Fixed 9 V rail at 1 A — dropout headroom and noise rejection
The LM2940SX-9.0 is a positive fixed-output LDO from Texas Instruments, delivering 1 A at a regulated 9 V. Its 1 V maximum dropout at full load means the input rail must stay above 10 V to maintain regulation — a 12 V bus provides comfortable margin, but a 9.5 V supply would drop out under load. The 64 dB PSRR at 120 Hz is the figure that matters for post-rectifier filtering: it knocks down the full-wave ripple by a factor of ~1600, making this part a clean choice for analog bias rails or audio supply lines where 120 Hz hum couples into the signal path.
Industrial temperature grade and integrated protections
The protection set includes over-current, over-temperature, reverse polarity, and short-circuit shutdown, which reduces the need for external clamp diodes or current-limiting resistors on the output. The 10 mA quiescent current is typical for a 1 A LDO of this generation; it is not a micropower part, so always-on battery applications should budget for the Iq draw.