RoHS Compliance Information	Size in Kbytes	Date
LM138/LM338 5-Amp Adjustable Regulators	396 Kbytes	3-Mar-99	Download
LM138 Mil-Aero Datasheet MNLM138-X	125 Kbytes		Download

Part Number

Package

Factory Lead Time

Models

Samples & Electronic Orders

Budgetary Pricing

Std Pack Size

Package Marking Format

Type

Pins

Spec.

MSL Rating

Peak Reflow

RoHS Report

CAD Symbols

Weeks

Qty

Qty

$US each

LM138K STEEL

TO-3

2

NOPB STD

1 1

NA NA

RoHS

N/A

Full production

N/A

1K+

$32.20

tray of 50

NS ZXYTTE# LM138K STEELP+

6 weeks

2000

LM138K-MIL

TO-3

2

STD

1

NA

RoHS

N/A

Full production

N/A

50+

$44.90

tray of 50

-

8 weeks

500

Obsolete Versions

General Description

The LM138 series of adjustable 3-terminal positive voltage regulators is capable of supplying in excess of 5A over a 1.2V to 32V output range. They are exceptionally easy to use and require only 2 resistors to set the output voltage. Careful circuit design has resulted in outstanding load and line regulation-comparable to many commercial power supplies. The LM138 family is supplied in a standard 3-lead transistor package.

A unique feature of the LM138 family is time-dependent current limiting. The current limit circuitry allows peak currents of up to 12A to be drawn from the regulator for short periods of time. This allows the LM138 to be used with heavy transient loads and speeds start-up under full-load conditions. Under sustained loading conditions, the current limit decreases to a safe value protecting the regulator. Also included on the chip are thermal overload protection and safe area protection for the power transistor. Overload protection remains functional even if the adjustment pin is accidentally disconnected.

Normally, no capacitors are needed unless the device is situated more than 6 inches from the input filter capacitors in which case an input bypass is needed. An output capacitor can be added to improve transient response, while bypassing the adjustment pin will increase the regulator's ripple rejection.

Besides replacing fixed regulators or discrete designs, the LM138 is useful in a wide variety of other applications. Since the regulator is "floating" and sees only the input-to-output differential voltage, supplies of several hundred volts can be regulated as long as the maximum input to output differential is not exceeded, i.e., do not short-circuit output to ground. The part numbers in the LM138 series which have a K suffix are packaged in a standard Steel TO-3 package, while those with a T suffix are packaged in a TO-220 plastic package. The LM138 is rated for -55°C < T_J < +150°C, and the LM338 is rated for 0°C < T_J < +125°C.

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