Method for optimizing the rotational speed of cooling fans

#This patent application is co-pending with related patent applications entitled Method for Monitoring Environmental Parameters At Network Sites (Navy Case No.77500) application Ser. No. 08/759,360 now pending; Apparatus For Monitoring Environmental Parameters At Network Sites (Navy Case No. 77501) application Ser. No. 08/759,361, now pending; and Apparatus for Optimizing The Rotational Speed Of Cooling Fans (Navy Case No. 77502) application Ser. No. 08/759,361, now pending, by the same inventor as this application.

#(1) Field of the Invention

#This invention is generally directed to cooling systems for digital computer and other electronic systems and more particularly to a method for minimizing the high airborne and structureborne noise generated by such cooling systems while maintaining effective cooling of electronic components and systems.

#The appended claims particularly point out and distinctly claim the subject matter of this invention. The various objects, advantages and novel features of this invention will be more fully apparent from a reading of the following detailed description in conjunction with the accompanying drawings in which like reference numerals refer to like parts, and in which:

#FIG. 1 is a block diagram of an electrical device with a cooling system constructed in accordance with this invention;

#FIG. 2 depicts the internal construction of a controller shown in FIG. 1; and

#FIG. 1 depicts an electrical system 10 including, as basic operating elements, a switching DC power supply 12 and an output conductor 14 to a variable electrical load device 16. The variable electrical load device is represented by a plurality of fixed and variable resistors 16A . . . 16N representing constant and variable loads. In a digital computer environment each of the resistors 16A through 16N could be constituted by individual circuit cards that are constant or variable loads and are located within a chassis, also represented as variable electrical load device 16. It can be seen that the device 16 also identifies the total electrical load of the power supply 12. In the following discussion the numeral 16 refers to the variable or total electrical load, the chassis of the digital computer or the digital computer itself as the context dictates.

#During operation, the switching power supply 12 connects to an external power source that provides a DC voltage V.sub.IN at a connection 18. A switching transistor 20 produces current pulses that an LC filter 22 smooths for transfer over the output conductor 14 to the electrical load 16 as a V.sub.OUT signal. A comparator 24 generates an error signal in response to the output signal (V.sub.OUT) and a reference signal V.sub.REF corresponding to the desired output voltage. A pulse-width modulated (PWM) control unit 26 converts the error signal into a PWM control signal that establishes the duty cycle for the operation of the switching transistor 20, as known in the art. Typically the PWM control unit 26 will vary the duty cycle of the control signal between minimum and maximum values that correspond to the minimum and maximum expected loads.

#Stated differently, the DC output voltage, V.sub.OUT, for the switching power supply 12 is proportional to the input unregulated voltage, V.sub.IN, and the ratio of the "ON" time, T.sub.ON, to the total time period T of the signal from PWM control unit 26. This relationship can be expressed mathematically as: