3.3 V fixed rail, 800 mA — what the dropout tells you
The LD1117V33C is a single-output positive LDO from STMicroelectronics, fixed at 3.3 V output with an 800 mA current rating. The 1.3 V maximum dropout at 800 mA means the input must stay above 4.6 V to regulate — a 5 V rail with 10 % tolerance (4.5 V min) is borderline; a 5 V rail with 5 % tolerance (4.75 V min) clears the headroom with 150 mV to spare. Below that, the output tracks the input minus dropout, and ripple rejection collapses. That attenuation knocks a 1 Vpp ripple down to about 180 µVpp at the output — clean enough for most analog loads, but if the load draws 800 mA the dropout rises and the PSRR curve shifts; the datasheet's PSRR-vs-frequency plot (not reproduced here) should be checked against your ripple spectrum.
Industrial temperature grade and protection
The TO-220-3 package with its exposed metal tab allows bolting to a heatsink; at 800 mA and 1.3 V dropout the dissipation is 1.04 W, which in still air at 25°C needs a heatsink to keep junction below 125°C. Built-in over-current and over-temperature protection means the part folds back rather than failing short — a useful behaviour for a rail that powers an MCU or sensor cluster where a hard short could damage downstream circuitry.
The base product number LD1117 covers a family of fixed and adjustable output voltages in TO-220 and SMD packages; the V33C suffix locks the 3.3 V fixed output and through-hole TO-220 variant. Because this is an active catalog part with a long production history, it is available through multiple distribution channels.