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timer for led flashlight

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shalomw

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Hi all

I want to add a timer circuit to a led flashlight so after I press the 'on' switch it will shut off after a few minutes automatically

1. It has to be small
2. it works on 3 AAA cells possibly nimh so v~1.2*3=3.6V
3. no drainage during the many many hours when the light is off (either main switch off or timer switch off) so i don't drain my batteries

Do you think NE555 is good ?
any other suggestions ?

Thanks
 

NE555 can be the best option ......because it is very cheap...and you can drive your led by using it as a load in transistor ...ie providing the O/P pin of 555 timer to the base of the transistor and placing the led in the collector....
if u have any question Do not hesitate
 

Cheers......
For a cheap timer circuit, the 555 is the best option. But the circuit's efficiency will be poor if u designed it for long time delays.
Because, the timer capacitance leakage is the problem. It is better for time delay's up to few minutes. U Should connect the load through a load transistor for better response
 

Thanks
supposing I only need ~ 50mA current for my LED can I just use the OUT leg to drive it , or do you think I should use a transistor anyway ?
 

If u want to drive only a LED, u can connect it to the 555 output pin(3)
Actually, it support 200mA of drive current
 

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