LM109/LM309

5-Volt Regulator

General Description

The LM109 series are complete 5V regulators fabricated on

a single silicon chip. They are designed for local regulation

on digital logic cards, eliminating the distribution problems

association with single-point regulation. The devices are

available in two standard transistor packages. In the

solid-kovar TO-5 header, it can deliver output currents in ex-

cess of 200 mA, if adequate heat sinking is provided. With

the TO-3 power package, the available output current is

greater than 1A.

The regulators are essentially blowout proof. Current limiting

is included to limit the peak output current to a safe value. In

addition, thermal shutdown is provided to keep the IC from

overheating. If internal dissipation becomes too great, the

regulator will shut down to prevent excessive heating.

Considerable effort was expended to make these devices

easy to use and to minimize the number of external compo-

nents. It is not necessary to bypass the output, although this

does improve transient response somewhat. Input bypass-

ing is needed, however, if the regulator is located very far

from the filter capacitor of the power supply. Stability is also

achieved by methods that provide very good rejection of load

or line transients as are usually seen with TTL logic.

Although designed primarily as a fixed-voltage regulator, the

output of the LM109 series can be set to voltages above 5V,

as shown. It is also possible to use the circuits as the control

element in precision regulators, taking advantage of the

good current-handling capability and the thermal overload

protection.

Features

n Specified to be compatible, worst case, with TTL and

DTL

n Output current in excess of 1A

n Internal thermal overload protection

n No external components required

Schematic Diagram

DS007138-1

April 1998

© 1999 National Semiconductor Corporation

DS007138

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