How to calculate required resistance? [duplicate]

Hello I have a question regarding resistance. I have a 5v supply and I want it to be brought down to 1v at a certain part in the circuit. How do I Know how much resistance I need to go from 5v to 1v? Thanks - Jack.

• It depends on the current at any given time. So you probably want to use a linear regulator instead of a resistor. Jul 3 '16 at 17:06

The simplest manifestation of reducing voltage is called a voltage divider, and requires two resistors to implement.

Typically the resistors are wired in series with one leg (call this R1) connected to a source voltage (call this V_in) and the other leg (call this R2) connected to ground.

In this configuration, the voltage at the midpoint of the divider, between the two resistors, under no load, is definitively equal to: V_in * R2 / (R1 + R2).

Pick R1 to be a standard resistor value, then solve for R2. The values you pick will determine how much steady current is demanded by the divider, namely: V_in / (R1 + R2).

If that output voltage is under load, you have to do something like run it through a non-inverting buffer (e.g. Op-amp) before using the voltage. There are amplifiers that are able to bring down the voltage. However, when you make the ratio of R1 and R2, you can make R2/R1 = 0.0001 or something very small. Vout/Vin should equal roughly 1/5. simulate this circuit – Schematic created using CircuitLab