gchristopher9
Member
- Location
- Boston MA
so how could you measure the current without removing the led & putting the meter in line with the load? also, what would actually limit current, I thought that the resistor would limit the voltage & the current, is it possible the resistor can limit it to the correct voltage but allow too much current to flow? I've always thought that current wasn't regulated externally, & that the load itself will determine the current draw...
if you can find a resistor in series with an LED, you can determine the current through it, and hence the LED using Ohms Law, which is V = I*R. the way to figure it out is to look at the spec sheet of the LED you are using. If the LED wants 3.2V and 0.01 amps, and your sources is a 5 volt source, you would pick the resistor value that would allow 0.01 amps to flow with 1.8V across it. So V=I*R. 1.8/0.01 = 180 OHMS. Then you would also need to make sure that the resistor is sized properly to dissipate the power it is absorbing, and that equation is V*I. 1.8*0.01 = .018 watts, which any resistor you find will happily dissipate. the type of circuits we use at work are much much more complex than this, as it is not efficient to dissipate power in a resistor to satisfy the current draw of the LED. we using switching power supplies, which basically turn on and off fast enough that it looks like a DC voltage to the LED, and you cant see it pulsing, but you dont have the losses associated with powering things with DC. But again this is alot different. We use LEDs that dissipate 0.75 amps, not 0.01-0.03 amps like the LEDs we see in our climate control.