Electricity: motive power systems – Automatic and/or with time-delay means – Responsive to thermal conditions
Reexamination Certificate
2001-02-14
2002-05-28
Masih, Karen (Department: 2837)
Electricity: motive power systems
Automatic and/or with time-delay means
Responsive to thermal conditions
C318S471000, C318S461000, C318S473000, C318S811000, C318S472000
Reexamination Certificate
active
06396231
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fan motor having two-step speed control, and more particularly to a fan motor that may output smooth voltage waveforms by a buffer circuit while altering the voltage level, such that the speed of the fan is increased or reduced gradually when the fan is switched between a low speed operation mode and a high speed operation mode, thereby lengthening longevity of the fan motor.
2. Description of the Related Art
It is common to employ heat-dissipating fans in computers and their peripherals to avoid break down of the system or burnt of the electronic elements resulting from temperature rise due to poor heat dissipation. During operation of a fan motor, the fan motor is operated in a low speed mode when the temperature in the system is not high. In this case, unnecessary load and noise are generated if the fan motor is operated at high speed. When the system is under full load and thus has a relatively high temperature that requires the fan operates in a high speed mode, otherwise the system may break down and/or the electronic elements may be burnt. In order to solve the above problems, speed-controllable heat-dissipating fans have been developed to adjust the speed of the fan in response to different system temperatures.
A conventional fan motor is shown in FIG.
1
and
FIG. 2
(including FIGS. 2A-2C) of the drawings that correspond to FIG.
2
and
FIG. 5
(including FIGS. 5A-5C) of U.S. Pat. No. 5,197,858 to Cheng issued on Mar. 30, 1993.
FIG. 1
is a circuit diagram of a controller for the fan.
FIG. 2
illustrates the output waveforms for the drive IC of the circuit. As illustrated in
FIG. 1
, when the power is on, via an reverse voltage protection diode D
1
, impellers start to rotate by mutual induction between winding coils and magnet. At this time, a Hall element IC
1
senses the variation of magnetic field between winding and magnet to cause the DC brushless motor to commute as follows: A predetermined current and DC level are supplied by resistors R
3
, R
2
. Positive (V+) and negative (V−) voltages are both output from the Hall element IC
1
to a driving integrated circuit IC
2
. The two voltage waveforms can be processed and shaped by means of the driving integrated circuit IC
2
by comparing them with an internal voltage to obtain the waveform shown in FIG.
2
A. This waveform controls semiconductor switches A
1
and A
2
to obtain the waveform shown as
FIGS. 2B and 2C
. Motor windings L
1
, L
2
, L
3
, and L
4
are controlled by the wave output from the semiconductor switches A
1
, A
2
to commutate in accordance with the magnetic couple of impeller ring-shaped magnet. The timing capacitor provides voltage to the driving integrated circuit IC
2
for re-starting of the motor from a completely stop state of the fan. As a result, a driving system composed of IC
1
and IC
2
can drive the fan and output a cycle-timing pulse signal.
IC
3
comprises three internal operational amplifiers IC
31
, IC
32
. IC
33
. Operational amplifiers IC
31
, with resistors R
4
, R
5
, R
6
, R
7
, R
8
, R
9
, R
10
and a thermal sensor Rth in combination, forms a control circuit for the slope of the curve of the speed versus the temperature of the thermal control variable speed fan. Because the resistance value of the thermal sensor Rth changes with temperature, the voltage Va which is dependent upon the resistance of sensor Rth and resistor R
4
will also be changed as the temperature changes. Voltage Va and the reference voltage Vref, which is controlled by the voltage divider formed by resistors R
9
and R
10
, are input into operational amplifier IC
31
, to obtain a variable voltage Vb, which causes the collector current of transistor TR
1
to change accordingly, changing the speed of the fan. Therefore, the object of the variable speed by thermal control is achieved.
Nevertheless, the waveforms output from the drive integrated circuit IC
2
to the windings L
1
, L
2
, L
3
, and L
4
are square waveforms, as shown in
FIGS. 2B and 2C
. In addition, although the change in the output voltage Vb by the operational amplifier IC
31
in response to change in the system environmental temperature make a change in the conductive current in the transistor TR
2
, output waveforms of the transistor TR
2
are still square waveforms. Thus, rotating speed of the system fan is increased or reduced dramatically due to square waveforms inputted to the windings L
1
, L
2
, L
3
, and L
4
. As a result, the fan wobbles and thus has a shortened longevity.
Another conventional fan motor is shown in
FIGS. 3 and 4
of the drawings that correspond to FIG. 2 and FIG. 3 of U.S. Pat. No. 5,942,866 to Hsieh issued on Aug. 24, 1999.
FIG. 3
is a schematic block diagram of a control circuit.
FIG. 4
shows the waveform signal outputted from a switching device of the control circuit. As illustrated in
FIG. 3
, a control circuit
10
for a DC brushless fan comprises a rectifying circuit
20
, a comparator
21
, and a switching device
22
. The rectifying circuit
20
receives a continuous, square wave signal from the fan
23
, which is indicative of the rotating speed of the fan
23
, and then sends a rectified and filtered DC voltage signal V
1
to inverted input terminal of the comparator
20
. The non-inverted input terminal of the comparator
21
is connected to a reference voltage signal Vref, which is used for setting the rotating speed of the fan
23
, and the output terminal of the comparator
21
is connected to the switching device
22
. The switching device
22
may be a transistor or an equivalent electronic switch that is serially connected between a source voltage Vcc and the source terminal of the fan
23
. The operation of the switching device
22
depends on the compared result of the rectified DC voltage signal V
1
outputted from the rectifying circuit
21
and the reference voltage signal Vref.
When the DC voltage signal V
1
outputted from the rectifying circuit
21
is lower than the reference voltage signal Vref, i.e., the rotating speed of the fan
23
is lower than its setting value, the comparator
21
outputs a Logic high value to the switching device
22
. Then, the switching device
22
is closed, and the fan
23
is powered on. Thus, rotating speed of the fan
23
will be increased.
In contrast, when the DC voltage signal outputted from the rectifying circuit
20
is higher than the reference voltage signal Vref, i.e., the rotating speed of the fan
23
is higher than its setting value, the comparator
21
outputs a Logic low value to the switching device
22
. Then, the switching device
22
is opened, and the fan
23
is powered off. Thus, rotating speed of the fan
23
will be decreased.
In operation, the switching device
22
is repeatedly closed and opened as the rotating speed of the fan varies, thus the fan is intermittently powered on, whereby the rotating speed of the fan
23
can be controlled and kept at a constant value. As illustrated in
FIG. 4
, the output signal of the switching device
22
is an intermittently opened and closed square wave, where the period (TIME ON) during which the switching device
22
is closed and the period (TIME OFF) during which the switching device
22
is opened are modulated so as to control the rotating speed of the fan
23
.
Nevertheless, the output waveform is an intermittently opened and closed square waveform, and the rotating speed of the fan
23
is increased or decreased dramatically in response to opening or closing of the sequare waveform or the switching device
22
. As a result, the fan wobbles and thus has a shortened longevity.
SUMMARY OF THE INVENTION
In view of the above drawbacks, the present invention provides a buffer circuit that is connected to the voltage source. The buffer circuit outputs different voltages in response to a change in the control voltage for driving the fan. During a change between a high voltage value and a low voltage value, the voltage waveform is a smooth linear waveform. Rotating speed of the fan
Horng Alex
Tsai Nan Long
Wang Ming-Sheng
Bacon & Thomas PLLC
Masih Karen
Sunonwealth Electric Machine Industry Co. Ltd.
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