Browse Prior Art Database

Driver With Short-Circuit Protection

IP.com Disclosure Number: IPCOM000046765D
Original Publication Date: 1983-Aug-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

Pelc, R: AUTHOR

Abstract

Using the current mirror properties of two adjacent transistor devices on the same semiconductor chip, the driver transistor current in a communications cable driver circuit is monitored and switched off before the occurrence of damage when electrical shorts in the cable occur. In the integrated circuit cable driver above, current I2 in transistor Q2 is proportional to current I1 in transistor Q1. As I1 increases I2 also increases, and the voltage across resistor R1 increases. During normal operation the voltage across R1 is not enough to turn on transistor Q3 and, therefore, transistor Q4 remains off. If I1 increases to a point at which Q2 can turn on Q3, then Q4 will turn on and attempt to turn off Q1.

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Driver With Short-Circuit Protection

Using the current mirror properties of two adjacent transistor devices on the same semiconductor chip, the driver transistor current in a communications cable driver circuit is monitored and switched off before the occurrence of damage when electrical shorts in the cable occur. In the integrated circuit cable driver above, current I2 in transistor Q2 is proportional to current I1 in transistor Q1. As I1 increases I2 also increases, and the voltage across resistor R1 increases. During normal operation the voltage across R1 is not enough to turn on transistor Q3 and, therefore, transistor Q4 remains off. If I1 increases to a point at which Q2 can turn on Q3, then Q4 will turn on and attempt to turn off Q1. This is not a stable condition since this sequence also removes the drive required to keep Q4 on, but the circuit will remain in this state as long as Q1 continues to drive excessive current. Normal operation can resume when the overcurrent condition of I1 is removed. This technique can accurately sense the current in the driver output device without affecting the circuit output specifications. Driver circuit reliability is improved at very small power dissipation expense and a higher degree of circuit integration is achievable.

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