JP2000324877A - Driving circuit for brushless dc motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress increase of the terminal voltage of a power source by short-circuiting motor windings using motor driving power devices, and consuming a regenerative current by the motor itself, while the regenerative current flows, or during an interval up to time when the terminal voltage of the power circuit lowers to a level where protection of a driving circuit is not required. SOLUTION: When an output signal representing unequal of the direction of rotation is sent from a direction-of-rotation discriminating circuit B to a conduction signal generating circuit T, power devices Tr1, Tr3, Tr5 are turned off, and power devices Tr2, Tr4, Tr6 are turned on. Consequently, currents which operate a motor do not flow in the windings M of the motor, and a regenerative current flows through Tr2, Tr4 and a flywheel diode D6 by counter electromotive force generated in the coils M. This regenerative current flows only between the motor windings end driving power devices and is consumed, and does not increase the terminal voltage of the smoothing capacitor of a power circuit.

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 a terminal voltage of a power supply circuit from rising due to a regenerative current generated when the motor reverses sharply.

[0002]

2. Description of the Related Art FIG. 7 is a main circuit diagram showing an example of a drive circuit for a brushless DC motor which has been conventionally implemented. A DC power supply E is connected to an output terminal of the DC power supply E internally or externally. A power supply circuit in which a smoothing capacitor C1 is provided in parallel via a backflow prevention diode Ds,
Control arm with power elements Tr1 and Tr2 connected in series
The upper and lower ends of a control arm 2 in which one and two power elements Tr3 and Tr4 are connected in series and a control arm 3 in which two power elements Tr5 and Tr6 are connected in series are output from the power supply circuit in parallel. A driving circuit of a brushless DC motor of a three-phase full-bridge configuration in which a connection point is connected to a terminal and an intermediate connection point of each control arm is connected to a motor winding M, respectively. An energization signal is supplied to the power element of the control arm in accordance with a determined sequence, and the motor M is sequentially energized to rotate the motor in a predetermined direction.

[0003]

In the circuit shown in FIG. 7, if the energizing sequence of the three control arms is abruptly reversed in order to rapidly reverse the rotation direction of the motor, the motor windings are A large current flows, and if this current is limited for protection, a regenerative current is generated. When the regenerative current charges the smoothing capacitor C1 provided in the power supply circuit, the terminal voltage of the power supply circuit increases. Therefore, when the terminal voltage of the power supply circuit exceeds the maximum withstand voltage of the power element, the power element is destroyed. In order to solve this problem, when it is conventionally necessary to protect a drive circuit from a power supply terminal voltage which increases due to a regenerative current, an expensive and large power element is connected in parallel to the power supply terminal as shown in FIG. Means for protecting the control circuit and FIG.
As shown in (1), means for connecting and protecting a Zener diode in parallel has been implemented, but it is necessary to add an expensive and large power element or a Zener diode.
An object of the present invention is to provide a small and inexpensive brushless DC motor drive circuit by suppressing an increase in the power supply terminal voltage of the drive circuit without specially adding an expensive and large power element or a zener diode. It is.

[0004]

According to the present invention, in order to solve the problem, a smoothing capacitor is connected to a DC power supply via a reverse current blocking diode which is internally or externally connected to an output terminal of the DC power supply. A 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 of the motor windings. When the rotation direction is suddenly reversed during operation, the regenerative current is generated in the brushless DC motor drive circuit that requires protection of the drive circuit from the rise in the terminal voltage of the drive circuit power supply circuit due to the generated regenerative current. During the period during which power is generated, or until the terminal voltage of the power supply circuit of the drive circuit drops to a level at which the drive circuit does not need to be protected even if regenerative current is generated, the winding of the motor is The motor is electrically short-circuited by using a power element, and the motor itself consumes a regenerative current, thereby suppressing a rise in a power supply circuit terminal voltage of the drive circuit.

In order to derive the structure of the present invention, first, the mechanism by which a regenerative current is generated when the motor is suddenly reversed and the terminal voltage of the power supply circuit is increased has been elucidated. FIG. 6 explains the cause of an increase in the power supply terminal voltage of the drive circuit when the rotation direction of the brushless DC motor is rapidly reversed. FIG.
(A) is a brushless DC motor at the time of forward rotation. 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 forward. FIG. 6B shows 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 normal rotation is represented by the motor driving DC power supply voltage E , Motor back electromotive force Vr1, Vr2, motor winding impedance Za1, Z
It can be seen from the relationship of a2 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 that the polarity of the voltage applied to the motor is rapidly reversed. I was just doing. The motor current Imr1 flowing at this time becomes: Imr1 = (E + (Va1 + Va2)) / (Za1 + Za2) (2) Since the motor is rapidly reversed, a large current flows when the polarity of the applied voltage is rapidly reversed. You can see that. Here, when Imr1 exceeds the allowable current of the drive circuit,
It is necessary to limit Imr1. FIG. 6D shows a case where Tr2 and Tr5 are turned off in order to limit Imr1. At this time, the regenerative current Ims1 includes the reverse blocking diode Ds of the DC power supply for driving the motor, so that the flywheel diode D1,
The current flows into the power supply smoothing capacitor C1 via D6, and the power supply terminal voltage Vc of the drive circuit rises. Vc rises and Tr1 ~
If the withstand voltage of Tr6 is exceeded, Tr1 to Tr6 are damaged, so that protection of the drive circuit is required.

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

In the present invention, in order to solve the above-mentioned problem, when the rotating direction is suddenly reversed during operation, a brushless DC which needs to protect the drive circuit from a rise in terminal voltage of the power supply circuit due to a regenerative current generated. In the motor drive circuit, a period during which a regenerative current is generated, or a period 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 the regenerative current is generated, The motor winding is electrically short-circuited by using a power element for driving the motor, so that the motor itself consumes regenerative current and suppresses a rise in 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 configuration diagram of a main part of a first embodiment of the present invention.
A DC power supply E, and a built-in output terminal of the DC power supply or
A power supply circuit provided with a smoothing capacitor C1 in parallel via an externally connected backflow preventing diode Ds, two power elements Tr1 and Tr2, TR3 and Tr4, and Tr5 and Tr6 were 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.
A drive circuit for a brushless DC motor with a three-phase full-bridge configuration connected to the power supply. When the rotation direction is suddenly reversed during operation, protection of the drive circuit is required from the rise in terminal voltage of the power supply circuit due to the regenerative current generated. A driving circuit for a brushless DC motor, wherein a two-phase encoder Y is attached to a rotor shaft of the brushless DC motor, and a circuit D for detecting a rotation direction of the motor from an output signal of the two-phase encoder Y; A drive circuit having an energizing signal generating circuit T for transmitting an energizing signal to a power element of a control arm, and a command circuit S for instructing the energizing signal generating circuit T to rotate in the direction of rotation; A rotation direction discrimination circuit B is provided for comparing the output of the motor rotation direction detection circuit D with the output of the motor to determine whether the rotation directions of the two signals match or not.

In the above configuration, if the command of the rotation direction command circuit S is changed in the reverse direction while the motor is rotating in a certain direction by the command of the rotation direction command circuit S, the motor operates in the same direction as the previous direction due to inertia. However, since the rotation direction of the energization signal generation circuit T is immediately reversed, the rotation direction discriminating circuit B sends an output signal having a rotational direction mismatch to the energization signal generation circuit T.

In the energization signal generation circuit T, a control signal is immediately sent to the power element group so that the power elements Tr1, Tr3, and Tr5 are turned off and Tr2, Tr4, and Tr6 are turned on. Then, as shown in FIG. 5, a current for driving the motor does not flow through the winding M of the motor, and the back electromotive forces Vr1 and Vr2 generated in the winding M regenerate 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 discriminating circuit B becomes zero and the energizing signal sent to the power element by the energizing signal generating circuit to generate the regenerative current is completely erased, and the new rotational direction command signal S Accordingly, the energization signal is sent from the energization signal generation circuit T to the power element, and the motor rotates in a new direction. FIG.
In the first embodiment described above, even if the motor is suddenly reversed in this manner, there is no risk of damaging the power control power element without increasing the terminal voltage of the smoothing capacitor C1 of the power supply circuit. In the above description, the operation has been described in which the power element on the upper side of the control arm is cut off and the power element on the lower side is turned on to control the regenerative current. And the same effect can be obtained by turning on the upper power element.

[0011]

[Embodiment 2] FIG. 2 is a block diagram showing a main part of a second embodiment of the present invention, in which a DC power supply E is connected to an output terminal of the DC power supply via a reverse current blocking diode Ds connected internally or externally. A power supply circuit in which a smoothing capacitor C1 is provided in parallel;
Two power elements Tr1 and Tr2, TR3 and Tr4, Tr5 and Tr6
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, when the direction of rotation is suddenly reversed during operation, the drive circuit of the brushless DC motor needs to protect the drive circuit from the increase in the terminal voltage of the power supply circuit due to the generated regenerative current. A circuit D for detecting the rotation direction of the motor from an output of a position detector H for detecting a magnetic pole position of the rotor; an energization signal generation circuit T for transmitting an energization signal to a power element of a control arm of the three-phase full bridge drive circuit; And a command circuit S for instructing the energization signal generation circuit T to indicate the direction of rotation. The output of the energization signal generation circuit T is compared with the output of a rotation direction detection circuit D of the motor, and the rotation of both signals is determined. It is configured to include a rotation direction discrimination circuit B for determining whether the directions match or not.

In the above configuration, if the command of the rotation direction command circuit S is changed in the reverse direction while the motor is rotating in a certain direction by the command of the rotation direction command circuit S, the motor moves in the same direction as the current direction by inertia. Although the rotation continues, the rotation direction of the energization signal generation circuit T immediately reverses, so that an output signal in which the output of the rotation direction discrimination circuit B does not match the rotation direction is sent to the energization signal generation circuit T.

In the energization signal generation 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, no current for driving the motor flows through the winding M of the motor, and Tr2 is generated by the back electromotive forces Vr1 and Vr2 generated in the winding M.
And a regenerative current flows through the transistor Tr4 and the flywheel diode D6. This regenerative current flows only between the winding M of the motor and the power element for driving and consumes the terminal voltage of the smoothing capacitor C1 of the power supply circuit. I won't let you. 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 to the power element by the energization signal generation circuit to generate the regenerative current is completely erased, and according to the new rotation direction command signal. The energization signal is sent from the energization signal generation circuit T to the power element, and the motor rotates in a new rotation direction. Even if the power is suddenly reversed in this manner, there is no possibility of damaging the power control power element without increasing the terminal voltage of the smoothing capacitor of the power supply. still,
In the above description, the operation has been described in which 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]

[Embodiment 3] FIG. 3 is a block diagram showing a main part of a third embodiment of the present invention, in which a DC power supply E and a backflow preventing diode Ds connected internally or externally to an output terminal of the DC power supply are shown.
A power supply circuit provided with a smoothing capacitor C1 in parallel via a power supply circuit, and three control arms in which two power elements Tr1 and Tr2, TR3 and Tr4, and Tr5 and Tr6 are connected in series, are connected in parallel to the power supply circuit. And a three-phase full-bridge brushless DC motor drive circuit in which the midpoint of each control arm is connected to the winding of the motor, and the regenerative current generated when the rotation direction is suddenly reversed during operation Is a drive circuit of a brushless DC motor that requires protection of the drive circuit from a rise in terminal voltage of the power supply circuit, and a two-phase encoder Y is attached to a rotor shaft of the brushless DC motor, and the output signal of the two-phase encoder Y A circuit D for detecting a rotation direction of the motor;
A circuit V for detecting a rotation speed of the motor; an energization signal generation circuit T for transmitting an energization signal to a power element of a control arm of the three-phase full bridge drive circuit; and a command circuit for instructing the energization signal generation circuit T of a rotation direction. In those having S,
A rotation direction discrimination circuit B which compares the output of the energization signal generation circuit S with the output of the rotation direction detection circuit D of the motor to determine whether the rotation directions of the two signals match or not, and an output V of the speed detection circuit. And a comparison circuit BV for comparing with a certain set value VE, that is, a voltage corresponding to the rotation speed when the terminal voltage of the power supply circuit reaches the withstand voltage of the power element.

In the above configuration, if the command of the rotation direction command circuit S is changed in the reverse direction while the motor is rotating in a certain direction by the command of the rotation direction command circuit S, the motor operates in the same direction as the previous direction due to inertia. , But the rotation direction of the energization signal generation circuit T is immediately reversed, so that the rotation direction discriminating circuit B outputs a rotation direction mismatch output signal,
The output of the speed discrimination circuit BV is sent to the energization signal generation circuit T.

In the energization signal generation 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, a current for driving the motor does not flow through the winding M of the motor, and a regenerative current flows through Tr2 and Tr4 and the flywheel diode D6 due to the back electromotive forces Vr1 and Vr2 generated in the winding. The current flows only between the winding M of the motor and the power element for driving 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 falls below the voltage corresponding to the rotation speed when the terminal voltage of the power circuit reaches the withstand voltage of the power element, ie, the set value VE of the speed discrimination circuit BV. Then, even if the output of the rotation direction discriminating circuit B does not become zero, the energization signal sent to the power element by the energization signal generation circuit to generate the regenerative current is completely erased, and the energization signal is generated according to the new rotation direction command signal. The energization signal is sent from the circuit T to the power element, and the motor rotates in a new rotation direction. Even if the power is suddenly reversed in this manner, there is no possibility of damaging the power control power element without increasing the terminal voltage of the smoothing capacitor of the power supply. In the above description, the operation has been described in which the power element on the upper side of the control arm is cut off and the power element on the lower side is turned on to control the regenerative current. And the same effect can be obtained by turning on the upper power element.

[0017]

[Fourth Embodiment] FIG. 4 is a block diagram showing a main part of a fourth embodiment of the present invention, in which a DC power supply E is connected to an output terminal of the DC power supply via a backflow preventing diode Ds connected internally or externally. A power supply circuit in which a smoothing capacitor C1 is provided in parallel and three control arms in which two power elements Tr1 and Tr2, TR3 and Tr4, and Tr5 and Tr6 are connected in series are connected in parallel to the power supply circuit. A drive circuit for a brushless DC motor having a three-phase full-bridge configuration in which the midpoint of each control arm is connected to the winding M of the motor, and a regenerative current generated when the rotation direction is suddenly reversed during operation. In a drive circuit of a brushless DC motor that requires protection of the drive circuit from an increase in 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 of the power element, Power cycle 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, the power elements Tr1, Tr3, Tr5 are turned off immediately after receiving the regeneration control signal.
F, and sends a control signal to the power element group so that Tr2, Tr4, and Tr6 are turned on. Then, no current for driving the motor flows through the winding M of the motor, and a regenerative current flows through Tr2 and Tr4 and the flywheel diode D6 due to the back electromotive forces Vr1 and Vr2 generated in the winding M. Flows only between the winding M of the motor and the driving power element and does not increase the terminal voltage of the smoothing capacitor C1 of the power supply circuit. Even if the power is suddenly reversed in this manner, there is no possibility of damaging the power control power element without increasing the terminal voltage of the smoothing capacitor of the power supply. still,
In the above description, the operation has been described in which 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 even when the upper power element is energized.

[0019]

As described above, the drive circuit of the brushless DC motor according to the present invention has the above-described configuration, so that even if the motor is suddenly reversely rotated, the rise of the terminal voltage of the power supply circuit is suppressed and the drive control circuit is protected. There is an effect that can be.

[Brief description of the drawings]

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

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

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

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

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

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

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

FIG. 8 is a first example of a protection circuit in a brushless DC motor drive circuit according to the related art.

FIG. 9 is a second example of the protection circuit in the brushless DC motor drive circuit according to the related art.

[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 detection device S Rotation direction command circuit T Energization signal generation circuit Tr1 to Tr6 power element Tr7 control transistor V speed detection circuit VE speed setting circuit BV speed comparison circuit Y 2-phase encoder

Claims (5)

[Claims] 1. A power supply circuit comprising: a DC power supply; and a power supply circuit in which a smoothing capacitor is provided in parallel with an output terminal of the DC power supply via a built-in or externally connected reverse current blocking diode.
A drive circuit for a brushless DC motor having a three-phase full bridge configuration in which three control arms each having a plurality of 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 of the motor windings. When the rotating direction is suddenly reversed during operation, a regenerative current is generated in a brushless DC motor drive circuit that requires protection of the drive circuit from a rise in the power supply terminal voltage of the drive circuit due to the generated regenerative current. During the power-on period, or until the terminal voltage of the power supply circuit of the drive circuit drops to a level at which the drive circuit does not need to be protected even if a regenerative current is generated, the power supply circuit cuts off the current and turns the motor. The wire is electrically short-circuited by using a power element for driving the motor, and the motor winding itself consumes a regenerative current to suppress an increase in the power supply terminal voltage of the drive circuit. Less DC motor drive circuit. 2. A power supply circuit comprising: a DC power supply; a power supply circuit provided in parallel with a smoothing capacitor via a reverse current blocking diode internally or externally connected to an output terminal of the DC power supply; and two power elements connected in series. A three-phase full-bridge brushless DC motor drive circuit 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. Is a brushless DC motor drive circuit that requires protection of the drive circuit from an increase in the terminal voltage of the drive circuit power supply circuit due to the regenerative current that is generated when the motor is rapidly reversed. A circuit for mounting an encoder, detecting a rotation direction of the motor from an output signal of the two-phase encoder, and a power supply signal to a power element of a control arm of the three-phase full-bridge drive circuit. A circuit having an energizing signal generating circuit to send, and a command circuit for instructing the energizing signal generating circuit in the direction of rotation, wherein an output of the energizing signal generating circuit is compared with an output of a rotational direction detecting circuit of the motor, and the two signals are compared. A rotation direction discriminating circuit for judging whether the rotation directions match or not coincide with each other, and during a period in which the output of the rotation direction discrimination circuit outputs a rotation direction mismatch output, a drive circuit is provided by the output of the energization signal generation circuit. The power element of the control arm is controlled to cut off the power supply from the power supply circuit, and the motor winding is electrically short-circuited by using the power element for driving the motor, and the regenerative current is consumed by the motor winding itself. 2. The device according to claim 1, wherein the power supply terminal voltage of the drive circuit is suppressed from rising.
4. A drive circuit for a brushless DC motor according to claim 1. 3. A power supply circuit comprising a DC power supply, a power supply circuit provided in parallel with a smoothing capacitor via a reverse current blocking diode connected internally or externally to an output terminal of the DC power supply, and two power elements in series. A three-phase full-bridge brushless DC motor drive circuit 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. Is a brushless DC motor drive circuit that requires protection of the drive circuit from a rise in the terminal voltage of the drive circuit power supply circuit due to the regenerative current generated when the motor is suddenly reversed. The position where the magnetic pole position of the motor rotor is detected A circuit for detecting a rotation direction of the motor from an output of the detector, an energization signal generation circuit for transmitting an energization signal to a power element of a control arm of the three-phase full-bridge drive circuit; And a command circuit for commanding the rotation direction to the circuit, wherein the output of the energization signal generation circuit and the output of the rotation direction detection circuit of the motor are compared to determine whether the rotation directions of the two signals match or not. A power discriminating circuit for controlling a power element of a control arm of a driving circuit with an output of the energization signal generating circuit during a period in which an output of the rotation direction discriminating circuit outputs an output in which the rotation direction does not match; The power supply from the circuit is cut off, and the motor winding is electrically short-circuited using the power element for driving the motor, so that the motor winding consumes the regenerative current and suppresses the rise of the power supply terminal voltage of the drive circuit. 2. The driving circuit for a brushless DC motor according to claim 1, wherein: 4. A power supply circuit comprising: a DC power supply; a power supply circuit provided in parallel with a smoothing capacitor via a reverse current blocking diode internally or externally connected to an output terminal of the DC power supply; and two power elements connected in series. A three-phase full-bridge brushless DC motor drive circuit 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 brushless D that needs protection of the drive circuit from the rise of the power supply terminal voltage of the drive circuit due to the regenerative current generated when
A driving circuit for a C motor, a two-phase encoder attached to a rotor shaft of the brushless DC motor, a circuit for detecting a rotation direction of the motor from an output signal of the two-phase encoder, and a circuit for detecting a rotation speed of the motor. An energizing signal generating circuit for transmitting an energizing signal to a power element of a control arm of the three-phase full bridge drive circuit; and a command circuit for instructing the energizing signal generating circuit to rotate in the energizing signal generating circuit. A rotation direction discrimination circuit that compares an output of the motor with an output of a rotation direction detection circuit of the motor to determine whether or not the rotation directions of the two signals match, and a comparison circuit that compares the output of the speed detection circuit with a set value. And the rotation direction discriminating circuit outputs an output in which the rotation direction does not match, and the energization is performed during a period when the output of the comparison circuit is equal to or greater than a certain set value. The power from the power supply circuit is cut off by controlling the power element of the control arm of the drive circuit with the output of the signal generation circuit, and the motor winding is electrically short-circuited by using the motor drive power element. The brushless DC according to claim 1, wherein the line itself consumes a regenerative current to suppress a rise in a power supply terminal voltage of the drive circuit.
Motor drive circuit. 5. A power supply circuit comprising: a DC power supply; a power supply circuit having a smoothing capacitor provided in parallel via a reverse current blocking diode internally or externally connected to an output terminal of the DC power supply; and two power elements connected in series. A three-phase full-bridge brushless DC motor drive circuit 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. When the terminal is suddenly reversed, the terminal voltage of the power circuit is required to be protected from a rise in the terminal voltage of the power circuit of the drive circuit due to the generated regenerative current. A comparison circuit for comparison is provided. At the moment when the terminal voltage of the power supply circuit exceeds a certain set value, the power of the control arm of the drive circuit is controlled by the output of the energization signal generation circuit. The power supply from the power supply circuit is cut off, and the motor winding is electrically short-circuited using a power element for driving the motor, and the motor winding itself consumes a regenerative current to suppress a rise in the power supply terminal voltage of the drive circuit. The driving circuit for a brushless DC motor according to claim 1, wherein the driving circuit is configured as described above.