LM317_16 Datasheet, PDF (10/32 Pages) Texas Instruments – 3-Terminal Adjustable Regulator

LM317
SLVS044W – SEPTEMBER 1997 – REVISED OCTOBER 2014
9 Application and Implementation
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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
D1
1N4002
Input
Output
V_I
LM317
C_i
0.1 µF
Adjust
R₁
240 W
V_ref = 1.25 V
I_Adj
D2
1N4002
R₂
C_ADJ
V_O
C_O
1.0 µF
Figure 9. Adjustable Voltage Regulator
9.2.1 Design Requirements
• R1 and R2 are required to set the output voltage.
• C_ADJ is recommended to improve ripple rejection. It prevents amplification of the ripple as the output voltage
is adjusted higher.
• C_i 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.
• C_O improves transient response, but is not needed for stability.
• Protection diode D2 is recommended if C_ADJ 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 C_O 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
V_O is calculated as shown in Equation 1. I_ADJ is typically 50 µA and negligible in most applications.
V_O = V_REF (1 + R2 / R1) + (I_ADJ × R2)
(1)
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