Electricity: motive power systems – Motor-reversing
Reexamination Certificate
2000-04-28
2002-05-07
Donels, Jeffrey (Department: 2837)
Electricity: motive power systems
Motor-reversing
C318S293000
Reexamination Certificate
active
06384555
ABSTRACT:
BACKGROUND OF THE INVETION
The present invention relates to a DC motor driving apparatus to drive a DC motor.
A DC motor driving apparatus to drive the DC motor is used in a toy car such as an electric radio control car.
FIG. 33
is a circuit diagram showing an example of the conventional DC motor driving apparatus used in the electric radio control car.
The DC motor driving apparatus in
FIG. 33
is structured by MOS type field effect transistors (hereinafter, called FET)
1
and
2
. The FET
1
is used for the speed control of a DC motor
3
, and the FET
2
is used for the braking of the DC motor
3
. Body diodes
4
and
5
respectively exist inside the FETs
1
and
2
. Incidentally, the user connects a Schottky diode
9
to a DC motor
30
, or assembles it in the DC motor driving apparatus.
A power supply terminal
301
is connected to a positive electrode of the DC power supply (not shown), and a ground terminal
302
is connected to a negative electrode of the DC power supply. As the DC power supply, for example, a nickel-cadmium cell is used. One terminal
3
a
of the DC motor
3
is connected to the power supply terminal
301
, and the other terminal
3
b
of the DC motor
3
is connected to the ground terminal
302
through the FET
1
. The FET
2
is connected between the one terminal
3
a
and the other terminal
3
b
of the DC motor. A control signal SWA is applied on a gate of the FET
1
, and a control signal SWB is applied on a gate of FET
2
.
The control signal SWA varies between the high level and the low level at the time of advance of the electric radio control car. Thereby, the FET
1
repeats turning ON and OFF. At this time, the control signal SWB is fixed on the low level. Thereby, the FET
2
is turned OFF. As the result, the current flows from the power supply terminal
301
to the ground terminal
302
through the terminal
3
a
, DC motor
3
, terminal
3
b
, and FET
1
, and the DC motor
3
is positively rotated. When the duty ratio of the control signal SWA applied on the gate of the FET
1
is changed, the speed control of the DC motor
3
is conducted.
At the time of braking of the electric radio control car, the control signal SWA is the low level, and the control signal SWB is the high level. Thereby, the FET
1
is turned OFF, and the FET
2
is turned ON, and terminals
3
a
and
3
b
are short circuited through the FET
2
. As the result, the DC motor
3
is braked.
FIG.
34
and
FIG. 35
are circuit diagrams showing the other example of the conventional DC motor driving apparatus used for the electric radio control car. The DC motor driving apparatus shown in FIG.
34
and
FIG. 35
is used for positively rotating and reversely rotating the DC motor, and
FIG. 34
shows the operation at the time of positive rotation of the DC motor, and
FIG. 35
shows the operation at the time of reversal rotation of the DC motor.
In FIG.
34
and
FIG. 35
, one terminal
31
of the DC motor
30
is connected to the power supply terminal
301
through FET
11
, and connected to the ground terminal
302
through the FET
13
. The other terminal
32
of the DC motor
30
is connected to the power supply terminal
301
through FET
12
, and connected to the ground terminal
302
through the FET
14
. Body diodes
21
,
22
,
23
, and
24
respectively exist inside the FETs
11
,
12
,
13
and
14
. The control signals SW
1
, SW
2
, Sw
3
and SW
4
are respectively applied on the gates of the FETs
11
,
12
,
13
, and
14
.
The control signal SW
1
becomes the high level at the time of positive rotation in
FIG. 34
, the control signal SW
2
becomes the low level, the control signal SW
3
becomes the low level, and the control signal SW
4
repeatedly changes between the high level and the low level. According to that, the FET
11
is turned ON, FETs
12
and
13
are turned OFF, and FET
14
repeats turned ON and OFF. As the result, as shown by an arrow, the current flows from the power supply terminal
301
to the ground terminal
302
through the FET
11
, terminal
31
, DC motor
30
, terminal
32
, and FET
14
, and the DC motor
30
is positively rotated. Thereby, the electric radio control car is moved forward.
The control signal SW
1
becomes the low level at the time of reversal rotation in
FIG. 35
, and the control signal SW
2
becomes the high level, the control signal SW
3
repeatedly changes between the high level and the low level, and the control signal SW
4
becomes the low level. According to that, the FET
11
is turned OFF, FET
12
is turned ON, FET
13
repeats turned ON and OFF, and FET
14
are turned OFF. As the result, as shown by an arrow, the current flows from the power supply terminal
301
to the ground terminal
302
through the FET
12
, terminal
32
, DC motor
30
, terminal
31
, and FET
13
, and the DC motor
30
is reversely rotated. Thereby, the electric radio control car is moved backward.
In the DC motor driving apparatus in
FIG. 33
, as described above, the FET
1
repeats turned ON and OFF at the time of the speed control. In this case, in the period in which the FET
1
is turned OFF, the counter electromotive force is generated in the DC motor
3
. When the counter electromotive force is generated in the DC motor
3
, because the drive efficiency of the DC motor
3
by the DC power supply is decreased, the regenerative current by the counter electromotive force is made to flow from the terminal
3
b
to the terminal
3
a
through the body diode
5
inside the FET
2
, thereby, the counter electromotive force is eliminated.
However, because the for ward voltage of the body diode
5
is comparatively high and about 0.6 V, the heat generation occurs due to the voltage drop, and the heat loss is generated. According to this, the drive efficiency is decreased, and the nickel-cadmium cell which is the DC power supply, is consumed uselessly. As the result, the running time period of the electric radio control car is reduced.
Accordingly, in order to increase the drive efficiency, a Schottky diode
9
is connected to the DC motor
3
, and the regenerative current due to counter electromotive force is made to flow from the terminal
3
b
to the terminal
3
a
through the Schottky diode
9
. The forward voltage of the Schottky diode
9
is about 0.4 V, and because it is not larger than the forward voltage of the body diode
5
inside the FET
2
, the regenerative current due to counter electromotive force of the DC motor
3
can be effectively made to flow.
However, a trouble for the user to connect the Schottky diode
9
to the DC motor
3
is generated. Alternatively, when the Schottky diode
9
is previously assembled in the DC motor driving apparatus, the size reduction of the DC motor driving apparatus can not be attained. It is desired that the DC motor driving apparatus is as small as possible so that the user can attach the DC motor driving apparatus to an arbitrary position of the electric radio control car.
Further, although the efficiency when the regenerative current flows to the Schottky diode
9
, is improved as compared to the case where the regenerative current flows to the body diode
5
inside the FET
2
, it is desired that the drive efficiency is further increased, and the heat generation amount is further decreased.
On the one hand, in the DC motor driving apparatus in FIG.
34
and
FIG. 35
, because
4
FETs
11
to
14
to drive the DC motor
30
positively and reversely, are used, it is difficult to decrease the size as compared to the DC motor driving apparatus in FIG.
33
. Accordingly, generally, when this DC motor driving apparatus is used, the Schottky diode is not connected. Accordingly, the regenerative current due to the counter electromotive force of the DC motor
30
flows to the body diodes
21
and
22
inside the FETs
11
and
12
.
In this case, because the heat generation amount due to the voltage drop is large, the drive efficiency is lowered, and nickel-cadmium cell which is the DC power supply, is consumed uselessly. As the result, the running time period of the electric rad
Donels Jeffrey
Keyence Corporation
Smith Patent Office
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