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"Hobby Circuits for your Hobby Projects"
Last Updated on:  08/31/2008 02:26:30 AM

12v Light/Dark Lamp Switch
designed by David A. Johnson, P.E.
Often, for certain low voltage lighting systems; you would like to turn off the lights during the bright light of the day.  Most commercial day/night switches are designed for AC lighting.  The circuit below was designed for a 12v DC system.  But, it could be modified for other voltage as well.  It uses an inexpensive phototransistor as the light detector.  An n-channel FET is used to switch power to the lights.  A transistor circuit is included to provide some hysteresis.  This keeps the circuit from fluttering the light during the transition from day to night and night to day.  It is recommended that a plastic tube be placed over the transistor to prevent it from being illuminated by the lights it is controlling.  By selecting the appropriate power FET, the circuit could control over 100 watts worth of 12v lighting.   (July 22, 2008)

Click on Schematic below to view PDF version of this Circuit
Circuit 12V Light / Dark Switch Circuit designed by David Johnson, P.E. (June 30, 2006)

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