How to Adjust a 5k Ohm Potentiometer to Act as a 100-Ohm Potentiometer

In electrical engineering and electronics, utilizing a potentiometer with a different resistance value can often pose challenges. For instance, if you have a 5k ohm potentiometer but need a 100-ohm potentiometer, how can you make that adjustment?

Understanding the Concept

To understand the solution, we first need to grasp the concept of parallel resistors. When two resistors are connected in parallel, their equivalent resistance can be adjusted to achieve a desired value. This is the basis for using a 5k ohm potentiometer as a 100-ohm potentiometer.

Steps to Configure a 5k Ohm Potentiometer as a 100-Ohm Potentiometer

Calculate the Required Resistor

The formula to calculate the equivalent resistance of two resistors in parallel is:

Req 1 / (1/R1 1/R2)

Here:

Req is the desired resistance (100 ohms). R1 is the potentiometer (5k ohms). R2 is the fixed resistor we need to calculate.

Rearranging the formula for R2 gives:

R2 (R1 x Req) / (R1 - Req)

Plugging in the values:

R2 (5000 x 100) / (5000 - 100) 500000 / 4900 ≈ 102.04 ohms

Connect the Resistor

To apply this in practice:

Connect a fixed resistor of approximately 100 ohms in parallel with the 5k ohm potentiometer.

Adjust the Potentiometer

You can now adjust the potentiometer to achieve the desired output voltage while maintaining the equivalent resistance close to 100 ohms.

Summary: By placing a fixed resistor of approximately 100 ohms in parallel with the 5k ohm potentiometer, you can effectively create a variable resistance that can be adjusted around 100 ohms.

Important Note: Keep in mind that the total resistance will vary slightly depending on the position of the potentiometer.

Alternative Methods and Their Limitations

There are alternative methods to achieve the required resistance, but they may have limitations:

Transistor Emitter Follower

One alternative is to use a transistor emitter follower. However, this option is not the most straightforward and can be more expensive and complex.

For example:

Place a 5k ohm pot in parallel with another 5k pot, then add a 2.5k ohm pot in parallel with a 1.25k ohm pot, and so on. This method is impractical and overly complicated. Another option is to place a 5k ohm pot in series with a 20k ohm pot and use a common base transistor to control the output resistance. While this method has its own merits, it is also complex and unnecessarily so.

Conclusion: The most practical and efficient solution is to get a 100 ohm potentiometer, as is commonly available in the market.

Keywords: potentiometer, resistor, parallel connection