LM138 - LM238 - LM338
Three-terminal 5 A adjustable voltage regulators
Features
■ Guaranteed 7 A peak output current
■ Guaranteed 5 A output current
) ■ Adjustable output down to 1.2 V
t(s ■ Line regulation typically 0.005 %/V
uc ■ Load regulation typically 0.1 %
d ■ Guaranteed thermal regulation
ro ■ Current limit constant with temperature
P ■ Standard 3-lead transistor package
olete Description
bs The LM138, LM238, LM338 are adjustable 3-
O terminal positive voltage regulators capable of
- supplying in excess of 5 A over a 1.2 V to 32 V
) output range. They are exceptionally easy to use
t(s and require only 2 resistors to set the output
voltage. Careful circuit design has resulted in
uc outstanding load and line regulation comparable
d to many commercial power supplies. The LM138
ro family is supplied in a standard 3-lead transistor
P package.
te A unique feature of the LM138 family is time-de-
le pendent current limiting. The current limit circuitry
o allows peak currents of up to 12 A to be drawn
s from the regulator for short periods of time. This
ballows the LM138 to be used with heavy transient
Oloads and speeds start-up under full-load
TO-3
protection 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 response. The
adjustment terminal can be bypassed to
achieve.very high ripple rejection ratios which are
difficult to achieve with standard 3-terminal
regulators.
Besides replacing fixed regulators or discrete
designs, the LM238 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 input
differential is not exceeded.
The LM138, LM238, LM338 are packaged in
standard steel TO-3 transistor package. The
conditions. Under sustained loading conditions,
LM138 is rated for operation from - 55 °C to
the current limit decreases to a safe value
150 °C, the LM238 from - 25 °C to 150 °C and the
protecting the regulator. Also included on the chip LM338 from 0 °C to 125 °C.
are thermal overload protection and safe area
protection for the power transistor. Overload
Table 1. Device summary
Part numbers
LM138
LM238
LM338
Order codes
LM138K
LM238K
LM338K
Temperature range
-55 °C to 150 °C
-25 °C to 150 °C
0 °C to 125 °C
April 2008
Rev 2
1/23
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