U.S. patent application number 09/879951 was filed with the patent office on 2001-12-27 for spindle motor drive circuit.
This patent application is currently assigned to NEC CORPORATION. Invention is credited to Oku, Koichiro.
Application Number | 20010054874 09/879951 |
Document ID | / |
Family ID | 18683008 |
Filed Date | 2001-12-27 |
United States Patent
Application |
20010054874 |
Kind Code |
A1 |
Oku, Koichiro |
December 27, 2001 |
Spindle motor drive circuit
Abstract
The spindle motor drive circuit of the present invention
comprises: a power source voltage varying device for varying a
voltage applied to a motor by controlling a power source voltage;
and a pulse width varying device for varying a pulse width by pulse
width modulation.
Inventors: |
Oku, Koichiro; (Tokyo,
JP) |
Correspondence
Address: |
YOUNG & THOMPSON
745 SOUTH 23RD STREET 2ND FLOOR
ARLINGTON
VA
22202
|
Assignee: |
NEC CORPORATION
|
Family ID: |
18683008 |
Appl. No.: |
09/879951 |
Filed: |
June 14, 2001 |
Current U.S.
Class: |
318/599 |
Current CPC
Class: |
H02P 6/085 20130101 |
Class at
Publication: |
318/599 |
International
Class: |
G05B 011/28 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 16, 2000 |
JP |
2000-182202 |
Claims
1. A spindle motor drive circuit having: a power source voltage
varying device for varying a voltage applied to a motor by
controlling a power source voltage; and a pulse width varying
device for varying a pulse width by pulse width modulation.
2. A spindle motor drive circuit according to claim 1, wherein the
power source voltage varying device varies the voltage around a
minimum rotation speed of the motor or around a maximum rotation
speed of the motor.
3. A spindle motor drive circuit according to claim 1, wherein the
power source voltage device sets the minimum pulse width or the
maximum pulse width as the fixed pulse width.
4. A spindle motor drive circuit according to claim 1, wherein the
applied voltage and the pulse width are controlled based on an
differential voltage between a control reference voltage and a
control input voltage.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a spindle motor driving
circuit using PWM (pulse width modulation) control and VM (applied
voltage) control.
[0003] 2. Description of the Related Art
[0004] FIG. 5 is a block diagram showing a conventional spindle
motor driving circuit which achieves general VM variable linear
drive.
[0005] A spindle motor driver 51 does not have a circuit for
controlling a duty cycle, but has an electric current setting
amplifier 511 and a VM selecting circuit 512, which differ from the
PWM control method which is described below.
[0006] The linear drive method directly controls an output electric
current of an output three-phase bridge depending on an input
voltage, to drive the spindle motor at a predetermined speed. In
the linear drive method, an electric current setting amplifier 511
outputs a signal depending on a signal VREF2-VIN, and this output
controls a phase excitation circuit 1.
[0007] A circuit (using two power sources) in FIG. 5 has two
systems of VM power sources in a switching regulator 52. In
response to an external logic signal, a VM selecting circuit
selects one of VM1 and VM2 as the VM power source.
[0008] FIG. 6 shows the structure of the conventional PWM control
spindle motor driving circuit, and FIG. 7 shows motor speed/input
differential voltage characteristics.
[0009] The PWM control spindle motor driving circuit shown in FIG.
6 comprises a spindle motor driver 61, a switching regulator 62,
and a control circuit 63.
[0010] The spindle motor driver 61 comprises a phase excitation
circuit 11, a duty cycle setting comparator 516, a reference power
source (VREF3) 19, a triangular wave oscillation circuit 17, and a
three-phase bridge circuit 12 controlled by an excess current
restriction comparator 18 and a phase excitation circuit 11.
[0011] A differential voltage between VREF2 and VIN of the control
circuit 63 is input to the duty cycle setting comparator 616 in the
spindle motor driver 61, and is compared with triangular waves from
the triangular wave oscillation circuit 17, to thereby produce
rectangular waves. The rectangular waves are supplied as the gate
voltage of the three-phase bridge circuit 12. The PWM switching of
the three-phase bridge circuit 12 is performed based on the gate
voltage, and the electric current in the spindle motor M is thus
adjusted so that the characteristics shown in FIG. 7 are
achieved.
[0012] The linear driving method shown in FIG. 5, however,
increases the electric power consumption because the method drives
the motor based on the electric current and because this electric
current flows continuously. Therefore, heat production is increased
when driving the motor at a high speed or when starting the
motor.
[0013] The PWM driving method shown in FIG. 6 eliminates the
problem of the power consumption, but makes the setting of the duty
cycle (the on-duty cycle setting) around the minimum speed of the
motor and around the maximum speed difficult. Therefore, a dead
zone occurs depending on the off-set voltage of the circuit, the
linearity characteristics deteriorate, the control of speed around
the minimum and maximum rotation speeds becomes difficult, and
therefore the access time is lengthened when the motor is used in a
disk drive.
BRIEF SUMMARY OF THE INVENTION
[0014] It is therefore an object of the present invention to
provide a spindle motor driving circuit which can operate linearly
from the minimum rotation speed to the maximum rotation speed.
[0015] In the first aspect of the present invention, the spindle
motor drive circuit comprises: a power source voltage varying
device for varying the voltage applied to the motor by controlling
the power source voltage; and a pulse width varying device for
varying the pulse width by pulse width modulation.
[0016] In the second aspect of the present invention, the power
source voltage varying device varies the voltage around a minimum
rotation speed of the motor or around a maximum rotation speed of
the motor.
[0017] In the third aspect of the present invention, the power
source voltage device sets the minimum pulse width or the maximum
pulse width as the fixed pulse width.
[0018] In the fourth aspect of the present invention, the applied
voltage and the pulse width are controlled based on the
differential voltage between the control reference voltage and the
control input voltage.
[0019] According to the present invention, in the high duty cycle
and the low duty cycle regions, the applied voltage is controlled.
In the other regions, the applied voltage is fixed, and PWM control
is performed. Therefore, the input dead zone can be eliminated, and
the linearity of the characteristics from low rotation speeds to
high rotation speeds can be improved.
[0020] Further, in the high duty cycle region, the applied voltage
is increased so that the maximum rotation speed is increased.
Therefore, the maximum torque can be advantageously increased.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a block diagram showing the structure of the
spindle motor drive circuit of the present invention.
[0022] FIGS. 2A and 2B are diagrams showing the relationship
between the control voltage and the duty cycle under the PWM
control according to the present invention.
[0023] FIG. 3 is a diagram showing the operation of an FB
coefficient varying circuit of the present invention.
[0024] FIG. 4 is a diagram showing the relationship between the
control voltage and the rotation speed of the spindle motor
according to the present invention.
[0025] FIG. 5 is a block diagram showing the structure of the
conventional spindle motor drive circuit using the VM variable
linear drive technique.
[0026] FIG. 6 is a block diagram showing the structure of a
conventional spindle motor drive circuit using the PWM control.
[0027] FIG. 7 is a diagram showing the relationship between the
control signal voltage and the motor rotation speed in the
conventional spindle motor drive circuit using the PWM control.
DETAILED DESCRIPTION OF THE INVENTION
[0028] The embodiment of the present invention will be explained
with reference to the drawings. FIG. 1 is a block diagram showing
the structure of the spindle motor driving circuit of the present
invention. FIG. 2 is a diagram showing the relationship between the
control voltage signal and the duty cycle of the PWM control.
[0029] The spindle motor driving circuit shown in FIG. 1 comprises
a spindle motor driver 1, a switching regulator 2, and a control
circuit 3.
[0030] The spindle motor driver 1 for driving a spindle motor M has
a phase excitation circuit 11 for outputting an excitation signal
for each phase, a three-phase bridge circuit 12 which is excited by
the phase excitation circuit 11. Further, the spindle motor driver
1 has an input differential voltage amplifier 13 for comparing and
amplifying the control input from the control circuit 3, a duty
cycle selecting circuit 14, and a duty cycle setting comparator 16
which operates as a circuit for producing a control signal to be
supplied to the phase excitation circuit 11. Further, the spindle
motor driver 1 has a triangular wave oscillation circuit 17, and an
external capacitor for triangular wave oscillation which oscillate
triangular waves as the reference of the output pulse width, and
has motor voltage varying setting switches SW1 and SW2. In
addition, the spindle motor driver 1 has a comparison amplifier 18
for controlling excess currents, a reference voltage source
(VREF3), and an external excess current setting resistor R1.
[0031] The switching regulator 2 comprises a switching element
(FET) 21 and a filter circuit 22 which generate a control power
source VDD which is for one of two power source systems, and a
switching element (FET) 23 and a filter circuit 24 which generate a
power VM for driving the spindle motor M.
[0032] The FETS 21 and 23 are controlled by comparison amplifiers
28 and 29 which operate depending on the outputs of the reference
voltage source (VREF1) 25, the oscillation circuit 26, and the FB
coefficient varying circuit 27.
[0033] The FB coefficient varying circuit 27 is provided in a
feedback group of the motor power source VM, and controls the
feedback voltage depending on the output of the input differential
amplifier 13 of the spindle motor driver 1.
[0034] The control circuit 3, whose internal circuit is not shown,
has a speed pulse input FGin for receiving a rotation speed signal
output from the phase excitation circuit 11 of the spindle motor
driver 1, a VREF2 for providing a control reference signal, a VIN
for providing a control signal, a VMvar for setting the mode to a
motor voltage variable mode, and a PWM-lock for fixing or varying
the PWM on-duty cycle (the pulse width) of the spindle motor driver
1.
[0035] The operation of the present invention will be explained
with reference to FIG. 1.
[0036] The main power sources for the spindle motor driver 1 are
the power source VDD for the control circuit and the power source
VM for driving the motor. The signals VREF2 and VIN are input to
the input differential amplifier 13. The input differential
amplifier 13 outputs a signal in proportion to the differential
voltage which is VREF2-VIN. The differential voltage signal is
input to the duty cycle selecting circuit 15.
[0037] The reference voltages H and L which have been divided and
generated by the resistors R3, R4, and R5 based on the VREF2 are
input to the duty cycle selecting circuit.
[0038] The reference voltages H and L are used to set the fixed
values of the maximum duty cycle and the minimum duty cycle. The
setting of the fixed cycle duty mode or the variable mode depends
on the PWM-lock signal from the control circuit 3.
[0039] When the PWM-lock signal is at the high level, the output of
the input differential amplifier 13 is always selected by the duty
cycle selecting circuit.
[0040] When the PWM-lock signal is at the low level, and when the
reference voltage H<(VIN-VREF2), the reference voltage H is
selected by the duty cycle selecting circuit. When the PWM-lock
signal is at the low level, and when the reference voltage
L<(VREF2-VIN), the (VREF2-VIN) is selected by the duty cycle
selecting circuit 14.
[0041] The output of the duty cycle selecting circuit is input to
the duty cycle setting comparator 16. That is, one of the output of
the input differential amplifier 13, the reference voltage H, and
the reference voltage L, which is selected by the duty cycle
selecting circuit 14 is input, and the triangular wave oscillation
signal generated by the triangular wave oscillation circuit 17 is
input.
[0042] In the duty cycle setting comparator 16, the triangular
waves intersect the output signal selected by the duty cycle
selecting circuit 14, and the phase excitation circuit 11 produces
rectangular waves for the PWM in the cycle based on the
intersections. The rectangular waves are input to a gate terminal
(not shown) of the three-phase bridge circuit 12.
[0043] As shown in FIG. 2, when the PWM-lock signal is at the low
level, the PWM for the low duty cycle is in the fixed cycle duty
mode based on the reference voltage L, the PWM for the high duty
cycle is in the fixed cycle duty mode based on the reference
voltage H, and the PWM for the medium duty cycle is in the PWM
variable mode based on the value VIN-VREF2.
[0044] The output of the input differential amplifier 13 is input
via the switch SW2 to the FB coefficient varying circuit 27 of the
switching regulator 2. The FB coefficient varying circuit 27 is
provided in the feedback group of the switching regulator 2, and
varies the FB coefficient according to the signal output from the
input differential amplifier 13 to vary the VM voltage.
[0045] The gate signal of the switch SW2 is input from the duty
cycle selecting circuit 14. When the duty cycle selecting circuit
14 selects the fixed cycle duty mode (when the reference voltage H
or L is selected), the signal at the high level is output.
[0046] Therefore, the output of the input differential amplifier is
input to the FB coefficient varying circuit 27 only in the fixed
cycle duty mode.
[0047] Next, the operation of the FB coefficient varying circuit 27
will be explained with reference to FIG. 3. In the variable duty
cycle mode, the FB coefficient varying circuit 27 does not operate,
and therefore a fixed motor voltage (VM1) is produced. Then, as the
duty cycle decreases or increases to the reference voltage L or H,
the mode enters the fixed cycle duty mode so that the motor voltage
VM is controlled.
[0048] The FB coefficient varying circuit 27, whose internal
circuit is not shown, comprises a bipolar transistor which varies
the voltage between the collector and the emitter of the transistor
by controlling the base electric current to change the FB
coefficient.
[0049] The variation of the FB coefficient for a low duty cycle
increases the feedback voltage, while the variation of the FB
coefficient for a high duty cycle decreases the feedback voltage.
As the result, the VM voltage is less than VM1 when the duty cycle
is low, and is greater than VM1 when the duty cycle is high.
[0050] Referring to FIG. 1, the switch SW1 of the spindle motor
driver 1 sets VM to be variable. When the VMvar output of the
control circuit 3 is at the high level, the switch SW1 is turned on
so that the FB is not varied.
[0051] The operation depending on the logic values of VMvar and
PWM-lock input from the control circuit will now be explained.
[0052] (1) When the VMvar is at the low level and when the PWM-lock
is at the low level, the voltage applied to the spindle motor is
variable. The VM is variable in the low duty cycle and the high
duty cycle regions in which the PWM output of the spindle motor
drive circuit is fixed.
[0053] That is, when the duty cycle is low, the duty cycle is fixed
based on the reference voltage L. When the duty cycle is high, the
duty cycle is fixed based on the reference voltage H.
[0054] (2) When the VMvar is at the low level, and when the
PWM-lock is at the high level, the voltage applied to the spindle
motor is variable. The PWM duty cycle depends on the output of the
input differential amplifier (the differential voltage of
VREF2-VIN), while the output pulse width is a low duty cycle, or a
high duty cycle, and the VM is variable.
[0055] (3) When VMvar is at the high level, and when PWM-lock is at
the low level, the FB coefficient varying circuit does not operate
so that the applied voltage VM is fixed.
[0056] When the duty cycle is low, the duty cycle is fixed based on
the reference voltage L. When the duty cycle is high, the duty
cycle is fixed based on the reference voltage H.
[0057] (4) When VMvar is at the high level, and when PWM-lock is at
the high level, the FB coefficient varying circuit does not operate
so that the applied voltage VM is fixed.
[0058] The PWM duty cycle depends on the output of the input
differential amplifier (the differential voltage of VREF2-VIN).
This operation is similar to that of a conventional PWM drive
circuit.
[0059] Reference numeral 19 in the spindle motor driver 1 denotes a
VREF3 which is a reference voltage source for restricting an excess
electric current. The comparator 18 compares the VREF3 with the
product of the motor electric current and the resistance for
restricting the excess electric current. When the VREF3 is less,
the output is forcibly turned off.
[0060] This control achieves the linear relationship between the
control signal voltage and the rotation speed of the spindle motor
as shown in FIG. 4.
[0061] This invention may be embodied in other forms or carried out
in other ways without departing from the spirit thereof. The
present embodiments are therefore to be considered in all respects
illustrative and not limiting, the scope of the invention being
indicated by the appended claims, and all modifications falling
within the meaning and range of equivalency are intended to be
embraced therein.
* * * * *