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Overcurrent Protection and Regulator Control

IP.com Disclosure Number: IPCOM000097525D
Original Publication Date: 1961-Jan-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 39K

Publishing Venue

IBM

Related People

Mikonis, P: AUTHOR

Abstract

The circuit provides positive turnoff of and protection for voltage regulator 1 when it is subjected to surges and overcurrents.

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Overcurrent Protection and Regulator Control

The circuit provides positive turnoff of and protection for voltage regulator 1 when it is subjected to surges and overcurrents.

Regulator 1 is operative only as long as control input 2 is not grounded. In the quiescent or normal operative state, the following conditions exist in the protection circuit. Transistor T1 is biased off because its conductive threshold is not exceeded by the normal voltage drop across resistor R1. Transistor T2 is maintained in conduction by the voltage developed across R4. This voltage results from the combined action of currents, one flows from line 10 through resistor R2 and the other flows from battery 11 through resistor R5. Neither the current flowing through resistor R2 nor that flowing through resistor R5 individually produces a sufficient voltage drop across R4 to maintain T2 conducting. T3 is nonconductive since its base is effectively at ground potential by virtue of T2's conduction.

In the presence of an overcurrent, the voltage across R1 increases thus enabling T1 to conduct. This brings the collector potential of T1 almost to ground, resulting in a voltage decrease at the base of T2 which cuts this off. This occurs because the current which previously flowed through R2 and provided a portion of the potential across R4 now flows through T1. Upon becoming nonconductive, T2's collector voltage rises to a point which is controlled by Zener diode Z2. This causes T3 to conduct and th...