onsemi MC7918CTG: -18V Fixed Negative Voltage Regulator Datasheet and Application Circuit Overview
The onsemi MC7918CTG is a member of the classic MC79XX series of three-terminal fixed negative voltage regulators. Designed to deliver a constant -18V output voltage at currents up to 1A, this device simplifies power supply design by integrating a voltage reference, an op-amp, current limiting, and thermal shutdown circuitry into a single, robust package. Its primary function is to maintain a stable negative DC output voltage despite variations in input voltage or load current, making it an essential component in a wide array of electronic equipment.
Housed in the industry-standard TO-220 package, the MC7918CTG is renowned for its rugged construction and reliability. Key features highlighted in its datasheet include internal current limiting, which protects the regulator against overloads; thermal overload protection, which shuts down the device to prevent damage from excessive junction temperatures; and output transistor safe operating area (SOA) protection. These built-in safeguards ensure a high degree of durability in demanding applications.
A typical application circuit for the MC7918CTG is straightforward, requiring only a handful of external components to create a complete regulated power supply. The basic configuration involves connecting the input capacitor (CIN, typically 0.33 µF) between the input pin and common ground (GND), and an output capacitor (COUT, typically 0.1 µF) between the output pin and GND. These capacitors are critical for ensuring circuit stability and improving transient response. The input voltage (VIN) must be more negative than the regulated -18V output; a typical requirement is an input voltage of at least -20.5V to -21V to maintain proper regulation, with a maximum input voltage of -35V.
For enhanced performance, especially when the regulator is located far from the power supply filter, a larger electrolytic capacitor (e.g., 1 µF to 10 µF) can be added at the input to improve ripple rejection. While not always necessary for stability, a larger tantalum or aluminum electrolytic capacitor (e.g., 10 µF to 100 µF) at the output can further improve the transient response.
ICGOODFIND: The onsemi MC7918CTG stands as a quintessential solution for generating stable -18V power rails. Its simplicity, robust protection features, and minimal external component requirement make it an excellent choice for designers seeking a reliable and cost-effective negative voltage regulator for analog circuits, operational amplifier systems, and various industrial controls.
Keywords: Negative Voltage Regulator, Fixed Output, -18V, TO-220, Application Circuit
