HOME Schematics Hobby Corner Dave's Circuits Electronic Resources Book Corner Contact Info

What the World Needs Now --
Day/Night AC Power Switch with Hysteresis

Previous Issues
Porch Light

I have several outside lights with built in day/night switches. The switch turns the light on at night and off during the day.  But, although small, the switch modules use simple a CdS photocell and a TRIAC switch circuit. 

They almost always flutter the lamp at dawn and dusk.  This fluttering action is caused by the lack of hysteresis in the circuit.  When the CdS cell says that the light should turn on, the act of turning it on increases the light intensity. 

The photocell then says that it is not dark enough and turns the light off again.  This on/off cycle is repeated for perhaps 5 minutes twice each day until finally it is either dark or light enough.

Then, the light remains stable.  This flickering action accelerates the failure rate of any light used in the fixture.  In fact, I’ve never be able to use any kind of compact fluorescent lamp other than a “dimmable” type for fixtures with day/night switches.

What I would like to see is a compact two wire switch module circuit with enough hysteresis to prevent lamp flicker.  I know some three wire modules have such a feature but they are usually too large to fit inside the lamp housing.   

A 1 Amp current rating should be enough, since most outside lights would use just 60 watt lamps.  Perhaps a pair of high voltage MOSFETs could be configured as a bidirectional switch, controlled by a simple daylight detector circuit.

3 Wire Dusk to Dawn Switch Module


3 Wire Dusk to Dawn Switch Module

November 2010     Issue 13

Page 1 Back
Good Idea
gone Badly
New Products Rants &
What the World
needs Now
Wily Widget

Imagineering Ezine    Discover Solar Energy Dave Johnson & Associates Faraday Touch Switches

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

Discovercircuits.com endeavors to credit original designers.   Please alert us by eMail so we can
delete links to material that have been copied without your permission
.   Thank you.

© Copyright of all original material on this website is the property
of David A. Johnson, P.E. (Dave Johnson & Associates ) unless otherwise noted.  

Linking is ALLOWED but COPYING any content or graphics to your web site is EXPRESSLY PROHIBITED.
All material is provided "as is" without guarantees or warranty of any kind, either expressed or implied.