Wide-range adjustable LDO in a compact surface-mount package
The LM317DCYG3 is the classic three-terminal adjustable positive voltage regulator from Texas Instruments, delivering up to 1.5 A continuous output from a 40 V max input rail, adjustable from 1.25 V to 37 V via two external resistors. Housed in a SOT-223-4 surface-mount package, it offers a compact footprint for designs where the traditional TO-220 through-hole version is too tall or incompatible with automated assembly. The 10 mA quiescent current is a trade-off for the wide input range and built-in protection — not a low-Iq choice for battery gear, but fine for industrial rails where the load current dwarfs the regulator's own draw.
PSRR and protection — what the numbers mean for your rail
PSRR is 64 dB typical at 120 Hz, dropping to 57 dB — this is the line ripple rejection from a full-wave rectifier's 120 Hz hum. It cleans up a bulk-capacitor filtered rail well enough for op-amp supplies or logic, but a noise-sensitive ADC front-end would need a post-filter or a higher-PSRR LDO. Built-in over-current, over-temperature, and short-circuit protection mean the regulator survives a momentary output short without external foldback circuitry — the thermal shutdown cycles the output until the fault clears. Operating temperature range is 0°C to 125°C — industrial ambient up to 85°C is fine, but the junction-to-ambient thermal resistance of the SOT-223-4 (typically 62°C/W with 1 in² copper) limits the continuous current at high ambient; derate accordingly.
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