Take the screenshot ...
Do I have to take the voltage drop into consideration?
Or is it always the voltage (before the forward voltage drop of the component...)
So to calculate led wattage...
5v × 0.595amp = wattage
NOT
5v - led fv - 0.6v diode drop...
Correct?
I think the question is mute. Aren't LEDs rated by current? ie, if the datasheet says it can handle 0.595 Amps then the wattage is irrelevant.
KenF:
I think the question is mute. Aren't LEDs rated by current? ie, if the datasheet says it can handle 0.595 Amps then the wattage is irrelevant.
Absolutely not... eg if you're told it's a 3watt LED.
3w/5v gives 0.6amps or 0.6×5v gives 3watts.
But add a transistor and other foward vf drops into the mix...
0.585 (5 - 2.93) = Wattage dissipation by LED
0.585 x 2.07 = 1.71 watts
It matters not what fancy components (correctly connected or otherwise) that are connected elsewhere in the circuit, it is simply the product of current-through and voltage-drop across the component that determines power "consumed" by it. As to the power emitted as light - that depends upon the chemistry of the diode but, obviously, can never be more than the power "consumed" (irrespective of what the manufacturer might claim)
jackrae:
0.585 (5 - 2.93) = Wattage dissipation by LED0.585 x 2.07 = 1.71 watts
It matters not what fancy components (correctly connected or otherwise) that are connected elsewhere in the circuit, it is simply the product of current-through and voltage-drop across the component that determines power dissipation across it.
And the forward voltage is pretty constant for a diode that's conducting. Hence my suggestion that it all comes down to current.
JohnLincoln:
I think you have the collector and emitter of the left hand transistor transposed in your simulation.
You only think it?
I am certain!
jackrae:
0.585 (5 - 2.93) = Wattage dissipation by LED0.585 x 2.07 = 1.71 watts
So why is it 700ma is classed as 3w?
Something don't add up...
OK...
Explain how an LED consuming 1000ma is '3 watt' lol
I think I may as well ignore wattage for LEDs.
cjdelphi:
So why is it 700ma is classed as 3w?
I'm told that my engine has over a hundred horse power, yet when I calculate it's power when cruising down the road, I find it's producing much less.
.7A x 4V Vf = 2.8W. Still have to be concerned about cooling it.
The spec sheet says 700mA with a typical forward voltage of 3.5V. That's 2.45W.
It says it can be pulsed at 1000mA with a 25% duty cycle which is 3.5W (assuming approximately the same forward voltage).
So, I guess it's "approximately" 3W but it can't dissipate 3W continuously.
I think I may as well ignore wattage for LEDs.
Well... We usually do need to know the approximate power we're dealing with... If I need to design a circuit for an LED, or if someone posts a question here about how to wire-up an LED, it's good to important to know if we are dealing with a normal-everyday ~40mW LED, or if we are in the 1W, 3W, 10W, or more range.