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Method for multiplexing signal functionality on a hot-swap fan LED and presence-detect interface

IP.com Disclosure Number: IPCOM000007646D
Publication Date: 2002-Apr-10
Document File: 2 page(s) / 50K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for multiplexing signal functionality on a hot-swap fan light emitting diode (LED) and presence-detection interface. Benefits include improved functionality.

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Method for multiplexing signal functionality on a hot-swap fan LED and presence-detect interface

Disclosed is a method for multiplexing signal functionality on a hot-swap fan light emitting diode (LED) and presence-detection interface. Benefits include improved functionality.

Background

              Conventional designs add a pin to drive the LED, resulting in additional cost and space on the assembly.  One design requires fan connections in the middle of the PCB, where the area is surrounded by traces.

Description

              The disclosed method enables the addition of an LED indicator lamp on a hot-plug fan without adding pins to the connector to operate the LED. The design combines the circuit on the fan connector and the external circuit driving the fan LED (see Figure 1). Fan presence is also detected. 

              The reduced pin count on the fan connector is important to assure the board is routable.

              The interface relies on the maximum operating forward voltage drop of the LED to assure that the combined LED drive/present detect pin voltage cannot exceed (typically) 3 volts if the fan is installed in the connector. When the fan is removed, an external pull-up resistor pulls the LED drive signal to a logical high. The presence-detect feature of the circuit works with the LED either on or off.

Advantages

              The disclosed method provides additional functionality to the fan connector.

Fig. 1

Disclosed description