I'm looking for a simple circuit that uses only a comparator (or an opamp) to detect the presence of a small current through a high-side current resistor. The idea is for a microcontroller input to go high when the current through the resistor exceeds a predefined value (of let's say 200mA).
This is to detect when a phone is actually pulling power from a +5V source. The circuit below illustrates my intent, by I feel that it is missing something, mainly that the comparator may not reset when the voltage across the sense resistor reaches zero. I'm not aiming for precision, but rather a rough "there is current" and "there is no current" type of circuit.
Best Answer
TC75S58' spec
- common mode input voltage range : VSS to VDD− 0.9 V .
So this IC as a high side current detector will not work.
But you might use it on the low side. (Or find a high side Comparator.)
Choose shunt R to read 50mV at full scale. ( most common)
simulate this circuit – Schematic created using CircuitLab
You must be careful on matched R tolerances, input offset since the current sense is very low mV
THis puts the high side in the acceptable CM range.
There are many advantages to low side sensing .