LM138, LM338

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SNVS771B – MAY 1998 – REVISED APRIL 2013

LM138/LM338 5-Amp Adjustable Regulators

Check for Samples: LM138, LM338

A unique feature of the LM138 family is time-

1

FEATURES

dependent current limiting. The current limit circuitry

2

•

Specified 7A Peak Output Current

allows peak currents of up to 12A to be drawn from

•

Specified 5A Output Current

the regulator for short periods of time. This allows the

LM138 to be used with heavy transient loads and

•

Adjustable Output Down to 1.2V

speeds start-up under full-load conditions. Under

•

Specified Thermal Regulation

sustained

loading

conditions,

the

current

limit

•

Current Limit Constant with Temperature

decreases to a safe value protecting the regulator.

Also included on the chip are thermal overload

•

protection and safe area protection for the power

•

Output is Short-Circuit Protected

transistor. Overload protection remains functional

even

if

the

adjustment

pin

is

accidentally

APPLICATIONS

disconnected.

•

Adjustable Power Supplies

Normally, no capacitors are needed unless the device

•

Constant Current Regulators

is situated more than 6 inches from the input filter

capacitors in which case an input bypass is needed.

•

Battery Chargers

An output capacitor can be added to improve

transient response, while bypassing the adjustment

DESCRIPTION

pin will increase the regulator's ripple rejection.

The LM138 series of adjustable 3-terminal positive

voltage regulators is capable of supplying in excess

Besides

replacing

fixed

regulators

or

discrete

of 5A over a 1.2V to 32V output range. They are

designs, the LM138 is useful in a wide variety of

exceptionally easy to use and require only 2 resistors

other applications. Since the regulator is “floating”

to set the output voltage. Careful circuit design has

and sees only the input-to-output differential voltage,

resulted

in

outstanding

load

and

line

supplies of several hundred volts can be regulated as

regulation—comparable to many commercial power

long as the maximum input to output differential is not

supplies. The LM138 family is supplied in a standard

exceeded, i.e., do not short-circuit output to ground.

3-lead transistor package.

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

Connection Diagram

Connection Diagrams

Figure 1. (TO-3) Metal Can Package

Figure 2. (TO-220) Plastic Package

Bottom View

Front View

See Package Number NDS0002A

See Package Number NDE0003B

1

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Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.

2

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PRODUCTION DATA information is current as of publication date.

Copyright © 1998–2013, Texas Instruments Incorporated

Products conform to specifications per the terms of the Texas

Instruments standard warranty. Production processing does not

necessarily include testing of all parameters.