Onsemi MC7818CD2TR4G 18V Positive Voltage Regulator: Datasheet, Pinout, and Application Circuits
The Onsemi MC7818CD2TR4G is a quintessential example of a classic linear voltage regulator, providing a robust and straightforward solution for delivering a stable +18V DC output. As part of the renowned 78xx series, this device is engineered to handle a wide range of input voltages and deliver a fixed, reliable output, making it a cornerstone in power supply design for countless electronic applications.
Datasheet Overview and Key Specifications
The datasheet for the MC7818CD2TR4G outlines its critical electrical and mechanical characteristics. Key specifications that define its performance include:
Output Voltage: A fixed +18V output with a typical tolerance of ±4%.
Output Current: Capable of delivering up to 1A of continuous output current with adequate heatsinking.
Input Voltage Range: For stable operation, the input voltage must typically be at least 2.5V above the output, recommending an input voltage (VIN) between 20.5V and 35V.
Line Regulation: Typically 16mV, meaning the output voltage varies very little with changes in input voltage.
Load Regulation: Typically 24mV, indicating excellent stability under varying load conditions.
Thermal Protection: The IC includes internal thermal overload protection that shuts down the circuit if the junction temperature exceeds safe limits, preventing catastrophic failure.
Short Circuit Protection: Features internal current limiting, safeguarding the regulator if the output is shorted to ground.
Package: Housed in the TO-252-3 (DPAK) surface-mount package, which offers a good balance between size and power dissipation capability.
Pinout Configuration
The pinout for the TO-252 package is straightforward:
1. Input (VIN): This pin receives the unregulated DC input voltage, which must be higher than 18V.
2. Ground (GND): The common reference point for both the input and output.
3. Output (VOUT): The regulated +18V DC output is supplied from this pin.
Application Circuits
The primary application for the MC7818CD2TR4G is as a fixed-output voltage regulator. The basic circuit requires only two capacitors for stability, though more complex designs can be implemented for improved performance.
1. Basic Fixed Voltage Regulator Circuit
This is the most common application. An unregulated DC input is applied to VIN, and a stable 18V is available at VOUT.
CIN (0.33μF): An input ceramic capacitor is used to bypass high-frequency noise and improve stability. It should be placed as close as possible to the regulator's input pin.
COUT (0.1μF): An output ceramic capacitor improves the transient response and stability of the regulator.
2. Regulator with Improved Ripple Rejection
For applications where the input voltage has significant noise or ripple, a larger electrolytic capacitor (e.g., 10μF to 100μF) can be added at the input to further smooth the voltage. A larger electrolytic capacitor (e.g., 10μF) can also be used at the output to handle larger load transients.
3. Powering High-Current Loads
When operating near the 1A maximum current, the regulator will dissipate significant power as heat (PDISS = (VIN - VOUT) IOUT). A heatsink attached to the tab of the DPAK package is absolutely essential to keep the junction temperature within safe operating limits and utilize its full current capability.
ICGOODFIND Summary
The Onsemi MC7818CD2TR4G is a highly reliable and easy-to-use linear voltage regulator ideal for projects requiring a stable +18V rail. Its built-in protections for thermal overload and short circuits make it exceptionally robust for industrial and consumer applications. While its efficiency is lower than switching alternatives due to heat dissipation, its simplicity, low noise output, and minimal external component count ensure it remains a popular choice for powering analog circuits, microcontrollers, and other subsystems where a clean voltage is paramount.
Keywords: Linear Voltage Regulator, 18V Output, Thermal Protection, DPAK Package, Application Circuit
