Importance of power rating: In electronic circuit design, the first thing to consider when selecting a resistor is its power rating. This indicator is defined at standard ambient temperature and humidity, assuming no air circulation around it, and indicates the maximum power a resistor can withstand under long-term continuous load without damaging or substantially changing its performance. An important rule for safe use is that resistors should generally be selected with a power rating 1-2 times higher than the power actually consumed in the circuit. Such a choice not only ensures stable operation of the resistor, but also improves the reliability of the entire circuit.
Selection of allowable deviation: The allowable deviation is the maximum allowable deviation range of the actual resistance value of the resistor from the nominal resistance value. This parameter reflects the accuracy of the product. Common accuracies are 5%, 1%, 0.5%, 0.1%, and 0.01%. In different application scenarios, the appropriate tolerance should be selected according to actual needs. For example, where high-precision control is required, it is crucial to select resistors with low tolerances.
Considerations for the maximum operating voltage: The maximum operating voltage refers to the maximum voltage that the resistor can withstand during long-term operation without overheating or electrical breakdown damage. If the voltage exceeds this specification value, it may cause internal sparks, noise, and even damage to the resistor. Therefore, when selecting a resistor, it is important to ensure that its maximum operating voltage meets or exceeds the needs of the circuit.
Consideration of invariance: Invariance is a measure of a resistor's ability to change in resistance value under different external conditions (such as temperature, humidity, voltage, time, load characteristics, etc.). The invariance of a resistor is critical to ensuring the long-term stability and reliability of a circuit.
Influence of noise electromotive force: In ordinary circuits, the noise electromotive force of resistors can usually be ignored, but in weak signal systems, this factor cannot be ignored. The noise of wirewound resistors is mainly thermal noise, while thin film resistors also have current noise in addition to thermal noise. These noises are related to resistance, temperature and frequency bands of external voltage, and require special consideration when designing sensitive circuits.
Examination of high-frequency characteristics: When resistors are used in high-frequency environments, their inherent inductance and capacitance effects need to be considered. At high frequencies, a resistor behaves like an equivalent circuit with a DC resistance in series with a distributed inductance and then in parallel with a distributed capacitance. Non-wirewound resistors and wirewound resistors behave differently in this regard. Wirewound resistors may have higher impedance in high-frequency environments, which in turn causes the power they bear to far exceed the nominal power, increasing the risk of burnout. . Therefore, the correct selection of resistor type is critical in high frequency applications.