive circuit9to inverter circuit11in accordance with a PWM signal outputted from PWM signal generation circuit8. In response to the supply, inverter circuit11supplies power from a DC power source, not illustrated, to a motor winding of motor12to thereby drive motor12.

Voltage monitoring circuit102monitors the voltage value of control power source1and monitors whether the voltage value is within a predetermined range. When the voltage value of control power source1is out of the specified range, voltage monitoring circuit102provides a cutoff signal to cutoff circuit103to cut off voltage supply to drive circuit9.

Consequently, output of drive circuit9is turned off to achieve emergency stop of motor driving regardless of a command of PWM signal generation circuit8.

CITATION LIST

Patent Literature

SUMMARY OF THE INVENTION

Technical Problem

However, when components of a protection circuit composed of conventional voltage monitoring circuit102and cutoff circuit103no longer operate normally, the output of drive circuit9cannot be turned off even upon excess of the voltage value of control power source1over the specified range. Thus, the safety of the motor drive device and also a system loaded with the motor drive device deteriorate.

To solve the problem described above, it is an object of the present disclosure to provide a motor drive device capable of turning off output of a drive circuit to stop a motor even when an abnormal voltage protection circuit no longer operates normally.

Solution to Problem

In order to address the object described above, a motor drive device according to one aspect of the present disclosure includes: an inverter circuit which supplies a power to a motor winding to drive a motor including the motor winding; drive circuit which receives a voltage supplied from a control power source and which provides the inverter circuit with a drive signal; a PWM signal generation circuit which provides the drive circuit with a pulse width modulation (PWM) signal; a first cutoff circuit which cuts off voltage supply from the control power source to the drive circuit; a second cutoff circuit which is connected between the first cutoff circuit and the drive circuit and which cuts off the voltage supply from the control power source to the drive circuit; a voltage detection circuit which detects a detection voltage corresponding to the voltage supplied from the control power source and which is capable of changing the detection voltage; a comparison circuit which determines, through comparison of the detection voltage and a determination threshold, whether the detection voltage is within a predetermined range, and upon determination that the detection voltage is not within the predetermined range, provides the first cutoff circuit with a cutoff signal to cut off the first cutoff circuit; and a diagnosis circuit which diagnoses whether operation of the first cutoff circuit is normal, wherein the diagnosis circuit changes the detection voltage to cause the comparison circuit to cut off the first cutoff circuit, performs diagnosis operation of diagnosing, based on a voltage level between the first cutoff circuit and the second cutoff circuit, whether the operation of the first cutoff circuit is normal, and upon diagnosing the operation of the first cutoff circuit as being abnormal, cuts off the second cutoff circuit.

Advantageous Effect of Invention

A motor drive device can be provided which can turn off output of a drive circuit to stop a motor even when an abnormal voltage protection circuit no longer operates normally.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, the embodiments of the present disclosure will be described. Note that each of the embodiments described below illustrates one detailed example of the present disclosure. Therefore, numerical values, components, arrangement positions of the components, connection modes, etc. as well as steps, a sequence of the steps, etc. indicated in the embodiments below form one example and are not intended to limit the present disclosure in any manner. Accordingly, of the components in the embodiments below, those which are not described in an independent claim indicating a superordinate concept will be described as optional components.

Moreover, each of the drawings is a schematic diagram and thus does not necessarily represent exact dimensions. Note that substantially same configurations are provided with same symbols in each of the drawings and overlapping descriptions will be omitted or simplified.

First, a circuit configuration of a motor drive device according to Embodiment 1 will be described with reference toFIG. 1.FIG. 1is a circuit configuration diagram of motor drive device100according to Embodiment 1.FIG. 1also illustrates motor12which is driven by motor drive device100.

As illustrated inFIG. 1, motor drive device100according to Embodiment 1 includes: control power source1, voltage detection circuit30, comparison circuit21, first cutoff circuit3, second cutoff circuit13, PWM signal generation circuit8, drive circuit9, driving power source10, inverter circuit11, and diagnosis circuit14.

Motor12is an AC electric motor which is driven by motor drive device100. Motor12includes a motor winding therein and is driven through power supply to the motor winding by motor drive device100.

Inverter circuit11is a circuit which supplies a power from a DC power source, not illustrated, to the motor winding to drive motor12including the motor winding. Inverter circuit11has, for example, a plurality of power semiconductor elements which are bridge-connected. A drive signal (gate drive signal) is supplied from drive circuit9to each of the plurality of power semiconductor devices included in inverter circuit11.

Control power source1is a supply circuit which supplies a DC voltage to drive circuit9.

Drive circuit9is a circuit which receives a voltage supplied from control power source1and which provides the drive signal to inverter circuit11. Drive circuit9mainly has: a photocoupler, an amplifier, and resistance elements. A PWM signal is provided from PWM signal generation circuit8to an input side of the photocoupler whereby the PWM signal is outputted from an output side insulated from the input side. The outputted PWM signal is amplified by the amplifier and supplied as the drive signal to inverter circuit11.

Driving power source10is a power source which supplies a power to drive circuit9. Driving power source10supplies the power to, for example, the amplifier of drive circuit9.

Note that the drive signal is generated for each power semiconductor device of inverter circuit11, and the photocoupler provided in drive circuit9is also provided for each power semiconductor device, which is illustrated in a simplified form inFIG. 1.

A voltage is supplied from control power source1to an anode of the photocoupler of drive circuit9. First cutoff circuit3and second cutoff circuit13are connected in series between control power source1and the anode in order from control power source1, and a cathode of the photocoupler is connected to PWM signal generation circuit8via the resistance element for current limitation.

Drive circuit9receives the voltage supplied from control power source1via first cutoff circuit3and second cutoff circuit13and the conducting current of a photodiode is subjected to ON/OFF control in accordance with the PWM signal generated by PWM signal generation circuit8.

PWM signal generation circuit8is a circuit which provides drive circuit9with a PWM signal. PWM signal generation circuit8generates the PWM signal based on a motor driving control signal inputted from the outside and provides drive circuit9with the PWM signal.

First cutoff circuit3is a circuit which cuts off the voltage supply from control power source1to drive circuit9. First cutoff circuit3switches between a conductive state and a cutoff state in accordance with the level of an input signal provided from comparison circuit21.

Second cutoff circuit13is a circuit which is connected between first cutoff circuit3and drive circuit9and which cuts off the voltage supply to drive circuit9. Second cutoff circuit13switches between a conductive state and a cutoff state in accordance with the level of an input signal provided from diagnosis circuit14.

Voltage detection circuit30is a circuit which detects a detection voltage corresponding to the voltage supplied from control power source1and which is capable of changing the detection voltage. Voltage detection circuit30is connected in series between a high potential side electric wire and a low potential side electric wire of control power source1and has three resistance elements4to6which generate two divided voltage values as the detection voltage. Voltage detection circuit30further has first switch circuit15connected in parallel with resistance element6which is included in three resistance elements4to6and which is connected to the low-potential side electric wire. Voltage detection circuit30further has second switch circuit16connected in parallel with resistance element4which is included in three resistance elements4to6and which is connected to the high-potential side electric wire.

Three resistance elements4to6are connected in series in order from the high-potential side electric wire of control power source1, i.e., resistance element4, resistance element5, and resistance element6. Consequently generated are a divided voltage value Vu and a divided voltage value Vo. The divided voltage value Vu is obtained by dividing a voltage Vc of control power source1by resistance element4and also by the series combined resistor of resistance element5and resistance element6. The divided voltage value Vo is obtained by dividing the voltage Vc by the series combined resistor of resistance element4and resistance element5and also by resistance element6.

Comparison circuit21is a circuit which compares the detection voltage detected by voltage detection circuit30with a determination threshold to thereby determine whether the detection voltage is within a predetermined range. Upon determination that the detection voltage is not within the predetermined range, comparison circuit21provides a cutoff signal to first cutoff circuit3to thereby cut off first cutoff circuit3. Comparison circuit21has window comparator2and reference power source7having a reference voltage Vr and monitors whether the voltage Vc of control power source1is within the predetermined range.

Window comparator2receives input of the divided voltage values Vu and Vo. Window comparator2also receives input of the reference voltage Vr from reference power source7to compare the divided voltage values Vu and Vo with the reference voltage Vr.

Here, a change in the voltage Vc results in changes in the divided voltage values Vu and Vo, thus permitting judgment on whether the voltage Vc falls within the specified range.

For example, in either of a case where the divided voltage value Vu is less than or equal to the reference voltage Vr (it has been detected that the voltage Vc of control power source is less than or equal to the lower limit) and a case where the divided voltage value Vo is greater than or equal to the reference voltage Vr (it has been detected that the voltage Vc of control power source is greater than or equal to the upper limit), window comparator2operates in a manner such that outputted signal S1is set at an H (high) level. On the other hand, in other cases (where it has been detected that the voltage Vc of the control power source is within the predetermined range), window comparator2operates to set signal S1at an L (Low) level.

Upon receiving input of signal S1at an L level, first cutoff circuit3operates to turn into a conductive state, and upon receiving input of signal S1at an H level, first cutoff circuit3operates to turn into a cutoff state. That is, first cutoff circuit3turns its state into a cutoff state when signal S1outputted by window comparator2is at an H level (a case where the voltage Vc of the control power source is not within the predetermined range). First cutoff circuit3turns its state into a conductive state when signal S1is at an L level (a case where the voltage Vc of the control power source is within the predetermined range). Therefore, cutoff operation of control power source1as protection taken for abnormal voltage is realized in motor drive device100.

Diagnosis circuit14is a circuit which diagnoses whether operation of first cutoff circuit3is normal.

Diagnosis circuit14monitors voltage level S2on an output side of first cutoff circuit3. It is recognized that voltage level S2is at an H level when first cutoff circuit3is in a conductive state while voltage level S2is at an L level when first cutoff circuit3is in a cutoff state.

Moreover, diagnosis circuit14provides second cutoff circuit13with signal S3to control conduction and cutoff of second cutoff circuit13. Here, second cutoff circuit13operates to turn into a cutoff state when signal S3is at an L level and turn into a conductive state when signal S3is at an H level.

Moreover, diagnosis circuit14provides first switch circuit15and second switch circuit16with signals S4and S5, respectively, to control conduction and cutoff of first switch circuit15and second switch circuit16. Here, first switch circuit15is conducted by setting signal S4at an H level and second switch circuit16is conducted by setting signal S5at an L level.

Here, first switch circuit15is connected in a manner such that both side electrodes of resistance element6are shorted and second switch circuit16is connected in a manner such that both side electrodes of resistance element4are shorted. When first switch circuit15has been conducted (the both side electrodes of resistance element6are shorted), the divided voltage value Vu turns into a value obtained by dividing the voltage Vc by resistance element4and resistance element5, and the values of resistance elements4to6are adjusted in a manner such that the divided voltage value Vu at that time becomes less than or equal to the reference voltage Vr. Moreover, when second switch circuit16has been conducted (the both side electrodes of resistance element4are shorted), the divided voltage value Vo turns into a value obtained by dividing the voltage Vc by resistance element5and resistance element6, and the values of resistance elements4to6are adjusted in a manner such that the divided voltage value Vo at that time becomes greater than or equal to the reference voltage Yr.

Such a configuration permits diagnosis circuit14to simulate upper limit voltage detection operation (operation of detecting that the voltage Vc of control power source1is greater than or equal to the upper limit) and low voltage detection operation (operation of detecting that the voltage Vc of control power source1is less than or equal to the lower limit). Consequently, the conduction and the cutoff of first cutoff circuit3can be performed on a trial basis. It can also be diagnosed, through logical comparison of the levels of signals S4and S5and voltage level S2on the output side of first cutoff circuit3, whether first cutoff circuit3operates normally.

As described above, diagnosis circuit14changes the detection voltage to thereby cause comparison circuit21to cut off first cutoff circuit3, and performs, based on the voltage level between first cutoff circuit3and second cutoff circuit13, diagnosis operation of diagnosing whether the operation of first cutoff circuit3is normal. Diagnosis circuit14cuts off second cutoff circuit13upon diagnosing the operation of first cutoff circuit8as being abnormal.

Next, the diagnosis operation performed by diagnosis circuit14will be described.

FIG. 2is a flowchart illustrating a flow of operation performed by motor drive device100according to Embodiment 1.

First, upon supply of control power source1, diagnosis of the operation of first cutoff circuit3is started by diagnosis circuit14, and diagnosis circuit14sets signal S3at an H level, signal S4at an L level, signal S5at an H level, and signal S6at an L level (Step A1). That is, first switch circuit15and second switch circuit16turn into a cutoff state and second cutoff circuit13turns into a conductive state.

Here, signal S6is a signal which indicates a PWM signal output permission flag provided to PWM signal generation circuit8. PWM signal generation circuit8is set to prohibit the output when signal S6is at an L level and permit the output when signal S6is at an H level.

Next, diagnosis circuit14detects voltage level S2and determines whether voltage level S2is at an H level (step A2).

When voltage level S2is at the H level (YES in step A2), diagnosis circuit14determines that comparison circuit21and first cutoff circuit3normally operate and the voltage Vc is normally supplied from control power source1, proceeding to next step A3.

Next, diagnosis circuit14sets signal S3at an H level, signal S4at an H level, signal S5at an H level, and signal S6at an L level (step A3). The setting corresponds to a case where the voltage Vc of control power source1has become equal or less than the lower limit of the predetermined range.

Next, diagnosis circuit14detects voltage level S2and determines whether the voltage level is at an L level (step A4).

When voltage level S2is at the L level (YES in step A4), diagnosis circuit14determines that comparison circuit21and first cutoff circuit3have operated normally, proceeding to the next step A5.

Next, diagnosis circuit14sets signal S3at an H level, signal S4at an L level, signal S5at an L level, and signal S6at an L level (step A5). The setting corresponds to a case where the voltage Vc of control power source1has become greater than or equal to the upper limit of the predetermined range.

Next, diagnosis circuit14detects voltage level S2and determines whether the voltage level is at an L level (step A6). When signal S2is at the L level (YES in step A6), diagnosis circuit14determines that comparison circuit21and first cutoff circuit3have operated normally, proceeding to next step A7.

Next, diagnosis circuit14sets signal S3at an H level, signal S4at an L level, signal S5at an H level, and signal S6at an L level (step A7). The setting corresponds to a case where the voltage Vc of control power source1is supplied as usual.

Next, diagnosis circuit14detects the voltage level of voltage level S2and determines whether the voltage level is at an H level (step A8). When voltage level S2is at the H level (YES in step A8), diagnosis circuit14determines that comparison circuit21and first cutoff circuit3operate normally and the voltage Vc is normally supplied from control power source1, proceeding to next step A9.

In step A9, diagnosis circuit14determines that comparison circuit21and first cutoff circuit3are normal and fixes signal S3at an L level, signal S4at an L level, signal S5at an H level, and signal S6at an H level, ending the diagnosis operation.

Since voltage level S2is at the H level here, first cutoff circuit3is in a conductive state. Since signal S3is at the L level, the second cutoff circuit13is in a conductive state. Since signal S6is at the H level, PWM signal generation circuit8is permitted to operate.

Therefore, drive circuit9is operated by the signal of PWM signal generation circuit8, thereby starting motor activation.

On the other hand, upon determination in each of steps A2, A4, A6, and A8that voltage level S2is not at the defined level (NO in steps A2, A4, A6, and A8), diagnosis circuit14determines that abnormality is occurring in at least one of comparison circuit21and first cutoff circuit3and sets signal S3at an H level, signal S4at an L level, signal S5at an H level, and signal S6at an L level (step A10).

Since signal S3is at the H level here, second cutoff circuit13is being cut off. Since signal S6is at the L level, PWM signal generation circuit8is not permitted to operate.

Therefore, the output of drive circuit9is fixed at OFF, and thus the activation of motor12is not performed. Diagnosis circuit14may notify that abnormality in a host device, not illustrated, loaded in motor drive device100has been detected.

As described above, according to Embodiment 1, the diagnosis operation of diagnosing whether first cutoff circuit3controlled by comparison circuit21operates normally can be performed. Upon diagnosing the operation of first cutoff circuit3as being not normal in the diagnosis operation, the voltage supply to drive circuit9is reliably cut off by second cutoff circuit13controlled by diagnosis circuit14, which can reliably turn off the output of drive circuit9. Thus, a motor drive device can be realized which can turn off the output of drive circuit9to stop the motor even when the abnormal voltage protection circuit composed of first cutoff circuit3, etc. no longer operates normally. Moreover, the safety of the system including motor12can be improved.

Moreover, the diagnosis operation can be performed in a state in which the voltage supply to drive circuit9is cut off, thus permitting execution of safe diagnosis operation even when control power source is in an abnormal voltage state such as overvoltage or low voltage during the diagnosis.

Moreover, when control power source1is turned on, motor drive device100may perform the diagnosis operation, may determine an operation mode defined by the result of the aforementioned diagnosis, and then may hold the determined operation mode until control power source1of motor drive device100is turned off. Consequently, the occurrence of misdiagnosis influenced by switching noise can be reduced.

Moreover, the diagnosis operation may be executed every time control power source1is turned ON. Consequently, it can frequently be diagnosed whether comparison circuit21and first cutoff circuit3controlled by comparison circuit21operate normally, which can more improve the safety.

Note that the description refers to the diagnosis operation performed when control power source1is turned on but the following diagnosis operation can also be performed.

Specifically, when no power is supplied to the motor winding while control power source1of motor drive device100is turned on and the PWM signal is turned off (that is, when motor12is in a standby state), the voltage supply to drive circuit9is not required, and thus first cutoff circuit3and second cutoff circuit13may be conducted and cut off. Therefore, it is possible for motor12to execute the same diagnosis operation as that in the operation flow ofFIG. 2when motor12is in a standby state.

Note that motor drive device100may include a timer so that the operation can be performed at predefined time intervals, for example, an operation mode is determined after the execution of the diagnosis operation and the operation mode is held until the next diagnosis operation. Consequently, the diagnosis operation can be executed on a regular basis.

Here, when the timer has been provided with a motor standby command from the host device, a count value is reset and counting is started. On the other hand, when the timer has been provided with a motor driving command from the host device, the count value is reset and the counting is stopped.

Note that when motor drive device100has been provided with the motor driving command during the execution of the diagnosis operation, motor drive device100executes the same diagnosis operation as the diagnosis operation in the operation flow illustrated inFIG. 2and starts the driving of motor12when it has been diagnosed that the operation is normal.

As described above, the diagnosis operation can be performed on a regular basis not only when control power source1of motor drive device100is turned on but also while motor12is on standby, which can more improve the safety of the system loaded with motor drive device100.

Summarizing the above, motor drive device100according to Embodiment 1 includes; inverter circuit11which supplies a power to the motor winding to drive motor12including the motor winding; and drive circuit9which receives a voltage supplied from control power source1and provides a drive signal to inverter circuit11. Motor drive device100further includes: PWM signal generation circuit8which provides drive circuit9with a PWM signal; first cutoff circuit3which cuts off the voltage supply from control power source1to drive circuit9; and second cutoff circuit13which is connected between first cutoff circuit3and drive circuit9and which cuts off the voltage supply from control power source1to drive circuit9. Motor drive device100further includes voltage detection circuit30which can detect the detection voltage corresponding to the voltage supplied from control power source1and also can change the detection voltage. Motor drive device100further includes: comparison circuit21which compares the detection voltage with the determination threshold to thereby determine whether the detection voltage is within the predetermined range and, upon determination that the detection voltage is not within the predetermined range, provides a cutoff signal to first cutoff circuit3to thereby cut off first cutoff circuit3; and diagnosis circuit14which diagnoses whether the operation of first cutoff circuit3is normal. Diagnosis circuit14changes the detection voltage to thereby cause comparison circuit21to cut off first cutoff circuit3and performs, based on the voltage level between first cutoff circuit3and second cutoff circuit13, the diagnosis operation of diagnosing whether the operation of first cutoff circuit3is normal, and upon diagnosing the operation of first cutoff circuit3as being abnormal, cuts off second cutoff circuit13.

Consequently, comparison circuit21can be activated on a trial basis to perform the diagnosis operation of diagnosing whether first cutoff circuit3controlled by comparison circuit21operates normally. Moreover, upon diagnosing the result of the diagnosis as being not normal, the voltage supply to drive circuit9is reliably cut off by second cutoff circuit13, turning off the output of drive circuit9. Thus, motor drive device100can be realized which can turn off the output of drive circuit9to stop the motor even when the abnormal voltage protection circuit composed of, for example, first cutoff circuit3no longer operates normally. In addition, the safety of the system loaded with motor drive device100can be improved.

Moreover, voltage detection circuit30in motor drive device100may have: three resistance elements4,5, and6which are connected in series between the high-potential side electric wire and the low potential side electric wire of control power source1and which generate the two divided voltage values as the detection voltage; first switch circuit15connected in parallel with resistance element6which is included in three resistance elements4,5, and6and which is connected to the low potential side electric wire; and second switch circuit16connected in parallel with the resistance element which is included in the three resistance elements and which is connected to the high potential side electric wire. Diagnosis circuit14may provide voltage detection circuit30with: a first diagnostic signal for cutting off first switch circuit15and also cutting off second switch circuit16; a second diagnostic signal for conducting first switch circuit15and cutting off second switch circuit16; and a third diagnostic signal for cutting off first switch circuit15and conducting second switch circuit16to change the detection voltage.

Consequently, the detection voltage of voltage detection circuit30can be changed on a trial basis only by providing the two switch circuits and conducting and cutting off the two, and thus a circuit including diagnosis circuit14can relatively easily be formed.

Moreover, diagnosis circuit14in motor drive device100may diagnose the operation of first cutoff circuit3as being normal and may operate to conduct second cutoff circuit13when a first condition, a second condition, and a third condition are satisfied. The first condition is that the voltage level between first cutoff circuit3and second cutoff circuit13is at a high level when the first diagnostic signal has been provided. The second condition is that the voltage level between first cutoff circuit3and second cutoff circuit13is at a low level when the second diagnostic signal has been provided. The third condition is that the voltage level between first cutoff circuit3and second cutoff circuit13is at a low level when the third diagnostic signal has been provided. Diagnosis circuit14may diagnose the operation of first cutoff circuit3as being abnormal and may cut off second cutoff circuit13when at least one of the first condition, the second condition, and third condition is not satisfied.

Consequently, diagnosis circuit14operates to perform the diagnosis operation for a plurality of patterns, thus permitting reliable detection whether first cutoff circuit3is normal.

Moreover, diagnosis circuit14may perform the diagnosis operation while second cutoff circuit13is cut off in motor drive device100.

Consequently, the diagnosis operation can be performed by second cutoff circuit13while the voltage supply to drive circuit9is cut off. Therefore, the diagnosis operation can safely be executed even in an abnormal voltage state such as overvoltage or low voltage during the diagnosis.

Moreover, diagnosis circuit14may perform the diagnosis operation when control power source1is turned on in motor drive device100.

Consequently, diagnosis circuit14performs the diagnosis operation when control power source1of motor drive device100is turned on. Therefore, compared to a case where the diagnosis operation is performed on a regular basis during the motor driving, the occurrence of misdiagnosis caused under the influence of switching noise can be reduced. Moreover, the diagnosis operation can be executed on a regular basis every time control power source1of motor drive device100is turned on, which can improve the safety of the system loaded with motor drive device100.

Moreover, diagnosis circuit14in motor drive device100may perform the diagnosis operation when no power is supplied to the motor winding as a result of turning off the PWM signal.

As described above, when motor12is in a standby state, that is, when the voltage supply to drive circuit9is not required, first cutoff circuit3and second cutoff circuit13may be conducted and cutoff, permitting the execution of the diagnosis operation. Therefore, not only when control power source1of motor drive device100is turned on, but also by executing the diagnosis operation on a regular basis while the motor is on standby, the safety of the system loaded with the motor drive device can be improved.

A circuit configuration of a motor drive device according to Embodiment 2 will be described with reference toFIG. 3.FIG. 3is a circuit configuration diagram of motor drive device200according to Embodiment 2. As is the case withFIG. 1,FIG. 3also illustrates motor12which is driven by motor drive device200.

Same portions inFIG. 3as those in the circuit configuration diagram of motor drive device100according to Embodiment 1 are indicated by the same symbols, and the description thereof will be omitted.

Moreover, the operation of diagnosis circuit14of Embodiment 2 is identical to that in the operation flowchart of motor drive device100according to Embodiment 1 illustrated inFIG. 2and thus the description thereof will be omitted.

Embodiment 2 differs from Embodiment 1 in an additional configuration such that signal S3provided by diagnosis circuit14and a PWM signal provided from PWM signal generation circuit8are inputs of AND circuit17and outputs thereof are connected to an anode side of the photodiode of drive circuit9.

Specifically, upon abnormality detection through the diagnosis operation by diagnosis circuit14, signal S3is set at an H level, and thus AND circuit17can cut off the output of the PWM signal outputted from PWM signal generation circuit8to fix the output of drive circuit9at OFF.

According to Embodiment 2, upon the abnormality detection through the diagnosis operation, the output of drive circuit9can be turned off by two different techniques including cutoff of control power source1by second cutoff circuit13and cutoff of the signal provided from PWM signal generation circuit8. Therefore, the safety can be more improved than the safety provided by the technique using only second cutoff circuit13as is the case with Embodiment 1.

Note that same portions as those of Embodiment 1 can provide same contents and same effects as those described in Embodiment 1.

Moreover, AND circuit17is used in Embodiment 2, but a different logic circuit may be used to realize the same operation.

Summarizing the above, motor drive device200includes, in addition to motor drive device100according to Embodiment 1, a logic circuit which cuts off the PWM signal, and when the result of the diagnosis is abnormal, diagnosis circuit14cuts off second cutoff circuit13and causes the logic circuit to cut off the PWM signal.

Consequently, upon diagnosing the operation of first cutoff circuit3as being not normal by diagnosis circuit14, the voltage supply to drive circuit9can reliably be cutoff by second cutoff circuit13and also the PWM signal to be provided to drive circuit9can simultaneously be cut off.

Therefore, the output of drive circuit9is turned off simultaneously by the two different cutoff methods, which can therefore more improve the safety of the system loaded with motor drive device200.

Variation and Others

The motor drive devices according to the present disclosure have been described above based on the embodiments, but the present disclosure is not limited to each of the embodiments described above.

For example, the motor drive device according to each of the embodiments described above includes control power source1, but control power source1may not be included in the motor drive device itself.

The present disclosure also includes: a mode obtained by providing each of the embodiments with various modifications conceived by those skilled in the art and a mode realized by combining the components and the functions of each of the embodiments in a desired manner within a range not departing from the spirits of the present disclosure.

INDUSTRIAL APPLICABILITY

The motor drive devices of the present disclosure include the comparison circuit which monitors the voltage of the control power source and the diagnosis circuit which judges whether it is normal to thereby improve the reliability of the abnormal voltage protection, and is thus useful for a motor drive device loaded in various devices which require safety.