Hi,
I am very desperate now. I try to monitor the primary current of an flyback converter. The converter works fine, so no issue with the converter itself. So far, the input current must also be as it should, triangle shape, ramping up and stopping as the controller switch off the power FETs.
Switching frequency is 100kHz, so should be no problem for the INA139.
I checked the schematic, I checked the traces on the PCB I changed the chip twice, evrytime the same result.. 0V at the 2k resistor and ~0V at the output of the OP-amp.
Now I am running out of ideas what to check and how to fix.
Vin is 28.8V out of a good desktop supply.
Vcntrl is 3V3 made by an on board LDO, checked.
The Output at pin 1 of the INA139 didn't show anything exept some small peaks, I probably picked up with the ground connection of my probe.
I measured the resistance between pin 3 and pin 4, ~200 Ohms as expected, so no short at the PCB ...
The INA139 should be able to handle 40V common mode voltage, we have ~29V, the supply voltage can be between 2V7 and 40V, we have 3V3 ...
Now I need help !!!
With best regards
Gerhard
