JPH03207286A - Speed control circuit for dc motor - Google Patents

Abstract

PURPOSE:To prevent flow of an overcurrent to a control IC even if a power source is erroneously connected reversely by connecting a diode from a power source terminal to a fifth terminal for applying a power source voltage to an error detector in a motor control IC. CONSTITUTION:A power source voltage VCC is applied to an error detector 1a through a terminal (5) in a motor control IC 1. A resistor R1 is connected from the terminal (5) to a terminal (l), and a diode 2 is connected from a power source terminal V0 to be connected to the positive side of a power source to the terminal (5). The diode 2 is forward from the terminal V0 toward the terminal (5). If the terminal V0 is now connected erroneously reversely to a terminal GND to the power source, the diode 2 prevents flow of an overcurrent to the terminal (5) and prevents flow of a current to the terminal, thereby preventing damage of the IC 1.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a speed control circuit for a DC motor using an IC for control.

(Prior Art) There is a DC motor whose speed is controlled by replacing a mechanical governor with a speed control IC, and this type of motor is called an electronic governor motor. JP-A-56-2
The techniques described in Japanese Unexamined Patent Publication No. 5392, Japanese Utility Model Application Publication No. 56-40491, etc. are related to this type of motor.

FIG. 2 shows the above-mentioned conventional technology, in which a DC motor control IC designated by reference numeral 1 has four terminals. The first terminal ■ is a reference terminal, the second terminal ■ is a detection terminal for detecting the equivalent voltage of the back electromotive force of the motor, the third terminal ■ is an output terminal, and the fourth terminal ■ is a ground terminal. The control ICI has the following internal circuits for each terminal. Between the first terminal (2) and the fourth terminal (2), the collector and emitter of a shunt transistor Q□ are connected in the forward direction via a resistor R□. Further, a plurality of drive transistors Q, , Q3 . . . . The collector and emitter of Qn are connected in parallel in the forward direction via resistors R2°R1, . . . Rn, respectively.

The control input terminals, that is, the bases of these drive transistors Q, Q,...Qn and the shunt transistors are commonly connected to the output terminal of the error detection circuit 1a.
...Qn constitutes a current mirror circuit.

The error detection circuit 1a is composed of, for example, a differential amplifier circuit. A reference voltage source 1b is provided between the lines between the first terminal (2) and the second terminal (2) and two input terminals of the error detection circuit 1a corresponding to the respective terminals (2). however,
A reference voltage Vref from a reference voltage source 1b is divided by resistors R, , R, and input to the error detection circuit 1a. The error detection circuit 1a detects the voltage at the second terminal (2) by comparing the voltage at the second terminal (2) with the reference voltage.

The following external circuits are connected to the DC motor control IC 1 configured as described above. A DC motor M is connected between the third terminal ■ and the power supply terminal vO. Resistors Rt, Rs, R are connected between both terminals of DC motor M.
b are connected in series. The resistors Rs and Rb constitute a voltage dividing circuit, and this voltage dividing circuit is connected between the first terminal ■ and the third terminal ■, and the voltage dividing point of this voltage dividing circuit is connected to the second terminal ■.
is connected to the terminal ■. The fourth terminal ■ is grounded. In the DC motor M, a back electromotive force is generated in the drive coil due to rotational driving, so the back electromotive force source Ea is equivalently
It can be expressed as a series connection of and an internal resistance Ra. By configuring the circuit in this manner, a current proportional to the load current Ia flowing to the third terminal (2) flows to the first terminal (2).

Now, connect the power terminal Vo to the positive side of the power supply and the ground terminal GN.
When D is connected to the negative side of the power source, power is supplied to the motor M to rotate its rotor, and a back electromotive voltage Ea corresponding to the rotational speed of the motor M is induced between the motor terminals A and C. The voltage corresponding to this back electromotive force Ea is the control ICI
It appears between the first terminal ■ and the third terminal ■. This voltage is divided by resistors Ra and Rb, and this divided voltage value is input to one terminal of the error detection circuit 1a. Error detection circuit 1
In a, a partial voltage value corresponding to the above-mentioned back electromotive force Ea and a reference voltage Vr
ef (more precisely, a voltage according to the reference voltage Vref) and outputs the error as a speed error signal. This speed error signal drives the shunt transistor Q1 and the drive transistors QatQat...Qn, controls the current Ia flowing through the motor M, and controls the rotational speed of the motor M.

As described above, the conventional example shown in FIG. 2 achieves certain effects as a so-called electronic governor motor. However, according to the above conventional example, power is directly supplied to the motor M, whereas power is supplied to the motor control ICI via the resistor Rt. Since a voltage lower by the voltage drop caused by the resistor Rt is supplied, there is a problem that the control ICI cannot fully utilize the power supply voltage Vcc.

Therefore, as shown in FIG. 3, by adding a fifth terminal (■) as a power supply terminal to the motor control IC 1 and connecting this terminal (■) directly to the power supply, a voltage equal to the power supply voltage Vcc supplied to the motor M can be obtained. A speed control circuit for a DC motor has also been proposed in which the voltage is also supplied to the control IC 1.

(Problems to be Solved by the Invention) A speed control circuit including a control ICI as shown in FIG. 3 is built into the DC motor body, and from the DC motor body,
Only the power terminal Vo to be connected to the positive side of the power source and the ground terminal GND to be connected to the negative side of the power source are drawn out. However, when connecting the motor M to the power source.

It is possible to accidentally connect it in the wrong direction. In the conventional example shown in FIG. 3, if the terminal Vo and the terminal GND are mistakenly connected in opposite directions with respect to the power supply,
The current flowing through each terminal of the control ICI is connected to each resistor Rt.
, Ra, and Rh, and each of these resistances acts as a limiting resistance and the current is limited to some extent, but the control IC
Since the fifth terminal (■) of No. 1 is directly connected to the positive side of the power supply, the current that flows in the forward direction from the ground terminal GND through the PN junction in the control ICI flows to the fifth terminal (■), and this current There is a problem in that an excessive current flows into the PN junction within the control ICI, causing the control ICI to be destroyed.

The present invention has been made in order to solve the problems of the prior art, and uses a motor control IC having five pins, so that even if the power supply is connected in the wrong direction, the An object of the present invention is to provide a speed control circuit for a DC motor that can prevent damage to an IC.

Another object of the present invention is to provide a speed control circuit for a DC motor that can correct temperature characteristics of rotation control.

(Means for Solving the Problems) The present invention provides a reference voltage source between lines between first and second terminals and two input terminals of an error detection circuit corresponding to each terminal, and a third terminal A drive transistor is connected between the terminal and a grounded fourth terminal, a power supply voltage is applied to the error detection circuit from the fifth terminal, and a shunt transistor is provided between the first terminal and the fourth terminal. , configured such that a current proportional to the load current flowing through the third terminal flows through the first terminal,
And a voltage corresponding to the voltage generated between the first and third terminals is applied to the second terminal, this voltage and the reference voltage are detected by the error detection circuit, and the output signal of the error detection circuit is divided into the above-mentioned shunt and the reference voltage. A DC motor control IC is provided to be applied to the control input terminal of the drive transistor, the DC motor is connected between the power supply terminal and the third terminal, and a resistor is connected between the fifth terminal and the first terminal. , a voltage dividing circuit is connected between the first terminal and the third terminal, a voltage dividing point of this voltage dividing circuit is connected to the second terminal, and a diode is connected between the power supply terminal and the fifth terminal. It is characterized by connecting.

(Function) Even if the terminal of the motor having the motor control IC is connected to the power supply in the opposite direction by mistake, the connection between the fifth terminal of the motor control IC and the power supply terminal for applying the power supply voltage to the error detection circuit is maintained. A diode connected between the two blocks the current and prevents the motor control ICI from being destroyed.

The magnetic flux of the drive magnet of the DC motor changes depending on the temperature change, but this magnetic flux change is caused by the fifth
The change in voltage drop caused by the temperature change of the diode connected between the terminal and the power supply terminal is canceled out, and the temperature change per rotation speed is suppressed.

(Example) Hereinafter, an example of a speed control circuit for a DC motor according to the present invention will be described with reference to FIG. However, since the embodiment shown in Fig. 1 has circuit parts added to the conventional example shown in Figs. 2 and 3, the explanation of the configuration will focus on the added parts. Components common to those of the conventional example shown in FIG.

In FIG. 1, the motor control ICIs are the first to fourth ICIs.
In addition to the terminal ■■■■, it has a fifth terminal ■, and the power supply voltage v is supplied to the error detection circuit 1a through this fifth terminal ■.
cc is applied. In addition, the fifth terminal ■
A resistor Rt is connected between and the first terminal (2), and a diode 2 is connected between the power supply terminal Vo, which should be connected to the positive side of the power supply, and the fifth terminal (2). The diode 2 is in a forward direction from the power supply terminal Vo toward the fifth terminal (2). Other configurations are the same as the conventional example shown in FIG.

Now, connect the power terminal ■0 to the positive side of the power supply and the ground terminal GN.
When D is connected to the negative side of the power supply, the rotor of the motor M is driven to rotate in the same way as the operation explained for the conventional example in FIG.
A speed control operation is performed based on the back electromotive voltage Ea induced between C and the rotational speed is controlled to be constant. Here, the load current flowing through the motor M is Ia, the current flowing through the resistor Rt is It, the current flowing through the resistor Ra is Is, the current flowing through the shunt transistor Q is Ik, the constant current for obtaining the reference voltage Vref is Ir, [ The current flowing through the dynamic transistor QZ9Q39...Qn is Io, and the equivalent internal resistance value of the motor M is Ra.
, the back electromotive force of the motor M is Ea, the reference voltage of the reference voltage source 1b is Vref, and the terminal voltage of the motor M is vO. In the motor control ICI, the current Ik is always 1/ of the current 0 due to the current mirror circuit made up of the shunt transistor QU and the drive transistors Q2gQ3e, . . . Qn. However, K is a proportionality constant. Moreover, Ia:KIt, Is=Vref/Ra. Find the voltage Vm applied to the motor M.

Vm=RtIt◆(Ra+Rh)Is+RtIr+Vx
Vm=Vref(1+(Rb/Ra))+RtIr+V
x+Rt(Ia/K)*+(1). (1)
The first and second terms on the right side of the equation take constant values regardless of changes in the power supply voltage vO or changes in the load current Ia due to changes in the load torque, if the values of the resistors Ra, Rb, and Rt are given. , the fourth term on the right side changes in proportion to the load current Ia. Therefore, if we consider the first to third terms on the right side of equation (1) as a voltage source Va, we can express it as shown in equation (2), and a resistor (-Rt/K) is connected in series to this voltage source Va. is equivalent to that given.

On the other hand, considering the motor M, the terminal voltage Vo of the motor M is: ■0=Ea+RaIa... (3), and Vo=Vm... (
4), so Va+ (Rt/K)I a=Ea+Ra I a・
・ ・ The relationship is as follows (5). Therefore, the back electromotive force Ea of the motor M is Ea-Va+ ((Rt/K)-Ra)Ia.
・It is expressed as (6). If the resistance Rt is adjusted to select Rt=KRa (7), then Ea:Va, and the motor M is driven at a rotational speed such that its back electromotive force Ea is always a constant voltage Va.

That is, the motor M is controlled to always have a constant rotational speed without being affected by load torque or the like.

In this way, even when the diode 2 is inserted between the power supply terminal 0 and the fifth terminal 2 of the control ICI, the speed control circuit for the DC motor M can be constructed.

Now, suppose that in the embodiment shown in FIG. 1, the power supply terminal Vo and the terminal GND are mistakenly connected in opposite directions relative to the power supply. For example, if the power supply terminal vO and the fifth terminal of the control ICI
If the diode 2 is not inserted between the control IC 1 and the control IC 1, an excessive current will flow through the PN junction in the control IC 1, resulting in destruction of the ICI, as described for the conventional example shown in FIG.

However, according to the embodiment shown in FIG. 1, the diode 2 inserted between the power supply terminal vO and the fifth terminal ■ of the control circuit C1 prevents excessive current from flowing to the fifth terminal ■. It also prevents current from flowing from the first and second terminals ■■ to the fifth terminal ■, thereby preventing the control IC from flowing.
I can be prevented from being destroyed.

By the way, the resistances Rt, Ra, and Rb are normally used.

We use a carbon film resistor whose resistance value changes little with temperature changes, and take care to suppress changes in motor current rotation speed due to temperature changes as much as possible.

However, the drive magnet of the motor has temperature characteristics, and the magnetic flux changes with temperature changes.

On the other hand, since the reference voltage temperature characteristic of the control IC1 is normally set to O, the temperature characteristic of the control IC1 can be ignored. Therefore,! The temperature characteristics of the M dynamic magnet become a factor in the rotational speed fluctuation of the motor.

However, according to the embodiment shown in FIG.
serves to compensate for rotational speed fluctuations due to temperature changes. That is, in the control equation (1) described above, the terminal voltage Vm of the motor M changes as the voltage drop Vx across the diode 2 changes. The voltage drop Vx across the diode 2 shows a change of approximately -2 (mV/''C) as the temperature changes. On the other hand, the temperature change in the magnetic flux of the magnet of the motor M is 0.
18 (%/'C). Therefore, the temperature change in the voltage drop Vx of the diode 2 and the temperature change in the magnetic flux of the drive magnet cancel each other out, and the temperature change in the rotational speed is suppressed.

Thus, according to the embodiment shown in FIG.
A diode 2 is connected between
By connecting the power supply, even if the power supply is connected in the wrong direction, excessive current will not flow to the control IC1.
The control ICI can be protected. Furthermore, temperature changes in the voltage drop Vx of the diode 2 and temperature changes in the magnetic flux of the drive magnet cancel each other out, and there is also an effect that temperature changes in the rotational speed are suppressed.

An example of a device in which a diode is inserted in the power supply circuit to the error detection circuit is disclosed in Japanese Utility Model Application Laid-Open No. 62-88489. However, the diode in this conventional example is inserted into a motor control IC and does not have a temperature compensation function as seen in the embodiment of the present invention.

(Effects of the Invention) According to the present invention, by connecting a diode between the power supply terminal and the fifth terminal for applying power supply voltage to the error detection circuit in the motor control IC, the power supply Even if they are connected in the opposite direction, an excessive current will not flow to the control IC, and the control IC can be protected. Further, there is also the effect that the temperature change in the voltage drop of the diode and the temperature change in the magnetic flux of the drive magnet cancel each other out, thereby suppressing the temperature change per rotation speed.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an embodiment of a speed control circuit for a DC motor according to the present invention, Fig. 2 is a circuit diagram showing an example of a speed control circuit for a conventional DC motor, and Fig. 3 is a circuit diagram showing an example of a speed control circuit for a conventional DC motor. FIG. 7 is a circuit diagram showing another example of the speed control circuit. 1... Motor control IC11a... error detection circuit,
1b... Reference voltage source, 2... Diode, M.
...Motor, Q□...Shunt transistor, Q21
Q3tQn...drive transistor, Vcc...power supply voltage, Vo...power supply terminal, Ia...load current,
Rt...resistance, Ra, Rb...divider resistance. 1 Iris Bu Retsuko Figure 2

Claims (1)

[Claims] A reference voltage source is provided between the lines between the first and second terminals and the two input terminals of the error detection circuit corresponding to each terminal,
A drive transistor is connected between the third terminal and a grounded fourth terminal, a power supply voltage is applied to the error detection circuit from the fifth terminal, and a drive transistor is connected between the first terminal and the fourth terminal. A shunt transistor is provided at the third terminal so that a current proportional to the load current flowing through the third terminal flows through the first terminal, and a voltage corresponding to the voltage generated between the first and third terminals is set at the second terminal. In addition to the second terminal, the DC motor control IC detects this voltage and the reference voltage by the error detection circuit, and applies the output signal of the error detection circuit to the control input terminal of the shunt and drive transistor. A DC motor is connected between the terminal and the third terminal, a resistor is connected between the fifth terminal and the first terminal, and a resistor is connected between the first terminal and the third terminal. A DC motor characterized in that a voltage dividing circuit is connected, a voltage dividing point of the voltage dividing circuit is connected to the second terminal, and a diode is connected between the power supply terminal and the fifth terminal. Speed control circuit.