Many custom libraries include the entire breakout board module (complete with terminal blocks, inductors, and potentiometers) rather than just the bare IC.
To ensure your downloaded library functions correctly during simulation, build a basic step-down circuit using the adjustable or fixed version of the LM2596 model.
Admit a hard truth: Proteus is not the best tool for heavy power electronics simulation. (free from Analog Devices) has a native, perfectly working LM2596 model from Texas Instruments. You can: Lm2596 Proteus Library Download
Connect a to the input (e.g., 12V or 24V). Place a DC Voltmeter across the output capacitor terminals.
Attach a and an Oscilloscope to the final output terminal. Many custom libraries include the entire breakout board
If typing "LM2596" yields no results, the files were likely pasted into the wrong directory. Double-check whether your version of Proteus utilizes the Program Files (x86) directory or the hidden ProgramData directory for storing active libraries.
(via Proteus itself)
You can find the library on various electronics forums and component websites. A common library includes both the .IDX and .LIB files needed for simulation.
This is the most critical step. Unfortunately, a dedicated, widely-available LM2596 library for Proteus is rare. Here's where to look and what to do if you can't find one: (free from Analog Devices) has a native, perfectly