79xx

79xx refers to a family of fixed negative voltage regulators used to provide stable negative supply voltages relative to ground. They are the negative counterparts to the 78xx series and are commonly used in dual-supply electronics to generate rails such as −5 V, −12 V, or −15 V. Typical parts include the 7905, 7910, 7912, and 7915, among others. Like their positive counterparts, 79xx devices are linear regulators, meaning they dissipate power as heat equal to the voltage difference between input and output multiplied by the output current.

Pinouts and packages vary by manufacturer and package type. In the common TO-220 package, the LM79xx pinout is usually ground, input, output (from left to right when facing the front). This differs from the 78xx series, so datasheets should be consulted for exact pin assignments and recommended capacitors for a given part.

Operational limits include a dropout voltage typically around 2 volts, meaning the input must be at least about 2 V more negative than the desired output. Maximum output current is typically around 1 A for standard through-hole devices, with higher currents requiring heatsinking. Protection features such as short-circuit protection and thermal shutdown are common.

Recommended external capacitors improve stability and transient response: a small input capacitor (approximately 0.33 µF) and a small output capacitor (approximately 0.1 µF) near the regulator, with larger electrolytics used to smooth ripple as needed.

Applications include providing negative rails in dual-supply analog circuits, op-amp and sensor circuitry, and any design requiring a fixed negative voltage reference. They are simple and inexpensive but less efficient than switching regulators, especially for larger voltage differences or higher currents.