JP3370292B2 - Drive circuit for brushless DC motor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit for a brushless DC motor, and more particularly to a circuit capable of preventing the terminal voltage of a power supply circuit from rising due to a regenerative current generated when abrupt reverse rotation occurs.

[0002]

2. Description of the Related Art FIG. 7 is a circuit diagram of an essential part showing an example of a conventional drive circuit for a brushless DC motor. The direct current power source E and an output terminal of the direct current power source E have a built-in or external connection. A power supply circuit in which a smoothing capacitor C1 is provided in parallel via a reverse current blocking diode Ds, and
Control arm with power elements Tr1 and Tr2 connected in series
1 and the control arm 2 in which two power elements Tr3 and Tr4 are connected in series and the control arm 2 in which two power elements Tr5 and Tr6 are connected in series, respectively A drive circuit of a brushless DC motor of a three-phase full bridge configuration in which the intermediate connection point of each control arm is connected to the motor winding M, respectively. An energization signal is given to the power element of the control arm in accordance with a predetermined sequence to sequentially energize the winding M of the motor so that the motor is driven to rotate in a predetermined direction.

[0003]

In the circuit shown in FIG. 7, when the energizing sequence of the three control arms is suddenly reversed by attempting to rapidly reverse the rotation direction of the motor, the motor winding is A large current flows, and when this current is limited for protection, a regenerative current is generated, and when the smoothing capacitor C1 provided in the power supply circuit is charged by the regenerative current, the terminal voltage of the power supply circuit rises. Therefore, when the terminal voltage of the power supply circuit exceeds the maximum withstand voltage value of the power element, the power element is broken. In order to solve this problem, in the conventional case where it is necessary to protect the drive circuit from the power supply terminal voltage increased by the regenerative current, an expensive and large power element is connected in parallel to the power supply terminal as shown in FIG. A means for protecting the control circuit and FIG.
Although a means for protecting the Zener diode by connecting it in parallel has been implemented as shown in (4), an expensive and large power element and a Zener diode have to be specially added.
An object of the present invention is to provide a small and inexpensive drive circuit for a brushless DC motor by suppressing an increase in the power supply terminal voltage of the drive circuit without adding an expensive and large power element or a Zener diode. Is.

[0004]

In the present invention, in order to solve the problems, a smoothing capacitor is provided through a DC power supply and a backflow prevention diode which is built in or externally connected to the output terminal of the DC power supply. Power supply circuit provided in parallel,
Driving a three-phase full-bridge brushless DC motor in which three control arms each having two power elements connected in series are connected in parallel to the power supply circuit, and the midpoint of each control arm is connected to each winding of the motor. In the drive circuit of the brushless DC motor, which requires protection of the drive circuit from the rise in the terminal voltage of the power supply circuit of the drive circuit due to the regenerative current generated when the rotation direction is suddenly reversed during operation, the regenerative current is The winding of the motor is not used for driving the motor during the period during which it is generated or until the terminal voltage of the power supply circuit of the drive circuit drops to a level that does not need to protect the drive circuit even if regenerative current is generated. The power element is used to electrically short-circuit and the motor itself consumes the regenerative current to suppress the rise in the power supply circuit terminal voltage of the drive circuit.

In order to derive the configuration of the present invention, first, the mechanism by which a regenerative current is generated and the power supply circuit terminal voltage is raised when the motor is rapidly reversed is clarified. The reason why the power supply terminal voltage of the drive circuit rises when the rotation direction of the brushless DC motor is rapidly reversed will be described with reference to FIG. Figure 6
(A) is a brushless DC motor at the time of normal rotation, and when the power elements Tr1 and Tr6 are turned on and Tr2 to Tr5 are turned off, the motor current Imf flows and the motor rotates normally. 6B is an equivalent circuit of the motor and the motor driving DC power supply E of FIG. 6A. From FIG. 6B, the motor current Imf at the time of forward rotation is the motor driving DC power supply voltage E. , Motor back electromotive force Vr1, Vr2, motor winding impedance Za1, Z
From the relationship of a2, it can be seen that Imf = (E- (Va1 + Va2)) / (Za1 + Za2) ... (1). FIG. 6C shows a brushless DC motor at the time of reverse rotation. In order to rapidly reverse the motor, Tr1 and Tr6 are turned off and Tr2 to Tr5 are turned on so as to rapidly reverse the polarity of the voltage applied to the motor. I have just done. The motor current Imr1 flowing at this time becomes Imr1 = (E + (Va1 + Va2)) / (Za1 + Za2) ... (2), so that the motor is rapidly reversed, and a large current flows when the applied voltage polarity is rapidly reversed. I understand. Here, if Imr1 exceeds the allowable current of the drive circuit,
Imr1 needs to be limited. In FIG. 6D, Tr2 and Tr5 are turned off in order to limit Imr1. At this time, since the regenerative current Ims1 has the reverse blocking diode Ds of the DC power source for driving the motor, the flywheel diode D1,
It flows into the power source smoothing capacitor C1 via D6 and the power source terminal voltage Vc of the drive circuit rises. Vc rises and Tr1 ~
If the withstand voltage of Tr6 is exceeded, Tr1 to Tr6 will be damaged and the drive circuit must be protected.

An example of means for solving the above problems according to the prior art will be described with reference to FIGS. FIG. 8 shows that when the terminal voltage Vc of the smoothing capacitor C1 is detected and Vc rises,
This is a method in which the switching element Tr7 is turned on and the regenerative current is consumed by the resistor Rr when a certain limit value (for example, the rated breakdown voltage value of the power element) detected by the control circuit is exceeded. FIG. 9 shows a method in which the Zener diode ZD1 consumes the regenerative current when the terminal voltage Vc of the smoothing capacitor C1 rises to a voltage to be protected (for example, the rated withstand voltage value of the power element). But,
Each of the above-mentioned two means requires the addition of another component, which causes a problem that the control circuit becomes large and expensive.

According to the present invention, in order to solve the above-mentioned problems, a brushless DC which requires protection of a drive circuit from an increase in terminal voltage of a power supply circuit due to a regenerative current generated when the rotation direction is rapidly reversed during operation is required. In the drive circuit of the motor, a period during which the regenerative current is generated, or a period until the terminal voltage of the power supply circuit of the drive circuit decreases to a level that does not need to protect the drive circuit even when the regenerative current is generated, The winding of the motor is electrically short-circuited by using the power element for driving the motor, and the motor itself consumes the regenerative current to suppress the rise of the terminal voltage of the power supply circuit.

[0008]

Embodiment 1 An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of the essential parts of a first embodiment of the present invention.
DC power source E and a built-in output terminal of the DC power source, or
A power supply circuit in which a smoothing capacitor C1 is provided in parallel via an externally connected backflow prevention diode Ds, and two power elements Tr1 and Tr2, TR3 and Tr4, Tr5 and Tr6 are connected in series. Three control arms are connected in parallel to the power supply circuit, and the midpoint of each control arm is connected to the winding M of the motor.
It is necessary to protect the drive circuit from the rise of the terminal voltage of the power supply circuit due to the regenerative current generated when the rotation direction is suddenly reversed during operation in the drive circuit of the three-phase full bridge configuration brushless DC motor connected to In a drive circuit of a brushless DC motor, a two-phase encoder Y is attached to a rotor shaft of the brushless DC motor, a circuit D for detecting the rotation direction of the motor from an output signal of the two-phase encoder Y, and the three-phase full bridge. An energization signal generation circuit T that sends an energization signal to the power element of the control arm of the drive circuit, and a command circuit S that commands the energization signal generation circuit T in the direction of rotation, the output of the energization signal generation circuit T A rotation direction discriminating circuit B for comparing the output of the rotation direction detection circuit D of the motor and determining whether or not the rotation directions of the two signals match is provided.

In the above-mentioned structure, when the command of the rotation direction command circuit S is changed to the reverse direction while rotating in a certain direction by the command of the rotation direction command circuit S, the motor is inertially moved in the same direction as the current direction. However, since the rotation direction of the energization signal generating circuit T immediately reverses, the rotation direction discriminating circuit B sends an output signal indicating that the rotation directions do not match to the energization signal generating circuit T.

In the energization signal generating circuit T, a control signal is sent to the power element group so that the power elements Tr1, Tr3, Tr5 are immediately turned off and Tr2, Tr4, Tr6 are turned on. Then, as shown in FIG. 5, the current for driving the motor does not flow in the winding M of the motor, and the back electromotive forces Vr1 and Vr2 generated in the winding M regenerate the power through Tr2 and Tr4 and the flywheel diode D6. A current flows, and this regenerative current flows only between the winding M of the motor and the driving power element and is consumed, and does not raise the terminal voltage of the smoothing capacitor C1 of the power supply circuit. Eventually, when the rotation of the motor becomes zero, the output of the rotation direction discrimination circuit B becomes zero and the energization signal sent from the energization signal generation circuit to the power element to generate the regenerative current is erased, and a new rotation direction command signal S is generated. Accordingly, the energization signal is sent from the energization signal generation circuit T to the power element, and the motor rotates in the new rotation direction. Figure 1
In the first embodiment shown in FIG. 3, even if the motor is rapidly reversed in this way, there is no risk of damaging the power element for controlling energization without increasing the terminal voltage of the smoothing capacitor C1 of the power supply circuit. In the above description, the operation is described so that the power element on the upper side of the control arm is shut off and the power element on the lower side is energized to control the regenerative current. The same effect can be obtained even if the power is cut off and the upper power element is energized.

[0011]

[Embodiment 2] FIG. 2 is a schematic view of the essential portions of a second embodiment of the present invention, in which a direct current power source E and a backflow prevention diode Ds connected to the output terminal of the direct current power source are incorporated or externally connected. Power supply circuit with parallel smoothing capacitor C1
Two power devices Tr1 and Tr2, TR3 and Tr4, Tr5 and Tr6
A brushless D having a three-phase full bridge configuration in which three control arms, each of which is connected in series, are connected in parallel to the power supply circuit, and the midpoint of each control arm is connected to the winding M of the motor.
In the drive circuit of the C motor, the drive circuit of the brushless DC motor, which requires protection of the drive circuit from the rise of the terminal voltage of the power supply circuit due to the regenerative current generated when the rotation direction is rapidly reversed during operation, A circuit D that detects the rotation direction of the motor from the output of a position detector H that detects the magnetic pole position of the rotor, and an energization signal generation circuit T that sends an energization signal to the power element of the control arm of the three-phase full bridge drive circuit. , A command circuit S for commanding the rotation direction to the energization signal generation circuit T, comparing the output of the energization signal generation circuit T and the output of the rotation direction detection circuit D of the motor to rotate both signals. The rotation direction discriminating circuit B for determining whether the directions match or not is provided.

In the above-mentioned structure, when the command of the rotation direction command circuit S is changed to the reverse direction while rotating in a certain direction by the command of the rotation direction command circuit S, the motor is inertially moved in the same direction as before. Although the rotation continues, the rotation direction of the energization signal generation circuit T immediately reverses. Therefore, the output signal of the rotation direction discriminating circuit B does not match the rotation direction and is sent to the energization signal generation circuit T.

In the energization signal generating circuit T, a control signal is sent to the power element group so that the power elements Tr1, Tr3, Tr5 are immediately turned off and Tr2, Tr4, Tr6 are turned on. Then, a current for driving the motor does not flow in the winding M of the motor, and Tr2 is generated by the counter electromotive forces Vr1 and Vr2 generated in the winding M.
, Tr4 and flywheel diode D6, a regenerative current flows, and this regenerative current flows only between the winding M of the motor and the power element for driving, and is consumed to raise the terminal voltage of the smoothing capacitor C1 of the power supply circuit. There is nothing to do. Eventually, when the rotation of the motor becomes zero, the output of the rotation direction discrimination circuit B becomes zero, and all the conduction signals sent from the conduction signal generating circuit to the power element to generate the regenerative current are erased, and the new rotation direction command signal is applied. An energization signal is sent from the energization signal generation circuit T to the power element, and the motor rotates in a new rotation direction. In this way, there is no risk of damaging the power element for controlling energization without increasing the terminal voltage of the smoothing capacitor of the power supply even if the reverse rotation is suddenly performed. still,
In the above description, the operation is explained so that the power element on the upper side of the control arm is turned off and the power element on the lower side is turned on to control the regenerative current. However, the same effect can be obtained by energizing the upper power element.

[0014]

[Third Embodiment] FIG. 3 is a block diagram of a third embodiment of the present invention, in which a DC power source E and a reverse current blocking diode Ds connected to the output terminal of the DC power source are incorporated or externally connected.
A power supply circuit in which a smoothing capacitor C1 is provided in parallel via a power supply circuit, and three control arms in which two power elements Tr1 and Tr2, TR3 and Tr4, Tr5 and Tr6 are connected in series, respectively, are connected in parallel to each other. Drive circuit of a brushless DC motor with a three-phase full-bridge configuration in which the middle point of each control arm is connected to the motor winding, and the regenerative current generated when the rotation direction is suddenly reversed during operation In the drive circuit of the brushless DC motor, which requires protection of the drive circuit from the rise of the terminal voltage of the power supply circuit, the two-phase encoder Y is attached to the rotor shaft of the brushless DC motor, and the output signal of the two-phase encoder Y A circuit D for detecting the rotation direction of the motor,
A circuit V for detecting the rotation speed of the motor, an energization signal generation circuit T for sending an energization signal to the power element of the control arm of the three-phase full bridge drive circuit, and a command circuit for instructing the energization signal generation circuit T in the direction of rotation. In those having S and
A rotation direction discriminating circuit B for comparing the output of the energization signal generating circuit S and the output of the motor rotation direction detecting circuit D to determine whether or not the rotation directions of the two signals match, and an output V of the speed detecting circuit. A certain set value VE, that is, a comparison circuit BV for comparing with a voltage corresponding to the rotation speed when the terminal voltage of the power supply circuit reaches the withstand voltage of the power element, is configured.

In the above structure, when the command of the rotation direction command circuit S is changed to the reverse direction while rotating in a certain direction by the command of the rotation direction command circuit S, the motor is inertially moved in the same direction as the current direction. However, since the rotation direction of the energization signal generating circuit T immediately reverses, the rotation direction discriminating circuit B outputs an output signal indicating a non-matching rotation direction.
The output of the speed discrimination circuit BV is sent to the energization signal generation circuit T.

In the energization signal generating circuit T, a control signal is sent to the power element group so that the power elements Tr1, Tr3 and Tr5 are immediately turned off and Tr2, Tr4 and Tr6 are turned on. Then, the current for driving the motor does not flow in the winding M of the motor, and the regenerative current flows through Tr2 and Tr4 and the flywheel diode D6 by the counter electromotive forces Vr1 and Vr2 generated in the winding, and this regenerative current is It flows only between the winding M of the motor and the power element for driving, and the current is consumed and does not increase the terminal voltage of the smoothing capacitor of the power supply circuit. Eventually, the rotation of the motor decreases and the output of the rotation speed detection circuit V becomes lower than the set value VE of the speed discrimination circuit BV, that is, the voltage corresponding to the rotation speed when the terminal voltage of the power supply circuit reaches the withstand voltage of the power element. Then, even if the output of the rotational direction discriminating circuit B does not become zero, all the energizing signals sent from the energizing signal generating circuit to the power element to generate the regenerative current are erased, and the energizing signal is generated according to the new rotating direction command signal. An energization signal is sent from the circuit T to the power element, and the motor rotates in a new rotation direction. In this way, there is no risk of damaging the power element for controlling energization without increasing the terminal voltage of the smoothing capacitor of the power supply even if the reverse rotation is suddenly performed. In the above description, the operation is described so that the power element on the upper side of the control arm is shut off and the power element on the lower side is energized to control the regenerative current. The same effect can be obtained even if the power is cut off and the upper power element is energized.

[0017]

[Fourth Embodiment] FIG. 4 is a schematic view of the essential portions of a fourth embodiment of the present invention, in which a direct current power source E and a backflow prevention diode Ds connected to the output terminal of the direct current power source are internally or externally connected. And a smoothing capacitor C1 provided in parallel, and three control arms in which two power elements Tr1 and Tr2, TR3 and Tr4, Tr5 and Tr6 are connected in series, respectively, are connected in parallel to the power circuit. , A drive circuit of a brushless DC motor of a three-phase full bridge configuration in which the midpoint of each control arm is connected to the winding M of the motor, and the power is generated by the regenerative current generated when the direction of rotation is suddenly reversed during operation. In the drive circuit of the brushless DC motor that requires protection of the drive circuit from the rise of the terminal voltage of the circuit, a comparison circuit BE for comparing the terminal voltage VE of the power supply circuit with a certain set voltage Vs, that is, the rated withstand voltage value of the power element, is provided. Power times Configured to send a regenerative current control signal to become equal to the setting value Vs which is the terminal voltage VE energization signal generating circuit T.

In the energization signal generation circuit T, as soon as it receives the regeneration control signal, the power elements Tr1, Tr3, Tr5 are turned off.
A control signal is sent to the power element group so that F is set and Tr2, Tr4, and Tr6 are turned on. Then, the current for driving the motor does not flow through the winding M of the motor, and the regenerative current flows through Tr2 and Tr4 and the flywheel diode D6 by the back electromotive forces Vr1 and Vr2 generated in the winding M, and this regenerative current. Flows only between the winding M of the motor and the power element for driving, and is consumed and does not increase the terminal voltage of the smoothing capacitor C1 of the power supply circuit. In this way, there is no risk of damaging the power element for controlling energization without increasing the terminal voltage of the smoothing capacitor of the power supply even if the reverse rotation is suddenly performed. still,
In the above description, the operation is explained so that the power element on the upper side of the control arm is turned off and the power element on the lower side is turned on to control the regenerative current. The same effect can be obtained by energizing the upper power element.

[0019]

Since the drive circuit of the brushless DC motor according to the present invention is configured as described above, the drive control circuit is protected by suppressing the rise of the terminal voltage of the power supply circuit even when the motor is rapidly rotated in the reverse direction. There is an effect that can be.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a main part of a first embodiment of a brushless DC motor drive circuit according to the present invention.

FIG. 2 is a circuit diagram of a main part of a second embodiment of a brushless DC motor drive circuit according to the present invention.

FIG. 3 is a circuit diagram of essential parts of a third embodiment of a brushless DC motor drive circuit according to the present invention.

FIG. 4 is a circuit diagram of an essential part of a fourth embodiment of a brushless DC motor drive circuit according to the present invention.

FIG. 5 is an explanatory diagram illustrating an operation of the brushless DC motor drive circuit according to the present invention.

FIG. 6 is an explanatory diagram illustrating a mechanism of regenerative current generation during reverse rotation control.

FIG. 7 is a circuit diagram of a main part of an example of a brushless DC motor drive circuit according to a conventional technique.

FIG. 8 is a first example of a protection circuit in a conventional brushless DC motor drive circuit.

FIG. 9 is a second example of the protection circuit in the conventional brushless DC motor drive circuit.

[Explanation of symbols]

B Rotation direction discrimination circuit BE voltage comparison circuit C1 smoothing capacitor D Rotation direction detection circuit D1 to D6 flywheel diode Ds Reverse element diode E DC power supply H rotor magnetic pole position detector S rotation direction command circuit T energization signal generation circuit Tr1 ~ Tr6 Power element Tr7 control transistor V speed detection circuit VE speed setting circuit BV speed comparison circuit Y 2-phase encoder

Claims (5)

(57) [Claims] 1. A DC power supply, and a power supply circuit in which a smoothing capacitor is provided in parallel via a backflow prevention diode which is built in or externally connected to the output terminal of the DC power supply, and 2.
A drive circuit for a brushless DC motor of a three-phase full bridge configuration in which three control arms in each of which power elements are connected in series are connected in parallel to the power supply circuit, and the midpoint of each control arm is connected to the winding of the motor. Then, when the direction of rotation is suddenly reversed during operation, regenerative current is generated in the drive circuit of the brushless DC motor, which requires protection of the drive circuit from the rise of the power supply terminal voltage of the drive circuit due to the regenerated current generated. For a period of time, or until the terminal voltage of the drive circuit power supply circuit drops to a level where the drive circuit is not protected even if regenerative current is generated, turn off the power supply from the power supply circuit and wind the motor. It is configured such that the wire is electrically short-circuited by using a power element for driving the motor, the regenerative current is consumed in the motor winding itself, and the rise of the power supply terminal voltage of the drive circuit is suppressed. Less DC motor drive circuit. 2. A DC power supply, a power supply circuit in which a smoothing capacitor is provided in parallel via a backflow prevention diode connected to the output terminal of the DC power supply, which is built-in or externally connected, and two power elements in series. A drive circuit for a brushless DC motor with a three-phase full bridge structure in which three connected control arms are connected in parallel to the power supply circuit, and the midpoint of each control arm is connected to the winding of the motor. In the drive circuit of the brushless DC motor, which is required to protect the drive circuit from the rise in the terminal voltage of the power supply circuit of the drive circuit due to the regenerative current generated when the motor is rapidly reversed, the rotor shaft of the brushless DC motor has two phases. An energizing signal is attached to the power element of the control arm of the circuit for mounting the encoder and detecting the rotation direction of the motor from the output signal of the two-phase encoder and the three-phase full bridge drive circuit. An energization signal generating circuit for sending and a command circuit for instructing the energization signal generating circuit to rotate direction, the output of the energization signal generating circuit and the output of the rotation direction detecting circuit of the motor are compared, and both signals are compared. Is configured to include a rotation direction discriminating circuit that determines whether the rotation directions are the same or not, and the drive circuit is the output of the energization signal generation circuit during the period when the output of the rotation direction discriminating circuit outputs the output of the rotation direction non-coincidence. Control the power element of the control arm to shut off the power supply from the power circuit, and electrically short the motor winding using the power element for driving the motor to consume the regenerative current in the motor winding itself. 2. A structure for suppressing an increase in the power supply terminal voltage of the drive circuit.
A drive circuit for the brushless DC motor according to 1. 3. A DC power supply, a power supply circuit in which a smoothing capacitor is provided in parallel via a backflow prevention diode that is built in or externally connected to the output terminal of the DC power supply, and two power elements are connected in series. A drive circuit for a brushless DC motor with a three-phase full bridge structure in which three connected control arms are connected in parallel to the power supply circuit, and the midpoint of each control arm is connected to the winding of the motor. The position where the magnetic pole position of the rotor of the motor is detected in the drive circuit of the brushless DC motor, which requires protection of the drive circuit from the rise in the terminal voltage of the power supply circuit of the drive circuit due to the regenerative current generated when the motor is rapidly reversed. A circuit for detecting the rotation direction of the motor from the output of the detector, an energization signal generation circuit for sending an energization signal to the power element of the control arm of the three-phase full bridge drive circuit, and the energization signal generation A circuit having a command circuit for commanding a rotation direction to a circuit, comparing the output of the energization signal generation circuit and the output of the rotation direction detection circuit of the motor, and determining whether the rotation directions of the two signals match or do not match. A direction discriminating circuit is provided, and while the output of the rotational direction discriminating circuit outputs an output that does not match the rotational direction, the power element of the control arm of the drive circuit is controlled by the output of the energization signal generating circuit. The current from the circuit is cut off, and the motor winding is electrically short-circuited by using a power element for driving the motor, so that the motor winding itself consumes the regenerative current and suppresses the rise in the power supply terminal voltage of the drive circuit. The drive circuit for a brushless DC motor according to claim 1, wherein the drive circuit is configured as described above. 4. A DC power supply, a power supply circuit in which a smoothing capacitor is provided in parallel via a backflow prevention diode that is built in or externally connected to the output terminal of the DC power supply, and two power elements are connected in series. A drive circuit for a brushless DC motor with a three-phase full bridge structure in which three connected control arms are connected in parallel to the power supply circuit, and the midpoint of each control arm is connected to the winding of the motor. Brushless D that requires protection of the drive circuit from the rise in the power supply terminal voltage of the drive circuit due to the regenerative current that occurs when the
A drive circuit for a C motor, in which a two-phase encoder is attached to the rotor shaft of the brushless DC motor, a circuit for detecting the rotation direction of the motor from an output signal of the two-phase encoder, and a circuit for detecting the rotation speed of the motor. , A three-phase full-bridge drive circuit having an energization signal generation circuit for sending an energization signal to a power element of a control arm and a command circuit for instructing the energization signal generation circuit to rotate in the energization signal generation circuit. A rotation direction discriminating circuit that compares the output and the output of the motor rotation direction detection circuit to determine whether the rotation directions of the two signals match or not, and a comparison circuit that compares the output of the speed detection circuit with a certain set value. And the rotation direction discriminating circuit outputs an output that does not match the rotation direction, and the comparison circuit output is equal to or more than a set value, the energization is performed. The output of the signal generation circuit controls the power element of the control arm of the drive circuit to shut off the power supply from the power supply circuit, and the motor winding is electrically short-circuited using the power element for motor drive to wind the motor. The brushless DC device according to claim 1, wherein the line itself consumes a regenerative current to suppress an increase in a power supply terminal voltage of the drive circuit.
Motor drive circuit. 5. A DC power supply, a power supply circuit in which a smoothing capacitor is provided in parallel via a backflow prevention diode that is built in or externally connected to the output terminal of the DC power supply, and two power elements are connected in series. A drive circuit for a brushless DC motor with a three-phase full bridge structure in which three connected control arms are connected in parallel to the power supply circuit, and the midpoint of each control arm is connected to the winding of the motor. In the drive circuit of the brushless DC motor, which requires protection of the drive circuit from the rise in the terminal voltage of the drive circuit due to the regenerative current generated when the voltage is rapidly reversed, the terminal voltage of the power supply circuit and a certain set voltage are A comparison circuit for comparison is provided, and at the moment when the terminal voltage of the power supply circuit tries to exceed a certain set value, the power element of the control arm of the drive circuit is controlled by the output of the energization signal generation circuit. The current from the source circuit is cut off, and the motor winding is electrically short-circuited by using the power element for driving the motor, and the motor winding itself consumes the regenerative current to suppress the rise in the power supply terminal voltage of the drive circuit. The drive circuit for the brushless DC motor according to claim 1, wherein the drive circuit is configured as described above.