In many circuit applications there is a requirement to convert 12 Volt to 5 Volt.
For example, a circuit may not be able to tolerate input voltages greater than 5V. However, the output device can only provide 12V.
In this case it becomes necessary to divide +12V down to +5V.
One way to do this is with a voltage divider network that consists of two resistors in series as shown in the picture below.
This tool calculates the resistor values for a maximum +5V drop across resistor R2.
Enter either R1 or R2 in milliOhm/Ohm/kiloOhm/megaOhm. The tool will calculate the other resistor value.
Formula
Ohm’s law is used to calculate the voltage drop across each resistor. The current through each series resistor is the same as the total current through the circuit.
Therefore the total current Itotal is given by
Itotal = Vin/(R1+R2) = V1/R1
V1=Vin*R1/(R1+R2)
Itotal = Vin/(R1+R2) = V2/R2
V2=Vin*R2/(R1+R2)
In this case, V2 = +5V and Vin = +12V.
How to Pick Resistor Values
In general, there are many combinations of resistor values that will give the same result. For instance,
- R1 = 10 kΩ and R2 = 7.14 kΩ
- R1 =10 MΩ and R2 = 7.14 MΩ
Both combinations provide +5V at the output.
Check the impedance requirements for the circuit that requires +5V. This will determine which resistor combination should be used.
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