Datasheet

LM317
R
1
240 Ω
I
Adj
R
2
Adjust
C
i
(Note A)
0.1 µF
C
O
(Note B)
1.0 µF
V
I
V
O
(Note C)
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:
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.
OutputInput
V
ref
= 1.25 V
V
O
+ V
ref
ǒ
1 )
R
2
R
1
Ǔ
) (I
Adj
R
2
)
D1 (Note E)
1N4002
D2 (Note E)
1N4002
C
ADJ
(Note D)
LM317
www.ti.com SLVS044V –SEPTEMBER 1997–REVISED FEBRUARY 2013
APPLICATION INFORMATION
Figure 1. Adjustable Voltage Regulator
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