LM79M05, LM79M12, LM79M15

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SNOS553D – MAY 1998 – REVISED APRIL 2013

DESIGN CONSIDERATIONS

The LM79MXX fixed voltage regulator series have thermal-overload protection from excessive power, internal

short-circuit protection which limits the circuit's maximum current, and output transistor safe-area compensation

for reducing the output current as the voltage across the pass transistor is increased.

Although the internal power dissipation is limited, the junction temperature must be kept below the maximum

specified temperature in order to meet data sheet specifications. To calculate the maximum junction temperature

or heat sink required, the following thermal resistance values should be used:

Package

(°C/W)

(°C/W)

TO-220

3

40

(1)

=

Where

= Junction Temperature

= Ambient Temperature

= Power Dissipation

= Junction-to-Case Thermal Resistance

= Case-to-Ambient Thermal Resistance

= Case-to-Heat Sink Thermal Resistance

= Heat Sink-to-Ambient Thermal Resistance

= Junction-to-Ambient Thermal Resistance

Typical Applications

Bypass capacitors are necessary for stable operation of the LM79MXX series of regulators over the input voltage

and output current ranges. Output bypass capacitors will improve the transient response of the regulator.

The bypass capacitors (2.2

μF on the input, 1.0μF on the output), should be ceramic or solid tantalum which have

good high frequency characteristics. If aluminum electrolytics are used, their values should be 10

μF or larger.

The bypass capacitors should be mounted with the shortest leads, and if possible, directly across the regulator

terminals.

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