onsemi MC78M08CDTRKG 8V 500mA Linear Voltage Regulator: Datasheet, Pinout, and Application Circuits

The onsemi MC78M08CDTRKG is a member of the classic 78Mxx series of fixed-output, positive voltage regulators. Designed to deliver a stable +8V output voltage at up to 500mA of continuous current, this device is a fundamental component for power management in a vast array of electronic circuits. Housed in a space-saving DPAK surface-mount package, it is well-suited for both consumer and industrial applications where a reliable, low-noise voltage rail is required from a higher unregulated input.

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

Datasheet Overview and Key Specifications

The datasheet for the MC78M08CDTRKG outlines its absolute capabilities and operational limits. Key parameters include:

Output Voltage: +8V (±4% tolerance under specified conditions)

Output Current: Up to 500 mA

Input Voltage Range: Up to 35V (A typical recommended input voltage is at least 2V above the output, e.g., 10.5V or higher for an 8V output).

Line Regulation: 10 mV (Typ.)

Load Regulation: 15 mV (Typ.)

Dropout Voltage: 2V (Max. at 500mA)

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

Internal Protection: The device incorporates essential internal thermal overload protection which shuts down the circuit when excessive temperature is detected, and internal short-circuit protection which limits maximum output current to protect the regulator.

Pinout Configuration (TO-252-3, DPAK)

The MC78M08CDTRKG comes in a 3-pin DPAK package. The pinout is standard for this series:

1. INPUT: This pin receives the unregulated DC input voltage from a source like a transformer/rectifier circuit or a battery. A capacitor is required near this pin for stability.

2. GROUND: The common reference point (0V) for both the input and output.

3. OUTPUT: The regulated +8V output. A capacitor is also required here for stability and to improve transient response.

Application Circuits

The primary application for the MC78M08CDTRKG is to create a simple, reliable voltage regulator circuit.

1. Basic Fixed Output Regulator:

This is the most common configuration. The circuit requires only two capacitors for stable operation.

An input capacitor (C1, typically 0.33μF) is placed between the INPUT pin and GND to suppress high-frequency noise and prevent oscillations. For inputs from a rectifier, a larger bulk electrolytic capacitor (e.g., 100μF) is also used.

An output capacitor (C2, typically 0.1μF) is placed between the OUTPUT pin and GND to improve the regulator's transient response and stability.

2. Regulator with Enhanced Ripple Rejection:

For applications where the input voltage has significant noise or ripple (ecommon after AC rectification), the ripple rejection performance can be improved. Adding a capacitor (Cbp, typically 10nF) between the GROUND pin and a separate, clean ground can significantly enhance the regulator's ability to reject input ripple.

ICGOODFIND Summary

The onsemi MC78M08CDTRKG is a quintessential linear voltage regulator that offers a perfect blend of simplicity, reliability, and robustness. Its built-in protections make it highly durable against common fault conditions like overheating and short circuits. While its dropout voltage of 2V makes it less efficient than modern LDOs for very low input-output differentials, it remains an excellent and cost-effective choice for the vast majority of applications requiring a stable +8V supply from an unregulated DC source up to 35V. Its straightforward implementation, requiring only two external components, solidifies its status as a go-to solution for engineers and hobbyists alike.

Keywords: Linear Voltage Regulator, 500mA, 8V Output, DPAK Package, Thermal Protection