Author Options:

Circuit Design Question Answered

Ok, I have a power source that outputs about .5 volts sometimes, but at other times as much as 12 volts. I want the power to illuminate an LED in both cases, without burning it out. I think I need a capacitor for this but I'm not entirely sure? Can anyone tell or lead me to a tutorial or circuit diagram that shows how to do this? Thanks!


1) a Vreg would get hot! a heat sink is a must 2) why does the power supply fluctuate?? maybe its time for a new one 3)if its alternating current, a choke could help, because it would induce a mirror current, opposing the voltage change and smoothing the transition.

As long as the voltage drops were not total collapses......that might bring further problems, don't you think?

a choke opposes change. as such, it would smooth the voltage change. unlike a Vreg, its passive so needs not electricity or bias voltage. i don't believe it would cause further problems. but WHY is your power flickering?

this power is coming though ethernet cable, with regular ethernet - only about .5 volts is coming through, but if the port is plugged into POE - power over ethernet - as much as 12 volts can come though.

why the Ethernet?? I'm obviously missing something hear. a linear or battery supply would be cheaper. if you want an activity LED, there are already ones on the Ethernet jacks; you could simply solder on some wire and another led.

Ok, I understand what you mean now,

Try hooking up a 100uF capacitor and a 5v regulator. From there, you should be able to scale down to whatever you need for the LED. 100uF may or may not be enough, not sure how fast it fluctuates -- experiment ;-) Both you should be able to get from any basic electronics store -- although I can't guarentee Radio Shack (unless they still have "bins"-- that is)

Duh on me......I went the long way around, didn't I ? :-) The regulator would could for that range.

a regulator as in a potentiometer or...??

Well, Zachninme pointed me in the correct direction :-)

If it's a predetermined pattern you can just use a resistor and a capacitor

Thanks - is there any more common way to do this, without using that part.