The voltage divider (also known as the potential divider) is a basic but very important electric circuit used to convert a high voltage to a small value in electronics. Voltage dividers are often used to decrease the size of a voltage or provide a reference voltage. They may also be used as a signal attenuator at low frequencies. Let’s study this in more detail.
What is the voltage divider rule?
In electric circuits, the voltage divider rule is used to decrease or increase the voltage levels of a source. This is an important concept, especially when creating increasingly complicated circuits. Engineers use this rule to analyse resistance and optimise electronic equipment.
An example diagram of a voltage divider circuit, Oğulcan Tezcan – StudySmarter Originals
Voltage divider formula
So, how is the voltage divider rule applied to electric circuits? Look at the diagram above: there is n number of resistors, and we want to take the voltage output from R1, so we want to calculate the voltage value of R1. The formula for finding the voltage value of R1 (VR1) is
\[V_{R1} = \frac{R_1}{R_1+R_2+...+R_N} \cdot V\]
Let’s break this down:
- Recall that the current of the resistors connected in series is the same.
- Because of Ohm’s law, we have \(V = I \cdot R\)
- So if I stays at the same value, then the voltage level V is directly proportional to the resistance value R.
- In the above formula, the voltage value of a resistor is equal to the resistance value of the component divided by the total resistance and multiplied by the voltage value of the source (V).
In the circuit below, the given values for the resistors are R1 = 3Ω, R2 = 7Ω, and R3 = 5Ω. Find the output voltage (Vo).
An example diagram of a voltage divider circuit, Oğulcan Tezcan – StudySmarter Originals
Solution
We take the output voltage (Vo) from the R3 resistor’s poles, which means it will be the same value as R3 resistance’s value voltage. To calculate the voltage value of R3, we can put the given values into the voltage divider equation:
\[V_0 = V_{R3} = \frac{R_3}{R_1+R_2+R_3} \cdot V\]
\[V_{R3} = \frac{5 \Omega }{3 \Omega+7 \Omega+5 \Omega} \cdot 30V\]
From this calculation, we can find the output voltage:
\[V_0 = V_{R3} = 10 V\]
In some sources, you may see that the voltage divider circuit is a little more simplistic. To help you feel comfortable with both voltage divider diagram types, let’s look at another example below.
In the circuit below, the given value for the input voltage (Vin) is 20 volts and the given values for the resistors are R1 = 5Ω and R2 = 5Ω. Find the value of the output voltage (Vo).
An example diagram of a voltage divider circuit, Oğulcan Tezcan – StudySmarter Originals
Solution
To solve a question in this diagram style, you must first understand what it represents. This is a complete loop circuit, and it is shown below.
An example diagram of a voltage divider circuit, Oğulcan Tezcan – StudySmarter Originals
The point shown as Vin in the first diagram shows the positive pole of the voltage source, and the ground resembles that the circuit is a loop connecting to the negative pole of the source Vin. Now let’s apply the voltage divider equation to find the output voltage (Vo), which is equal to the voltage value of R2.
\[V_0 = \frac{R_2}{R_2+R_1} \cdot V_{in}\]
Let’s put the values in their correct places in the equation:
\[V_0 = \frac{5 \Omega}{5 \Omega + 5\Omega} \cdot 20V\]
\[V_0 = 10V\]
Where are voltage dividers used?
Voltage dividers are used to control the level of a signal and to test voltages. They are also used for the bias of active components in amplifiers. Voltage dividers are found in multimeters as well.
High voltage measurement
Although there are many types of voltmeters for different levels of voltage measurement, if the voltage value to be measured is too big, it can’t be done with a voltmeter alone. This is where voltage dividers come into play: the voltage is applied across the voltage divider, and then the voltage output, which is the lowered amount of voltage, will be measured by a voltmeter. For the final step, the measured voltage is multiplied by the factor that the input voltage was lowered by.
Sensor measurement
A microcontroller can read the resistance value of a sensor using voltage dividers. A voltage divider is formed by wiring the sensor in series with a known resistance and applying a fixed voltage across the divider. The analogue-to-digital converter on the microcontroller is linked to the divider’s centre tap. This is so that it can read the tap voltage and calculate the sensor resistance using the observed voltage and determined resistance and voltage.
Logic level shifting
Voltage dividers are also used as logic level shifters. Logic level shifters connect two logic circuits in series to each other.
Some logic circuits operate at 5V, and others operate at 3.3V. Let’s say we are going to connect two circuits in series to each other:
- The first one operates at 5V. This means its input and output voltage will be 5V.
- The second one operates at 3.3V, which means its input and output voltage will be 3.3V.
If we connect these two circuits directly, the first circuit’s output of 5V can damage the second circuit over time because its input value is 3.3V. However, the problem will be solved if we connect a voltage divider circuit with an output ratio of 3.3/5 serial between these two circuits.
Voltage Divider - Key takeaways
- In electronics, a voltage divider is a fundamental and important electric circuit that is used to transform a large voltage into a smaller value.
- Voltage dividers are used to control the level of a signal and to test voltages. They are also used for the bias of active components in amplifiers.
- Voltage dividers are used in sensor measurement, high voltage measurement, and logic level shifting.
- The output voltage of a voltage divider can be found from the resistance value of the output component divided by the total series resistance and multiplied by the voltage value of the source.
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