Battery Equivalents and Replacements

Voltage Divider Calculator | Explanation, Formula, Circuit

A voltage divider circuit is a simple circuit that converts a higher voltage into a lower one. The voltage divider consists of two resistors in series connected to an input voltage supply.

The desired voltage can be taken from the connection point between the resistors. A resistor-based voltage divider is sensitive to external load.

Published: August 2, 2023.

Voltage Divider Circuit

The voltage divider is a very common element in many circuits and systems, such as potentiometers for volume control in audio equipment, adjusting levels of signals, and biasing transistors in amplifiers.

A voltage divider circuit is a very simple one:

voltage divider no load condition

Note: This is a so-called "unloaded" voltage divider circuit, where the R1 current equals the R2 current.

Here's a simple description of how it works:

The input voltage is applied across two resistors connected in series.

According to Ohm's law, the voltage across a resistor in a series circuit is proportional to its resistance. So, the total voltage is divided between the two resistors.

The output voltage (Vout) can be taken from the junction of these two resistors.

The formula for a voltage divider is:

Uout(V) = Uin(V) * [R2(Ω) / (R1(Ω) + R2(Ω))]

Where:

  • Uin is the input voltage
  • Uout is the output voltage
  • R1 is the resistance closest to the input voltage
  • R2 is the resistance closest to ground

It's important to note that this formula assumes no current is being drawn from the output (R1 current equals R2 current).

Voltage Divider Calculator

To find out voltage, current, and resistance according to Ohm's Law, feel free to use the following Ohm's Law calculator - write your values and click Calculate:

Voltage Output (V)

Uout = Uin * [R2/(R1+R2)]


Resistance R1 (Ω):

Resistance R2 (Ω):

Input Voltage Uin (V):

Output Voltage Uout (V):

 

Loaded Voltage Divider Circuit

If the output is connected to a circuit that draws a significant current, it will affect the output voltage, and the simple voltage divider equation may not apply. This is due to the fact that more current will pass through the resistors, leading to a greater voltage drop, according to Ohm's law.

A loaded voltage divider circuit is very similar to the unloaded voltage divider, with the external load being represented with additional RL(Ω).

voltage divider under load condition

When the voltage divider is under load, the current passing through the R1 does NOT equal the current that passes through R2 since some of the current also passes through the RL.

In this situations, Uout(V) formula is:

Uout = Uin * [(R2 || RL) / (R1 + R2||RL)]

Where "R2||RL" is the resistance of R2 and RL connected in parallel:

R2||RL = R2*RL / (R2 + RL)

As one can see, the unloaded voltage divider R2 equals to the loaded voltage divider R2||RL, making it easy to remember.

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