Browse Prior Art Database

Thermal Printer Chip Protection Circuit

IP.com Disclosure Number: IPCOM000079967D
Original Publication Date: 1973-Oct-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 2 page(s) / 37K

Publishing Venue

IBM

Related People

Hong, JH: AUTHOR

Abstract

This thermal printer chip protective circuit provides a means for sensing the temperature of thermal elements 10 on a printer chip, so that preventive measures can be taken before irreversible damage is done due to excessive heating.

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 76% of the total text.

Page 1 of 2

Thermal Printer Chip Protection Circuit

This thermal printer chip protective circuit provides a means for sensing the temperature of thermal elements 10 on a printer chip, so that preventive measures can be taken before irreversible damage is done due to excessive heating.

The thermal printer chip is made of silicon on which thermally isolated elements or islands 10 are arranged. For example, in a matrix or straight line. Each island 10 prints a dot on a chemically treated piece of paper, when its temperature is raised sufficiently high by the current flowing through it. The power involved in this printing processing is high; and if the duty cycle of an island exceeds a certain limit, a hot spot develops which ultimately results in an open circuit. It is, therefore, necessary to monitor the temperature of each island 10 and shutdown the printer, or at least slow down the printing speed, when any of the islands become too hot.

In the circuit shown in Fig. 1, the temperature of each element is measured and averaged by sensing the forward voltage drop of base-emitter diodes D1-Dn located in each island, respectively. This average voltage V2 is compared with the forward voltage drop V1 of the reference diode DREF, which is on the same chip but not located in the thermal area.

The spread of forward voltage drop between diodes on the same chip is small - typically 2mv - and the temperature dependence of forward voltage drop is quite predictable. Therefore, if the bias...