Application Information

The LM78MXX/LM341XX regulators have internal thermal

shutdown to protect the device from over-heating. Under all

possible operating conditions, the junction temperature of

the LM78MXX/LM341XX must be within the range of 0˚C to

125˚C. A heatsink may be required depending on the maxi-

mum power dissipation and maximum ambient temperature

of the application. To determine if a heatsink is needed, the

power dissipated by the regulator, P

I

P

shows the voltages and currents which are present in the

circuit.

The next parameter which must be calculated is the maxi-

mum allowable temperature rise, T

θ

If the maximum allowable value for

θ

≥60˚C/W for TO-220 package or ≥92˚C/W for TO-252 pack-

age, no heatsink is needed since the package alone will

dissipate enough heat to satisfy these requirements. If the

calculated value for

θ

required.

As a design aid, Table 1 shows the value of the

θ

TO-252 for different heatsink area. The copper patterns that

we used to measure these

θ

Application Note Section. reflects the same test results as

what are in the Table 1

shows the maximum allowable power dissipation vs. ambi-

ent temperature for theTO-252 device. shows the maximum

allowable power dissipation vs. copper area (in

TO-252 device. Please see AN1028 for power enhancement

techniques to be used with TO-252 package.

01048423

FIGURE 1. Cross-sectional view of Integrated Circuit

Mounted on a printed circuit board. Note that the case

temperature is measured at the point where the leads

contact with the mounting pad surface

01048424

FIGURE 2. Power Dissipation Diagram

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