5 V fixed LDO — why the 75 dB PSRR matters
The STMicroelectronics LM2931BV50 is a single-output positive fixed 5 V LDO regulator rated for 100 mA continuous output. Its 75 dB PSRR at 120 Hz knocks down 100/120 Hz ripple from a rectified alternator or mains supply, keeping the 5 V rail clean for analog sensors or a microcontroller's ADC reference.
Dropout and thermal budget at 100 mA
Maximum dropout is 0.6 V at the full 100 mA load, so the input can dip to 5.6 V before the output folds. The TO-220 package with its tab can shed about 2–3 W in still air; at 100 mA and a 12 V input the regulator dissipates roughly 0.7 W — well within the thermal budget even at 125 °C junction, as long as the tab is soldered to a reasonable copper area or bolted to a small heatsink.
Obsolete — sourcing path
That means new-design qualification should target a current-production pin-compatible LDO in the LM2931 family — the TO-220 footprint and pinout are shared across the series, so a drop-in alternate from ST or a second source is the practical path.