FandagoTech
Newbie
Ok, I promise I have checked and rechecked values here.
I needed to make an LED circuit for a Christmas display using one white LED inside a Santa Claus figure to replace the incandescent light bulb because the whole thing was so old it fell apart.
Ok, piece of cake. The white LED had minimal info, 20mA 5mm. I checked it with a component checker that had a readout that it had Vf (I take to mean forward voltage) = 2.82 and C = 36pF.
I am using two AA batteries in series for (measured) 3.11v when fresh.
Calculated 3.11/0.020 (3.11v/20mA) required a 155 ohm resistor. However when I set up the circuit the LED was way too dim, and the current measured was around 2mA.
I experimented with some resistors and ended up with (and this is all measured with two different voltohm ammeters) 4 niminal 10 ohm resistors for a resistance of 2.9-3 ohms, 3.11 volt supply voltage. Measuring current I measured 16.6mA and voltage drops of 0.05v drop on the 4 parallel 10 ohm resistors, and 3.06v drop across the LED. The LED is an appropriate brightness. But none of this adds up. Should be over 1 amp.
Have been running this setup for three days now, still glowing brightly. But it makes no sense. Anyone know what is happening here?
Th voltage drop tells me the LED has resistance. Around 180 ohms I think. Why? Is there something special about white LED’s? The LED is lit as it ought to be, but Im missing something here. calculating in the proscribed way does not work.
I needed to make an LED circuit for a Christmas display using one white LED inside a Santa Claus figure to replace the incandescent light bulb because the whole thing was so old it fell apart.
Ok, piece of cake. The white LED had minimal info, 20mA 5mm. I checked it with a component checker that had a readout that it had Vf (I take to mean forward voltage) = 2.82 and C = 36pF.
I am using two AA batteries in series for (measured) 3.11v when fresh.
Calculated 3.11/0.020 (3.11v/20mA) required a 155 ohm resistor. However when I set up the circuit the LED was way too dim, and the current measured was around 2mA.
I experimented with some resistors and ended up with (and this is all measured with two different voltohm ammeters) 4 niminal 10 ohm resistors for a resistance of 2.9-3 ohms, 3.11 volt supply voltage. Measuring current I measured 16.6mA and voltage drops of 0.05v drop on the 4 parallel 10 ohm resistors, and 3.06v drop across the LED. The LED is an appropriate brightness. But none of this adds up. Should be over 1 amp.
Have been running this setup for three days now, still glowing brightly. But it makes no sense. Anyone know what is happening here?
Th voltage drop tells me the LED has resistance. Around 180 ohms I think. Why? Is there something special about white LED’s? The LED is lit as it ought to be, but Im missing something here. calculating in the proscribed way does not work.
