Electricity: motive power systems – Reciprocating or oscillating motor – Energizing winding circuit control
Reexamination Certificate
2002-04-17
2004-11-09
Martin, David (Department: 2837)
Electricity: motive power systems
Reciprocating or oscillating motor
Energizing winding circuit control
C318S434000, C318S723000, C318S503000
Reexamination Certificate
active
06815916
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a speed-control drive circuit for a D.C. brushless fan motor. In particular, the present invention relates to a fan motor that supplies source by means using pulse width modulation to adjust the power of the fan motor, i.e., to adjust the drive circuit that controls the rotational speed of the fan motor.
2. Description of the Related Art
The heat-dissipating devices for computers, particularly portable computers (or so-called “notebooks”), are low electricity-consuming rate and low noise. In order to save electricity, the fan motor of the heat-dissipating device must change its speed in response to the change in the ambient air. In particular, the speed of the fan motor is increased when the ambient temperature rises, and the speed of the fan motor is reduced when the ambient temperature lowers. A typical method for controlling the speed of the fan motor is to directly control the voltage of the source input end. However, this causes a considerable rise in the temperature due to power consumption of the control circuit; namely, another heat source is generated. As a result, the heat source not only causes a rise in the ambient temperature but also increases the power consumption and thus fails to save electricity.
In order to improve the electricity-saving effect, current speed-control systems of fan motors for portable computers adopt pulse width modulation to supply source, thereby adjusting the power of the fan motor. A drive integrated circuit (model no. PT308F manufactured by Prolific Technology Inc.) for a D.C. brushless fan motor adopts pulse width modulation to adjust the duty ratio of the fan motor. However, the specification of PT308F drive integrated circuit could not meet that of current drive circuits for fan motors. As a result, redesigning of the drive circuit of the fan motor is required and the complexity of the fan motor increases accordingly. Further, the PT308F drive integrated circuit is expensive and thus increases the overall cost for the fan motor. Further, the volume specification of the PT308F drive integrated circuit is greater than that of ordinary drive integrated circuits such that the PT308F drive integrated circuit could not be used with small fan motors.
When a drive circuit for an ordinary fan motor uses pulse width modulation to supply source, the pulse width modulation signal of a portable computer must be connected to the drive circuit so as to control the power output of the source for the drive circuit. Thus, the drive circuit for an ordinary fan motor saves electricity and has low noise and thus can be used as a drive circuit for a low-cost small fan motor while saving the cost for redesigning for the specification. Structures, functions, and operations of typical examples of single-phase and two-phase fan motor drive circuits are explained below.
Refer to
FIG. 1
that shows a drive circuit of a single-phase D.C. brushless fan motor. The drive circuit includes a motor winding CL
1
, a Hall element IC
1
, and a drive element IC
2
. The drive element IC
2
includes a transistor for driving the motor winding CL
1
. The Hall element IC
1
detects a change in the polarity of the permanent magnet of the rotor and generates a weak Hall voltage which is then outputted to the drive element IC
2
for amplification. The amplified Hall voltage is outputted by the drive element IC
2
through the output ends
01
and
02
to the motor winding CL
1
to excite/unexcite the motor winding CL
1
and to alternately change the direction of the current, thereby driving the rotor of the motor to turn by means of excitation. The drive element IC
2
further includes a frequency generating/outputting end FG for connection with the user's end. Further, the drive element IC
2
includes a control input end ST for controlling starting or stopping of the motor, wherein the motor starts to turn when the control input end ST is at a low level, and wherein the motor stops turning when the control input end ST is at a high level.
FIG. 2
illustrates a circuitry of a conventional drive circuit for a two-phase D.C. brushless fan motor. As shown
FIG. 2
, the drive circuit for a two-phase D.C. brushless fan motor includes a first motor winding CL
1
, a second motor winding CL
2
, a Hall element IC
1
, a first transistor Q
1
, a second transistor Q
2
, a first resistor R
1
, a second resistor R
2
, a third resistor R
3
, a first Zener diode ZD
1
, and a second Zener diode ZD
2
. The first transistor Q
1
, the second transistor Q
2
, the first resistor R
1
, the second resistor R
2
, the third resistor R
3
, the first Zener diode ZD
1
, and the second Zener diode ZD
2
together form a motor winding drive circuit. The Hall element IC
1
detects a change in the polarity of the permanent magnet of the rotor and generates a weak Hall voltage which is then outputted through the second resistor R
2
to the first transistor Q
1
and the second transistor Q
2
to thereby drive the first motor winding CL
1
and the second motor winding CL
2
respectively connected to the collectors of the first transistor Q
1
and the second transistor Q
2
. Thus, the motor windings CL
1
and CL
2
are excited/unexcited and the direction of the current is alternately changed, thereby driving the rotor of the motor to turn by means of excitation. The fan motor drive circuit further includes a frequency divider element IC
3
. The detected signal from the Hall element is amplified by the resistor R
4
and the transistor Q
3
, and the amplified signal is then inputted to the input end IN of the frequency divider element IC
3
. Then, the amplified signal is connected through the output end A to a frequency generating/outputting end FG for connection with the user's end.
FIG. 3
illustrates a circuitry of another conventional drive circuit for a two-phase D.C. brushless fan motor. As shown
FIG. 3
, the drive circuit for a two-phase D.C. brushless fan motor includes a first motor winding CL
1
, a second motor winding CL
2
, a Hall element IC
1
, a drive element IC
2
, a first transistor Q
1
, a second transistor Q
2
, a first resistor R
1
, a second resistor R
2
, a third resistor R
3
, and a capacitor C. The first transistor Q
1
, the second transistor Q
2
, the first resistor R
1
, the second resistor R
2
, the third resistor R
3
, and the as capacitor C together form a motor winding drive circuit. The Hall element IC
1
detects a change in the polarity of the permanent magnet of the rotor and generates a weak Hall voltage. The detected signal (i.e., the Hall voltage) is inputted to the input end IN of the drive element IC
2
and then outputted through the output ends
01
and
02
to the first transistor Q
1
and the second transistor Q
2
for amplification to thereby drive the first motor winding CL
1
and the second motor winding CL
2
respectively connected to the collectors of the first transistor Q
1
and the second transistor Q
2
. Thus, excitation/unexcitation is generated and the direction of the current is alternately changed, thereby driving the rotor of the motor to turn by means of excitation. The output end FG of the drive element IC
2
is connected to the user's end.
Referring to
FIGS. 1 through 3
, when using conventional fan motor drive circuits adopting pulse width modulation to supply source, it is necessary to input the pulse width modulation signal into the motor winding drive circuit of the fan motor drive circuit, thereby controlling excitation/unexcitation of the motor winding and alternately changing the direction of current.
The present invention is intended to provide a speed-control drive circuit for a D.C. brushless fan motor that eliminates the above-mentioned drawback.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a D.C. brushless fan motor having a speed-control drive circuit, wherein a pulse width modulation signal is inputted to a motor winding drive circuit for a fan motor drive circuit to thereby control the motor winding drive circuit to g
Horng Alex
Lu Ying-Ya
Wang Ming-Shen
Bacon & Thomas PLLC
Colon Santana Eduardo
Martin David
Sunonwealth Electric Machine Industry Co. Ltd.
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