It has worked for me... Maybe between a new 9V being close to 9.6V and a crappy transistor, it works.

So, why don't you go ahead and give the guy a circuit, Hero999, go ahead...
be a hero!

 

ahh see i dont' have a 50K pot, just 2 100K resistor paralleled. maybe i can find something in my old radio. hehe

 

Try resistors 10K or less in place of the 50K pot. You should see a difference.

 

The origional circuit with the 9V will work.

Your modified version with the 3V battery won't work.

You removed R7 so the LED will overheat, you should have reduced its value to between 47hm: and 68hm: depending on the forward voltage.

With the 9V version R4 and R5 form a potential divider to stop Q1 turning on when the 741 is low as it's minimum output voltage is 2V which is above 0.6V, the turn on voltage of Q1.

Unfortuantely with the 3V version the potential divider formed by R4 and R5 will mean the voltage at Q1's base will only reach 0.5V when the TLC25L2's output goes high.

Remove R5 and make R4 2k and it should work.

Another thing you could do is connect a 100k resistor between pin 6 and pin 3, this will introduce so hysteresis and prevent the LED from flickering slightly when it turns on or off.

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ok here is my main question of concern. at a run time of 8 hours.... how long should the batterys keep up to this LED?

 

Simply visit a battery manufacturer's website and look at their datasheets.
www.energizer.com shows that AAA alkaline cells can power an LED at an average of 25mA for about 48 hours. A 9V alkaline battery can power an LED at an average of 25mA for about 24 hours. The voltage continues to drop so the LED dims.
Ni-MH rechargable cells are also shown.

__________________
Uncle $crooge

 

<b>Hero999,</b>
Thank you for the assistance. I was only trying to give Team_NightStalker some help/options. I knew the 3V circuit was a stretch and was hoping for the aid of
others to jump in and help.