LM317T - Adjustable Positive Voltage Regulator (1.5A, TO-220)

The LM317T is an adjustable positive voltage regulator capable of supplying 1.5A over a 1.2V to 37V output range. It is the industry's most recognizable adjustable linear regulator - in production for over four decades and still widely specified in new designs for its simplicity, robustness, and built-in protection features (short-circuit, thermal overload, and safe-area compensation). The "T" suffix denotes the TO-220 through-hole package, which allows easy heatsink mounting. Requiring only two external resistors to set the output voltage - V_OUT = 1.25V × (1 + R2/R1) - and offering 0.1% typ line regulation and 0.1% typ load regulation, it remains the go-to choice for benchtop power supplies, battery chargers, and prototyping. ICMASS stocks the LM317T in genuine STMicroelectronics and ON Semiconductor variants with pricing starting at $0.25/unit (1K quantity).

What Are the Technical Specifications of LM317T?

What Are the Alternatives to LM317T?

Output Voltage Setting (Two Resistor Values)

How Much Does LM317T Cost and Is It in Stock?

Last updated: 2026-06-08 | Warehouse: Shenzhen

What Are the Typical Applications of LM317T?

• Benchtop Power Supplies: The LM317T is the most common regulator in DIY and commercial adjustable bench supplies. Its 1.5A rating and 1.2–37V range cover most lab use cases.
• Battery Chargers: Used in constant-voltage lithium, lead-acid, and NiMH chargers. The adjustable output and current-limiting capability (with an external resistor) make it a flexible charger controller.
• Local/On-Card Regulation: Provides a clean adjustable rail for analog circuits, sensor bias, and op-amp supplies where switching noise from a DC-DC converter is unacceptable.
• Prototyping & Education: The LM317 is a staple in electronics education. Its three-pin TO-220 package is breadboard-friendly.
• Constant Current Source: Configured with a single resistor between OUT and ADJ, the LM317T becomes a precision 1.25V-referenced current source - commonly used for LED drivers and sensor excitation.

Why Buy LM317T from ICMASS?

• Genuine branded parts: We stock LM317T from STMicroelectronics, ON Semiconductor, and Texas Instruments - authentic, traceable, and datasheet-guaranteed.
• Multi-vendor sourcing: If ST is out of stock, we can offer ON Semi or TI equivalents without changing the design.
• Heatsink-mounting compatible: The TO-220 package is designed for chassis or PCB-mount heatsinks. We also stock compatible TO-220 hardware kits.
• Volume-ready: From 10-piece prototyping to 50K+ production reels with competitive lead times.

Frequently Asked Questions About LM317T

Q1: How do I set the output voltage of LM317T?
A: V_OUT = 1.25V × (1 + R2/R1) + (I_ADJ × R2), where I_ADJ ≈ 50µA typical. For 5V output with R1=240Ω, R2 ≈ 720Ω (use 750Ω standard value). Use 1% or better resistors for accuracy.

Q2: What is the minimum load current for LM317T?
A: The LM317 requires a minimum load of 3.5mA typical (10mA max) to maintain regulation. If your load can drop below 10mA, add a preload resistor: R = 1.25V / 10mA = 125Ω.

Q3: What is the dropout voltage of LM317T?
A: The LM317T has a dropout voltage (V_IN - V_OUT) of approximately 2.5V at 1.5A load, up to 3V maximum. For low-dropout applications, consider an LDO like AMS1117-ADJ (1.3V dropout).

Q4: Does LM317T need a heatsink?
A: At low power (<1W), the TO-220 package can operate without a heatsink. At 1.5A with 12V→5V (10.5W dissipation), a substantial heatsink (≥10°C/W thermal resistance) is required.

Q5: Can LM317T be used as a current source?
A: Yes. Connect a resistor between the OUT and ADJ pins: I_OUT = 1.25V / R. For 100mA, use R = 12Ω. For 500mA, use R = 2.7Ω (1W resistor minimum).

Q6: What's the difference between LM317T, LM338T, and LM350T?
A: LM317T = 1.5A (the most common). LM350T = 3A. LM338T = 5A. All are pin-compatible in TO-220.

Q7: What capacitors does LM317T need?
A: Recommended: 0.1µF on the input and 1µF tantalum or 10µF aluminum on the output. Avoid ceramic on the output without series resistance.

Q8: Can LM317T output negative voltages?
A: The LM317T is a positive regulator. For negative voltages, use the LM337T (negative complement).

Q9: Is LM317T suitable for automotive applications?
A: Standard LM317T is rated 0°C to +125°C, which does not meet full automotive requirements (-40°C).

Q10: What causes LM317T oscillation?
A: Most common causes: output capacitor too far from the output pin, ceramic output capacitor with too-low ESR, or input supply leads too long without bypass.

Q11: Can LM317T survive an output short circuit?
A: Yes. The LM317T includes both current limiting (typically 2.2A) and thermal shutdown (165°C). Under a short circuit, it will cycle safely.

Q12: What is the maximum input voltage for LM317T?
A: The maximum input-output differential is 40V. For output of 5V, the maximum input is 45V.

Q13: Does LM317T have reverse polarity protection?
A: No. Reverse input voltage or output voltage higher than input will damage the LM317T.

Q14: What is the thermal shutdown temperature?
A: Typical thermal shutdown is 165°C with about 20°C hysteresis. The device restarts at ~145°C.

Q15: Is LM317T still in production?
A: Yes. Despite being a 1970s design, the LM317 is still produced by ST, ON Semi, TI, and multiple Chinese manufacturers.

Internal Links

• AMS1117-3.3 Product Page - Fixed 3.3V LDO alternative
• LM2596S-ADJ Product Page - Switching regulator alternative
• LDO vs DC-DC vs Adjustable Comparison - Power regulator selection guide