The LM317 is an adjustable three-terminal positive-voltage regulator capable of supplying more than 1.5 A over an output-voltage range of 1.25 V to 37 V. It is exceptionally easy to use and requires only two external resistors to set the output voltage. Furthermore, both line and load regulation are better than standard fixed regulators.
In addition to having higher performance than fixed regulators, this device includes on-chip current limiting, thermal overload protection, and safe-operating-area protection. All overload protection remains fully functional, even if the ADJUST terminal is disconnected.
The LM317 is versatile in its applications, including uses in programmable output regulation and local on-card regulation. Or, by connecting a fixed resistor between the ADJUST and OUTPUT terminals, the LM317 can function as a precision current regulator. An optional output capacitor can be added to improve transient response. The ADJUST terminal can be bypassed to achieve very high ripple-rejection ratios, which are difficult to achieve with standard three-terminal regulators.
Look at the schematic given below:
A. Ci is not required, but 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 provides sufficient bypassing for most applications, especially when adjustment and output capacitors are used.
B. CO improves transient response, but is not needed for stability.
C. VO is calculated as shown:
Because IAdj typically is 50 μA, it is negligible in most applications.
D. CADJ is used to improve ripple rejection; it prevents amplification of the ripple as the output voltage
is adjusted higher. If CADJ is used, it is best to include protection diodes.
E. If the input is shorted to ground during a fault condition, protection diodes provide measures to prevent the possibility of external capacitors discharging through low-impedance paths in the IC. By providing low-impedance discharge paths for CO and CADJ, respectively, D1 and D2 prevent the capacitors from discharging into the output of the regulator.
This is one of the many power supply circuits made using LM317. You can more circuits on the datasheet of LM317.
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