Introduction
A resistor is a key component in electrical circuits, helping to control the flow of current. Unlike fixed resistors, a variable resistor allows adjustment of voltage and resistance, making it essential in many applications. It has two terminals and is often represented by a special symbol in circuit diagrams.
According to Ohm’s Law, resistance is expressed as the ratio of voltage to current, influencing how power is managed. This passive device dissipates energy as heat, and it can obstruct or regulate electrical signals. Engineers rely on it for precise control, ensuring smooth operation in various electronic systems.
What is a variable resistor?
A variable resistor changes its electric resistance to control current in a circuit. It has a wiper that moves over a resistive element, adjusting resistance smoothly. When it has two terminals, it works as a rheostat, while with three terminals, it acts as a potentiometer or potential divider.
Some resistors use mechanical action, while others are electronically controlled for precision. These digital potentiometers function like traditional ones but are controlled electronically. As an electromechanical transducer, they play a key role in devices needing adjusted resistance for smooth performance.
Variable Resistor Definition
A resistor with an ohmic resistance that can be adjusted is called a variable resistor. It works mechanically as a potentiometer or rheostat, or electronically as a digital potentiometer, depending on its value and function.
Variable Resistors symbol
Working Mechanism of Variable Resistors
Variable resistors are used in electric circuits to adjust the resistance and control the current or input voltage. A voltage source is connected to terminals 1 and 3, allowing the resistance to change while keeping a constant current flow.
The output voltage between terminals 1 and 2 is calculated using the voltage division formula. By setting a specific value, these resistors help maintain stable circuit operation and precise voltage control.
Structure of a Variable Resistor
The working principle of a variable resistor remains the same across different types. Inside, a fixed resistance element called the resistive track is connected between terminals 1 and 3. The wiper and slider move along this track to modify the resistance.
A knob in the middle is used for adjusting the value, with terminal 2 having direct contact with the wiper. When the knob is turned, the resistance between terminals 1 and 2, or 2 and 3, is changed, allowing precise control over electrical flow.
Types of variable resistors
There are three common types of variable resistors.
Potentiometers
Rheostats
Digital Resistor
Potentiometers
A potentiometer is a common type of variable resistor used in many applications. It works as a resistive divider, adjusting the voltage signal based on its position. These are essential in circuits for tuning and precise measurement of distance and angles.
In audio systems, potentiometers help with amplifier gain control and audio volume adjustment. Trimmer potentiometers, or trimpots, are small, mounted on a circuit board, and can be adjusted using a screwdriver to calibrate electrical components for a wide variety of uses.
Rheostats
Rheostats are a type of variable resistor designed for power control by adjusting variable resistance in circuits. Unlike potentiometers, they use only two terminals instead of three and do not work as a potential divider. The wiper moves along the resistive element, changing resistance to regulate the load.
Earlier, rheostats were used in series with devices like a light bulb, but this method became inefficient. Now, switching electronics are preferred, and preset variable resistors, often wired as rheostats, are used for tuning and calibration in modern circuits.
Digital Resistor
A digital variable resistor is a modern variable resistor that adjusts resistance without mechanical movement. Instead, it is controlled by electronic signals and follows digital protocols like I²C.
It changes resistance in discrete steps, responding to up/down signals for precise control. This makes it ideal for automated systems that require accurate changes in resistance.
Applications of Variable Resistors
They are widely used in electronics for voltage control and current adjustment. They are found in home electronic appliances like TVs, radios, and speakers, where they help with volume level control. In smart home control devices, they manage speed control and other automated functions.
Potentiometers are common in oscillators and microphones, ensuring smooth operation in devices. Rheostats adjust resistance levels for dimming lights and regulating power in circuits. These components are essential in various applications, improving performance in everyday homes and industries.
Conclusion
A variable resistor is an essential component in electrical circuits, allowing precise adjustment of ohmic resistance. It can function mechanically as a potentiometer or rheostat, or electronically as a digital potentiometer for automated control. These resistors play a key role in voltage regulation, current adjustment, and tuning across various devices and applications.
