Electronic Circuits and electronic circuits, electronic schematics plus an extensive resource for hobbyists, inventors and engineers

DiscoverCircuits.com, has 45,000+ electronic circuits, cross-referenced into 500+ categories.
We have searched the web to help you find quick solutions & design ideas.

Got Designs?
Please eMail
if you want me to link to and/or post your original design
NOTE:  We make every effort to link to original material posted by the designer. 
Please contact us if our link is not to your site!  Thanks.

DiscoverCircuits.com -- Hobby Corner
Last Updated on: Tuesday, June 01, 2021 03:06 PM

Hobby Circuits List

The contents & graphics of Discovercircuits.com are copyright protected.
LINK to Dave's circuit, but DO NOT COPY any files to your WEB SITE server

More  Indicator Circuits


Often there is a need to monitor when AC current flows into a load.  The circuit below works well for this application.  It uses an off-the-shelf torrid type AC-1020 current transformer from Triad, available from Mouser.  A wire carrying the AC current is routed through the hole in the center of the device.  Current flowing through that wire induces a voltage in the secondary winding of the coil.
At a current of about 0.5 Amps, the voltage is sufficient to start turning on the green LED indicator light.  The schottky diode in the circuit prevents reverse biasing the LED and the resistor limits the peak current.  There is sufficient resistance in the current transformer winding, so even at a 40 Amps of AC current, the LED will not be driven with excessive current.  Since the current transformer offers exceptional voltage isolation, the LED can be located some distance from the transformer, using inexpensive low voltage insulated wire. 

If you wish, you can wrap more than one turn of wire around the core of the transformer to detect even lower AC current.  With one wire, the LED glows nicely with 0.5 Amps.  With two turns, the LED should glow with 0.25 Amps.  With four turns, the LED should turn on with only 0.125 Amps of AC current, which corresponds to only 15 watts of 120vac power.

Click on Circuit Below to view PDF of Schematic

Self-powered AC Indicator Schematic, 12/15/2004

More  Indicator Circuits

Hobby Circuits List
eMail David A. Johnson, P.E. about this circuit

HOME Schematics Index Hobby Corner Dave's Circuits Contact Info
Imagineering Ezine Dave Johnson & Associates Faraday Touch Switches

 About Us   |  Advertise on DiscoverCircuits.com   |   Report Broken Links  |    Link to DiscoverCircuits.com  |    Privacy Policy

Copyright  January, 1998 - June, 2021     David A. Johnson  All Rights reserved. 
 Linking is ALLOWED but COPYING any content or graphics to your web site is EXPRESSLY PROHIBITED.