Fixed -5 V negative rail — what the 1.5 A rating buys you
The LM7905CT is a fixed -5 V output negative voltage regulator from the LM79xx family, delivering up to 1.5 A continuous. It is the complement to the positive LM7805, providing a clean negative rail for dual-supply op-amp circuits, bipolar ADC/DAC front-ends, or any system that needs a symmetrical supply. The dropout voltage is 1.1 V max at 1 A load, so the input must be at least -6.1 V to maintain regulation under full load.
66 dB PSRR — ripple rejection for analog loads
With 66 dB of power-supply rejection ratio at 120 Hz, the LM7905CT attenuates full-wave-rectified ripple by a factor of roughly 2000. That matters when the negative rail feeds a precision op-amp or a low-noise sensor bias — the regulator keeps mains-frequency hum off the supply bus without an additional LC filter stage.
TO-220-3 — heatsinking and board fit
The TO-220-3 through-hole package has a metal tab that bolts to a heatsink or a chassis ground plane. For a 1.5 A load with a 3 V input-to-output differential, the regulator dissipates about 4.5 W — a TO-220 in free air cannot shed that without a heatsink.
Obsolete — no official replacement on record
For a production BOM that requires this exact negative rail, the procurement path is last-time-buy inventory or the independent surplus channel — date-code provenance and traceability matter more here than with an active part, because mystery stock surfacing years after the last buy window may be relabeled or out-of-spec.