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- How can I efficiently drive an LED? 4 answers
This might sound like a stupid question, but I want a confirmation. I watched a video on Youtube about using LEDs. Those LEDs required a voltage around 2 volts at 20 mA.
In order to power one LED using a 5 volts power supply, the author used a resistor in series. He calculated he needed around 150 ohms (using U=RI, 5-2=3 volts, 3V/20mA=150ohms).
What I find disturbing is that the resistor, in order to control the voltage must be consuming energy too. P=UI, so 3x20mA=60mW, on top of the LED 2x20mA=40mW. In other words, adding +150% energy consumption to the actual need for lighting up the LED.
Am I missing something or is it typical to spend extra energy just to be able to use electronic components that require a lower voltage? And second question, is there a way to avoid doing it for this type of circuit (5V source, 2V LED)?
- I use the term of voltage instead of current because this is how Ben Eater in his video presented it
- I am mostly interested in the general issue of using extra components in order to reduce consumption locally while introducing a waste when taking the circuit as a whole. This is not just about LEDs, which serve here as an example so suggesting this is a duplicate of "How can I efficiently drive an LED?" is missing the main point (although I agree the second part of my question is related).