LM138/238

LM338

March 1993

ADJUSTABLE VOLTAGE REGULATORS

THREE-TERMINAL 5-A

.

GUARANTEED 7A PEAK OUTPUT CURRENT

.

GUARANTEED 5A OUTPUT CURRENT

.

ADJUSTABLE OUTPUT DOWN TO 1.2V

.

LINE REGULATION TYPICALLY 0.005% /V

.

LOAD REGULATION TYPICALLY 0.1%

.

GUARANTEED THERMAL REGULATION

.

CURRENT LIMIT CONSTANT WITH TEM-

PERATURE

.

STANDARD 3-LEAD TRANSISTOR PACKAGE

DESCRIPTION

The LM138/LM238/LM338 are adjustable 3-terminal

positive voltage regulators capable of supplying in ex-

cess 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 re-

sulted in outstanding load and line regulation com-

parable to many commercial power supplies. The

LM138 family is supplied in a standard 3-lead transis-

tor package.

A unique feature of the LM138 family is time-de-

pendent 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 sus-

tained 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 pro-

tection remains functional even if the adjustment pin

is accidentally disconnected.

Normally, no capacitors are needed unless the device

is situated far from the input filter capacitors in which

case an input bypass is needed. An optional output

capacitor can be added to improve transient res-

ponse. The adjustment terminal can be bypassed to

achieve very high ripple rejection ratios which are dif-

ficult to achieve with standard 3-terminal regulators.

Besides replacing fixed regulators ordiscrete designs,

the LM238 is useful in a wide variety of other applica-

tions. Since the regulator is ”floating” and sees only

theinput-to-output differential voltage, supplies of sev-

eral hundred volts can be regulated as long as the

maximum input to input differential is not exceeded.

The LM138/LM238/LM338 are packaged in standard

steel TO-3 transistor packages. The LM138 is rated

for operation from -55

–25

°C to + 150°C and the LM338 from 0°Cto +

125

°C.

TO3

K SUFFIX

(Steel Can)

ORDER CODE

PART

NUMBER

TEMPERATURE

RANGE

PACKAGE

K

LM138

LM238

LM338

-55

-25

0

•

•

•

EXAMPLE: LM138K

PIN CONNECTION

(bottom view)

Case is output

1/12