LM109/LM309 5-Volt Regulator
April 1998
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
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Specified to be compatible, worst case, with TTL and
DTL
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Output current in excess of 1A
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Internal thermal overload protection
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No external components required
Schematic Diagram
DS007138-1
© 1999 National Semiconductor Corporation
DS007138
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