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What does a "current sense" pin generally do?


Jim from Chicago:
Hi, on some schematics I've seen "current sense" as a label (usually on the pin of an op amp or IC) and I'm wondering what exactly it means. My googling suggests these pins are used for some sort of feedback, but I'm not sure if that's right, or if that's all they're used for. Thanks!

Often, it means a connection to an external, relatively low value, resistor in series with the output current to be sensed.  A typical use is for the voltage from the desired current limit to equal a BE junction voltage (0.7 V), at which point the BJT steals drive from the output device.

Exact technical meaning really depends on the circuit.

Obviously it always has something to do with sensing current.

Typical places where I could add such a label to a net would include:

* Simple voltage as measured from one terminal from a current shunt resistor, another side being connected to GND or Vcc. This voltage is relative to the current going through that resistor

* Voltage relative to current measured using some more sophisticated circuitry, for example a hall effect current sensor, or a shunt + amplifier circuit

Very often such signal carries a voltage level that represents the measured current, for example so that 1 volt corresponds to say 10 amps or whatever.

The destination for such a signal could be a switch-mode supply controller IC so it can, using the current sense information, provide current limiting. Or it could go to an analog-to-digital converter inside a microcontroller so it can measure and log current in some circuit.

It means what the datasheet says it means. :)

There isn't really much to generalize?  It could be an input to a control circuit, or the output of a sense circuit.  Or the input to a sense circuit.  It could be poorly named or entirely irrelevant; sometimes datasheets themselves aren't all that much help.



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