Voltage Scaler (Voltage Divider)

Introduction

Sometimes you need to quickly and easily scale a voltage down to another voltage, within a circuit.

There's a two component circuit which can take in any voltage as its input, and have an exact percentage of that voltage as its output. If the input voltage doubles or triples, the output voltage doubles or triples as well.

Note: 1. This can only scale a voltage down, it can never scale up to voltage higher than its input. 2. The output will be much lower current than what is supplied to the input (Only low milli amps).

Applications

Some examples of situations where you'd need a voltage divider:

1. Voltage from a 0-32 Volt sensor is too high for a 5 Volt micro-controller or a common 20 Volt meter to read without being damaged.
2. A 12 Volt power supply is too high a voltage to power a 5 volt Micro-Controller, a sensor or an LED.

The circuit

Ingredients:
2 x Resistors (Any wattage, Resistance values determined by formula below).

Strange as it sounds, you really do only need two resistors. That's the easy part, the slightly difficult part is the calculation of their values (If you've used fractions, its easy as!).

Diagram:



OutputV = InputV/(R1Ohms+R2Ohms)*R2Ohms

Commonly Needed Combinations

For upto 32 volts input, scaled to 5 volts output: Scale 32 volts down to 15.625% (1/6.4).
 - R1=640 Ohms, R2=100Ohms. Are close enough.


For upto 5 volts input, scaled to 3.3 volts output: Scale 5 volts down to 66% (3/2).
 - R1=8.2K Ohms, R2=5.6K Ohms. Are close enough.