How to Use It?
To use the calculator, simply enter the source voltage and resistor values, and the calculator will calculate the output voltage of the divider circuit.
Keep in mind that the output voltage in actual circuits may vary due to load resistance (where the output voltage is connected). So, to determine the output voltage under load, simply select the “Under Load” option and enter the load resistance.
How to Calculate the Output Voltage of a Divider Circuit
A voltage divider is one of the most fundamental circuits in electronics. The primary purpose of this circuit is to scale down the input voltage to a lower value.
It consists of two resistors connected in series across an input voltage source (Vin). The output voltage (Vout) is taken across one of the resistors and is a fraction of the input voltage. The fraction depends on the ratio of the resistors.
Let’s refer to the resistor nearest the input voltage (Vin) as R1 and the resistor nearest ground as R2. The voltage drop across R2 is our scaled down voltage.
A simple voltage divider circuit looks like this:
The voltage divider equation assumes that you know three values of the above circuit: the input voltage (Vin), as well as the values of both resistors (R1 and R2). Given those values, we can use this equation to calculate the output voltage (Vout):
Where:
Vout is the Output voltage. This is the scaled down voltage.
Vin is the Input voltage.
R1 and R2 are the resistor values.
The ratio R2/(R1+R2) determines the scale factor.
Here’s how the voltage divider equation is derived.
The voltage divider equation relates the output voltage to the input voltage and the resistor values. It can be derived using Ohm’s law and Kirchhoff’s voltage law.
We know that the current (I) flowing through both resistors is the same, so when we apply Ohm’s law to each resistor, we get:
Solving for I in terms of Vin and R1 and R2, we get:
Substituting I into the equation for Vout, we get:
Example
Let’s consider an example: Suppose we have a voltage divider circuit with R1 = 4 kΩ and R2 = 8 kΩ, and the input voltage Vin = 12 V.
Using the voltage divider equation, we can calculate the output voltage Vout as follows:
Plugging in the values, we get:
Simplifying, we get:
So the output voltage is 8 V.
How to Calculate the Output Voltage of a Divider Circuit With Load
The above voltage divider equation assumes that no current flows out of the output node, i.e., there is no load connected to it. However, in reality, there may be some load connected to the output node that draws some current from it. This affects the current flowing through the resistors and thus the output voltage.
The output voltage under load is lower than the output voltage without load. To find the output voltage under load, we need to consider the load resistance as part of the voltage divider circuit.
The modified circuit looks like this:
To find the output voltage under load, we can use the above voltage divider equation with R2 replaced by R2∣∣RL.
Where:
R2∣∣RL is the equivalent resistance of R2 and RL in parallel.
Example
Using the previous circuit as an example, let’s say a load with resistance RL=6k has been connected.
Let’s first find out the equivalent resistance of R2 and RL in parallel.
Plugging in the values, we get:
Now we can use this value to calculate the output voltage Vout as follows:
Plugging in the values, we get:
So the output voltage under load is 5.54 V, which is lower than the output voltage without load (8 V).
