Patent Application
20090278484
Fans for cooling electrical equipment typically operate on DC voltage. The DC fans consume current in pulses proportional to the speed of the fan. The pulses of current are generally seen at fairly low frequencies, such as in the 50 to 500 hertz range in some cases. The pulses of current generate conducted electrical noise that can interfere with electrical equipment circuitry. With increased circuit density in electrical equipment, more and more heat is generated, resulting in the need for increased airflow. To increase the airflow from fans, even higher current pulses are used, further increasing the amount of conducted electrical noise generated by the fans.
LC filters can be used to filter the conducted noise to reduce the amount of noise fed back to a power supply. Due to high current levels and relatively low frequency of noise generated, larger filters are used to reduce the noise seen by the electrical equipment. New ways are needed to reduce conducted noise fed back to power supplies resulting from driving fans. In many electronic equipment devices, fans may be the only devices that generate low frequency conducted noise.
In the following description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific embodiments which may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural, logical and electrical changes may be made without departing from the scope of the present invention. The following description of example embodiments is, therefore, not to be taken in a limited sense, and the scope of the present invention is defined by the appended claims.
The functions or algorithms described herein may be implemented in software or a combination of software and human implemented procedures in one embodiment. The software may consist of computer executable instructions stored on computer readable media such as memory or other type of storage devices. Further, such functions correspond to modules, which are software, hardware, firmware or any combination thereof. Multiple functions may be performed in one or more modules as desired, and the embodiments described are merely examples. The software may be executed on a digital signal processor, ASIC, microprocessor, or other type of processor operating on a computer system, such as a personal computer, server or other computer system.
As circuit density in electronics has increased, so has the need for additional airflow to cool such electronics. In just a few years, five to ten times more powerful fans are being used to cool electronics. Such fans generally consume length limited pulses of current at frequency ranges similar to the audible range of frequencies, such as 50-500 Hz. The pulses of current are currently in the 20 Amp range at approximately 48 volts. These parameters are shown merely for example, and the parameters of various fans may vary significantly. In any event, it is difficult to reduce the electrical motor commutation noise generated at such low frequencies, as LC filters tend to get much larger and more expensive at lower frequencies. Several embodiments are described that operate to reduce the amount of noise conducted back into power supplies from the fans, and also may increase the frequency of the noise, allowing smaller LC filters to be used to reduce the noise so conducted. The embodiments may be separately used, or combined in further embodiments.
The frequency of conducted electrical noise generated from such current pulses that are staggered and phase lock looped is multiple times higher than would result from pulsing a single fan at the same frequency. In still further embodiments, the input 210 includes an LC filter 275 sized to reduce noise fed back to the power supply at the higher frequency. Since the effective conducted noise frequency is higher a conducted noise frequency resulting from pulsing a single fan, the physical size of the LC filter need not be as large, since the size needed to reduce noise is inversely proportional to the frequency of the noise. The higher frequency of the noise also result in the ability to reduce the cost of the LC filter.
In various embodiments, two, three or more fans may be operated with staggered pulses at the same frequency. In one embodiment, 6 or more fans may be so driven. In one embodiment, the different phases of the pulses are equally spaced over one cycle of pulsing the multiple fans.
In one embodiment, a method of controlling multiple fans includes driving a first fan with first limited length current pulses at a first frequency, driving a second fan with second limited length current pulses at the first frequency, and staggering the first and second limited length current pulses to increase an effective frequency of conducted noise resulting from driving the fans.
The method may further include driving one or more additional fans by additional current pulses at the first frequency, wherein all current pulses are staggered substantially equally to further increase the effective frequency of conducted noise resulting from driving the fans. In one embodiment, the different phases are equally spaced over one cycle of pulsing the multiple fans and the current pulses may be controlled by multiple phase lock loop circuits. Noise conducted back to a power supply may be filtered in some embodiments.
The phase lock loop function may also be implemented using electrical circuitry, or a combination of electrical circuits, micro processor and software.
In a further embodiment, the input circuit 310 includes a linear FET that may be slowly turned on to control inrush current on start up of the fan 330. The slow turn on allows the capacitor 325 to charge to a sufficient level to start providing pulses to operate the fan 330. In one embodiment, the switching circuit provides pulses to the fan or fans from the capacitor. The pulses to multiple fans may be provided at the same time in one embodiment. The input current recharges the capacitor between the pulses and is fairly constant. Little if any noise from pulsing the fan or fans is provided back to the power supply 315. In one embodiment, the input circuit 310 may include a DC to DC converter for controlling voltage provided to the fan 330. In one embodiment, the capacitor is electrically isolated from the power supply by the DC to DC converter.
In one embodiment, the switching circuit is operable to couple to a power supply 315 and regulate current drawn from the power supply 315 to minimize variations in such current drawn from the power supply 315. The capacitor 325 may be a circuit coupled to the switching circuit to provide current pulses to run the cooling fan or fans 330. The capacitor 325 may be isolated from the power supply. In one embodiment, the switching circuit comprises a linear FET in series with the power supply. The FET may turn on slowly to reduce current spikes when the system begins operating. Many components of the fan system 300, such as capacitor 325 and circuit 320 may be repeated for multiple fans, and/or phase switched as above to further reduce conducted noise back to the power supply 315.
The Abstract is provided to comply with 37 C.F.R. §1.72(b) to allow the reader to quickly ascertain the nature and gist of the technical disclosure. The Abstract is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.
This application claims priority to U.S. Provisional Application Ser. No. 61/051,937, filed May 9, 2008, and entitled “FAN CONDUCTED NOISE REDUCTION,” which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61051937 | May 2008 | US |
