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AC Line Cord Check Circuit with Options

IP.com Disclosure Number: IPCOM000105455D
Original Publication Date: 1993-Aug-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 4 page(s) / 103K

Publishing Venue

IBM

Related People

Clemmons, E: AUTHOR [+3]

Abstract

Described is a hardware circuit implementation to provide a check of the wiring of an AC line cord. The design ensures that the wiring of an AC line cord is correct and will not damage equipment using the cord. Also included are two optional use additions to the circuit implementation.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

AC Line Cord Check Circuit with Options

      Described is a hardware circuit implementation to provide a
check of the wiring of an AC line cord.  The design ensures that the
wiring of an AC line cord is correct and will not damage equipment
using the cord.  Also included are two optional use additions to the
circuit implementation.

      Occasionally, a standard molded AC line cord will be miswired
in that the hot leads and the ground connection is reversed.  This
miswiring can cause safety problems and could cause damage to
sensitive equipment that are dependent upon correct ground and hot
lead wiring.  The concept described herein provides circuitry to
detect any miswiring of the AC line cord and is typically used to
test the AC line cord prior to installation.

      Fig. 1 shows the circuit to detect incorrect AC line cord
wiring.  The circuit consists of rectifiers CR1, CR2, CR3 and CR4;
resistors R1, R2, R3 and R4; capacitor C1; and indicator LP1.
Typically, rectifiers CR1 through CR4 are contained in a module for
full wave rectification.  Indicator LP1 is typically a light, light
emitting diode (LED) or a horn.  The normal operation of the circuit
is such that when the AC line cord is plugged into its source, AC
voltage is applied to points A and B of full wave rectifiers CR1
through CR4.

      In the case of 110V operation, the line cord's hot and neutral
connections connect directly to points A and B while the ground (not
shown) connects to the chassis ground.  In the case of 220V
operation, point A is again connected to the hot side while point B
is connected to an AC ground in the system which returns to the line
cord.

      Figs. 2a and 2b show two examples of how an AC ground in the
220 voltage power is obtained.  Fig. 2a shows the AC ground connected
to the center of the power supply bulk capacitors CB1 and CB2.  Fig.
2b shows the AC ground connected at the center tap of windings A and
B of a 50/60 Hz bias power supply transformer.

      After the AC voltage is rectified by rectifiers CR1 through
CR4, the voltage is divided down by means of voltage divider
resistors R1 and R2.  Capacitor C1 smooths the voltage and is applied
to the base of transistor Q1 through current limiting resistor R4.
Resistor R3...