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Fan speed limiter before the active control ready Disclosure Number: IPCOM000225173D
Publication Date: 2013-Jan-28
Document File: 2 page(s) / 49K

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The Prior Art Database


Disclosed id a hardware design circuit to clamp the fan speed before the firmware is ready to suppress the noise at first power on.

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Page 01 of 2

Fan speed limiter before the active control ready

To manage the fan speed to an acceptable range before system management control is ready for that. No known solution is available.

Use the tachometer information to use as a clock source to cap the fan speed to a target range to avoid run-away like situation as if the system is out of control.

In a computer system with fan solution, the fan speed is controlled by embedded controller. Usually, in order to keep the minimum fan conducting requirement when system powered on, 100% duty cycle is the only option before the controller is ready and system is turned on. The full speed is usually not required, and annoying especially that the action to push power button is an attended one.

This purpose provided a method to cap the fan speed before the controller is ready. Usually the first image to a noisy system is cranky instead of powerful from user experience.

Method 1. Static Fan speed control.

The most used fan control signal is PWM( pulse width modulation), the other is level driven.

The tachometer signal is the passive one depends on external pull-up resistor to target voltage. Please see Fig 1.

Fig 1.


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Usually 50% is good enough to achieve initial cooling requirement, the minimum schematics can be used to lock the fan here.

Method 2. Fixed rotation speed at designed value:

When more control is required to meet higher air flow or better user experience, an adjustment with extra components can be used t...