Hello there,
The circuit, although interesting, is a bit superfluous. All the circuit is doing is
increasing the voltage so that it can run an LED that has a forward voltage that
is higher than a single battery. Why does the circuit have to do this? It's because
the battery voltage isnt high enough to run the LED by itself. If the battery
voltage WAS high enough, we wouldnt need a circuit anymore.
Enter a *second* battery here, in series with the first.
With TWO batteries in series we can easily drive a red LED and we dont need a
circuit to do that, just a single resistor.
What's the run time for two cells instead of one? Im glad you asked
The run time will be longer because the current draw from the two cells
will be approximately one half of what it would be with a voltage double
circuit. This means the run time will be twice as long as with only one cell.
So in the long run it is better to use two cells in series than to bother with
a circuit unless there is some real need to run off of one single cell.
It's true we would need two cells then, but they will last twice as long so
that's about the same average battery usage meaning over time we will use
the same number of batteries.
Besides the circuit looking like it could use a lot of improvement, one drawback i
see right away is that it doesnt look like it can run a white LED. That's a big
drawback because we often dont want to have to navigate down a hallway
with a dim red light, we would rather have white light. I've been there and done
that so i have a good idea about the difference here. Try it if you want to see
the difference.
Using three cells and a resistor we can drive a small while LED now, and we can
find white LEDs that run on very low current these days and are very efficient
at low currents too. The run time will be about three times that of a single
cell, so we wont be wasting batteries, and we get a nice white light to see by.
Try it and you'll see the difference.