Datasheet

LM317L, NCV317LB
http://onsemi.com
8
Protection Diodes
When external capacitors are used with any IC regulator
it is sometimes necessary to add protection diodes to prevent
the capacitors from discharging through low current points
into the regulator.
Figure 14 shows the LM317L with the recommended
protection diodes for output voltages in excess of 25 V or
high capacitance values (C
O
> 10 mF, C
Adj
> 5.0 mF). Diode
D
1
prevents C
O
from discharging thru the IC during an input
short circuit. Diode D
2
protects against capacitor C
Adj
discharging through the IC during an output short circuit.
The combination of diodes D
1
and D
2
prevents C
Adj
from
discharging through the IC during an input short circuit.
D
1
V
in
C
in
1N4002
LM317L
V
out
R
1
+
C
O
D
2
R
2
C
Adj
1N4002
Adjust
Figure 19. Voltage Regulator with
Protection Diodes
Figure 20. Adjustable Current Limiter Figure 21. 5.0 V Electronic Shutdown Regulator
Figure 22. Slow Turn-On Regulator
Figure 23. Current Regulator
V
ref
+25V
V
in
LM317L
V
out
R
1
V
O
1.25k
Adjust
I
O
D2
1N914
1N5314
R
2
500
* To provide current limiting of I
O

to the system ground, the source of
the current limiting diode must be tied to
a negative voltage below - 7.25 V.
R
2
≥
V
ref
R
1
=
V
SS
*
D1
1N914
V
O
< P
OV
+ 1.25 V + V
SS
I
Lmin
- I
P
< I
O
< 100 mA - I
P
As shown O < I
O
< 95 mA
+
10mF
V
in
V
out
240
1N4002
LM317L
Adjust
MPS2907
R
2
50k
V
in
D
1
1N4002
V
out
120
Adjust
720
+
1.0mF
MPS2222
1.0k
TTL
Control
LM317L
Minimum V
out
= 1.25 V
D
1
protects the device during an input short circuit.
LM317L
V
in
R
1
R
2
Adjust
I
Adj
I
out
I
outmax
=
V
ref
+ I
Adj
^
5.0 mA < I
out
< 100 mA
V
out
1.25 V
I
outmax
=
V
ref
+ I
Adj
^
1.25 V
I
DSS
I
Omax
+ I
DSS
R
1
R
1
+ R
2
R
1
R
1
+ R
2