How to Accurately Calculate the Resistance for Desired Potentiometer Output Voltage
In electrical engineering and electronics, understanding how to set the resistance in a potentiometer to achieve a specific output voltage is crucial. This article will guide you through the process using the voltage divider principle and provide practical examples to ensure clarity.
Components Required
To accurately calculate the resistance needed in a potentiometer, you will need the following components:
Potentiometer RTotal Power supply VIn (voltage input) Desired output voltage VOutStep-by-Step Guide
Step 1: Understand the Potentiometer Configuration
A potentiometer can be thought of as a variable resistor with three terminals: two connected to the voltage supply and one connected to the output voltage. The resistance between the middle terminal (wiper) and one end of the potentiometer is what determines the output voltage.
Step 2: Apply the Voltage Divider Formula
The output voltage from a potentiometer can be calculated using the voltage divider formula:
VOut VIn × Rwiper / RTotal
Step 3: Rearrange the Formula to Find Rwiper
To find the resistance at the wiper terminal, rearrange the formula:
Rwiper VOut / (VIn / RTotal) VOut × RTotal / VIn
Step 4: Perform the Calculation
Once you have identified the input voltage VIn and the total resistance RTotal of the potentiometer, substitute these values into the formula to find Rwiper.
Example Calculation
Suppose you have a potentiometer with RTotal 10kΩ and you want an output voltage VOut 5V from a VIn 10V power supply.
Using the formula:
Rwiper (5V / 10V) × 10kΩ 0.5 × 10kΩ 5kΩ
Conclusion
To achieve a specific output voltage from a potentiometer, use the voltage divider formula to calculate the required resistance at the wiper terminal. Ensure that the wiper is adjusted to reach the desired voltage.
Power Dissipation in Potentiometers
While the voltage divider principle is straightforward, it is important to consider the power dissipation in the potentiometer, especially for practical applications. The power dissipated by the pot is position-dependent and load-dependent. The equation for this is:
P V1 × V2 / Rwiper
where V1 is the voltage across the wiper and V2 is the voltage from the wiper to ground.
Consider Load Resistance and Power Dissipation
The power dissipated by the potentiometer is not only dependent on its position but also on the load resistance. A load that is 1/10 of the potentiometer's value can still result in significant power dissipation. For detailed calculations, refer to the HHC 2017 paper by rjnelsoncf for a comprehensive analysis and power dissipation plots.
Understanding the power dissipation is crucial to prevent the potentiometer from overheating, especially in positions where the power dissipation is highest, typically between 75 and 99 degrees of rotation. Ensuring this can prevent damage to the potentiometer and improve the overall reliability and longevity of the electronic device.