Dismiss
InnovationQ will be updated on Sunday, Oct. 22, from 10am ET - noon. You may experience brief service interruptions during that time.
Browse Prior Art Database

Automatic Compensation for LED/PTX End of Life

IP.com Disclosure Number: IPCOM000060443D
Original Publication Date: 1986-Apr-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 2 page(s) / 44K

Publishing Venue

IBM

Related People

Kruppa, RW: AUTHOR

Abstract

Sensing of paper in impact printers is usually performed by a LED/PTX sensor. This method works well if the LED bias current is chosen high enough to compensate for the end-of-life degradation of the LED. Typically an LED will degrade up to 40% of its initial light output at end-of-life. Therefore, bias networks set the LED current high enough in anticipation of this future degradation. When the LED/PTX is used for sensing paper, this high bias current will cause sufficient energy to be radiated by the LED, such that enough energy will pass through the paper and not be sensed by the PTX. This is especially true when sensing lightweight papers. From a paper point of view, the bias current should be set as low as possible, such that the presence of paper will be detected. This contradiction creates a difficult design problem.

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 53% of the total text.

Page 1 of 2

Automatic Compensation for LED/PTX End of Life

Sensing of paper in impact printers is usually performed by a LED/PTX sensor. This method works well if the LED bias current is chosen high enough to compensate for the end-of-life degradation of the LED. Typically an LED will degrade up to 40% of its initial light output at end-of-life. Therefore, bias networks set the LED current high enough in anticipation of this future degradation. When the LED/PTX is used for sensing paper, this high bias current will cause sufficient energy to be radiated by the LED, such that enough energy will pass through the paper and not be sensed by the PTX. This is especially true when sensing lightweight papers. From a paper point of view, the bias current should be set as low as possible, such that the presence of paper will be detected. This contradiction creates a difficult design problem. The circuit shown in the figure solves this problem by automatically setting the LED bias current each time a circuit is powered up or reset. The current level is set at the lowest value that allows the LED/PTX device to operate. This also satisfies the requirement for sensing lightweight paper. As the LED degrades, the magnitude of the "lowest value" of current increases and the circuit adjusts the LED current accordingly. The LED current is adjusted by increasing the current in incremental steps, such as 2 milliamps per step, until the PTX "turns on." This is accomplished by sequencing through a...