Saturday, 19 April 2014

operational amplifier - How does this overcurrent detection circuit work?


This is a overcurrent protection circuit. It'll triggered when it's more than 2Amps. I'm wondering how does that LM339 works related to the circuit. On the datasheet of LM339 page 11-13, it says:


– If IN– is higher than IN+ and the offset voltage, the output is low and the output transistor is sinking current


– If IN– is lower than IN+ and the offset voltage, the output is high impedance and the output transistor is not conducting.


I'm trying to figure out how does the output go to short detection when IN- is higher than IN+, and the output will go to 3.3V when IN- is lower than IN+ (based on my spice simulation). Like how does the current flow in the high impedance mode and how does the current flow to the short detection node? The short detection node is a digital input to a microcontroller.





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