12v 2 second cooldown circuit help..

[supadave]

First off, I'm a newb and will admit it. I know how to read circuit schematics for the most part but unfortunetly with my limited experience working at this level I need some help. I've never actually built a circuit but I have replaced components and such with direction. With that said, here is what I need and I hope it is simple. I'll try to keep it simple.

I got a 12vDC power source feeding an LED light. When the power source gets turned off I need about 2 seconds of residual charge going to the device and it doesn't need to be 12vDC it can slow drain like I imagine a Capacitor would do. I just don't know what I need to build such a circuit. What type and size cap and if I need anything else, etc. Please, I really need this for a project and need some help. I tried searching for a while but couldn't find anything. I may not of searched the right keywords either but I did try.

Thank you.
David

 

[Reloadron]

Hi David

This is where some info is needed about the LED and LED circuit. Maybe a circuit drawing? For example using a capacitor as you mention the LED current would need to be known to determine how long the LED would remain on after the supply was removed.

Ron

 

[supadave]

It's a standard 12V LED light that you buy from radio shack. it does have a built in resistor, but I assume that is to just rugulate the 12V I hooked it up to a 12V switching power supply on my bench and it will do a 3 second slow drain when I turn off the switching power supply. That's what I need. The 12v source from withen the device doesn't provide that fade. I need to interject someting that will. Im at work so I'm not sure what the amps are on the LED if that is what you are needing. Told you I was a newb.

 

[Reloadron]

Based on PM and subsequent conversation now I got it and yes what you want is a re triggerable one shot.

For those or anyone curious a system delivers 12 volt pulses. While pulses are arriving the user wants a LED to remain lit. When the pulses stop the LED should time out and extinguish. Along the lines of a missing pulse detector or re triggerable one shot. Dave found something online that will work.

Ron

 

[colin55]

You just need a diode and 10,000u electrolytic.

 

[supadave]

Yes, Thank you again Ron for helping me understand my needs.