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Browse Prior Art Database

Short Protection for Transistor Circuits

IP.com Disclosure Number: IPCOM000098826D
Original Publication Date: 1958-Jun-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 2 page(s) / 28K

Publishing Venue

IBM

Related People

Clapper, GL: AUTHOR

Abstract

The present circuit relates to the use of a small incandescent lamp to safeguard transistors. The figure shows a complementary inverter driver protected against shorts to ground. By placing the lamp in the circuit between the transistors, the open circuited input condition cannot harm the transistors, since most of the wattage will be in the lamp. The lamp is useful not only to limit the current but to give an indication of the location of the circuit fault.

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Short Protection for Transistor Circuits

The present circuit relates to the use of a small incandescent lamp to safeguard transistors. The figure shows a complementary inverter driver protected against shorts to ground. By placing the lamp in the circuit between the transistors, the open circuited input condition cannot harm the transistors, since most of the wattage will be in the lamp. The lamp is useful not only to limit the current but to give an indication of the location of the circuit fault.

For the circuit shown a short to ground increases the current in the lamp until the resistance rises to about 140 ohms. At this time, a little over 30 milliamperes flows in the circuit and most of the voltage is across the lamp rather than the transistor. The voltage across the transistor will be less than 0.5 volt, so that the wattage dissipated in the transistor is under 15 milliwatts, a safe value.

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