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Method for detecting and removing power to voltage-controlled cooling fans on a desktop board system

IP.com Disclosure Number: IPCOM000012200D
Publication Date: 2003-Apr-16
Document File: 5 page(s) / 101K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for detecting interference and removing power to the voltage-controlled cooling fans of a desktop board system. Benefits include improved thermal performance, improved usability, and improved reliability.

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Method for detecting and removing power to voltage-controlled cooling fans on a desktop board system

Disclosed is a method for detecting interference and removing power to the voltage-controlled cooling fans of a desktop board system. Benefits include improved thermal performance, improved usability, and improved reliability.

Background

              Customers have requested that motherboard designs control the power delivered to cooling fans for processors in an effort to reduce the acoustic level of systems. This control is conventionally performed by a Pulse Width Modulation  (PWM) signal to switch power in and out though a power field-effect transistor (FET). If the fans stop rotating, the FET could be electrically over stressed (burn out).

              If a fan becomes stuck or stops rotating due to mechanical interference, a sudden inrush of electrical current can overload the FET and the passive components of the low-pass filter. This surge could damage the FET and the series elements of the low-pass filter.

General description

              The disclosed method detects and removes power to the voltage-controlled cooling fans of a desktop board system if the cooling fan stops rotating. averting damage to on board components.

Advantages

              The disclosed method provides advantages, including:

•             Improved thermal performance due to reducing power when the fan stops rotating

•             Improved usability due to improved acoustic noise

•             Improved reliability due to preventing surge damage to the FET and the series elements of the low-pass filter

Detailed description

             

              CPU_FAN_PWM is a PWM output from a control application-specific integrated circuit (see Figure 1). The negative-positive-negative (NPN) transistor buffers the PWM input to the gate of the p-channel FET. By varying the duty cycle and frequency of the PWM input to the FET, the voltage to the fan connector, pin2 of J1B1, is varied. The ripple is smoothed by a low-pass filter. By implementing a simple circuit to detect such an event, physical damage to the components of the board can be averted.

              The fan shutdown circuit uses simple hardware to detect if a fan is stuck. If so, power is removed...