JPH06169589A - Motor drive circuit - Google Patents

Abstract

PURPOSE:To prevent the oversaturation of an output transistor on saturation side and reduce noise. CONSTITUTION:A group of diodes 76 detect the minimum value of output voltage, and they apply it to the base of a transistor 13. The voltage across a resistor Rf, etc., is applied as saturation control voltage to the base of a transistor Q14. If the saturation of any of output transistors Q2, Q4, and Q6 on saturation side advances, the output of a current mirror circuit 72 increases relatively by the operation of a differential circuit 68, and the ratios of the driving currents of the output transistors Q2, Q4, and Q6 to the driving currents of the output transistors Q1, Q3, and Q5 are limited.

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 having means for distributing a drive current to each output transistor.

[0002]

2. Description of the Related Art A three-phase brushless motor or the like used in an optical disk system is required to have a low driving sound. Among the methods of energizing the motor coil, the ones capable of suppressing the drive noise include, for example, 120 ° soft switching and 180 ° trapezoidal wave energization.

FIG. 4 shows an example of the configuration of a motor drive circuit capable of implementing these methods. The circuit shown in this figure includes a position detection signal synthesis unit 10, a voltage conversion unit 12,
It is provided with three upper and lower differential distribution circuits 14 and an output circuit 16.

The motor to be driven by the circuit shown in FIG.
A sensor is provided for detecting the rotational angle position of the rotor.
Usually, this sensor is configured as Hall elements arranged on the stator at a predetermined electrical angle from each other.
The input terminals IN1 to IN3 are connected for each phase. The position detection signal synthesizing unit 10 includes three differential circuits 18 and 20 each having a differential input from the input terminals IN1 to IN3.
And 22. The collectors of the respective transistors forming the differential circuits 18, 20 and 22 are selectively connected to the collectors of the input side transistors of the current mirror circuits 24, 26 and 28. Specifically, the differential circuit 1
One of the eight differential transistors is a current mirror circuit 24, the other is a current mirror circuit 28, and the differential circuit 2
One of the 0 differential transistors is connected to the current mirror circuit 26, the other is connected to the current mirror circuit 24, and the differential circuit 2
One of the two differential transistors is connected to the current mirror circuit 28, and the other is connected to the current mirror circuit 26. Current mirror circuits 24, 26 and 28
The collector of the output side transistor of is used for current output to the voltage conversion unit 12. The current sources 30, 32, 3
4, 36, 38 and 40 are differential circuits 18 and
Equal currents are supplied to each of 20, 22 and the current mirror circuits 24, 26, and 28. Also, VCC
1 is a power supply voltage terminal.

The voltage conversion unit 12 includes a position detection signal synthesis unit 1
The current supplied from 0 is converted into a voltage and output to the upper and lower three differential distribution circuits 14. When the motor to be driven is rotating, the output current from the position detection signal synthesizer 10 is a sine wave current having a cycle corresponding to the rotation speed. The voltage converter 12 converts this into a voltage having a waveform as shown in FIGS. 5 (a) and 5 (b) in the case of 120 ° soft switching, and the electric power of the motor in the case of 180 ° trapezoidal wave conduction. It is converted into a trapezoidal wave over all corners and output to the upper and lower three differential distribution circuit 14. In addition, "120 °" of 120 ° soft switching means that, as shown in FIG. 5A, the electrical conduction period to the motor coil is 120 ° in electrical angle during a half cycle.

The upper and lower three differential distribution circuit 14 includes a voltage conversion unit 1
2 is a circuit that distributes the drive currents of the output transistors of each phase according to the voltage output from 2. The output circuit 16 is supplied with the power supply voltage from the power supply voltage terminal VCC2 and has three pairs of output transistors Q1 and Q2, Q3 and Q4, and Q5.
From each connection point of Q6 and Q6
Supply current to 2, 44 and 46. Output terminal OUT
Are terminals for connecting the coils 42, 44 and 46. Of these output transistors, the source side output transistors Q1, Q3 and Q5 receive the distribution of the driving current by the transistors Q7, Q9 and Q11 which form the upper and lower three differential distribution circuit 14, and the sink side output transistors Q2, Q4 and Q6 The drive current is distributed by the transistors Q8, Q10, and Q12 that form the upper and lower three differential distribution circuits 14.

More specifically, first, the output voltage of the voltage converter 12 is applied to the bases of the transistors Q7, Q9 and Q11. These transistors Q7, Q9 and Q1
Current Id1 from the current source 48 connected to the emitter of 1
Are distributed to the current mirror circuits 50, 52 and 54 by three differential operations of the transistors Q7, Q9 and Q11. The current mirror circuits 50, 52 and 54 use the source side output transistors Q1, Q3 and Q5 as output side transistors. That is, the source side output transistors Q1, Q3 and Q5 are driven by the base current (driving current) distributed by the transistors Q7, Q9 and Q11 according to the output voltage of the voltage conversion unit 12.

Similarly, the output voltage of the voltage converter 12 is also applied to the bases of the transistors Q8, Q10 and Q12. A current source 56 that outputs a current Id2 is connected to the emitters of these transistors Q8, Q10, and Q12. This current Id2 is applied to the transistors Q8 and Q1.
It is distributed to the sink side output transistors Q2, Q4 and Q6 via the buffers 58, 60 and 62 by three differential operations of 0 and Q12. That is, the sink-side output transistors Q2, Q4, and Q6 are also driven by the base current (driving current) distributed by the transistors Q8, Q10, and Q12 according to the output voltage of the voltage conversion unit 12.

The current sources 48 and 56 are the current feedback amplifier 6
Received return by 4. The resistor Rf connected between the output circuit 16 and the ground converts the output currents of the output transistors Q1 to Q6 into a voltage and inputs the voltage to the current feedback amplifier 64. A control target value (control input) of the output current is supplied to the other input end of the current feedback amplifier 64. That is, the circuit of this figure detects the output currents of the output transistors Q1 to Q6 and outputs the currents Id1 and Id of the current sources 48 and 56.
2 has a current feedback loop for feedback control. In addition,
VCC2 is a power supply terminal of the output circuit 16.

By the way, current feedback is added, but voltage feedback is not added. Therefore, the output voltage of the output transistors Q1 to Q6, that is, the source side output transistors Q1, Q3 and Q5 and the sink side output transistor. The voltage at the connection point of Q2, Q4 and Q6 is hf
It is uncertain due to the influence of e. Extreme fluctuation is hfe
Causes the transistor to be oversaturated, which causes driving noise of the motor having the coils 42 to 46.
As a method of preventing this, for example, the coils 42 to 4
There is a method in which the output voltage of the output transistors Q1 to Q6 is swung around about 1/2 of the power supply voltage by feeding back the midpoint potential of 6. But this method
An external capacitor or the like is required to prevent oscillation. As a method without such a problem, there is a method of driving either the source side output transistor or the sink side output transistor in a saturated state.

The circuit of FIG. 4 is a circuit capable of performing such driving by one-sided saturation. That is, when the output transistors Q1 to Q6 are driven without adding the midpoint feedback, the source side output transistors Q1, Q3, and Q6 are provided in order to avoid the influence of the variation in hfe of the transistors Q1 to Q6.
5 or the sink side output transistors Q2, Q4 and Q6 are selectively saturated. This is the current source 48
This can be realized by setting in advance the ratio (current distribution ratio) of the current Id1 to the current Id2 of the current source 56.
For example, when Id1> Id2 is set, the source side output transistors Q1, Q3 and Q5 can be used in a saturated state,
When Id1 <Id2 is set, the sink side output transistors Q2, Q4 and Q6 can be used in a saturated state. With this arrangement, the output voltages of the output transistors Q1 to Q6 are biased to either the power supply side or the ground side, and are less susceptible to the hfe variation.

[0012]

However, when the output transistor is used with one-sided saturation, the drive current is different and the gains of the upper and lower output transistors are different. As a result, there is a problem that the output transistor is oversaturated at the time of switching of the output current (current between the collector and emitter) of the saturation side output transistor, and the output current is distorted.

For example, in the case of using the source side saturation (upper side saturation) by 120 ° soft switching, FIG.
As shown in (c) and (d), the waveform is distorted when the source-side output current (upper current) is switched. Similarly,
When the sink side saturation (lower side saturation) is used by 120 ° soft switching, as shown in FIGS. 5 (e) and 5 (f), the waveform changes at the sink side output current (lower side current). Distorted. Such distortion also occurs when 180 ° trapezoidal wave is applied. This kind of distortion causes the generation of motor drive noise.

The present invention has been made to solve the above problems, and an object thereof is to suppress the distortion of the output current caused by the oversaturation of the output transistor and to reduce the motor driving noise. .

[0015]

In order to achieve such an object, the present invention provides an output used in a saturated state by detecting a minimum value or a maximum value of an output voltage from an output circuit to a motor coil. A means for detecting the minimum value of the collector-emitter voltage of the transistor, a means for comparing the detected output voltage with a saturation control voltage which is controlled slightly higher than the saturation voltage so as not to cause oversaturation of the output transistor, and a source The current value of the current source provided for each of the source side output transistor and the sink side output transistor is compared so that the ratio between the drive current of the side output transistor and the drive current of the sink side output transistor is close to 1 sufficiently. And a means for supplying a bias current having a value corresponding to the output current of the output transistor to each of the current sources. Characterized in that it obtain.

[0016]

According to the present invention, the minimum value or the maximum value of the output voltage from the output circuit to the motor coil is detected, and this voltage is compared with the saturation control voltage. Since one of the source side and sink side output transistors is used in the saturated state, the detected voltage represents the minimum value of the collector-emitter voltage of each output transistor used in the saturated state. The currents of the current sources provided corresponding to the source-side output transistor and the sink-side output transistor are adjusted so that the drive current distribution ratio to the source-side output transistor and the sink-side output transistor is sufficiently close to 1 according to the comparison result. , Set. At this time, if the saturation control voltage is controlled to be slightly higher than the saturation voltage of the output transistor,
Within this control range, the hfe of the output transistors is almost the same on the saturated side and the non-saturated side. Therefore, regardless of the output current of the output transistors, all the output transistors are driven by the currents close to each other. Therefore, oversaturation of the output transistor is prevented.

The output transistor usually has a characteristic that the saturation voltage rises in a region where the output current is large. Therefore, the saturation control voltage ≤
There is a possibility of saturation voltage, in which case the output voltage waveform of the output transistor is distorted. In the present invention, a bias current having a value corresponding to the output current of the output transistor is supplied to each of the current sources. By doing so, the current distribution ratio in a region where the output current is large can be suppressed to a relatively small value. As a result, even if the output current is large,
Oversaturation of the output transistor is less likely to occur.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings. The same components as those of the conventional example shown in FIGS. 4 and 5 are designated by the same reference numerals and the description thereof will be omitted.

FIG. 1 shows the configuration of a motor drive circuit according to an embodiment of the present invention. Like the circuit of FIG. 4, the circuit of this figure is a circuit for driving a three-phase brushless motor or the like used in an optical disk system or the like.

The circuit of this embodiment is composed of the position detection signal synthesizing unit 1
0, a voltage conversion unit 12, three upper and lower differential distribution circuits 14, and an output circuit 16. The circuit of this embodiment is different from the circuit of the conventional example in that a saturation control differential distribution circuit 66 is further provided. Saturation control differential distribution circuit 66
Is a differential setting of the current distribution ratio between the current source for supplying the driving current to the source side output transistors Q1, Q3 and Q5 and the current source for supplying the driving current to the sink side output transistors Q2, Q4 and Q6. It is a circuit to do. The saturation control differential distribution circuit 66 includes a differential circuit 68 and current mirror circuits 70, 72 and 74.

Transistor Q1 forming the differential circuit 68
Among 3 and Q14, the voltage applied to the base of the transistor Q13 is the lowest output voltage value detected by the diode group 76. When the output circuit 16 is used in the lower saturation, that is, the sink side output transistor Q2,
When Q4 and Q6 are driven in a saturated state, the voltage applied to the base of the transistor Q13 represents the lowest value among the collector voltages of the sink side output transistors Q2, Q4 and Q6.

Transistor Q1 constituting the differential circuit 68
Of 3 and Q14, the voltage applied to the base of the transistor Q14 is the saturation control voltage. In this embodiment, a voltage applied to the feedback resistor Rf, that is, a voltage proportional to the output current of the output transistors Q1 to Q6 is used as the saturation control voltage. However, it is sufficient to control the saturation control voltage to be slightly higher than the saturation voltage actual value indicated by the solid line with respect to changes in the output current, as indicated by the broken line in FIG. By controlling the saturation control voltage in this manner, oversaturation of the saturation side output transistors (sink side output transistors Q2, Q4 and Q6 in this embodiment) can be prevented within the control range by the operation described later. Therefore, a voltage other than the voltage across the resistor Rf may be used.

One of the output side transistors of the current mirror circuit 70 is connected to the emitter side of the transistors Q13 and Q14. Current mirror circuit 70
Is an input side transistor Q15, which is supplied with the output current of the current feedback amplifier 64, and transistors Q13 and Q1.
4 is composed of an output side transistor Q16 for supplying a current to No. 4, an output side transistor Q17 for supplying a bias current to the current mirror circuit 72, and an output side transistor Q18 for supplying a bias current to the current mirror circuit 74.

On the other hand, the input of the current mirror circuit 72 is connected to the collector side of the transistor Q13, and the input of the current mirror circuit 74 is connected to the collector side of the transistor Q14. The output of the current mirror circuit 72 is the output transistors Q1, Q3 and Q5 on the source side.
Is connected to transistors Q7, Q9 and Q11 for supplying a drive current to the sink side output transistors Q2, Q4 and Q6 via the current mirror circuit 78. Are connected to transistors Q8, Q10 and Q12.

Therefore, the saturation side output transistor Q2,
When the saturation of either Q4 or Q6 progresses, the base voltage of the transistor Q13 decreases and the input current of the current mirror circuit 72 increases. Therefore, in the conventional example of FIG. 4, the current Id1 increases. Become. As a result, the drive currents of the source side output transistors Q1, Q3 and Q5 increase, and the source side output transistors Q1, Q3 and Q5.
Sink side output transistors Q2, Q4 and Q6 for
The overdrive ratio (ratio of drive current) of is decreased. In other words, the saturation of the sink-side output transistors Q2, Q4, and Q6 is suppressed, and the saturation control voltage is balanced. As a result, the linearity of hfe of the output transistors Q1 to Q6 becomes substantially the same on the source side and the sink side, and the output current waveform Is, for example, as shown in FIGS. 5 (a) and 5 (b),
The waveform has less distortion. As a result, the driving noise of the motor is reduced.

Furthermore, since the saturation control voltage is controlled according to the output currents of the output transistors Q1 to Q6,
As shown in FIG. 2, as long as the saturation control voltage exceeds the saturation voltage, in other words, as long as the output current is within the predetermined range, the above-described effect of reducing distortion can be secured.

In addition, in this embodiment, the current mirror circuit 70 is different from the current mirror circuits 72 and 74.
Bias current is supplied from. Transistor Q1
7 and Q18 have an emitter area which is n times as large as that of the transistor Q15. Therefore, the bias current is n times as large as the output current of the current feedback amplifier 64. This bias current is applied to the source side output transistors Q1, Q3 and Q5 and the sink side output transistor Q, especially in the case of large current drive.
2, it has the effect of limiting the current distribution ratio to Q4 and Q6.

For example, when the motor efficiency is to be increased, the saturation control voltage is set to a value close to the saturation voltage as shown by the broken line in FIG. In such a setting, the saturation control voltage is equal to the saturation voltage V when the output current Io is large.
It is equal to or higher than sat. In the case of such a large current drive,
It is difficult to limit the current distribution ratio only by the differential distribution by the differential circuit 68. Therefore, in the present embodiment, a bias current that is n times the output current of the current feedback amplifier 64, that is, a bias current according to the value of the output current Io is added to the output current from the differential circuit 68. By doing so, even in the case of driving with a large current, the output transistors Q2, Q
4 and Q6 are less likely to be oversaturated, and drive noise can be reduced. The mirror ratio n can be appropriately selected and set.

Although the energization method is not mentioned in the above description of the embodiments, it can be applied to any of 120 ° soft switching, 180 ° trapezoidal wave energization and the like. Further, the present invention can be applied not only to lower saturation but also to upper saturation. In that case, the maximum value of the output voltage is detected instead of the minimum value.

[0030]

As described above, according to the present invention,
To prevent the saturation side output transistor from becoming oversaturated,
Since the current distribution ratio to the output transistor is feedback-controlled by using the saturation control voltage which is controlled slightly higher than the saturation voltage of the output transistor, the distortion at the output current switching without adding the midpoint feedback, and by extension, the motor Driving noise can be suppressed.

Further, since the bias current having a value corresponding to the output current of the output transistor is supplied to the current source related to the current distribution to the output transistor, the output current is large in the region where the saturation control voltage ≦ saturation voltage. The current distribution ratio can be limited, and the driving noise can be further reduced.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a control content of a saturation control voltage in this embodiment.

FIG. 3 is a diagram showing a region where saturation control voltage ≦ saturation voltage.

FIG. 4 is a circuit diagram showing a configuration of a motor drive circuit according to a conventional example.

FIG. 5 is a diagram for explaining a problem in this conventional example by taking an example of energization by 120 ° soft switching, and FIGS. 5A and 5B show an ideal drive current waveform.
(C) and (d) show the drive current waveform at the time of upper saturation.
(E) And (f) is a figure which shows the drive current waveform at the time of lower side saturation about 1 phase and 3 phases, respectively.

[Explanation of symbols]

10 Position Detection Signal Synthesizer 12 Voltage Converter 14 Upper and Lower Three Differential Distribution Circuit 16 Output Circuit 42, 44, 46 Motor Coil 64 Current Feedback Amplifier 66 Saturation Control Differential Distribution Circuit 68 Differential Circuit 70, 72, 74, 78 current mirror circuit 76 diode group Q1, Q3, Q5 source side output transistor Q2, Q4, Q6 sink side output transistor Q7, Q9, Q11 source side current distribution transistor Q8, Q10, Q12 sink side current distribution transistor Q13, Q14 Transistor of differential circuit Rf Feedback resistance n Mirror ratio (for bias current supply)

Front page continuation (72) Inventor Yutaka Kamoki 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (1)

[Claims] 1. An output circuit that has a source-side output transistor and a sink-side output transistor for each phase and outputs a current to a corresponding motor coil from a connection point of the output transistors of each phase, and a source-side output transistor and a sink-side A distribution circuit that distributes the current of the current source corresponding to each output transistor to each output transistor as a drive current,
A motor drive circuit comprising: current feedback means for setting the current value of each of the current sources according to the output current of the output transistor, and driving either the source side output transistor or the sink side output transistor in a saturated state, The current feedback means detects the minimum value or the maximum value of the output voltage from the output circuit to the motor coil, thereby detecting the minimum value of the collector-emitter voltage of the output transistor used in the saturated state; Means to compare the output voltage with the saturation control voltage that is controlled slightly higher than the saturation voltage so that the output transistor is not oversaturated, and the ratio of the drive current of the source side output transistor to the drive current of the sink side output transistor is sufficient. And a means for setting the current value of each of the current sources according to the comparison result so as to be close to 1. In the path, the motor drive circuit is provided with means for supplying a bias current having a value corresponding to the output current of the output transistor to each of the current sources.