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Current Breaker Activated by an Output Short-Circuit Fault and Deactivated at the Fault Suppression

IP.com Disclosure Number: IPCOM000009810D
Publication Date: 2002-Sep-19
Document File: 3 page(s) / 38K

Publishing Venue

The IP.com Prior Art Database

Abstract

A new circuit method turns off the output transistors of an output buffer when a fault is detected. The fault state is maintained until it is cleared. Typically, output buffer circuits limit the current to some level. This current level may be 2 or 3 times the normal current level of the circuit. Maintaining such high current levels may result in failure of the circuit unless some form of thermal protection is added for protection. Unlike typical digital buffers circuits, this circuit can be used with currents in the range of hundreds of milliamps to several amps. Naming a few applications, this circuit can be used in the output of an audio amplifier, the output of a low drop out regulator (LDO) and as power supply output. Key Words Output Buffer Fault Fault Clearing

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Current Breaker Activated by an Output Short-Circuit Fault and Deactivated at the Fault Suppression

A new circuit method turns off the output transistors of an output buffer when a fault is detected.� The fault state is maintained until it is cleared.

Typically, output buffer circuits limit the current to some level.� This current level may be 2 or 3 times the normal current level of the circuit.� Maintaining such high current levels may result in failure of the circuit unless some form of thermal protection is added for protection.� � Unlike typical digital buffers circuits, this circuit can be used with currents in the range of hundreds of milliamps to several amps.� Naming a few applications, this circuit can be used in the output of an audio amplifier, the output of a low drop out regulator (LDO) and as power supply output.

Key Words

Output Buffer

Fault

Fault Clearing

Circuit Operation

Conditions:

·        M3 is the output transistor in which we want to limit the current at a given level.

·        M2 mirrors M3, such that if the current at M3 increases, then the current at M2 increases.

·        The gate driver (AND gate- shown) drives the gate of the M3 output transistor.� This is the normal operation.� Note: the gate driver represents all circuitry used to drive the gate of M3.

·        The current limit value of M3 is fixed by the proper dimensioning of M0/M1/M2/R1/I0/I1.

Operation:

·        Let us suppose that M6 is off (then no current through M7). If a low current flows through M2 then the curr...