How to choose a chip resistor
In recent years, in addition to electronic product developers developing new products with SMD devices, maintenance personnel have also begun to repair electronic products assembled with SMT technology in large numbers.
Here are the main parameters and specifications of chip resistors with a large application volume, in order to help developers and maintenance personnel to purchase these chip components.
At present, the models of chip resistors are not uniform, they are set by each manufacturer, and the models are special. If the various parameters and specifications of chip resistors can be correctly proposed when purchasing, then the required resistors can be easily purchased.
SMD resistors have 5 parameter sizes, resistance values, tolerances, temperature coefficients and packaging.
1. Size series SMD resistor series generally have 7 sizes, which are represented by two size codes.
One size code is an EIA code represented by a 4-digit number. The first two digits and the last two digits indicate the length and width of the resistor, in inches.
The other is the metric code, which is also represented by 4 digits, and its unit is millimeters. Different sizes of resistors have different power ratings.
2. Resistance series Nominal resistance value is determined by series. Each series is divided by the tolerance of resistance, among which the most commonly used is E-24 (the tolerance of resistance value is ±5%).
On the surface of the chip resistor, three digits are used to indicate the resistance value. One and two digits are valid digits, and the third digit indicates the number of zeros followed. When there is a decimal point, it is represented by "R" and occupies one effective digit.
3. Tolerance The tolerance of chip resistors has 4 levels, namely F level, ±1%; G level, ±2%; J level, ±5%; K level, ±10%.
4. Temperature coefficient The temperature coefficient of chip resistors has 2 levels, namely w level, ±200ppm/℃; X level, ±100ppm/℃. Only resistors with tolerances of class F use class x, and resistances with tolerances of other classes are generally class w.
5. There are two main types of packaging: bulk and strip-shaped rolls.
The working temperature range of chip resistors is -55--+125℃, and the working voltage is related to the size: 0201 is extremely low, 0402 and 0603 are 50V, 0805 is 150V, and other sizes are 200V.