What is a Resistor?
- A resistor is a passive electrical component used in circuits to limit or control the flow of electric current.
- It’s one of the basic elements in electronics, playing an important role in managing both current and voltage.
- Resistors measure resistance in Ohms (Ω), with 1 ohm being equal to 1 volt divided by 1 ampere
- i.e. 1Ω = 1V/1A
- In simple terms, resistors are devices that resist the flow of electrical current.
- They’re two-terminal components commonly used to adjust signal levels, reduce current flow, and divide voltages.
- Materials like glass, mica, wood, and rubber are examples of resistive substances.
Types of Resistors:
Linear Resistors:
Linear resistors change their resistance value based on temperature and voltage. Their value remains constant over a wide range of such operating conditions.
Most resistors fall into this category, causing a voltage drop when current flows through them. There are two primary types:
- Fixed Resistors – The name itself explains that these have a fixed resistance value.
- Variable Resistors – These resistors allow for the adjustment of resistance either manually or electronically.
Fixed Resistors:
Carbon Composition Resistors:
- The carbon composition resistors are made by depositing carbon onto a ceramic base. The resistance is controlled by cutting a helix into the carbon layer. These are inexpensive and offer a wide range of resistance values.
Wirewound Resistors:
- The wirewound resistors are made by winding a metal wire (usually nichrome) around a ceramic, plastic, or fiberglass core. They’re good for high-power applications but tend to be bulky. They provide a precise resistance values
Thin Film Resistors:
- The thin film resistors are constructed by depositing a thin layer of metal onto a ceramic base, they provide precise control over resistance, making them highly accurate and stable. They produce less noise as compared to carbon composition resistors. There are 2 types of thin film resistors Carbon film resistors and Metal film resistors.
Carbon Film Resistors:
- The carbon film resistors are similar to carbon composition resistors but made by depositing carbon onto a ceramic rod. Due to negligible noise and wide operating range these resistors are used in electronic circuits.
Metal Film Resistors:
- Instead of using carbon, a metal film is applied to a ceramic rod. These are valued for their precision, low noise, and stable performance at varying temperatures.
Thick Film Resistors:
- Thick film resistors are created by applying a thick layer of resistive material onto a ceramic base. This material, typically a mix of metal oxides and glass, is fired at high temperatures to form a durable layer. These resistors have high power handling capability and good stability.
Variable Resistors:
Potentiometer:
- A potentiometer is a three-terminal device that adjusts voltage in a circuit by turning a movable wiper. The wiper’s position changes the resistance between the terminals.
Rheostats:
- Rheostat is a two-terminal adjustable resistor that changes resistance by moving a terminal along a resistive track. Rheostats are often used in applications like dimming lights or controlling motor speeds.
Trimmer Resistors:
- Trimmer is small (Semi Variable) adjustable resistor used for fine-tuning or calibrating circuits. They allow the precise adjustments of a resistance.
Non-Linear Resistors:
Non-linear resistors don’t follow Ohm’s Law, meaning the current flowing through these resistors does not affect resistance but the change in voltage and temperature can affect the resistance.
Thermistors:
- Temperature-sensitive resistors where resistance decreases as temperature increases. They’re made from materials like cobalt, nickel, strontium, and manganese metal oxides.
Varistors (Voltage-Dependent Resistors):
- Used to protect circuits from sudden voltage spikes by absorbing excess energy and preventing damage to sensitive components.
Photoresistors (Light Dependent Resistors):
- The resistance of a photoresistor decreases as light intensity increases, making them useful for light-sensing applications. They’re made from materials like cadmium sulfide.
Applications of Resistors:
- Current Limiting: Resistors prevent excessive current from damaging sensitive components like LEDs and transistors.
- Voltage Division: By using a resistor network, you can divide a large input voltage into smaller, manageable levels.
- Signal Conditioning: Resistors adjust or filter signal levels to ensure proper functioning of electronic circuits.
- Biasing: In devices like transistors and amplifiers, resistors help provide the correct voltage or current to enable proper operation.
- Temperature Sensing: Thermistors, for example, change resistance with temperature, making them ideal for monitoring and controlling temperatures.
- Protective Circuits: Resistors help protect circuits from overvoltage conditions, such as in surge protectors.
- Feedback Networks: In amplifiers, resistors control the gain, improving the stability and performance of the circuit.
- Shunt in Ammeters: Resistors act as shunts, providing a low-resistance path to measure current accurately.