Electricity: motive power systems – Limitation of motor load – current – torque or force
Reexamination Certificate
2003-07-08
2004-12-14
Ip, Paul (Department: 2837)
Electricity: motive power systems
Limitation of motor load, current, torque or force
C318S434000, C318S254100, C318S286000, C324S161000
Reexamination Certificate
active
06831434
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns a control circuit for a brushless DC motor. More particularly, the present invention concerns a control circuit for a brushless DC motor equipped with a protective circuit.
2. Description of the Prior Art
FIG. 2
shows an example of a circuit diagram of a control circuit for a brushless DC motor equipped with a protective circuit of the prior art.
In
FIG. 2
, a Hall device
1
detects magnetic pole position of a rotor (not illustrated) having N-S magnetic poles, being rotatably supported and opposing to stators (also not illustrated) with an air-gap between the rotor and the stators. The stators are provided with single phase stator windings
9
,
10
. Output signal of the Hall device
1
is transmitted to a Hall amplifier
1
-
1
that amplifies the output signal. A logical circuit
2
-
1
receives output of the Hall amplifier
1
-
1
and generates two-phase half wave power supply signals. The two-phase half wave power supply signals are transmitted to power amplification semiconductor devices (power devices)
4
,
5
. The power amplification semiconductor devices
4
,
5
supply currents alternately to a stator winding
9
or to a stator winding
10
, connected respectively to the power amplification semiconductor device
4
or to the power amplification semiconductor device
5
. Thus the rotor is rotated in a predetermined rotational direction.
A rotation detection circuit
2
-
3
receives AC signal of the output of the Hall device
1
transmitted from the logical circuit
2
-
1
, and charges or discharges a locking detection capacitor
2
-
4
according to the AC signal. A comparator
2
-
5
detects voltage at a not grounded end portion of the locking detection capacitor
2
-
4
. A reset circuit
2
-
6
makes an output signal circuit of the logical circuit
2
-
1
“ON” or “OFF” state according to the output of the comparator
2
-
5
, as will be explained later. A combination circuit
2
-
7
combines outputs of the reset circuit
2
-
6
and the logical circuit
2
-
1
, and outputs locking detection signal.
Output of the combination circuit
2
-
7
is connected to an output terminal
3
, outputs of the logical circuit
2
-
1
are respectively connected to output terminals
7
,
8
, and the not grounded end portion of the locking detection capacitor
2
-
4
is connected to a terminal
6
.
Additionally, a driving IC
2
comprises the Hall amplifier
1
-
1
, the logical circuit
2
-
1
, the rotation detection circuit
2
-
3
, the comparator
2
-
5
, the reset circuit
2
-
6
and the combination circuit
2
-
7
.
It sometimes happens that a rotor of a brushless DC motor is locked by some cause such as an overload, and the motor stops to rotate. In case that the rotor is locked, since no induced voltage is generated in the stator windings
9
,
10
, the resistances of the stator windings
9
,
10
become the only factors to restrict the currents flowing through the stator windings
9
,
10
. Accordingly, there is a risk that excessive currents may flow in the stator windings
9
,
10
as well as in the power amplification semiconductor devices
4
,
5
, and that the stator windings
9
,
10
and the power amplification semiconductor devices
4
,
5
may be damaged by heat.
In the driving IC
2
as explained above, if the rotor is locked, no output signal is transmitted from the Hall device
1
, and no AC signal of the output of the Hall device
1
is transmitted from the logical circuit
2
-
1
to the rotation detection circuit
2
-
3
. Accordingly, the rotation detection circuit
2
-
3
merely charges the locking detection capacitor
2
-
4
without discharging it. Therefore, voltage at the not grounded end portion of the locking detection capacitor
2
-
4
is raised. The comparator
2
-
5
detects the raised voltage at the not grounded end portion of the locking detection capacitor
2
-
4
, and makes the output signal circuit of the logical circuit
2
-
1
“OFF” state, through the reset circuit
2
-
6
, to cut off the output signal of the logical circuit
2
-
1
, if the voltage at the not grounded end portion of the locking detection capacitor
2
-
4
exceeds a predetermined value. Thus, the two-phase half wave power supply signals are not transmitted into the power amplification semiconductor devices
4
,
5
, and currents are not supplied to the stator windings
9
,
10
of the brushless DC motor. Thus the stator windings
9
,
10
and the power amplification semiconductor devices
4
,
5
can be prevented from being damaged by heat.
After the currents to the stator windings
9
,
10
having been cut off, the voltage at the not grounded end portion of the locking detection capacitor
2
-
4
falls due to natural discharge with the passage of time. The comparator
2
-
5
detects the voltage that has fallen, and makes the output signal circuit of the logical circuit
2
-
1
“ON” state, through the reset circuit
2
-
6
, to allow the logical circuit
2
-
1
to transmit the output signal, if the voltage is lower than the predetermined value. Thus, function of the control circuit is automatically reset, currents are fed again to the stator windings
9
,
10
of the brushless DC motor, and the motor returns to normal rotation, if the cause of the locking of the rotor has been removed.
However, if the cause of the locking of the rotor has not been removed, no output signal is transmitted from the Hall device
1
since the rotor can not rotate, and no AC signal of the output of the Hall device
1
is transmitted from the logical circuit
2
-
1
to the rotation detection circuit
2
-
3
. Accordingly, the rotation detection circuit
2
-
3
merely charges the locking detection capacitor
2
-
4
without discharging it. Therefore, voltage at the not grounded end portion of the locking detection capacitor
2
-
4
is again raised. The comparator
2
-
5
detects the raised voltage at the not grounded end portion of the locking detection capacitor
2
-
4
, and makes the output signal circuit of the logical circuit
2
-
1
“OFF” state, through the reset circuit
2
-
6
, to cut off the output signal of the logical circuit
2
-
1
, if the voltage exceeds the predetermined value. Thus, the two-phase half wave power supply signals are not transmitted into the power amplification semiconductor devices
4
,
5
, and currents are not supplied to the stator windings
9
,
10
of the brushless DC motor.
Thus, “ON” and “OFF” states of the output signal circuit of the logical circuit
2
-
1
are repeated, and the stator windings
9
,
10
and the power amplification semiconductor devices
4
,
5
are prevented from being damages by heat.
Repetition frequency of “ON” and “OFF” states of the output signal circuit of the logical circuit
2
-
1
can be adjusted by suitably selecting resistance of the rotation detection circuit
2
-
3
and capacitance of the locking detection capacitor
2
-
4
.
Additionally, the function of the control circuit can be returned to the normal state by removing the cause of the locking of the rotor.
In case that a brushless DC motor is used as a fan motor for cooling of an electronic equipment for example, a control circuit of a small size having a high output power is strongly requested to be used. As a result, since the temperature in a power amplification semiconductor device rises rapidly when the rotor is locked, there is a problem that it is difficult to deal with the problem concerning the raised temperature by adjusting the repetition frequency of “ON” and “OFF” states of the currents in a driving IC.
SUMMARY OF THE INVENTION
It is an object of the present invention to solve the above problem in the prior art and to provide a control circuit for brushless DC motor equipped with protective circuit, that is capable of preventing stator windings and power amplification semiconductor devices from being damaged by heat when a rotor is locked and excessive currents flow through the stator windings, that is small in size, that has high output power, and that is low in cost.
To achieve the above obje
Birch Stewart Kolasch & Birch, LLP.
Ip Paul
Japan Servo Co. Ltd.
LandOfFree
Control circuit for brushless DC motor equipped with... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Control circuit for brushless DC motor equipped with..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Control circuit for brushless DC motor equipped with... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3310104