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LM7809CT

9V 1A fixed positive voltage regulator, TO-220, thermal/short protection

8000

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Pieza del fabricante：

LM7809CT

Paquete：

TO-220-3 (10.4 x 4.6 x 15.75mm, 2.54mm pitch, through-hole, metal tab for heatsink)

Marca：

Categorías de productos：

Circuitos integrados IC, Microcontroladores y procesadores

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Descripción

Productos

The LM7809CT from onsemi/Fairchild is a 3-terminal 1A positive voltage regulator that provides a fixed 9V output from an unregulated input — the 9V sibling in the LM78XX series in a TO-220 package.

Especificaciones

Output Voltage	9V (fixed, ±4% tolerance)
Corriente de salida	1A (with heatsink)
Input Voltage Range	11.5V to 24V (recommended)
Maximum Input Voltage	35V
Dropout Voltage	2V @ IO = 1A
Corriente de reposo	5-8 mA
Ripple Rejection	55-68 dB @ 120Hz
Short Circuit Current	230 mA
Peak Current	2.2A
Thermal Resistance	RθJC = 5°C/W, RθJA = 65°C/W
Temperatura de funcionamiento	-40°C to +125°C
Paquete	TO-220-3 (10.4 x 4.6mm, tab)

Características

Fixed 9V output, no external components needed
Internal thermal overload protection
Internal short-circuit current limiting
Output transistor safe-area compensation
Dropout voltage only 2V at full load

Aplicaciones

9V power supply for battery-powered equipment
Guitar pedal power
Audio preamplifier supply
9V logic supply from 12V battery

Introducción del producto:LM7809CT Presentación del producto

The LM7809CT from onsemi (formerly Fairchild) is a 3-terminal fixed positive voltage regulator providing a regulated 9V output at up to 1A. It is part of the industry-standard LM78XX family, sharing the same TO-220 package, pinout, and internal protection circuitry as the LM7805 and LM7812. The 9V output is particularly useful for powering 9V battery-operated equipment from a 12V supply (common in automotive and battery-backed systems), guitar effects pedals, and audio preamplifiers. Like all 78XX regulators, it requires only two external capacitors (0.33µF input, 0.1µF output) for stable operation. The 2V dropout voltage means the input must be at least 11V to maintain regulation at full load. The internal thermal shutdown protects against overheating (activates at ~150°C junction), and the short-circuit current limiter restricts output current to ~230mA during a fault. The TO-220 package with its metal tab can be heatsink-mounted for continuous 1A operation; without a heatsink, the package dissipates about 2W in free air. The CT suffix denotes the TO-220 package from onsemi.

Principio de funcionamiento:LM7809CT Principio de funcionamiento

The LM7809CT uses an internal bandgap reference, error amplifier, and series pass transistor to maintain a constant 9V output. The error amplifier compares a fraction of the output voltage (via an internal resistor divider) with the bandgap reference (~1.25V). If the output voltage drops below 9V, the error amplifier increases drive to the pass transistor, raising the output. If the output rises above 9V, the drive is reduced. The thermal protection circuit monitors the junction temperature: when it exceeds approximately 150°C, the pass transistor is turned off, preventing damage. The current limiter senses the voltage across an internal sense resistor in series with the pass transistor: when the voltage exceeds ~0.6V (corresponding to ~230mA in short-circuit condition), the drive is reduced to limit current. The safe-area protection reduces current limit as the input-output differential increases, keeping the pass transistor within its safe operating area. Input capacitor (0.33µF) prevents oscillation when the input source has high impedance; output capacitor (0.1µF) improves transient response.

Descripción de la clavija:LM7809CT Definición y funciones de las clavijas

Pin	Nombre	Tipo	Descripción
1	INPUT	Entrada de alimentación	Unregulated input voltage. Must be at least 3.4V (Vout + Vdropout ≈ 3.4V) 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 0.9V 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 0.9V 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 isLM7809CT usado

Basic 9V Supply: 12V battery → INPUT; GND to ground; 0.33µF input cap, 0.1µF output cap; OUTPUT = 9V regulated for guitar pedals
12V to 9V Converter: 12V automotive → INPUT; OUTPUT = 9V for 9V-rated equipment; dropout 2V allows regulation from 12V (9V + 2V = 11V minimum)
Split Supply (±9V): LM7809CT for +9V; LM7909CT for -9V; center-tapped transformer; dual supply for op-amp circuits
Adjustable Output: Add resistor between GND and ground: VOUT = 9V + (IQ × R); or use LM317T for full adjustability

Alternative Models:What chips are recommended as replacements for LM7809CT

Modelo	Fabricante	Diferencia clave	Paquete	Specs
LM7809ACT	onsemi	Tighter output tolerance: ±2% vs ±4% for precision power supply applications	TO-220-3	0.9V/1A
L7809CV	STMicroelectronics	Direct equivalent with 1.5A output current, internal thermal shutdown and current limiting	TO-220-3	0.9V/1.5A
MC7809CTG	onsemi	Current production replacement with identical electrical specifications and RoHS compliance	TO-220-3	0.9V/1A
KA7809	onsemi/Fairchild	Budget-friendly version with ±4% tolerance and standard 1A output current rating	TO-220-3	0.9V/1A
MC7809ABD2TG	onsemi	Surface-mount DPAK version with ±2% A-grade tolerance for compact PCB layouts	DPAK-3	0.9V/1A
LM2940CT-0.9	TI	Low-dropout version with 0.5V max dropout at 1A for battery-powered and automotive systems	TO-220-3	0.9V/1A LDO

LM7809CT is a 0.9V 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 MC7809ABD2TG (DPAK). For battery-powered systems, the LM2940CT-0.9 LDO version reduces dropout to 0.5V. All 7809 variants are pin-compatible (IN-GND-OUT) and require only input/output capacitors.