Board logo

LED's - Damaged by 2 +'s?
Howlor - 26/5/06 at 06:56 PM

Hi,

Just a quick question. I wired an LED into a circuit that is normally a switched negative, but I want to turn it off by switching the neg lead from earth to positive. The thing is that the LED is now dead. Does it normally dmage LED's with two +'s?

Thanks,
Steve

DIY Si - 26/5/06 at 07:00 PM

Why would you switch it off by going to +'ve? Isn't it easier to just switch the connecton off, ie to an open/not connected part of a switch?
Oh, and no it shouldn't damaged it if both +'s are the same voltage.

[Edited on 26/5/06 by DIY Si]

Bob C - 26/5/06 at 07:13 PM

LEDs die easy - too many reverse volts, or no current limit in forward direction. A few microseconds is all it takes....
Bob

tks - 27/5/06 at 07:59 AM

mhhh

just put a diode in that V+ line
for example a N4007

then the voltage wound reach the led and it would shut down...

they are really cheaps

a diode is like a one way valve..
it consumes som pressure (0,6 voltage)
but it will block reversing voltages...

Tks

MikeRJ - 27/5/06 at 11:34 AM

quote:
Originally posted by Howlor
Hi,

Just a quick question. I wired an LED into a circuit that is normally a switched negative, but I want to turn it off by switching the neg lead from earth to positive. The thing is that the LED is now dead. Does it normally dmage LED's with two +'s?

Thanks,
Steve


The answer is that applying the same potnential to both wires will cause no current flow, and so will not damage the LED. It is the same as connecting both wires to groud from the LED's perspective.

Putting more than around 5 volts backwards accross an LED will make it break down, and the resulting current flow, if not limited to a low value will kill it.

Did you use a suitably rated current limiting resistor in series with the LED?