SNVS771B – MAY 1998 – REVISED APRIL 2013
LM138/LM338 5-Amp Adjustable Regulators
Check for Samples:
1
FEATURES
Specified 7A Peak Output Current
Specified 5A Output Current
Adjustable Output Down to 1.2V
Specified Thermal Regulation
Current Limit Constant with Temperature
P
+
Product Enhancement Tested
Output is Short-Circuit Protected
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APPLICATIONS
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Adjustable Power Supplies
Constant Current Regulators
Battery Chargers
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.
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.
Connection Diagram
Connection Diagrams
Figure 1. (TO-3) Metal Can Package
Bottom View
See Package Number NDS0002A
1
Figure 2. (TO-220) Plastic Package
Front View
See Package Number NDE0003B
2
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Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
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Copyright © 1998–2013, Texas Instruments Incorporated
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
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