# 6 unpopular parameters that are often overlooked when choosing a resistor

2023-10-04Archive

01

Rated power

1/16W (upper right of image above). The current blocked by resistor becomes thermal. A small resistor, if heat is not removed in time, it will overheat and burn out.

When designing equipment, it is necessary to calculate current passing through resistor, power = current squared x resistance, and power cannot be exceeded.

02

Operating temperature and power limit at high temperature

Operating temperature range from -55℃ to +155℃

Operating temperature from -55 to +115.

However, in actual use, there is a power limit at high temperatures.

There is a power and temperature curve at end of specification. After +70 degrees, you need to reduce power for use. When an extreme temperature of +155 degrees is reached, power must be reduced to almost 0.

The reason is very simple: if it is still running at full power at high temperatures, temperature will rise higher and higher, and soon exceed the maximum temperature, and it will burn out.

03

Maximum operating voltage

The maximum operating voltage is 50V, maximum overload voltage is 100V. These are maximum operating voltage and maximum overload voltage respectively.

These two parameters refer to instantaneous peak voltage. If it continues at 50 V, power rating of resistor has already been exceeded.

In normal version, voltage can be controlled so that it does not exceed standard according to actual operating power. If there are failures in circuit, you need to consider whether peak value exceeds normative one.

04

Warm drift

Temperature coefficient, 10 Ω < R ≤ 10 MΩ ±100 ppm/°C.

When down-converted, resistance value changes by one ten-thousandth for every degree change in temperature. One ten-thousandth is not much, but when operating temperature rises from -50 ° C to + 50 ° C, resistance value will change by 1%, which is equivalent to a 1% error of precision resistors.

If you need to use precision resistors in scenes with large temperature changes, you need to pay attention to this.

05

Write method

When some engineers design, they code material in great detail to exactly match weaving method. Although there are three binding methods for 0402 resistors, 7-inch disks are commonly used with 10,000 per disk.

If it is written in large length, it may not be easy to buy, and it may not fit in feeder of some chip factories.

06

Zero resistance

Ohm resistors are not absolutely 0 ohms. The number 0 cannot be calculated, so error and power are different from ordinary resistors.

Inaccuracy <0.05 ohm, power is not calculated, only passing current is calculated. The 0 ohm resistor 0402 is rated for 1 A.

When designing equipment, if a 0 ohm resistor is connected in series with a power line, current must be accurately calculated.