pushbutton led voltage

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spaspecker

Copper - Posts: 59

Joined: September 07, 2006

Location: United Kingdom

Posted: February 19, 2008 at 4:33 PM / IP Logged

I already have pushbutton ignition in my car, but want to replace the button I have with this one:

illuminated pushbutton

as I want the button to light up

My question is how do I wire the LED? I know I can take 12v from pretty much anywhere in the car but the spec on the button says the LED uses 1.85v - so how do I "step down" 12v to 1.85v?

spaspecker

Copper - Posts: 59

Joined: September 07, 2006

Location: United Kingdom

Posted: February 19, 2008 at 4:36 PM / IP Logged

sorry guys, something wrong with the linky - try this link

Ween

Platinum - Posts: 1,366

Joined: August 01, 2004

Location: Illinois, United States

Posted: February 19, 2008 at 10:11 PM / IP Logged

hi,

assume that when the vehicle is running, you'll probably have more than 12 volts available then

lets make it a bit higher than typical (14.4=Vs). forward voltage for the led (1.85=Vled) then subtract

Vled from Vs......14.4 - 1.85 = 12.55 now take this amount and divide by the forward current of the led.

from the spec sheet iled = 50mA max(you'd probably not need to run the led at max current) so lets run it

at 25 mA...... 12.55 / .025 = 502 ohms. so start with a value around there but don't go any lower than

251. less current equals less brightness

hope this helps

mark

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pushbutton led voltage

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