12V rail regulator — 1.5A output with 80dB ripple rejection
The Texas Instruments LM340SX-12/NOPB is a fixed-output positive-voltage linear regulator delivering 12V at up to 1.5A from a maximum 35V input rail. The 80dB PSRR at 120Hz means it attenuates full-wave rectifier ripple by a factor of 10,000 — relevant for powering analog stages or audio circuits where the 100/120Hz fundamental must stay off the supply bus. Maximum dropout is 2V at 1A load, so the input rail needs to stay above 14V to maintain regulation at full current. Below that headroom the output falls out of spec — factor this into the minimum bulk-cap voltage under load.
Package and thermal — DDPAK/TO-263-3 footprint
Surface-mount DDPAK/TO-263-3 (3 leads plus tab). The exposed copper tab on the bottom is the main thermal path — the board layout must connect it to a sufficient copper plane area to keep the junction below the 125°C max operating temperature at 1.5A output. The tab is also the ground return; the datasheet's recommended footprint and via pattern are the starting point for the thermal simulation. Available in Tape & Reel (TR) for automated pick-and-place or Cut Tape (CT) for prototype and low-volume builds. The reel quantity is standard for the DDPAK carrier; the CT option avoids committing to a full reel for engineering samples.
Protection and compliance — built-in fault tolerance
On-chip over-temperature shutdown and short-circuit current limiting protect the regulator and the load from fault conditions. The 8 mA quiescent current is drawn regardless of load — budget this into the system standby power when the 12V rail is enabled but unloaded.