The LM2931CT/LF03 is a positive adjustable low-dropout regulator from Texas Instruments, delivering up to 100 mA with a dropout voltage of 0.3 V at full load. Its 55 dB PSRR at 120 Hz provides meaningful ripple rejection on rectified AC or switching supply inputs, keeping the output clean for sensitive analog loads. The single regulator is configured for positive output and includes over-temperature, reverse polarity, and short-circuit protection — reducing the need for external clamp diodes or crowbar circuits in harsh environments.
Dropout and quiescent current — the battery-budget numbers
With a maximum dropout of 0.3 V at 100 mA, the LM2931CT/LF03 maintains regulation with only 300 mV of headroom above the output voltage. This suits post-battery or post-rectifier rails where the input sags under load. Quiescent current is 1 mA typical, rising to 15 mA maximum under heavy supply current — a reasonable idle draw for always-on automotive or industrial circuits. Input voltage range extends to 26 V, covering nominal 12 V and 24 V industrial buses with margin. The TO-220-3 package (through-hole) allows heatsinking for continuous 100 mA operation at elevated ambient temperatures up to 85°C.