LM317KCS datasheet(10/32 Pages) TI1

10 / 32 page

LM317

240 W

IAdj

Adjust

0.1 µF

1.0 µF

Output

Input

Vref = 1.25 V

1N4002

CADJ

LM317

SLVS044W – SEPTEMBER 1997 – REVISED OCTOBER 2014

www.ti.com

9 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

9.1 Application Information

The flexibility of the LM317 allows it to be configured to take on many different functions in DC power

applications.

9.2 Typical Application

Figure 9. Adjustable Voltage Regulator

9.2.1 Design Requirements

•

R1 and R2 are required to set the output voltage.

•

CADJ is recommended to improve ripple rejection. It prevents amplification of the ripple as the output voltage

is adjusted higher.

•

Ci 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 capacitor provides sufficient bypassing for most applications, especially when

adjustment and output capacitors are used.

•

CO improves transient response, but is not needed for stability.

•

Protection diode D2 is recommended if CADJ is used. The diode provides a low-impedance discharge path to

prevent the capacitor from discharging into the output of the regulator.

•

Protection diode D1 is recommended if CO is used. The diode provides a low-impedance discharge path to

prevent the capacitor from discharging into the output of the regulator.

9.2.2 Detailed Design Procedure

VO is calculated as shown in Equation 1. IADJ is typically 50 µA and negligible in most applications.

VO = VREF (1 + R2 / R1) + (IADJ × R2)

(1)

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