JPH1169875A - Motor control circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a motor control circuit which can supply a sufficient driving current under heavy load without requiring any semiconductor switch having high breakdown voltage, e.g. an FET, and thereby without increasing the size. SOLUTION: The control circuit for controlling the revolutions of a motor in a motor mower or a motor tool comprises a motor 1 having a plurality of brushes, an FET 2 provided at a part of conduction circuit to the brush of the motor 1, a constant voltage circuit 3 for setting the driving voltage of the motor 1 while sustaining the load voltage at a constant level, a triangular wave generation circuit 4, a circuit 6 for comparing the output from the triangular wave generation circuit 4 with a reference voltage being set by a variable resistor 5 to determine the duty ratio of PWM control, and an FET driving circuit 7 for turning the FET 2 on/off at that duty ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control circuit for an electric lawn mower or a power tool using an electric motor, and more particularly to a technique effective when applied to a motor control circuit using a semiconductor switch such as an FET.

[0002]

2. Description of the Related Art As a technique studied by the inventor, for example, a motor control circuit generally uses a semiconductor switch such as an FET on a power supply side or a ground side of a motor. This is based on FET ON / OFF control (PW
M control) makes it possible to control the drive current, and the motor speed and torque can be controlled freely, which is effective as motor control.

[0003]

By the way, in the motor control circuit as described above, since a starting current of the motor or a large current under a high load flows through a semiconductor switch such as an FET when the motor is controlled, the FET or the like is used. For the semiconductor switch, an element capable of sufficiently withstanding the current amount is selected. In this case, the size of the device is increased, and the size of the device is increased in consideration of heat radiation of a semiconductor switch such as an FET.

Therefore, an object of the present invention is to provide a high withstand voltage F
It is an object of the present invention to provide a motor control circuit that can supply a sufficient drive current under a heavy load without using a semiconductor switch such as an ET, and thus without increasing the size of the device.

[0005] The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0006]

SUMMARY OF THE INVENTION Among the inventions disclosed in the present application, the outline of a representative one will be briefly described.
It is as follows.

That is, a motor control circuit according to the present invention comprises a motor having a plurality of brushes, a semiconductor switch provided in a part of a circuit for energizing the brushes of the motor, and an input for setting a drive output of the motor. Determining means for determining a duty ratio of the PWM control for driving the motor based on an input signal of the input means, and control means for controlling the motor by controlling ON / OFF of the switch means based on the determined duty ratio. It is.

Therefore, according to the motor control circuit, the switch means provided in a part of the circuit for energizing the brush of the motor can be controlled by the duty ratio of the PWM control determined by the input signal of the input means. . That is,
The control means turns on / off the switch means according to the duty ratio.
The motor can be PWM-controlled by performing the OFF control.

As a result, even when a semiconductor element such as an FET is used as the switch means, a drive current suitable for the load can be supplied to the motor while reducing the size of the semiconductor switch.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a block diagram schematically showing an electric motor control circuit in which a motor control circuit according to an embodiment of the present invention is used for an electric lawn mower, a power tool or the like.

First, a schematic configuration of an electric motor control circuit using the motor control circuit of the present embodiment will be described with reference to FIG.

An electric motor control circuit using the motor control circuit of the present embodiment is a control circuit for controlling the number of revolutions of an electric motor such as an electric lawn mower or an electric tool.
A motor 1 having a plurality of brushes, an FET 2 provided in a part of a circuit for energizing the brushes of the motor 1, a constant voltage circuit 3 for converting a DC power supply to, for example, 5 V, and a triangular wave generating circuit 4 for generating a triangular wave A comparison circuit 6 for comparing the output of the triangular wave generation circuit 4 with a reference voltage from the variable resistor 5 to determine a duty ratio of the PWM control, and an FET drive circuit 7 for ON / OFF controlling the FET 2 based on the duty ratio.
It is composed of

The motor 1 includes a stator that generates a magnetic field by a permanent magnet, and a rotor that rotates by generating a torque in the magnetic field generated by the stator. For example, the armature of the rotor is formed by winding coils in six parallel circuits in a superimposed manner. And a brush is provided for each parallel circuit,
It has a six-pole motor structure having six brushes, and a plurality of energizing circuits are connected to these brushes. Through these energizing circuits, three positive brushes are commonly connected via a switch 8. Connected to the power supply voltage of the DC power supply 9, one of the three negative brushes is directly
Are respectively connected to the ground side of the DC power supply 9.

The FET 2 is a switch means for turning on / off the negative electrode of the motor 1 by using an output signal from the FET drive circuit 7 as an input.
For the signal, the two negative brushes of the motor 1 are connected to the ground side and the six brush circuits of the motor 1 are energized, while for the OFF signal, the two negative brushes from the two negative brushes to the ground side are turned on. The connection is cut off, and only the four brush circuits are turned on. This switch means can be applied to other semiconductor switches such as transistors, for example, in addition to the FET2.

The constant voltage circuit 3 converts the voltage of the DC power supply 9 to, for example, 5 V and supplies the converted voltage of the triangular wave generation circuit 4 and the variable resistor 5.

The triangular wave generating circuit 4 is a circuit for periodically generating a triangular waveform having an arbitrary oscillation frequency in order to set the duty ratio of the PWM control for driving the motor 1. Is output to the comparison circuit 6 and compared with the reference voltage set arbitrarily by the variable resistor 5 from the voltage of the constant voltage circuit 3.

The comparison circuit 6 sets the output of the triangular wave generation circuit 4 as a positive input (+) and the reference voltage from the variable resistor 5 as a negative input (-), and compares these voltages to determine the duty ratio of the PWM control. A circuit in which the duty ratio is determined based on the ratio of the portion where the triangular waveform exceeds the reference voltage to the portion below the reference voltage, and the portion exceeding the reference voltage is at a high level (“H”) and below the reference voltage. , A low-level (“L”) voltage is output periodically.

The FET drive circuit 7 receives the output voltage from the comparison circuit 6 as an input, and switches the FET 2 on the basis of this voltage.
This circuit performs N / OFF control. When the output voltage from the comparison circuit 6 is “H”, a “H” voltage that turns on the FET 2 is output, and when the output voltage is “L”, “L” that turns off the FET 2 is “L”. Is output.

Next, as for the operation of the present embodiment, PWM control in the operation of the electric motor control circuit will be described.

(1) The comparison circuit 6 outputs “H” when the periodic triangular wave output from the triangular wave generation circuit 4 exceeds the reference voltage by the variable resistor 5 and “L” when the periodic triangular wave is less than the reference voltage. Outputs each voltage. As a result, the motor 1
The duty ratio for M control can be determined.

(2) The FET drive circuit 7 turns on the FET 2 when the output voltage is "H" based on the duty ratio determined by the comparison circuit 6, and connects the two negative brushes to the ground side. Thus, the six brush circuits of the motor 1 can be turned on in combination with one negative brush connected directly to the ground side.

On the other hand, when the output voltage of the comparison circuit 6 is "L", the FET 2 is turned off. However, since one negative electrode brush is directly connected to the ground side, the motor 1 has only this brush circuit. It can be turned on.

(3) In the above PWM control, two of the three brush circuits on the ground side of the motor 1
By performing the M control, it is possible to adjust the amount of current flowing through these two brush circuits. That is, if the PWM control has a duty output of 0%, the current supplied to the motor 1 is only one ground-side brush circuit, the rotation speed of the motor 1 is low, and if the duty output is 100%, the ground-side brush circuit is All are energized, and the rotation speed of the motor 1 becomes high. By controlling the duty output, the rotation speed of the motor 1 can be controlled between the earlier low rotation speed and the high rotation speed.

Therefore, according to the electric motor control circuit of the present embodiment, two of the three brush circuits on the ground side of the motor 1 are handled by the FET 2, so that the rotation speed of the motor 1 can be controlled. However, since the current flowing through the FET 2 is only a current obtained by dividing the current flowing through the motor 1, the load on the FET 2 during the control of the motor 1 is reduced.

In particular, when a starting current of the motor 1 or a large current at the time of a high load flows, only the divided current needs to flow through the FET 2, so that a withstand voltage such that all the current flowing through the motor flows as in the prior art. There is no need to use a large FET,
The size of the FET 2 can be reduced.

Although the invention made by the inventor has been specifically described based on the embodiments of the present invention, the present invention is not limited to the above embodiments, and various modifications may be made without departing from the gist of the invention. Needless to say, it can be changed.

For example, in the above embodiment, 6
Although the description has been given of the case of a six-pole motor having three brushes, the present invention is not limited to the above-described embodiment, and may be applied to a multi-pole brush motor having a large number of brushes such as four or eight brushes. The present invention can be widely applied, and a part of a motor energization circuit may be intermittently controlled.

In the above embodiment, the case where the negative brush side is energized or the current is cut off and the current is de-energized has been described. On the contrary, the positive brush side may be energized / de-energized. Needless to say,

In the above description, a case has been described in which the invention made mainly by the inventor is applied to a motor control circuit used in an electric lawnmower, a power tool or the like, which is a technical field to which the invention belongs, but the invention is not limited to this. However, the present invention is widely applicable to motor control circuits of other devices and devices having a DC brush motor.

[0031]

Advantageous effects obtained by typical ones of the inventions disclosed in the present application will be briefly described.
It is as follows.

(1) The switch means provided in a part of the circuit for supplying electricity to the brush of the motor is controlled by the duty ratio of the PWM control determined by the input signal of the input means. Even when a semiconductor element is used, the current flowing through the semiconductor switch can be obtained by dividing the current flowing through the motor, so that the motor rotation speed can be controlled, but the current flowing through the motor is reduced as in the past. There is no need to use an FET having a large withstand voltage for flowing, and the FET 2 can be downsized.

(2) According to the above (1), it is possible to realize a motor control circuit that can supply a sufficient drive current under a high load without using a semiconductor switch having a large withstand voltage and, consequently, without increasing the size of the device. Becomes possible.

[Brief description of the drawings]

FIG. 1 is a configuration diagram schematically showing an electric motor control circuit in which a motor control circuit according to an embodiment of the present invention is used for an electric lawn mower, a power tool, or the like.

[Explanation of symbols]

 Reference Signs List 1 motor 2 FET 3 constant voltage circuit 4 triangular wave generation circuit 5 variable resistor 6 comparison circuit 7 FET drive circuit 8 switch 9 DC power supply

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Norikazu Shimizu 1-4-1 Chuo, Wako-shi, Saitama Prefecture Inside Honda R & D Co., Ltd. (72) Hiroo Sugaya 1-4-1-1 Chuo, Wako-shi, Saitama Prefecture No. Within Honda R & D Co., Ltd. (72) Inventor Yoshihisa Hirose 1-4-1 Chuo, Wako-shi, Saitama Pref.

Claims (1)

[Claims] 1. A motor having a plurality of brushes, semiconductor switch means provided in a part of a circuit for energizing the brushes of the motor, input means for setting a drive output of the motor, and input signal of the input means. Determining means for determining the duty ratio of the PWM control for driving the motor according to the above, and setting the switching means to O by the determined duty ratio.
A control unit for controlling the motor by N / OFF control.