What Is Current Sense Resistor?

A current sense resistor translates a current into a voltage that can be measured. These types of resistors are used in many circuit designs and applications that need to monitor the level of current.

Typically, current sense resistors are positioned in-line on the conduction path between the power source and the load. This reduces the voltage drop and the power loss, as well as increasing the accuracy of the circuit.

The resistance values of these types of resistors are extremely low, often falling into the milliohm range and lower. This is why they are such a popular choice for applications where accuracy, cost, and performance are key considerations.

These types of resistors can be manufactured in a number of different technologies and are typically available in a variety of packages. These include bare and wire wound components, and metal foil components.

They can be used in a wide range of applications including power supplies, motor drives, and battery management systems. However, their performance can be influenced by PCB layout and component selection, as well as the temperature of the components themselves.

Using an incorrect value for a current sense resistor can lead to errors in the circuit that are more than just a matter of temperature sensitivity, so ensuring an accurate design requires careful attention to details.

It is essential that the resistance of the solder pad and copper traces of the printed circuit board are correctly calibrated to ensure an accurate reading. This can be difficult, but can be accomplished with the help of a precision shunt or an accuracy amplifier.

Another important factor is the resistance of the element itself, which may be very different from the resistance of the solder pads and traces. This is because the temerpature coefficient of resistance (TCR) is much higher in a surface mount element than in a wire wound or metal foil part and can cause a significant error.

This error can also result in a large difference in the signal voltage required to make a reading. It is therefore essential to select a sensing resistor that has a very low TCR and that can be accurately calibrated.

Finally, a current SEM Sensor should be rated to dissipate a proportion of its rating. This is calculated by subtracting the power it dissipates from its ohmic value to calculate P = Irms2.

If the circuit needs to operate under fault conditions or overloads, these factors must be considered in the selection of the resistor and its power rating. A good way to do this is to apply a simple mathematical equation to the ohmic value and to the power rating, allowing for overload or fault conditions and high ambient temperatures.

The power rating of a current sensing resistor can be affected by many different factors, and should be determined before the final design is completed. This is especially true when the application involves motors, which can have a start and run current that can exceed 100A. You can get more enlightened on this topic by reading here: https://en.wikipedia.org/wiki/Resistor.