Types of Resistors: Linear and Non-Linear Resistors Explained

Introduction

Resistors are one of the most fundamental components in electronics. They are used to control current and voltage in a circuit. Based on their behavior, resistors are broadly classified into linear and non-linear resistors.

1. Linear Resistors

Linear resistors are those in which the current flowing through them is directly proportional to the applied voltage. These resistors follow Ohm’s Law.

Types of Linear Resistors

1. Fixed Resistor

A fixed resistor has a constant and predetermined resistance value that cannot be changed. Ideally, its resistance remains unaffected by temperature, voltage, or frequency.

2. Variable Resistor

A variable resistor allows the resistance value to be adjusted. It works by moving a contact (called a wiper) across a resistive element.

• Potentiometer: A three-terminal device used as a voltage divider.
• Rheostat: A two-terminal variable resistor used to control current.
• Digital Potentiometer: Electronically controlled variable resistor.

2. Non-Linear Resistors

Non-linear resistors do not follow Ohm’s Law. Their resistance changes with factors such as temperature, light, or voltage.

Types of Non-Linear Resistors

1. Thermistor

A thermistor is a temperature-dependent resistor. Its resistance changes with temperature.

• NTC (Negative Temperature Coefficient): Resistance decreases as temperature increases.
• PTC (Positive Temperature Coefficient): Resistance increases as temperature increases.

Thermistors are used in temperature measurement and protection circuits.

2. Photoresistor (LDR)

A photoresistor, also known as a Light Dependent Resistor (LDR), changes its resistance based on light intensity.

• More light → Less resistance
• Less light → More resistance

It is widely used in light sensing and control applications.

3. Varistor

A varistor is a voltage-dependent resistor. Its resistance changes with applied voltage.

• Higher voltage → Lower resistance
• Lower voltage → Higher resistance

Varistors are commonly used for voltage surge protection.

Surface Mount Resistors

Surface mount resistors (SMD resistors) are compact resistors designed to be mounted directly onto printed circuit boards (PCBs).

Advantages of Surface Mount Resistors

• Small size and space-saving
• High stability
• Better heat dissipation
• Suitable for modern compact electronic devices

Conclusion

Resistors are essential components in electronic circuits. Understanding the types of resistors—linear and non-linear—helps in selecting the right component for specific applications such as current control, voltage division, sensing, and protection.