The inhibitory effect of the conductor on the current is called the resistance of the conductor; it is represented by R, and the unit is ohm; the resistance of the conductor is the resistance of the conductor to the current.
For example, RC0402JR-07100KL: stands for 0402 package / 5% accuracy / paper tape packaging / resistance value 100K;
The smallest SMD resistor package is 0075, with a length and width of only 0.3mm * 0.15mm; the package size of the resistor needs to be used when building a PCB package.
At the same time, the package with two powers, the larger one is the high-power series, which is more expensive than the conventional power. Choose the high-power type carefully, and it is easy to be out of stock.
The resistance has the following main parameters, which need to be considered when selecting the resistance;
Nominal resistance: the resistance indicated on the resistor, such as 1002 refers to a 10K resistance;
Allowable error: The maximum allowable deviation of the actual resistance value from the nominal value is called the allowable error; for a resistance of 10K1% accuracy, the actual resistance value range is (9.9K~10.1K);
Rated power: refers to the maximum allowable power when the ambient temperature is 70°C;
Rated voltage: The rated voltage can be calculated according to the rated power and resistance;
Temperature coefficient: When the temperature changes by 1, the relative change of the resistance value.
Generally, the resistance value is marked on the SMD resistor. According to the mark, the resistance value can be known. Usually we understand the labeling rules. 0201 and 0402 are generally not marked due to the small package.
According to resistance characteristics: fixed resistance, adjustable resistance, special resistance.
According to manufacturing materials: carbon film resistor, metal film resistor, wire wound resistor, non-inductive resistor, thin film resistor, thick film resistor, etc.
According to the installation method: plug-in resistance, SMD resistance; according to function: load resistance, sampling resistance, shunt resistance, protection resistance, etc.
7. Pull up and drag
Pull-up and pull-down resistor, refer to the article I wrote before: talk about pull-up resistor, pull-down resistor, usage scenarios and resistance selection
8. High frequency characteristics
At high frequency, the resistance is no longer a resistance, and the content is too much, so I won't repeat it for the time being.
9.0 ohm resistor
0Ω resistance is not a true non-resistance value, general resistance value, generally has three levels of 20mΩ, 30mΩ and 50mΩ, the current can be calculated according to the following formula;
10. Use attention
1. When the use temperature of the SMD resistor exceeds 70℃, the power will be reduced, so it is generally recommended to design and use it according to 70% of the rated power.