LM317L, NCV317L

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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 (CO > 10 mF, CAdj > 5.0 mF). Diode

D1 prevents CO from discharging thru the IC during an input

short circuit. Diode D2 protects against capacitor CAdj

discharging through the IC during an output short circuit.

The combination of diodes D1 and D2 prevents CAdj from

discharging through the IC during an input short circuit.

D1

Vin

Cin

1N4002

LM317L

Vout

R1

+

CO

D2

R2

CAdj

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

Vref

+25V

Vin

LM317L

Vout

R1

VO

1.25k

Adjust

IO

D2

1N914

1N5314

R2

500

* To provide current limiting of IO

to the system ground, the source of

the current limiting diode must be tied to

a negative voltage below - 7.25 V.

R2 ≥

Vref

R1 =

VSS*

D1

1N914

VO < POV + 1.25 V + VSS

ILmin - IP < IO < 100 mA - IP

As shown O < IO < 95 mA

+

10

mF

Vin

Vout

240

1N4002

LM317L

Adjust

MPS2907

R2

50k

Vin

D1

1N4002

Vout

120

Adjust

720

+

1.0

mF

MPS2222

1.0k

TTL

Control

LM317L

Minimum Vout = 1.25 V

D1 protects the device during an input short circuit.

LM317L

Vin

R1

R2

Adjust

IAdj

Iout

Ioutmax =

Vref

+ IAdj ^

5.0 mA < Iout < 100 mA

Vout

1.25 V

Ioutmax =

Vref

+ IAdj ^

1.25 V

IDSS

IOmax + IDSS

R1

R1 + R2

R1

R1 + R2