Browse Prior Art Database

Additional Protecting Circuit for a Monolithic EIA Driver

IP.com Disclosure Number: IPCOM000045260D
Original Publication Date: 1983-Feb-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 3 page(s) / 54K

Publishing Venue

IBM

Related People

Delaporte, FX: AUTHOR [+2]

Abstract

This article describes a circuit for an EIA (Electrical Industry Association) driver whose function is to protect the driver against destruction in case of overvoltages applied to the output terminal.

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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.

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Additional Protecting Circuit for a Monolithic EIA Driver

This article describes a circuit for an EIA (Electrical Industry Association) driver whose function is to protect the driver against destruction in case of overvoltages applied to the output terminal.

The principle consists in turning the driver into the off state whenever an externally applied voltage (outside the power supply range (/- Vcc)) is sensed at its ouput. This turning off is simply obtained due to the drivers tristate feature.

A line driver, in accordance with international standards such as EIA RS 232 C, is shown in the figure. Basically, it is a slightly modified version of the line driver detailed in U.S. Patent 4,340,922. Although the latter driver was implemented with various protecting circuits in case of overvoltages applied to its input terminals, recently the need of an additional protecting circuit connected to the output terminal has been demonstrated.

The problem arises from the fact that, under normal conditions, the ouput voltage of the driver cannot be more positive or more negative than the power supply values (+/- Vcc).

As a consequence, if the actual voltage on a driver ouput is outside the power supply range, it is an indication that this driver is being overloaded.

Overloading means that driver operation may be discontinued and that the driver may be allowed to go in "open output tristate mode" in which current compliance of the driver is very low.

This mode of operation is the one used during poweron to avoid wrong signals being sent to the external world. In this state, the driver will let very little current to flow into its output whatever the voltage applied to it.

These features are intended to limit to an acceptable value the amount of current that the driver will accept from the external world. They could, however, reduce this current to a value low enough to avoid a sizable increase in dissipated power; thus, there was an actual need for a circuit that exhibits a still lower current compliance at its output.

Op...