JP2549452Y2 - Stepping motor failure detection circuit - Google Patents

Description

The present invention relates to a circuit for detecting a failure of a stepping motor.

2. Description of the Related Art An air conditioner uses a stepping motor for setting a valve opening of an electronic expansion valve. If the windings of each phase of the stepping motor are disconnected or short-circuited, the phase-locking or stopping of the stepping motor may be caused, or the motor drive circuit may be damaged by an excessive current. JP-A-59-56819 is known as a conventional example for preventing such a situation. In this prior art,
An overload state and a light load state of the motor are detected by detecting a load current flowing through the motor by a current transformer.

Problems to be Solved by the Invention In such prior art, it is necessary to use a current transformer as described above, and the current transformer has a relatively large configuration, and a winding of each phase of a stepping motor is used. In addition, there is a problem that the provision of each of the current transformers and the components associated therewith complicates the entire configuration and becomes extremely large.

Further, the load current level detected by the current transformer is compared with a predetermined reference level, and when the load current level becomes equal to or higher than the reference level, the load current is cut off, and the like.
For example, a configuration that prevents the destruction of circuit elements such as switches can be considered, but a configuration that compares the current transformer output with a reference level is required, and if the winding is short-circuited, the load current increases rapidly. Therefore, if the operation of the above configuration takes time, there is a problem that the circuit element is destroyed.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a stepping motor failure detection circuit capable of detecting a failure of a stepping motor, reducing the size of the configuration, and simplifying the configuration.

Means for Solving the Problems The present invention according to claim 1, wherein at least one stepping unit 2 is provided.
A switching means 4 provided for each of the motors, connected in series to one end of each winding φ of each phase, and energized to each winding φ in response to a stepping control signal; A driving unit 24 connected to the other end of each winding φ of the stepping motor 2 for exciting the winding φ in response to a driving control signal; a memory 31; a control signal generating unit 7a; and a failure detecting unit 7b.
And a processing means 7 provided in common to one or more stepping motors 2. The memory 31 selectively stores each winding φ in a time-sequential manner with a predetermined polarity selectively for each stepping motor 2. A plurality of control modes provided for excitation, and normal switching data corresponding to the levels of the switching control signal and the drive control signal in each control mode when the stepping motor 2 is normally driven based on each control mode. The control signal generating means 7a switches the control mode stored in the memory 31 in a time-sequential manner while switching the control mode common to each winding φ. A signal and a drive control signal for each winding are generated and provided to the switching means 4 and the drive means 24, respectively. Detecting the level at each connection point 28, 29 between the windings φ1, φ2 and the driving means 24, comparing the detected level with the reference detection value corresponding to the control mode being switched, and detecting whether or not the state is normal. A failure detection circuit for a stepping motor.

According to the second aspect of the present invention, the driving means 24 includes a first transistor Ta to which a control signal is applied to a base.
A second transistor Tb whose base is supplied with an output from the collector of the first transistor Ta; a first diode D1a connected in series with the collector of the first transistor Ta with the opposite polarity; A second diode D1b connected in series with the collector and having the opposite polarity; and a resistor R11b for applying a base bias in a direction to cut off the second transistor Ta. The collector of the first transistor Ta and the first diode
The end of each winding φ is connected to the connection point of D1a and the connection point of the collector of the second transistor Tb and the second diode D1b to excite each winding, and the predetermined winding φ1 of the connection points , φ2, the output of the connection point between the collector of the second transistor Tb and the second diode D1b is provided to the failure detecting means 7b.

The present invention according to claim 3, wherein the switching means (4) is provided.
Is a switching transistor, a resistor R1 is connected in series to the emitter of the switching transistor, and a diode means is provided between the base of the switching transistor and the power supply terminal of the resistor R1.
The diode means PD1 is turned on when an excessive current flows through the emitter of the switching transistor and the resistor R1, and supplies a predetermined constant voltage to the power supply of the base of the switching transistor and the resistor R1. It is characterized in that it occurs between the side terminals.

The present invention according to claim 4 provides a diode means PD1.
Is a light emitting diode, further provided with a light receiving element PT for receiving light from the light emitting diode PD1, wherein the failure detecting means 7b detects a failure in response to an output of the light receiving element PT. .

According to a fifth aspect of the present invention, the stepping motor drives the electronic expansion valve of the air conditioner to control the valve opening, and the failure detecting means 7 detects the failure when the failure is detected. The operation is stopped.

According to a sixth aspect of the present invention, the electronic expansion valve 22 of the air conditioner 25 is connected to each winding φ of each phase of the stepping motor 2 for controlling the valve opening degree by responding to a drive control signal. A driving means 24 for exciting and driving the winding φ by selectively exciting and controlling the winding φ selectively and sequentially with time in order to rotate the stepping motor 2 for each winding φ. A control signal generating means 7a for generating a drive control signal and supplying the generated drive control signal to the drive means 24;
In response to the level at each connection point with the control signal generator 24 and the respective drive control signals of the control signal generating means 7a, the level at the time of generation of the drive control signal is compared with a predetermined normal level to determine a fault. And a failure detection means for stopping operation of the air conditioner when detected.

According to the present invention of claim 7, a series of switching means 4 is provided in common for the plurality of windings φ, and the control signal generating means 7a further comprises a switching control signal for changing the switching state of the switching means 4. The failure detection means 7b compares the drive control signal for each winding φ with the switching control signal of the switching means 4 when the level is generated to a predetermined normal level. 7. A failure detection circuit for a stepping motor according to claim 6, wherein the failure is detected by detecting the failure.

According to the invention of claim 1, a switching control signal common to each winding φ and a drive control signal for each winding are generated based on the control mode stored in the memory 31 from the control signal generating means 7a. , A control signal is applied to the driving means 24, and each winding φ of each phase of the stepping motor 2 is selectively excited in a time sequential manner with a predetermined polarity. When the control signal is generated, the level of the connection point between each winding φ and the driving means 24 is compared with a predetermined value in a normal state stored in the memory 31, whereby the stepping motor fails, that is, Short-circuit and disconnection of each winding φ and the driving means 24 can be detected.

According to the invention of claim 2, an exciting current flows through the winding via the first and second transistors Ta and Tb. For example, when the first transistor Ta is turned on, the second transistor Tb is turned off. In this state, the output of the second transistor Tb is normally at the high level while being at the potential, but the second transistor Tb is short-circuited, or the winding φ1 connected to the second transistor Tb, When an abnormality occurs when one transistor Ta is shut off, the output of the second transistor Tb is, for example, the other potential at a low level, whereby a failure can be detected.

Also, when a control signal to shut off the first transistor Ta is given to the first transistor Ta, the second transistor Tb is turned on and the second transistor Tb is turned on.
When the output of the transistor Tb is normal, it is at the other potential, but when the first transistor Ta is short-circuited, or when the winding φ3 connected to the first transistor Ta or the second transistor Tb is interrupted, an abnormality occurs. Second
The output of the transistor Tb becomes the one potential, and thus a failure can be detected.

According to the invention of claim 3, the switching means 4 is constituted by a switching transistor, and when an excessive current flows, the diode means PD1 conducts and the power supply of the base of the switching transistor 4 and the resistor R1. When a constant voltage is generated between the switching transistor 4 and the side terminal, a further increase in the load current causes a decrease in the base-emitter voltage of the transistor.
Is increased to prevent an abnormally large current from flowing when a short circuit occurs.

According to the invention of claim 4, the diode means PD1 is constituted by a light emitting diode, and the output light of the light emitting diode is received by the light receiving element PT. A failure can be detected in response to the output of the element PT.

According to the invention of claim 5 to claim 7, the stepping motor is configured to drive an electronic expansion valve of the air conditioner, and when a failure is detected by the failure detection means 7b, the air conditioner is controlled. The operation of the device is stopped. In order to detect a failure, the failure detection means 7b includes the second transistor Tb described above.
, The output of the first transistor Ta may be applied.

FIG. 1 shows a motor failure detecting device 1 according to an embodiment of the present invention.
It is a block diagram which shows a structure of. In the present embodiment, for example, the opening degree of an electronic expansion valve provided in a refrigerant type air conditioner is set. This is to detect a failure relating to the two-phase excitation type four-phase stepping motor 2. The DC power supply 3 of the failure detection device 1 of this embodiment is connected in series to a PNP-type power switching transistor 4 serving as switching means via a power control limiting resistor R1.

A parallel circuit of a resistor R2 for giving a base bias and a photodiode PD1 having the DC power supply 3 side as an anode is connected between the base of the transistor 4 and the DC power supply 3. The base of the transistor 4 is connected via a resistor R3, a zener diode 5, and an inverting circuit 6 to a control terminal C of a control signal generating circuit 7a in a processing circuit 7 including, for example, a microcomputer.

The collector of the transistor 4 is connected to power supply lines 8 and 9, and the power supply lines 8 and 9 are connected to windings φ1 to φ4 (sometimes abbreviated as φ) constituting the stepping motor 2 respectively. The winding φ1 is connected to a control terminal A for outputting a control signal SA of the control signal generation circuit 7a, and a pair of inversion circuits 10
They are connected at a connection point 28 via a and 11a. Winding φ3 is connected between inverting circuits 10a and 11a.

Inverting circuits 10b and 11b are also provided for the windings φ2 and φ4 in the same manner as described for the windings φ1 and φ3. The output terminal of the inverting circuit 10b is connected to the winding φ4. The output terminal of the inverting circuit 11b is connected to the winding φ2 at a connection point 29. The output terminals of the inversion circuits 11a and 11b are connected to the input terminals X and Y of the failure detection circuit 7b via the resistors R4 and R5 and the pull-down resistors R6 and R7, respectively. The failure detection circuit 7b is supplied with control signals SA, SB, SC from the control signal generation circuit 7a or signals related thereto. Here, the inverting circuits 10a, 11a; 10b, 11b
4b (may be abbreviated as 24).

In this embodiment, for example, four sets (not shown) of the stepping motor 2 including the windings φ1 to φ4 for each phase shown in FIG.
Thus, four sets of the transistor 4 and the photodiode PD1 shown in FIG. 1 are also provided.
Such photodiodes and phototransistors PT1 to PT4 forming a photocoupler are provided in parallel with each other. The collectors of the phototransistors PT1 to PT4 are connected to the DC power supply 3, and the emitters are connected in common to the electrolytic capacitor C1 and the failure detection circuit 7b via the resistor R8, the inverting circuit 12, and the pull-up resistor R9.
Is connected to the input terminal D.

FIG. 2 shows the inverting circuits 10a, 11a and the windings φ1,
FIG. 4 is an electric circuit diagram showing a specific example of a configuration including φ3. Second
Referring to the figure, the inverting circuit 10a is configured such that the control signal SA
And an NPN transistor Ta applied to the base via the base, the emitter of which is grounded, and a resistor R11a connected between the base and the emitter. On the other hand, the transistor Ta
Is connected to the DC power supply 3 via a diode D1a that is connected in reverse polarity with the collector side as the anode. The inverting circuit 11a has the same configuration as the inverting circuit 10a,
It has resistors R10b and R11b, a transistor Tb, and a diode D1b. The collector of the transistor Ta is connected to the resistor R10b and to the winding φ3. Transistor Tb
Is connected to the winding φ1. Diode D1a, D1
b prevents the currents I1a and I3a from flowing to the power supply 3 side.

FIG. 3 is a system diagram showing a configuration example of an air conditioner 25 in which the failure detection device 1 shown in FIG. 1 is implemented. The air conditioner 25 includes an indoor unit 13 and an outdoor unit 14, and the indoor unit 13 is provided with a heat exchanger 15 and a blower 16 that blows air to the heat exchanger 15.

The outdoor unit 14 has a compressor 17 for compressing the refrigerant, and the refrigerant from the compressor 17 is transferred to the heat exchanger 18 on the outdoor unit 14 side or the indoor unit 13.
A four-way switching valve 19 for switching the delivery path to the heat exchanger 15 is provided. An accumulator 20 is provided between the four-way switching valve 19 and the compressor 17. The heat exchanger 18 is provided with a fan 21 for blowing air, and between the heat exchangers 18 and 15, an electronic expansion valve 22 for heating and an electronic expansion valve 23 for cooling are arranged, respectively. The electronic expansion valve 22 is provided with a stepping motor 2, and the other electronic expansion valves 23 are also provided with stepping motors. Detection of these failures is performed according to the present embodiment.

FIG. 4 is a waveform diagram illustrating the basic operation of the stepping motor 2. During the operation of the stepping motor 2, the control signal generating circuit 7a derives a control signal from the control terminal C and turns on the transistor 4. When the control signal SA shown in FIG. 4 (1) is input to the inverting circuit 10a shown in FIG. 2 together with FIG. 4, the transistor Ta conducts during the high-level rising periods W2 and W3, The current flowing through the winding φ3 when the transistor 4 in FIG.
I3 flows as indicated by arrow 13a in FIG.
Are excited as shown in FIG. 4 (5). At this time, the transistor Tb is turned off. Therefore, the current I1 does not flow through the winding φ1 as shown in FIG. 4 (3).

In the falling periods W4 and W1 of the control signal SA, the state is the reverse of the above, the current does not flow through the winding φ3, the current I1 of the winding φ1 flows as indicated by the arrow 11a in FIG. It is energized.

As for the inverting circuits 10b and 11b, a control signal SB as shown in FIG. 4 (2) is given, and the windings φ2 and φ4 are wound as shown in FIGS. 4 (4) and 4 (6). Line φ1, φ3
Driving is performed in the same energized state / interrupted state. In this way, a quarter cycle of the control signals SA and SB is one step of the stepping motor 2. In this embodiment, when the signal waveforms in FIG. 4 change with time in the order of the periods W1, W2, W3, W4,..., This is defined as the valve opening direction of the electronic expansion valves 22, 23, and the periods W4, W
If it changes in the order of 3, W2, W1,...

FIG. 5 is a flowchart for explaining the failure detection operation of this embodiment. In FIG. 5 step a1, the electronic expansion valve
Since it is necessary to change the opening degree of the valve 22, it is determined whether or not the operation signal of the stepping motor 2 is inputted from the air conditioning operation control circuit 30 of FIG. 1 to the control signal generation circuit 7 a. When input, the control signal SC is set to the high level, and the transistor 4
Is turned on.

Thereafter, prior to the driving of the stepping motor 2 corresponding to the actual change in the valve opening due to the operation signal, at step a2, for example, N1 step (for example, 20 steps)
Control signals SA and SB to drive circuit 2 so that
Output to 4a and 24b.

At this time, the failure detection circuit 7b sets the input terminal D at step a3.
To detect the level of the detection signal SD input to the. That is, if any one of the windings φ1 to φ4 is short-circuited,
The value of the current flowing through the transistor 4 increases. When a normal current flows through the transistor 4, the potential difference between both ends of the resistor R1 is small, and thus the photodiode PD1
Remains blocked and does not emit light. When the current flowing through the transistor 4 increases as described above, the resistance R1
The voltage drop across the resistor R1 and the voltage between the base and the emitter of the transistor 4, for example, 0.7 V, are applied to the photodiode PD1, and the photodiode PD1 conducts. This photodiode P
When D1 conducts, the voltage across it is 1.5V, for example, and becomes a constant value.

Further, when the current flowing through the resistor R1 and the transistor 4 further increases, the voltage at the time when the photodiode PD1 conducts is constant, although the voltage drop of the resistor R1 increases. Therefore, the voltage between the base emitters of the transistor 4 decreases.
Therefore, the impedance of the transistor 4 increases. In this manner, the transistor 4 and the line 8,
9 prevents excessive current from flowing.

At the time of the short circuit, the current I4 flowing through the transistor 4 increases, the photodiode PD1 conducts and emits light, and the corresponding phototransistor PT1 is brought into the conducting state.
As a result, charges are accumulated in the electrolytic capacitor C1 with a time constant corresponding to the capacitance, and the detection signal SD, which is the output of the inverting circuit 12, is output.
Switches from the high level to the low level. The capacitor C1 functions to prevent malfunction due to noise. This is the same even if any of the phototransistors PT1 to PT4 becomes conductive.

Thus, the failure detection circuit 7b can detect that at least one of the windings φ1 to φ4 is in a short-circuit state. When such a state is detected, the process proceeds to step a4, in which the air-conditioning operation control circuit 30 stops the operation of the air conditioner 25, and abnormalities occur in a control panel (not shown) or the like installed in the indoor unit 13. In addition to displaying the state, the control signal SC is derived from the circuit 7a, and the transistor 4 is turned off.

Thereafter, detection of a disconnection state of each of the windings φ1 to φ4 or detection of a short-circuit state or a disconnection state of the drive circuits 24a and 24b is performed. For example, when focusing on the windings φ1 and φ3,
A predetermined high-level or low-level combination value is given to each of the control signal SA and the control signal SC. At this time, the state of the signal SX input to the input terminal X is detected,
This is to simultaneously compare with the normal level state stored in the memory 31. Accordingly, data corresponding to the table shown in Table 1 below is stored in the failure detection circuit 7b in advance.

In Table 1, N1 and N2 indicate the output states of the transistors Ta and Tb in the inverting circuits 10a and 11a, and TR indicates the state of the switching transistor 4.

The following description focuses on the windings φ1 and φ3. At step a5, the control signals SA and SC are set to the high level to execute the mode (1). Thus, in a normal state, the transistor 4 conducts, and a current flows through the winding φ3. The output terminal of the inversion circuit 11a is at a high level. Therefore, when the detection signal SX is at a high level, the signal is normal, but when the detection signal SX is at a low level, the signal is abnormal. That is, it is determined in step a6 whether or not the detection signal SX is at a high level. If affirmative, the process proceeds to step a7, and if negative, the process proceeds to step a4. For example, when the transistor Tb is short-circuited, or when the winding φ1, the transistor Ta or the transistor 4 is shut off,
The detection signal SX is at a low level, and an abnormality is detected.

At step a7, the control signal SA is set to the high level and the control signal SC is set to the low level for execution of the mode (2). Thus, in a normal state, the transistor 4 is turned off, the transistor Ta shown in FIG. 2 is turned on, and the transistor Tb is turned off. Therefore, the output terminal of the inverting circuit 11a is grounded via the resistors R4 and R6, and its level is low. That is, when the detection signal SX is at a low level, it is normal, and when it is at a high level, it is abnormal. This determination is made in step a8. If the determination is affirmative, the process proceeds to step a9. If the determination is negative, the process proceeds to step a4. For example, when transistor 4 is short-circuited,
The detection signal SX becomes high level, and abnormality is detected.

At step a9, the control signal SA is set to the low level and the control signal SC is set to the high level to execute the mode (3). As a result, in a normal state, the transistor 4 is turned on,
The transistor Ta shown in FIG.
Tb is conducted. As a result, the winding φ1 becomes the transistor Tb
, And the detection signal SX becomes low level. That is, when the detection signal SX is at a low level, it is normal, and when it is at a high level, it is abnormal. Such a determination is made in step a10. If the determination is negative, the process proceeds to step a4. If the determination is affirmative, the processes of the above-described steps a5 to a10 relating to the windings φ1 and φ3 in FIG. 1 are performed. For example, if the transistor Ta is short-circuited or the winding φ3 or the transistor Tb is shut off, the detection signal SX becomes high level, and an abnormality is detected.

Further, such processing is sequentially performed for the windings φ2 and φ4, and further performed sequentially for the other stepping motors described above. When it is finally determined that all the stepping motors are normal. The operation of the stepping motor 2 corresponding to the operation signal is performed.

As described above, in this embodiment, for example, in detecting the short-circuit state and the disconnection state of the windings φ1 to φ4 of the stepping motor 2, and detecting the disconnection state and the short-circuit state of the drive circuits 24a and 24b, For example, it can be realized without using a complicated configuration such as a current transformer. Further, when the windings φ1 to φ4 are short-circuited and an excessive current flows, if the current flowing through the transistor 4 exceeds a predetermined value, the state is detected by the photodiode PD1 and the phototransistors PT1 to PT4. The transistor 4, the resistor R1, and the photodiode PD
Due to 1, excessive current is suppressed from flowing. As a result, it is possible to prevent a situation in which one of the windings φ1 to φ4 is short-circuited, and an excessive current flows through the transistor 4 or the transistors Ta and Tb to destroy them.

Instead of the photodiode PD1, for example, a zener diode may be connected to the opposite polarity, and another diode may be used.

As described above, according to the first aspect of the present invention, it is possible to detect disconnection of the winding φ of the stepping motor 2, short-circuit and interruption of the driving means 24, and failure of the switching means 4. .

Since such a configuration does not use the current transformer described in relation to the above-described prior art, the configuration can be downsized and the entire configuration can be simplified.

According to the invention of claim 2, the winding φ is controlled by the first and second transistors Ta and Tb, and the output of the connection point between the winding φ and the first and second transistors Ta and Tb. The failure detection can be performed based on the

According to the third aspect of the present invention, an excessive current is prevented from flowing through the switching transistor 4.

According to the fourth aspect of the present invention, the diode means PD1 is a light emitting diode, and its light is received by the light receiving element PT, so that a failure of a plurality of stepping motors can be detected.

According to the invention of claims 5 to 7, when the stepping motor for driving the electronic expansion valve fails, the operation of the air conditioner is stopped to prevent the failure from expanding.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a motor failure detecting device 1 according to one embodiment of the present invention, FIG. 2 is a block diagram showing a configuration example of a drive circuit 24a, and FIG. FIG. 4 is a system diagram showing a configuration example of the air conditioner 25. FIG. 4 is a timing chart for explaining a basic operation of the failure detection device 1, and FIG.
The figure is a flowchart for explaining the operation of the present embodiment. 1 ... failure detection device, 2 ... stepping motor, 3 ...
... DC power supply, 4 ... Switching transistor, 7 ...
Processing circuit, 7a: Control signal generation circuit, 7b: Failure detection circuit, 24a, 24b: Drive circuit, 25: Air conditioner

Claims (7)

(57) [Scope of request for utility model registration] A switching circuit provided for each of one or more stepping motors and connected in series to one end of each winding of each phase in common and energizing each winding in response to a stepping control signal. A driving means 24 connected to the other end of each winding φ of the stepping motor 2 for exciting the winding φ in response to a drive control signal; and a memory 31 corresponding to the switching means 4. , A control signal generating means 7a and a failure detecting means 7b, and a processing means 7 provided in common to one or more stepping motors 2. The memory 31 stores, for each stepping motor 2,
Control modes provided for selectively exciting the motor sequentially with a predetermined polarity, and a switching control signal and drive control in each control mode when the stepping motor 2 is normally driven based on each control mode. Corresponding to the signal level, a reference detection value having a predetermined level predetermined as normal data is stored, and the control signal generating means 7a switches the control mode stored in the memory 31 in a time sequential manner. , A switching control signal common to each winding φ and a drive control signal for each winding are generated and supplied to the switching means 4 and the driving means 24, respectively. The failure detecting means 7b outputs predetermined windings φ1, φ2 And the level at each connection point 28, 29 between the control means and the drive means 24, and compares the detected level with the reference detection value corresponding to the control mode being switched to the normal state. A failure detection circuit for a stepping motor, wherein the failure detection circuit detects whether or not the failure has occurred. 2. A driving means 24 comprising: a first transistor Ta to which a control signal is applied to a base; a second transistor Tb to which an output from a collector of the first transistor Ta is applied to a base; and a collector of the first transistor Ta. A first diode D1a connected in series and with the opposite polarity; a second diode D1b connected in series with the collector of the second transistor Tb and with the opposite polarity; and a base bias in a direction to cut off the second transistor Ta. The collector of the first transistor Ta and the first diode D1
The end of each winding φ is connected to the connection point of a and the connection point of the collector of the second transistor Tb and the second diode D1b to excite each winding, and the predetermined winding φ1 of the connection points 2. The stepping motor fault detecting circuit according to claim 1, wherein the output of the connection point of the collector of the second transistor Tb and the second diode D1b corresponding to .phi.2 is supplied to the fault detecting means 7b. 3. The switching means 4 is a switching transistor. A resistor R1 is connected in series to an emitter of the switching transistor. To the diode means PD
This diode means PD1 conducts when an excessive current flows through the emitter of the switching transistor and the resistor R1, and supplies a predetermined constant voltage to the power supply of the base of the switching transistor and the resistor R1. 2. The stepping motor fault detection circuit according to claim 1, wherein the fault occurs between the side terminal and the side terminal. 4. The diode means PD1 is a light-emitting diode, and further includes a light-receiving element PT for receiving light from the light-emitting diode PD1, and the failure detecting means 7b responds to an output of the light-receiving element PT.
4. A failure detecting circuit for a stepping motor according to claim 3, wherein the failure is detected. 5. A stepping motor drives an electronic expansion valve of an air conditioner to control a valve opening thereof, and a failure detecting means stops operation of the air conditioner when a failure is detected. The first to fourth features, characterized in that:
Fault detection circuit for one of the terms stepping motor. 6. A stepping motor 2 for driving an electronic expansion valve 22 of an air conditioner 25 to control the valve opening thereof is connected to each winding .phi. And a drive control signal for each winding φ for rotatingly driving the stepping motor 2 by selectively exciting the winding φ in a time-sequential manner with a predetermined polarity selectively. A control signal generating means 7a which is generated and supplied to the driving means 24;
In response to the level at each connection point and the respective drive control signals of the control signal generating means 7a, comparing the level at the time of generation of the drive control signal with a predetermined normal level,
A failure detection means for stopping operation of the air conditioner when a failure is detected, and a failure detection circuit for a stepping motor. 7. A series switching means 4 is provided in common for a plurality of windings φ, and a control signal generating means 7a further generates a switching control signal for changing a switching state of the switching means 4 to perform switching. The failure detection means 7b compares the level when the drive control signal for each winding φ and the switching control signal of the switching means 4 are generated with a predetermined normal level to detect a failure. 7. The stepping motor failure detection circuit according to claim 6, wherein: