Description

The LM317A adiustable 3-terminal，positive-voltageregulators are capable of supplying current in excessof 1.5 A over a 1.25-V to 37-V output range andprovide 1% output-voltage accuracy. The LM317Adevice is available in an SOT-223 package, whichmakes it ideal for space-constrained applications thatrequire high-performance regulation. The device isexceptionally easy to use and requires only twoexternal resistors to set the output voltage. Both lineregulation and load regulation are better achievedwith the LM317A device than with standard fixeoregulators.

The LM317A offers full overload protection such ascurrent limit. thermaloverload protection, and safearea protection. All overload protection circuitryremains fully functional even if the adiustmentterminal is disconnected.

Typically, no capacitors are needed unless the deviceis situated more than 6 inches from the input filtercapacitors, in which case an input bypass is neededAn optional output capacitor can be added to improvetransient response. The adiustment terminal can bebypassed to achieve very high ripple-reiection ratiosthat are difficult to achieve with standard 3-terminalregulators.

Because the LM317A regulator is floating and detectsonly the input-to-output differential voltage, suppliesof several hundred volts can be regulated as long asmaximum input-to-output differential is nottheexceeded. Exceeding the maximum input-to-outputdeferential will result in short-circuiting the output.By connecting a fixed resistor betweentheadjustment pin and output, the LM317A can be alsoused as a precision current regulator. Supplies withelectronic shutdown can be achieved by clamping theadjustment terminal to ground, which programs theoutput to 1.25 V where most loads draw little current.For applications requiring greater output current, seedata sheets for LM150 series (3A)，SNVS772，andLM138 series (5A)， SNVS771. For the negativecomplement, see LM137 (SNVS778) series datasheet.