L7818ACF Просмотр технического описания (PDF) - STMicroelectronics

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L7818ACF

PRECISION 1A REGULATORS

STMicroelectronics 

L7800AB/AC SERIES

APPLICATION INFORMATION

DESIGN CONSIDERATION

The L7800A 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 0.33mF 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 2V

greater than the regulator voltage.

The circuit of figure 6 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 4 : DC Parameter

Figure 5 : DC Parameter

VO, 7.0 to 20V

VI - VO ≥ 2.0V

Figure 6 : DC Parameter

R1 = IREVQBE-QβI1QQ11

IO = IREG + Q1 (IREG VBRE1Q1)

Figure 7 : DC Parameter

IO = VRx1x + Id

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