How to keep an LED ON even after the voltage drops to zero?
How to keep an LED ON even after the voltage drops to zero?
(OP)
I need to use an LED in such a way that the LED will lit when the voltage across the LED is sufficient to lit it but the LED will remain lit even after the voltage across it drops to zero. Is there any simplest way to do that?





RE: How to keep an LED ON even after the voltage drops to zero?
Julian
RE: How to keep an LED ON even after the voltage drops to zero?
However, if you are trying to latch on the LED (once the voltage is present once, then you want the LED to stay on until you manually reset it) then you might want to look at the 74LS74. This is a D flip-flop. Try poking around in those app notes and see if there is something that will work for you there.
LM555 - www.national.com
74ls74 - www.onsemi.com/home
Good luck and keep us posted!!!
RE: How to keep an LED ON even after the voltage drops to zero?
RE: How to keep an LED ON even after the voltage drops to zero?
How long is the voltage zero for ?. If its for a long time
then this simple circuit might be suitable.
The diode is to stop the battery powering the circuit when
there is no power.
The first resistor limits the charging current to the battery.
The second to the LED (when its powered by the battery)
Both resistors together are the current limiting for the LED with power applied.
You'll have to do the calcs depending on your choice of components.
Any help ?, yes no let me know.
Regards
RE: How to keep an LED ON even after the voltage drops to zero?
Thanks in advance
Julian
RE: How to keep an LED ON even after the voltage drops to zero?
RE: How to keep an LED ON even after the voltage drops to zero?
In answer to your question about posting graphics.
You are not able to store graphics on the server that hosts eng-tips, but you can put in references to graphics on another server.
I set up a small web site just to hold the graphics at
http://www.laffalot.freeservers.com/
Then in your post you refer to the images on your site/directory like this
*img http://www.laffalot.freeservers.com/workb.jpg*
but replace the * with open & close square brackets [].
I had to put stars otherwise all you would have seen is the image like this
which is were I do my electronics stuff.
Any help ?, yes no let me know.
Regards
RE: How to keep an LED ON even after the voltage drops to zero?
Anyway, I thank you very much for your kindness.
Regards.
Julian