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LM7812CT

12V 1A positive linear regulator, TO-220, thermal/short-circuit protection

21000

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Pieza del fabricante：

LM7812CT

Paquete：

TO-220-3 (15.6 x 10.6 x 4.6mm, through-hole, tab=GND)

Marca：

Categorías de productos：

Circuitos integrados IC, Microcontroladores y procesadores

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Descripción

Productos

The LM7812CT from onsemi is a 3-terminal 1A positive voltage regulator providing a fixed 12V output with internal thermal overload protection, short-circuit protection, and output transistor safe operating area compensation in a TO-220 package.

Especificaciones

Output Voltage	12V fixed (±2% at 25°C for A-grade)
Corriente de salida	1A (up to 1.5A with heatsink)
Input Voltage Range	14.5V to 27V (14.5V min for regulation)
Maximum Input Voltage	35V
Dropout Voltage	2V typical @ 1A
Line Regulation	10mV typical (14.8V to 27V, IO=500mA)
Load Regulation	12mV typical (5mA to 1A)
Corriente de reposo	6mA typical
Ripple Rejection	61dB typical @ 120Hz
Output Noise Voltage	75µV typical (10Hz to 100kHz)
Short-Circuit Current	1.5A typical
Peak Output Current	2.4A typical
Thermal Shutdown	~170°C junction
Temperatura de funcionamiento	-40°C to +125°C (junction)
Paquete	TO-220-3 (through-hole, tab=GND)

Características

Fixed 12V output with ±2% tolerance
1A continuous output current
Internal thermal overload protection
Internal short-circuit current limiting
Output transistor safe operating area protection
High ripple rejection: 61dB at 120Hz
Only two external capacitors needed

Aplicaciones

12V power supply regulation
Analog circuit power rails
Relay and solenoid driver supply
Post-regulator after switching supply
Automotive 12V systems

Introducción del producto:LM7812CT Presentación del producto

The LM7812CT from onsemi (formerly Fairchild/National Semiconductor) is a 3-terminal positive voltage regulator providing a fixed 12V output at up to 1A load current. It is part of the ubiquitous 78xx series that has been the backbone of linear power supply design for decades. The device requires only two external capacitors (0.33µF input, 0.1µF output) for stable operation. Internal protection includes thermal shutdown (disables output at ~170°C junction), current limiting (short-circuit current limited to ~1.5A), and safe operating area compensation (reduces current limit as input-output differential increases). The 2V dropout voltage means the input must be at least 14V to maintain 12V output at full load. The 61dB ripple rejection at 120Hz makes it effective for cleaning up rectified AC or noisy switching supply outputs. The CT suffix denotes the TO-220 package with commercial/industrial temperature range. Note: DigiKey lists this part as obsolete; the MC7812CTG from onsemi is the current production equivalent.

Principio de funcionamiento:LM7812CT Principio de funcionamiento

The LM7812CT uses a series pass transistor (NPN Darlington) between the input and output, controlled by a feedback loop that compares a fraction of the output voltage with an internal bandgap reference. The error amplifier drives the pass transistor to maintain VOUT = 12V. When the output voltage drops below 12V (due to increased load or decreased input), the error amplifier increases the drive to the pass transistor, increasing current flow and raising the output voltage. When the output rises above 12V, the drive is reduced. The thermal protection circuit uses a temperature sensor on the die; when junction temperature exceeds approximately 170°C, the pass transistor is disabled until the device cools to a safe temperature. The current limiting circuit monitors the pass transistor current; when it exceeds approximately 1.5A at low input-output differential, the drive is limited to prevent damage. The safe operating area (SOA) protection further reduces the current limit as the input-output voltage differential increases, keeping the pass transistor within its safe operating region. The 6mA quiescent current flows through the ground pin and provides bias for the internal reference and error amplifier. The 0.33µF input capacitor prevents oscillation when the input source has high impedance, and the 0.1µF output capacitor improves transient response.

Descripción de la clavija:LM7812CT Definición y funciones de las clavijas

Pin	Nombre	Tipo	Descripción
1	INPUT	Entrada de alimentación	Unregulated input voltage. Must be at least 3.7V (Vout + Vdropout ≈ 3.7V) for proper regulation. Maximum 35V. Bypass with 0.33µF ceramic capacitor to GND if supply is more than 6 inches from the regulator.
2	GND	Suelo	Common ground reference. The TO-220 tab is electrically connected to this pin and serves as the primary heat dissipation path. Use thermal compound and heatsink for currents above 500mA.
3	OUTPUT	Potencia de salida	Regulated 1.2V DC output at up to 1A continuous current with ±4% tolerance. Bypass with 0.1µF ceramic capacitor to GND to improve transient response and output impedance. Do not apply external voltage higher than 1.2V to prevent reverse bias damage.

Pin assignment follows standard TO-220-3 layout: Pin 1 (left) = Input, Pin 2 (center) = Ground/Tab, Pin 3 (right) = Output, when viewed from the front with pins pointing down. The metal tab on the back is electrically connected to Pin 2 (GND) and must be insulated from the heatsink when the heatsink is not at ground potential. Output capacitance of 0.1µF is required for stability; input capacitance of 0.33µF is recommended when the input supply is remote.

Application Scenarios:In which products and applications isLM7812CT usado

12V Bench Supply: 18V AC transformer → bridge rectifier → 2200µF filter → LM7812CT; 12V regulated output at up to 1A
Post-SMPS Regulator: 15V switching supply → LM7812CT; 61dB ripple rejection cleans switcher noise; Pdiss = (15-12)×1A = 3W
Automotive 12V: 14.4V car battery → LM7812CT; stable 12V for analog circuits despite battery voltage variation
Split Supply: LM7812CT (+12V) + LM7912CT (-12V) from center-tapped transformer; ±12V for op-amp circuits
Adjustable Output: LM7812CT with external op-amp and resistor divider to set output above 12V (e.g., 13.8V for battery charging)

Alternative Models:What chips are recommended as replacements for LM7812CT

Modelo	Fabricante	Diferencia clave	Paquete	Specs
LM7812ACT	onsemi	Tighter output tolerance: ±2% vs ±4% for precision power supply applications	TO-220-3	1.2V/1A
L7812CV	STMicroelectronics	Direct equivalent with 1.5A output current, internal thermal shutdown and current limiting	TO-220-3	1.2V/1.5A
MC7812CTG	onsemi	Current production replacement with identical electrical specifications and RoHS compliance	TO-220-3	1.2V/1A
KA7812	onsemi/Fairchild	Budget-friendly version with ±4% tolerance and standard 1A output current rating	TO-220-3	1.2V/1A
MC7812ABD2TG	onsemi	Surface-mount DPAK version with ±2% A-grade tolerance for compact PCB layouts	DPAK-3	1.2V/1A
LM2940CT-1.2	TI	Low-dropout version with 0.5V max dropout at 1A for battery-powered and automotive systems	TO-220-3	1.2V/1A LDO

LM7812CT is a 1.2V fixed positive voltage regulator in TO-220-3 with 1A output and ±4% tolerance. The ACT suffix offers ±2% precision. For surface-mount designs, use MC7812ABD2TG (DPAK). For battery-powered systems, the LM2940CT-1.2 LDO version reduces dropout to 0.5V. All 7812 variants are pin-compatible (IN-GND-OUT) and require only input/output capacitors.