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Browse Prior Art Database

A LOAD CONTROLLED AC SWITCH

IP.com Disclosure Number: IPCOM000007755D
Original Publication Date: 1996-Aug-01
Included in the Prior Art Database: 2002-Apr-19
Document File: 1 page(s) / 56K

Publishing Venue

Motorola

Related People

Daniel Folz: AUTHOR

Abstract

A circuit was required that would detect when current was drawn by a varying AC load and once this current was detected, switch on the load's AC line voltage to other circuitry. The circuit would also need to meet the following requirements: 1) draw zero current until the varying AC load was activated, 2) have Universal AC voltage compatibility (90 to 264 VAC), and 3) be low in parts count and compact in size.

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M-ROLA Technical Developments

A LOAD CONTROLLED AC SWITCH

by Daniel Folz

allow insertion of the device in series with the AC load.

PROBLEM DESCRIPTION:

CIRCUIT DESCRIPTION:

  A circuit was required that would detect when current was drawn by a varying AC load and once this current was detected, switch on the load's AC line voltage to other circuitry. The circuit would also need to meet the following requirements: 1) draw zero current until the varying AC load was activated,
2) have Universal AC voltage compatibility (90 to 264 VAC), and 3) be low in parts count and compact in size.

PROBLEM SOLUTION:

One problem of concern was the varying AC load.

This load could draw as little as 50 mA yet be as high as 2 A depending on conditions in the field. What was needed was a device that would have a relatively constant and low voltage drop across it no matter what the current through the device was (a diode). If this condition could be met, it would

  As shown in the circuit below, ultrafast power rectifiers were used in series with the load. Since the voltage across the diodes are relatively constant no matter what the field conditions, the sensing is independent of load and a voltage will only develop across the diodes when current through them are present. This fact meets the zero current "off-state" requirement. The Power Opto-Isolator chosen con- tains a zero-cross triac driver and has the Universal AC voltage requirements. The remaining circuitry contains a four times m...