JPS6011549B2 - Small DC motor speed control device - Google Patents

Description

[Detailed Description of the Invention] The present invention compares the back electromotive force generated by the rotation of the motor with a reference voltage, detects the difference voltage, controls the DC motor drive transistor, and keeps the motor rotation speed constant. The present invention relates to a speed control device for a small DC motor, and its purpose is to prevent irregularities in the input current to the differential amplifier that constitutes the speed control device.

In recent years, this type of speed control device has also been integrated into semiconductor integrated circuits, and as an example, a configuration as shown in FIG. 1 has been put into practical use.

The configuration will be explained below based on the drawings. The circuit part within the dotted line frame is a semiconductor integrated circuit, and has four external lead-out terminals 1, 2, 3, and 4, and between terminals 1 and 2. is connected to the resistor 5 as an external passive circuit element, and the terminal 2
, 3, a variable resistor 6 for speed adjustment is connected between the terminals 4 and 3.
is grounded.

Further, a DC motor 8 is connected between terminal 1 and terminal 3 which are connected to power supply terminal 7 . On the other hand, inside an integrated circuit,
A first NPN transistor 11 whose emitter is connected to the terminal 2 via two NPN transistors 9 and 10 whose collectors are Darlington-connected, and whose base is commonly connected to the first transistor 11 and which conducts current. NPN type DC motor driving transistors 12 and 13 forming a mirror, having collectors connected to terminal 3 and emitters grounded, and emitters having opposite polarity to the first transistor 11 and DC motor driving transistors 12 and 13; A pair of PNPs constituting a differential amplifier that are commonly connected and have one base connected to the collector of the DC motor drive transistors 12 and 13 and the other base connected to the reference voltage source 14.
Transistors 15 and 16 and a pair of NPN transistors 17 whose bases are commonly connected to form a current mirror.
, 18, a second NPN transistor 19 whose collector is connected to the terminal 1', whose emitter is grounded and connected to the base of the first transistor 11, and whose emitter is connected to the base of the second transistor 9. A third transistor 20 of PNP type is connected to the transistor 16, the base of which is connected to the collector of the transistor 16 constituting the differential amplifier, and the collector of which is grounded. Note 21, 22
, 23, 24 are constant current sources, in which constant current i is supplied from constant current source 21, constant current i2 is supplied from constant current source 22, constant current source 2
3, a constant current i3 is applied to each of them. In the above configuration, the constant current i3 from the constant current source 23 becomes the input current to the differential amplifier, and the voltage difference between the reference voltage and the back electromotive force generated at the terminal 3 due to the rotation of the DC motor 8 causes Current flows through either.

The emitter current of the third transistor 20 changes depending on the voltage drop and the cap voltage obtained by subtracting the base-emitter voltage of the transistors 15 and 16. As a result, the emitter current of the second transistor 19 changes, and the emitter current of the second transistor 19 changes. DC motor drive transistors 12, 1 including transistor 11
Drive 3. In this case, when considering the emitter current i of the third transistor 20, it is considered that the total current flowing through the output stage transistors 11 to 13 is approximately ia. The second transistor 19 is a base current supply source for the output stage transistors 1 to 13, and its current value needs to be ia/hFE,2. Furthermore, the base current of the second transistor 19 is (111/hFE
, 2)・ia/hF8.2・hF8,9 is required.

Further, the source of the base current of the second transistor 19 is i
, and since it is a constant current, the current value must be satisfied even when ia is at its maximum. On the other hand, the base of the third transistor 20 is connected to the collector of the transistor 17, and i, is connected to the emitter of the third transistor 20 through the base of the transistor 1 of the differential amplifier.
7 as the collector current i,/hF82. only flows.
If the collector current of transistor 17 is ia, then i4
The following relationship holds true: =j60i,/hF8,6. Here, since the transistors 17 and 18 have a common base and form a current mirror circuit, i4=i5. If i4=i5, the input current of the differential amplifier formed by the constant current source 23, transistors 15, 16, 17, 18, and resistors 25, 26, i.e., . Comparing the collector current j7 of the transistor 15 and the collector current i6 of the transistor 4, since i6=i40h;
i6 must be reduced by 4.times. by the amount of current flowing from the base of transistor 20.

Currents having different current values flow through the resistors 25 and 26 from the current i3 flowing from the constant current source 23. Assuming that the VBEs of transistors 15 and 16 are approximately the same, the base voltages of transistors 15 and 16 will be different. Here, the base voltage of transistor 16 becomes high. This voltage difference is caused by a voltage drop caused by the resistors 25 and 26, and this appears as an imbalance in the differential amplifier. These resistors 25 and 26 are large relative to temperature fluctuations, and depending on the positional relationship when used as an IC, the influence may be very large.

When considering the influence on temperature, the motor characteristics have a negative effect on the rotation speed. Assuming that the input voltages of the duty amplifier are equal, Ea+ia・Ra;R,・iT0R
s･is...mVref=Rs･is
……■Ea=Ka・N
......[3'Ea: Motor back electromotive force, ia: Motor armature current, Ra: Motor armature resistance value, RT・Rs: Resistance value of resistors 5 and 6, N:
Motor rotation speed, Vref; reference voltage, i.・is: Current value holds true.

If unbalanced, [Formula 2' is Vref=Rs・is+Q
(Q is the voltage imbalance) Therefore, if Q fluctuates,
Ea will vary, and the rotation speed N will be affected according to equation {31. According to the measured results, the change in motor rotational speed due to temperature is as shown in A in FIG. 2. It should be noted that the hF in the current circuit is about 10, which corresponds to A in FIG. The present invention has been made in view of the above-mentioned drawbacks, and as shown in FIG. h as a whole
It is a higher version of F8.

That is, the collector of the third transistor 20 is ungrounded, the collector is connected to the base of the fourth transistor 27, the emitter of the fourth transistor is grounded, and the emitter of the third transistor 20 and the fourth transistor are connected to each other. The collector of the transistor 27 is connected thereto. In this case, the overall hP8 will be 50 pseudostellar degrees, and its temperature characteristics will be as shown in FIG. 2B. FIG. 4 shows another embodiment of the present invention, in which a vertical PNP transistor is used as the third transistor 20. In this case, hFE is 5 beats, as shown by C in FIG. Becomes a characteristic.

Note that the collector current i of the transistors 15 and 16 of the differential amplifier when changing hF8 of the third transistor 20
6. According to experiments, the relationship with i7 was as follows.
From the above experimental results, the hFE of the third transistor 20
It was confirmed that the unbalance of the difference amplifier can be reduced by increasing the

As is clear from the above explanation, according to the present invention, the rate of change of the motor with respect to temperature is reduced, a stable rotational speed is ensured at each temperature, and a stable rotational speed is obtained even when the motor is operated for a long time. It will be done.

In addition, oscillation due to system instability caused by unbalance of the differential amplifier is also reduced at the same time.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a conventional speed control device for a small DC motor, Fig. 2 is a temperature-rotation speed change rate characteristic diagram when the third transistor is different from hF8, and Fig. 3 is a diagram of the speed control device of the present invention. Circuit Diagram According to the Embodiment FIG. 4 is a circuit diagram according to another embodiment of the present invention. 5...Resistor, 7...Power terminal, 8...
...DC motor, 11...first transistor, 1
2, 13...Motor for driving a DC motor, 14...Reference voltage source, 15, 16...Transistor constituting a differential amplifier, 19...Second transistor, 20...
...Third transistor, 27...Fourth transistor. Figure 2 Figure 1 Figure 4 Figure 3

Claims (1)

[Claims] 1. A first transistor whose collector is connected to a power supply terminal via a resistor and whose emitter is grounded, and whose base is commonly connected to the first transistor to form a current mirror, and whose collector is connected to the power terminal via a resistor and whose emitter is grounded. A DC motor driving transistor is connected to the power supply terminal via the DC motor and has an emitter grounded.The emitter is commonly connected, one base is connected to the collector of the DC motor driving transistor, and the other base is connected to the resistor. a differential amplifier consisting of a pair of transistors of opposite polarity to the DC motor drive transistor, each connected to a reference voltage source connected to a power supply terminal via the DC motor drive transistor;
a second transistor whose collector is connected to the power supply terminal, whose emitter is grounded and connected to the bases of the first transistor and the DC motor drive transistor; and whose emitter is connected to the power supply terminal via a constant current source. a PNP type third transistor whose base is connected to the base of the second transistor and whose base is connected to the collector of one of the transistors constituting the differential amplifier; and whose base is connected to the collector of the third transistor. and a fourth NPN transistor whose collector is connected to the emitter of the third transistor and whose emitter is grounded. 2. A first transistor whose collector is connected to the power supply terminal via a resistor and whose emitter is grounded, and whose base is commonly connected to the first transistor to form a current mirror, and whose collector is connected to the power supply terminal via a DC motor. A DC motor drive transistor connected to a terminal and whose emitter is grounded, and a reference whose emitter is commonly connected, one base is connected to the collector of the DC motor drive transistor, and the other base is connected to the power supply terminal via the resistor. a differential amplifier consisting of a pair of transistors of opposite polarity to the DC motor driving transistors each connected to a voltage source; a differential amplifier having a collector connected to a power supply terminal and an emitter grounded; A second transistor connected to the base of the driving transistor and an emitter connected to the power supply terminal via a constant current source and connected to the base of the second transistor, the base forming a differential amplifier. and a third transistor of a vertical PNP type, the collector of which is connected to the collector of one of the transistors, and whose collector is grounded.