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L7805CD2T-TR View Datasheet(PDF) - STMicroelectronics

Part Name
Description
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L7805CD2T-TR
ST-Microelectronics
STMicroelectronics ST-Microelectronics
L7805CD2T-TR Datasheet PDF : 54 Pages
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L78
Application information
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 13: "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 8: Fixed output regulator
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.
DocID2143 Rev 34
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