Current sensor: electronic circuits that monitor the current flow by measuring the voltage drop across a resistor placed in the current path (while other technologies exist, such as magnetic, everything discussed here is limited to shunt resistor current measurement).  (see figure 1) The current sensor outputs either a voltage or a current that is proportional to the current through the measured path.

A wide variety of applications benefit from the ability to measure current flow. Traditionaly, current sensing was primarily for circuit protection and reporting. However, as technology advances, current sensing is becoming more and more important as a way to monitor performance (and ultimately enhance it).

Some applications that benefit from current sensing:

• Overcurrent-protection and supervising circuits
• 4-20 mA systems
• Programmable current sources
• Linear and switch-mode power supplies
• Battery chargers
• Battery-operated circuits for which you need to know the ratio of current flow into and out of a rechargeable battery.
• Proportional solenoid control, linear or PWM

• More about low side current sensing
• More about high side current sensing