Fixed 5V rail for legacy boards
The STMicroelectronics LD1117V50-DG is a fixed 5V output LDO positive voltage regulator in a TO-220-3 through-hole package. It delivers up to 800 mA with a maximum dropout voltage of 1.2 V at full load — the sort of part you find holding up a 5 V analog rail or powering a microcontroller on older industrial or consumer boards.
The 5 V fixed output is the first thing to confirm when you're swapping this into a board that lost its regulator — no resistor divider to set the voltage, just drop it in and it's 5 V out. The 800 mA current rating covers moderate loads like a small MCU plus a few op-amps; if the board draws more than that, you'll see the output sag or the thermal protection kick in at 125°C.
The LD1117V50-DG is listed as obsolete. No official successor is listed on the record, but the LD1117 family includes other fixed-output variants (e.g., LD1117V33 for 3.3 V) that share the same pinout and TO-220-3 footprint.