Negative rail regulator for analog and mixed-signal supplies
The L7905CV is a fixed -5V output linear regulator from STMicroelectronics, rated for 1.5A continuous output current. It is designed to generate a clean negative rail from a raw negative input up to -35V maximum. With a PSRR of 60dB at 120Hz, this part attenuates mains-frequency ripple on the input by a factor of 1000, making it suitable for powering analog circuits such as op-amps, ADCs, and audio stages that require a low-noise negative supply. Built-in protection features include over-temperature shutdown and short-circuit current limiting, which guard against load faults and thermal runaway in confined enclosures.
Dropout voltage and quiescent current for BOM planning
The typical dropout voltage is 1.4V at 1A output, meaning the input must be at least -6.4V to maintain regulation at full load. This is a standard figure for a three-terminal negative regulator of this era and class. Quiescent current is 3 mA typical, which is the current drawn by the regulator's internal bias circuitry. It does not vary significantly with load, so the total input current is the output current plus this 3 mA overhead. For industrial or automotive environments requiring -40°C operation, a different negative regulator with a wider temperature grade would be needed.
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