Features Guaranteed 7A peak output current Guaranteed 5A output current Adjustable output down to 1.2V Guaranteed thermal regulation Current limit constant with temperature P+ Product Enhancement tested Output is short-circuit protected 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 < TJ < +150°C, and the LM338 is rated for 0°C < TJ < +125°C. Applications Adjustable power supplies Constant current regulators Battery chargers

Typical Application *click for larger image	Connection Diagram *click for larger image
Typical Performance *click for larger image

Datasheets

Title		Size	Date	Other Language
	LM138 5 Amp Adjustable Regulator	396 Kbytes	3-Mar-99
	LM138 Mil-Aero Datasheet MNLM138-X	125 Kbytes

Other Technical Documents

Title		Type	Date
	A New Production Technique for Trimming Voltage Regulators	App Note	2002-10-03

Part Number(s) (NSID)	Top View	Availability	Current Reported Stock	Budgetary Pricing	Pack Size
LM138K STEEL/NOPB LM138K STEEL RoHS Status	TO-3	Full production Lead Time: 6 weeks	Distributor Region Qty ARROW Worldwide 17 DIGI-KEY Worldwide 0	$32.20 each at 1K+ pcs	tray of 50

Obsolete Versions

Obsolete Part	Alternate Part or Supplier	Source	Last Time Buy Date
LM138KG MW8	NONE	NATIONAL SEMICONDUCTOR	03 Dec 2008

All information pertaining to the RoHS Compliance Standard can be found at http://www.national.com/en/packaging/leadfree.html.

Moisture Sensitivity Level Data for LM138.

A RoHS compliance or an IPC 1752 report can be acquired at http://www.national.com/en/packaging/greennopb.html.

National's certificate of product compliance for LM138 is located at RoHS Status.

Part Number(s) (NSID)	Weight (milligrams)	Type	Pins	MSL Rating	Peak Reflow	RoHS Status	CAD Symbols	Models	Package Marking Format
LM138K STEEL/NOPB LM138K STEEL	12405.316 12405.866	TO-3	2	1 1	NA NA	Detail	N/A	N/A	NS ZXYTTE# LM138K STEELP+

All information pertaining to the RoHS Compliance Standard can be found at http://www.national.com/en/packaging/leadfree.html.

Moisture Sensitivity Level Data for LM138.

A RoHS compliance or an IPC 1752 report can be acquired at http://www.national.com/en/packaging/greennopb.html.

National's certificate of product compliance for LM138 is located at RoHS Status.

CAD Symbols and Models N/A

Models N/A

Obsolete Versions

Obsolete Part	Alternate Part or Supplier	Source	Last Time Buy Date
LM138KG MW8	NONE	NATIONAL SEMICONDUCTOR	03 Dec 2008