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Low voltage cutout Answered

Hello,
I need a simple circuit to switch off a high brightness LED that draws 200ma when my four cell Ni-MH battery pack drops to 4.0v(1.0v per cell)
Nothing too complicated, something with a transistor, a comparator circuit, and a zener or an all in one IC? I've tried a few "this should work" circuits and then have been told, "well I haven't actually built one".
Thanks.

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jefflahay
jefflahay

9 years ago

From fully charged at ~5.2v.
They are standard 1.2v NiMH 2500mah batteries.

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lemonie
lemonie

Reply 9 years ago

Does the battery read 5.2 under the 200mA load?
You want it to switch off when the batteries are low, but I think that it's going to do that anyway (LED forward voltage)?

L

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jefflahay
jefflahay

Reply 9 years ago

Hi lemonie,
Yes, that's under load, and then starts dropping slightly. Many people have told me the LED will shutdown around 3.xx volts, but as a test I put some dropping resistors inline and it is still glowing at 2.42v and is drawing .02ma. I think I even had at one point 2.15v and it had a very faint glow.
I bought these from
http://www.wayjun.com/index.php?main_page=product_info&cPath=53_194&products_id=645
in China. They are high brightness 1W @350ma and put out between 90-100 lumens at max. I want to run them at 150-200ma because they are plenty bright at that level for my application.

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lemonie
lemonie

9 years ago

What's it dropping from?

L