Browse Prior Art Database

Failsafe Fan Control in a highly reliable Electronic System incorporating Pulse Width Modulated Fan Control

IP.com Disclosure Number: IPCOM000124606D
Original Publication Date: 2005-Apr-29
Included in the Prior Art Database: 2005-Apr-29
Document File: 4 page(s) / 123K

Publishing Venue

IBM

Abstract

Failsafe Fan Control in a Highly Reliable Electronic System incorporating Pulse Width Modulated Fan Control

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 54% of the total text.

Page 1 of 4

Failsafe Fan Control in a highly reliable Electronic System incorporating Pulse Width Modulated Fan Control

Typical storage systems have an enclosure management system (e.g. SCSI Enclosure Services or SES) for monitoring and control of air moving devices (e.g. fans) for system cooling. Standard methods of fan management include a SES resource (herein referred to as Controller) which monitors and appropriately controls, closed loop or open loop, the system fans. Most systems today have redundant fans as well as redundant Controllers. In such redundant systems a common practice is to have one Controller as the master while the other Controller is the slave, or inactive controller, refer to Figure 1. In this case the master Controller would control all the system fans until such time that the master is deemed inoperative and then the slave Controller would take over mastership control.

In either case, the operating Controller master will control all the system fans which become a single point of failure which seemingly can be resolved by the alternate Controller taking over control should the current master Controller fail its fan control duties. This topology suggests an implementation whereby the fan interface signals must be shared or "dotted" between the two Controllers. Given this dotted network if a single Controller fails in such a way that the control signals are left inoperative even from the other Controller such as a short to ground, whether it is master or slave the entire network can be rendered inoperable to the point where all the system fans shut down creating the single point of failure.

Figure 1

C ontroller 0

PW M 0 PW M 1

  PW M n PW M n+1

C ontroller 0

PW M 0 PW M 1

  PW M n PW M n+1

C ontroller 1

PW M 0 PW M 1

  PW M n PW M n+1

C ontroller 1

PW M 0 PW M 1

  PW M n PW M n+1

In the topology described above, incorporating air moving devices such as PWM controlled fans and a fail-safe circuit can be implemented such the system fans are not exposed to a single point of failure. The Controller generally controls "n" number of fans by asserting "n" number of pulse width modulated (PWM) signals, one to each of the individual fans. Should the Controller fail such that all the signals are in a state that would shut down the fans, a fail-safe circuit targeted at each of the "n" fans is employed to detect the failed signal state and override it such that a fan cannot be shut down. One method to create a very low cost and low complexity fail-safe circuit is to convert the incoming PWM signal to an analog signal and in turn comparing thi...