audioguru Posted April 10, 2013 Report Share Posted April 10, 2013 R7 is 0.47 0hms and is in series with the load. Load current causes a voltage drop across R7. 3A x 0.47 ohms= 1.41V. With a low load current then the voltage across R7 is very low.The voltage across R7 is fed to pin 2 input of U3.U3 is used as a comparator. Normally its output is high so the LED is turned off and D9 does not reduce the output voltage.When the voltage across R7 exceeds the voltage of P2 then the output of U3 goes low enough to reduce the output voltage so that the load current is reduced to the setting of P2.Your U3 is not detecting the voltage across R7, it acts like an on-off switch. Maybe R7 is the wrong value or is connected wrong.What is the part number of your opamps? Quote Link to comment Share on other sites More sharing options...
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