LM7812 - 12V Positive Voltage Regulator

Overview

The LM7812 is a widely used linear voltage regulator that provides a fixed +12V output voltage. It is part of the LM78xx series of regulators, which are known for their simplicity, reliability, and ease of use. The device is designed to deliver up to 1.5A of output current with adequate heat sinking and includes built-in protection features such as thermal shutdown and current limiting.

This regulator is ideal for applications requiring a stable +12V power supply from an unregulated DC input. The LM7812 is commonly used in power supply circuits for consumer electronics, industrial equipment, and automotive systems.

Features

• Fixed +12V Output: Provides a stable 12V DC output with a tolerance of ±4% under specified conditions.
• High Current Capability: Delivers up to 1.5A of continuous output current with proper heat dissipation.
• Thermal Overload Protection: Built-in thermal shutdown prevents damage due to excessive heat.
• Short Circuit Protection: Current limiting circuitry safeguards the regulator during output short conditions.
• Wide Input Voltage Range: Operates with input voltages from 14.5V to 35V (absolute maximum 35V).
• Low Dropout Voltage: Requires only 2V difference between input and output for proper regulation.
• No External Components Required: Basic operation requires only input and output capacitors for stability.
• TO-220 Package: Industry-standard package allows for easy mounting and heat sinking.

Applications

The LM7812 voltage regulator finds use in a wide variety of electronic systems:

• Power Supplies: Fixed voltage power supplies for electronic equipment
• Consumer Electronics: Televisions, audio equipment, and gaming consoles
• Industrial Controls: Machine controllers, PLCs, and automation systems
• Automotive Electronics: Aftermarket car audio systems and accessories
• Test Equipment: Bench power supplies and measurement devices
• Embedded Systems: Microcontroller and microprocessor power regulation
• Battery Chargers: Voltage regulation in charging circuits

Electrical Characteristics

All specifications are given for T_A = 25°C, V_IN = 19V, I_O = 100mA unless otherwise noted.

Absolute Maximum Ratings

• Input Voltage (V_IN): 35V
• Power Dissipation (P_D): Internally Limited (15W with adequate heat sink)
• Operating Temperature Range (T_J): 0°C to +125°C
• Storage Temperature Range: -65°C to +150°C

Electrical Specifications

• Output Voltage (V_O):
  • Test Condition: I_O = 5mA to 1.5A, V_IN = 15V to 27V
  • Typical: 12V
  • Range: 11.5V to 12.5V (±4%)
• Line Regulation (REG_V):
  • Test Condition: V_IN = 14.5V to 30V
  • Typical: 120mV
  • Maximum: 240mV
• Load Regulation:
  • Test Condition: I_O = 5mA to 1.5A
  • Typical: 120mV
  • Maximum: 240mV
• Quiescent Current (I_Q):
  • Typical: 4.2mA
  • Maximum: 8mA
• Dropout Voltage:
  • Test Condition: I_O = 1A
  • Typical: 2V
• Ripple Rejection:
  • Test Condition: f = 120Hz
  • Typical: 55dB

Package Information

The LM7812 is available in several package options, with the TO-220 being the most common:

TO-220 Package Details

• Package Type: TO-220-3 (also known as TO-220AB)
• Dimensions: 10.4mm x 4.6mm x 15.75mm (LxWxH)
• Pin Configuration:
  1. Input (V_IN)
  2. Ground (GND)
  3. Output (V_OUT)
• Mounting: Through-hole with option for heat sink attachment
• Thermal Resistance (Junction-to-Ambient): 50°C/W (without heat sink)
• Thermal Resistance (Junction-to-Case): 5°C/W
• Weight: Approximately 2 grams

Recommended PCB Layout Considerations

• Place input capacitor (0.33μF) as close as possible to the input pin
• Place output capacitor (0.1μF) near the output pin
• Use wide traces for input and output connections to minimize voltage drop
• Provide adequate copper area for heat dissipation if operating near maximum current
• When using a heat sink, ensure proper electrical isolation if needed

Thermal Considerations

Proper heat sinking is critical when operating the LM7812 at higher currents or with large input-output voltage differentials. The power dissipation can be calculated as:

P_D = (V_IN - V_OUT) × I_OUT

For reliable operation, the junction temperature should be kept below 125°C. The required heat sink thermal resistance can be calculated using:

θ_SA ≤ (T_JMAX - T_A)/P_D - θ_JC - θ_CS

Where:
θ_SA = Heat sink-to-ambient thermal resistance
θ_JC = Junction-to-case thermal resistance (5°C/W)
θ_CS = Case-to-heat sink thermal resistance (typically 0.5-2°C/W with thermal compound)

Typical Application Circuit

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