Electricity: motive power systems – Induction motor systems – Primary circuit control
Reexamination Certificate
2001-02-14
2003-02-04
Masih, Karen (Department: 2837)
Electricity: motive power systems
Induction motor systems
Primary circuit control
C318S254100, C318S132000, C318S434000, C318S473000, C388S934000
Reexamination Certificate
active
06515447
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fan motor with variable frequency/constant speed control, and more particularly to a fan motor which compares a signal frequency of an input pulse with a frequency of a signal detected from a fan and then varies an output voltage by a differential integrating circuit and a differential amplifier, such that the output voltage outputted to the fan has a smooth waveform, thereby saving electricity and precisely keeping the fan operate at a constant speed. Longevity of the fan is lengthened accordingly.
2. Description of the Related Art
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 inverse 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 integrating circuit IC
2
. The two voltage waveforms can be shaped by means of the driving integrating 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 with magnet. The capacitor C
1
provides voltage to the driving integrating circuit IC
2
for re-starting of the motor from a completely motionless 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 Vth which is dependent upon the resistance of sensor Rth and resistor R
4
will also be changed as the temperature changes. Voltage Vth and the reference voltage Vref, which is controlled by the voltage divider formed ho by resistors R
9
and R
10
, are input into operational amplifier IC
31
, to obtain a variable voltage Vo, 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 integrating circuit IC
2
to the windings L
1
, L
2
, L
3
, and L
4
are rectangular 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 environmental temperature make a change in the conductive current in the transistor TR
2
, output waveforms of the transistor TR
2
are still rectangular waveforms. Thus, rotating speed of the fan is increased or reduced suddenly due to rectangular 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 voltage 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, rectangular 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 rectangular 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 rectangular waveform, and the rotating speed of the fan
23
is increased or decreased suddenly in response to opening or closing of the rectangular 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 fan motor which compares a signal frequency of an input pulse with a frequency of a signal detected from a fan and then uses a differential integrating circuit and a differential amplifier to calculate the difference between the two frequencies. The difference is converted into a voltage signal which is then added to or subtracted from a predetermined voltage. The resultant voltage is connected to a voltage input end of the fan to thereby change the input voltage for the fan. Thus, the speed of the fan is increased or decreased gradually to avoid sudden change in the fan speed. Longevity of the fan is lengthened and the speed of the fan is kept at a constant value.
Accordingly, it is the primary object of the present invention to provide a fan motor which compares a signal frequency of an input pulse with a frequency of a signal detected from a fan and then varies an output voltage by a differential integrating circuit and a differential amplifier, such that the output voltage outputted to the fan has a smooth
Horng Alex
Tsai Nan Long
Bacon & Thomas
Masih Karen
Sunonwealth Electric Machine Industry Co. Ltd.
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