Resistance can be divided into three categories: fixed linear resistance, fixed nonlinear resistance, variable resistance

The reliability of the resistance mainly depends on the temperature of the resistance, and the temperature is the effect of the superposition of the ambient temperature and the heat generated by its own power loss.

Both power and voltage limit the choice and use of resistors:

For resistors with resistance values below the critical resistance value, use is limited by power, and for resistors above the critical resistance value, use is limited by voltage. The power limit for a single pulse depends on the shape of the pulse. At the same time, the peak voltage of the pulse must not exceed the rated limit.

Usage rules for derating resistors:

1, the use of metal glaze resistors in circuits with instantaneous high voltage pulses

2, in the case of large impulse current use winding resistance

3, continuous power <50%× rated power

4, do not use a carbon film resistor >1MΩ, because the long-term stability is too poor

5, the resistance with high resistance value and good long-term stability should be metal glaze resistance

6, after the thermal shock test, the resistance value of the resistor must be within the rated range of ±5%

7, fuse resistance, such as fuse resistance, do not get too close to the PCB, so as not to overheat the PCB

8, try not to use rectangular patch resistors in ESD protection circuits, because the sharp corners of the rectangle are easy to discharge

9, in the voltage, current sampling, if the patch resistor is used, try to use the size of more than 1206.

10, voltage derating use:

For carbon film, metal film, metal oxide film resistance:

When R>100K, VRMS<50% x rated maximum continuous operating voltage

When R≤100K, VRMS<90% x rated maximum continuous operating voltage or 90% x (P x R)0.5, whichever is lower.

For carbon resistors, metal glaze resistors and wire wound resistors:

VRMS<90% x rated maximum continuous operating voltage or 90% x (P x R)0.5, whichever is lower.

11, the instantaneous power when there is an impulse current in the circuit can be calculated according to the following empirical formula:

P=I2×R×t/4, where t is the time when the current drops to 38% of its maximum value.