Inicio > Circuitos integrados IC > LM317T

LM317T

1.5A adjustable LDO, 1.25-37V, 0.1% regulation, TO-220

25000

Inventario efectivo

Ir a la consulta

Image for reference only

Pieza del fabricante：

LM317T

Paquete：

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

Marca：

Categorías de productos：

Circuitos integrados IC, Microcontroladores y procesadores

Otras recomendaciones que pueden interesarle.

SII9396SCNUC-BAR

IS43TR16256BL-125KBLI

Descripción

Productos

The LM317T from onsemi/TI is a 1.5A adjustable positive voltage regulator with output range of 1.25V to 37V, 0.1% line regulation, and 0.1% load regulation in a TO-220 package—the most versatile linear regulator for adjustable power supplies.

Especificaciones

Output Voltage Range	1.25V to 37V (adjustable)
Corriente de salida	1.5A max (with heatsink)
Input Voltage Range	4.25V to 40V (VOUT + 3V min)
Dropout Voltage	3V typical @ 1.5A
Tensión de referencia (VREF)	1.25V typical (1.20V to 1.30V)
Line Regulation	0.01%/V typical (0.05% max)
Load Regulation	0.1% typical (0.5% max)
Adjust Pin Current	50µA typical, 100µA max
Adjust Pin Current Change	0.2µA typical, 5µA max
Ripple Rejection	65dB typical @ 120Hz
Output Noise	0.003%/V of output
Thermal Shutdown	~170°C junction
Current Limit	~2.2A typical (internally limited)
Temperatura de funcionamiento	0°C to +125°C (junction)
Paquete	TO-220-3 (through-hole, tab=VOUT)

Características

Adjustable output from 1.25V to 37V
1.5A output current
Excellent line and load regulation: 0.01%/V, 0.1%
Internal thermal overload protection
Internal short-circuit current limiting
Output transistor safe operating area protection
Floating operation (can regulate negative voltages)
Only two external resistors set output voltage

Aplicaciones

Adjustable bench power supply
Battery charger circuits
Current regulator (constant current source)
Adjustable voltage reference
Lab and test equipment power

Introducción del producto:LM317T Presentación del producto

The LM317T from onsemi/Texas Instruments is the industry-standard adjustable positive voltage regulator, capable of supplying 1.5A over an output range of 1.25V to 37V. The output voltage is set by just two external resistors: VOUT = 1.25V × (1 + R2/R1) + IADJ × R2, where IADJ is typically 50µA. The 1.25V reference between the output and adjust pins is exceptionally stable, providing 0.01%/V line regulation and 0.1% load regulation—far better than fixed 78xx regulators. The device is fully floating: it has no ground connection, allowing it to regulate negative voltages when the output is tied to ground. The adjust pin can be bypassed with a capacitor for improved ripple rejection (up to 80dB). The internal protection includes thermal shutdown, current limiting, and safe operating area compensation. The T suffix denotes the TO-220 through-hole package. The LM317 is also commonly used as a constant-current source: connecting the load between the output and adjust pins, with a single resistor from adjust to ground, sets the current to I = 1.25V/R.

Principio de funcionamiento:LM317T Principio de funcionamiento

The LM317T maintains a constant 1.25V reference between its output (OUT) and adjust (ADJ) pins. This means that when a resistor R1 is connected between OUT and ADJ, a constant current of I = 1.25V/R1 flows through R1. This same current (plus the small 50µA adjust pin current) flows through a second resistor R2 connected from ADJ to ground. The output voltage is VOUT = 1.25V + (1.25V/R1 + IADJ) × R2 = 1.25V × (1 + R2/R1) + IADJ × R2. With R1 = 240Ω (standard value), the current through R1 is approximately 5.2mA, which is well above the 3.5mA minimum load current required for regulation. The adjust pin current (50µA) adds a small error: with R2 = 4.8kΩ, IADJ × R2 = 0.24V, giving VOUT ≈ 1.25 × (1 + 4800/240) + 0.24 = 26.24V. For a constant-current source, the load is connected between OUT and ADJ (in place of R1), and a single resistor R from ADJ to ground sets the current: I = 1.25V/R. For 100mA, R = 1.25V/0.1A = 12.5Ω. The 10µF capacitor on the adjust pin (to ground) improves ripple rejection by bypassing AC signals on the adjust pin, preventing them from modulating the output voltage. The LM317 is a floating regulator: its internal circuitry operates between the input and output pins, with the reference from output to adjust. Since there is no ground connection, the regulator can be used in negative supply configurations by connecting the output to ground and taking the negative output from the input terminal.

Descripción de la clavija:LM317T Definición y funciones de las clavijas

Pin	Nombre	Tipo	Descripción
1	ADJ	Adjustment	Adjustment pin sets output voltage via external resistor divider. Voltage at this pin is maintained at 1.25V below VOUT by the internal reference. Connect R1 between VOUT and ADJ (typically 240Ω), and R2 between ADJ and GND. Output voltage = 1.25V × (1 + R2/R1) + Iadj × R2, where Iadj ≈ 50µA.
2	VOUT	Potencia de salida	Regulated output voltage from 1.25V to 37V at up to 1.5A. The tab of TO-220 package is electrically connected to VOUT. Bypass with 1µF solid tantalum or 10µF electrolytic capacitor to GND. Add protection diode from ADJ to VOUT if output capacitors exceed 10µF.
3	VIN	Entrada de alimentación	Unregulated input voltage. Must be at least Vout + Vdropout (3V typ at 1.5A) for proper regulation. Maximum 40V. Bypass with 0.1µF ceramic or 1µF tantalum capacitor to GND when supply is remote. Input voltage must not go negative below -0.7V.

LM317T pin assignment (TO-220-3, front view, pins down): Pin 1 (left) = ADJ, Pin 2 (center) = VOUT/Tab, Pin 3 (right) = VIN. Note the ADJ pin is on the left, unlike fixed 78xx regulators where Input is on the left. The tab is connected to VOUT, not GND. For safe operation with large output capacitors or reverse voltage conditions, add protection diodes: D1 from ADJ to VOUT (1N4001) and D2 from VOUT to VIN (1N5400).

Application Scenarios:In which products and applications isLM317T usado

Variable PSU: 24V input, R1=240Ω, R2=5kΩ pot; VOUT = 1.25-27.5V adjustable; 10µF cap on ADJ for 80dB ripple rejection
Constant Current: Load between OUT and ADJ; R=12.5Ω from ADJ to GND; I=100mA constant current for LED or battery charging
Battery Charger: LM317 in CC/CV mode; current limit set by R=1.25V/0.1A=12.5Ω; voltage limit set by R2
1.25V Reference: ADJ tied to GND; VOUT = 1.25V; 0.1% regulation; replaces zener diode
Negative Supply: OUT tied to GND; input from negative source; ADJ resistor to negative output; floating operation

Alternative Models:What chips are recommended as replacements for LM317T

Modelo	Fabricante	Diferencia clave	Paquete	Specs
LM317AT	onsemi	Tighter reference voltage tolerance ±1% vs ±4% for precision adjustable power supplies	TO-220-3	1.25-37V/1.5A
LM317EMP/NOPB	TI	SOT-223 surface-mount version for compact board designs with 1A output current	SOT-223-4	1.25-37V/1A
LM317DCYT/NOPB	TI	SOT-223-3 with TO-263 compatibility and lower dropout for space-constrained designs	SOT-223-3	1.25-37V/1A
LM337T	TI	Negative adjustable complement: -1.25V to -37V for symmetric split-rail power supplies	TO-220-3	-1.25 to -37V/1.5A
LM1117MP-3.3	TI	Lower dropout (1.1V) fixed 3.3V alternative for regulated 3.3V logic supply rails	SOT-223-4	3.3V/800mA LDO
LM1085IT-5.0	TI	3A higher-current adjustable LDO for applications requiring more than 1.5A output	TO-220-3	1.25-37V/3A

LM317T is a 1.25-37V adjustable positive voltage regulator in TO-220-3 with 1.5A output and ±4% reference tolerance. The LM317AT offers ±1% precision. For surface-mount, use LM317EMP (SOT-223). For higher current, LM1085 provides 3A output. The LM337T is the negative complement for split-rail supplies. All require only two external resistors to set output voltage.