Differences between the Various Types of Resistors
Aug 02, 2024
Differences between the Various Types of Resistors
Resistors can be broadly classified into three categories: fixed resistors, variable resistors, and special resistors. Fixed resistors have a constant resistance value, while variable resistors can adjust their resistance values as needed. Special resistors are electronic components with specific resistance characteristics for certain applications.
1.Fixed resistors can be further subdivided into metal film resistors, carbon film resistors, wirewound resistors, and other types.
Metal Film Resistors Metal film resistors are widely used in high-precision measurement circuits and high-stability applications due to their characteristics of high precision, low noise, and good stability. The resistance value can be precisely controlled during the manufacturing process of metal films, and their temperature coefficient is very small, making changes in resistance thanks to temperature variations negligible.
Carbon Film Resistors Carbon film resistors are manufactured using carbon film materials and are cost-effective, widely used in ordinary electronic devices and circuits that do not require particularly precise resistance values. Compared to metal film resistors, carbon film resistors have a larger temperature coefficient, meaning their resistance values change more significantly with temperature variations. Therefore, they should be used cautiously in applications requiring high temperature stability.
Wirewound Resistors Wirewound resistors are made by tightly winding fine metal wires (such as nichrome) around insulating materials (such as ceramic rods). These resistors are typically used in high-power dissipation applications like power supply equipment and amplifiers due to their good high-temperature resistance and high power tolerance. However, due to their manufacturing process, wirewound resistors are generally not suitable for high-frequency applications because they have higher parasitic inductance (current noise and voltage fluctuations). 2.Variable resistors include potentiometers, adjustable resistors, etc.
Potentiometers Potentiometers are commonly used variable resistor devices that can continuously adjust the current or voltage in a circuit through rotation or sliding operation. Potentiometers play an important role in various devices such as volume control and light intensity adjustment. Adjustable resistors are mainly used in the debugging stage of circuits to obtain the optimal operating state by adjusting the resistance value.
Adjustable Resistors Adjustable resistors can change their resistance values through sliding or rotating operations. They are small, lightweight, and have the characteristics of high precision, strong stability, high reliability, and long lifespan, providing accurate resistance values. However, they also have some disadvantages. For example, the adjustment process is relatively complex and requires professional operation. Furthermore, in high-temperature or high-humidity environments, the performance of adjustable resistors may be affected. 3.Special resistors include thermistors, varistors, photoconductive resistors (or photoresistors), force-sensitive resistors, humidity-sensitive resistors, gas-sensitive resistors, etc.
Thermistors Thermistors are electronic components that can change their resistance values according to temperature changes. Their role is to sense ambient temperature through temperature changes and convert them into changes in resistance values, thus enabling temperature measurement and control. Their resistance decreases as temperature increases and increases as temperature decreases.
Varistors Varistors are electronic components used to protect circuits from lightning strikes and overvoltage. They have high impedance and low voltage response characteristics, can automatically adjust the resistance value in the circuit, and maintain the voltage within a safe range. Lightning protection varistors play an important role, allowing circuit systems to operate stably in lightning environments and during instantaneous inrush currents when powering on. They are safe, reliable, sensitive, and rapid, capable of quickly absorbing and discharging overvoltage.
Photoconductive Resistors (or Photoresistors) Photoconductive resistors have a high sensitivity and fast response speed, making them suitable for electronic products such as photocontrol switches and photo-sensing lights. The working principle of photoconductive resistors is to use light to irradiate the PN junction, changing the concentration of internal carriers and thereby altering the resistance value. In dark environments or at night, the resistance value is higher, and the current is smaller; in bright environments or during the day, the resistance value is lower, and the current is larger. This allows photoconductive resistors to automatically adjust the working state of the circuit according to changes in ambient light.
Force-Sensitive Resistors Force-sensitive resistors are sensors used to measure force. They are small, lightweight, have a fast response speed, high measurement accuracy, reliability, and durability. However, they also have some disadvantages. They are sensitive to temperature and humidity changes, requiring temperature and humidity calibration. Additionally they are also sensitive to the distribution of loads and need to be appropriately adjusted according to the load conditions.
Humidity-Sensitive Resistors Humidity-sensitive resistors are electronic components that change their resistance values according to changes in ambient humidity. Their advantages include high sensitivity, simple structure, small size, fast response speed, and relatively low cost. However, they are very sensitive to temperature changes, which may lead to reduced sensitivity and stability. Additionally, they have a nonlinear response to humidity changes, which may make accurate measurements difficult in certain humidity ranges. They are also susceptible to contamination from the external environment, which may lead to inaccurate changes in resistance values. Their lifespan is limited, and they need to be replaced regularly.
Gas-Sensitive Resistors Gas-sensitive resistors are variable resistor devices whose resistance changes with the concentration of ambient gas. They have the advantages of fast response, high sensitivity, good reliability, and high stability. However, they are greatly affected by the environment and have different responses to different gases. Different gas-sensitive resistors have different response characteristics to different types of gases, requiring precise calibration. Moreover, their lifespan is limited, and they need to be replaced regularly. 4.Factors to Consider in the Practical Application of Different Types of Resistors
Voltage Rating The voltage rating of a resistor refers to its ability to withstand the maximum voltage without breakdown. Determining whether the voltage rating of a resistor is suitable is one of the important factors to ensure circuit safety.
Power Rating The power rating of a resistor determines the maximum power it can continuously dissipate without damage due to overheating. Using resistors with low power ratings in high-power applications is dangerous because they can easily overheat or even burn out.
Package Type When selecting resistors, their package type should also be considered, depending on the design requirements and space constraints of the final product. Surface Mount Technology (SMT) resistors are suitable for automated production and space-saving modern electronic devices, while Through-Hole (TH) resistors are more suitable for applications requiring manual soldering.
Operating Temperature Range The performance of resistors within their operating temperature range is also crucial. The resistance values of some resistors change significantly with temperature variations, which is unacceptable in certain precision control applications.
