7809

7809 commonly denotes a fixed positive voltage regulator in the 78xx family, most often the LM7809. It provides a regulated +9-volt output from a higher DC input and is widely used in electronic power supplies and educational projects.

Overview and specifications: The 7809 is a three-terminal linear regulator capable of delivering roughly one ampere of load current, with a dropout voltage typically around 2 V depending on current and temperature. The maximum input voltage is usually about 30 to 35 V. The device includes protection features such as current limiting and thermal shutdown to guard against short circuits and overheating. The output voltage is nominally 9 V, with tolerance depending on temperature and load.

Pinout and packaging: In the common TO-220 package, facing the front (label side) with leads downward, the pins are from left to right: input, ground, output. Pinouts can vary by package or manufacturer, so datasheets should be consulted for non-TO-220 variants. The 7809 is part of the broader 78xx family of positive regulators; negative regulators use the 79xx designation.

Applications and use: The regulator is used to obtain a stable 9 V rail for microcontrollers, analog circuits, and other electronics in linear power supplies. Stability typically relies on input and output capacitors; common practice is to place about 0.33 µF on the input and 0.1 µF on the output, with larger capacitors as needed for transient response.

Variants and related parts: Other fixed regulators in the family include 7805, 7812, and 7815. There are many manufacturers producing LM7809-compatible devices, with variations in packaging, temperature range, and efficiency.