Im working on led tail lights for my vehicle. the standard bulb is a 21w 12v bulb. what i need to try and figure out is whether or not i am able to recreate this same load using leds without a load resistor. the led in question is a 3.2v forward 20ma. i would like to avoid a load resistor due to its high heat output. Basically i need to fool my car into thinking that it is a normal bulb. im still working on finding the specifics of the circuit for the car so i know what range i need to be in to be successful, but in the meantime im just wondering if there is actually any way to do what i have suggested.
closed as unclear what you're asking by Olin Lathrop, PeterJ, Daniel Grillo, Keelan, Chetan Bhargava Sep 2 '14 at 17:38
Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.
You don't draw voltage, you draw current from a voltage source/supply, and you can connect as many LEDs in parallel as you want to - up to the current limit of the supply - but you must first connect a current-limiting resistor in series with each LED and then connect each of the strings in parallel, like this:
This won't work as your Source is of 5V. If you connect 2 LED groups in parallel then effective voltage required will be still 3.4V but current will increased to 40mA. This arrangement will need series resistor as well to avoid excessive current from LEDs. If you connect LEDs in series then required voltage to ON LEDs will be 6.8V which is more than 5V source. You'll not able to see Light from LED. Better to use series resistor to make circuit easy.