onsemi MC78M15CTG 15V Positive Voltage Regulator: Datasheet, Pinout, and Application Circuits
The onsemi MC78M15CTG is a classic, fixed-output positive voltage regulator belonging to the renowned 78xx series. It is engineered to deliver a stable +15V DC output voltage at currents up to 500mA, making it an ideal choice for a vast array of power supply applications. This component is prized for its internal current limiting, thermal shutdown protection, and safe-area compensation, which enhance the durability and reliability of both the regulator itself and the overall system.
This article provides a detailed overview of its key specifications, pinout configuration, and practical circuit implementations.
Datasheet Overview and Key Specifications
The datasheet for the MC78M15CTG outlines its absolute maximum ratings and electrical characteristics. Key parameters include:
Output Voltage: +15V (Typically at 5mA ≤ I_O ≤ 500mA, V_I ≤ 28V)
Output Current: Up to 500mA
Input Voltage Range: Up to 35V (Recommended maximum for reliable operation is typically a few volts above the output)
Line Regulation: 60mV (Typical)
Load Regulation: 120mV (Typical)
Dropout Voltage: 2V (Maximum at I_O = 500mA, T_J = 25°C)
Operating Junction Temperature: -40°C to +125°C
Packages: Available in TO-252 (DPAK), TO-220, and TO-263 (D2PAK) packages. The "TG" in MC78M15CTG denotes the TO-252 (DPAK) package, which is a surface-mount type designed for efficient power dissipation.
Pinout Configuration
The pinout for the TO-252 (DPAK) package is standard for three-terminal regulators:
1. Input (Pin 1): This pin receives the unregulated DC input voltage. A capacitor (typically 0.33μF) should be connected between this pin and ground to suppress high-frequency oscillations and improve stability.
2. Ground (Pin 2): This is the common ground reference for both the input and output.
3. Output (Pin 3): This pin provides the regulated +15V DC output. A capacitor (typically 0.1μF) should be connected from this pin to ground to improve the transient response and stability.
Application Circuits
The MC78M15CTG is straightforward to implement in basic circuits.
1. Basic Fixed Output Regulator Circuit:
This is the most common application. The input capacitor (C_IN) filters the incoming DC voltage, while the output capacitor (C_OUT) ensures stability. The input voltage (V_IN) must be at least 2V greater than the 15V output (i.e., V_IN > 17V) to remain within regulation.
```
Unregulated DC Input
(V_I > 17V)
|
+---+
| |
C_IN 0.33μF
| |
+---+
|
+----[INPUT] MC78M15CTG [OUTPUT]----+-----> +15V Regulated Output
| | |
| GND |
| |
+++ +++
GND C_OUT 0.1μF
+++ +++
| |
| | |
+------------------+-----------------+
|
GND
```
2. Regulator with Protection Diodes:
For scenarios where the input voltage can be shorted to ground or where a large output capacitor is used, adding protection diodes is advisable. Diode D1 protects the regulator against input short circuits, while diode D2 protects against reverse biasing from the output capacitor discharging through the regulator when the input is shorted.
```
Unregulated DC Input
|
+---+
| |
C_IN 0.33μF
| |
+---+
|
+----[INPUT] MC78M15CTG [OUTPUT]----+-----> +15V Output
| | | |
| +++ +++ +++
| D1 \ / D2 C_OUT 100μF
| | | +++
| GND GND |
| | |
+------------------+-----------------+
|
GND
```
Summary by ICGOODFIND
ICGOODFIND: The onsemi MC78M15CTG remains a fundamental and highly reliable building block for medium-current power supply designs. Its robust protection features, including thermal shutdown and internal current limiting, make it exceptionally durable for industrial and consumer applications. While its ~2V dropout voltage may not be suitable for very low-input scenarios, its simplicity, cost-effectiveness, and stability continue to secure its place as a go-to solution for generating clean +15V rails from a higher unregulated input source.
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Keywords:
Positive Voltage Regulator, 15V Output, 500mA, Thermal Protection, DPAK Package
