Ericsson Gmbh

Dan Lee Todd

Ronald J Lenk

A circuit for limiting the current flow in a 'pluggable' circuit during start-up or circuit fault conditions employs a MOSFET in conjunction with a feedback system, wherein a source terminal of the MOSFET is connected to a power supply bus and a drain terminal of the MOSFET is connected to the circuit to be current limited, respectively. A gate terminal of the MOSFET is controlled by a pair of op amps, wherein the first op amp amplifies the voltage across a current sensing resistor between the MOSFET and the circuit and outputs this pre-amplified voltage into the second op amp, and the second op amp amplifies the difference between this pre-amplified voltage and a first reference voltage. The output of the second op amp is connected to the gate terminal of the MOSFET, thereby varying the voltage at the gate terminal, as the output of the second op amp varies. A comparator may be provided to turn the MOSFET completely OFF during a circuit fault, wherein an output of the comparator is connected to the input of the second op amp. During a circuit fault, a comparator produces a high voltage at its output when a transient voltage across an RC circuit rises above a second reference voltage, thereby latching the second operational amplifier high and turning OFF the MOSFET.

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Union City, CA, United States of America

Dan Lee Todd