BETATypical reference1.24 V · OUT minus ADJ
5 A adjustable positive regulator
LM338T Specifications
Review LM338T electrical specifications, operating conditions and package details.
Key specifications
The error amplifier controls a series pass stage to hold OUT minus ADJ near 1.24 V. The divider sets output voltage; current, safe-area and thermal controls constrain overloads.
Adjustment range1.2–32 V · adequate headroom required
Current class5 A · safe area and cooling apply
Operating junction0–125 °C · LM338
Package details
LM338T/NOPB · TO-220
| Property | Details |
|---|---|
| Manufacturer | Texas Instruments |
| Part number | LM338T/NOPB |
| Package | TO-220 |
| Connections | 3 pins |
| Mounting | Through-hole |
| Lead pitch | 2.54 mm |
| Package code | NDE |
| Thermal reference | Output tab; use a suitable thermal path |
Operating reference
LM338 · TI SNVS771D
Manufacturer specifications 8 parameters
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| Parameter | Value | Conditions / notes |
|---|---|---|
| Nominal adjustable output | 1.2–32 V | Subject to headroom, load and thermal limits |
| Operating junction | 0–125°C | LM338 rating; not ambient temperature |
| Reference voltage min / typ / max | 1.19 / 1.24 / 1.29 V | 3–35 V differential; 10 mA–5 A; 0–125°C |
| Adjustment current | 45 µA typical; 100 µA maximum | Flows out of ADJUST |
| Adjustment current change | 0.2 µA typical; 5 µA maximum | 10 mA–5 A; 3–35 V differential |
| Recommended differential | 3–40 V | Allow design margin; reference accuracy tests use 3–35 V |
| Absolute differential range | −0.3 to +40 V | Stress rating; not a regulation guarantee |
| Storage temperature | −65 to +150°C | Unpowered storage |
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Electrical limits apply under the manufacturer power and test conditions. Individual maxima cannot be combined.
Regulation and rejection
Values at constant junction temperature
Manufacturer specifications 8 parameters
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| Parameter | Value | Conditions / notes |
|---|---|---|
| Line regulation, 25°C | 0.005 typical / 0.03 max. %/V | 3–35 V differential |
| Line regulation, 0–125°C | 0.02 typical / 0.06 max. %/V | Same differential range |
| Load regulation, 25°C | 0.1 typical / 0.5 max. % | 10 mA–5 A |
| Load regulation, 0–125°C | 0.3 typical / 1 max. % | 10 mA–5 A |
| Thermal regulation | 0.002 typical / 0.02 max. %/W | 20 ms pulse |
| Ripple rejection, no CADJ | 60 dB typical | 10 V output; 120 Hz |
| Ripple rejection, 10 µF CADJ | 60 dB minimum; 75 dB typical | 10 V output; 120 Hz |
| Output noise | 0.003% RMS typical | 10 Hz–10 kHz; percentage of output |
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The manufacturer load-regulation and temperature-stability rows omit printed percent unit symbols; these values are percentages as defined by the regulation parameters. Typical values are not guarantees.
Load and time-dependent limiting
Specified conditions matter
Manufacturer specifications 6 parameters
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| Parameter | Value | Conditions / notes |
|---|---|---|
| Minimum load | 3.5 mA typical; 10 mA maximum required | 35 V differential; 0–125°C |
| DC current limit | 5 A minimum; 8 A typical | Differential ≤10 V; thermal/power restrictions |
| 0.5 ms peak limit | 7 A minimum; 12 A typical | Differential ≤10 V; not continuous output |
| Limit at 30 V differential | 1 A typical | No minimum listed in the LM338 row |
| Example divider current | 1.24 / 110 ≈11.27 mA | Nominal reference |
| Worst-case divider minimum | 1.19 / 111.1 ≈10.71 mA | 110 Ω at +1%; exceeds 10 mA requirement |
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Electrical specifications are limited to 25 W for TO-220 up to 15 V differential; above that internal protection imposes additional limits. This is not a no-heatsink power rating.
TO-220 thermal reference
NDE package · source test-board metrics
Manufacturer specifications 8 parameters
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| Parameter | Value | Conditions / notes |
|---|---|---|
| RθJA | 22.9°C/W | Junction-to-ambient; standardized source conditions |
| RθJC(top) | 15.7°C/W | Junction to package top |
| RθJC(bot) | 0.7°C/W | Junction to bottom case / metal heat path |
| RθJB | 4.1°C/W | Junction-to-board |
| ψJT / ψJB | 2.1 / 4.1°C/W | Characterization parameters, not thermal resistances |
| Metal tab | Electrically OUTPUT | Insulate from a grounded heatsink as required |
| Example pass-stage loss | ≈0.446 W | (9−4.96) × (4.96/50 + 1.24/110) |
| 5 A with a 4 V drop | Approximately 20 W | Requires a designed thermal path and safe-area check |
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Do not apply the tab thermal path to the plastic top or use board θJA as a universal heatsink figure. Estimate junction temperature for the actual mounting.
Bypass and discharge paths
Manufacturer application guidance
Manufacturer specifications 6 parameters
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| Parameter | Value | Conditions / notes |
|---|---|---|
| Input bypass | 0.1 µF disc or 1 µF solid tantalum | Near INPUT and common return |
| Output capacitor | 1 µF solid tantalum or 25 µF aluminum | Improves transient response; optional in suitable circuits |
| Small output capacitance | 500–5000 pF may ring | See source stability guidance |
| Adjustment bypass | 10 µF for improved ripple rejection | Optional; omitted in this example |
| Output discharge diode | No diode needed in stated ≤100 µF, ≤15 V case | Source section 7.2.1.2.3; evaluate externally driven rails separately |
| Adjustment discharge diode | No protection needed in stated ≤10 µF, ≤25 V case | Review larger stored charge and short-circuit paths |
No specifications match. Try a parameter name or a unit.
This example has 1 µF output capacitance near 5 V and no ADJ bypass; follow the manufacturer protection topology when conditions change.
Nominal near-5 V supply
9 V input · calculated example
Manufacturer specifications 7 parameters
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| Parameter | Value | Conditions / notes |
|---|---|---|
| R1 / R2 | 110 Ω / 330 Ω, 1% | OUT-to-ADJ / ADJ-to-GND |
| Output before IADJ | 1.24 × (1+330/110) = 4.96 V | Uses typical reference |
| Typical IADJ contribution | 45 µA × 330 Ω = 14.85 mV | Output becomes about 4.97485 V |
| 50 Ω load | 99.2 mA; 0.492 W at 4.96 V | Use at least a 1 W resistor |
| Total nominal output current | 110.47 mA | Load plus divider; ignores small IADJ correction |
| Pass-stage dissipation | About 0.446 W | Nominal 9 V input |
| Reference/resistor bounds before IADJ | 4.689–5.238 V | 1.19–1.29 V reference and independent 1% divider extremes |
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Illustrative calculations, not a running circuit measurement. Check actual output and heating.
Physical pins and package
LM338T/NOPB · TO-220
Manufacturer specifications 6 parameters
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| Parameter | Value | Conditions / notes |
|---|---|---|
| Front-view lead order | 1 ADJUST · 2 OUTPUT · 3 INPUT | Marking toward you, leads down |
| Tab | OUTPUT | Not ground |
| Lead pitch | 2.54 mm nominal | TI NDE0003B |
| Footprint | 1.30 mm finished holes; 2.00 mm pads | Original TEP vertical starting footprint |
| Other family package | LM338K metal TO-CAN | Different pin layout; not the selected footprint |
| SMD option | No SMD package verified in this TI sheet | No unrelated substitute is presented |
No specifications match. Try a parameter name or a unit.
Confirm the ordered part, actual lead forming, fabrication clearance and heatsink space.
Connections by function
Select a pin for its function, connection guidance and electrical notes.