Comparator help

[MrHeckles]

This is my current circuit as it stands

What I am trying to get is the LED to turn on when the voltage across the sense resistor (0.32 ohm) gets above 0.2v

I have set up the LM311 comparator as shown. However it doesnt seem to work as I thought it would. The LED turns on as soon as there is ANY voltage across the sense resistor (ie when the mosfet starts switching on).

I have also tried it with the inputs round the other way. That didnt work as I wanted either.

Please could someone let me know where my schematic is incorrect.

Thanks

 

[audioguru2]

The datasheet shows that there are voltage spikes across the sense resistor. It needs a filter like this, but it will cause a small delay.

View attachment 37946

 

[MrHeckles]

I put the filter in and after fiddling with the values of things got it all working.

Many thanks audioguru