7909

7909 is a designation used for a negative voltage regulator in the 79xx family of three‑terminal linear regulators. It provides a fixed output of minus nine volts when used in a negative supply, and is commonly employed to generate a symmetrical dual‑rail power supply together with a positive regulator such as the 7809 or 7805.

The device is a three‑terminal regulator that requires an input voltage more negative than the desired output. Typical performance parameters include a dropout voltage of about 2 volts, and a maximum input voltage that varies by manufacturer but is commonly in the range of a few tens of volts negative. The output current is typically up to 1 A with appropriate heat sinking. Regulators of this family are available in standard packages such as TO‑220, as well as smaller forms for surface-mount assemblies.

Pinout and polarity are defined by the manufacturer's datasheet and can differ between parts and packaging; designers should verify the exact pin arrangement before use. In general, the 79xx parts are the negative‑voltage counterparts to the 78xx family, sharing similar thermal and electrical characteristics.

Common applications include dual‑supply circuits for op‑amps and other analog and digital ICs, where a stable -9 V rail is required, and as part of power‑supply modules in consumer electronics and instrumentation.

Notes: the 7909 is sometimes referred to by vendor prefixes (for example KA7909, LM7909); always consult the specific datasheet for electrical limits and pin configuration.