LM317A

• For a newer drop-in alternative, see the LM317
• Typical 0.005%/V line regulation
• 1% output voltage tolerance
• 1.5-A output current
• Adjustable output down to 1.25 V
• Input-output differential up to 40 V
• Current limit constant with temperature
• No output capacitor required
• Short-circuit protected output
• −40°C to 125°C operating temperature range

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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. Both line regulation and load regulation are better achieved with the LM317A device than with standard fixed regulators.

The LM317A offers full overload protection such as over current, 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 and can be replaced with a ceramic and appropriate ESR. The adjustment terminal can be bypassed to achieve very high ripple-rejection ratios that are difficult to achieve with standard 3-terminal regulators.

Because the LM317A regulator is floating 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.

For applications requiring greater output current, see the LM150 series (3A) and LM138 series (5A) data sheets. For the negative complement, see the LM137 series data sheet.