JP2844081B2 - DC motor drive circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC motor drive circuit, and is particularly suitable for use in a DC motor drive circuit that drives a DC motor in both forward and reverse directions. .

[Summary of the Invention]

The DC motor drive circuit of the present invention applies a drive voltage to the DC motor via a relay capable of switching the application direction, and detects the rotation direction of the DC motor based on the polarity of the induced electromotive force. The switching operation of the relay is controlled by the detection output, so that the DC motor can be driven in the forward and reverse directions without connecting a driving element for large current control to the bridge.

[Conventional technology]

2. Description of the Related Art There is known an induced electromotive force sensing type DC motor drive circuit which detects an induced electromotive force generated in proportion to the rotation speed of an armature and controls driving of a DC motor. In such induced electromotive force sensitive DC motor drive circuit, in order to allow both forward and reverse directions of drive, the motor drive element Q ₁ ~ power transistor such as shown in principal part circuit diagram of FIG. 2 Q ₄
Connected to the bridge. Then, for example, the transistors Q ₁ and Q ₃ are turned on by induced electromotive force generated when the armature of the DC motor M rotates in the positive direction. Thereby, the positive electrode of the power supply E and the transistor
A closed circuit is formed that connects Q ₃ , DC motor M, transistor Q ₁ and the negative electrode of power supply E, and drives DC motor M in the positive direction by passing a drive current in the direction of T ₂ from terminal T ₁ .

Further, the transistors Q ₂ and Q ₄ are turned on by induced electromotive force generated when the armature of the DC motor M rotates in the reverse direction. In this case, as shown by the arrow R, a closed circuit is formed that connects the positive electrode of the power source E, the transistor Q ₂ , the DC motor M, the transistor Q ₄ and the negative electrode of the power source E. Therefore, this case can be allowed to flow in the T ₁ direction drive current from the terminal T _2, it is possible to drive the DC motor M in the reverse direction.

[Problems to be solved by the invention]

An element for controlling a large current such as a driving current of a motor is expensive. Thus, placing and use four bridge driving elements Q ₁ to Q ₄ of the high-current control as in the conventional circuit of FIG. 2, there is an inconvenience that the cost of manufacturing the driving circuit is increased.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to drive a DC motor in forward and reverse directions without connecting a drive element for large current control to a bridge.

[Means for solving the problem]

The DC motor drive circuit according to the present invention includes a terminal of the DC motor M.
A voltage comparator 1 that senses the induced electromotive force generated at T ₁ and T ₂ and outputs a voltage corresponding to the rotation direction of the DC motor M; And a relay 3 for switching an application direction in accordance with the voltage output from the voltage comparator 1.

[Action]

The function of switching the direction in which the drive current is supplied to the DC motor M is separated from the function of sensing the induced electromotive force to detect the rotation direction of the DC motor M, and the direction switching operation is controlled by the rotation direction detection output. Then, the DC motor is driven in the forward or reverse direction.

〔Example〕

FIG. 1 is a main part circuit diagram of a DC motor drive circuit showing one embodiment of the present invention.

The DC motor drive circuit according to the embodiment has two voltage comparators 1 and 2 for detecting an induced electromotive force of the DC motor M. The first voltage comparator 1 controls the relay 3 for switching the direction of the voltage applied to the DC motor M, a DC motor M via a resistor R ₁ to the inverting input terminal
Together with the terminal T ₁ of the are connected, the terminal T ₂ of the DC motor M is connected via a resistor R ₂ to the non-inverting input terminal.

Resistor R ₁ has one end resistor connected to the inverting input terminal
Through R ₃ is grounded, the other end is connected to the positive V supply through a resistor R _5. Further, the resistor R ₂ at one end which is connected to the non-inverting input terminal is grounded via a resistor R _4. Though the DC motor M is at rest, in a state in which the induced electromotive force E _M to the terminal T _1, T ₂ does not appear, than the input voltage e ₂ towards the input voltage e ₁ of the inverting input terminal is the non-inverting input terminal are set resistance values of the resistors R ₁ to R ₄ to be larger. Therefore, when the DC motor M is stationary, the output of the first voltage comparator 1 is low, and in this case, the coil X of the application direction switching relay 3 is not energized.

Applying direction changeover relay 3 Two switching device 3a, it has 3b, motor terminal T ₁ is connected to the switching contact of the first switching unit 3a, switching motor terminal T ₂ of the second switching unit 3b Connected to contacts. These switching contacts are located on the fixed contact b side when the coil X is not energized, and are switched to the fixed contact a side when the coil X is energized.

The fixed contact b of the first switch 3a and the fixed contact a of the second switch 3b are connected to the positive electrode of the power source E. The fixed contact a of the first switch 3a and the fixed contact b of the second switch 3b are grounded via the drain electrode D and the source electrode S of the field effect transistor 4.

Field effect transistor 4 than those provided for driving current control of the DC motor M, and controls the driving current of the DC motor M in response to the control signal S _E, which is derived from the AND circuit 5.

The input side of the AND circuit 5, and the rectangular wave signal S ₂ output from the second voltage output S ₁ and the rectangular wave oscillation circuit 6 of the comparator 2 are given. The non-inverting input terminal of the second voltage comparator 2 through the resistor R ₆ and the variable resistor RV is connected to the plus V supply voltage changes its size depending on the position of the movable terminal of the variable resistor RV e ₃ is added as a comparison voltage.

Also, with is connected to the positive V power inverting input terminal of the second voltage comparator 2 via a resistor R _8, the fixed contact b and the switching of the switching device 3b via the resistor R ₇ exchanger
3a have been fixed contact a to each connection, voltage e ₄ of these resistors whose magnitude varies in accordance with the induced electromotive force E _M
The signal is supplied to the inverting input terminal via R ₇ and R ₈ . When the DC motor M is not rotated, i.e. when the induced electromotive force E _M to the terminal T _1, T ₂ does not occur, e ₃ <Each resistor such that e ₄ R ₆ ~R ₈ and RV Is set. Therefore, the control signal S _E in this case the output S ₁ of the second voltage comparator 2 output from the AND circuit 5 because a low level also becomes low. As a result, the transistor 4 is turned off, so that no drive current flows through the DC motor M.

Next, an operation when the DC motor M is rotated by an external force will be described. DC motor M when that is rotated forward, the terminal T ₁ side terminal T ₂ side generates the negative induced electromotive force E _M positive. Also, when it is rotated reversely the terminal T ₁ side terminal T ₂ side generates the positive induced electromotive force is negative.

Therefore, positive induced electromotive force E _M is added to the first inverting input terminal of the voltage comparator 1 when rotated forward the DC motor M by an external force. Further, since the negative induced electromotive force E _M is added to the non-inverting input terminal, the magnitude relation between the voltage e _1, e ₂ applied to the input terminals does not change, e _1> relationship e ₂ is maintained It is. Therefore, when the DC motor M rotates forward, the output of the first voltage comparator 1 remains at a low level, and the switching contacts of the switches 3a and 3b are held at the fixed contacts b.

On the other hand, it applied to the inverting input terminal of the second voltage comparator through negative induced electromotive force generated in the motor terminal T ₂ is switching device 3b 2 by forward rotation DC motor M.
Thereby, the voltage value of the input voltage e ₄ of the inverting input terminal is lowered, the second voltage is in the voltage comparator 2
The magnitude relation between e ₃ and e ₄ is reversed, and e ₃ > e ₄ . Therefore, the output voltage S ₁ of the second voltage comparator is inverted to high level, the control signal S _E, which is output from the AND circuit 5 becomes high level. Thus, the control transistor 4 is turned on, the driving current I _F of forward rotation is supplied from the power source E to the DC motor M, a DC motor M to sustain the normal rotation.

Since the low-level period of the square wave signal S ₂ output from the rectangular wave oscillation circuit 6 is the control signal S _E applied to the gate electrode G becomes a low level, the control transistor 4 is on periodically momentarily off. Thus, this off period is not supplied a drive current to the DC motor M, the induced electromotive force E _M when the DC motor M continues to rotate by inertia subsequently occurs. By this induced electromotive force E _M , the magnitude relation of the voltage input to the second voltage comparator 2 is determined by the control transistor 4.
Is kept off while e ₃ > e ₄ . Thus, the comparator output S _1, so off period also held much high, so that the rectangular wave signal S ₂ is the control signal S _E of high level from the AND circuit 5 is output becomes a high level. Since this the control transistor 4 is turned on again through the drive current I _F, the DC motor M is driven in the forward direction.

As described above, since the control transistor 4 is momentarily turned off, the induced electromotive force E _M is not generated due to the DC motor M being in the constrained state or the state immediately before the stop,
When the input voltage of the second comparator 2 becomes e ₃ > e ₄ , the control transistor 4 does not turn on again. Therefore,
When the DC motor M is restrained, it is possible to reliably prevent the restraining current from flowing.

Incidentally, it is possible to adjust the rotational speed of the DC motor M by controlling the duty ratio of the rectangular wave signal S _2. Further, the torque of the motor M can be controlled by changing the resistance value of the variable resistor RV.

Next, a case where the DC motor M is driven in the reverse direction will be described.

When rotated in reverse DC motor M by an external force, the terminal T ₂ is the terminal T ₁ is induced electromotive force E _M of negative polarity is generated at the positive. As a result, the input voltage of the first voltage comparator 1 becomes e ₁ <e ₂ , and the output of the first voltage comparator 1 is inverted to a high level. Therefore, since a drive current flows through the coil X,
The application direction switching relay 3 operates to switch the switching contacts of the switches 3a and 3b to the fixed contact a side.

When the switching contact is replaced with the fixed contact a, the terminal T ₁
The negative induced electromotive force generated in the second voltage comparator 2
To the inverting input terminal. Thus, the input voltage of the second voltage comparator 5 also becomes e ₃ > e _{4 in} this case.
Therefore, the control transistor 4 is turned on by the same operation as described above, and the drive current flows through the motor M. In this case, since the switching contact is switched to the fixed terminal a, the drive current is a driving current I _R for reverse rotation flowing from the motor terminal T ₂ side to the T ₁ side, the DC motor M is driven in the reverse direction Is done.

In the DC motor drive circuit according to the embodiment, the direction in which the drive current is supplied to the DC motor M is switched in this manner, so that the motor M can be driven forward and reverse only by providing one motor drive control terminal. Can be.

Further, since the start and stop of the motor M are performed by an external force, an on / off operation switch may not be provided. The circuit according to the embodiment having such features can sufficiently exhibit its advantages when used in an auxiliary power unit such as an electric golf cart and a sliding door for an automobile.

〔The invention's effect〕

As described above, the present invention detects the induced electromotive force generated with the rotation of the DC motor with a voltage comparator to detect the rotation direction of the DC motor, and uses the detected output to switch the application direction switching relay. Is controlled, it is possible to configure an induced electromotive force sensing type DC motor drive circuit that can be driven forward and reverse without using a bridge circuit of a DC motor drive element such as a large current control transistor. Therefore, one motor drive element is required.
The motor can be driven forward / reverse only by using
The manufacturing cost of the DC motor drive circuit can be significantly reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a DC motor driving circuit showing an embodiment of the present invention, and FIG. 2 is a circuit diagram of a main part of a conventional DC motor driving circuit. In the reference numerals used in the drawings: 1... First voltage comparator 3... Application direction switching relay 4... Field effect transistors (motor driving elements) T ₁ , T ₂ ... Motor terminals _M. …… Induced electromotive force.

Claims (1)

(57) [Claims] 1. A voltage comparator for detecting an induced electromotive force generated at a terminal of a DC motor and outputting a voltage corresponding to a rotation direction of the DC motor, and applying a drive voltage to the DC motor and determining a direction in which the drive voltage is applied. A DC motor drive circuit comprising: an application direction switching relay that switches according to the voltage output from the voltage comparator.