I have a very basic current limit circuit configured with an IRF4905 and a fixed -VGS, intended to limit charge current into a 12VDC battery. The idea was to use the least possible parts to accomplish the task, so not PWM, no Rsense/bipolar feedback, etc. By allowing the MOSFET to transition from saturation and drop through ohmic as the difference between supply and battery voltage equalize, current would be max initially, then drop to some minimum value.
Simulations in LTSpice show expected results, but on the bench the current tends to climb above the limit set by VGS. If an additional current load is placed in parallel with the battery to test current limiting, the current through the MOSFET will also increase. I've confirmed there is no drift in the VGS voltage, no parts are overheating, etc. Can anyone offer suggestions on what might be going on? Thanks.
Simulations in LTSpice show expected results, but on the bench the current tends to climb above the limit set by VGS. If an additional current load is placed in parallel with the battery to test current limiting, the current through the MOSFET will also increase. I've confirmed there is no drift in the VGS voltage, no parts are overheating, etc. Can anyone offer suggestions on what might be going on? Thanks.