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Browse Prior Art Database

Short-Circuit Protection for Driver Transistor

IP.com Disclosure Number: IPCOM000041352D
Original Publication Date: 1984-Jan-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 2 page(s) / 27K

Publishing Venue

IBM

Related People

Acquanita, RM: AUTHOR

Abstract

A bipolar transistor is conventionally connected to drive a load in its emitter circuit. If a short to ground occurs in the load circuit, a relaxation oscillator is actuated to turn the driver off and on with a period and a duty cycle that prevents damage to the driver. A low value resistor is connected in the collector circuit of the driver transistor and produces a voltage that is a measure of the load current. This voltage is applied to the baseemitter circuit of the first transistor and it turns on when the load current exceeds a threshold value that corresponds to a fault. The collector voltage of the first transistor is applied through a second transistor that is connected as an inverter to turn off the driver when the first transistor turns on.

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Short-Circuit Protection for Driver Transistor

A bipolar transistor is conventionally connected to drive a load in its emitter circuit. If a short to ground occurs in the load circuit, a relaxation oscillator is actuated to turn the driver off and on with a period and a duty cycle that prevents damage to the driver. A low value resistor is connected in the collector circuit of the driver transistor and produces a voltage that is a measure of the load current. This voltage is applied to the baseemitter circuit of the first transistor and it turns on when the load current exceeds a threshold value that corresponds to a fault. The collector voltage of the first transistor is applied through a second transistor that is connected as an inverter to turn off the driver when the first transistor turns on. When the driver is turned off by the oscillator, the circuit resets, but the accumulation of charge in the baseemitter junction of the second transistor keeps the driver turned off for a while longer. A diode is connected to prevent the charge from leaking from the second transistor through the collector resistor of the first transistor. Until the short is removed, the circuit cycles with a relatively short on time and a relatively long off time. The drawing shows the driver transistor 2 and a short 3 in its emitter circuit. A resistor 4 in the collector circuit of the driver produces a voltage to turn on the first transistor 5. Resistor 4 is tapped to turn on transisto...