I ordered a sample of an 8mm 100mA LED that produces 90K mcd, which I'm super excited to test out. I thought I was pretty good at determining power dissipation and resistance, etc, but I'm getting different info from different sources and I wanted to ask here just to be sure I don't blow up my sample, or a resistor for that matter.
Vf = 3.0V
If = 100mA
Vcc = 9V battery (just to test the diode, not a permanent power source)
So, 9V - 3V = 6V drop across the resistor at 100mA = 60 Ohms. Don't think that's a standard value, but we'll just use that for now.
So, as for power dissipation across the resistor for testing, my math figures 6V x 100mA = 600mW. I'm not getting any discrepancies there... However, let's say I want to do 5 diodes in series with a 16V power supply. 5x3Vf = 15 V, so 1V drop across the resistor at 100mA for the string... wouldn't this result in a power dissipation for the resistor at 100mW? After all, 1V x .1A = .1W? The reason I ask is because using a resistor calculator with this info in place gives me a power dissipation across the resistor of 1.3W, which I believe is wrong but has left enough doubt in my mind to want to ask.
Thanks.
Vf = 3.0V
If = 100mA
Vcc = 9V battery (just to test the diode, not a permanent power source)
So, 9V - 3V = 6V drop across the resistor at 100mA = 60 Ohms. Don't think that's a standard value, but we'll just use that for now.
So, as for power dissipation across the resistor for testing, my math figures 6V x 100mA = 600mW. I'm not getting any discrepancies there... However, let's say I want to do 5 diodes in series with a 16V power supply. 5x3Vf = 15 V, so 1V drop across the resistor at 100mA for the string... wouldn't this result in a power dissipation for the resistor at 100mW? After all, 1V x .1A = .1W? The reason I ask is because using a resistor calculator with this info in place gives me a power dissipation across the resistor of 1.3W, which I believe is wrong but has left enough doubt in my mind to want to ask.
Thanks.