Fixed 12V rail, 1A continuous — where the headroom sits
The LM2940S-12 is a fixed-output 12V positive LDO regulator from the LM2940 family, rated for 1A continuous output current. The 1V maximum dropout at full load means the input rail must stay above 13V to maintain regulation — a common margin for 12V bus-powered designs running off a 14V automotive or 15V industrial supply. Output is fixed at 12V with no external divider needed, simplifying the BOM for a single-rail application. The single regulator configuration keeps the footprint small in the D2Pak (TO-263-3) package, which has an exposed tab for heatsinking.
Dropout voltage is specified at 1V maximum at 1A output. That 1V headroom is the minimum input-to-output delta; below it the regulator drops out of regulation and the output follows the input minus the dropout. For a 12V output, budget a 13V minimum input under all load and temperature conditions. PSRR is 66dB at 120Hz. Built-in protection covers over-current, over-temperature, reverse polarity, and short circuit. The 15mA maximum supply current and 10mA quiescent current are moderate — not a low-Iq part for battery operation, but fine for always-on industrial or automotive rails where the load current dominates the power budget.
That means it remains available for existing production but is not intended for new designs. For a new BOM, evaluate the LM2940 series pin-compatible alternatives or a different LDO with the same 12V fixed output and 1A rating. For existing designs, confirm last-time-buy windows and secure inventory through independent distribution.