Onsemi MC7808BD2TG 8V Positive Voltage Regulator Datasheet and Application Circuit Design Guide

The Onsemi MC7808BD2TG is a classic, fixed-output linear voltage regulator belonging to the renowned 78xx series. It is engineered to deliver a stable +8V DC output voltage at currents up to 1.0 A, making it a fundamental component in a vast array of power supply designs. This device integrates internal current limiting, thermal shutdown, and safe operating area protection, ensuring a high degree of reliability and robustness for both commercial and industrial applications.

Key Electrical Characteristics and Absolute Maximum Ratings

Understanding the datasheet parameters is critical for reliable operation. The absolute maximum input voltage for the MC7808 is 35V. However, for optimal performance and to minimize power dissipation, the input voltage should be maintained several volts above the 8V output, typically between 10.5V and 25V. The device requires a minimum voltage difference, or dropout voltage, of 2.0V (typical) between the input (VIN) and output (VOUT) to maintain regulation.

A primary design consideration is the internal power dissipation, calculated as PD = (VIN – VOUT) IOUT. Exceeding the maximum junction temperature of 150°C will trigger the internal thermal shutdown circuit, protecting the IC from damage. Proper heatsinking is essential when operating at high input voltages or output currents.

Standard Application Circuit Design

The basic application circuit for the MC7808BD2TG is straightforward, requiring only two external capacitors for stable operation.

Input Capacitor (CIN): A 0.33 μF ceramic or tantalum capacitor should be placed between the input pin and ground. This capacitor is crucial for reducing input impedance and suppressing any high-frequency oscillations, especially when the regulator is located far from the primary power filter.

Output Capacitor (COUT): A 0.1 μF ceramic capacitor on the output is necessary to improve transient response and stability. While the regulator is stable without it, including this capacitor ensures optimal performance under dynamic load conditions.

For applications requiring higher currents or improved heat distribution, the D2PAK (TO-263) package offers an excellent footprint with a very low thermal resistance, allowing it to be effectively mounted to a PCB copper area or an external heatsink to dissipate excess heat.

Enhancing Performance and Protection

For scenarios involving higher input voltages or large capacitive loads, additional protection components are recommended:

Reverse Voltage Protection: A diode (1N4002) connected between the input and output terminals can prevent damage if the input is shorted to ground, as it provides a path for the output capacitor to discharge.

Back-EMF Protection: A flyback diode placed across the load is essential when driving inductive loads (e.g., motors, solenoids) to absorb voltage spikes generated when the load is switched off.

ICGOODFIND Summary

The Onsemi MC7808BD2TG remains a highly reliable and cost-effective solution for deriving a stable 8V supply from an unregulated higher DC voltage. Its simplicity, built-in protections, and minimal external component count make it an ideal choice for designers seeking a robust linear regulator for low-to-medium power applications. Careful attention to input voltage range, thermal management, and basic external capacitor selection is the key to a successful and long-lasting design.

Keywords:

Linear Voltage Regulator

Thermal Shutdown Protection

Fixed 8V Output

Application Circuit Design

Power Dissipation