U.S. patent application number 10/178732 was filed with the patent office on 2002-12-26 for speed control circuit of brushless dc fan motor.
This patent application is currently assigned to MINEBEA CO., LTD.. Invention is credited to Xi, Junnan.
Application Number | 20020197068 10/178732 |
Document ID | / |
Family ID | 19030018 |
Filed Date | 2002-12-26 |
United States Patent
Application |
20020197068 |
Kind Code |
A1 |
Xi, Junnan |
December 26, 2002 |
Speed control circuit of brushless DC fan motor
Abstract
There is provided a brushless DC fan motor which can eliminate
an oscillator for PWM, control the motor speed at a low cost with
high accuracy, and efficiently adjust the temperature in a housing
for electronic appliances when radiating the heat in the housing.
The brushless DC fan motor with the rotational speed thereof
controlled by controlling the voltage of a control input terminal
of a drive circuit comprises a differential amplifier in which the
voltage signal for controlling the speed is inputted in a first
input terminal and the reference voltage signal is inputted in a
second input terminal. The differential amplifier is linear in the
input-output characteristic, and can set the rise characteristic of
a desired gradient, and control the motor speed with high accuracy
without using the PWM signal for the input signal. The voltage
signal from the output terminal of the differential amplifier is
given to the control input terminal of the drive circuit.
Inventors: |
Xi, Junnan; (Miyota-machi,
JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
MINEBEA CO., LTD.
Miyota-machi
JP
|
Family ID: |
19030018 |
Appl. No.: |
10/178732 |
Filed: |
June 25, 2002 |
Current U.S.
Class: |
388/825 |
Current CPC
Class: |
H02P 6/08 20130101 |
Class at
Publication: |
388/825 |
International
Class: |
H02P 007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 25, 2001 |
JP |
2001-191385 |
Claims
What is claimed is:
1. A speed control circuit of a brushless DC fan motor which is
driven by a drive circuit, and controlled in the rotational speed
thereof by controlling the voltage of a control input terminal of
the drive circuit comprising: a differential amplifier in which the
voltage signal for controlling the speed is inputted in a first
input terminal and the reference voltage signal is inputted in a
second input terminal, wherein the differential amplifier is linear
in the input-output characteristic, and can set a rise
characteristic of a desired gradient, and give the voltage signal
from the output terminal of the differential amplifier to the
control input terminal of the drive circuit.
2. A speed control circuit of a brushless DC fan motor according to
claim 1, wherein the reference voltage signal of the differential
amplifier is given from a resistance voltage division point of a
resistance voltage divider connected between a power source for
driving the circuit and the ground, and the resistance of the
resistance voltage divider is set to be an appropriate value in
order to obtain a desired minimum rotational speed.
3. A speed control circuit of a brushless DC fan motor according to
claim 1 or claim 2, wherein the voltage signal for controlling the
speed is inputted in the first input terminal of the differential
amplifier via a first resistor for setting the amplification
degree, a second resistor for setting the amplification degree is
connected between the first input terminal and the output terminal
of the differential amplifier, a desired amplification degree is
obtained for the differential amplifier by suitably setting the
resistance of the first and second resistors for setting the
amplification degree, and a desired rate of change in the
rotational speed is set.
4. A speed control circuit of a brushless DC fan motor according to
any one of claims 1 to 3, wherein the first input terminal and the
second input terminal of the differential amplifier are grounded
individually via a capacitor.
5. A speed control circuit of a brushless DC fan motor according to
any one of claims 1 to 4, wherein the voltage signal from the
output terminal of the differential amplifier is given to the
control input terminal of the drive circuit via a resistor for
finely adjusting the rotational speed.
6. A speed control circuit of a brushless DC fan motor according to
any one of claims 1 to 5, wherein a voltage signal transmission
line from the output terminal of the differential amplifier to the
control input terminal of the drive circuit is grounded at a
desired point via a capacitor.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a brushless DC fan motor
suitable for a fan radiating heat from a housing of an electronic
appliance, and more particularly to a speed control circuit
thereof.
[0003] 2. Description of the Related Art
[0004] In electronic appliance such as OA appliances including
personal computers and copiers, a large number of electronic
components are accommodated in a small housing, whereby heat is
generated from the electronic components and accumulated in the
housing so as to have a possibility to damage the electronic
components.
[0005] To solve this problem, a ventilation hole is provided in a
wall or a ceiling of the housing, and a fan motor is mounted on the
ventilation hole so as to radiate heat outside of the housing.
[0006] For using the brushless DC fan motor by making the
temperature of the housing controlled, the speed of the motor
should be accurately controlled.
[0007] FIG. 2 shows a speed control circuit of a conventional
brushless DC fan motor meeting this request.
[0008] In the figure, numeral 21 denotes the speed control circuit
of the brushless DC fan motor (circuit) 22. The two-phase motor 22
is employed here.
[0009] As shown in the figure, the brushless DC fan motor 22
comprises field coils L1 and L2, switching elements SW1 and SW2,
Zener diodes ZD1 and ZD2, resistors R1 to R4, a diode D1 and a
drive circuit 22a.
[0010] The field coils L1 and L2 are mounted on a stator (not
shown) and electrified in an alternately switching manner to form
the rotating magnetic field by the switching elements SW1 and SW2
alternately turning ON/OFF by the control signal from the drive
circuit 22a. A rotor (not shown) is rotated by rotating a permanent
magnet mounted thereon following the above rotating magnetic
field.
[0011] The position signals S1 and S2 from a sensor to detect the
position of rotation of the rotor are inputted in the drive circuit
22a as the timing signal of switching and electrifying the field
coils L1 and L2.
[0012] The speed control circuit 21 comprises resistors R5 to R10
and an NPN transistor Q1. The signal (PWM signal) in which the
temperature in a housing for an OA appliance (not shown) is
Pulse-Width Modulated (PWM), i.e., the signal in which the
temperature in the above housing is converted into the pulse width
(time) ratio on the H (High) and L (Low) levels of the voltage is
inputted as the input signal in an input terminal IN of the speed
control circuit 21. The inverted signal of the above input signal
is outputted from an output terminal OUT of the speed control
circuit 21.
[0013] The speed control circuit 21 either validates or invalidates
the control signal to the switching elements SW1 and SW2 of the
motor 22 in the drive circuit 22a by the voltage level of the
output
[0014] More specifically, the speed control circuit 21 validates
the above control signal when the voltage Vb of the output terminal
OUT (a control input terminal 22b of the drive circuit 22a) is less
than a predetermined value (the L-level). As a result, the
switching elements SW1 and SW2 are alternately turned ON/OFF. When
the voltage Vb is not less than the predetermined value (the
H-level), the speed control circuit invalidates the above control
signal, and turns off the switching elements SW1 and SW2.
[0015] The driving force is given to the rotor by alternately
electing the field coils L1 and L2, or the driving force is not
removed from the rotor by shutting off the electrification to the
field coils L1 and L2, and the rotational speed of the motor 22 is
thus controlled.
[0016] In such a speed control circuit 21, when the temperature in
the housing increases and the H-level time of the PWM signal to be
inputted in the input terminal IN is increased, the H-level time of
the base voltage of the transistor Q1 also increases, and the
L-level time of the voltage Vb of the output terminal OUT
increases.
[0017] As a result, the L-level time of the input voltage in the
drive circuit 22a, i.e., the time in which the above control signal
is valid is also increased, the time in which the driving force is
continuously given to the rotor (not shown) is increased, and the
rotational speed of the motor is thus increased.
[0018] As a result, the heat radiation effect is improved so as to
decrease the temperature in the above housing. Thus, if the PWM
signal in which the temperature in the housing is pulse-width
modulated is set to be the input signal of the speed control
circuit 21, the drive circuit 22a can be finely controlled by the
ratio of the H-level to the L-level, the speed of the motor 22 can
be accurately controlled such that the temperature in the housing
can be efficiently adjusted.
[0019] In the conventional speed control circuit 21 described
above, the PWM signal has been used for the input signal for the
following reason. That is, an operational point is established on
the voltage level in a rise characteristic curve of the transistor
Q1 when the output voltage is taken out from a collector by using
the voltage signal of the continuously changing level for the base
input signal of the transistor Q1 like the temperature detecting
output voltage from a thermistor.
[0020] However, the transistor Q1 has a steep but non-linear rinse
characteristic, and is difficult to set the above operational
point. Thus, it is difficult to improve the accuracy in controlling
the speed by either validating or invalidating the control signal
to the switching elements SW1 and SW2 with a predetermined
temperature (the voltage level of the input signal) as a
reference.
[0021] On the other hand, when the PWM signal is used for the input
signal, the temperature is expressed by the pulse width, i.e., the
length on the time axis, and thus, the above operational point need
not be finely set, and the setting thereof can be simplified.
Accordingly, the conventional speed control circuit 21 has used the
PWM signal for the input signal.
[0022] However, the conventional speed control circuit 21 requires
an element to convert the original physical quantity used to
control the speed, i.e., the temperature here into the electric
signal for example, an expensive oscillator for PWM to convert the
electric signal into the electric signal in addition to the
thermistor, and there occurs a problem, in that the cost required
for a circuit of the prestage is considerably increased.
SUMMARY OF THE INVENILON
[0023] Accordingly, the present invention has been made in light of
the above problems, and an object of the present invention is to
provide a speed control circuit of a brushless DC fan motor which
can eliminate any expensive elements or circuits of the prestage,
control the motor speed at a low cost with high accuracy, and
efficiently adjust the temperature in a housing for an electronic
appliance especially when applied for radiating heat outside of the
housing.
[0024] In order to solve the above problem, according to a first
aspect of the present invention, there is provided a speed control
circuit of a brushless DC fan motor driven by a drive circuit, and
controlled in the rotational speed thereof by controlling the
voltage of a control input terminal of the drive circuit, and
comprises a differential amplifier in which the voltage signal for
controlling the speed is inputted in a first input terminal and the
reference voltage signal is inputted in a second input terminal,
wherein the differential amplifier is linear in the input-output
characteristic, and can set a rise characteristic of a desired
gradient, and give the voltage signal from the output terminal of
the differential amplifier to the control input terminal of the
drive circuit.
[0025] According to a second aspect of the present invention, a
speed control circuit of a brushless DC fan motor of the first
aspect is characterized in that the reference voltage signal of the
differential amplifier is given from a resistance voltage division
point of a resistance voltage divider connected between a power
source for driving the circuit and the ground, and the resistance
of the resistance voltage divider is set to be an appropriate value
in order to obtain a desired minimum rotational speed.
[0026] According to a third aspect of the present invention, a
speed control circuit of a brushless DC fan motor according to the
first or second aspect of the present invention is characterized in
that the voltage signal for controlling the speed is inputted in
the first input terminal of the differential amplifier via a first
resistor for setting the amplification degree, a second resistor
for setting the amplification degree is connected between the first
input terminal and the output terminal of the differential
amplifier, a desired amplification degree is obtained for the
differential amplifier by suitably setting the resistance of the
first and second resistors for setting the amplification degree,
and a desired rate of change in the rotational speed is set.
[0027] According to a fourth aspect of the present invention, a
speed control circuit of a brushless DC fan motor according to any
one of the first to third aspects of the present invention is
characterized in that the first input terminal and the second input
terminal of the differential amplifier are grounded individually
via a capacitor.
[0028] According to a fix aspect of the present invention, a speed
control circuit of a brushless DC fan motor according to any one of
the first to fourth aspects of the present invention is
characterized in that the voltage signal from the output terminal
of the differential amplifier is given to the control input
terminal of the drive circuit via a resistor for finely adjusting
the rotational speed.
[0029] According to a sixth aspect of the present invention, a
speed control circuit of a brushless DC fan motor according to any
one of the first to fifth aspects of the present invention is
characterized in that a voltage signal transmission line from the
output terminal of the differential amplifier to the control input
terminal of the drive circuit is grounded at a desired point via a
capacitor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 shows a speed control circuit of a brushless DC fan
motor according to a first embodiment of the present invention;
and
[0031] FIG. 2 shows a speed control circuit of a conventional
brushless DC fan motor.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0032] The embodiments of the present invention will be described
with reference to attached drawings.
[0033] FIG. 1 shows a speed control circuit of a brushless DC fan
motor according to a first embodiment of the present invention.
[0034] In the figure, numeral 11 denotes a speed control circuit of
a brushless DC fan motor (circuit) 22. A two-phase motor 32 is
shown here. Symbols +V and +Vcc denote a power source for driving
the motor and the speed control circuit, respectively.
[0035] The above brushless DC fan motor 22 comprises field coils L1
and L2, switching elements SW1 and SW2, Zener diodes ZD1 and ZD2,
resistors R1 to R4, a diode D1 and a drive circuit 22a.
[0036] In this configuration, the field coils L1 and L2 are mounted
on a stator (not shown), and electrified in an alternately
switching manner to form the rotating magnetic field by the
switching elements SW1 and SW2 which are alternately turned ON/OFF
by the control signal from the drive circuit 22a. A rotor (not
shown) is rotated by rotating a permanent magnet mounted thereof
following the above rotating magnetic field.
[0037] The position signals S1 and S2 from a sensor to detect the
position of rotation of the above rotor (the permanent magnet), for
example, a Hall element, are inputted in the drive circuit 22a as
the timing signal of switching and electrifying the field coils L1
and L2.
[0038] The speed control circuit 21 comprises resistors R11 to R18,
capacitors C1-C3, and a differential amplifier AMP. The speed
control circuit 21 either validates or invalidates the control
signal to the switching elements SW1 and SW2 of the motor 22 in the
drive circuit 22a by the voltage level of the output signal
therefrom.
[0039] More specifically, the speed control circuit 21 validates
the above control signal when the voltage level Vb of the output
terminal OUT (a control input terminal 22b of the drive circuit
22a) is less than a predetermined value (the L-level). As a result,
the switching elements SW1 and SW2 are alternately turned ON/OFF.
When the voltage level Vb is not less than the predetermined value
(the H-level), the speed control circuit invalidates the above
control signal, and turns off the switching elements SW1 and
SW2.
[0040] This means that the driving force is given to the rotor by
alternately electrifying field coils L1 and L2, or the driving
force is removed from the rotor by shutting off the electrification
to the field coils L1 and L2, and the rotational speed of the motor
22 is thus controlled.
[0041] The speed control circuit 11 will be described below in
detail.
[0042] The differential amplifier AMP is linear in the input-output
characteristic and easy in setting the rise characteristic (the
amplification degree) of a desired gradient, and comprises an
operational amplifier. The voltage signal Vi for controlling the
rotational speed of the motor which is inputted in an input
terminal IN is inputted in an inverting input terminal - of the
differential amplifier (the operational amplifier) AMP via the
resistor R13. The reference voltage signal Va with the voltage
level set by the resistance voltage dividers (the resistors R11 and
R12) connected between the above power source +Vcc and the ground
is inputted in a non-inverting input terminal + of the differential
amplifier AMP via the resistor R14.
[0043] The above control voltage signal Vi is the voltage signal
with the level thereof continuously changed according to the
temperature in a housing of an OA appliance, for example, the
temperature detecting output voltage signal by a thermistor (not
shown). The reference voltage signal Va is the voltage
corresponding to the preset temperature of detection, in other
words, the voltage corresponding to the minimum rotational speed,
and the minimum rotational speed of the motor 22 corresponding to
the predetermined temperature of detection is set by the set value
of this voltage.
[0044] The resistor R15 is a resistor to set the amplification
degree (the gradient of the rise characteristic) of the
differential amplifier AMP, in other words, the rate of change of
the rotational speed of the motor 22 together with the resistor
R13, and connected by the inverting input terminal - and the output
terminal of the differential amplifier AMP.
[0045] The resistors R16 and R17 are resistors to set the voltage
of the control input terminal 22b of the drive circuit 22a at a
predetermined voltage level. The output signal Vo of the speed
control circuit 21 controls the voltage level Vb of the output
terminal OUT in a predetermined range with the voltage set by the
above resistors R16 and R17 as the reference.
[0046] The resistors R13 and R14 are set to be the same resistance.
Symbols R13 and R14 also denote each resistance thereof, and
symbols Vi and Va also denote each voltage level) thereof.
[0047] In the above configuration, the output voltage Vo of the
differential amplifier AMP is obtained by the following formula
(1)
Vo={(Vi-Va).multidot.(R13/R15)} (1)
[0048] The voltage level Vb of the control input terminal 22b is
obtained by the follow formula (2)
Vb=-Va(R13/R15).multidot.Vi+Va(R13/R15) (2)
[0049] The resistor R18 is inserted between an output terminal o of
the differential amplifier AMP and the above control input terminal
22b in order to finely adjust the voltage level Vb of the control
input terminal 22b of the drive circuit 22a, and is valid in finely
adjusting the rotational speed of the motor.
[0050] The capacitor C1 and the capacitor C2 are capacitors for
removing noise which are inserted between the inverting input
terminal - of the differential amplifier AMP and the ground, and
between the non-inverting input terminal + of the differential
amplifier AMP and the ground, respectively, and are effective to
obtain the stable rotational speed.
[0051] The capacitor C3 is a smoothing capacitor connected between
the control input terminal 22b of the drive circuit 22a and the
ground. The capacitor C3 is not essential in the speed control
circuit 11 in accordance with the present invention. However, the
PWM signal can be used for the input signal if this capacitor is
added to the speed control circuit.
[0052] Next, the operation will be described.
[0053] The differential amplifier AMP outputs the voltage signal
which is obtained by amplifying the difference in the voltage level
between the control voltage signal Vi and the reference voltage
signal Va at the amplification degree set by the resistors R13 and
R15. The output voltage Vo of the differential amplifier AMP is
reverse in polarity to the control voltage signal Vi (refer to the
formula (1) above).
[0054] When the temperature in the housing for the OA appliance
increases, and the temperature detecting output voltage by the
thermistor (not shown) is dropped, the voltage level of the control
voltage signal Vi inputted in the input terminal IN (the inverting
input terminal of the differential amplifier AMP) of the speed
control circuit 21 is dropped. As a result, the output voltage Vo
from the output terminal o of the differential amplifier AMP is
increased to the voltage obtained by the formula (1) above, and the
voltage level Vb of the output terminal OUT of the speed control
circuit 21 (the control input terminal 22b of the drive circuit
22a) is also increased to the voltage obtained by the formula (2)
above.
[0055] When the increased voltage level Vb is not less than the
voltage level to validate the control signal to the switching
elements SW1 and SW2 of the motor 22, the control signal becomes
valid.
[0056] Thus, the switching elements SW1 and SW2 of the motor 22 are
alternately turned ON/OFF, the field coils L1 and L2 are
alternately electrified, and the driving force is given to the
rotor (not shown). As a result, the motor 22 is started or
accelerated, and the radiation of heat in the housing is started or
increased so as to drop the temperature in the housing.
[0057] The above operation is continued until the voltage level Vb
is dropped below the voltage level at which the control signal to
the switching elements SW1 and SW2 is validated, and the
temperature in the housing is continuously dropped.
[0058] When the temperature in the housing is dropped, and the
temperature detecting output voltage by the thermistor (not shown)
is increased, the voltage level of the control voltage signal Vi
inputted in the input terminal IN of the speed control circuit 21
(the inverting input terminal - of the differential amplifier AMP)
is increased. As a result, the output voltage Vo from the output
terminal o of the differential amplifier AMP is dropped to the
voltage obtained by the formula (1) above, and the voltage level Vb
of the output terminal OUT of the speed control circuit 21 (the
control input terminal 22b of the drive circuit 22a) is also
dropped to the voltage obtained by the formula (2) above.
[0059] When the dropped voltage level Vb reaches the voltage level
at which the control signal to the switching elements SW1 and SW2
of the motor becomes invalid, the control signal becomes
invalid.
[0060] As a result, the switching elements SW1 and SW2 of the motor
22 are turned off, the electrification to the field coils L1 and L2
is shut off, and the driving force on the rotor is removed. As a
result, the rotor is subjected to the inertial rotation, i.e., the
decelerated rotation, the radiation of heat in the housing is
gradually reduced, and soon, the rotor is stopped, and the heat
radiation is completed.
[0061] When the temperature in the housing increases while the
rotor is stopped or under the decelerated rotation, and the voltage
level Vb of the output terminal OUT of the speed control circuit 21
is not less than the voltage level at which the control signal to
the switching elements SW1 and SW2 of the motor 22 is valid, the
above switching elements SW1 and SW2 are alternately turned ON/OFF
again.
[0062] As a result, the field coils L1 and L2 are alternately
electrified, and the driving force is given to the rotor, and the
rotor is started or accelerated. As a result, heat is started to be
radiated outside of the housing, or the radiation is increased, and
the temperature in the housing is dropped. These operations are
repeated to efficiently adjust the temperature in the housing to be
within a predetermined range.
[0063] In addition, the speed of the motor 22 can be accurately
controlled without using any PWM signal for the input signal, and
the temperature in the housing can be efficiently adjusted.
[0064] This means that not a transistor (refer to Q1 in FIG. 2) in
a conventional circuit, but the differential amplifier AMP which is
linear in the input-output characteristic and easy in setting the
rise characteristic (the amplification degree) of a desired
gradient is used in the present invention. As a result, the
accuracy in controlling the speed by either validating or
invalidating the control signal to the switching elements SW1 and
SW2 with a given temperature (the voltage level of the input
signal) as the reference can be improved not by using the PWM
signal for the input signal, but by using the temperature detecting
output voltage signal by an inexpensive sensor such as a
thermistor.
[0065] In the above embodiment, an explanation is given with the
two-phase brushless DC fan motor as an example, but any polyphase
brushless DC fan motor such as a three-phase motor can be
controlled.
[0066] Further, the above embodiment describes a case in which the
speed of the brushless DC fan motor is controlled by detecting the
temperature, but the brushless DC fan motor may be controlled by
other physical quantities including the humidity and the
concentration of the smoke or the gas.
[0067] As described above, the speed control circuit of the
brushless DC fan motor in accordance with the present invention has
advantages in that any expensive elements or circuits of the
presage are unnecessary, the motor speed can be controlled at a low
cost with high accuracy, and the temperature in the housing can be
efficiently adjusted particularly when the speed control circuit is
used for radiating the heat in electronic appliances.
[0068] Further, in the present invention, the minimum rotational
speed, the rate of change of the rotational speed, the fine
adjustment of the rotational speed, and the stable rotational speed
can be realized by a simple means by adding resistors and/or
capacitors, or setting these values. In addition, the PWM signal
can be used for the input signal.
* * * * *