78xx

78xx denotes a family of positive fixed‑voltage linear voltage regulators used in low-cost power supplies. The suffix xx represents the nominal output voltage in volts, for example 7805 provides about 5 V. Common members include 7805, 7809, 7812, and 7824, which are available in several packages. The related 79xx family consists of negative fixed‑voltage regulators.

Operation: The devices contain a pass transistor controlled by an internal reference to hold the output at the fixed voltage. They regulate line and load variations within a specified range. The input must be higher than the output by a dropout voltage, typically around 2 V at rated current. Standard 78xx devices deliver about 1 A; higher‑current variants exist with appropriate heat sinking.

Protections and limitations: Thermal shutdown and current limiting help protect against overheating and short circuits. The regulator dissipates power equal to (Vin − Vout) × Iout, so heat management is important. Because regulation is linear, efficiency is low for large input–output differentials, and designers often choose switching regulators for efficiency or use adequate heat sinking with 78xx parts.

Usage and practical notes: They are widely used in simple linear power supplies for logic and embedded systems. Packages include TO‑220 and similar formats suitable for through‑hole or surface-mount boards. It is common to include input and output capacitors to improve transient response and stability, following the manufacturer’s recommendations.

History and context: The 78xx family originated in the era of early integrated regulators and has been produced by many manufacturers under various part numbers (for example LM78xx, MC7805). While still common in low-cost or hobby designs, many modern systems rely on switching regulators for higher efficiency.