Can someone point me to an efficient easy to make led circui
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Can someone point me to an efficient easy to make led circui

 
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SA Development
Guest
Posted: Fri Mar 11, 2005 2:09 am    Post subject: Can someone point me to an efficient easy to make led circui Reply with quote
Hi,

I need to have a regular LED (doesn't need to be anything special like a
superbright LED) stay lit as long as possible on either a single D cell or
two D cells. D cells are rated for about 20.5A if used down to 0.8V. I'm
assuming I would need some sort of regulator to do this... I think a
regular LED is 20ma forward voltage 1.9v ?...

Thanks,

SA Dev

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PeteS
Guest
Posted: Fri Mar 11, 2005 5:19 pm    Post subject: Re: Can someone point me to an efficient easy to make led ci Reply with quote
You are corect in the forward voltage assumption. Note, however, that
different colours have different forward voltages. Most green, red and
yellow (amber) LEDs are in the range of 1.6-2V when fully on.
If you don't need much current (you don't), you could use a switched
capacitor boost driver, or even a flying capacitor device. These things
are all over the place - look at Maxim (http://www.maxim-ic.com),
National Semiconductor (http://www.national.com) and Linear technology
(http://www.linear.com) for typical devices.

Cheers
PeteS
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dB
Guest
Posted: Fri Mar 11, 2005 10:08 pm    Post subject: Re: Can someone point me to an efficient easy to make led ci Reply with quote
"SA Development" <nospam38925@forme.com> wrote

Quote:
I need to have a regular LED (doesn't need to be anything special like a
superbright LED) stay lit as long as possible on either a single D cell or
two D cells. D cells are rated for about 20.5A if used down to 0.8V. I'm
assuming I would need some sort of regulator to do this... I think a
regular LED is 20ma forward voltage 1.9v ?...

You will need two, not one, cell.

Experiment with values of series resistor, and choose the highest
value which will give you an acceptable light intensity.

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PeteS
Guest
Posted: Fri Mar 11, 2005 10:48 pm    Post subject: Re: Can someone point me to an efficient easy to make led ci Reply with quote
This can be done with one cell if a switched capacitor boost regulator
is used. One might even use a low power/low voltage RS232 converter
from maxim (output typically +/-5V).

Cheers

PeteS
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