Electricity: motive power systems – Positional servo systems – Pulse-width modulated power input to motor
Reexamination Certificate
2001-11-21
2003-05-13
Masih, Karen (Department: 2837)
Electricity: motive power systems
Positional servo systems
Pulse-width modulated power input to motor
C318S716000, C318S798000, C318S811000
Reexamination Certificate
active
06563284
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to electronic circuits and, more particularly, to a circuit, system, structure and method for controlling and monitoring the speed of a motor.
BACKGROUND OF THE INVENTION
Electronic circuits are employed in numerous consumer and industrial applications. Such applications are extremely diverse; from computers, to wireless portable communications devices, to industrial controls, etc. In such myriad applications, the electronic circuits, typically fabricated and packaged as integrated circuit (IC) chips, are utilized to achieve various types of functions, for example, digital control, digital-to-analog (D/A) or analog-to-digital (A/D) conversion, mixed signal analysis, etc.
One exemplary circuit application relates to the drive and control of DC cooling fans which are employed in systems such as portable, notebook computers. Such cooling fans operate to cool the various notebook computer components located therein and are controlled using, for example, a DC brushless motor. The DC brushless motor, in turn, is driven and controlled by a control system, as illustrated in prior art
FIG. 1
, and designated at reference numeral
10
.
The exemplary system
10
includes a fan speed controller circuit
12
and a fan driver circuit
14
. The fan speed controller circuit
12
provides a control signal, for example, a pulse width modulation (PWM) signal to the fan driver circuit
14
based on a desired fan speed. The system
10
further may include a motor position detection circuit
16
such as a Hall sensor which monitors the relative rotor/stator position of the DC brushless motor
18
and provides motor position information back to the fan driver circuit
14
for commutation control thereof.
The system
10
of prior art
FIG. 1
is powered by a system power supply
20
, for example a 5 V DC battery. In such systems where circuits such as the fan driver circuit
14
interface with the power supply
20
, protection mechanisms such as an external blocking diode
22
may be employed to prevent a reverse bias system condition from causing a reverse current to flow through the fan driver circuit
14
back to the power supply
20
.
When providing fan speed control in the system
10
of prior art
FIG. 1
, prior art solutions often employed two wires between the fan controller circuit
12
and the fan driver circuit
14
, respectively. The multiple wires therebetween were used to pass various portions of required data between the fan controller circuit
12
and the fan driver circuit
14
, which are typically separate integrated circuit chips (ICs). Using extras wires has several disadvantages since it requires extra IC pins and internal pads associated with the chips. A second prior art solution used an analog feedback methodology. The analog solution, however, requires analog circuitry which may be not be available or suitable in many cases. Lastly, another prior art speed control solution utilized a single wire serial interface, wherein multiple pieces of data of serially multiplexed along the single wire. Such a solution, however, disadvantageously requires an excessive amount of logic overhead to manage and control such data and impacts a driving efficiency of the motor.
There is a need in the art for improvements in fan speed control circuits and systems which overcome the disadvantages associated with the prior art.
SUMMARY OF THE INVENTION
The present invention relates to a system and method of controlling the speed of a motor in a variety of applications, for example, fan speed control in portable electronics systems. In particular, the present invention relates to a system and method of generally concurrently controlling and monitoring a motor speed over a single wire via a convolution of motor speed information in a pulse width modulation (PWM) control signal which serves as a speed control signal.
According to one aspect of the present invention, a motor driver system is disclosed in which motor speed control information and actual motor speed information is conveyed over a single wire between system components. The motor driver system comprises a motor controller circuit which is operable to generate a PWM control signal which dictates a duty cycle (and a target speed) at which the motor is to be driven. The system further comprises a motor driver circuit which drives the motor as dictated by the PWM control signal and the desired commutation scheme.
The motor driver circuit is operable to utilize motor position information to draw current associated with the PWM control signal, thereby convolving the motor speed control information with motor speed information over a single wire between the two circuits, respectively, which carries the PWM control signal. Detection circuitry associated with the motor controller circuit detects the current draw associated with the PWM control signal and uses successive detected current draws to determine the actual motor speed. The determined motor speed may then be used to modify the PWM control signal (e.g., vary the duty cycle) to maintain a desired or target motor speed or motor speed range, as may be desired.
According to another aspect of the present invention, a motor driver system having tachometer feedback is disclosed. The motor driver system comprises a motor controller circuit which is operable to generate a PWM control signal which dictates a duty cycle and thus a desired speed at which the motor is to be driven. The system further comprises a motor driver circuit which is operable to drive the motor at a duty cycle associated with the PWM control signal. The motor driver circuit comprises a motor position detection circuit and a current pulse generation circuit. The motor position detection circuit is operable to generate a signal or other type indication which is associated with a predetermined motor rotor position and the current pulse generation circuit is operable to generate a current event such as a current pulse which is convolved with the PWM control signal in response to the rotor position detection signal or indication. The motor controller circuit further comprises a motor speed determination circuit which is operable to utilize the generated current pulses associated with the predetermined motor rotor position to determine the motor speed.
According to still another aspect of the present invention, the current pulse generation circuit comprises a transistor, for example, an NMOS transistor, having a terminal such as a drain coupled to the PWM control signal. The transistor further comprises a control terminal, for example, a gate, which is coupled to the motor position detection circuit. The transistor then conducts for a predetermined time period when the motor position detection circuit provides an indication that the predetermined rotor position has been detected, thereby generating current draw for a predetermined time period which is convolved on the PWM control signal.
According to yet another aspect of the present invention, the motor speed determination circuit comprises a timer circuit which is operable to generate data which indicates a time period between successive current pulses on the PWM control line. The motor speed determination circuit further comprises a decoder circuit which is operable to determine a motor speed based on the data generated by the timer circuit and, alternatively, with information relating to a type of motor being employed in the system. In addition, the motor speed determination circuit may comprise a current pulse detection circuit having a resistive component and a comparator circuit associated therewith, wherein the comparator trips when a voltage across the resistive component exceeds a predetermined threshold, thereby indicating the existence of a current pulse conducting therethrough. The timer circuit may then ascertain a time period between successive comparator trip points at its output.
According to another aspect of the present invention, the motor position detection circuit comprises a Hall sensor which is operable to d
Baldwin David John
Lata Zbigniew Jan
Teggatz Ross E.
Teutsch Alexander Noam
Masih Karen
Moore J. Dennis
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