Resistors can be classified into several types based on different criteria, such as resistance adjustability, manufacturing materials, and special functions. Here are the common types:
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By Resistance Adjustability:
- Fixed Resistors: These resistors have a constant resistance value and cannot be adjusted. They are widely used in various circuits where a specific resistance is required to control the current or voltage. For example, in power supply circuits, signal processing circuits, and many other basic electronic circuits, fixed resistors are essential components1.
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Variable Resistors: Resistors whose resistance values can be continuously or discretely changed. They are further divided into two types:
- Potentiometers: Also known as rheostats in some cases. They have a sliding contact that can be adjusted to vary the resistance. Potentiometers are often used for adjusting the volume of audio equipment, the brightness of lamps, and other applications where continuous resistance adjustment is needed.
- Trimming Resistors: These are used for fine-tuning or calibrating the resistance in a circuit. Their resistance adjustment range is relatively small and is usually used to make precise adjustments to the circuit to ensure its proper operation.
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By Manufacturing Materials1:
- Carbon Film Resistors: Made by depositing a carbon film on a ceramic substrate. They have good high-frequency characteristics, a wide range of resistance values, and are relatively inexpensive. However, their accuracy is not very high. They are commonly used in radios, televisions, and other consumer electronics.
- Metal Film Resistors: Produced by depositing a metal film (such as an alloy) on a ceramic or other substrate. They have advantages such as low noise, small temperature coefficient, high precision, and good high-frequency characteristics. They are widely used in high-end audio equipment, computers, test instruments, and other precision electronic devices.
- Wirewound Resistors: Consist of a resistance wire wound around a heat-resistant core (such as a ceramic or glass fiber core). They have good heat resistance, a small temperature coefficient, and high power handling capacity. But their inductance is relatively large, which limits their application in high-frequency circuits. They are often used in power supplies, power amplifiers, and other circuits that require high power handling.
- Metal Oxide Resistors: Made of metal oxide materials, they have high resistance values and good stability. They are suitable for use in high-voltage and high-resistance applications.
- Foil Resistors: Use a thin metal foil as the resistance element. They have extremely high precision, low temperature coefficient, and excellent stability. Foil resistors are mainly used in high-precision measurement instruments and aerospace equipment.
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By Special Functions:
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Thermistors: Resistance values change with temperature. There are two types:
- Negative Temperature Coefficient (NTC) Thermistors: The resistance decreases as the temperature rises. They are often used for temperature sensing, temperature compensation, and overcurrent protection in circuits.
- Positive Temperature Coefficient (PTC) Thermistors: The resistance increases sharply when the temperature exceeds a certain value (the Curie point). They are used in applications such as temperature control, overcurrent protection, and self-resetting fuses.
- Varistors (Voltage-dependent Resistors): The resistance changes with the applied voltage. They have a high resistance value at normal voltages but can become conductive when the voltage exceeds a certain threshold. Varistors are used for surge protection in circuits to protect electronic devices from voltage spikes and surges.
- Light-dependent Resistors (LDRs): The resistance changes with the intensity of light. They are used in applications such as automatic lighting control, light sensors, and optical communication systems.
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Thermistors: Resistance values change with temperature. There are two types: