JPH0819284A - Motor driving circuit - Google Patents

Abstract

PURPOSE:To maintain the drive power voltage of an output transistor at proper value. CONSTITUTION:The first saturation preventive circuit 40 detects the lower envelope voltage of the voltage ripple (motor output voltage) of output ends OUT1-3, and detects saturation degree by this being close to earth voltage, and outputs a signal regarding this saturation degree. A PWM comparator 42 compares the signal of saturation degree with triangular waves, and outputs a signal with pulse width depending on the saturation degree, and a VM generating circuit decides the drive power voltage VM of transistors Q1-Q6 from this pulse signal. Moreover, a middle point control circuit 50 sets the middle point of motor output voltage to the middle point of drive power voltage VM. Hereby, the saturation in the output transistors Q1-Q6 can be prevented by lowering the drive power voltage VM as far as possible. Furthermore, when the output voltage of the motor goes high abnormally, the second saturation preventive circuit 52 lessens the torque value. Hereby, the saturation of the output transistor can be prevented by suppressing the rise of motor output voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor drive circuit, and more particularly to control of output voltage and output current of a motor in an output stage.

[0002]

2. Description of the Related Art Conventionally, a three-phase brushless motor has been used to rotate a polygon mirror of a laser beam printer. This three-phase brushless motor has three-phase coils on the stator side, and sequentially supplies a predetermined alternating current to the rotor to rotate the rotor.

Then, three pairs of output transistors are used for this current supply. That is, three pairs of output transistors connected in series between the power source and ground are provided, the connection points of these output transistors are connected to the motor coil, and the output transistors are turned on in a predetermined combination, so that a desired current is supplied to the motor coil. To supply.

In order to control the rotation speed, a rotation frequency signal corresponding to the rotation speed of the rotor is generated, an error between the rotation frequency signal and the reference clock is output as a torque signal, and the rotation speed is speed controlled. .

Here, if the drive power supply voltage VM, which is the power supply side voltage of the output transistor, is kept at a high potential necessary for the maximum torque generation at all times, during low rotation and high torque operation,
There is a problem that the power loss in the output transistor becomes large and the output transistor generates heat.

Therefore, when the drive power supply voltage VM is set low, the output transistor is saturated during high torque and high speed rotation, and the waveform of the output current is distorted. When the waveform is distorted, noise is generated or the motor cannot be smoothly rotated. Further, when saturation occurs in the output transistor, the off of the transistor that should be turned off is delayed, the time for turning on both of the output transistor pairs is generated, and the through current flows. It should be noted that such a problem mainly occurs in the current linear drive system.

For this reason, conventionally, a saturation prevention circuit is provided in the motor drive circuit. This saturation prevention circuit constantly detects the upper envelope voltage or the lower envelope voltage in the voltage change of the motor output voltage flowing through the motor coil, and the collector-emitter voltage of the output transistor becomes low according to this detected voltage. The drive power supply voltage VM is controlled so that it does not become excessive, and saturation is prevented.

Specifically, PWM control is used to control the drive power supply voltage VM. That is, a signal corresponding to the motor output voltage is compared with a triangular wave, and a pulse signal (PWM signal) having a duty ratio corresponding to this is generated.
PWM control is performed to generate the drive power supply voltage VM of the output transistor from the M signal.

In this saturation prevention circuit, by detecting both the upper envelope voltage and the lower envelope voltage of the motor output voltage and controlling the drive power supply voltage based on this, complete saturation prevention can be achieved. You can

As described above, both the speed control and the PWM control are used to rotate the three-phase brushless motor at a constant speed and the drive power supply voltage is controlled. Feedback control from a Hall element is used for phase control of the motor output voltage.

[0011]

However, when two types of envelopes of the motor output voltage, that is, the upper envelope and the lower envelope, are both detected and one drive power supply voltage is generated based on the detected envelopes, the circuit is generated. There is a problem that the configuration becomes complicated.

On the other hand, if one of the upper envelope voltage and the lower envelope voltage of the motor output voltage is detected and the drive power supply voltage is controlled accordingly, one voltage may be generated from one detected voltage. Therefore, the circuit can be greatly simplified.

However, with this configuration, when the driving conditions of the sink-source transistor are different (or vary), the motor output voltage shifts toward the upper envelope voltage or the lower envelope voltage, as shown in FIG. However, there was a problem that it was saturated on one side.

Furthermore, when the motor rotation speed becomes extremely high in the maximum torque state, the motor output voltage becomes extremely high due to the back electromotive force of the motor. The saturation prevention circuit as described above attempts to prevent saturation of the output transistor by increasing the drive power supply voltage VM of the output transistor.
The maximum voltage among them is usually limited by the power supply voltage Vcc of the IC, and the drive power supply voltage VM cannot be further exceeded. Therefore, in such a case, there is a problem that the output transistor is saturated.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a motor drive circuit capable of suitably preventing saturation.

[0016]

According to the present invention, an output means for generating and outputting a plurality of phases of motor output voltage from a drive power supply voltage according to a torque command value, and an upper envelope voltage in a change of the motor output voltage or Envelope voltage detection means for detecting one of the lower envelope voltage, drive power supply voltage control means for controlling the drive power supply voltage of the output means according to the detection result of the envelope voltage detection means, and motor output voltage The midpoint control means for controlling the midpoint in the change to the midpoint of the drive power supply voltage and the detection result of the envelope voltage detection means cause the motor output voltage to fall within the maximum range in which the drive power supply voltage can be changed. And a torque command value control means for reducing the torque command value when the approach is detected.

The motor output means has a source side output transistor whose one end is connected to the drive power supply voltage, one end which is connected to the downstream side of the source side output transistor, and the other end which is connected to the ground side. A plurality of pairs of sink side output transistors are provided, and a motor coil is connected to a connection point of the source side transistor and the sink side transistor.

[0018]

As described above, in the present invention, the envelope voltage detecting means detects either the upper envelope voltage or the lower envelope voltage of the voltage change of the motor output voltage due to the change of the motor output voltage. Then, the drive power supply voltage, which is a voltage for generating the motor output voltage, is changed according to the detected value. For example, the lower envelope voltage of the motor output voltage is detected, and the drive power supply voltage is set so that the lower envelope voltage is higher than ground by a predetermined value. As a result, the lowest drive power supply voltage can be obtained while maintaining the waveform of the motor output voltage. On the other hand, as described above, when only the lower envelope voltage of the motor output voltage is detected, the upper envelope voltage may rise to the drive power supply voltage, and the waveform of the motor output voltage may not be kept correct. . In the present invention, the midpoint of the motor output voltage is detected, and this is matched with the midpoint of the drive power supply voltage. Therefore, even if only the lower envelope voltage of the motor output voltage is detected and the drive power supply voltage is controlled as described above, the upper envelope voltage can be maintained at a value lower than the drive power supply voltage by a predetermined value or more, It is possible to prevent saturation of the output transistor. In this way,
A suitable drive power supply voltage can be controlled with a simple configuration.

In the present invention, the motor output voltage is
When the IC power supply voltage approaches the maximum value of the drive power supply voltage, the torque command value is set to a small value. Therefore, even when the motor output voltage becomes very large at the time of high rotation of the motor, the motor output voltage can be prevented from exceeding the predetermined value, and the saturation of the output transistor can be reliably prevented.

In particular, if the motor output voltage output means is composed of a transistor, high-speed and accurate rotation of the three-phase brushless motor can be achieved. Since the drive power supply voltage is controlled as described above, it is possible to prevent the transistor of the motor output voltage output means from being saturated, and to prevent the through current due to the saturation of the transistor. Further, since the drive power supply voltage can be set to an optimum magnitude in accordance with the motor output voltage, power loss in the transistor can be made appropriate and heat generation in the transistor can be prevented.

[0021]

Embodiments of the present invention will be described below with reference to the drawings.

[Overall Configuration] FIG. 1 is a block diagram showing the overall configuration of the embodiment. This drive circuit is composed of an IC 10, and this IC 10 has coils L1 to L3 for each phase of the motor.
Is supplied with a current of a predetermined sine curve.

The output section 12 has three output terminals OUT1 to OUT1.
Three pairs of output transistors Q1 to Q6 corresponding to OUT3
It consists of Among the output transistors Q1 to Q6, the transistors shown on the upper side in the figure are the source side output transistors Q1, Q3, Q5, and the lower transistors are the sink side output transistors Q2, Q4, Q6. The output terminals OUT1 to OUT3 are connected to the connection points of the output transistors Q1 and Q2, Q3 and Q4, and Q5 and Q6, which are connected in series.

The output terminals OUT1 to OUT3 are connected to the respective phase coils L1, L2, L3 of the motor to be driven. Therefore, the output transistor Q1 of the output unit 12
~ By controlling the energization amount of Q6, the coil L1 ~
A desired current can be passed through L3.

On the other hand, in this drive circuit, the rotation of the motor is detected and feedback control is performed in order to make the amount of rotation of the motor desired. For this reason, a predetermined number (for example, three) of Hall elements 20 for detecting the angular position of the rotor of the motor are arranged in the stator of the motor with a predetermined angle therebetween. In the drawing, the position of the hall element 20 is drawn apart from the phase coils L1 to L3, but it is actually arranged in the vicinity of the coils L1 to L3. The Hall element 20 is connected to the corresponding Hall input terminals IN1, IN2, IN3. Therefore, a signal about the rotor position of the motor is input to the IC 10.

The hall amplifier section 18 is connected to the hall element 20 via the hall input terminals IN1, IN2, IN3, amplifies the outputs from the hall element 20, respectively, detects the position, and generates a predetermined position detection signal. To do.

The upper and lower three differential distribution units 16 connected to the Hall amplifier unit 18 distribute the position detection signal from the Hall amplifier unit 18 for each phase, and the source side output transistors Q1, 3 of the output unit 12. , 5 corresponding to predetermined phase switching signals I1, I2, I3 and the output transistor Q on the sink side.
Predetermined phase switching signals I1 ', I2 corresponding to 2, 4, 6
And I3 '.

The speed control unit 22 generates an error output between the clock signal CLK having a predetermined frequency and the FG signal indicating the current number of rotations of the motor, smoothes the error output, and controls the driving force of the motor. A torque command signal is generated and supplied to the upper and lower three differential distribution units 16. Then, this torque command signal is output to the source side and sink side output transistors Q of each phase in the upper and lower three differential distributor 16.
Phase switching signals I1, I2, I3, I corresponding to 1 to Q6
1 ', I2', I3 '. That is, the upper and lower three differential distributor 16 outputs the phase switching signals I1, I2, I3, I1 ', I2', I3 'having a magnitude corresponding to the torque command signal. The pre-drive unit 34 includes three upper and lower differential distribution units 1.
6 and the midpoint control circuit 50, and the output unit 1
The base currents of the second output transistors Q1 to Q6 are generated to control the currents of the output transistors Q1 to Q6.

In this way, each phase coil L1 of the motor
Power supply to L3 is controlled, and the rotation speed of the motor is controlled to a desired value.

In this embodiment, in order to generate the driving power supply voltage VM of the output transistors Q1 to Q6, the first
It has a saturation prevention circuit 40, a PWM comparator 42, a triangular wave generation circuit 44, and an external VM generation circuit 46,
In addition, in order to complete saturation prevention, the midpoint control circuit 5
Has 0.

The first saturation prevention circuit 40 includes an output unit 12
The lower envelope voltage of the motor output voltage output from is detected and compared with a predetermined reference voltage VREF1. And
According to this detection result, a signal having a lower voltage as the lower envelope voltage is lower is supplied to the PWM comparator 42. This voltage is applied to the output transistor Q on the sink side.
It is a voltage indicating how close the collector voltages of Q2, Q4 and Q6 are to the emitter voltage, and the deeper the saturation, the lower the voltage. The PWM comparator 42 uses the triangular wave generation circuit 4
4 and a predetermined saturation prevention circuit 40
A signal corresponding to the lower envelope voltage of the motor output voltage supplied from is compared, and a pulse signal (PWM signal) having a duty ratio according to the comparison result is output. That is, when the lower envelope voltage is low, a PWM signal with a small duty ratio is output. Therefore, in the VM generation circuit 46,
By inverting and integrating this PWM signal, the drive power supply voltage VM can be increased when the lower envelope voltage is low, and saturation can be prevented.

Here, the sink side outputs I1 ', I2', I3 'of the upper and lower three differential distributors 16 are directly fed to the predrive unit 34.
To the lower output transistor Q2,
Although Q4 and Q6 are controlled, source side outputs I1, I2,
I3 is supplied to the predrive unit 34 via the midpoint control circuit 50.
Is supplied to. The midpoint control circuit 50 divides the voltage obtained by summing the voltages of the current output terminals OUT1 to OUT3 to the motor to obtain the midpoint voltage of the motor output voltage and the drive power supply voltage VM. The upper output transistors Q1, Q3 and Q5 are compared so that they match each other.
Control the base current of. As a result, the midpoint voltage of the motor output voltage always matches the midpoint voltage obtained by dividing VM.

As described above, according to this embodiment, the lower envelope voltage of the motor output voltage is detected and compared with the predetermined reference voltage VREF1 to obtain the optimum collector-emitter voltage at which the output transistor is not saturated. At the same time, the midpoint of the motor output voltage is adjusted to the midpoint of the drive power supply voltage VM of the output transistors Q1 to Q6. Therefore, the saturation prevention of both the upper envelope voltage and the lower envelope voltage of the motor output voltage can be achieved. Further, since the drive power supply voltage VM is generated only from the lower envelope voltage, the circuit configuration can be simplified. In the first saturation prevention circuit 40, the upper envelope voltage may be detected. In this case, the saturation may be detected depending on how close the upper envelope voltage is to the drive power supply voltage VM.

Further, in this embodiment, a second saturation prevention circuit 52 is provided. The second saturation prevention circuit 52 has the same configuration as the first saturation prevention circuit 40, detects the lower envelope voltage of the three-phase motor output voltage, and compares it with a predetermined reference voltage VREF2. Here, the reference voltage VREF2 in the second saturation prevention circuit 52 is equal to the first saturation prevention circuit 4
It is a voltage lower than the reference voltage VREF1 at 0. Therefore, the second saturation prevention circuit 52 can detect that the lower envelope voltage of the motor output voltage approaches the ground. In this way, the lower envelope voltage of the motor output voltage approaches the ground, which means that the upper envelope voltage of IC10 is
It means that the power supply voltage Vcc, which is the highest voltage among the above, is approached. In the circuit of this embodiment, the drive power supply voltage VM
Cannot exceed the power supply voltage Vcc, and the output transistor is saturated despite the control by the first saturation prevention circuit 40.

However, in the present embodiment, when such a motor output voltage is detected by the second saturation prevention circuit, the second saturation prevention circuit 52 detects it and controls the speed control unit 22. , Reduce the torque command signal. As a result, the phase switching signals I1, I2, I3, I1 ', I2', I3 ', which are the outputs from the upper and lower three differential distributors 16, are reduced, and the saturation of the output transistor can be prevented. The motor output voltage increases in accordance with the motor rotation speed and the torque force, and when the rotation speed is high and the torque is high, the motor output voltage becomes very large, and the above-described state occurs. According to the present embodiment, even in such a case, the second saturation prevention circuit 52 detects this and controls the torque command signal, so that saturation of the output transistor can be prevented.

[Structure of Saturation Preventing Circuit] The first and second saturation preventing circuits 40 and 52 are connected to the reference voltage VREF (VREF1, VRE).
Since the configurations are exactly the same except for F2), both will be described with reference to FIG. To the bases of the three PNP transistors Q102, Q104, Q106, output terminals OUT1, OUT2, OUT3 of the motor output voltage to which the motor coils L1, L2, L3 are connected are respectively connected. Then, the transistors Q102 and Q1
The emitters of 04 and Q106 are connected to the power supply through a common resistor R102, and the collectors are connected to the ground.
Transistors Q102, Q104 and Q106 have terminals O
It is turned on by the lowest voltage of UT1 to OUT3,
A current is passed through the corresponding transistors Q102, Q104, Q106. Therefore, the terminal OUT is provided below the resistor R102.
A voltage corresponding to the lowest voltage of 1 to OUT3, that is, a voltage corresponding to the lower envelope of the three-phase motor output voltage is generated.

Transistors Q102, Q104, Q10
The common emitter of 6 is connected to the base of PNP transistor Q108. The emitter of the transistor Q108 is connected to the emitter of the PNP transistor 110, and both common emitters are connected to the power source via the constant current source CS102. And the transistor Q10
The collector of 8 is connected to ground through the collector-base of NPN transistor Q112. The transistor Q112 has an emitter connected to the ground and a collector and a base that are short-circuited to each other. The base of the transistor Q112 is connected to the base of an NPN transistor Q114 whose emitter is connected to the ground. Therefore, the transistor Q112 and the transistor Q114 form a current mirror. The current flowing in the transistor Q114 is the output of the saturation prevention circuit 40.

On the other hand, the transistor Q110 receives a current supply from the same constant current source as the transistor Q108, and operates as a differential circuit thereof. The base of the transistor Q110 is connected to the ground via the PNP transistor Q116 and the resistor R1 is connected.
It is connected to the power source through 04. Further, the reference voltage VREF (VREF1 or VREF2) that determines the saturation detection voltage in this circuit is connected to the base of the transistor Q116.

In such a circuit, the reference voltage VREF
Is a constant voltage, the emitter potential of the transistor Q116, that is, the base voltage of Q110 is a constant voltage. Here, this reference voltage VREF (VREF1 or VRE
F2) should be changed according to the current flowing through the motor. That is, a current detection resistor having a low resistance value is arranged between the emitters of the output transistors Q2, Q4, Q6 and the ground, and the motor current is detected by the voltage across the current detection resistor. When the motor current is large, VREF (VREF1
Alternatively, more preferable saturation detection can be performed by controlling VREF2) to be large.

On the other hand, since the lower envelope voltage of the motor output voltage is supplied to the base of the transistor Q108 as described above, the current flowing through Q108 is the lower envelope voltage and the reference voltage VREF. It depends on the difference.
Therefore, the current value according to the saturation can be obtained in the transistor Q114. That is, when the lower envelope voltage is low and the degree of saturation is high, the current of the transistor Q114, that is, the amount of current output from the saturation detection circuit increases.

The reference voltage VREF1 of the first saturation prevention circuit 40 is higher than the reference voltage VREF2 of the second saturation prevention circuit 52. Therefore, the first saturation prevention circuit 40 starts to operate first, and then the second saturation prevention circuit 52 starts to operate. As a result, the drive power supply voltage VM is increased under the control of the first saturation prevention circuit 40.
The second saturation prevention circuit 52 can detect the state where M cannot be increased.

The output of the second saturation prevention circuit 52 controls the magnitude of the torque command signal to control the motor output voltage and prevent saturation of the output transistor.

[Configuration of PWM Comparator] PW shown in FIG.
The structure of the M comparator 42 is shown. In this example, the transistor Q114 in the first saturation prevention circuit 42 is indicated by the constant current source CS202. Therefore, a larger current flows through the constant current source CS202 as the saturation degree becomes higher.

The constant current source CS202 supplies a current according to the degree of saturation toward the ground.
The resistor R202 is connected in parallel with the resistor R202 on the most downstream side (the other end is connected to the ground) of the resistors R202, 204, 206 connected in series from the power source to the ground. Therefore, the amount of current flowing through the resistor R206 changes according to the amount of current of the constant current source CS202, and the resistor R20
The potential on the upstream side of 6 fluctuates. Resistor R204 and resistor R2
The connection point of 02 is connected to the base of the NPN transistor Q202. Since the constant current source CS202 has a large amount of current when the degree of saturation is large, a lower voltage is supplied to the base of the transistor Q202 as the degree of saturation is higher.

The emitter of the transistor Q202 has N
The emitter of the PN transistor Q204 is connected, and this common emitter is connected to the ground via the constant current source CS204. The collector of the transistor 202 is connected to the power supply via a PNP transistor Q206 whose collector and base are short-circuited, and the transistor 204
The collector of is connected to the power supply via a PNP transistor Q208 whose collector and base are short-circuited. Therefore, the transistor Q202 and the transistor Q204 operate as a differential circuit, and its output is the transistor Q206.
And appears as the current in transistor Q208. Then, since a triangular wave having a predetermined amplitude is supplied to the base of the transistor Q204, the transistor Q202 and the transistor 204 compare the triangular wave and the voltage according to the saturation, and output the result as the current of the transistors Q206 and 208. To do. In the triangular wave generation circuit 44, a triangular wave is formed by repeating charging and discharging of the capacitor at a predetermined frequency.

Here, the transistor Q20 in FIG.
The voltage applied to 2 is the highest potential of the triangular wave applied to the base of the transistor Q204 (may be set slightly lower than the highest potential) when the constant current source CS202 becomes minimum (non-saturated state). Further, when the base potentials of the transistors Q110 and Q108 of the first saturation prevention circuit of FIG. 2 become the same potential and the current value of the constant current source CS202 becomes a value indicating the saturated state, the voltage is applied to the base of the transistor Q204. Resistance R202, R so that it becomes the lowest potential of the triangular wave (may be set slightly higher than the lowest potential).
Set the values of 204 and R206. By doing so, the voltage of the saturation signal can be made equal to the voltage of the triangular wave, and the duty ratio can be set accurately.

A PNP transistor Q210 whose emitter is connected to a power source is connected to the base of the transistor Q208, and this transistor Q210 forms a current mirror together with the transistor Q208. The collector of the transistor Q210 is connected to the ground through an NPN transistor Q212 whose collector base is short-circuited, and the base of the transistor Q212 is connected to the base of an NPN transistor Q214 whose emitter is connected to the ground. Therefore, the transistor Q21
2, 214 also constitute a current mirror. Therefore, the same current as the current flowing through the transistor Q204 flows through the transistors Q208, Q210, Q212 and the transistor Q214.

On the other hand, the collector of the transistor Q214 is connected to the collector of the PNP transistor Q216, and the base of this transistor Q216 is the transistor Q20.
6 is connected. Here, the transistor Q216
Form a current mirror with the transistor Q206. Therefore, the same current as that flowing through the transistor Q202 flows through Q206 and Q216.

The connection point between the transistor Q216 and the transistor Q214 is the NPN transistor Q218.
Of the transistor Q218, the emitter of which is connected to the ground and the collector of which is connected to the power source through the resistor R208. Therefore, the transistor Q20
When the current amount of 2 is larger than that of the transistor Q204, the current amount of the transistor Q216 becomes larger than that of the transistor Q214, and the transistor Q218 is turned on. On the other hand, when the amount of current of the transistor Q204 is larger than that of the transistor Q202, the amount of current of the transistor Q214 becomes larger than that of the transistor Q216, and the transistor Q21
8 turns off. When the transistor Q218 is on, this collector has a low potential and the transistor Q21
When 8 is off, the collector potential becomes high potential.

The collector of the transistor Q218 is PW
It is connected to the base of an NPN transistor Q220 that outputs an M signal. Therefore, the transistor Q220 turns off when the transistor Q218 is on, and turns on when the transistor Q218 is off.

For example, assuming that the base potential (VH) of the transistor Q202 is constant, the transistor Q20
When the base potential (voltage of triangular wave) of 4 becomes VH or more, the amount of current in the transistor Q204 increases, which turns off the transistor Q218 and causes the transistor Q220.
Turns on, and the collector of the transistor Q220 falls to the ground potential. On the other hand, when the base potential (triangular voltage) of the transistor Q204 becomes VH or less, the transistor Q2
02 The amount of current increases, which causes the transistor Q
218 turns on, transistor Q220 turns off, and the collector of transistor Q220 opens. As a result, a rectangular wave is obtained in the transistor Q220. When the base potential of the transistor Q202 is changed by the amount of current of the constant current source CS202, the voltage to be compared with the triangular wave voltage changes. Therefore, the ratio between the low level and the high level of the rectangular wave obtained in the transistor Q220, that is, the duty ratio of the pulse signal is changed.

For example, as shown in FIG. 4, when the transistor Q202 is set to VH1, the transistor Q202
A pulse as shown in (a) is obtained at the collector of 218, and when set to VH2 of the transistor Q202, a pulse as shown in (b) is obtained at the collector of the transistor Q218. In the case of the present embodiment, when the degree of saturation increases, the current amount of the constant current source CS202 increases and the transistor Q20
The base potential of 2 decreases, and the duty ratio of the pulse signal (PWM signal) output from the transistor Q220 decreases. On the contrary, when the saturation degree becomes small, the constant current source C
The amount of current in S202 decreases, the base potential of the transistor Q202 increases, and the duty ratio of the pulse signal (PWM signal) output from the transistor Q220 increases.

[Configuration of VM Generating Circuit] VM Generating Circuit 46
The configuration will be described with reference to FIG. This circuit inverts and integrates the PWM signal output from the PWM comparator 42 to generate a predetermined drive power supply voltage VM.
Since this circuit includes a large-capacity capacitor, a coil, etc., it is not an internal circuit of the IC 10 but an external circuit of the IC 10.

The collector of the output transistor Q220 of the above-mentioned PWM comparator 42 is connected to P through the resistor R302.
It is connected to the base of the NP transistor Q302.
The emitter of this transistor Q302 is a resistor R304.
Is connected to the power source via a resistor and the collector is connected to the ground via a resistor R306. Therefore, the transistor Q22
When 0 is turned on, the transistor Q302 is turned on, and when transistor Q220 is turned off, the transistor Q302 is turned off.

The emitter of the transistor Q302 is a PNP transistor Q304 whose emitter is connected to the power supply.
The base of is connected. The potential on the emitter side of the transistor Q302 becomes the non-bias level when the transistor Q302 is off, and the bias level when the transistor Q302 is on. Therefore, this transistor Q304 is
When 302 is on, it is on, and when it is off, it is off. Therefore, by turning on the transistor Q304,
A current is output from the transistor Q304, and the output of the current is stopped by turning off the transistor Q304.

The collector of the transistor Q304 is connected to the VM output terminal via the coil L302, and this VM output terminal is connected to the ground via the capacitor C302. Therefore, the AC component is integrated by the coil L302 and the capacitor C302, and the PWM
The drive power supply voltage VM corresponding to the duty ratio of the pulse signal output from the comparator is obtained. The emitter of the transistor Q304 is connected to a diode D304 that allows a current to flow from the ground side. Therefore, the potential on the emitter side of the transistor Q304 is kept between the ground potential -VF (this VF corresponds to the transistor VBE, which is a voltage drop in the diode) and the power supply potential. As a result, it is possible to prevent the transistor Q304 from being destroyed by the negative voltage due to the kickback of the coil that occurs during switching.

As described above, according to the VM generating circuit of this embodiment, the PW in the output from the PWM comparator 42 is
The larger the duty ratio of the M signal, the lower the drive power supply voltage VM. Therefore, when the lower envelope voltage of the voltage at the motor output terminals OUT1 to OUT3 is low (that is, the collector-emitter voltage of the lower output transistors Q2, Q4, Q6 is low) and the saturation degree is deep, the duty ratio is small. A PWM signal is obtained, the drive power supply voltage VM rises, and saturation is prevented in advance. On the other hand, the motor output terminal O
When the lower envelope voltage of the voltage in UT1 to OUT3 is high (the collector-emitter voltage of the sink side output transistors Q2, Q4, Q6 is high) and the saturation degree is shallow, a PWM signal with a large duty ratio is obtained, Since the drive power supply voltage VM is lowered and the collector-emitter voltage of the output transistors Q1 to Q6 can be suppressed to a necessary minimum without being saturated, power loss can be reduced.

[Configuration of Midpoint Control Circuit] FIG. 6 shows the configuration of the midpoint control circuit 50. In this circuit, the midpoint potential at the output terminal is the drive power supply voltage V of the output transistors Q1 to Q6
Control to the midpoint of M.

Source side output transistor Q1 of one phase
And the sink side output transistor Q2 is driven by the drive power supply voltage V
Connected in series between M and ground. At the base of the sink side output transistor Q2, a current mirror CM502 for controlling the base current of this output transistor is provided. On the other hand, the collector of the PNP transistor Q502, whose emitter is connected to the power supply VCC, is connected to the base of the source side transistor Q1.

At the base of the transistor Q502,
PNP transistor Q50 whose emitter is connected to Vcc
4 is connected to the base. This transistor Q50
The collector bases of 4 are short-circuited. The collector of the transistor Q504 is the NPN transistor Q50.
It is connected to the constant current source CS 502 via 6. on the other hand,
The other end of the constant current source CS502 is connected to the power supply VCC
The PN transistor Q508 is connected, and the transistors Q506 and Q508 form a differential circuit in which the emitters are commonly connected.

A voltage obtained by dividing the driving power supply voltage VM by the resistors R502 and R504 is applied to the base of the transistor Q506. Therefore, the base voltage of the transistor Q506 is a voltage that is uniquely determined by the drive power supply voltage VM and is set to the midpoint control reference voltage.

On the other hand, at the base of the transistor Q508, output terminals OUT1 to OUT3 are resistors R506, respectively.
It is connected via R508 and R510. The base of the transistor Q508 is connected to the ground via the resistor R512. Therefore, the output terminals OUT1 to OU
The current from T3 flows through the resistors R506, R508, R510 and the resistor R512 to the ground, and the transistor Q50
The base of 8 outputs the combined voltage of the output terminals OUT1 to OUT3 to the resistors R506 (or R508 and R510) and the resistor R.
It becomes what was divided by 512. And this resistance R5
06 (and R508 and R510) have the same resistance value as R502, and resistor R512 has substantially the same resistance value as resistor R504, so that transistor Q5
The base voltage of 08 (and the corresponding transistor of the other phase) becomes the midpoint comparison potential on the fluctuation side of the motor output voltage.

When there is a difference between the base potentials of the transistor Q506 and the transistor Q508, this difference is fed back to the transistor Q1 via the transistors Q504 and Q502, and the base potential of the transistor Q508 is controlled by the midpoint control of the base of the transistor Q506. It acts so as to have the same potential as the reference voltage. At this time,
The midpoint voltage of the motor output voltage fluctuation is the drive power supply voltage VM
It is controlled so as to have the midpoint potential VM / 2.

Here, the operation of such a midpoint control is effective only when a current is flowing through the constant current source CS502 in the midpoint control circuit. On the other hand, in this FIG.
Although the circuit for one phase is shown, a similar differential circuit is provided in the drive circuits for the other two-phase output transistors Q2 and Q3, and the same midpoint control is performed. Therefore, when the motor is driven, one of the midpoint control circuits operates to perform the midpoint control.

As described above, the midpoint control circuit of this embodiment controls the midpoint of the voltage fluctuation of the motor output voltage to the midpoint potential of the driving power supply voltage VM of the output transistors Q1 to Q6. Therefore, not only the saturation prevention on one side but also the saturation prevention on both sides of the sink source transistor is achieved by combining the control of the lower envelope voltage of the motor output voltage of the first saturation prevention circuit described above with this midpoint control. It is possible,
With a simple circuit, reliable saturation prevention and control of the drive power supply voltage VM of the output transistor can be achieved.

[Structure of Torque Command Control] FIG. 7 shows a structure for torque command control. The speed control unit 22 of FIG.
A torque command signal is generated according to the state of rotation, and this is output as a current of the constant current source CS601 (hereinafter referred to as torque command current). Below the constant current source CS601, the collector of an NPN transistor Q601 whose emitter is connected to ground and the collector of Q114 which is an output transistor of the second saturation prevention circuit 52 are connected. Therefore, the second saturation prevention circuit 52
Is 0, the transistor Q601 outputs the torque command current as it is. On the other hand, when the second saturation prevention circuit 52 detects saturation, a current corresponding to the saturation level flows in the transistor Q114, so that the transistor Q601 corresponds to the current flowing in the transistor Q114.
The current that flows through is reduced. As a result, the torque command signal supplied to the upper and lower three differential distributors can be reduced.

The upper and lower three differential distributors drive the NPN transistors Q602 to Q604 and the PNP transistors Q605 to Q607 according to the logic outputs of the three phases to output the phase switching signals I1 and I2 corresponding to the upper and lower output transistors.
, I3, I1 ', I2', I3 '. Here, a transistor Q60 for generating these phase switching signals
2 to Q607 are PNP transistors Q608 and Q on the upper side.
It is connected to the power source voltage Vcc via 609. Therefore, the magnitude of the phase switching signal is controlled by the currents flowing through these transistors Q608 and Q609.

Then, the transistors Q608 and Q609
Is connected to a transistor Q610 whose collector base is short-circuited, and these constitute a current mirror. Therefore, the transistors Q608 and Q60
9 flows the same current as the transistor Q610. Also,
A collector of an NPN transistor Q611 is connected to the downstream side of the transistor Q610, and the transistor Q611 is connected to a transistor Q601 whose collector base is short-circuited. Therefore, the transistors Q611 and Q601 form a current mirror, and the transistor Q611 supplies the same current as the transistor Q601.

Here, as described above, the transistor Q601 supplies a torque command current according to the output of the second saturation prevention circuit 52, whereby the phase switching signal is output to the second saturation prevention circuit 52. The torque command changes accordingly.

As a result, when the motor output voltage approaches the power supply voltage VCC when the motor rotates at high speed, the torque command can be suppressed and the output transistor can be prevented from being saturated.

The output of the transistor Q602, I1, determines the current of the constant current source CS502 in FIG. 6, and the output of the transistor Q605, the current I1 '.
Determines the current amount of the current mirror CM502 in FIG.

[0072]

As described above, according to the motor drive circuit of the present invention, the upper envelope voltage or the lower envelope curve of the voltage change of the motor output voltage due to the change of the motor output voltage by the envelope voltage detecting means. Either one of the voltages is detected. Then, the drive power supply voltage, which is a voltage for generating the motor output voltage, is changed according to the detected value.
For example, the lower envelope voltage of the motor output voltage is detected, and the drive power supply voltage is set so that the lower envelope voltage is higher than ground by a predetermined value. As a result, the lowest drive power supply voltage can be obtained while maintaining the waveform of the motor output voltage. On the other hand, as described above, when only the lower envelope voltage of the motor output voltage is detected, the upper envelope voltage may rise to the drive power supply voltage, and the waveform of the motor output voltage may not be kept correct. . In the present invention, the midpoint of the motor output voltage is detected, and this is matched with the midpoint of the drive power supply voltage. Therefore, even if only the lower envelope voltage of the motor output voltage is detected and the drive power supply voltage is controlled as described above, the upper envelope voltage can be kept lower than the drive power supply voltage by a predetermined amount or more, It is possible to prevent saturation of the output transistor. In this way, it is possible to control the suitable drive power supply voltage with a simple configuration.

In the present invention, the motor output voltage is
When the IC power supply voltage approaches the maximum value of the drive power supply voltage, the torque command value is set to a small value. Therefore, even when the motor output voltage becomes very large at the time of high rotation of the motor, the motor output voltage can be prevented from exceeding the predetermined value, and the saturation of the output transistor can be reliably prevented.

In particular, if the motor output voltage output means is composed of a transistor, high-speed and accurate rotation of the three-phase brushless motor can be achieved. Since the drive power supply voltage is controlled as described above, it is possible to prevent the transistor of the motor output voltage output means from saturating, and to prevent the generation of a through current due to the saturation of the transistor. Further, since the drive power supply voltage can be set to an optimum magnitude in accordance with the motor output voltage, power loss in the transistor can be made appropriate and heat generation in the transistor can be prevented.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall configuration of an embodiment.

FIG. 2 is a circuit diagram showing a configuration of a saturation prevention circuit.

FIG. 3 is a circuit diagram showing a configuration of a PWM comparator.

FIG. 4 is an explanatory diagram showing a waveform of a PWM signal.

FIG. 5 is a circuit diagram showing a configuration of a VM generation circuit.

FIG. 6 is a circuit diagram showing a configuration of a midpoint detection circuit.

FIG. 7 is a circuit diagram showing a configuration for torque command control.

FIG. 8 is an explanatory diagram showing an example of a conventional motor output voltage waveform.

[Explanation of symbols]

 12 Output Section 40 First Saturation Prevention Circuit 42 PWM Comparator 44 Triangular Wave Generation Circuit 46 VM Generation Circuit 52 Second Saturation Prevention Circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiki Tsubouchi 1006, Ojima, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. In the company

Claims (2)

[Claims] 1. An output means for generating and outputting a plurality of motor output voltages of a plurality of phases according to a torque command value from a drive power supply voltage, and one of an upper envelope voltage and a lower envelope voltage of the motor output voltage. Envelope voltage detection means for detecting, drive power supply voltage control means for controlling the drive power supply voltage according to the detection result of the envelope voltage detection means, and the middle point in the change of the motor output voltage is the middle point of the drive power supply voltage. When it is detected that the motor output voltage is close to the maximum changeable range of the drive power supply voltage by the detection result of the midpoint control means for controlling to match A motor drive circuit, comprising: a torque command value control means for reducing the value. 2. The circuit according to claim 1, wherein the output means has a source-side output transistor whose one end is connected to a driving power supply voltage, one end which is connected to the downstream side of the source-side output transistor, and the other end. A plurality of pairs of sink-side output transistors connected to the ground side, and a motor coil connected to a connection point of the source-side transistor and the sink-side transistor.