onsemi MC7805BT 5V Linear Voltage Regulator: Datasheet, Pinout, and Application Circuits

The onsemi MC7805BT is a classic and widely used linear voltage regulator IC, providing a cornerstone solution for power supply design. As a member of the renowned 78xx series, it is designed to deliver a fixed +5V DC output at up to 1A of current, making it an essential component for powering a vast array of digital logic circuits, microcontrollers, sensors, and other low-power devices.

This article provides a detailed overview of its key specifications, pinout configuration, and practical application circuits.

Datasheet Overview and Key Specifications

The MC7805BT datasheet outlines the critical parameters that define its operation and limitations. Key specifications include:

Output Voltage: +5V ±4% (typically very accurate).

Output Current: Up to 1A (requires adequate heatsinking).

Input Voltage Range: 7V to 25V. A minimum 2V dropout voltage (VI - VO) is required for proper regulation.

Line Regulation: 6 mV (Typ.) - Measures the output voltage change due to input voltage variations.

Load Regulation: 9 mV (Typ.) - Measures the output voltage change due to output current variations.

Operating Junction Temperature: -40°C to +125°C.

Package: TO-220, which is ideal for mounting on a heatsink to dissipate power.

The device incorporates internal current limiting, thermal shutdown, and safe-area compensation, making it remarkably rugged and resistant to overload conditions.

Pinout Configuration

The MC7805BT comes in a standard TO-220 package with three pins. When facing the front (marked side) of the component, the pins are, from left to right:

1. Input (IN): This pin connects to the positive raw, unregulated DC input voltage (e.g., from a transformer/bridge rectifier circuit).

2. Ground (GND): The common ground pin, which must be connected to both the input and output grounds.

3. Output (OUT): This pin provides the regulated +5V output.

Application Circuits

The most fundamental application for the MC7805BT is as a fixed output regulator.

1. Basic Fixed +5V Regulator Circuit:

This is the standard configuration found in countless designs.

Input Capacitor (C1 - 0.33μF): Used to bypass high-frequency noise present on the input line. It should be placed as close as possible to the regulator's input pin.

Output Capacitor (C2 - 0.1μF): Improves the transient response of the regulator and helps stabilize the output. For higher loads, a larger electrolytic capacitor (e.g., 10μF to 470μF) is often added in parallel to handle transient current demands.

2. Regulator with Protection Diodes:

For scenarios where the input voltage can be quickly switched off or where the output is connected to a large capacitive load, adding protection diodes is recommended.

Diode D1 protects the regulator against input short circuits.

Diode D2 protects against a discharged output capacitor (C2) back-feeding into the regulator's output pin when the input is shorted to ground.

ICGOODFIND Summary:

The onsemi MC7805BT remains a highly reliable and cost-effective solution for generating stable 5V power rails. Its simplicity of use, built-in protection features, and robust performance make it an excellent choice for hobbyists, prototypes, and industrial equipment alike. While switching regulators offer higher efficiency, the MC7805BT's low noise output and minimal external component count ensure its continued relevance in analog and mixed-signal circuits.

Keywords:

Linear Voltage Regulator

Fixed 5V Output

TO-220 Package

Application Circuit

Power Supply