onsemi MC78L15ABDR2G 15V Positive Voltage Regulator: Datasheet, Pinout, and Application Circuits
The onsemi MC78L15ABDR2G is a classic, reliable three-terminal positive linear voltage regulator designed to provide a fixed 15V DC output with up to 100 mA of current. As part of the ubiquitous 78Lxx family, this device is instrumental in simplifying power supply design for countless low-power electronic applications, offering internal current limiting, thermal shutdown, and safe-area compensation for enhanced robustness.
Datasheet Overview and Key Specifications
A thorough review of the MC78L15ABDR2G datasheet reveals its critical operating parameters and absolute maximum ratings, which are essential for reliable circuit design.
Output Voltage: +15V (Typically with a tolerance of ±4% under specified conditions)
Output Current: Up to 100 mA
Input Voltage Range: Up to 30V (A minimum of 17.5V is required for proper regulation, considering the 2.5V dropout voltage)
Dropout Voltage: 2.5V Max. (The minimum required difference between input and output for regulation)
Line Regulation: 60 mV (Typ.)
Load Regulation: 150 mV (Typ.)
Operating Junction Temperature: -40°C to +125°C
Package: SOIC-8
The device is housed in an SOIC-8 surface-mount package, making it suitable for automated PCB assembly and space-constrained designs. Its ability to operate over a wide temperature range makes it a versatile choice for industrial and consumer applications.
Pinout Configuration
Understanding the pinout is crucial for correct PCB layout. The SOIC-8 package has a specific pin assignment:
Pin 1 (Input): This is the unregulated input voltage pin. A capacitor must be connected between this pin and ground to suppress any high-frequency noise or oscillations.
Pin 2 (Ground): The common ground reference for both the input and output.
Pin 3 (Output): The regulated +15V output. A capacitor placed here improves stability and transient response.
The remaining pins (4 through 8) are internally connected and often recommended to be tied to the Ground (Pin 2) on the PCB for improved thermal performance.
Application Circuits
The primary application of the MC78L15ABDR2G is to create a simple, regulated DC power supply. Two fundamental circuits demonstrate its use.
1. Basic Fixed Output Regulator Circuit:
This is the most common configuration. An unregulated DC input (e.g., from a transformer and rectifier) is applied to Pin 1. A 0.33μF ceramic or electrolytic capacitor (C1) is placed at the input to suppress any incoming noise. The output at Pin 3 is filtered by a 0.1μF ceramic capacitor (C2) to ensure stability and handle fast transient load changes. This circuit provides a clean, stable +15V for microcontrollers, op-amps, sensors, and other low-power ICs.
2. Current Source / Battery Charger Circuit:
By using a single external resistor, the regulator can be configured as a precision current source. The regulated 15V output appears across a resistor (R1) connected between the Output and Ground pins. The constant current (I = Vout / R1 + IQ) is then delivered to the load. This is highly effective for charging small batteries or driving LEDs with a constant current, though the power dissipation in the regulator must be carefully considered.
Design Considerations:
Heat Dissipation: While the SOIC-8 package has limited power handling, the maximum power dissipation (PD = (VIN - VOUT) IOUT) must be calculated. For high input voltages or high load currents, adequate PCB copper area for the ground pins acts as a heatsink.
Stability: The use of the recommended output capacitor (C2) is critical for preventing oscillations and ensuring stable operation.
ICGOODFIND Summary
The onsemi MC78L15ABDR2G remains a fundamental component for engineers seeking a simple, cost-effective, and robust solution for generating low-power 15V regulated voltage. Its integration of protection features like thermal shutdown and internal current limiting significantly enhances system reliability. While switching regulators offer higher efficiency, the 78L15's simplicity, low noise output, and ease of use make it an enduring and excellent choice for a vast array of applications where efficiency is not the primary concern.
Keywords: Positive Voltage Regulator, 15V Output, 100mA Current, SOIC-8 Package, Linear Regulator
