LM317 参数 Datasheet PDF下载

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3-TERMINAL ADJUSTABLE REGULATOR

SLVS044R – SEPTEMBER 1997 – REVISED APRIL 2007

APPLICATION INFORMATION

D1 (Note E)

1N4002

V

I

Input

LM317

Output

V

O

(Note C)

Adjust

I

Adj

V

ref

= 1.25 V

R

1

240

Ω

D2 (Note E)

1N4002

C

O

(Note B)

1.0

µF

C

i

(Note A)

0.1

µF

R

2

C

ADJ

(Note D)

NOTES: A. C

i

is not required, but is recommended, particularly if the regulator is not in close proximity to the power-supply filter

capacitors. A 0.1-µF disc or 1-µF tantalum provides sufficient bypassing for most applications, especially when adjustment

and output capacitors are used.

B. C

O

improves transient response, but is not needed for stability.

C. V

O

is calculated as shown:

V

O

+

V

ref

1

)

R

2

R

1

)

(I

Adj

R

2

)

Because I

Adj

typically is 50

µA,

it is negligible in most applications.

D. C

ADJ

is used to improve ripple rejection; it prevents amplification of the ripple as the output voltage is adjusted higher. If

C

ADJ

is used, it is best to include protection diodes.

E. If the input is shorted to ground during a fault condition, protection diodes provide measures to prevent the possibility of

external capacitors discharging through low-impedance paths in the IC. By providing low-impedance discharge paths for

C

O

and C

ADJ

, respectively, D1 and D2 prevent the capacitors from discharging into the output of the regulator.

Figure 1. Adjustable Voltage Regulator

7