LM317L
Protection Diodes
D
1
1N4002
V
in
LM317L
R
1
Adjust
R
2
C
Adj
V
out
+
C
in
D
2
C
O
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.
1N4002
Figure 18. Voltage Regulator with
Protection Diodes
+25V
V
in
Adjust
* 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
≥
R
1
=
V
ref
I
DSS
V
ref
I
Omax
+ I
DSS
V
out
R
1
1.25k
D1
1N914
D2
1N914
V
O
I
O
D
1
1N4002
V
in
LM317L
V
out
+
1.0mF
MPS2222
720
V
SS
*
1.0k
TTL
Control
LM317L
R
2
500
120
Adjust
1N5314
Minimum V
out
= 1.25 V
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
D
1
protects the device during an input short circuit.
Figure 19. Adjustable Current Limiter
Figure 20. 5.0 V Electronic Shutdown Regulator
V
in
LM317L
R
1
V
out
I
Adj
R
2
I
out
V
in
LM317L
V
out
240
1N4002
50k
MPS2907
+
10mF
Adjust
Adjust
R
2
I
outmax
=
V
ref
R
1
V
ref
R
1
+ R
2
+ I
Adj
^
1.25 V
R
1
1.25 V
R
1
+ R
2
I
outmax
=
+ I
Adj
^
5.0 mA < I
out
< 100 mA
Figure 21. Slow Turn−On Regulator
Figure 22. Current Regulator
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