What size resistor do I need to change 5 vdc to 3.4 vdc,or 7.5 vdc to 3.4 vdc?

kelseymh8 years ago
A resistor alone is not sufficient, unless your circuit has a constant and known current draw. Recall that V = IR, so you can calculate the voltage drop (V) across a resistor R only if you know the current I through the resistor.

If you are needing some "standard" voltage output (like 3.4V) you're better off using a three-pin voltage regulator with a heat sink.
Well, do you know the supply current? If so, use R = V/I (where V is the voltage you want, and I is the supply current) work it out and that should give you the desired resistor value.
lemonie8 years ago
You could just tell us what you want to run @ 3.4V and from which 5 or 7.5V supply? L