500 mA adjustable rail — what it covers
The Texas Instruments LM317MDTX/NOPB is a three-terminal adjustable positive voltage regulator delivering up to 500 mA output current. The output voltage is set with two external resistors over a 1.25 V to 37 V range, matching the maximum input voltage of 37 V. A single regulator channel with overcurrent, overtemperature, and short-circuit protection built in — no external clamp diodes needed for most loads.
Power-supply rejection ratio is 80 dB at 120 Hz, rolling off to 65 dB at the same frequency under heavier load. That 80 dB floor means the output ripple from a full-wave-rectified mains supply is attenuated by a factor of 10,000 — enough to keep 120 Hz hum out of sensitive analog front ends. Quiescent current is 10 mA typical — the regulator burns that much just to run the internal reference and error amp, so the load budget should account for it.
TO-252-3 surface-mount — thermal and footprint reality
Housed in a TO-252-3 (DPak) with a single exposed tab on the back side. Without adequate copper area, the 500 mA output at high dropout will push the junction above the 125 °C maximum. Not rated for continuous operation below freezing or in under-hood automotive environments without qualification testing.