Electricity: motive power systems – Constant motor current – load and/or torque control
Reexamination Certificate
2000-03-09
2001-11-27
Donels, Jeffrey (Department: 2837)
Electricity: motive power systems
Constant motor current, load and/or torque control
C318S434000
Reexamination Certificate
active
06323612
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a motor driving device for driving a motor.
2. Description of the Prior Art
A motor driving device is incorporated, for example, in a disk recording/reproducing apparatus for recording data on and reproducing data from a disk-shaped recording medium. In such a motor driving device, to keep the rotation speed of a motor constant, the rotation rate of the motor is detected, and the amplitude of a motor driving signal is controlled in accordance with the difference signal (error signal) that represents the difference between the detected rotation rate and the specified rotation rate. Here, when an extremely large error occurs, there is a risk of an overcurrent flowing through the motor. To prevent this, a current limiter circuit is provided to restrict the current flowing through the motor within a certain limit.
FIG. 4
shows the current limiter circuit employed in a conventional motor driving device. As shown in this figure, in this current limiter circuit, the output of a constant-current circuit CC is connected to the input of a current mirror circuit CM composed of an input-side NPN-type transistor Q
1
and an output-side NPN-type transistor Q
2
.
The emitter of the transistor Q
1
and the emitter of the transistor Q
2
are connected through resistors R
2
and R
3
, respectively, to a reference voltage GND. The collector of the output-side transistor Q
2
of the current mirror circuit CM is connected through a resistor R
1
to a supplied voltage V
CC
, with which a spindle motor is driven. The voltage at the node between the resistor R
1
and the collector of the transistor Q
2
is fed out as a current limit voltage V
CL
.
The error signal (error voltage) mentioned above is, together with the current limit voltage V
CL
output from the current limiter circuit, fed to a selector. The selector outputs the error voltage when the error voltage is higher than the current limit voltage and outputs the current limit voltage when the error voltage is lower than the current limit voltage. The output of this selector is fed through a current feedback amplifier to an amplitude control circuit for controlling the amplitude of the motor driving signal;.
However, configured as shown in
FIG. 4
, this current limiter circuit employed in a conventional spindle motor driving device as mentioned above has the following disadvantage. Suppose that the output current of the constant current circuit CC is I, the resistance of the resistor R
1
is R, and the resistors R
2
and R
3
have equal resistances. Then, the current limit voltage V
CL
is given by
V
CL
=V
CC
−I·R
Here, since the resistance varies with temperature, the current limit voltage VCL is prone to be influenced by heat. That is, it is difficult to keep the value of I·R (=V
CC
−V
CL
) within±several percent of 200 [mV] irrespective of temperature.
Accordingly, the limit of the driving current of the spindle motor is prone to vary with heat, and thus there is a risk of a current higher than the intended limit flowing through the spindle motor, causing thermal runaway. This often affects adversely the other circuits constituting the motor driving device, making the motor driving device unreliable against heat.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a motor driving device that offers higher reliability against heat.
To achieve the above object, according to the present invention, a motor driving device having a current limiter circuit that produces a current limit voltage, which is a fixed voltage determined in accordance with the driving voltage of the motor, usually controls the driving current of the motor in accordance with the signal representing the error of the actual rotation rate of the motor from the specified rotation rate thereof, but, when this requires that the driving current of the motor be higher than a predetermined level, controls the driving current of the motor in accordance with the current limit voltage. In this way, this motor driving device can restrict the driving current of the motor. Here, the current limiter circuit is composed of a plurality of resistors for dividing a given voltage, a first transistor that receives at its base a voltage obtained by voltage division achieved by the resistors, a constant current circuit for keeping the emitter current of the first transistor constant, a second transistor having its base connected to the emitter of the first transistor, a resistor connected between the emitter of the second transistor and one of the higher- and lower-potential sides of the driving voltage of the motor, and a resistor connected between the collector of the second transistor and the other of the higher- and lower-potential sides of the driving voltage of the motor. This current limiter circuit outputs as the current limit voltage the collector voltage of the second transistor. According to this circuit configuration, the current limit voltage is little affected by heat, and this helps suppress variation of the limit of the driving current of the motor with heat.
REFERENCES:
patent: 4639798 (1987-01-01), Harrison et al.
patent: 5847523 (1998-12-01), Rappenecker et al.
patent: 6130989 (2000-10-01), Mizumoto et al.
patent: 6166507 (2000-12-01), Uegami
Arent Fox Kintner & Plotkin & Kahn, PLLC
Donels Jeffrey
Rohm & Co., Ltd.
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