JPH0119599Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a speed control circuit for a direct current motor using a shunt ratio method. The purpose is to reliably prevent hunting when the resistance value becomes larger than the normal value due to variation or when the ambient temperature drops, and to improve the speed response of the motor in which this hunting phenomenon is prevented. shall be.

FIG. 1 shows a conventional speed control circuit. The dotted line 1 is the monolithic IC part, and 2 to 6
is its external lead-out terminal. 7 is an error detector (arithmetic amplifier) having two input terminals (-, +);
One terminal is connected to the fourth terminal, and the + terminal is connected to the fifth terminal via the reference voltage source 8.
This error detector 7 is connected to a No. 2 terminal (power supply) and a No. 6 terminal (earth) through terminals 7a and 7b. Q ₁ is a shunt transistor, and terminals 3 and 6
_Q2 terminal (earth)
is a drive transistor connected between the fifth terminal and the sixth terminal. The output terminal of the error detector 7 is connected to the bases of transistors Q ₁ and Q ₂ . R ₃ and R ₄ each represent a resistor connected to the emitter. The above is the configuration inside the IC. To each lead-out terminal of this speed control IC, a resistor R ₁ is connected between terminals 2 and 3, a resistor volume R V1 is connected between terminals 3 and 4, and a resistor volume R _V1 is connected between terminals 4 and 5. A resistor R ₂ is connected between the terminals numbered respectively. Furthermore, a DC motor M is connected between terminals No. 2 and No. 5. Eg and Rg represent a back electromotive force generated by the rotation of the motor M and an internal resistance (winding resistance) of the motor M, respectively. Vcc indicates a power supply voltage terminal, and the No. 6 terminal is connected to ground.

In the circuit having the above configuration, the area ratio of the emitters of transistors Q ₁ and Q ₂ is 1:K. Here, it is assumed that the load current flowing through the motor M is Ia, the current flowing through the shunt transistor Q ₁ is I _K , the current flowing through the resistor R ₂ is I _S , and the voltage generated across them is V ₂ . In addition, the input impedance of each error detector 7 is very high, and if the current flowing into it is ignored, the following relationship holds true.

Eg＋RgIa = (R ₁ +R _V1 +R ₂ )I _S +R ₁ I _K …(1) I _S =V ₂ /R ₂ …(2) Here, if Ia≫I _S , I _K = 1/K・Ia K=Ia/I _K (3) Substitute equations (2) and (3) into equation (1) to obtain the following equation.

Eg + RgIa = V ₂ / R ₂ (R ₁ + R _V1 + R ₂ ) + R ₁ I _K …(4) The first term on the left side and the first term on the right side, and the second term on the left side and the second term on the right side of equation (4) are as follows. It is designed to be equal as shown in the formula.

Eg=V ₂ /R ₂ (R ₁ +R _V1 +R ₂ ) …(5) RgIa=R ₁ I _K …(6) When formulas (5) and (6) are satisfied, this speed control circuit is
It is perfectly balanced and its rotational speed is controlled to remain constant even when the load fluctuates.

Note that the load characteristics under the balance conditions of equations (5) and (6) are such that the rotational speed is maintained constant with respect to the load torque, as shown by the solid line in FIG.

From equations (3) and (6), R ₁ =KRg (7) is derived.

The parameter of the load characteristic curve shown in FIG. 5 is the ratio of resistance R ₁ to KRg, which indicates that when R ₁ =KRg, there is no variation in the rotational speed even if the load torque varies.

The control operation in the speed control circuit will be explained. Now considering the case where the load increases and the rotation speed decreases, as the load increases, the load current Ia
increases, the voltage across the internal resistance Rg also increases, and the back electromotive voltage Eg decreases accordingly. At the same time, the current I _K increases in proportion to its load current Ia, and the voltage drop across the resistor R ₁ increases. Then, the potential at the negative input terminal of the error detector 7 drops, its output potential rises, and the collector currents of the shunt and drive transistors _Q1 and _Q2 increase, and at the same time, their collector potentials decrease. Therefore, a correspondingly large voltage is applied to the motor M, and the rotation speed is controlled to increase to the specified rotation speed.

On the other hand, when the load decreases and the rotational speed increases, contrary to the above, the speed is controlled to the specified rotational speed by operating in the opposite manner.

As described above, a current proportional to the load current (I _K =Ia/K) flows through the resistor R ₁ , and the voltage across it (I _K R ₁ ) fluctuates as the current changes. This variation is detected by the error detector 7 to control the drive transistor _Q2 . Therefore, this resistor _R1 is called a feedback resistor.

The condition for obtaining the ideal load characteristics in the conventional speed control circuit explained above is when formula (7) is satisfied.However, there are variations in this resistance R ₁ , so R ₁ >KRg, Also, since Rg has a positive temperature coefficient,
Similarly, when the ambient temperature decreases, R ₁ >KRg may occur, and in that case, the control system becomes positive feedback, causing hunting (oscillation) and speed control becoming impossible.

Therefore, in order to prevent such hunting, the value of R ₁ is generally selected such that R ₁ <KRg.

However, reducing R ₁ in this way has the problem that the rotational speed decreases as the load torque increases, as shown by the dotted line in the load characteristics in FIG.

The present invention is intended to prevent the occurrence of hunting and deterioration of load characteristics as explained in the above conventional example, and also to improve the deterioration of speed response after hunting is prevented.One embodiment of the present invention will be described below.
FIG. 2 shows a speed control circuit for a DC motor according to an embodiment of the present invention. Components that are the same as those in FIG. 1 are designated by the same reference numerals, and their explanations will be omitted.

In Fig. 2, the basically different parts from Fig. 1 are a resistor R and a capacitor C connected in parallel to the feedback resistor _R1 .
is the part that is connected.

When we measured the hunting frequency of the conventional circuit shown in FIG. 1, we found that it ranged from several Hz to several tens of Hz. Therefore, in order to lower the feedback rate in this frequency band, connect a capacitor in parallel to resistor _R1 to lower their combined impedance.
Hunting is prevented by satisfying equation (7).

In the conventional example shown in Figure 1, in order to prevent hunting, the ratio of resistance R ₁ to KRg was selected to be approximately 0.84, taking into account the temperature characteristics of Rg and the variation in resistance R ₁ . Since the capacitor C is connected in parallel with the resistor _R1 to prevent hunting as in the present invention, the center value of the resistor _R1 can be set to KRg, and therefore its load characteristic is The ideal load characteristics shown by the solid line in the figure were achieved.

When the value of resistance _R1 exceeds KRg, the load characteristic curve shows a phenomenon in which the rotational speed increases as the load torque increases, as shown by the dashed line in Figure 5, but hunting does not occur even in this case. The rotation is controlled constantly.

By the way, by connecting such a capacitor C, although the hunting phenomenon could be prevented, as a side effect, the combined impedance between terminals 2 and 3 would be reduced unnecessarily, and the speed response of the motor would be affected. This results in the problem that the wah characteristic (wah characteristic) deteriorates. Therefore, by connecting a resistor R in series with the capacitor C, the speed response of the motor is improved.

FIG. 3 shows a modification in which the embodiment of the present invention shown in FIG. 2 is applied to another speed control circuit. Components that are the same as those in FIGS. 1 and 2 are designated by the same reference numerals, and their explanations will be omitted. The parts that differ from the circuit in Figure 2 are:
The point within the dotted line 1 is that there is no terminal No. 4 among the lead-out terminals of the IC, and therefore one input of the error detector 7, which was connected to it, is connected to the terminal No. 3 via the reference voltage source 8. Even in such a control circuit, the resistance
By connecting capacitor C in parallel to _R1 ,
This embodiment has the same functions and effects as the embodiment shown in FIG. 2 above. Note that a resistor R for improving the speed response of the motor is also connected to this circuit.

FIG. 4 shows a modification in which the embodiment of the present invention shown in FIG. 2 is applied to another speed control circuit. The same parts as in FIGS. 1 and 2 are designated by the same reference numerals, and their explanation will be omitted. The difference from the circuit diagram in Fig. 2 is that the error detector 7 is connected to each terminal corresponding to the 3rd and 4th terminals, and the reference voltage source 8 is connected to one input of the error detector 7 and the 3rd terminal. The difference is that the volume R _V2 is inserted between the 4th and 5th terminals. Even with such a control circuit, by connecting the capacitor C in parallel to the resistor _R1 , the same operation and effect as in the embodiment shown in FIG. 2 can be obtained. Note that a resistor R for improving the speed response of the motor is also connected to this circuit.

As mentioned above, in the present invention, in a speed control circuit using a shunt ratio method, a series circuit of a capacitor and a resistor is connected in parallel to a feedback resistor through which a current proportional to the motor load current flows.
Even if the feedback resistor _R1 exceeds KRg, it is possible to prevent the hunting phenomenon caused by the oscillation state. Conventionally, to prevent this hunting, a feedback resistor was used.
Considering the variation in R ₁ and the temperature characteristics of Rg, the value of R ₁ is set as small as 0.84 times KRg so that the value of R ₁ does not exceed _KRg . Increasing the center value of R1 by 0.84 will worsen the load characteristics, but in this invention, the center value of the feedback resistor _R1 can be set to KRg, so the center value is , it is possible to select an ideal load characteristic curve where there is no variation in rotational speed with respect to load variation, and it is possible to realize a speed control circuit without rotational variation. In addition, by selecting the value of the feedback resistor _R1 to be an arbitrary value greater than KRg, it is possible to obtain a speed control circuit that arbitrarily increases the motor rotation speed as the load torque increases. . Furthermore, by connecting a resistor to the capacitor C to improve the hunting phenomenon, it was possible to reliably prevent the resulting deterioration in the speed response of the motor.

[Brief explanation of the drawing]

Figure 1 shows the speed control circuit of a conventional DC motor.
FIG. 2 shows an embodiment of the present invention, a speed control circuit for a DC motor, and FIGS. 3 and 4 show a modification of FIG. 2.
FIG. 5 shows load characteristic curves of load torque versus rotation speed, respectively. 1... Monolithic IC, 2-6... Monolithic IC lead-out terminal, 7... Error detector, 8...
Reference voltage source, _R1 to _R5 , R...Resistance ( _R1 is especially called feedback resistance), Rg...Internal resistance of the DC motor (armature resistance), C...Capacitor, Eg...
...Back electromotive force of DC motor, M...DC motor,
Q ₁ , Q ₂ ...transistor.

Claims (1)

[Scope of utility model registration request] A first resistor and a second resistor are connected in series, a DC motor is connected in parallel to these series-connected resistors, a connection point between the first resistor and the DC motor is connected to a power supply, and the second resistor is If there is only one second resistor, two inputs are connected to both ends of that resistor, and if multiple second resistors are connected in series, two inputs are connected to both ends of one of the resistors. A reference voltage source is connected to one of the two input terminals of the error detector, and a shunt transistor is connected between the connection point of the first and second resistors and ground. a driving transistor is connected between the connection point of the second resistor and the DC motor and ground, base electrodes of the shunt transistor and the driving transistor are respectively connected to the output of the error detector; A speed control circuit for a DC motor, wherein a current proportional to the load current flowing through the transistor flows through the shunt transistor, and a series circuit of a capacitor and a resistor is connected in parallel to both ends of the first resistor. .