A voltage divider lets you convert an input voltage to a lower output voltage. For example a 5V input can be converted to a 3V3 output quite easily. The basic setup is made of two resistors:
But choosing the right resistors is quite tricky. You could take the formula and try some values in order to approximate the values or use the calculator formula:
| Input Voltage | V | |
| Desired Output Voltage | V | |
Possible resistor values for input voltage of 5V and output voltage of 3.3V, ordered by error:
| R1 | R2 | Actual | Error | Power Loss |
|---|---|---|---|---|
| 330Ω | 680Ω | 3.366V | 0.066V | 0.025W |
| 47Ω | 100Ω | 3.401V | 0.101V | 0.170W |
| 47kΩ | 100kΩ | 3.401V | 0.101V | 0.000W |
| 4.7kΩ | 10kΩ | 3.401V | 0.101V | 0.002W |
| 470Ω | 1kΩ | 3.401V | 0.101V | 0.017W |
| 4.7Ω | 10Ω | 3.401V | 0.101V | 1.701W |
| 220Ω | 470Ω | 3.406V | 0.106V | 0.036W |
| 22kΩ | 47kΩ | 3.406V | 0.106V | 0.000W |
| 2.2kΩ | 4.7kΩ | 3.406V | 0.106V | 0.004W |
| 10kΩ | 22kΩ | 3.438V | 0.138V | 0.001W |
| 100Ω | 220Ω | 3.438V | 0.138V | 0.078W |
| 1kΩ | 2.2kΩ | 3.438V | 0.138V | 0.008W |
| 220Ω | 330Ω | 3.000V | 0.300V | 0.045W |
| 2.2kΩ | 3.3kΩ | 3.000V | 0.300V | 0.005W |
Please note: Don't use a voltage divider for high voltages, as the entire current has to pass the resistors, which will hurt them a lot. Alternatives are voltage regulators! And even more important: You shouldn't use low value resistors in real world voltage dividers. The power loss column states how much energy is converted into heat and should be as low as possible.