What are the parameters of surface mount power resistors?

The parameters of surface mount power resistors mainly include the following aspects:

1、 Size and packaging
Size: The size of surface mount resistors is usually expressed in inches, and common packaging sizes include 0201, 0402, 0603, 0805, 1206, etc. These numbers represent the length and width of the resistor, for example, 0402 represents a length of 0.04 inches and a width of 0.02 inches.
Encapsulation: Encapsulation refers to the external shape and size of a resistor, as well as the arrangement of pins or pads. Different packaging forms are suitable for different application scenarios and circuit board layouts.
2、 Resistance value
Nominal resistance value: The nominal resistance value of a resistor refers to the resistance value marked on the resistor. The common nominal resistance series include E24 series and E96 series, where the resistance values are distributed according to specific rules to meet different precision and resistance range requirements.
Resistance value representation method: Usually, numerical codes are used to represent the resistance value of a resistor. For the E24 series, it is usually represented by three digits, with the first two digits being significant figures and the third digit representing the number of zeros (or powers of 10) following the significant figures. For example, 103 represents 10k Ω. For the E96 series, it is usually represented by four digits, with the first three digits being significant figures and the fourth digit representing the number of zeros (or powers of 10) following the significant figures. For example, 1003 represents 100k Ω.
3、 Accuracy
Accuracy: The accuracy of a resistor refers to the range of error between the actual resistance value and the nominal resistance value of the resistor. Common accuracy levels include ± 1%, ± 5%, ± 10%, etc. The higher the precision, the smaller the resistance error of the resistor, but the price is relatively high.
4、 Power
Rated power: Rated power refers to the maximum power that a resistor can withstand under normal operating conditions. Beyond this power, the resistor may overheat and be damaged. Different packaging sizes and resistance materials have different rated power.
5、 Temperature coefficient
Temperature coefficient: The temperature coefficient refers to the degree to which the resistance of a resistor changes with temperature. Usually expressed in ppm/℃ (parts per million change per degree Celsius). The smaller the temperature coefficient, the better the temperature stability of the resistor.
6、 Other parameters
Allowable deviation: The allowable deviation of a resistor refers to the maximum allowable error between the actual resistance value and the nominal resistance value of the resistor.
Load reduction curve: The load reduction curve describes the corresponding relationship between ambient temperature and the actual rated power of the resistor. When the ambient temperature rises, the heat dissipation of the resistor is suppressed, and its rated power value will decrease accordingly.
Packaging methods: Common packaging methods include bulk and strip roll packaging. Bulk resistors are suitable for manual welding, while ribbon wound resistors are suitable for automated production.
In summary, the parameters of surface mount power resistors include size and packaging, resistance, accuracy, power, temperature coefficient, and other related parameters. When selecting and using, comprehensive consideration should be given to specific application requirements and circuit design requirements.