JP2000233090A - Controller of sewing machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a controller of a sewing machine capable of minimizing a DC-DC converter used in the controller, and providing the excess current protection not affected by the magnetic connection of a switching transformer and the winding position. SOLUTION: A controller of a sewing machine comprises a sewing machine control circuit comprising a rectifying part and a smoothening part for producing a first DC power source from an external AC power source, a motor driver, and a processing unit for driving and controlling the sewing machine, a protective circuit for protecting the control circuit of the sewing machine, and a DC-DC converter 15A. The DC-DC convertor 15A is a switching regulator comprising a main winding P inputting a first DC power source and a control winding B for switching the main winding P, at a primary side of a transformer 22, and the control winding B is used in common as one or both of a control power source for motor driver and a driving power source of the protective circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rectifying unit and a smoothing unit for generating a first DC power supply from an external AC power supply, a motor drive driver for driving a sewing machine motor, a control system circuit including an arithmetic processing unit, and a circuit from an excessive current. Circuit for protecting the power supply, DC-DC for converting and outputting the voltage of the first DC power supply
The present invention relates to a control device for a sewing machine including a converter.

[0002]

2. Description of the Related Art FIG. 4 is a perspective view showing an example of the configuration of a conventional industrial sewing machine. In the figure, 1 is a sewing machine main body, 2 is a sewing machine motor, 3 is a control box as a control device, 4
Is a power switch, 5 is a pedal, and 6 is an operation panel.
Recent industrial sewing machines are equipped with a plurality of actuators 18 (see FIG. 5) such as solenoids and air cylinders on the sewing machine main body 1 to automate operations of a thread cutting device, a reverse stitching mechanism, and the like. The sewing machine motor 2 generally uses an inverter motor, a servo motor, or the like for performing position control or speed control.

The control box 3 has a circuit for supplying power to the sewing machine motor from a commercial power supply and a circuit for driving the actuator, and is constituted by a microcomputer (arithmetic processing unit) for controlling these. The power switch 4 connects / disconnects the commercial power input to the control box 3. The pedal 5 is for a sewing operator (hereinafter referred to as an operator) to control the sewing machine. The sensor attached to the control box 3 converts the movement of the pedal into an electric signal.
Control the actuator. Operation panel 6
Is for the operator to set various sewing patterns and the like, and this information is sent to the control box 3 to realize the sewing operation instructed by the operator.

FIG. 5 is a block diagram showing a configuration of a control box 3 of a known sewing machine. A commercial AC power supply, which is an external AC power supply, passes through the power supply switch 4, is filtered to remove noise by a filter unit 7, is rectified by a diode bridge of a rectification unit 8, and is smoothed by a smoothing capacitor 10 such as an electrolytic capacitor. By doing so, it is converted to the first DC power supply V _IN . Current limiting resistor 9a and inrush current prevention relay contact 9
b and the relay coil 9c together with the protection circuit controller 14 constitute an inrush current prevention circuit,
The inrush current prevention circuit controls the relay coil 9c by a signal from the protection circuit control unit 14 to turn off the relay contact when the power is turned on, and to turn on the relay contact after a predetermined time, so that the smoothing capacitor 10c is turned on when the power is turned on. Has the function of minimizing the current flowing into the device. Regenerative power absorption resistor 11a
The regenerative power control transistor 11b forms a regenerative absorption circuit together with the protection circuit control unit 14. The regenerative absorption circuit monitors a voltage detection signal connected to the protection circuit control unit 14, and when the voltage V _IN of the first DC power supply exceeds a specified value, the protection circuit control unit 14 sends a signal to the transistor 11b. A regenerative absorption signal is output, and the transistor 1
1b is turned on so that the back electromotive force generated at the time of motor braking is consumed by the resistor 11a so that the withstand voltage of the smoothing capacitor 10 and the motor driver 12 is not exceeded. The current detection resistor 19 forms an overcurrent control circuit together with the protection circuit control unit 14, and the overcurrent limiting circuit includes the current detection resistor 19 connected to the protection circuit control unit 14.
When the potential difference between both ends exceeds the specified value, the current limit signal is
Motor driver (inverter unit) 12 to output to PU 16
In this case, the excitation signal to the motor 2 is controlled to limit the current flowing to the motor 2 to prevent an overcurrent from flowing to the motor and the inverter. The protection circuit control unit 14 monitors the voltage detection signal connected to the protection circuit control unit 14 and, if the voltage of the first DC power supply is too low or too high, the CPU 16 A power supply voltage monitoring circuit that outputs a power supply voltage abnormality signal and stops the motor is configured. As described above, the protection circuit of the present control device includes the inrush current prevention circuit, the regenerative absorption circuit, the overcurrent limiting circuit, and the power supply voltage monitoring circuit, and is supplied from the DC-DC converter 15 to the protection circuit control unit 14. Protection circuit drive power supply V
Driven at _OUT5 .

[0005] Motor driver (motor drive driver) 1
2 converts the DC power supply into an AC signal in response to a motor excitation command from the CPU 16 and supplies power to the motor. The power transformer 13 converts the voltage of a commercial AC power supply into
And a power supply for driving a plurality of actuators, such as a thread trimming solenoid of a thread trimming device, a thread sweeping solenoid, and an operating solenoid of a reverse stitching mechanism. The DC-DC converter 15 converts the first DC power supply to “+5 V” “+1”.
2V, + 15V, etc., are converted to various control DC power supplies, and drive power supplies (V _OUT 6, V _OUT 6,
7), a drive power supply (V _OUT 5) for the protection circuit, and
It supplies the control power of the motor driver _{12 (V OUT 1~V OUT 4)} .

A CPU (arithmetic processing unit) 16 sends an excitation signal to the motor based on a sewing machine start command from an operator, monitors a power supply abnormality signal from the protection circuit, and stops the motor when an abnormality occurs. It is a one-chip microcomputer for turning on / off an actuator such as a thread trimming solenoid or a thread removing solenoid mounted on the sewing machine at an optimum timing. The actuator driver 17 is a circuit for driving an actuator such as a thread cutting solenoid or a thread removing solenoid provided in the sewing machine. The actuator 18 is a solenoid (or an electromagnetic valve that operates an air cylinder) mounted on the sewing machine. By driving these solenoids, various functions of the sewing machine such as a thread cutting operation of a thread cutting device and switching of a reverse sewing mechanism are performed. Can be done automatically.

FIG. 6 is a circuit diagram showing an internal configuration of a DC-DC converter 15 provided in a conventional sewing machine control device. Since the DC-DC converter 15 has a relatively small number of parts, a flyback method is generally used in a control device of the sewing machine. When the first DC power supply V _IN obtained by rectifying and smoothing the commercial AC power supply is input to the DC-DC converter, the switching transistor Tr20 is turned on by the starting resistor Rg, and the current i flows through the main winding P of the switching transformer 22. ₁ flows. Also,
At the same time a voltage is generated in the control windings B of the switching transformer 22 (control winding) current i _B flows.

The switching transistor Tr20 is kept on by the current i _B , but is turned off when the switching transistor Tr20 reaches a certain current value due to the limitation of the DC current gain (h _fe ) of the switching transistor Tr20. When the switching transistor Tr20 is turned off, the collector-emitter voltage of the switching transistor Tr20 increases due to flyback of the main winding P.
The flyback energy is escaped to protect the switching transformer 20 from exceeding the withstand voltage.

The flyback type DC-DC converter stores energy in the switching transformer 22 by turning on the switching transistor Tr20,
When the switching transistor Tr20 is turned off, energy is output to the output side (windings C1 to C5, windings S1 and S5).
This is a switching regulator that repeats switching in a mechanism that discharges to 2) and then turns on again by flyback of the switching transformer 22 itself after discharge. When the output voltage of the control winding B is increased, by bypassing the current i _B through the Zener diode Dz, the output side of the winding C1 to C5, the voltage output to the windings S1, S2 and stabilized I have.

The output windings of the switching transformer 22 include windings C1 to C5 and windings S1 and S2. Winding C1
From -C4, inverter power supplies arm power to the motor driver 12 V _OUT 1~V _OUT 4 (for example, a voltage value "+ 15V") is output. Specifically, the windings C1 to C1
C3 upper transistors of each motor driver 12 Uv, Vu, Wu based on arm power supplying base current (FIG. 5), the lower transistors U _D windings C4 motor driver 12, V _D, the W _D Each outputs a lower arm power supply for supplying current. From the winding C5, a protection circuit driving power supply V _OUT5 (for example, a voltage value of “+12 V”) is output to the protection circuit control unit 14, and the protection circuit control unit 14
It is used as a drive power supply for relays, operational amplifiers, etc., connected to the power supply.

From the windings S1 and S2, drive power supplies V _OUT 6 and V _OUT 7 (for example, a voltage value “+
12V "and" + 5V ") are output to the CPU 16 and its peripheral circuits. Drive power supply V _{OUT for} these control systems
6, V _OUT 7 is open to the user as a control power supply on the secondary side, and the small signal power supply can be easily taken by the user by modifying the sewing machine or adding optional equipment. Since the power supply from the windings S1 and S2 is open to the user, the windings S1 and S2 are protected from accidents such as electric shock.
A thick tape or the like is inserted between S2 and the other windings (windings P and B, windings C1 to C5) to provide high-voltage insulation. Here, the high voltage is AC1500V or AC3750V
It is.

Furthermore, the secondary-side control power source is on the relationship between open to the user, the power output from the other winding (the inverter power supply V _OUT 1 to V _OUT 4, the protection circuit drive power source V _OUT 5) than Since the load current increases, the windings S1 and S2 are generally wound near the main winding P as shown in the cross-sectional view of the switching transformer 22 shown in FIG. As described above, since the thick tape 42 for insulating from the other windings is inserted in the windings S1 and S2, the winding C1
C4, winding C5 is the core 4 of the switching transformer 22.
Since the coil is wound at a position far from zero, the degree of coupling of the transformer tends to decrease. The degree of coupling of the transformer is determined by the voltage response to the output load fluctuation and the input voltage (first DC power supply V _IN )
Affects the stability of the output voltage with respect to changes in the power supply. When the degree of coupling is reduced, the performance tends to be reduced.

Here, overcurrent protection of the DC-DC converter 15 will be described. When the output current on the output side increases, the current i ₁ flowing through the main winding P increases accordingly. By bypassing the current i _B currents i ₁ grow to larger than a predetermined value and the overcurrent protection transistor Tr21 is turned on, thereby forcibly turned off the switching transistor Tr20.

[0014] As a result, the output-side power source V _OUT 1~V _OUT
7, when a load abnormality occurs and an overcurrent occurs, the overcurrent protection is activated and the switching transistor Tr20 detects the current i.
_No damage by increasing ₁ . However, actually, for example, the protection circuit drive power supply V _OUT 5 (+
When 12 V) is short-circuited due to an abnormality in the device or the like, the load current increases and the current i1 increases accordingly.
Depending on the degree of coupling of the transformer, the level does not reach the level at which the overcurrent protection transistor 21 is turned on.
C4, windings S1 and S2) may output a normal voltage and the protection function may not work. Therefore, in general, voltage detection is performed for each of the output windings C1 to C4 and the windings S1 and S2, and this is transmitted to the CPU 16, and when at least one of the output voltages is detected as a voltage drop, the motor is started. In some cases, a protection operation such as stopping and notifying an error is performed.

[0015]

In the control box 3 of the conventional sewing machine, many windings such as the windings C1 to C5, S1 and S2 are required as the winding output of the switching transformer 22. When the switching transformer 22 is mounted on a printed circuit board, it is necessary to maintain a constant space and creepage distance between terminals of the switching transformer 22 (between terminals on the printed circuit board) in order to maintain insulation on the printed circuit board. Therefore, there is a problem that as the number of windings increases, the number of terminals increases, and accordingly the area occupied on the printed circuit board increases. In addition, it is necessary to insert a thick tape for providing high-voltage insulation to the windings S1 and S2 that output the secondary-side control power supply opened to the user, and the switching transformer 22 generally becomes large. is there.

Further, the windings C1 to C5 may be
In case of short-circuit or voltage drop, these windings located far from the core 40 have a further low degree of coupling due to the thick tape, and the protection by the overcurrent protection transistor 21 does not work as described above. In some cases. Also,
For this reason, even if the voltage of each winding is detected, a low voltage detection signal is transmitted to the CPU 16 and a protection function such as stopping the motor works.
5 occurs, the power supply (+
5V) may have an abnormality.
6 did not always operate normally, and the reliability of the protection function was not so high.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and it is possible to reduce the size of a DC-DC converter provided in a control device of a sewing machine, and furthermore, to prevent an overcurrent from being influenced by a magnetic coupling and a winding position of a switching transformer. It is an object of the present invention to provide a sewing machine control device that can be protected.

[0018]

According to a first aspect of the present invention, there is provided a rectifying unit and a smoothing unit for rectifying and smoothing an external AC power supply to generate a first DC power supply. A motor drive driver for driving a sewing machine motor with a power supply, and a sewing machine control circuit including an arithmetic processing unit for performing drive control of an actuator included in the sewing machine motor and the sewing machine; a protection circuit for protecting the sewing machine control circuit; DC-D for converting a voltage of a DC power supply to generate a DC power output of at least a control power supply of the motor drive driver and a control power supply of the protection circuit
And a C converter,
The DC-DC converter is a switching regulator including, on a primary side of a transformer, a main winding for inputting the first DC power supply, and a control winding for switching the main winding. The control winding is shared as one or both of a control power supply of the motor drive driver and a drive power supply of the protection circuit.

According to the first aspect of the present invention, since at least one DC power output is obtained from the control winding of the switching regulator, the number of windings of the transformer can be reduced accordingly. . Therefore, the DC-DC converter can be made smaller, lighter, and cheaper than in the past. Also, if a load abnormality occurs in the circuit sharing the DC power supply from the control winding and an overcurrent output or voltage drop occurs, this overcurrent or voltage drop will directly By lowering the output voltage and stopping the switching of the switching regulator, DC
-The supply of the output voltage of the DC converter is stopped. Therefore, a direct circuit protection is realized with respect to the voltage drop of the control winding (voltage drop due to short circuit or overcurrent) regardless of the magnetic coupling and winding position of the winding in the transformer. In addition, since this direct circuit protection does not rely on the detection of the voltage of each winding by a control system circuit such as a CPU, the drive power supply of the control system circuit already malfunctions when an abnormal voltage is detected, and the circuit protection does not operate. Inconvenience is also avoided, and reliable circuit protection can be realized. In addition, the winding of the control system circuit and the other windings are insulated from the high voltage because of the unique configuration of the control device of the industrial sewing machine that opens the drive power supply of the control system circuit to the user. This is one of the causes of the increase in the size of the DC-DC converter. Even in this configuration, the DC-DC converter has an appropriate size by acquiring and sharing one DC power supply output from the control winding of the switching regulator. It is particularly effective because it can be held down.

According to a second aspect of the present invention, in the control device for a sewing machine according to the first aspect, the protection circuit limits an inrush current flowing through the rectifying unit and the smoothing unit when the external AC power is turned on. An inrush current prevention circuit, a regenerative absorption circuit that absorbs a regenerative voltage generated in the first DC power supply unit by a back electromotive force of the motor during braking of the sewing machine motor, and detects an excessive current flowing through the sewing machine motor to detect the excessive current. An overcurrent limiting circuit for protecting the circuit;
The protection circuit includes at least one of a power supply voltage monitoring circuit that detects an abnormal voltage of the DC power supply.

The protection circuit is provided in a motor drive unit in which a large current is generated at a relatively high voltage in a control device of the sewing machine.
According to the second aspect of the present invention, since the control winding is shared as a drive power supply for the protection circuit, a switching stop function of the DC-DC converter works in response to an abnormality in the drive power supply. The reliable protection function works and is especially effective.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to FIGS. The control device of the sewing machine according to the embodiment of the present invention differs from the control box 3 of the sewing machine shown in the prior art only in the configuration of the DC-DC converter, and the other configurations are the same. The same components are denoted by the same reference numerals and description thereof is omitted.

FIG. 1 is a circuit diagram showing a configuration of a DC-DC converter 15A provided in a control device of a sewing machine according to an embodiment of the present invention. The DC-DC converter 15A of this embodiment generates the output power supply V _OUT5 from the electromotive force of the control winding B. Therefore, the number of windings provided in the switching transformer 22 is reduced by one as compared with the conventional one, and the switching transformer 22 is downsized. In this example, the Zener diode Dz2
Uses a Zener voltage whose zener voltage is higher than that used in the conventional circuit, and changes the output voltage of the winding B to V _OUT 5
The voltage rise caused by the increase in accordance with the output voltage of (+12 V) is absorbed.

Next, the operation of the control device of the sewing machine according to this embodiment will be described. The operation at the normal time is the same as the conventional one. If the load abnormality or the protection circuit drive power source V _OUT 5 of the protection circuit control section 14 (+ 12V) is short-circuited, the output voltage of the control winding B does not flow a current i _B to become zero, the switching transistor Tr20 is turned off the switching remains the is stopped, the other output (inverter power supply V _OUT 1 to V _OUT 4, of the control system driving the power source V _OUT
6, V _OUT 7) are also turned off at the same time, and there is no need to provide a protection function for the CPU 16, and the sewing machine motor 2 is immediately stopped. In addition, the protection function operates as described above without the need to separately provide a detection circuit for detecting a voltage drop of the protection circuit drive power supply V _OUT5 .

Other output windings (windings C1 to C4, winding S
As in the conventional case, the short-circuit operation of (1, S2) follows when the output current on the output side increases due to the short-circuit of the other output windings (windings C1 to C4, windings S1, S2). As a result, the current i ₁ flowing through the main winding P also increases. When the current i ₁ exceeds a certain value, the overcurrent protection transistor Tr21 is turned on, bypassing the current i _B and switching the transistor i
Is forcibly turned off. Whereby other output power (the inverter power supply V _OUT 1 to V _OUT 4, the protection circuit drive power source V _OUT
5. The drive power sources V _OUT 6 and V _OUT 7) of the control system are also stopped. In this case, the responsiveness of the overcurrent protection circuit with respect to a load change is improved as compared with the related art by improving the degree of coupling of the transformer as the switching transformer is downsized.

As described above, according to the control device of the sewing machine of this embodiment, since the protection circuit drive power supply V _OUT 5 is obtained from the control winding B, a switching transformer (transformer) is accordingly provided. The number of 22 windings can be reduced. Therefore, the DC-DC converter 15
A can be made small, lightweight, and inexpensive. The windings S1 and S2 are insulated against high voltage in order to open the drive power supplies V _OUT6 and V _OUT 7 of the control system to the user.
Although the size of the C converter 15A has been increased, the DC-
The DC converter 15A is kept at an appropriate size. Further, since the number of windings of the switching transformer 22 is reduced, the number of terminals of the transformer 22 is also reduced. When the transformer 22 is mounted on a printed circuit board, the area occupied by the printed circuit board is reduced by the reduced number of pins. Can be done.

As described above, the protection circuit driving power supply V
Against abnormalities _OUT 5, separately without need to prepare a detecting circuit of the voltage drop of the protection circuit drive power source V _OUT 5, immediately DC-
Since the output from the DC converter 15A is stopped, direct and reliable circuit protection can be realized. In addition, since the number of windings of the switching transformer 22 is reduced and the size of the windings is reduced, the degree of coupling between the transformers is improved, so that the main winding with respect to the load fluctuation of the output windings (windings C1 to C4, windings S1 and S2). The response of the line P is improved, and the other output windings (windings C1 to C
4. Even if the windings S1 and S2) are short-circuited, the protection function of the switching regulator works well, so that more reliable circuit protection is realized.

The present invention is not limited to the sewing machine control device according to the present embodiment. 2 and 3,
FIG. 10 is a circuit diagram of a configuration of DC-DC converters 15B and 15C provided in a sewing machine control device according to another embodiment of the present invention. For example, as shown in FIG. 2, as a power supply output from the control winding B of the switching regulator, an inverter power supply V _OUT 4 that supplies a base current to the lower transistors U _D , V _D , and W _D of the motor driver 12 is used. It is possible to apply. With this configuration, the DC-DC converter 15B can be configured to be small and lightweight, and a direct and reliable circuit protection against a load abnormality of the inverter power supply V _OUT 4 can be realized. Further, as shown in FIG. As the power supply output from the control winding B, both the protection circuit drive power supply V _OUT5 and the inverter power supply V _OUT 4 can be applied. With this configuration, the DC-DC converter 15C can be made smaller and lighter.

In addition, the details of the switching regulator system (flyback type), the circuit protection configuration of the switching regulator, and the voltage of each power supply, etc., depart from the spirit of the present invention. It can be changed appropriately within a range not to be performed.

[0030]

As described above, according to the sewing machine control device of the present invention, the following effects can be obtained. Since the number of windings of the transformer can be reduced, the DC-DC converter can be reduced in size, weight, and cost. Direct circuit protection can be realized without the influence of the magnetic coupling and winding position of the transformer on the load abnormality of the power supply output from the control winding.
It is possible to realize reliable protection against load abnormality of a power supply output from the control winding without relying on circuit protection of a control system circuit based on voltage detection. With respect to the power supply output from the control winding, the voltage detection means for circuit protection can be omitted. As a result, it is possible to reliably protect the device from abnormalities, and it is possible to prevent the failure of the device from being further expanded. In addition, since the degree of coupling between the windings is improved due to the downsizing of the transformer, the protection function of the switching regulator against a short circuit of another winding that does not share the control winding works more reliably.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a DC-DC converter provided in a control device of a sewing machine according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a DC-DC converter provided in a sewing machine control device according to another embodiment of the present invention.

FIG. 3 is a circuit diagram showing a configuration of a DC-DC converter provided in a sewing machine control device according to another embodiment of the present invention.

FIG. 4 is a perspective view showing an example of a configuration of a conventional industrial sewing machine.

FIG. 5 is a block diagram showing a configuration of a control box of a conventional sewing machine.

FIG. 6 is a circuit diagram showing an internal configuration of a DC-DC converter provided in a conventional sewing machine control device.

FIG. 7 is a cross-sectional view of a switching transformer provided in the DC-DC converter.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Sewing machine main body 2 Sewing machine motor 3 Control box (control device of sewing machine) 4 Power switch 5 Pedal 6 Operation panel 8 Rectification unit 10 Smoothing capacitor 12 Motor driver 13 Power transformer 14 Protection circuit control unit 15A to 15C DC-DC converter 16 CPU 17 actuator driver 18 actuator 22 switching transformer Tr20 switching transistor Tr21 overcurrent protection transistor P main winding B control windings C1 to C5, S1, S2 winding Dz2 Zener diode V _IN the first DC power supply V _OUT 1 to V _OUT 4 inverter Power supply V _OUT 5 Protection circuit drive power supply V _OUT 6, V _OUT 7 Control system drive power supply

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3B150 CE00 CE22 CE23 CE25 CE27 KA00 QA05 QA06 5H007 BB06 CA01 CB05 CC01 CC23 CD03 DB07 DB09 DC02 DC05 FA01 FA03 GA03 5H730 AA15 AA20 AS13 BB43 BB55 DD02 EE02 EE07 XXXXX XX26 XX28 XX33 XX35 XX43

Claims (2)

[Claims] 1. A rectifying unit and a smoothing unit for rectifying and smoothing an external AC power supply to generate a first DC power supply, a motor driving driver for driving a sewing machine motor by the first DC power supply, and a sewing machine motor and a sewing machine. A control circuit of the sewing machine including an arithmetic processing unit that performs drive control of the actuator; a protection circuit that protects the control circuit of the sewing machine; and a control power supply of at least the motor drive driver that converts a voltage of the first DC power supply; And a DC-DC converter that generates a DC power output of a control power supply of the protection circuit. The DC-DC converter includes a first DC power supply on a primary side of a transformer. And a control winding for switching the main winding. A control device for a sewing machine, wherein a line is shared as one or both of a control power supply of the motor drive driver and a drive power supply of the protection circuit. 2. The inrush current prevention circuit for limiting an inrush current flowing through the rectifying unit and the smoothing unit when the external AC power is turned on, and a back electromotive force of the motor during braking of the sewing machine motor. A regenerative absorption circuit that absorbs a regenerative voltage generated in the first DC power supply, an overcurrent limiting circuit that detects an excessive current flowing through the sewing machine motor and protects the circuit from the excessive current, and a first DC power supply. 2. The control device for a sewing machine according to claim 1, wherein the control device is a protection circuit including at least one of a power supply voltage monitoring circuit that detects a voltage abnormality.