Overview

The LM7812 (L7812CV / MC7812) is a 3-terminal fixed positive linear voltage regulator in the classic 78xx series manufactured by STMicroelectronics, Texas Instruments, and ON Semiconductor. Capable of supplying in excess of 1.5A output current at a fixed +12.0V DC, it incorporates internal current limiting, thermal overload shutdown, and safe-area compensation.

Operating with input voltages between 14.5V and 35.0V DC, it is widely used to provide clean, regulated +12V rails for operational amplifiers, audio preamps, 12V relays, cooling fans, and analog sensors from unregulated DC bench power supplies or AC transformer rectifiers.

Quick reference

Output Voltage (VOUT)+12.0 V DC (±4%\pm 4\% tolerance)
Minimum Input Voltage (VIN_MIN)14.5 V DC (VOUT+2.5VVOUT + 2.5\text{V} dropout margin)
Maximum Input Voltage (VIN_MAX)35.0 V DC
Maximum Output Current1.5 A (with adequate heatsinking)
Dropout Voltage2.0 V typical at IOUT=1.0AI_{OUT} = 1.0\text{A}
Quiescent Current4.3 mA typical
PackageTO-220 / TO-263 (D2PAK) / DPAK / TO-3

Pinout & Terminal Identification (TO-220 Package)

text
        ┌─────────┐
        │  O O O  │  Heatsink Tab (Connected to Pin 2 Ground)
        ├─────────┤
        │ LM7812  │
        └─┬──┬──┬─┘
          │  │  │
          1  2  3
         IN GND OUT
PinNameTypeDescription
1INPUTPowerUnregulated DC input voltage (+14.5V to +35.0V DC)
2GNDPowerGround reference (0 V, connected to metal heatsink tab)
3OUTPUTPowerRegulated +12.0V DC output rail

Specifications

ParameterSymbolMinTypMaxUnitConditions
Output VoltageVOUTV_{OUT}11.512.012.5VIOUT=500mA,VIN=19VI_{OUT} = 500\text{mA}, V_{IN} = 19\text{V}
Line RegulationReglineReg_{line}—10120mV14.5V≤VIN≤30V,IOUT=500mA14.5\text{V} \le V_{IN} \le 30\text{V}, I_{OUT} = 500\text{mA}
Load RegulationRegloadReg_{load}—12120mV5mA≤IOUT≤1.5A,VIN=19V5\text{mA} \le I_{OUT} \le 1.5\text{A}, V_{IN} = 19\text{V}
Quiescent CurrentIdI_d—4.38.0mAIOUT=0,TA=25∘CI_{OUT} = 0, T_A = 25^\circ\text{C}
Output Noise VoltageVNV_N—75—µV10Hz≤f≤100kHz10\text{Hz} \le f \le 100\text{kHz}
Peak Output CurrentIMAXI_{MAX}1.52.2—ATJ=25∘CT_J = 25^\circ\text{C}

Basic Application Circuit

text
  Unregulated DC In ───┬───[Pin 1: IN]   [Pin 3: OUT]───┬─── Regulated +12V DC Out
  (+15V to +24V)       │        LM7812                  │
                    [C_IN 0.33µF] [Pin 2: GND]      [C_OUT 0.1µF]
                       │               │                │
  GND ─────────────────┴───────────────┴────────────────┴─── GND
  • Input Capacitor (CIN=0.33 μFC_{IN} = 0.33\ \mu\text{F} ceramic): Required if the regulator is located more than 2 inches (5 cm5\text{ cm}) from the power supply filter capacitor to prevent high-frequency oscillation.
  • Output Capacitor (COUT=0.1 μFC_{OUT} = 0.1\ \mu\text{F} ceramic): Improves transient response and stability against load current surges.

Common mistakes

  • Input voltage below 14.5V: The LM7812 requires a minimum dropout voltage of 2.0V…2.5V2.0\text{V} \dots 2.5\text{V}. Powering it from a 12V12\text{V} wall adapter or a 12V12\text{V} lead-acid battery results in dropout, causing output voltage to sag and pass input AC ripple straight through to the load.
  • Neglecting thermal dissipation at high input voltages: Heat generated (PDP_D) equals (VIN−12V)×IOUT(V_{IN} - 12\text{V}) \times I_{OUT}. For example, reducing 24V24\text{V} to 12V12\text{V} at 1.0A1.0\text{A} dissipates 12W12\text{W} of heat in the TO-220 package. Without an adequate heatsink, the IC will rapidly enter thermal shutdown.
  • Connecting the metal tab to Ground without electrical insulation when mounting to grounded metal chassis: The TO-220 metal tab is internally connected to Pin 2 (Ground). If mounting several different 78xx/79xx regulators to a shared metal heatsink, use mica or silicone insulating washers.

Notes

  • LM7812 vs LM7805 vs LM7912: LM7812 is a +12V positive regulator; LM7805 is a +5V positive regulator; LM7912 is a -12V negative linear voltage regulator.

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