The L78M08CDT-TR is a fixed 8 V positive-output linear regulator from STMicroelectronics, rated for 500 mA continuous output. That 8 V rail is unusual — most fixed regulators land at 5 V or 12 V — so this part is likely specified for a dedicated analog supply or a legacy logic rail that needs exactly 8 V. Input voltage tolerance is 35 V max, which gives plenty of headroom for an unregulated rectified supply or a loosely regulated 12 V or 24 V bus. PSRR is 56 dB at 120 Hz, which is the ripple frequency from a full-wave rectified mains supply. That means the output ripple from a 1 Vpp input ripple at 120 Hz is attenuated to about 1.6 mVpp — clean enough for most analog front-ends and sensor bias rails without a post-filter.
Protection and operating envelope
Built-in over-current, over-temperature, and short-circuit protection mean the regulator survives a momentary output short or a thermal overload without external crowbar circuitry. The 0 °C to 125 °C operating range covers commercial equipment and some industrial cabinets, but the lower bound excludes cold-start automotive or outdoor telecom applications. Quiescent current is 6 mA — this is the current the regulator draws from the input rail to run its internal bias, regardless of load. For a 500 mA output that is 1.2 % overhead, acceptable in most line-powered designs but worth noting for battery-operated gear where every milliamp matters.
The tab is the output terminal and also the primary thermal path — the PCB copper area under the tab sets the junction-to-ambient thermal resistance. A 1-inch-square copper pad on a 2-layer board typically keeps the junction below 125 °C at 500 mA with a 10 V input-to-output differential. CT suits prototyping or small-batch builds.
Lifecycle and compliance
RoHS3 compliant, meaning it meets the EU Restriction of Hazardous Substances directive without exemptions for lead, mercury, cadmium, or the other restricted substances.