|
 |
Circuits designed by David Johnson, P.E.
Last Updated on:
Monday, December 25, 2017 02:05 PM
List of Dave's Circuit Designs
The contents & graphics
of Discovercircuits.com are copyright protected.
LINKING to Dave's circuits is permitted but DO NOT COPY any files to your WEB
SITE server |
|
|
|
|
|
|
|
More
Timer Circuits
Lamp Controls
Control Circuits |
|
Closet Light
with Automatic 3 Minuite Timeout
|
| The
circuit below is powered by three 1.5v alkaline AA cells. With a finger tap to
the pushbutton trigger switch, a cluster of 6 wide angle white LEDs is turned on. The
lights remain on for about 3 minutes, then will turn off. The circuit’s standby
current is only a few microamps. A set of fresh batteries should last at least
200 light applications. |
|
|
|
The circuit uses a Schmitt trigger inverter and two transistors. When
the pushbutton switch S1 is pressed, the 10uF capacitor C1 is discharged. When the switch
is released, the capacitor is charged through R1. With the capacitor C1 discharged, the
Schmitt trigger output swings to 4.5v, which turns on transistor Q2. The combination of R4
and Q1 form a constant current control circuit. The current is set about 15ma per
LED. When the capacitor charges up to about 2.3v, the Schmitt trigger changes state,
turning off the LEDs. |
|
|
Click
on Drawing Below to view PDF version of Schematic |
|
 |
| |
|
|
|
|
