onsemi MC78M12ACDTRKG 12V Positive Voltage Regulator: Datasheet, Pinout, and Application Circuits
The onsemi MC78M12ACDTRKG is a member of the popular 78xx series of fixed positive linear voltage regulators. Designed to deliver a stable +12V output voltage at currents up to 500mA, this regulator is a fundamental component in countless electronic designs, providing a simple and reliable solution for power management.
Datasheet Overview and Key Specifications
The device is offered in the space-saving DPAK surface-mount package, making it suitable for modern PCB designs. Key absolute maximum ratings and electrical characteristics from its datasheet define its operational limits and performance.
Input Voltage (VI): Up to 35V (A recommended 2V minimum dropout voltage means a practical input should be at least 14V for proper regulation).
Output Voltage (VO): +12V (±4% tolerance over line and load conditions).
Output Current (IO): Up to 500mA.
Dropout Voltage: Typically 2V at IO=500mA, TJ=25°C.
Line Regulation: Typically 6mV (ΔVI = 7.5V to 25V).
Load Regulation: Typically 12mV (IO = 5mA to 500mA).
Operating Junction Temperature: -40°C to +125°C.
The regulator includes essential internal protection features such as internal current limiting, which protects the device during overloads, and thermal shutdown, which disables the circuit if the junction temperature exceeds safe limits, ensuring high reliability.
Pinout Configuration
The MC78M12ACDTRKG in the DPAK (TO-252) package has three pins:
1. Input (Pin 1): This pin receives the unregulated input DC voltage, which must be higher than the output voltage.
2. Ground (Pin 2): The common reference point for both the input and output voltages.
3. Output (Pin 3): Provides the regulated +12V DC output.
Application Circuits
The primary application for the MC78M12ACDTRKG is to create a stable +12V power rail from a higher, unregulated DC source. Two classic circuit configurations are shown below.
1. Basic Fixed Regulator Circuit
This is the most common application. The input capacitor (CIN, typically 0.33μF) helps suppress high-frequency noise and instability, especially when the regulator is located far from the primary power filter. The output capacitor (COUT, typically 0.1μF) improves the transient response and stability of the regulator.
```
Unregulated DC Input
(14V - 35V)
|
+---+
| |
CIN COUT
(0.33μF) (0.1μF)
| |
+---+
|
+----[MC78M12]----+-----> +12V Regulated Output
| IN OUT |
| GND |
| |
+-----------------+-----> Ground
```
2. Regulator with Protection Diodes
For scenarios where the input voltage can be switched off quickly or where the output is connected to a back-emf source, adding diodes is critical for protection.
Diode D1 protects the regulator if the input is shorted to ground. It provides a discharge path for the output capacitor (COUT) back to the input, preventing the internal pass transistor from being damaged by a reverse voltage.
Diode D2 protects against voltages on the output that could be higher than the input voltage, a condition that can occur with inductive loads.
```
Unregulated DC Input
(14V - 35V)
|
+---+
| |
CIN |
(0.33μF)|
| |
+---+
|
+----[MC78M12]----+-----> +12V Output
| IN OUT | |
| GND | D2
| | (1N4002)
+-----------------+-----> Ground
|
D1
(1N4002)
|
C_OUT
(0.1μF)
|
Ground
```
ICGOODFIND Summary
The onsemi MC78M12ACDTRKG is a highly robust and cost-effective solution for generating a stable +12V power supply. Its integration of critical protection features like current limiting and thermal shutdown, combined with a simple three-terminal design, makes it an excellent choice for a wide range of applications, including consumer electronics, industrial controls, and automotive systems. Its surface-mount package ensures compatibility with automated assembly processes for high-volume production.
Keywords: Linear Regulator, 12V Output, 500mA, Thermal Protection, DPAK Package
