JPH084391B2 - DC motor speed control device - Google Patents

Description

The present invention relates to a multi-stage speed control device for a small DC motor capable of stepwise switching the rotation speed of a DC motor connected to a DC motor speed control IC. It is a thing.

[Conventional technology]

A conventional speed control device for a small DC motor, for example, a speed control device for a small DC motor disclosed in Published Utility Model Application 56-73195, has a structure as shown in FIG.

In FIG. 2, 2 is an IC for speed control of a small DC motor
2 shows an external circuit connected to 2.

The direct current motor speed control IC 2 is provided with a reference terminal 1, a detection terminal 2 for detecting the equivalent voltage of the back electromotive force E ₀ , an output terminal 3, and a grounded terminal 4. Hereinafter, for convenience of explanation, the terminals 1 to 4 are sequentially arranged in order of the first, second, third, and fourth terminals.
I'll call it the terminal.

The shunt transistor is connected to the first terminal 1.
This shunt transistor is connected to the collector of Q _1.
The emitter of Q ₁ is connected to the fourth terminal 4 via the resistor R ₁ . The collectors of the plurality of drive transistors Q _{2 to} Q _n are connected to the third terminal 3, and the emitters of the plurality of transistors Q _{2 to} Q _n are resistors.
It is connected to the fourth terminal 4 via R _{2 to} R _n . The bases of these transistors Q ₁ , Q ₂ , ..., Q _n are respectively connected to the output terminals of the error detection circuit 2a. The error detection circuit 2a controls the transistors Q ₁ , Q ₂ , ..., Q _n by the potential difference between the input terminals B and C, and the current flowing from the first terminal 1 to the fourth terminal 4 through the resistor Rt. It and the current Ia flowing from the third terminal 3 to the fourth terminal 4 through the DC motor M are adjusted. A reference voltage source Eref is provided between the input terminal of the error detection circuit 2a and the first terminal 1, while the input terminal C of the error detection circuit 2a is connected to the second terminal 2. .

The speed control IC 2 having four terminals is configured as described above, and the external circuit 3 is connected to the speed control IC 2.

A DC motor M represented by an internal resistance R ₀ and a back electromotive force Eo is connected to the power supply terminal V _CC and the third terminal 3, and a resistance is connected to the power supply terminal V _CC and the first terminal 1. Rt is connected. Further, the first terminal is connected to the second terminal via the switch S ₁ .
A plurality of voltage dividing resistors Ra ₁ , Ra ₂ , Ra ₃ respectively connected to the terminal 2 and the voltage dividing resistor Rb are connected. By this plurality of voltage dividing resistors Ra _1, Ra _2, Ra ₃ and dividing resistor Rb, a plurality of voltage dividing circuit is configured, the dividing resistors Ra _1, Ra _2, Ra ₃ and dividing resistor Rb A voltage division ratio changeover switch S ₁ is interposed between and.
The rotation speed N of the DC motor M can be changed stepwise by operating the switch S ₁ .

Hereinafter, the rotation speed N in the case of the rotation speed control device having the above configuration will be described based on an equation.

Generally, the counter electromotive force Eo of the DC motor M and the rotation speed N have a relationship of Eo = N · K ₂ Zφ (2) K ₂ ... proportional constant.

In addition, the current Ia flowing through the DC motor M and the DC motor M
There is a relationship of Td = K ₁ Zφ · Ia …… (3) K ₁ …… proportional constant with the load torque Td applied to.

The voltage Vm across the DC motor M and the DC motor M
The relationship of Vm = Eo + RoIa (4) holds with the current Ia flowing through the.

Then, a current It corresponding to the ratio of the width increase of the shunt transistor Q _{1 to} the width increase of the drive transistors Q ₂ , ..., Q _n flows through the resistor Rt due to the speed control IC ₂ . Where K is K, the relationship Ia = K · It (5) holds between the current It and the current Ia.

When the rotation speed of the DC motor M is correctly controlled, it can be considered that the input terminals BC of the error detection circuit 2a are short-circuited.

Is = Eref / Ra ₁ (6) However, Is passes through resistor Ra ₁ and switch S ₁ and voltage dividing resistor Rb
Is the current that flows through.

On the other hand, in the fixed resistor Rt, the current Is flowing through the voltage dividing resistor, the minute bias current Ir that operates the speed control IC 2 and the current It flowing through the drive transistor Q ₁ flow, so the power supply terminal V _CC and the error detection are detected. Voltage V _AB between input terminal B of circuit Ia
V _AB = Eref + (Is + Ir + It) ・ Rt …… (7 ′) Currents Is and Ir can be regarded as minute compared to the current It. Therefore, formula (7 ′) is V _AB ＝ Eref + It ・ Rt …… (7)

On the other hand, in the voltage V _AC between the power supply terminal V _CC and the input terminal C of the error detection circuit 2a, the current Ia flows through the resistor Ro and the current Is flows through the resistor Rb, so V _AC = Eo + Ia · Ro− Rb · Is (8 ′) By transforming (8 ′) using Eq. (6), we obtain V _AC = Eo + Ro · Ia−Rb · Eref / Ra ₁ (8).

Since the voltage V _AB is equal to the voltage V _AC , the formulas (7) and (8) are obtained.

Eo = Eref (1 + Rb / Ra ₁ ) + It · Rt−IaRo (9) Then, by deleting It in equation (9) using equation (5), Eo = Eref (1 + Rb / Ra ₁ ) + (Rt / K−Ro) Ia ・ ・ ・ (10) is obtained.

 Also, the resistance Rt and the internal resistance Ro of the motor are set to the relationship of Rt = KRo (11).

By applying the equations (2), (3) and (11) to the equation (10), the following control equation for the rotational speed N can be obtained.

When the voltage dividing resistor Ra ₂ and the voltage dividing resistor Rb constitute a voltage dividing circuit by switching the switch S ₁ , the control expression of the rotation speed N ′ is Becomes

Similarly, when the voltage dividing circuit is composed of the voltage dividing speed Ra ₃ and the voltage dividing resistor Rb, the control formula of the rotation speed N ″ is Becomes

Therefore, when resistors having different resistance values are used for the voltage dividing resistors Ra ₁ , Ra ₂ , and Ra ₃ , since the voltage dividing ratios of the voltage dividing circuits are different from each other, by switching the switch S ₁ , The rotation speed N has been switched.

In the case of the conventional example shown in the figure, even if the voltage dividing resistor Rb is a resistor having a large value of the temperature coefficient of resistance, the voltage dividing resistors Ra ₁ , Ra ₂ and Ra ₃ are substantially divided by the voltage dividing resistors Rb. If resistors with the same temperature coefficient of resistance are used, Rb / Ra can be calculated as Rb / Ra in the first term of equations (12), (13), and (14).
Since the a and the resistance Rb are expressed, it is possible to cancel the change in the resistance value due to the temperature fluctuation, so that the rotation speeds N, N ′, and N ″ are stable regardless of the temperature fluctuation.

Furthermore, in the case of this embodiment, when changing the speed of the rotation speed N, switched by the voltage dividing resistors Ra ₁ of the switch S _1,
Even if the connection between Ra ₂ and Ra ₃ and the voltage dividing resistor Rb is cut off, the second
Since the terminal 2 of is connected to the voltage dividing resistor Rb, the internal impedance of the error detection circuit 2a is high, so that the noise fluctuation generated in the error detection circuit 2a can be prevented when the second terminal 2 floats in a circuit. .

In this way, a stable multi-stage speed control device for a small DC motor could be constructed.

[Problems to be solved by the invention]

As described above, although a multi-stage speed control device for a small direct current motor that has been stabilized against temperature has been obtained in the past, there is a problem in that the load torque characteristic deteriorates when the rotation speed is switched and increased. It was FIG. 3 shows the characteristics of the rotational speed versus the load torque for two types of rotational speed settings. As shown in FIG. 3, in the conventional example, when the rotation speed was set faster, the load torque characteristic was significantly deteriorated.

This is equivalently because the internal resistance Ro of the motor is not a constant value but increases with the rotation speed. This is shown in FIG. That is, FIG. 4 shows that the internal resistance R0 of the DC motor increases as the rotation speed of the DC motor increases. When the internal resistance Ro of the motor increases, the rotation speed decreases as shown in expressions (12) to (14), and the load torque Td decreases the rotation speed.

[Means for solving problems]

The multi-stage speed control device for a small DC motor according to the present invention has means for switching the resistance Rt connected between the first terminal and the power supply terminal V _CC to the setting of the rotation speed in order to solve the above-mentioned drawbacks. There is.

〔Example〕

FIG. 1 shows an embodiment of the present invention. The resistor Rt connected between the first terminal 1 and the power supply terminal is replaced with the switch S ₂ which is interlocked with the switches S ₁ and Rt ₁ , Rt ₂ , Rt ₃ in comparison with the conventional example shown in FIG. The only difference is that the others are the same.

FIG. 5 shows another embodiment of the present invention. In the circuit diagram, the operation is the same as the conventional example of FIG. 1 except that the switch S ₁ position is changed. However, the rotation speed changeover switch S ₁ , S ₂
The second terminal 2 has a high impedance and the effect of being able to reduce the wire necessary for pulling out the wire for a long time.
Since it does not need to be routed directly, it has the advantage of being less susceptible to external noise.

FIG. 6 shows the characteristics of the multi-stage speed control device for a small DC motor according to the present invention.

〔The invention's effect〕

As described above, according to the present invention, there is an effect that the load characteristics can be prevented from deteriorating even if the rotation speed of the motor is increased.

In addition, in FIG. 1, the (+) terminal of the circuit 2a may be connected to the terminal to eliminate the need for the terminal.

[Brief description of drawings]

FIG. 1 is an embodiment diagram of the present invention, FIG. 2 is a conventional example diagram, FIG. 3 is a load characteristic diagram of a conventional example, and FIG. 4 is an internal resistance of a motor.
FIG. 5 is a diagram showing the relationship between Ro and rotation speed, FIG. 5 is a diagram of another embodiment of the present invention, and FIG. 6 is a load characteristic diagram of the present invention. 2 ...... rate controlling IC, 2a ...... error detection circuit, 3 ...... external circuit, M ...... miniature DC motor, Ra _1, Ra _2, Ra _3, Rb ...... dividing resistors, Rt, Rt _1, Rt ₂ , Rt ₃ …… Fixed resistance, Eref …… Reference voltage source.

Claims (2)

[Claims] 1. A first node connected to a DC motor having an internal resistance; a first drive unit connected to the first node for driving the DC motor according to a control signal; A first resistance circuit connected between the node and the second node, each of which has a resistance value for setting a predetermined operating speed of the DC motor, A first resistance circuit having a first switch for selectively electrically connecting the plurality of first resistance paths between the first node and the second node; and the second node A second resistance circuit connected between the power supply and a power source, the second resistance circuit having a resistance value proportional to the internal resistance of the DC motor according to each set operating speed of the DC motor. A resistance path and the plurality of second resistance paths selectively to the power source and the second node A second resistance circuit having a second switch electrically connected between the second drive circuit and a second drive circuit connected to the second node and supplying a current to the second node in response to the control signal. And a detector that detects a predetermined potential difference that occurs in the first resistance circuit and that supplies the control signal to the first and second drive units according to the potential difference. A speed control circuit for a DC motor characterized in that 2. A first node connected to the DC motor, a first drive unit connected to the first node and driving the DC motor according to a control signal, the first node and the first node. A first resistance circuit connected between two nodes, each of which has a resistance value for setting a predetermined operating speed of the DC motor; and a second resistance; A first resistance circuit having a first switch connected to the plurality of first resistances to selectively form a series circuit having one of the plurality of first resistances and the second resistance. And a second resistance circuit connected between the second node and a power supply, the resistance value being proportional to the internal resistance of the DC motor corresponding to each set operating speed of the DC motor. And a plurality of third resistors having a plurality of, and the plurality of third resistors selectively A second switch having a second switch connected between a source and the second node; and supplying a current to the second node in response to the control signal and connected to the second node. A second drive unit, a detection unit that detects a predetermined potential difference generated in the series circuit by one of the plurality of first resistors and the second resistor, the first and A speed control circuit for a DC motor, comprising: a detection unit that supplies the control signal to a second drive unit.