JP2003134878A - Brushless motor drive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a brushless motor drive circuit, which can prevent a regenerative current from flowing in reverse to a power supply line, avoid the rise of a power supply voltage, avoid circuit oscillation, exhibit sufficient protective effects with respect to an overcurrent, and utilize regenerative energy effectively. SOLUTION: Currents, applied to a plurality of driving coils, are switched by a drive current output unit 30 having power supply side output transistors 31 and a ground side output transistors 32. There are provided a current control switch circuit 22, which turns off the transistors 31 or the transistors 32, if the driving currents of the drive coils exceed a prescribed value, an overcurrent detection circuit 21 detecting regenerative current which is made to flow reversely to a power supply line, when the regeneration route of the driving current is cut off by turning off the output transistors, which are not turned off by the current control switch circuit 22, for switching the current application, while the transistors 31 or the transistors 32 are turned off by the current control switch circuit 22, and a regenerative current application device Cc, which constitutes a regenerative current route for making the regenerative current detected by the overcurrent detection circuit 21 flow.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brushless motor drive circuit, and more particularly, by ensuring a regenerative current path during braking, it is possible to prevent regenerative current from flowing back to a power supply circuit. At the same time, it is possible to avoid momentary power supply voltage spikes,
Furthermore, the regenerative current can be reused.

[0002]

2. Description of the Related Art In a brushless motor drive circuit, Japanese Patent Application Laid-Open No. 9-182474 discloses a technique for suppressing power loss in the drive circuit when reverse brake is applied. This conventional technique will be described with reference to FIG. In the brushless motor drive circuit shown in FIG. 5, the drive coil 40 has a three-phase configuration, and three sensors 10 each including a Hall element for switching energization to the drive coils Lu, Lv, and Lw of each phase are provided. Are arranged. Each sensor 10 detects a magnetic pole of a rotor magnet (not shown), and its output is amplified by the hall amplifier 12 and input to the matrix circuit 14. The matrix circuit 14 outputs an energization switching timing signal to each phase drive coil 40 of the three-phase configuration based on the phase difference of the detection output of each sensor 10. This signal is input to the motor drive current output unit 30 via the pre-driver 16.

In the motor drive current output section 30, three sets of output transistors are formed by three power source side output transistors 31 and three ground side output transistors 32. Different motor drive coils Lu, Lv, and Lw are connected to the connection points of each set transistor. By using the three power source side output transistors 31 and the three ground side output transistors 32, the motor drive current is passed through the motor drive coils Lu, Lv, Lw and the energization is switched to rotate the rotor of the motor. Has become. The principle of rotation itself is well known.

At one terminal of the level shift circuit 18,
The torque command Vc is supplied, and the reference voltage Vref is supplied to the other terminal of the level shift circuit 18. The torque command Vc is a signal corresponding to a deceleration command, an acceleration command, a braking command, or the like. The level shift circuit 18 uses the reference voltage Vref.
Based on the above, the voltage value of the torque command Vc is shifted to a desired value, and this is supplied to the matrix circuit 14 as a torque control signal. Further, the drive direction detection circuit 20 drives the motor in the normal rotation direction (acceleration, constant speed drive) based on the torque control command from the level shift circuit 18.
Alternatively, it is configured to detect which one of reverse driving (reverse braking) is to be performed and generate a normal / reverse rotation command signal.

The matrix circuit 14 is adapted to receive the normal / reverse rotation command signal. The matrix circuit 14 responds to the command of the rotation direction to drive each phase drive coil 4
The energization switching timing signal to 0 is recombined and output. A low resistance Rf as a drive current detecting means is connected to the ground side of the drive current output section 30 so that a voltage proportional to the drive current is generated between the terminals of the resistor Rf. The terminal voltage of the resistor Rf is input to the comparison circuit 19, which compares the lower one of the current limit values V _{LL M} with the terminal voltage of the resistor Rf, and when the terminal voltage of the resistor Rf is high. , The current control switch circuit 22 is operated, and the power supply side output transistor 31 or the ground side output transistor 32 of the drive current output unit 30 is operated.
Is turned off.

Next, the operation of the above conventional example will be described. When the rotation direction is switched by switching the forward / reverse rotation command signal input to the matrix circuit 14 from the driving direction detection circuit 20, the electric reverse braking is applied until the rotation direction of the rotor is reversed. During reverse rotation braking of the motor,
The resistor Rf detects the drive current, and the comparison circuit 24 compares the drive current with a predetermined current limit value. When the driving current in the reverse rotation direction exceeds a predetermined current limit value, the switch circuit 22 operates and the output transistor of the driving current output unit 30 on the power source (source) side or the ground (sink) side is turned off. The output transistor is turned on again after a certain period of time, and turned off again when the drive current exceeds the current limit value. In this way, the output transistors are PWM-controlled when the motor is braked, so that each switch element of the drive current output unit 30 is controlled so as not to be in a non-saturated state.

As a result, the power loss generated in the non-saturated switch element is significantly reduced, and the heat generation of the drive circuit during reverse braking can be suppressed.

[0008]

When the PWM control is performed in the reverse rotation brake mode as in the above-mentioned prior art, there are the following problems. During reverse braking, the drive current increases more than usual, so the time to reach the current limit value is short, and the time during which the output transistor is off-controlled becomes long. If the power-side or ground-side output transistor that is on-controlled during this off-control period is turned off for switching the energization, the drive current regeneration path will be cut off for a moment, and the drive current will need to be regenerated. Flows back into the motor power line. Here, if the motor power supply does not have a sink (absorption) capability, the drive current may lose its place of travel, and the motor drive voltage may suddenly rise, causing breakdown of the drive circuit and the power supply circuit.

As a countermeasure against this, it is general to add an electrolytic capacitor or a Zener diode between the motor power supply and the ground to give the power supply side a sink capability.
However, this measure has a drawback that the cost is increased. Further, the electrolytic capacitor directly connected to the motor power source is always in a fully charged state, and there is a limit in absorbing regenerative current.

Therefore, the applicants of the brushless motor configured to detect the occurrence of the reverse current regenerative current by the overvoltage detection circuit and forcibly turn on the output transistor of the drive circuit to secure the regenerative current path. I applied for a patent for the drive circuit. That is the invention of Japanese Patent Application No. 2001-226200.

However, according to the above-mentioned Zener diode or the overvoltage detection circuit which attempts to absorb the regenerative current, only the regenerative current is converted into heat and the regenerative energy of the motor is wasted. Will be. Further, according to the one using the above-mentioned overvoltage detection circuit, the overvoltage detection circuit works so as to turn off the transistor at the moment when the output transistor is forcibly turned on, so that a circuit oscillation that repeatedly turns on and off occurs in a short time. However, the sensitivity of the overvoltage detection circuit cannot be increased so much. The fact that the sensitivity of the overvoltage detection circuit cannot be increased leads to a weaker effect of protecting against overvoltage.

The present invention has been made to solve the above-mentioned problems of the prior art. Even if an electrolytic capacitor or a Zener diode is not added between the motor power source and the ground, the regenerative current at the time of braking can be obtained. By forming the path of (1), it is possible to prevent the regenerative current from flowing backward to the power supply line and to avoid an increase in the power supply voltage, and at the same time, to prevent circuit oscillation and to have a sufficient protection effect against overvoltage. Moreover, it is an object of the present invention to provide a brushless motor drive circuit capable of effectively utilizing regenerative energy.

[0013]

When the regenerative current tries to flow back to the power supply line, this regenerative current is detected by an overvoltage detection circuit, and a regenerative current path is formed to avoid an increase in the power supply voltage. In addition, the regenerative energy was recovered by a charging element so that it could be reused. Since the charging element is not directly connected to the motor power source and is discharged each time it is reused, the charging ability is always preserved and the regenerative current can be effectively absorbed.

According to a first aspect of the present invention, there is provided a brushless motor drive circuit configured to switch energization of a plurality of drive coils by a drive current output section including a power supply side output transistor and a ground side output transistor. A current control switch circuit that turns off either the power supply side output transistor or the ground side output transistor when the coil drive current exceeds a predetermined value, and either of the power supply side output transistor or the ground side output transistor by the current control switch circuit. An overvoltage detection circuit that detects the regenerative current that flows back to the power supply line when the drive current regeneration path is cut off by turning off one of them and turning off the output transistor on the side that is not turned off by the current control switch circuit for switching the conduction. , Regenerated by overvoltage detection circuit And having a regenerative current energization element to detect the flow to form a regenerative current path energizing regenerative current.

According to a second aspect of the present invention, in the first aspect of the present invention, the overvoltage detection circuit is operated by a current based on an induced electromotive voltage flowing instead of the drive current when the motor is rotated by an external force. It is characterized in that a regenerative current is caused to flow through the regenerative current conducting element by the operation of overvoltage detection.

The invention according to claim 3 is the invention according to claim 1 or 2.
In the invention described above, the backflow detection means detects the regenerative current by detecting that one of the two-phase drive coils has a power supply voltage or more and the other has a predetermined level or less with respect to the ground level. Characterize.

According to a fourth aspect of the present invention, in the first, second or third aspect of the invention, the regenerative current is collected from the backflow detecting means by being supplied to the charging element.
The invention according to claim 5 is the same as the invention according to claim 4,
The regenerative current collected by the charging element is reused as a power source.

According to a sixth aspect of the present invention, in the fifth aspect of the invention, the regenerative current recovered by the charging element is reused as a power source through the current conversion circuit. The invention according to claim 7 is characterized in that, in the invention according to claim 6, the operation of the booster circuit is temporarily stopped when the charging element is charged with the regenerative current.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a brushless motor drive circuit according to the present invention will be described below with reference to the drawings. First, an outline of an embodiment of a brushless motor drive circuit according to the present invention will be described with reference to FIG. In the example shown in FIG. 1, the drive coil has a three-phase configuration, and three sensors 10 each including a Hall element for switching energization are arranged for the drive coil of each phase. Each sensor 10 detects a magnetic pole of a rotor magnet (not shown), and its output is amplified by the hall amplifier 12 and input to the matrix circuit 14. The matrix circuit 14 uses the phase difference of the detection output of each sensor 10
An energization switching timing signal is output to each phase drive coil 40 having a three-phase configuration. This signal is input to the motor drive current output unit 30 via the pre-driver 16.

The motor drive current output section 30 includes three sets of three transistors Q1, Q3 and Q5 on the power supply side output transistor 31 and three transistors Q2, Q4 and Q6 on the ground side output transistor 32. An output transistor is formed. At the connection point of each group of transistors, different motor drive coils Lu,
Lv and Lw are connected. More specifically, one end of the coil Lu is connected to the connection point between the transistors Q1 and Q2.
One end of the coil Lv is connected to the connection point between the transistors Q3 and Q4, and the coil Lv is connected to the connection point between the transistors Q5 and Q6.
One end of w is connected. The other ends of the coils are directly connected to each other. The above three power source side output transistors 31
By using the three ground side output transistors 32, the motor drive current is passed through the motor drive coils Lu, Lv, Lw and the energization is switched to rotate the rotor of the motor.

A normal / reverse rotation command signal F / R is input to the matrix circuit 14. The matrix circuit 14 rearranges and outputs the energization switching timing signal to each phase drive coil 40 in response to the instruction of the rotation direction. A low resistance Rf as a drive current detection means is connected to the ground side of the drive current output section 30,
A voltage proportional to the drive current is generated between the terminals of the resistor Rf. The terminal voltage of the resistor Rf is input to the comparison circuit 19, and in the comparison circuit 19, the lower one of the motor control signal CTL and the current limit value V _LIM and the resistance Rf.
When the terminal voltage of the resistor Rf is high and the terminal voltage of the resistor Rf is high, the current control switch circuit 22 is operated to turn off the power supply side output transistor of the drive current output unit 30.

An overvoltage detection circuit 21 is provided which detects the voltage at the connection point of each of the set transistors, that is, at the connection point of each drive coil, and turns on the regenerative current recovery element to flow a regenerative current according to the result. The overvoltage detection circuit 21 uses the current control switch circuit 22 to supply the output transistor 3 on the power supply side.
1 is turned off and the ground side output transistor 32 is turned off for switching the energization, thereby forming a backflow detecting means for detecting a regenerative current flowing back to the power supply line when the drive current regeneration path is cut off.

The overvoltage detection circuit 21 as the above-mentioned reverse current detecting means also includes a regenerative current conducting element which, when the regenerative current is detected, detects the regenerative current to form a regenerative current path to pass the regenerative current. The regenerative current recovery element included in the overvoltage detection circuit 21 is connected to the regenerative current recovery terminal, and the regenerative current recovery terminal is connected to the charging element Cc that is charged by the regenerative current. The charging element Cc is composed of, for example, an electrolytic capacitor. The regenerative current recovery terminal is connected to the current conversion circuit 23, and the current conversion circuit 23 can be supplied with power from the charging element Cc. Charging element C
When the voltage of c exceeds the power supply voltage Vcc of the small signal circuit, a constant current is supplied from the charging element Cc to the small signal circuit. The power supply voltage Vcc of the small signal circuit is lower than the voltage of the motor drive circuit. Current conversion circuit 23
There is a booster circuit as an example.

Next, the operation of the above embodiment will be described. The rotation position of a drive magnet (not shown) is detected by the hall element 10, and the signal amplified by the hall amplifier 12 is converted into an energization switching signal by the matrix circuit 14. This signal is amplified by the pre-driver 16 and supplied to the drive current output section 30, and a drive current is passed through the motor drive coil 40.

On the other hand, in the comparison circuit 19, the motor control signal C
The lower one of TL and the current limit value V _LIM is compared with the voltage of the resistor Rf through which the motor drive current flows. When the voltage of the resistor Rf is higher, the current control switch circuit 22
Operates to turn off the output transistor on the power supply side of the drive current output section 30. As a result, the motor drive current gradually decreases, but after a certain period of time, the output transistor is turned on again, so that the drive current starts to increase.
By repeating this operation, the output transistor becomes P
WM controlled.

When the forward / reverse rotation signal F / R is switched, the motor first enters the reverse rotation braking state, a large amount of reverse rotation drive current flows into the resistor Rf, and the OFF control time of the output transistor becomes extremely long. At this time, if the ground-side output transistor 32 that is on-controlled is turned off for switching the energization, the regeneration path of the drive current is interrupted for a moment, so that any two phases of the drive coil 40 are respectively supplied with the power supply voltage. Above all, it jumps below the ground level and tries to return the regenerative current to the power supply.

Overvoltage detection circuit 2 including a regenerative current conducting element
Reference numeral 1 detects a vertical jump of the output of the drive coil 40, conducts a regenerative current conducting element of a phase protruding above the power supply voltage, and supplies a regenerative current to the charging element Cc connected to the regenerative current recovery terminal. To charge. Accordingly, the regenerative current that tries to return to the power supply can be directed to the charging element Cc and suppressed. It should be noted that the downward protrusion detection level may be equal to or lower than the ground level as described above, or may be equal to or lower than a predetermined level with respect to the ground level.

As described above, the regenerative current is the charging element Cc.
Is charged to charge the charging element Cc and is collected. The regenerative current collected by the charging element Cc is converted into an appropriate voltage by the current conversion circuit 23 and is reused as a power source for driving a small signal circuit such as the Hall amplifier 12.

FIG. 2 shows a detailed circuit example of the drive current output section 30 and the overvoltage detection circuit 21. First, the drive current output unit 3
The detailed configuration of 0 will be described. On the input side of the power supply side output transistor Q1, a current mirror circuit controlled by the pre-driver 16 and composed of two transistors Q21 and Q31 is connected, and a regenerative current diode D1 is connected in parallel. Similarly, the transistor Q3
A current mirror circuit composed of transistors Q23 and Q33 is connected to the input side of the regenerative current diode D3.
Are connected in parallel. A current mirror circuit including transistors Q25 and Q35 is connected to the input side of the transistor Q5, and a regenerative current diode D5 is connected in parallel.

The ground side output transistor is also constructed in the same manner. A current mirror circuit composed of transistors Q22 and Q32 is connected to the input side of the transistor Q2, and a regenerative current diode D2 is connected in parallel. The transistor Q4 has a transistor Q on the input side.
A current mirror circuit composed of 24 and Q34 is connected, and a regenerative current diode D4 is connected in parallel. The transistor Q6 has transistors Q26 and Q3 on the input side.
A current mirror circuit composed of 6 is connected, and a regenerative current diode D6 is connected in parallel.

The overvoltage detection circuit 21 includes three transistors Q11, Q13, Q15 on the power supply side and a ground side 3 transistors.
It has three transistors Q12, Q14, Q16 and three transistors D12, D14, D16 connected in series to these transistors and functioning as diodes. Power supply side three transistors Q11, Q1
3. Q15 detects that the voltage of any drive coil jumps above the power supply voltage level. The three transistors Q12, Q14, Q16 on the ground side and the three transistors D12, D14, D16 detect that the voltage of one of the drive coils jumps below the ground level. Further, the base is connected to the bases of the three transistors Q12, Q14, Q16 on the ground side, and a transistor Q10 that generates a voltage Vbe by constantly supplying a constant current from the constant current source Io is provided. The U-phase drive coil Lu is connected to the connection point of the transistor Q11 and the diode D12,
The V-phase drive coil Lv is connected to the connection point of the diode 13 and the diode D13, and the transistor Q15 and the diode D1 are connected.
A W-phase drive coil Lw is connected to a connection point with 5.

Transistor Q of the overvoltage detection circuit 21
11, Q13, and Q15 also serve as regenerative current conducting elements, and when the voltage of a certain phase becomes a predetermined level or lower than the ground level and another coil voltage becomes the power supply voltage level or higher, the power supply voltage level or higher is exceeded. The regenerative current-carrying element of the phase is turned on to allow the regenerative current to flow. The collectors of the transistors Q11, Q13, and Q15, which also function as regenerative current energizing elements, are connected to each other, and the regenerative currents that are the collector currents of the transistors Q11, Q13, and Q15 are charged by a regenerative current recovery terminal and a charging element C including an electrolytic capacitor.
The charging element Cc is charged and the regenerative current is recovered. The recovered regenerative current is reused via the current conversion circuit as described with reference to FIG.

Next, the operation of the drive current output section 30 and the overvoltage detection circuit 21 shown in FIG. 2 will be described. A constant current is supplied from the constant current source Io to the diode-connected transistor Q10, and a voltage Vbe is generated between the base and the emitter. Now, if the U point of the U-phase output is lower than the ground level by 1 Vbe or more, the diode D12 and the transistor Q12 become conductive, a current flows through the transistor Q20, and the voltage V between the base and emitter of the transistor Q20.
be occurs. Here, when the point W of the W-phase output jumps above the ground power supply voltage Vco, the transistor Q15, which is a W-phase regenerative current conducting element, becomes conductive, and a current flows through the charging element Cc. As a result, the regenerative current path indicated by the arrow in FIG. 2, that is, Lu → Lw → Q15 → Cc → Rf → D.
A regenerative current path via 2 → Lu is secured, and regenerative current that attempts to return to the power supply is suppressed.

In this way, since the regenerative current is directed to the charging element Cc connected to the regenerative current path, the backflow regenerative current attempting to return to the power source is effectively suppressed,
It is possible to effectively suppress the rise of the motor power supply voltage during reverse rotation braking and prevent breakdown of the drive circuit element and the power supply circuit element. Since the rise of the motor power supply voltage is suppressed, the upper limit of the motor applied voltage can be raised, and a larger rotation speed and torque can be obtained. Charging element Cc
The regenerative energy is stored in, and the stored regenerative energy is supplied as a power source to the small signal circuit via the current conversion circuit 23 as described above.

In addition, the regenerative current, which wasted in the prior art, is stored in the charging element Cc as electric energy in the above embodiment and can be reused, so that the power consumption of the power source can be saved. You can The motor may be rotationally driven by an external force, at which time an induced electromotive voltage is generated in the drive coil, and this induced electromotive voltage raises the power supply voltage. However, according to the above-described embodiment, it is possible to suppress the voltage rise and prevent breakdown of the circuit component due to withstand voltage. Also in this case, the induced electromotive voltage causes a current to flow in the charging element Cc to accumulate electric energy, and the accumulated electric energy can be reused.

According to the above-described embodiment, since the operation is performed by the counter electromotive voltage or the induced electromotive voltage generated by the drive coil, the above effect can be obtained even when the motor power supply or the drive circuit power supply is not turned on. . Since the overvoltage detection circuit 21 according to the above embodiment does not feed back, it does not oscillate even if its sensitivity is increased, and the effect of protecting against overvoltage is enhanced.

FIG. 3 shows a specific example of the current conversion circuit 23 in the above embodiment. This circuit is configured such that when the voltage of the charging element Cc exceeds the voltage Vcc of the power supply 51 of the small signal circuit 50, a constant current is supplied from the charging element Cc to the small signal circuit 50. More specifically, the current mirror circuit 52 and another current mirror circuit 53 are connected in series between the terminals of the charging element Cc, and the small signal circuit 50 is connected to the output side of the current mirror circuit 52. Has been done. The voltage of the charging element Cc is the power source 5 of the small signal circuit 50.
When the voltage Vcc of 1 is exceeded, the current mirror circuit 52 becomes conductive, and the current is supplied from the charging element Cc to the small signal circuit 50 via the current mirror circuit 52.

FIG. 4 shows another example of regenerative current reuse.
In this example, the voltage of the charging element Cc is boosted by a booster circuit 55 such as a charge pump, and when the output of the booster circuit 55 exceeds the voltage Vco of the motor power source 57, the voltage is fed to the motor drive circuit 31 via a diode 56. It is configured to supply an electric current. According to this circuit, the electric power supplied from the motor power source 57 can be saved. In the above circuit, when the motor drive circuit 31 does not require current, that is, when the overvoltage detection circuit 21 is the charging element Cc.
If the booster circuit 55 is operating while the regenerative current is being charged, the voltage Vco of the motor power supply 57 will increase.
Therefore, the operation of the booster circuit 55 is configured to be temporarily stopped in synchronization with the charging timing.

In the illustrated embodiment, a transistor is used as an element that turns on and off, and the word "transistor" is used for convenience of explanation. However, the concept of "transistor" includes FET and It includes a thyristor that is turned on and off by inputting a control signal to a control terminal, and other active elements.

[0040]

According to the invention of claim 1 or 3,
The regenerative current flowing back to the motor power supply line can be largely suppressed, the rise of the motor power supply voltage at the time of reverse braking can be effectively suppressed, and the breakdown voltage of the drive circuit element and the power supply circuit element can be prevented.

According to the second aspect of the invention, even when the motor is rotated by an external force and an induced electromotive force is generated, the rise of the power supply voltage is effectively suppressed, and the breakdown voltage of the drive circuit element or the power supply circuit element is destroyed. Can be prevented.

According to the present invention, the regenerative current collected by the charging element can be reused as the power source, so that the power consumption of the power source can be saved and the charging element can be saved. Since the regenerative energy recovered by is always consumed, it is possible to effectively suppress an increase in the motor power supply voltage during reverse braking.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a brushless motor drive circuit according to the present invention.

FIG. 2 is a circuit diagram specifically showing the embodiment.

FIG. 3 is a circuit diagram showing an example of a current conversion circuit applicable to the present invention.

FIG. 4 is a block diagram showing an example of a regenerative current utilization circuit applicable to the present invention.

FIG. 5 is a circuit block diagram showing an example of a conventional brushless motor drive circuit.

[Explanation of symbols]

10 sensors 12 Hall amplifier 14 Matrix circuit 16 pre-driver 21 Overvoltage detection circuit 22 Current control switch 23 Current conversion circuit 30 Drive current output section 31 Power supply side output transistor 32 Ground side output transistor 40 drive coil

Claims (7)

[Claims] 1. A drive circuit for a brushless motor configured to switch energization of a plurality of drive coils by a drive current output section including a power supply side output transistor and a ground side output transistor. A current control switch circuit that turns off one of the power supply side output transistor and the ground side output transistor when it exceeds a predetermined value, and one of the power supply side output transistor and the ground side output transistor that is turned off by the current control switch circuit. And an overvoltage detection circuit for detecting a regenerative current flowing back to the power supply line when the regenerative path of the drive current is cut off by turning off the output transistor on the side not turned off by the current control switch circuit for switching the conduction, Regeneration by overvoltage detection circuit A drive circuit for a brushless motor, comprising: a regenerative current conducting element that detects a current to form a regenerative current path to pass a regenerative current. 2. The overvoltage detection circuit operates by a current based on an induced electromotive voltage that flows instead of a drive current when the motor rotates by an external force, and the operation of this overvoltage detection time causes the regenerative current to flow to a regenerative current conducting element. The brushless motor driving circuit according to claim 1, wherein the brushless motor driving circuit flows. 3. The overvoltage detection circuit detects the regenerative current by detecting that one of the two-phase drive coils has a power supply voltage or more and the other has a predetermined level or less with respect to the ground level. The drive circuit for a brushless motor according to claim 1, wherein the drive circuit is a brushless motor. 4. The drive circuit for a brushless motor according to claim 1, wherein the regenerative current is supplied from the regenerative current energizing element to the charging element to be recovered. 5. The brushless motor drive circuit according to claim 4, wherein the regenerative current recovered by the charging element is reused as a power source. 6. The drive circuit for a brushless motor according to claim 5, wherein the regenerative current collected by the charging element is reused as a power source via the booster circuit. 7. The drive circuit for the brushless motor according to claim 6, wherein the operation of the booster circuit is temporarily stopped when the charging element is charged with the regenerative current.