|Publication number||US7567749 B2|
|Application number||US 11/703,183|
|Publication date||28 Jul 2009|
|Filing date||7 Feb 2007|
|Priority date||19 Nov 2003|
|Also published as||US7242857, US20050105897, US20070160354|
|Publication number||11703183, 703183, US 7567749 B2, US 7567749B2, US-B2-7567749, US7567749 B2, US7567749B2|
|Inventors||Chia-feng Wu, Ching-sen Hsieh, Yueh-Lung Huang, Ming-Shi Tsai|
|Original Assignee||Delta Electronics, Inc.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (40), Referenced by (1), Classifications (10), Legal Events (1)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This application is a continuation of U.S. application Ser. No. 10/895,902, filed Jul. 22, 2004, now U.S. Pat. No. 7,242,857, and claims the priority benefit of Taiwan Patent Application No. 092132441 filed on Nov. 19, 2003, hereby incorporated by reference herein in its entirety.
(a) Field of the Invention
The invention relates to a motor control circuit and, more particularly, to a motor control circuit capable of diminishing back electro-motive force (emf) to reduce switching noise.
(b) Description of the Related Art
However, in conventional PWM control as illustrated in
An object of the invention is to provide a motor control circuit that can effectively diminish back electro-motive force (emf) to reduce switching noise.
According to the design of the invention, a motor control circuit includes a pulse width modulation (PWM) signal generating circuit, a driving circuit and a waveform-shaping circuit connected between the PWM signal generating circuit and the driving circuit. The PWM signal generating circuit generates a square wave with a sequence of alternating on-time and off-time. The waveform-shaping circuit adjusts the rise-time and the fall-time of the square wave to be both within a range of 5% to 15% of the square wave period, and the driving circuit outputs a driving signal to a fan motor according to the adjusted square wave.
Through the design of the invention, since the square wave is modified by the waveform-shaping circuit to have a lengthened rise time and fall time, the abrupt change in pulse level is eliminated and thus the back emf induced in a motor coil is diminished, and the switching noise of the motor control circuit is greatly reduced as a result.
In conventional PWM control, the switching time from “On time” period to “Off time” period, or from “Off time to “On time”, is very short to result in an abrupt change in pulse level, and this may result in a considerable back electromotive force (emf). To solve this problem, according to the invention, a waveform-shaping circuit 24 is arranged between the PWM signal generating circuit 22 and the driving circuit 26 to lengthen the rise-time and the fall-time of the square wave.
Accordingly, since the square wave, modified by the waveform-shaping circuit, is transformed into a trapezoidal wave with lengthened rise time TR and fall time TF, the abrupt change in pulse level is eliminated and thus the back emf induced in a motor coil is diminished when the driving circuit feeds a driving signal according to the trapezoidal wave.
Therefore, the switching noise of the motor control circuit is greatly reduced, especially in the event that the fan motor operates at a low speed.
The transistors may be bipolar transistors, and the waveform-shaping unit may be a phase delay circuit having operational amplifiers, resistors and capacitors, such that the rise time TR and fall time TF can be limited in a range from 5% to 15% of the trapezoidal wave period T by varying the resistance and the time constant.
The waveform-shaping circuit 24 is only for modifying the waveform of the square wave generated from the PWM signal generating circuit 22, and thus its configuration is not limited to aforesaid embodiments. Referring to
Further, the driving circuit 26 may be incorporated in a driver IC, and, in that case, the function of waveform control that achieved by the waveform-shaping circuit may be also incorporated in the driver IC.
While the invention has been described by way of examples and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements as would be apparent to those skilled in the art. Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.
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|U.S. Classification||388/831, 318/254.1, 318/811, 318/599|
|International Classification||H02P7/29, H02P27/08, H02P25/04, H02P29/00|