LM7808 Technical Summary

Overview

The LM7808 is a member of the LM78XX series of three-terminal positive voltage regulators. This series is widely used in electronic circuits to provide a stable and regulated output voltage. The LM7808 specifically provides a fixed +8V output, making it suitable for applications requiring this voltage level. Housed in a TO-220 package, the LM7808 is designed for ease of use and reliability, featuring internal protections that enhance its durability and safety in various operating conditions.

These regulators are ideal for both commercial and industrial applications due to their robust design, which includes internal current limiting, thermal shutdown, and safe operating area protection. When paired with adequate heat sinking, the LM7808 can deliver output currents exceeding 1A, making it a versatile choice for power supply designs.

Features

• Output Current: Up to 1A, suitable for a wide range of low to medium power applications.
• Fixed Output Voltage: Provides a stable +8V output with a tolerance of ±4% (standard) or ±2% (A-grade).
• Thermal Overload Protection: Automatically shuts down the regulator if the junction temperature exceeds safe limits, preventing damage due to overheating.
• Short Circuit Protection: Safeguards the regulator and the connected circuitry in the event of a short circuit.
• Output Transistor Safe Operating Area Protection: Ensures the internal power transistor operates within its safe limits, enhancing reliability.
• Wide Operating Temperature Range: Standard versions operate from -40°C to +125°C, while A-grade versions operate from 0°C to +125°C.
• Package: Available in the TO-220 package, which is easy to mount and provides good thermal performance.

Applications

The LM7808 is a versatile component used in a variety of applications where a stable +8V supply is required. Below are some common use cases:

• Power Supplies: Used in linear power supply designs to provide a regulated +8V output for analog and digital circuits.
• Consumer Electronics: Found in devices such as audio amplifiers, gaming consoles, and small appliances requiring a fixed voltage.
• Industrial Equipment: Employed in control systems, sensors, and instrumentation where voltage stability is critical.
• Automotive Electronics: Suitable for automotive applications where a regulated +8V is needed, provided the operating conditions are within the specified limits.
• Embedded Systems: Used to power microcontrollers, FPGAs, and other embedded components that require a stable voltage source.
• Adjustable Voltage Circuits: Although designed as a fixed regulator, the LM7808 can be used with external components to create adjustable voltage or current sources.

Electrical Characteristics

The following table summarizes the key electrical specifications of the LM7808 under typical operating conditions (unless otherwise noted):

Absolute Maximum Ratings

• Input Voltage (V_IN): 35V (maximum)
• Output Current (I_OUT): 1A (continuous)
• Operating Junction Temperature (T_J): -40°C to +125°C (standard), 0°C to +125°C (A-grade)
• Storage Temperature Range (T_STG): -65°C to +150°C

Electrical Specifications

• Output Voltage (V_OUT): 8V ±4% (standard), 8V ±2% (A-grade)
• Line Regulation: 0.01%/V (typical)
• Load Regulation: 0.1%/A (typical)
• Dropout Voltage: 2V (typical at 1A)
• Quiescent Current: 5mA (typical)
• Ripple Rejection: 62dB (typical at 120Hz)

Package Information

The LM7808 is available in the TO-220 package, which is a through-hole mounting style package with good thermal dissipation properties. Below are the key details of the TO-220 package:

TO-220 Package Dimensions

• Package Type: TO-220-3 (3-pin)
• Mounting Style: Through-hole
• Pin Count: 3
• Pin Configuration:
  • Pin 1: Input (V_IN)
  • Pin 2: Ground (GND)
  • Pin 3: Output (V_OUT)
• Dimensions: Approximately 10.4mm x 4.6mm x 9.15mm (L x W x H)
• Weight: Approximately 2g

Thermal Considerations

The TO-220 package is designed to be mounted on a heat sink to dissipate the heat generated during operation. The thermal resistance from junction to case (R_θJC) is typically 5°C/W, and the thermal resistance from junction to ambient (R_θJA) is approximately 50°C/W without a heat sink. For high current applications, a heat sink is strongly recommended to maintain safe operating temperatures.

Ordering Information

The LM7808 is available in different variants based on output voltage tolerance and operating temperature range. Below are the common ordering codes:

• LM7808CT: Standard version with ±4% tolerance, TO-220 package, operating temperature range of -40°C to +125°C.
• LM7808ACT: A-grade version with ±2% tolerance, TO-220 package, operating temperature range of 0°C to +125°C.

When ordering, specify the desired part number to ensure the correct voltage tolerance and temperature range for your application.

Conclusion

The LM7808 is a reliable and widely used voltage regulator that provides a stable +8V output for a variety of electronic applications. Its robust design, featuring thermal and short-circuit protection, makes it a durable choice for both commercial and industrial environments. With its TO-220 package and ease of use, the LM7808 is an excellent component for designers seeking a simple yet effective solution for voltage regulation.