Hi all,
This is all a bit non-consequential, but thought I'd dive in anyway.
I'd like to replace the standard power LED on a computer with a white one, (DSE part Z-3980), purely for aesthetic reasons. I don't want to drive it at full brightness - the spec sheets claim 2000mcd with 30mA and 4V, I'd settle for about 1/1000 of that brightness.
I haven't tested this, but I suspect that the power / hard drive LED headers on a motherboard won't give 4V. My thought was using the signal from the MB to drive a FET, fed from the +5V PSU rail via a dropper resistor to drive the LED.
My problem is not knowing enough to be able to choose a suitable FET, or values of resistor suitable to bias the gate, or the dropper resistor. The FET would only need to be hard off or on.
The dropper resistor should be easy; 4V across the LED, 0.5V (say) dropped across the FET when fully on, and maybe 5mA for a non-lethal brightness. Fed from 5V that leaves a resistor dropping 0.5V with 5mA through it ie 100ohm.
Just wondering if anyone's done this before, or any suggestions ?
Thanks Rob