How to Use LM78xx Voltage Regulator: Examples, Pinouts, and Specs

The LM78xx series is a family of self-contained fixed linear voltage regulator integrated circuits. These regulators are designed to provide a constant output voltage with a range of fixed values such as 5V, 12V, and others, from a variable input voltage. They are widely used in electronic devices to maintain a stable DC voltage, which is critical for the sensitive components within the device. Common applications include power supplies for computer motherboards, battery chargers, and standalone voltage regulation for embedded systems.

• Output Voltage Options: 5V, 6V, 8V, 9V, 12V, 15V, 18V, 24V (depending on the specific model, e.g., LM7805 for 5V)
• Input Voltage Range: Typically 2V higher than the output voltage up to 35V
• Output Current: Up to 1A (with proper heat sinking)
• Quiescent Current: 5mA to 8mA (typical)
• Output Voltage Tolerance: ±5% over full line and load conditions
• Thermal Overload Protection: Yes
• Short Circuit Protection: Yes
• Operating Temperature Range: 0°C to 125°C

1. Input Voltage: Ensure that the input voltage is within the specified range for the LM78xx being used and at least 2V higher than the desired output voltage.
2. Capacitors: It is recommended to use a capacitor at the input and output to improve stability. A typical value is 0.33µF at the input and 0.1µF at the output.
3. Heat Sinking: If the regulator is expected to dissipate significant power, attach a heat sink to prevent overheating.
4. Wiring: Connect the input voltage to the IN pin, the ground to the GND pin, and the load to the OUT pin.

• Decoupling Capacitors: Always use decoupling capacitors close to the input and output pins to minimize voltage spikes and noise.
• Thermal Management: Ensure adequate heat sinking and airflow around the regulator, especially under high load conditions.
• Protection Diodes: In cases where there is a risk of a voltage spike at the output (e.g., when driving inductive loads), a protection diode may be necessary across the input and output pins.

• Voltage Drop Under Load: If the output voltage drops significantly under load, check for inadequate input voltage or excessive power dissipation.
• Overheating: If the regulator overheats, improve heat sinking or reduce the load current.
• Noise on Output: Noise can be caused by insufficient decoupling or layout issues. Ensure capacitors are close to the regulator pins.

• Check Input Voltage: Verify that the input voltage is within the specified range and stable.
• Inspect Capacitors: Ensure that the input and output capacitors are of the correct value and in good condition.
• Review Heat Sinking: If overheating occurs, consider a larger heat sink or reducing the power load.

Q: Can I use the LM78xx without a heat sink? A: It depends on the load current and the voltage drop across the regulator. For small loads and low voltage drops, a heat sink may not be necessary.

Q: What is the maximum input voltage for the LM78xx series? A: The maximum input voltage is typically 35V, but always refer to the specific datasheet for the model you are using.

Q: Can I get a different voltage output than the fixed values? A: The LM78xx series provides fixed output voltages. For adjustable output voltages, consider the LM317 series.

// No specific code is required for the LM78xx series when used with an Arduino UNO,
// as it is a hardware component used to regulate voltage. However, ensure that the
// regulated 5V from the LM7805 is connected to the 5V pin on the Arduino if you are
// using it to power the board.

// Always make sure to follow the usage instructions and best practices when connecting
// the LM78xx to any microcontroller or electronic circuit.

Remember to always consult the specific datasheet for the LM78xx variant you are using for the most accurate and detailed information.