LM317L View Datasheet(PDF) - Tiger Electronic

Part Name

Description

Manufacturer

LM317L

3-TERMINAL ADJUSTABLE REGULATOR

Tiger Electronic 

LM317

10V application.

Although the LM317 is stable with no output capacitance, like any feedback

circuit, certain values of external capacitance can cause excessive ringing. An output

capacitance (Co) in the form of a 1.0µF tantalum or 25µF aluminum electrolytic

capacitor on the output swamps this effect and insures stability.

4. 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. Most 10µF capacitors have low enough internal

series resistance to deliver 20A spikes when shorted. Although the surge is short,

there is enough energy to damage parts of the IC.

When an output capacitor is connected to a regulator and the input is shorted, the

output capacitor will discharge into the output of the regulator. The discharge current

depends on the value of the capacitor, the output voltage of the regulator, and the rate

of decrease of Vin . In the LM317, this discharge path is through a large junction that

is able to sustain a 2A surge with no problem. This is not true of other types of

positive regulators. For output capacitors of 25µF or less, the LM317’s ballast

resistors and output structure limit the peak current to a low enough level so that there

is no need to use a protection diode.

The bypass capacitor on the adjustment terminal can discharge through a low

current junction. Discharge occurs when

either the input or output is shorted. Internal

D1 IN400

to the LM317 is a 50Ω resistor which limits

the peak discharge current. No protection is

VIN

needed for output voltages of 25V or less and

10µF capacitance. Figure in right shows an LM

317 with protection diodes included for

use with outputs greater than 25V and high

LMW33171 L7 L

VIN ADJ VOU

D2

VOU

T

T

R1 C1

IN400

240

R2

10u + C2

values of output capacitance.

Regulator with protection diodes

5/14

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