JPH10257799A - Output open-circuiting detection device of multichannel output device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect the output open-circuit of multiple channels inexpensively by an output open-circuit detection device of a multiple-channel output device. SOLUTION: Coils 10a-10d of a stepping motor are connected between a driving circuit 12 and a ground and high-resistance resistors 24a-24d are connected in parallel with output transistors 20a-20d. A diode OR circuit 34 is connected to output terminals 13a-13d. When either one of the coils 10a-10d is disconnected, the voltage of a driving voltage source 22 is outputted to the output terminals via the resistors 24a-24d and the potential of the output terminals is maintained at a high level. In this case, the output level of the diode OR circuit 34 becomes high and the output is charged to a timer capacitor 72, and a high-level voltage is outputted from a comparison circuit 40 when the charged voltage exceeds a specific value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-channel output device having a multi-channel current output, such as a stepping motor driving device, and more particularly to a multi-channel output suitable for detecting its output open with a simple configuration. The present invention relates to a device output open detection device.

[0002]

2. Description of the Related Art Conventionally, as a driving device for a stepping motor, for example, a configuration disclosed in Japanese Patent Application Laid-Open No. 3-218298 is known. The above-described conventional device includes a drive circuit that energizes each coil of the stepping motor in accordance with the applied command pulse. When each coil is switched and energized, the stepping motor is driven. If the frequency of the command pulse becomes too high, the stepping motor cannot follow the command pulse, causing step-out. If step-out occurs, the stepping motor cannot exhibit its intended characteristics. For this reason, it is necessary to accurately detect step-out of the stepping motor in monitoring whether or not the operation state of the stepping motor is abnormal.

Generally, when step-out occurs in a stepping motor, almost no back electromotive force is generated in the coil of the stepping motor. A fixed relationship is established between the voltage between the terminals of the coil, the current supplied to the coil, and the back electromotive force. Therefore, when the back electromotive force is not generated due to the step-out, the voltage between the terminals of the coil changes with respect to the normal operation. Therefore, in the above-described conventional device, the presence or absence of step-out of the stepping motor is determined by detecting a change in the voltage between terminals of the coil.

[0004]

However, if any of the coils of the stepping motor is disconnected, the stepping motor cannot exhibit the desired characteristics. Therefore, it is necessary to detect the disconnection of the coil in order to monitor whether or not the operation state of the stepping motor is abnormal. However, the above-mentioned conventional device does not include any means for detecting the disconnection of the coil. In addition, as described above, the above-described conventional apparatus detects motor out-of-step on the assumption that a drive current normally flows through the coil. Therefore, when the coil is disconnected, the motor is disconnected. Key cannot be detected accurately.

[0005] As a technique for detecting disconnection of a coil of a stepping motor, a minute current that does not affect the operation of the motor is supplied to each coil, and a voltage between terminals of each coil is compared with a predetermined reference voltage. There is known a device that detects whether or not a disconnection has occurred in the coil based on the above. However, in the above-described conventional technology, the comparison between the voltage between the terminals of the coil and the reference voltage is performed for each coil.
A circuit for comparing voltages must be provided. For this reason, according to the above-described conventional technology, the cost of the stepping motor driving device is greatly increased in order to detect the presence / absence of disconnection of the coil.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has a multi-channel output capable of detecting an open output of a multi-channel output device at low cost, such as a coil disconnection of a stepping motor drive circuit. An object of the present invention is to provide a device output open detection device.

[0007]

The above object is achieved by the present invention.
As described in the above, a multi-channel output device including a plurality of switching elements, and a plurality of output terminals corresponding to each of the plurality of switching elements, the output current is turned on and off according to the on and off of the corresponding switching element An output open detection device of a multi-channel output device that detects an output open of a multi-channel output device, comprising: a minute current supply unit configured to supply a predetermined minute current to a load connected to each of the plurality of output terminals; OR output means for outputting a high level when the inter-terminal voltage is at a high level, and outputting a low level when the inter-terminal voltages of all loads are at a low level, and an output of the OR output means. Open detection means for outputting an output open signal indicating that an output open has occurred when the output is maintained at a high level for a predetermined period or more. It is accomplished by the output open detection device channel output device.

In the present invention, a minute current is supplied to a load connected to each output terminal. Therefore, when one of the output terminals is open and the load is in a high resistance state, the voltage between the terminals of the load connected to the output terminal is at a high level. The OR output means outputs a high level only when the voltage between the terminals of any load is at a high level. Therefore, when any of the output terminals is open, the output of the OR output means is maintained at a high level. The open detection means outputs an output open signal when the output of the OR output means is maintained at a high level for a predetermined period or more. As described above, in the present invention, the OR output means outputs a single signal based on the voltage between the terminals of each load, and the open detection means determines the presence or absence of the output open based on the output. Therefore, the open detecting means is provided in common for all output terminals, and it is not necessary to provide the open detecting means for each of the output terminals.

According to a second aspect of the present invention, in the output open detecting device of the multi-channel output device according to the first aspect, the output terminal is provided on a lower potential side with respect to the switching element. In addition, the logical sum output means is also achieved by an output open detection device of a multi-channel output device including a logical OR circuit using the potential of the output terminal as an input signal.

In the present invention, the output terminal is provided on the low potential side with respect to the switching element. Therefore, the load is connected to the low potential side with respect to the output terminal. For this reason,
When any of the output terminals is opened and the voltage between the terminals of the load becomes high level, the potential of the output terminal becomes high level. When the potential of any one of the output terminals becomes high, the logical OR circuit outputs a high-level voltage.

Further, the above object is achieved by the output open detecting device of the multi-channel output device according to the present invention, wherein the output terminal is provided on the high potential side with respect to the switching element. In addition, the OR output means is achieved by an output open detection device of a multi-channel output device comprising a logical NAND circuit using the potential of the output terminal as an input signal.

In the present invention, the output terminal is provided on the high potential side with respect to the switching element. Therefore, the load is connected to the high potential side with respect to the output terminal. For this reason,
When any of the output terminals is opened and the voltage between the terminals of the load becomes high level, the potential of the output terminal becomes low level. When the potential of any one of the output terminals becomes low, the logical NAND circuit outputs a high-level voltage.

[0013]

FIG. 1 is a circuit diagram of an output circuit of a stepping motor driving apparatus according to a first embodiment of the present invention. As shown in FIG. 1, the circuit according to the present embodiment includes coils 10a to 1a for each phase of a four-phase unipolar drive type stepping motor.
0d, a driving circuit 12 for supplying a driving current to the
and a detection circuit 14 for detecting the presence / absence of a disconnection between a and d.

As shown in FIG. 1, the drive circuit 12 has output terminals 13a to 13d. Output terminals 13a to 13d
Is connected to one end of each phase coil 10a to 10d. The other ends of the coils 10a to 10d are grounded. The drive circuit 12 is composed of the same circuits corresponding to the coils 10a to 10d. Therefore, hereinafter, portions corresponding to the coils 10a to 10d of the drive circuit 12 are indicated with suffixes "a" to "d", respectively, and the circuit corresponding to the coil 10a will be described representatively.

The drive circuit 12 has an output transistor 20a. The collector terminal of the output transistor 20a is connected to the output terminal 13a and grounded via the protection diode 21a. The emitter terminal of the output transistor 20a is connected to a drive voltage source 22 that outputs a predetermined drive voltage V _IG . A resistor 24a is connected between the collector terminal and the emitter terminal of the output transistor 20a. The resistance value of the resistor 24 a is determined by the drive voltage source 22 via the resistor 24 and the coil 1.
0a is set to a high value so that a very small current that does not affect the operation of the stepping motor is supplied. Further, a resistor 28a is connected between the base terminal and the emitter terminal of the output transistor 20a. Further, the base terminal of the output transistor 20a is connected to the resistor 30
It is connected to the collector terminal of the pre-drive transistor 32a via a. Predrive transistor 32
The emitter terminal of a is grounded. A CP (not shown) is connected to the base terminal of the predrive transistor 32a.
The control output terminal of U is connected.

Next, the configuration of the detection circuit 14 will be described. The detection circuit 14 includes a diode OR circuit 34, a reset circuit 36, a charging circuit 38, and a comparison circuit 40. The diode OR circuit 34 has its output 4
7, the resistor 48 and the drive circuit 1
And two output terminals 13a to 13d and diodes 50a to 50d, respectively. Diodes 50a to 50d are output terminals 13a to 1 respectively.
It is provided to allow a current flow from the 3d side to the resistor 48 side. The reset circuit 36 is connected to the output section 47 of the diode OR circuit 34.

The reset circuit 36 has a transistor 54. The base terminal of the transistor 54 is connected to the output 47 of the diode OR circuit 34,
It is grounded via a resistor 56. The emitter terminal of the transistor 54 is grounded. Further, the collector terminal of the transistor 54, as well through a resistor 58 is connected to a constant voltage source 60 for outputting a predetermined constant voltage V _CC, it is grounded via the resistor 62 and 64 connected in series ing. A base terminal of the transistor 66 is connected to a connection portion between the resistor 62 and the resistor 64. The emitter terminal of the transistor 66 is grounded. The collector terminal of the transistor 66 is connected to the charging circuit 38.

The charging circuit 38 includes a resistor 70 and a timer capacitor 72. The resistor 70 and the timer capacitor 72 are connected in series between the constant voltage source 60 and the ground so that the resistor 70 is on the constant voltage source 60 side. The collector 73 of the transistor 66 of the reset circuit 36 is connected to a portion 73 between the resistor 70 and the timer capacitor 72, and the comparison circuit 40 is connected to the portion 73.

The comparison circuit 40 has an operational amplifier 68. The comparison circuit 40 is connected to the positive input terminal of the operational amplifier 68.
Are connected. The negative input terminal of the operational amplifier 68 is connected to the constant voltage source 60 via the resistor 74 and is grounded via the resistor 76. Therefore, a reference voltage V _TH obtained by dividing the voltage V _CC by the resistors 74 and 76 is applied to the negative input terminal of the operational amplifier 68. Therefore, the operational amplifier 68 outputs a low-level voltage when the potential of the portion 73 of the charging circuit 38, that is, the terminal voltage V _CHARGE of the timer capacitor 72 is equal to or lower than the reference voltage V _TH , and V _CHARGE changes V _TH If it exceeds, a high level voltage is output. The output voltage of the operational amplifier 68 becomes the output voltage V _OUT of the comparison circuit 40.

Next, the operation of the circuit shown in FIG. 1 will be described. Note that in the following description, the potentials of the collector terminal and the base terminal of each transistor are referred to as a collector potential and a base potential, respectively. CPU not shown
When a low level voltage is applied to the base terminal of the predrive transistor 32a, the predrive transistor 32a is turned off. In this case, when the voltage V _IG is applied to the base terminal of the output transistor 20a, the output transistor 20a is also turned off. Therefore, no drive current is supplied to the coil 10a, and the resistor 24a
, Only a small current which does not affect the operation of the stepping motor is supplied.

On the other hand, when a high level voltage is applied to the base terminal of the predrive transistor 32a from the CPU, the predrive transistor 32a is turned on. When the predrive transistor 32a is turned on, the output transistor 20a is turned on because the base potential of the output transistor 20a decreases due to a voltage drop caused by the resistor 30a. In this case, the driving voltage source 2
2 through the output transistor 20a and the coil 10a
Is supplied with a drive current, so that the coil 10a is excited. Similarly, the coils 10b to 10d are excited by applying a high-level voltage to the base terminals of the predrive transistors 32b to 32d. The stepping motor is driven by the CPU (not shown) sequentially outputting a high-level voltage to the base terminals of the predrive transistors 32a to 32d so that the coils 10a to 10d are excited at a predetermined timing. .

FIG. 2 shows an operation time chart of the circuit according to the present embodiment, in which no disconnection occurs in any of the coils 10a to 10d (sections (I) and (III) in the figure), and the coils 10a to 10d. When a disconnection occurs in any of 10d (section in the figure)
(II)). In FIG. 2, in order from the top in the figure,
(A) ON / OFF state of the output transistors 20a to 20d, (b) output voltage of the diode OR circuit 34, that is,
The potential of the output section 47 of the diode OR circuit 34, (c) the voltage V _CHARGE between the terminals of the timer capacitor 72, and (d)
4 shows a time chart of the output voltage V _OUT of the comparison circuit 40. FIG. 2A shows the output transistors 20a to 20d superimposed on / off state, that is,
The case where any one of the output transistors 20a to 20d is turned on is shown as an on state.

In this embodiment, the stepping motor, which is a load, is of a PM type capable of maintaining a stop angle by detent torque. For this reason, in the stationary state after braking, it is not necessary to energize any phase, and there is a timing at which the drive current is not supplied to any of the coils 10a to 10d as shown in FIG. Coil 10a-1
When the output transistor 20a is turned on when no disconnection has occurred in any of the output transistors 20d, a drive current is supplied from the drive voltage source 22 to the coil 10a via the output transistor 20a, and the output transistor 20a and the diode 50a The current flows to the ground via the resistor 48 and the resistor 56. Therefore, a high level voltage corresponding to the voltage drop by the resistor 56 is output from the diode OR circuit 34. Similarly, when any of the output transistors 20b to 20d is turned on,
When current flows through the corresponding diodes 50b to 50d and the resistors 48 and 56, the diode OR
The circuit 34 outputs a high-level voltage. That is, when any of the output transistors 20a to 20d is turned on, the output voltage of the diode OR circuit 34 becomes high level.

On the other hand, when all the output transistors 20a are turned off, the coils 10a to 10d respectively
A minute current is supplied through the resistors 24a to 24d.
However, since the resistance values of the resistors 24a to 24d are sufficiently larger than the winding resistance values of the coils 10a to 10d,
The potentials of the output terminals 13a to 13d become low level. Therefore, no current flows through any of the diodes 50a to 50d, and the output voltage of the diode output circuit 34 becomes low.

As described above, when no disconnection occurs in any of the coils 10a to 10d, the section shown in FIG.
As shown in (I) and (III), the output transistors 20a to 20a
In synchronization with the on / off state of 20d, the output voltage of the diode OR circuit 34 changes between a high level and a low level. When the output voltage of the diode OR output circuit 34 becomes high level, the transistor 54 of the reset circuit 36 turns on. When the transistor 54 is turned on,
Since a current flows from the constant voltage source 60 to the ground via the resistor 58 and the transistor 54, the collector potential of the transistor 54 becomes low due to the voltage drop by the resistor 58. In this case, the base potential of the transistor 66 is also at a low level, and the transistor 66 is turned off. When the transistor 66 is off, the charging circuit 3
The eight timer capacitor 72 is charged by the constant voltage source 60 via the resistor 70. Therefore, the voltage between the terminals of the timer capacitor 72 gradually increases at constant T _RC time determined by the capacity of the timer capacitor 72 and the resistance value of the resistor 70.

On the other hand, when the output voltage of the diode OR circuit 34 goes low, the transistor 54 is turned off and the transistor 66 is turned on. In this case, the electric charge charged in the timer capacitor 72 is discharged via the transistor 66, so that the voltage between the terminals of the timer capacitor 72 is instantaneously reduced to 0V. Therefore, as shown in the sections (I) and (III) in FIG. 2C, the voltage V _CHARGE between the terminals of the timer capacitor 72 is the diode O
The reference voltage V _TH is synchronized with the change in the output voltage of the R circuit 34.
Increase and decrease without exceeding. As a result, FIG.
As shown in sections (I) and (III) of (d), the coil 10a
If no disconnection has occurred in any of 10 to 10d, the operational amplifier 68 outputs a low-level voltage.

On the other hand, when a disconnection occurs in any of the coils 10a to 10d, for example, when the coil 10a is disconnected, if the output transistor 20a is in the ON state, the above-described disconnection occurs. As if not
When a current flows through the output transistor 20a, the diode 50a, and the resistors 48 and 56, the output voltage of the diode OR circuit 34 becomes a high level. on the other hand,
When the output transistor 20a is turned off, the drive voltage V _IG is output to the output terminal 13a via the resistor 24a. Therefore, when a current flows through the diode 50a, the resistor 48, and the resistor 56, the diode OR circuit 34 outputs a high-level voltage. As described above, when the coil 10a is disconnected, regardless of the on / off state of the output transistor 20a, the diode OR
The output voltage of the circuit 34 becomes high level. Similarly, even when the coils 10b to 10d are disconnected, regardless of the on / off state of the output transistors 20b to 20d.
The output voltage of the diode OR circuit 34 becomes high level.

As described above, when a disconnection occurs in any of the coils 10a to 10d, as shown in the section (II) of FIG. 2B, regardless of the on / off state of the output transistors 20b to 20d. , The output voltage of the diode OR circuit 34 is maintained at a high level. For this reason, the timer capacitor 72 is continuously charged, and as shown in FIG.
As shown in the section (II), the terminal voltage V _CHARGE of the timer capacitor 72 continues to increase. As a result, the diode O
When the output voltage of the R circuit 34 is maintained at a high level for a predetermined period T, V _CHARGE exceeds V _TH and the comparison circuit 4
0 outputs a high-level voltage. here,
The predetermined period T is the maximum value of the continuous energizing time that can occur in the system, for example, the sum of the energizing time in any phase when reciprocating within the movable range at the minimum pulse rate when the origin position is determined. The time is set to be sufficiently large in consideration of circuit constants, variations, transient characteristics, and the like. Accordingly, it is possible to detect that any of the coils 10a to 10d is disconnected due to the high level of the output voltage V _OUT of the comparison circuit 40.

In order to prevent erroneous detection of coil disconnection, the charging voltage V _CHARGE of the timer capacitor 72 is set to the voltage V _CHARGE when no disconnection occurs in the coils 10a to 10d.
_It must increase or decrease within a range not exceeding _TH , and increase above the voltage _VTH only when a disconnection occurs in any of the coils 10a to 10d. Therefore, the reference voltage V _TH and the time constant T _RC are set such that the voltage V _CHARGE exceeds the reference voltage V _TH only when the charging time for the timer capacitor 72 exceeds the above-mentioned predetermined period T. The minimum pulse rate of a stepping motor is generally several tens.
pps, the predetermined period T is on the order of several hundred ms. Therefore, the time constant _TRC is also set on the order of several hundred ms.

As described above, in this embodiment, the logical OR of the output voltage levels of the output terminals 13a to 13d of the drive circuit 12 is determined by the diode OR circuit 34, and the time history of the logical sum, that is, the high Disconnection of each of the coils 10a to 10d is detected based on the time maintained at the level. Therefore, it is not necessary to provide a detection circuit for detecting disconnection for each of the coils 10a to 10d, and the detection circuit 14 can be shared with the coils 10a to 10d. As described above, according to the present embodiment, the disconnection of the coil can be detected without causing a large increase in the cost of the stepping motor driving device.

As described above, in this embodiment,
Disconnection can be detected regardless of the on / off state of the output transistors 20a to 20d, that is, regardless of the energized state of the coils 10a to 10d. Therefore, it is not necessary to add a circuit for masking the coil being driven to the inside of the drive circuit 12 in detecting the disconnection of the coil. For this reason, as can be seen from FIG. 1, in the present embodiment, resistors 24a to 24d are provided between the output terminals 13a to 13d and the drive voltage source 22, respectively, of the ordinary stepping motor driving device, and the output terminals 13a The above function is realized by connecting the detection circuit 14 to .about.13d. Therefore, according to the present invention, the coil disconnection detecting function can be realized only by retrofitting components to the conventional stepping motor drive device having no function of detecting coil disconnection.

Further, in the above embodiment, the determination of the presence / absence of disconnection is performed based on a comparison between the charging voltage V _CHARGE of the timer capacitor 72 and the reference voltage V _TH . As described above, the time constant T _RC of the charging circuit 38 is sufficiently large, on the order of several hundred ms, so that the charging voltage V _{CH ARGE} is hardly affected by external noise. The reference voltage V _TH is a stable constant voltage source 60.
Since obtained by applying the output voltage V _CC min, and external noise, it is highly stable to disturbance of the voltage change of the driving voltage source 22 due to the energization of the coil 10 a to 10 d. Therefore, according to the present embodiment, even when external noise or disturbance acts, it is possible to detect coil disconnection with high reliability.

In this embodiment, the output terminals 13a to 13a
If the period during which the high-level voltage is output to d exceeds a predetermined period, coil disconnection is detected. Therefore,
In addition to the disconnection of the coil, for example, the output transistor 20a
~ 20d short circuit between terminals, CPU runaway, or
Output terminals 13a to 13d due to a short circuit in the circuit wiring, etc.
Is output in the same manner. Therefore, the circuit according to the present embodiment includes the coils 10a to 10d
In addition to detecting the disconnection, it can function widely as an abnormality monitoring system for the stepping motor driving device.

Next, a second embodiment of the present invention will be described. As described above, in the first embodiment, the coil 1
When the energized state to 0a to 10d is switched,
It is assumed that a timing is provided at which no current is supplied to any of the coils 10a to 10d. However, for example, when a large static torque is to be obtained, when the stepping motor is stopped, the drive current is continuously supplied to the coil of the phase corresponding to the stop position. In such a case, since one of the coils 10a to 10d is always energized, that is, one of the output transistors 20a to 20d is always turned on, the coil according to the above-described embodiment is disconnected. Does not occur, a high-level voltage is output from the comparison circuit 40, and it is erroneously determined that the coil is disconnected. On the other hand, the present embodiment is characterized in that the coil disconnection can be correctly detected even when any one of the output transistors 20a to 20d is always turned on as described above. doing.

Hereinafter, this embodiment will be described with reference to FIG. FIG. 3 is a circuit diagram of an output stage of the stepping motor drive circuit according to the present embodiment. In FIG. 3, the same components as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. FIG. 3 shows only a circuit for one phase corresponding to the coil 10a. As shown in FIG. 3, in the circuit of this embodiment, a resistor 78a is connected between the output terminal 13a and the diode 50a. The control output terminal of the CPU (not shown) is connected to the base terminal of the pre-drive transistor 32a via the resistor 80a. The input terminal of the resistor 80a is connected to the base terminal of the transistor 84a via the resistor 82a. The collector terminal of the transistor 84a is connected to a connection between the resistor 78a and the diode 50a. Also,
The emitter terminal of the transistor 84a is grounded.

According to the above-described configuration, when the CPU outputs a high-level voltage to, for example, the base terminal of the pre-drive transistor 32a, the pre-drive transistor 32a and the output transistor 20a are turned on in the same manner as in the first embodiment. Both are turned on, and the drive voltage V _IG is output to the output terminal 13a, so that a drive current is supplied to the coil 10a. In this case, a high-level voltage is also applied to the base terminal of the transistor 84a, so that the transistor 84a is turned on. Therefore, the resistor 78a
Is connected to the diode 50a by a transistor 84a.
, And the potential thereof becomes a low level. Therefore, a low-level voltage is applied from the diode 50a to the reset circuit 36. Similarly, when a high-level voltage is applied to the base terminals of the pre-drive transistors 32b to 32d, the diodes 50b to 50d corresponding to the output transistors 20b to 20d that are turned on are also provided.
Therefore, a low-level voltage is applied to the reset circuit 36.

As described above, according to the present embodiment, the coil 1
A low-level voltage is applied to the reset circuit 36 from the circuit corresponding to the coil being driven among the coils 0a to 10d, and only when the other phase coil is disconnected, the circuit corresponding to the disconnected coil is reset to the reset circuit. A high-level voltage is applied to 36. Therefore, according to the present embodiment, the stepping motor is always connected to any of the coils 10a to 10a.
Even when driven so as to be energized to 10d,
Disconnection of the coil can be correctly detected.

In the first and second embodiments, the output transistors 20a to 20d serve as the above-described switching elements, the resistors 24a to 24d serve as the above-described minute current supply means, and the diode OR circuit 26 serves as the above-described logic. The OR circuit, the reset circuit 36, the charging circuit 38, and the comparison circuit 40 correspond to the above-described output open detection means.

Next, a third embodiment of the present invention will be described with reference to FIG. This embodiment is different from the first embodiment in that the output transistor is provided on the ground side from each coil of the stepping motor. In FIG. 4, the same components as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. In FIG. 4, illustration of the pre-drive transistor is omitted.

As shown in FIG. 4, the circuit of the present embodiment includes a driving section 102 for supplying a driving current to the coils 10a to 10d.
And a disconnection detecting unit 104 for detecting whether or not the coils 10a to 10d are disconnected. Coil 10a ~
10d are connected between the drive voltage source 22 and the output terminals 103a to 103d of the drive circuit 102, respectively.
The drive circuit 102 includes output transistors 120a to 120d
It has. The collector terminals of the output transistors 120a to 120d are connected to the output terminals 103a to 103d, respectively. Also, the output transistors 120a-1
The collector terminal of 20d is connected to the protection diode 12
It is connected to the drive voltage source 110 via 2a to 122d and is grounded via resistors 124a to 124d. The resistors 124a to 124d are connected to the driving voltage source 2
2 is set to a high value so that a small current that does not affect the operation of the stepping motor is supplied to the coils 10a to 10d.

The collector terminals of the output transistors 120a to 120d are connected to the transistor NAN of the detection circuit 104.
The D circuit 126 is connected. Transistor nand
The circuit 126 includes transistors 128a to 128d corresponding to the output transistors 120a to 120d, respectively. The base terminals of the transistors 128a to 128d are connected to the collector terminals of the output transistors 120a to 120d via the resistors 130a to 130d, respectively. A resistor 1 is connected between the base terminal and the emitter terminal of each of the transistors 128a to 128d.
32a to 132d are connected.

The emitter terminal of the transistor 128a is grounded. The collector terminal of the transistor 128d is connected to the output unit 13 of the transistor NAND circuit 126.
3 is connected. Transistors 128a to 128d
Are connected in series with respect to the emitter terminal and the collector terminal in this order from the ground side. The output unit 133 of the transistor NAND circuit 126 is connected to the charging circuit 3
8 between the resistor 70 and the timer capacitor 72
3 is connected. Therefore, the output voltage of the transistor NAND circuit 126 is applied to the timer capacitor 72.

In this embodiment, similarly to the circuit of the first embodiment, when any one of the output transistors 120a to 120d is turned on by a control signal given from the CPU, the coils 10a to 10d are turned on. Of these, the drive current is supplied to the coil corresponding to the output transistor that has been turned on. And the output transistors 120a-1
20d is sequentially turned on so that a drive current is supplied to the coils 10a to 10d at a predetermined timing, whereby the stepping motor is driven.

FIG. 5 is an operation time chart of the circuit of the present embodiment, in which no disconnection occurs in any of the coils 10a to 10d (sections (I) and (III) in the figure), and the coils 10a to 10d. When a disconnection occurs in any of 10d (section in the figure)
(II)). In FIG. 5, in order from the top in the figure,
(A) ON / OFF state of output transistors 120a to 120d, (b) Terminal voltage V of timer capacitor 72
_CHARGE and (c) a time chart of the output voltage V _OUT of the comparison circuit 40, respectively.

FIG. 5 (a) shows the output transistors 120a to 120d in a superimposed on / off state as in FIG. 2 (a), that is, the output transistors 120a to 120d.
The case where any of 20d is turned on is shown as the on state. As shown in FIG. 5A, in the present embodiment, similarly to the case of the first embodiment, the stepping motor which is a load is a PM type which can self-hold the stop angle by the detent torque. For this reason, in the stationary state after braking, it is not necessary to energize any phase, and the coil 10a
There is a timing at which the drive current is not supplied to any of the drive signals.

When no disconnection occurs in any of the coils 10a to 10d, for example, when the output transistor 120a is turned on, a drive current is supplied from the drive voltage source 22 to the ground via the coil 10a and the output transistor 120a. Since the current flows, the potential of the output terminal 103a is at a low level. Therefore, in this case, the base voltage of the transistor 128a becomes low level,
Is turned off. On the other hand, when the output transistor 120a is turned off, a minute current flows from the drive voltage source 22 via the coil 10a and the resistor 124. In this case, a voltage corresponding to a voltage drop by the resistor 124a is applied to the base terminal of the transistor 128a. Therefore, the base potential of the transistor 128a becomes high level, and the transistor 128a is turned on. Similarly, when output transistors 120b to 120d are turned on, corresponding transistors 128b to 128d are turned off, while output transistors 120b to 120d are turned off.
When 8d is turned off, the corresponding transistor 128b
To 128d are turned on.

Therefore, if no disconnection occurs in any of the coils 10a to 10d, the output transistors 120a to 120a
120d are all turned off, the transistor 12
Since all of 8a to 128d are turned on, the output unit 133 of the transistor NAND circuit 126 is grounded via the transistors 128a to 128d. For this reason,
The potential of the output unit 133 becomes low level, and the charge stored in the timer capacitor 72 is
Discharged through a to 128d. On the other hand, when any of the output transistors 120a to 120d is turned on, one of the transistors 128a to 128d is turned off. Therefore, the output unit 133 of the transistor NAND circuit 126 is connected to the constant voltage source 6 via the resistor 70.
0, the timer capacitor 72 is charged by the constant voltage source 60 via the resistor 70. Therefore, FIG.
As shown in (2), the timer capacitor 72 is charged and discharged in synchronization with the on / off change of the output transistors 120a to 120d, and the voltage between its terminals repeatedly increases and decreases without exceeding the reference voltage _VTH . Therefore, the section of FIG.
As shown in (I) and (III), when no disconnection occurs in any of the coils 10a to 10d, the operational amplifier 68 outputs a low level voltage.

On the other hand, when the coil 10a is disconnected, for example, the potential of the output terminal 130a is at a low level regardless of the on / off state of the output transistor 120a. Therefore, the base voltage of the transistor 128a is also at a low level, and the transistor 128a is turned off. Similarly, when the coils 10b to 10d are disconnected, the corresponding transistors 128b to
8d is turned off. Thus, the coils 10a-1
0d, the transistor 128a
When any one of to 128d is turned off, the terminal of the timer capacitor 72 on the constant voltage source 60 side is cut off from the ground side. Therefore, the timer capacitor 72 is charged,
As shown in section (II) of FIG.
The terminal-to-terminal voltage V _CHARGE of _No. 2 keeps increasing. Then, the charging time of the timer capacitor 72 reaches the predetermined period T, and
_{When the CHARGE} exceeds the reference voltage V _TH , the comparison circuit 40
Becomes high level. Therefore, the comparison circuit 40
That the output voltage has become high level, it is possible to detect that a disconnection has occurred in any of the coils 10a to 10d.

As described above, also in the present embodiment, as in the case of the first embodiment, only the provision of the common detection circuit 104 for each of the coils 10a to 10d allows the operational amplifier 6 to operate.
The disconnection of the coils 10a to 10d can be detected based on the output voltage of 0. In the present embodiment,
Connect the resistors 124a to 124d to the output terminals 103a to 103
d and ground, and the output terminal 103a
The above-described function is realized by connecting the detection circuit 104 to ３103d. Therefore, in the present embodiment as well, it is possible to easily detect a coil disconnection simply by retrofitting components to a conventional stepping motor driving device, as in the case of the above embodiment.

In this embodiment, as in the second embodiment shown in FIG. 3, a circuit for masking the coil being driven is provided, so that the output transistor 120a is always turned on.
Even in the case where any one of -120d is turned on, the disconnection of the coil can be accurately detected. In the first and second embodiments, the output transistors 120a to 120d correspond to the switching elements described above, the resistors 124a to 124d correspond to the minute current supply means, and the transistor NAND circuit 126 corresponds to the logic NAND circuit described above. The charging circuit 38 and the comparing circuit 40
Correspond to the output open detection means described above.

In the first to third embodiments,
The disconnection of the coil is detected by determining whether or not the voltage V _CHARGE between terminals of the timer capacitor 72 has exceeded the reference voltage V _TH by the comparison circuit 40. However, the present invention is not limited to this. No, diode OR circuit 3
4 (first and second embodiments) or transistor NAN
A period in which the output voltage of the D circuit 126 (third embodiment) is at a high level may be measured, and the disconnection of the coil may be detected based on whether or not this period has exceeded a predetermined period T.

In the first to third embodiments,
Output transistors 20a-20d or 120a-1
The minute current is supplied to the coils 10a to 10d by the resistors 24a to 24d or 124a to 124d provided in parallel with the 20d. The current sources are output transistors 20a to 20d or 120a to 120
By providing in parallel with d, a minute current may be supplied to the coils 10a to 10d.

In the first to third embodiments,
Although the present invention is applied to the output circuit of the stepping motor drive circuit, and the case where the output is detected to be open due to disconnection of the coil of the stepping motor has been described, the present invention is not limited to this. The present invention can be applied to detection of an open output of a multi-channel output device of any type in which a plurality of output switching elements are provided, and on / off of each output switching element controls on / off of an output current of each channel.

[0054]

As described above, according to the first to third aspects of the present invention, open output detection of a multi-channel output device can be realized at low cost.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an output circuit of a stepping motor driving device according to one embodiment of the present invention.

FIG. 2 is an operation time chart of the circuit of the present embodiment.

FIG. 3 is a circuit diagram of a circuit according to a second embodiment of the present invention.

FIG. 4 is a circuit diagram of a circuit according to a third embodiment of the present invention.

FIG. 5 is an operation time chart of the circuit of the present embodiment.

[Explanation of symbols]

12a to 12d, 120a to 120d Output transistors 13a to 13d, 103a to 103d Output terminals 24a to 24d, 124a to 124d Resistor 34 Diode OR circuit 36 Reset circuit 38 Charging circuit 40 Comparison circuit 126 Transistor NAND circuit

Claims (3)

[Claims] 1. A multi-channel comprising: a plurality of switching elements; and a plurality of output terminals corresponding to each of the plurality of switching elements and having an output current turned on / off according to on / off of the corresponding switching element. An output open detection device of a multi-channel output device that detects an output open of an output device, comprising: a minute current supply unit configured to supply a predetermined minute current to a load connected to each of the plurality of output terminals; OR output means for outputting a high level when the voltage between any of the loads is at a high level and outputting a low level when the voltages between the terminals of all the loads are at a low level; Open detection means for outputting an output open signal indicating that an output open has occurred when the output of the means is maintained at a high level for a predetermined period or more. An output open detection device for a multi-channel output device, comprising: 2. The output open detection device of a multi-channel output device according to claim 1, wherein said switching element is provided on a high potential side with respect to said output terminal, and said OR output means outputs said output. An output open detection device for a multi-channel output device, comprising a logical OR circuit that uses each potential of a terminal as an input signal. 3. The output open detection device for a multi-channel output device according to claim 1, wherein said switching element is provided on a low potential side with respect to said output terminal, and said OR output means outputs said output. An output open detection device for a multi-channel output device, comprising a logical NAND circuit using the potential of each terminal as an input signal.