Global trends such as the demand for lower CO2 emissions, the smartening of the electricity supply grid and the electrification of our automobiles are all driving the need for electronic circuits to become more efficient. For circuit designers and systems operators, understanding what level of current is flowing through a circuit and being delivered to a load can be very helpful. Maximizing the operating performance of a battery, controlling motor speeds, and the ability to hot swap server units are examples of applications that can all benefit from the use of accurate current measurement.
Current sense resistors also feature a very low Temperature Coefficient of Resistance (TCR), which defines drift with varying ambient temperature, and excellent long term stability. These characteristics make current measurement accuracy very high and the temperature dependency of the measurement is very low. While they are ideal for applications in virtually all market segments, current sense resistors are particularly useful in helping developers precisely measure current in their automotive, industrial and computer electronics designs.
Current sense resistors work by detecting and converting current to voltage. These devices feature very low resistance values, and therefore, cause only an insignificant voltage drop of 10 to 130 mV in the application.
A shunt resistor is placed in series with the electrical load whereby all the current to be measured will flow through it. Following Ohm’s law, a voltage drop is generated across the resistor of known value, which is proportional to the current. The voltage drop across the resistor can be measured by various amplifier options such as operational, difference and instrumentation amplifiers. To choose the right current sense resistor for a given application, it is important to look at the input common-mode voltage specification. Input common-mode voltage is the average voltage present at the input terminals of the amplifier.
As shunt resistors sit in series with the load, they are able to directly measure the current. This is in contrast to indirect current measurement techniques such as coils where voltage is induced across the coil that is proportional to the current. The fact that shunt resistors use direct current sensing techniques means power is
dissipated from the resistor, resulting in very low resistance values.
