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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
Drawing Below to view PDF version of Schematic
