JPH05958B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a motor drive control circuit suitable for controlling the speed of a DC motor such as a micromotor.

Conventional Structure and Problems The drive control circuit for a DC motor such as a micromotor usually uses a circuit system in which the rotational speed is controlled by controlling the current of a drive transistor.

FIG. 1 shows an example of a conventional circuit, in which the area indicated by the broken line is integrated into an integrated circuit and formed on a single semiconductor chip. And from the integrated circuit section,
A power supply terminal 1, first and second control terminals 2 and 3, a motor connection terminal 4, and a ground terminal 5 are provided as external terminals. Then, the DC motor 6 is externally connected between the power supply terminal 1 and the motor connection terminal 4,
A first resistor 7 is externally connected between the power supply terminal 1 and the first control terminal 2, and a second resistor 8 is externally connected between the first control terminal 2 and the second control terminal 3. Ru.

Next, inside the integrated circuit, a reference voltage section 1 generates a constant voltage by supplying current from a constant current source 9.
0 and connected to the output of the reference voltage section 10, a transistor 14 connected to its output, and a resistor 13 connected to its emitter.
The circuit constituted by the circuit constitutes a negative feedback type constant current source, and outputs a highly accurate constant current from the collector of the transistor 12. Then, this constant current output is supplied to the first and second resistors 7 and 8 via the second control terminal 3, and a constant voltage is generated between the terminals of the second resistor 8.

A transistor 14 whose emitters are commonly connected,
15 constitutes a differential amplification section, in which a current source 16 is connected to the common emitter connection point, current mirror circuits 17 and 18 are connected to the collector of the transistor 15, and a current source 19 is connected to the load circuit. By providing a transistor 20 for an emitter follower, a high gain amplifier is constructed, and the transistor 14
The reference voltage of the second control terminal 3 is input to the base of the resistor 30, 3, and the voltage between the terminals of the DC motor 6 is
The voltage divided by 1 is input to the base of the transistor 15, the back electromotive force Ea of the DC motor 6 is compared with the reference voltage, and the error voltage is amplified.

The emitter of the emitter follower transistor 20 is connected to the base common connection point of the transistors 21 to 24 and a load resistor 25, and the resistors 26 to 29 are connected between the emitters of the transistors 21 to 24 and the ground potential, respectively. be done.

Then, the transistors 21 to 24 and the resistor 2
6 to 29 are composed of elements with the same characteristics, and are set so that each collector current flows equally, ensuring a relative ratio between the collector current of the first transistors 22 to 24 and the collector current of the second transistor 21. , the first transistors 22 to 24 drive the DC motor 6 connected to their collectors with a large current.

Further, the collector current of the second feedback transistor 21 is applied to the first resistor 7 via the first control terminal 2, and a voltage corresponding to the voltage drop across the internal resistance of the DC motor 6 is applied to the terminal of the resistor 7. occur in between,
The voltage is fed back to the second control terminal 3 (reference potential side input terminal) of the differential amplifier section.

In the conventional example with such a configuration, the rotational speed of the DC motor 6 is controlled as follows.

The basic operation is that the differential amplifiers 14 to 18 compare the back electromotive force Ea of the DC motor 6 and a reference voltage (voltage drop across the second resistor 8), and the first transistors 22 to 24 compare The DC motor 6 is driven with a current according to the output voltage. However, since the voltage drop due to the internal resistance of the DC motor 6 causes a loss, the first
The relative ratio of the collector currents of the transistors 22 to 24 and the second transistor 21 is set, and a voltage drop corresponding to the voltage drop due to the internal resistance of the DC motor 6 is generated between the terminals of the first resistor 7, is applied to the second control terminal 3 in addition to the reference voltage, and the differential amplifiers 14 to 18 compare the back electromotive force Ea and the reference voltage and control the back electromotive force Ea and the reference voltage so that they match. be done.

Then, if the rotational speed of the DC motor 6 increases beyond a predetermined value, the back electromotive force Ea of the DC motor 6
increases accordingly, and the midpoint potential divided by resistors 30 and 31 decreases. Then, the differential amplifier section compares the midpoint potential with the potential of the second control terminal 3, and if the midpoint potential is lower than the potential of the second control terminal 3, the output of the differential amplification section is (Collector of transistor 18) voltage decreases, reducing the drive current of the first transistors 22 to 24, and controlling the rotational speed of the DC motor 6 in a decreasing direction.

On the other hand, if the rotational speed of the DC motor 6 decreases below the predetermined value, the back electromotive force Ea of the DC motor 6
becomes smaller accordingly, and the midpoint potential divided by the resistors 30 and 31 rises. Then, the differential amplifier section compares the midpoint potential with the potential of the second control terminal 3, and if the midpoint potential is higher than the potential of the second control terminal 3, the output of the differential amplification section is The voltage (at the collector of the transistor 18) increases, increasing the drive current of the first transistors 22 to 24, and controlling the rotational speed of the DC motor 6 in an increasing direction.

That is, the feedback loop of the differential amplifiers 14 to 18, the first transistors 22 to 24, and the voltage dividing circuit of the resistors 30 and 31 forms a negative feedback, and the back electromotive force Ea and the reference voltage are set to a predetermined value. The drive control circuit stabilizes the rotational speed of the DC motor 6 so that the rotational speed of the DC motor 6 coincides with the rotational speed of the DC motor 6.

However, the conventional motor drive control circuit has the following problems.

In order to apply the collector current of the transistor 21 to the resistor 7 as a means to generate a voltage corresponding to the voltage lost in the internal resistance of the DC motor 6 between the terminals of the resistor 7, the motor drive control circuit as a whole uses the above-mentioned negative feedback loop. In addition, differential amplifier sections 14 to 18
A positive feedback loop is formed from the output of the transistor 21, the resistor 7, the resistor 8, and the base of the transistor 14. Therefore, if the loss voltage of the internal resistance of the DC motor 6 and the voltage between the terminals of the first resistor 7 are balanced and these voltages are input in phase to both input terminals of the differential amplifier section, the DC The loss voltage of the internal resistance of the motor 6 is not amplified as an error, and the back electromotive force Ea is compared with the reference voltage to operate stably.
However, in order to operate the drivability control circuit stably, the first transistors 22 to 24 and the second transistor 21 are always operated in an active state, and the first transistors 22 to 24 and the second transistor 21 are
h It is necessary to maintain the balance of _FE .

However, when the load torque of the DC motor 6 increases, the collector current of the first transistors 22 to 24 that drive the DC motor 6 is controlled to increase, but the collector current of the second transistor 21 increases accordingly. The collector current increases and the voltage drop across the resistor 7 increases to compensate for the increase in voltage loss due to the internal resistance of the DC motor 6. However, at the same time, the collector potentials of the transistors 22-24 decrease to saturation, and the h _FE of the first transistors 22-24 decreases. As a result, the ratio of the collector currents of the first transistors 22 to 24 becomes smaller than the predetermined ratio of the collector currents of the first transistors 22 to 24 to the collector currents of the second transistor 21. Then, the aforementioned loss voltage compensation due to the voltage drop across the resistor 7 becomes overcompensated, and the amount of positive feedback becomes relatively larger than the amount of negative feedback, causing the entire circuit to oscillate. This phenomenon occurs because the entire circuit operates so that the base potentials of the transistors 14 and 15 are balanced, so the collector potential of the first transistors 22 to 24 is at a low potential, and the collector potential of the second transistor 21 is at a high potential. This is a phenomenon that occurs because the first transistor is likely to reach a saturated state, and is particularly likely to become a problem when operated at a low power supply voltage.

The above-mentioned oscillation phenomenon can be prevented from lowering the loop gain at high frequencies by inserting the capacitor 32 between the first control terminal 2 and the ground potential point. However, it was not possible to prevent disturbances in the rotational speed, and it was not possible to improve the disturbance in the rotational speed when the load torque was large, as shown in characteristic A shown in FIG.

OBJECTS OF THE INVENTION The present invention provides a motor drive control circuit that eliminates disturbances in rotational speed caused by an increase in load torque and performs stable speed control.

Structure of the Invention To summarize, the present invention comprises first and second transistors 22 to 24, 21 of one conductivity type whose bases are commonly connected and whose emitters are commonly connected, and whose emitters are connected to the first and second transistors. 22-24,2
a third transistor 20 of one conductivity type connected to a base common connection point of the first transistor 20; a DC motor 6 connected between the collectors of the first transistors 22 to 24 and the power supply end 1; a first resistor 7 connected to the power supply end 1 and the other end connected to the collector of the second transistor 21; one end connected to the other end of the first resistor 7, and a constant current applied to the other end; A second resistor 8 which generates a constant voltage between the terminals is compared with the potential at the other end of the second resistor 8 and the potential obtained by dividing the voltage between the terminals of the DC motor 6, and a comparison output is generated. differential amplification units 14 to 18 that output the voltage to the third transistor 20 and the base of the transistor 20, and negative feedback from the collectors of the first transistors 22 to 24 to one input terminal (base of 15) of the differential amplification unit. a first feedback loop that connects the collector of the second transistor 21 to the first and second resistors 7,
8 to the other input terminal (14) of the differential amplifier section.
In the motor drive control circuit, a rectifying element 33 that is conductive when the first transistors 22 to 24 are in a saturated state is connected to the first transistor 2.
2 to 24 collectors and the third transistor 2
This is a motor drive control circuit characterized in that the circuit is connected between the base of When the transistors 22 to 24 are about to become saturated, the rectifying element 33 becomes conductive to lower the base potential of the third transistor 20 and prevent the first transistors 22 to 24 from becoming saturated. Thereby, the first transistor 2
2 to 24 and the second _transistor 21 is maintained, the negative feedback loop that compares the back electromotive force Ea of the motor with the reference voltage, and the feedback amount of the positive feedback loop are balanced, and the DC motor 6 Control of rotation speed becomes stable.

DESCRIPTION OF EMBODIMENTS An embodiment of the motor drive control circuit of the present invention will be described below with reference to the drawings.

FIG. 3 is a circuit diagram of the embodiment, and parts having the same functions as those in FIG. 1 are given the same symbols. The difference from the conventional example shown in FIG. 1 is that a rectification control element 33 is connected between the collectors of the first transistors 22 to 24 connected in parallel and the base of the third transistor 20 for emitter follower, and Also, a resistor 34 is connected between the point where the bases of the transistors 22 to 24 are commonly connected and the emitter of the transistor 20.

In the circuit of this embodiment, the action of the rectifying element 33 is such that when the collector potential of the first transistors 22 to 24 decreases and the first transistors 22 to 24 are about to reach a saturated state, the rectifying element 33 conduction. Conversely, the first transistors 22-24
When the collector potential of is high, the rectifying element 33 is cut off.

With such a configuration, the first transistors 22 to
24 is about to reach a saturated state, the rectifying element 33 becomes conductive, and the excess current supplied from the collector of the transistor 18 is grounded through the rectifying element 33 and the collector-emitter circuits of the first transistors 22 to 24. Pass to the potential side. Then, the base potential of the transistor 20 is limited to prevent saturation of the first transistors 22 to 24. Then, the h _FE balance between the first transistors 22 to 24 and the second transistor 21 is maintained, and the
The collector current of the second transistor can be operated at a predetermined ratio, and the feedback amounts of the negative feedback loop and positive feedback loop that compare the back electromotive force Ea of the motor with the reference voltage are balanced, and the DC motor 6 rotates. The speed becomes stable. As a result, in this embodiment, the oscillation prevention capacitor 32 required in the conventional example can be dispensed with.

To describe the operation of the embodiment in more detail by giving a specific example of the rectifying element 33, first, as shown in FIG. 4a,
Diode-connected NPN transistor 35,3
A configuration in which 6 are connected in series will be described.

Differential amplifiers 14 to 18 perform error amplification, and a third emitter follower transistor 20 connected to the output thereof drives the common base of transistors 21 to 24 via a resistor 34. Now, let the base potential of the transistor 20 be V _B20 , the base-emitter voltage of the transistor 20 be V _BE20 , its emitter current I _E20 , the resistance value of the resistor 34 be _R34 ,
If the base-emitter voltage of the transistors 22 to 24 is V _BE22 , then the base potential of the transistor 20, V _B20 , can be expressed as follows.

V _B20 = V _BE20 + I _E20・R ₃₄ + V _BE22 ...(1) Then, while the DC motor 6 is rotating, the load torque of the DC motor 6 increases, and the collector potential of the first transistors 22 to 24 increases. As the transistors 22 to 24 approach saturation,
The rectifying element 33 is electrically connected, and the rectifying element 33 and the first
Excess current supplied from the collector of the transistor 18 is passed to the ground potential side through the collector-emitter circuits of the transistors 22-24.
Then, the base potential of the transistor 20 is limited to prevent saturation of the first transistors 22 to 24. At this time, the voltage between the terminals of the rectifying element 33 is
V ₃₃ and the collector-emitter saturation voltage of the first transistors 22 to 24 is V _CESAT22 , then the terminal voltage V ₃₃ of the rectifying element 33 may be set to satisfy the following equation.

V ₃₃ <V _B20 −V _CESAT22 ...(2) If the rectifying element 33 is a series connection of two diode-connected NPN transistors as shown in FIG. 4a, then the transistor 3
The base-emitter voltage of 5 and 36 is V _BE35 ,
If V _BE36 , the voltage between the terminals of the rectifying element 33 is V ₃₃
is expressed by the following formula.

V ₃₃ = V _BE35 + V _BE36 ...(3) First and second transistors 2 that drive large current
The base-emitter voltage V _BE22 of transistors 1 to 24 is a little larger than the base-emitter voltage V _BE of a normal transistor, but assuming that the V _BE of all transistors is equal, V ₃₃ is the same as that of transistors 22 to 24. The base-emitter voltage V _BE22 of transistor 24 and the base-emitter voltage of transistor 20
It corresponds to the sum of V _BE20 , and it can be seen that the voltage drop I _E20 ·R ₃₄ between the terminals of the resistor 34 should be set to be slightly larger than V _CESAT22 .

Characteristic B in FIG. 2 is a diagram showing the drive characteristic of the DC motor of the above-mentioned example circuit, and the range of load torque that can control a constant rotational speed is smaller than that of characteristic A of the conventional example. However, even without the oscillation prevention capacitor 32 required in the conventional example, the oscillation phenomenon and rotational speed disturbance are eliminated.

Next, another embodiment of the present invention shown in FIG. 4b will be described. In FIG. 4b, Darlington-connected transistors 35 and 36 are diode-connected. In this configuration, since the emitter current of the transistor 35 becomes the base current of the transistor 36, the V _BE of the transistor 35 is smaller than that of the transistor 36, and the voltage drop is smaller than that of the diode-connected structure shown in FIG. 4a. This further satisfies the condition of equation (2). Furthermore, if the voltage between the terminals of the rectifying element 33 in FIG. 3 is within a range that satisfies equation (2), the resistor 34 can be made unnecessary. That is, the resistor 34 is for suppressing the base current of the transistors 22 to 24, and is set in consideration of the voltage between the terminals of the rectifying element 33.
The voltage between the terminals of the rectifying element 33 is (V _BE20 +V _BE22 )
If the resistor 34 is smaller than that, it becomes possible to reduce the base current of the transistors 22 to 24 even if the resistor 34 is removed, and by removing the resistor 34, it becomes possible to operate under a low power supply voltage condition.

FIGS. 4C and 4B show a structure capable of achieving a high withstand voltage, and is a diode-connected structure in which PNP transistors 37 and 38 are coupled in two stages. A PNP transistor in a bipolar integrated circuit uses a transistor with a horizontal structure in which its base region is also the collector region of an NPN transistor, so the reverse breakdown voltage between the emitter and base is equivalent to the collector-base breakdown voltage of an NPN transistor. death,
Motor drive control becomes possible even with a fairly high power supply voltage.

Note that the rectifying element 33 can also operate with a single diode configuration, but in that configuration, the base current of the first transistors 22 to 24 is significantly limited.
Cannot obtain large drive current. However, the configuration of two diodes requires that the first transistors 22 to 24
It is advantageous to connect two diodes in series because the collector-emitter voltage of can operate close to V _CESAT22 and can operate over a wider range than a configuration with one diode.

Effects of the Invention As explained above, the motor drive control circuit of the present invention prevents the first transistor from becoming saturated when the first transistor that drives the DC motor operates at maximum torque, The negative feedback loop that compares the back electromotive force of the motor with the reference voltage and the positive feedback loop have the special effect of eliminating imbalance in the amount of feedback and stabilizing the rotational speed of the DC motor at maximum torque.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a conventional motor drive control circuit.
Fig. 2 is a diagram for explaining the control characteristics of the rotation speed, Fig. 3 is a configuration diagram of a motor drive control circuit according to an embodiment of the present invention, and Fig. 4 is an equivalent circuit of a rectifying element used in the embodiment. It is a diagram. 6...DC motor, 10...Reference voltage section, 11
...Amplifier, 12, 14, 15, 17, 18, 2
0 to 24... NPN transistor, 33... Rectifying element, 34... Resistor, 37, 38... PNP transistor.

Claims (1)

[Claims] 1. First and second transistors 22 of one conductivity type whose bases and emitters are respectively commonly connected.
~24, 21, and the emitters are the first and second transistors 22.
A third transistor 20 of one conductivity type connected to the base common connection point of the first transistors 24 and 21; a DC motor 6 connected between the collectors of the first transistors 22 to 24 and the power supply end 1; a first resistor 7 whose one end is connected to the power source end 1 and whose other end is connected to the collector of the second transistor 21; A second resistor 8 is supplied with a constant current and generates a constant voltage between its terminals. The potential at the other end of the second resistor 8 is compared with the potential obtained by dividing the voltage between the terminals of the DC motor 6. death,
Differential amplifiers 14 to 18 that output comparison outputs to the bases of the third transistors 20, and terminals from the collectors of the first transistors 22 to 24 to one input end (base of 15) of the differential amplifiers. A first feedback loop that provides negative feedback; and positive feedback from the collector of the second transistor 21 to the other input terminal (base of 14) of the differential amplifier section via the first and second resistors 7 and 8. Second to do
In the motor drive control circuit, a rectifying element 33 that becomes conductive when the first transistors 22 to 24 are in a saturated state connects the collectors of the first transistors 22 to 24 and the third transistor. 20. A motor drive control circuit characterized in that the circuit is connected between the base of the motor drive control circuit and the base of the motor drive control circuit. 2. The motor drive control circuit according to claim 1, wherein the rectifying element 33 is composed of two diodes connected in series.