The LM317A adjustable 3-terminal, positive-voltage regulators are capable of supplying
current in excess of 1.5 A over a 1.25-V to 37-V output range and provide 1% output-voltage
accuracy. The LM317A device is available in an SOT-223 package, which makes it ideal for
space-constrained applications that require high-performance regulation. The device is
exceptionally easy to use and requires only two external resistors to set the output voltage. Both
line regulation and load regulation are better achieved with the LM317A device than with standard
The LM317A offers full overload protection such as current limit, thermal-overload
protection, and safe-area protection. All overload protection circuitry remains fully functional
even if the adjustment terminal is disconnected.
Typically, no capacitors are needed unless the device is situated more than 6 inches from
the input filter capacitors, in which case an input bypass is needed. An optional output capacitor
can be added to improve transient response. The adjustment terminal can be bypassed to achieve very
high ripple-rejection ratios that are difficult to achieve with standard 3-terminal
Because the LM317A regulator is and detects
only the input-to-output differential voltage, supplies of several hundred volts can be regulated
as long as the maximum input-to-output differential is not exceeded. Exceeding the maximum
input-to-output deferential will result in short-circuiting the output.
By connecting a fixed resistor between the adjustment pin and output, the LM317A can be
also used as a precision current regulator. Supplies with electronic shutdown can be achieved by
clamping the adjustment terminal to ground, which programs the output to 1.25 V where most loads
draw little current.
For applications requiring greater output current, see data sheets for LM150 series (3A),
SNVS772, and LM138 series (5A),
SNVS771. For the negative complement, see LM137 (SNVS778) series data sheet.
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