Input voltage for feedback pin on LM2596 Voltage regulator
It's a feedback loop. It will vary the output and read the output voltage, compare that with the internal reference and set the output voltage one way or the other until the output voltage divided by the resistors matches the internal reference.

What you have done is cut the loop. The regulation of the output will have no effect on the input to the feedback pin, so it will basically do all sorts of stuff, if you hit the internal reference exactly it should stop changing the output, but that is only a theoretical case.

If you want to regulate your output you can inject a current on the bottom feedback resistor, but you need to have the resistor divider still connected:







simulate this circuit &ndash; Schematic created using CircuitLab

Depending on the choice of R1 and R3 you get a settable range of the output.