Datasheet

6 Application information
6.1 Design consideration
The L78 Series of fixed voltage regulators are designed with thermal overload protection that shuts down the
circuit when subjected to an excessive power overload condition, internal short-circuit protection that limits the
maximum current the circuit will pass, and output transistor safe-area compensation that reduces the output short-
circuit current as the voltage across the pass transistor is increased. In many low current applications,
compensation capacitors are not required. However, it is recommended that the regulator input be bypassed with
capacitor if the regulator is connected to the power supply filter with long lengths, or if the output load capacitance
is large. An input bypass capacitor should be selected to provide good high frequency characteristics to insure
stable operation under all load conditions. A 0.33 µF or larger tantalum, mylar or other capacitor having low
internal impedance at high frequencies should be chosen. The bypass capacitor should be mounted with the
shortest possible leads directly across the regulators input terminals. Normally good construction techniques
should be used to minimize ground loops and lead resistance drops since the regulator has no external sense
lead.
The addition of an operational amplifier allows adjustment to higher or intermediate values while retaining
regulation characteristics. The minimum voltage obtained with the arrangement is 2 V greater than the regulator
voltage.
The circuit of Figure 14. High current voltage regulator can be modified to provide supply protection against short
circuit by adding a short circuit sense resistor, RSC, and an additional PNP transistor. The current sensing PNP
must be able to handle the short circuit current of the three terminal regulator Therefore a four ampere plastic
power transistor is specified.
Figure 9. Fixed output regulator
GAMG220920161007MT
1. Although no output capacitor is need for stability, it does improve transient response.
2. Required if regulator is located an appreciable distance from power supply filter.
L78
Application information
DS0422 - Rev 36
page 22/55