Why does my LM317T output voltage drift when it gets hot?

The internal reference voltage has a temperature coefficient of about 0.7 mV per degree C. A 50 degree C temperature rise equals 35 mV drift, which is normal and within spec.

Do I need input and output capacitors for LM317T?

TI recommends Cin = 0.1 microfarad or higher (ceramic), Cout = 1 microfarad or higher (tantalum or electrolytic). Without capacitors, the regulator can oscillate, especially with long input leads.

What causes the LM317T to oscillate?

Three common causes: (1) No output capacitor, (2) Output capacitor is all-ceramic with ESR below 0.1 Ohm, (3) Long input wires without a local input cap.

No - major manufacturers including TI, ST, Onsemi, and Diodes Inc continue to produce LM317T in high volume. It remains a top-20 selling linear regulator globally.

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Q: What is the maximum input voltage for LM317T?

40V absolute maximum (Vin minus Vout). Continuous operation above 37V differential is not recommended. Use LM317HV (60V) for higher voltage applications.

Q: Can LM317T output more than 1.5A?

No - 1.5A is the absolute maximum rating. Sustained operation above 1.3A requires careful thermal management. For more than 1.5A, use LM350 (3A) or LT1083 (5A, 7.5A).

Q: Can I use LM317T as a current source?

Yes - the LM317T maintains 1.25V between ADJ and Vout. Connect a resistor R between these pins, and the output current is 1.25V divided by R. Works for 10mA to 1.5A.

Q: Where to buy genuine LM317T in volume?

ICMASS stocks LM317T from TI, STMicroelectronics, and Onsemi with full traceability. Volume pricing available for quantities above 1,000 units.

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LM317T Voltage Regulator: Buying Guide & Top 5 Applications

2026/6/25 11:16:47

LM317T Voltage Regulator: Buying Guide & Top 5 Applications | ICMASS

LM317T Voltage Regulator: Buying Guide & Top 5 Applications

The LM317T is the most widely used adjustable linear voltage regulator in electronics history. Since its introduction in the 1970s, it has shipped in the billions - and it's still the first part engineers reach for when they need a clean, adjustable voltage rail from 1.25V to 37V at up to 1.5A.

But its long history comes with a downside: the market is flooded with counterfeit, relabeled, and out-of-spec parts. This guide covers the LM317T's specs, five proven applications, thermal design rules, and how to tell genuine parts from fakes.

Quick Specs - What the LM317T Can (and Can't) Do

Parameter	Rating	Notes
Output Voltage Range	1.25V to 37V	Set by two external resistors
Max Output Current	1.5A	Derates with input-output differential and temperature
Dropout Voltage	≈2.0V (typ)	Needs ≈3V headroom for reliable regulation
Line Regulation	0.01%/V typ	Very clean output for a linear regulator
Load Regulation	0.1% typ	At Iout = 10mA to 1.5A
Ripple Rejection	80 dB typ (120 Hz)	With optional 10 µF bypass cap
Reference Voltage	1.25V (±2%)	Between ADJ and Vout

Key Limitations:

Dropout is 2V+ - For 5V output, input must be ≥7V. Use an LDO (like AMS1117) for low-dropout applications.
1.5A max at best case - At high differential (24V→5V), max current drops to ~400mA before thermal shutdown.
No reverse polarity protection - If input is reversed, the load sees the full negative voltage.
Minimum load current: 3.5mA - Always use a minimum load resistor.

Top 5 Real-World Applications

Application 1: Variable Bench Power Supply (The Classic)

The most common LM317T application. With a potentiometer as R2, you get a continuously adjustable 1.25V–25V supply.

Component	Part	Cost (qty 10)
Regulator	LM317T	$0.35
Potentiometer	5kΩ trimpot or panel pot	$0.50–$2.00
Resistor R1	240Ω, 1%	$0.02
Protection diodes	1N4007 × 2	$0.06
Total		$1.01–$2.51

Sourcing tip: ICMASS stocks LM317T at competitive volume pricing.

Application 2: Fixed 5V or 3.3V Output

Set it with two resistors - no need to buy a separate 7805. For 5.0V output: R1 = 240Ω, R2 = 720Ω (or closest: 750Ω → 5.16V). For 3.3V output: R1 = 240Ω, R2 = 394Ω (or closest: 390Ω → 3.28V).

Cost tip: For volume production, fixed LDOs (AMS1117, 7805) are cheaper than LM317T + resistors.

Application 3: Current-Limited Battery Charger

The LM317T can regulate current instead of voltage. Iout = 1.25V / R. For 500mA: R = 2.5Ω (use 2.7Ω, 3W rated). ICMASS carries wirewound power resistors suitable for this application.

Application 4: Precision 1.25V Reference

Connect ADJ to GND → Vout = 1.25V. Add a 120Ω load resistor → output stable at 1.25V with ±0.5% accuracy using a 10-turn trimpot.

Application 5: Low-Noise Audio Pre-Regulator

80 dB ripple rejection at 120 Hz means 100 mVpp ripple input becomes 0.01 mVpp output - clean enough for all but high-end audio.

Thermal Management - Don't Skip This

The #1 field failure of LM317T is thermal shutdown from undersized heatsinking.

Vin−Vout Differential	Max Current	Heatsink?
3V (8V→5V)	1.5A (full)	Yes - clip-on or 1 sq in copper
7V (12V→5V)	~1.0A	Yes - moderate heatsink
12V (15V→3.3V)	~500mA	Yes - small clip-on
20V (24V→5V)	~350mA	Yes - thermal shutdown without

Practical rule: If Vin − Vout >5V or Iout >500mA, add a heatsink.

Genuine vs Counterfeit - How to Tell

Check	Genuine (TI/ST/Onsemi)	Counterfeit
Marking laser quality	Crisp, consistent depth	Faded, blurry, misaligned
Top surface (TO-220 tab)	Smooth, flat	Rough, pitted, or uneven
Output voltage accuracy	±2% at 25°C	±5% or drifts with temperature
Weight	~1.95–2.05g	Lighter (~1.7–1.8g)
Short-circuit current limit	1.5A typ	>2A (no limit - may damage load)
Thermal shutdown	Engages at 125°C	Missing or triggers at 90°C

Buyer recommendation: Purchase from ICMASS with traceable batch numbers.

LM317T vs Common Alternatives

Regulator	Choose LM317T When…	Choose Alternative When…
AMS1117 ($0.10)	-	Low dropout needed (<1.2V), 3.3V/5V fixed only
LM2596 ($0.85)	-	Needs 3A+ or high efficiency (80%+ vs 50%)
LM7805 ($0.15)	-	Fixed 5V, <1A, low cost, no adjustment needed
LT1083 ($3.00+)	-	Needs 5A+ or ultra-low dropout

FAQ

Q1: What is the maximum input voltage for LM317T?

40V absolute maximum (Vin − Vout). Use LM317HV (60V) for higher voltages.

Q2: Can LM317T output more than 1.5A?

No - 1.5A is absolute max. For >1.5A, use LM350 (3A) or LT1083 (5A+).

Q3: Why does my LM317T output drift when hot?

The reference voltage has ~0.7 mV/°C tempco. A 50°C rise = 35 mV drift - within spec.

Q4: Can I use LM317T as a current source?

Yes - Iout = 1.25V / R between ADJ and Vout. Works for 10mA to 1.5A.

Q5: Do I need input/output capacitors?

Yes - Cin = 0.1 µF ceramic, Cout = 1 µF tantalum. Without them, the regulator can oscillate.

Q6: What causes LM317T to oscillate?

Three common causes: (1) No output cap, (2) All-ceramic output with ESR <0.1Ω, (3) Long input wires without local cap.

Q7: Is LM317T obsolete?

No - TI, ST, Onsemi continue production. ICMASS stocks current-date-code parts.

Q8: Where to buy genuine LM317T in volume?

ICMASS stocks LM317T from multiple manufacturers with full traceability and volume pricing.

Final Verdict - ICMASS Recommendation

Need	Recommendation
General-purpose adjustable (<1.5A)	LM317T
Production (500+ units)	LM317T with 1% resistors
5V output, low cost	AMS1117-5.0 or LM7805
High-current (>1.5A)	LM350 (3A) or LT1083
Low dropout needed	AMS1117 - not LM317T
Efficiency critical	LM2596 (80%+ vs 50% linear)