JP3954815B2 - Brushless motor drive circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a drive circuit for a brushless motor, and in particular, by ensuring a regenerative current path during braking, the regenerative current can be prevented from flowing back to a power supply circuit.
[0002]
[Prior art]
Japanese Patent Laid-Open No. 9-182474 discloses a technique for suppressing power loss of a drive circuit when a reverse brake is applied in a brushless motor drive circuit. This prior art will be described with reference to FIG. 1, which shows an embodiment of the present invention.
The drive circuit of the brushless motor shown in FIG. 1 has a drive coil having a three-phase configuration, and three sensors 10 including Hall elements for switching energization to the drive coils of the respective phases 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 driving coil 40 having a three-phase configuration from the phase difference between the detection outputs of the sensors 10. This signal is input to the motor drive current output unit 30 via the pre-driver 16.
[0003]
The motor drive current output unit 30 includes three power transistor output transistors 31 and three ground output transistors 32 to form three sets of output transistors. Different motor drive coils Lu, Lv, and Lw are connected to the connection points of the respective transistors. Using the three power supply side output transistors 31 and the three ground side output transistors 32, a motor drive current is supplied to the motor drive coils Lu, Lv, and Lw, and the motor rotor is rotated by switching energization. It has become. The rotation principle itself is well known.
[0004]
A forward / reverse command signal is input to the matrix circuit 14, and the matrix circuit 14 recombines and outputs an energization switching timing signal to each phase drive coil 40 in accordance with the rotation direction command. . A low resistance Rf as a drive current detecting means is connected to the ground side of the drive current output unit 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, and the comparison circuit 19 compares the lower one of the motor control signal CTL and the current limit value V _ILM with the terminal voltage of the resistor Rf, and the terminal voltage of the resistor Rf. Is high, the current control switch circuit 22 is operated to turn off the drive current output unit 30 on the power supply side or the ground side.
[0005]
Next, the operation of the conventional example will be described. When the direction of rotation is switched by switching the F / R signal while the motor is rotating, an electric reverse brake is applied until the direction of rotation of the rotor is reversed. During reverse braking of the motor, the resistor Rf detects the drive current, and the comparison circuit 19 compares this drive current with a predetermined current limit value. When the drive current in the reverse direction exceeds a predetermined current limit value, the switch circuit 22 operates to turn off the output transistor on the power source (source) side or ground (sink) side of the drive current output unit 30. The output transistor is turned on again after a certain period of time, and is turned off again when the drive current exceeds the current limit value. In this way, the PWM control is performed on the output transistor when the motor is braked, so that each switch element of the drive current output unit 30 is controlled so as not to be desaturated.
[0006]
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.
[0007]
[Problems to be solved by the invention]
When PWM control is performed in the reverse brake mode as in the above 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 is long. If the output transistor on the power supply side or ground side that is on-controlled during this off-control period is turned off due to switching of energization, the regeneration path of the drive current is momentarily interrupted, and the drive current seeks the regeneration path. Flows back into the motor power line.
[0008]
Here, if the motor power supply does not have a sink (absorption) capability, the drive current loses its place, and the motor drive voltage suddenly rises and the drive circuit and the power supply circuit may be broken down.
As a countermeasure, it is common to add an electrolytic capacitor or a Zener diode between the motor power supply and the ground to provide a sink capability on the power supply side. However, this measure has a drawback associated with an increase in cost.
[0009]
In the case of measures by electrolytic capacitor, there is a problem that can not be suppressed increase of the power supply voltage sufficient for the following reasons. In other words, during reverse braking, the PWM on-control time is extremely short, so almost no external supply current is required. On the contrary, the reverse flow of the regenerative current as described above frequently occurs. Much more charging current than discharging current. For this reason, the power supply voltage gradually increases every time the regenerative current flows.
[0010]
The present invention has been made to solve the above-described problems of the prior art, and it is possible to provide a regenerative current path during braking without adding an electrolytic capacitor or a Zener diode between the motor power supply and the ground. An object of the present invention is to provide a drive circuit for a brushless motor that can prevent backflow of regenerative current to a power supply line and avoid an increase in power supply voltage.
[0011]
[Means for Solving the Problems]
Whenever the regenerative current flows backward to the power supply line, any two-phase voltage of the motor drive coil protrudes above the power supply voltage and below the ground level. Therefore, the present invention pays attention to this point, and this state is detected by the overvoltage detection circuit, and the ground side output transistor that protrudes above the power supply voltage, or protrudes below the ground level or below the predetermined level with respect to the ground level. The power supply side output transistor is forcibly turned on. As a result, a regenerative current path is formed in the motor drive circuit, so that the backflow to the power supply line is stopped and the increase of the power supply voltage is suppressed.
[0012]
According to the first aspect of the present invention, a plurality of sets of output transistors are formed by the power supply side output transistors and the ground side output transistors, and different motor drive coils are connected to connection points of the respective set transistors, In a brushless motor drive circuit in which a motor drive current is caused to flow through the motor drive coil using an output transistor to rotate the motor, whether the voltage at the connection point of each pair of transistors is a predetermined level or higher than the power supply voltage. An overvoltage detection circuit that detects whether the ground level is lower than a predetermined level is provided, and is lower than the predetermined level with respect to the ground-side output transistor connected to the connection point that is higher than the predetermined level from the power supply voltage or the ground level. Power supply side output transistor connected to the connection point Characterized in that it is configured to turn on the output of the overvoltage detecting circuit.
[0013]
According to a second aspect of the present invention, in the first aspect of the invention, the overvoltage detection circuit drives the motor with a power supply side detection transistor connected to the power supply voltage line and a ground side detection transistor connected to the ground line. A connection point between the power supply side detection transistor and the ground side detection transistor is connected to the corresponding motor drive coil.
[0014]
The invention described in claim 3 has a sensor for detecting the rotational position of the rotor magnet, and based on the position signal detected by the sensor, the motor driving current is supplied to the motor driving coil to rotate the motor, In a brushless motor drive circuit capable of braking a motor by flowing a motor drive current in the direction of reversing the motor during braking, a drive current detection means for detecting the motor drive current and a detection by the drive current detection means The comparison means for comparing the motor drive current value with a predetermined reference current value, and the power source side output transistor and the ground side output transistor form a plurality of sets of output transistors, and the connection points of the respective set transistors are different. A motor drive coil is connected, and using the plurality of sets of output transistors, A motor drive current output unit supplying a motor drive current to the serial motor driving coil, according to the comparison result of the comparing means, the current control switch unit for turning on and off the motor drive current output unit, the coil end of the motor driving coil An overvoltage detection circuit for detecting whether the voltage is higher than a predetermined level from the power supply voltage or lower than a predetermined level with respect to the ground level, and connected to the connection point at which the voltage is higher than the predetermined level from the power supply voltage The power supply side output transistor connected to the connection point that is lower than a predetermined level with respect to the output transistor or the ground level is configured to be turned on by the output of the overvoltage detection circuit .
[0015]
The invention according to claim 4 is the invention according to claim 3, wherein the motor drive coil is configured in three phases, and the overvoltage detection circuit is configured such that the voltage at the coil end of one motor drive coil in any two phases is a power supply voltage. It is further characterized in that it is detected that it is above a predetermined level and that the other is below a predetermined level with respect to the ground level.
[0016]
The invention according to claim 5 is the invention according to claim 3, wherein the motor drive current output section includes a regenerative current diode, and this diode forms a regenerative current path in the motor drive current output section. To do.
[0017]
According to a sixth aspect of the invention, in the third aspect of the invention, the operation of the power supply side output transistor or the ground side output transistor of the drive current output unit is temporarily stopped by the output of the overvoltage detection circuit. .
[0018]
According to a seventh aspect of the invention, in the third aspect of the invention, during motor braking, the current control switch performs on / off control of the motor drive current output unit according to the comparison result of the comparison means, and the motor voltage is output by the output of the overvoltage detection circuit. A regenerative current path is formed in the drive current output unit.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of a drive circuit for a brushless motor according to the present invention will be described with reference to the drawings.
First, the embodiment shown in FIG. 1 will be described. In the embodiment shown in FIG. 1, the drive coil has a three-phase configuration as described above, and the three sensors 10 including Hall elements for switching energization to the drive coils of the respective phases are provided. Has been placed. 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 driving coil 40 having a three-phase configuration from the phase difference between the detection outputs of the sensors 10. This signal is input to the motor drive current output unit 30 via the pre-driver 16.
[0020]
The motor drive current output unit 30 includes three sets of output transistors including a power supply side output transistor 31 including three transistors Q1, Q3, and Q5 and a ground side output transistor 32 including three transistors Q2, Q4, and Q6. Is formed. Different motor drive coils Lu, Lv, and Lw are connected to the connection points of the respective transistors. More specifically, the coil Lu is connected to the connection point between the transistors Q1 and Q2, the coil Lv is connected to the connection point between the transistors Q3 and Q4, and the coil Lw is connected to the connection point between the transistors Q5 and Q6. Yes. Using the three power supply side output transistors 31 and the three ground side output transistors 32, a motor drive current is supplied to the motor drive coils Lu, Lv, and Lw, and the motor rotor is rotated by switching energization. It has become.
[0021]
The matrix circuit 14 is supplied with a forward / reverse command signal F / R, and the matrix circuit 14 recombines the energization switching timing signal to each phase drive coil 40 in accordance with the rotation direction command. Output. A low resistance Rf as a drive current detecting means is connected to the ground side of the drive current output unit 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, and the comparison circuit 19 compares the lower one of the motor control signal CTL and the current limit value V _ILM with the terminal voltage of the resistor Rf, and the terminal voltage of the resistor Rf. Is high, the current control switch circuit 22 is operated to turn off the drive current output unit 30 on the power supply side or the ground side.
[0022]
An overvoltage detection circuit 21 is provided that detects the voltage at the connection point of each of the above-described transistors, that is, the connection point of each drive coil, and forcibly controls the transistors that constitute the drive current output unit 30 according to the result. This is an unprecedented feature. The overvoltage detection circuit 21 detects whether or not the voltage jumps out at the connection point of each set of transistors, that is, the connection point of each drive coil, that is, whether the voltage is higher than a predetermined level or lower than the ground level from the power supply voltage. The phase power supply side output transistor or the ground side output transistor is forcibly turned on.
[0023]
Next, the operation of the above embodiment will be described. A rotation position of a drive magnet (not shown) is detected by the Hall element 10, and a 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 unit 30, and the drive current is passed through the motor drive coil 40.
[0024]
On the other hand, in the comparison circuit 19, the lower of the motor control signal CTL and the current limit value V _ILM 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 power supply side or ground side output transistor of the drive current output unit 30. As a result, the motor drive current gradually decreases, but the output transistor is turned on again after a certain period of time, so that the drive current starts to increase. By repeating this operation, the output transistor is PWM-controlled.
[0025]
When the forward / reverse signal F / R is switched, the motor first enters the reverse brake state, a large amount of reverse drive current flows into the resistor Rf, and the off-control time of the output transistor becomes extremely long. If the power-side or ground-side output transistor that is on-controlled at this time is turned off due to switching of energization, the regeneration path of the drive current is momentarily interrupted, so that any two phases of the drive coil are powered It jumps above the voltage and below the ground level and tries to return the regenerative current to the power supply.
[0026]
The overvoltage detection circuit 21 detects the upper and lower protrusions of the drive coil, and forcibly turns on the ground side output transistor of the phase protruding above the power supply voltage or the phase of the power supply side output transistor protruding below the ground level. Control. Thereby, the regenerative current which tries to return to a power supply can be 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.
[0027]
FIG. 2 shows a detailed circuit of the drive current output unit 30 and the overvoltage detection circuit 21. First, a detailed configuration of the drive current output unit 30 will be described. A current mirror circuit controlled by the pre-driver 16 and composed of two transistors Q21 and Q31 is connected to the transistor Q1, and a regenerative current diode D1 is connected in parallel. Similarly, a current mirror circuit composed of transistors Q23 and Q33 is connected to the input side of the transistor Q3, and a regenerative current diode D3 is connected in parallel. A current mirror circuit composed of transistors Q25 and Q35 is connected to the transistor Q5 on the input side, and a regenerative current diode D5 is connected in parallel. A current mirror circuit composed of transistors Q22 and Q32 is connected to the transistor Q2 on the input side, and a regenerative current diode D2 is connected in parallel. A current mirror circuit composed of transistors Q24 and Q34 is connected to the transistor Q4 on the input side, and a regenerative current diode D4 is connected in parallel. A current mirror circuit composed of transistors Q26 and Q36 is connected to the transistor Q6 on the input side, and a regenerative current diode D6 is connected in parallel.
[0028]
The overvoltage detection circuit 21 includes three power supply side transistors Q11, Q13, Q15 and three ground side transistors Q12, Q14, Q15 that detect when the voltage of any of the drive coils protrudes beyond the power supply voltage. Q16 and three transistors D12, D14, and D16 connected in series to these transistors and functioning as diodes, and the base is connected to the bases of the three transistors Q12, Q14, and Q16 on the ground side, and the three on the power supply side When any of the transistors Q11, Q13, Q15 is turned on, the transistor Q10 has a transistor Q10 in which a current flows and generates a voltage Vbe. A U-phase drive coil Lu is connected to a connection point between the transistor Q11 and the diode D12, a V-phase drive coil Lv is connected to a connection point between the transistor Q13 and the diode D13, and a connection point between the transistor Q15 and the diode D15. A W-phase drive coil Lw is connected.
[0029]
Next, operations of the drive current output unit 30 and the overvoltage detection circuit 21 shown in FIG. 2 will be described. This circuit turns on the power supply side output transistor of the phase protruding below the ground level.
Assuming that the U point of the U-phase output jumps above the power supply voltage Vco, the transistor Q11 is turned on, a current flows through the transistor Q10, and the voltage Vbe is generated. Here, when the W point of the W-phase output jumps below the ground GND, the transistor Q16 and the diode D16 are brought into conduction, and a collector current flows through the transistor Q16. This current flows through a current mirror circuit composed of transistors Q25 and Q35 in the drive current output unit 30, and supplies a base current to the W-phase power supply side output transistor Q5. As a result, the transistor Q5 is temporarily turned on, so that a regenerative current path indicated by an arrow in FIG. 2, that is, a regenerative current path passing through Lu → D1 → Q5 → Lw → Lu is secured and the power is returned to the power source. Suppress regenerative current.
[0030]
Next, another example of an overvoltage detection circuit applicable to the brushless motor drive circuit according to the present invention shown in FIG. 3 will be described. This circuit turns on the ground-side output transistor of the phase protruding beyond the power supply voltage. In FIG. 3, three transistors Q51, Q53, and Q55 and transistors D51, D53, and D55 that are connected in series and function as diodes are connected to the power supply side, and three transistors Q52, Q54, Q56 and transistors D52, D54, D56 connected in series and functioning as diodes are connected. Further, the base is connected to the bases of the three power supply side transistors Q51, Q53, and Q55, and any of the three ground side transistors Q52, Q54, and Q56 is turned on so that a current flows and generates a voltage Vbe. Q40. Other connections are the same as in the example shown in FIG.
[0031]
Assuming that the U point of the U-phase output protrudes below the ground GND, the transistor Q52 is turned on, a current flows through the transistor Q40, and the voltage Vbe is generated at the transistor Q40. Here, when the W point of the W-phase output jumps above the power supply voltage Vco, the transistor Q55 and the diode D55 become conductive, and a collector current flows through the transistor Q55. This current flows through a current mirror circuit including transistors Q26 and Q36, and supplies a base current to the W-phase ground-side output transistor Q6. As a result, the transistor Q6 is temporarily turned on, so that a regenerative current path is secured and the regenerative current that attempts to return to the power source is suppressed.
[0032]
FIG. 4 shows a connection change example of the overvoltage detection circuit. In this connection example, the operation of the current control switch circuit 22 is temporarily stopped when the overvoltage detection circuit 21 detects a vertical jump of the drive coil. That is, the current control switch circuit 22 does not turn off the output transistor on the power supply side or the ground side of the drive current output unit 30, and keeps the output transistor on. Also in this case, a regenerative current path is ensured in the drive circuit, and the regenerative current trying to return to the power source is suppressed.
[0033]
In the case of the connection example shown in FIG. 4, when the current control switch circuit 22 performs on / off (PWM) control of the power supply side output transistor, an overvoltage detection method of the type shown in FIG. 2 is used. When the output transistor is on / off (PWM) controlled, an overvoltage detection method of the type shown in FIG. 3 is used.
[0034]
In the illustrated embodiment, a transistor is used as an element that performs an on / off operation. For convenience of explanation, the term “transistor” is used. However, in the concept of “transistor”, a control signal is applied to an FET or a control terminal. It includes a thyristor that is turned on and off by inputting, and other active elements.
[0035]
【The invention's effect】
According to the first and second aspects of the invention, the following effects can be obtained.
(1) It is possible to omit an electrolytic capacitor and a Zener diode that cause a cost increase. Even if electrolytic capacitors or Zener diodes are used, their capacities can be reduced.
(2) Since the power supply voltage does not increase, the upper limit of the motor applied voltage can be increased, and a larger rotational speed and torque can be obtained.
(3) When the motor is rotated by an external force, an induced electromotive voltage is generated in the drive coil and the power supply voltage is raised. However, the provision of the drive circuit according to the present invention suppresses the voltage rise, The breakdown voltage can be prevented.
(4) Since the operation is performed with the back electromotive force or the induced electromotive voltage generated by the drive coil, the desired effects as described above can be obtained even when the motor power supply or the drive circuit power is not turned on.
[0036]
According to the third to seventh aspects of the present invention, since the regenerative current flowing back to the motor power line can be significantly suppressed, an increase in the motor power voltage can be suppressed during reverse braking, and a drive circuit and a power circuit Will not break down.
According to the conventional drive circuit, even when the power supply is released while the motor is energized, the terminal voltage of the drive coil may jump up and down, but in this case, the regenerative current cannot return to the power line. In some cases, a high voltage is instantaneously generated, and the drive circuit may be broken down. Since the drive circuit according to the third to seventh aspects of the invention works effectively against such an increase in drive coil terminal voltage due to unexpected handling, any manufacturing process, finished product transportation process, assembly process, etc. Useful for fail-safe situations.
[Brief description of the 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 showing details of a drive current output unit and an overvoltage detection circuit in the embodiment.
FIG. 3 is a circuit diagram showing another example of an overvoltage detection circuit applicable to the present invention.
FIG. 4 is a block diagram showing a modification of an overvoltage detection unit applicable to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Sensor 12 Hall amplifier 14 Matrix circuit 16 Pre-driver 19 Comparison circuit 21 as a comparison means 21 Overvoltage detection circuit 22 Current control switch part 30 Drive current output part 31 Power supply side output transistor 32 Ground side output transistor 40 Drive coil

Claims (7)

A plurality of output transistors are formed by the power supply side output transistor and the ground side output transistor, and different motor drive coils are connected to the connection points of the respective set transistors, and the motor is configured using the plurality of sets of output transistors. In the drive circuit of the brushless motor, in which the motor drive current is passed through the drive coil to rotate the motor,
An overvoltage detection circuit for detecting whether a voltage at a connection point of each of the above set transistors is higher than a predetermined level from a power supply voltage or lower than a predetermined level with respect to a ground level;
A ground-side output transistor connected to the connection point that is equal to or higher than a predetermined level from the power supply voltage or a power-side output transistor connected to the connection point that is equal to or lower than a predetermined level relative to the ground level is output by the output of the overvoltage detection circuit. A drive circuit for a brushless motor, wherein the drive circuit is configured to be turned on.   The overvoltage detection circuit includes a power supply side detection transistor connected to the power supply voltage line and a ground side detection transistor connected to the ground line, corresponding to the motor drive coil. 2. The brushless motor drive circuit according to claim 1, wherein a connection point with the detection transistor is connected to the corresponding motor drive coil. A sensor that detects the rotational position of the rotor magnet. Based on the position signal detected by the sensor, a motor drive current is supplied to the motor drive coil to rotate the motor, and the motor is reversely rotated when the motor is braked. In the drive circuit of a brushless motor that can flow the motor drive current to brake the motor,
Drive current detection means for detecting the motor drive current;
Comparison means for comparing the motor drive current value detected by the drive current detection means with a predetermined reference current value;
A plurality of output transistors are formed by the power supply side output transistor and the ground side output transistor, and different motor drive coils are connected to the connection points of the respective set transistors, and the motor is configured using the plurality of sets of output transistors. A motor drive current output unit for passing a motor drive current to the drive coil;
In accordance with the comparison result of the comparison means, a current control switch unit that controls on / off of the motor drive current output unit,
An overvoltage detection circuit that detects whether the voltage at the coil end of the motor drive coil is a predetermined level or higher than the power supply voltage or lower than a predetermined level with respect to the ground level,
A ground-side output transistor connected to the connection point that is equal to or higher than a predetermined level from the power supply voltage or a power-side output transistor connected to the connection point that is equal to or lower than a predetermined level relative to the ground level is output by the output of the overvoltage detection circuit. A drive circuit for a brushless motor, wherein the drive circuit is configured to be turned on .   The motor drive coil is configured in three phases, and the overvoltage detection circuit detects that the voltage at the coil end of one motor drive coil in any two phases is higher than a predetermined level from the power supply voltage, and the other is at ground level. 4. The brushless motor driving circuit according to claim 3, wherein the driving circuit detects that the level is not more than a predetermined level.   4. The brushless motor drive circuit according to claim 3, wherein the motor drive current output unit includes a regenerative current diode, and the diode forms a regenerative current path in the motor drive current output unit.   The brushless motor drive circuit according to claim 3, wherein the operation of the power supply side output transistor or the ground side output transistor of the drive current output unit is temporarily stopped by the output of the overvoltage detection circuit.   The current control switch controls on / off of the motor drive current output unit according to the comparison result of the comparison means during motor braking, and forms a regenerative current path in the motor drive current output unit based on the output of the overvoltage detection circuit. Drive circuit for brushless motor.

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