TLH5177

June 1992

LM1851 Ground Fault Interrupter

General Description

The LM1851 is designed to provide ground fault protection

for AC power outlets in consumer and industrial environ-

ments Ground fault currents greater than a presettable

threshold value will trigger an external SCR-driven circuit

breaker to interrupt the AC line and remove the fault condi-

tion In addition to detection of conventional hot wire to

ground faults the neutral fault condition is also detected

Full advantage of the US UL943 timing specification is tak-

en to insure maximum immunity to false triggering due to

line noise Special features include circuitry that rapidly re-

sets the timing capacitor in the event that noise pulses intro-

duce unwanted charging currents and a memory circuit that

allows firing of even a sluggish breaker on either half-cycle

of the line voltage when external full-wave rectification is

used

Features

Y

Internal power supply shunt regulator

Y

Externally programmable fault current threshold

Y

Externally programmable fault current integration time

Y

Direct interface to SCR

Y

Operates under line reversal both load vs line and hot

vs neutral

Y

Detects neutral line faults

Block and Connection Diagram

TLH5177 – 1

Order Number LM1851M or LM1851N

See NS Package Number M08A or N08E

C1995 National Semiconductor Corporation

RRD-B30M115Printed in U S A